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Experimental realization of quantum cryptography communication in free space

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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. {2. of Physics, Key Laboratory for Quantum Information and Measurements, Tsinghua Univer- sity, {2., china 2. Center for Atomic and Molecular Nanosciences, Tsinghua University, {2., china department of Physics Key Laboratory for Quantum Information and Measurements Tsinghua University Beijing 100084 China Atomic and Molecular Nanosciences Tsinghua University Beijing 100084 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.

Study on the two and three-parameter working stability regions of 3Y-TZP suspension

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Science china(Technological sciences) 2006年第5期49卷 547-568页

作者： CHEN Youqiang1, 2. zhang Xinni3, CHEN Sha’ou3 & QI Ping3 1. department of Chemistry, Qingdao University, Qingdao 2.6071, {2. 2. department of Chemistry, Tsinghua University, beijing 100084, {2. 3. department of Physics, Qingdao University, Qingdao 2.6071, {2. 1. department of Chemistry Qingdao University Qingdao 266071 China 2. department of Chemistry Tsinghua University Beijing 100084 China 3. department of Physics Qingdao University Qingdao 266071 China

We determined the variation tendency of viscosity (η) at various solids load- ing (α) for 3Y-TZP suspension as a function of dispersant concentration (Cw) using vis- cosity measurement, measured the diameter of particles as a function of Cw in very dilute suspension using light scattering method, and obtained the surface features of the sedi- ment of suspension with different Cw using SEM. We also discussed the influence of the microstructure of adsorbed polymer layers on particles and their interactions in the dis- persing medium on the stability of suspension. Then two different stable states and two different unstable states for 3Y-TZP suspension were given. Accordingly, the (Cw, η), (Cw, α), and (α, η) two-parameter, and (Cw, α, η) three-parameter stability maps were con- structed. Based on the DLVO theory calculations, the dispersant concentration, particle distance (r), and interparticle potential energy (VT) maps with various solids loading for 3Y-TZP aqueous suspension were also constructed. In (Cw, r) two-parameter coordinate system, the stable motion region map for particles was established. The Cw, α, and VT,max (the highest potential energy) surface of the potential barrier map was obtained through calculation and simulation on the basis of the surfaces of Cw, r, VT maps introduced above. The (Cw, α) two-parameter stability map was then obtained from the Cw, α, VT,max map. The results showed that this theoretical map can qualitatively prove the experimentally obtained results—the existence of different dispersed states of particles in suspension system and the variation tendency of suspension stability with changing each parame- ter—were reasonable.

关键词： 3Y-TZP, suspension, stability, DLVO theory, interparticle potential energy.

Approximation of functions on the Sobolev space with a Gaussian measure

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Science china Mathematics 2010年第2期53卷 373-384页

作者： WANG HePing 1, zhang YanWei 2.& ZHAI XueBo 1 1 School of mathematical {2., Capital Normal University, beijing 100048, china 2.department of Mathematics, Zaozhuang University, Zaozhuang 2.7160, china 1. School of mathematical sciences Capital Normal University Beijing 100048 China2. Department of Mathematics Zaozhuang University Zaozhuang 277160 China

We discuss the best approximation of periodic functions by trigonometric polynomials and the approximation by Fourier partial summation operators, Valle-Poussin operators, Ces`aro operators, Abel opera-tors, and Jackson operators, respectively, on the Sobolev space with a Gaussian measure and obtain the average error estimations. We show that, in the average case setting, the trigonometric polynomial subspaces are the asymptotically optimal subspaces in the L q space for 1≤q 1≤q < ∞.

关键词： average width best approximation approximation by linear operators Sobolev space Gaussian measure

Centralizers and Iterate Radicals of Morse-Smale Diffeomorphisms of the Circle

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Acta Mathematica Sinica,English Series 1995年第1期11卷 1-11页

作者： zhang meirong {2. of Applied Mathematics Tsinghua University beijing,100084 china department of Applied Mathematics Tsinghua University Beijing People's Republic of China

In this paper,we will use the embedding flows in[1],[2.to give a complete descrip- tion of the smooth centralizers and iterate radicals of all C^r(r≥2.Morse-Smale diffeomorphisms of the circle S^*** a result,we prove... 详细信息

关键词： Centralizers and Iterate Radicals of Morse-Smale Diffeomorphisms of the Circle TDFs

Investigation on extremal and critical characteristics of ignition time for H_2.O_2.combustion system and their applications

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Science china(Technological sciences) 2009年第5期52卷 1161-1166页

作者： CHEN JianHua1,zhang HuiQiang2.LI ZhuoYi2.& zhang GuiTian1 1 School of Aerospace,North Western Polytechnical University,Xi’an 710072.{2. 2.department of Engineering Mechanics,Tsinghua University,beijing 100084,{2. School of Aerospace North Western Polytechnical University Xi’an 710072 China department of Engineering Mechanics Tsinghua University Beijing 100084 China

The L,H and C curves in P-T phase are proposed to describe the minimal,maximal and critical char-acteristics of ignition time of H2.O2.combustion system,*** features of H2.O2.Air) com-bustion system,including explosion or not as well as the time delay to achieve its explosion status,can be well shown by explosion limits and these proposed *** curves can be described by 1.2.1=ks[Ms],(k11/k10+1)k1=ks[Ms],and 2.1=ks[Ms],respectively,which provide a physical explanation for these curves and give another way to establish *** on the contour of ignition time,the Z-type explosion limits can be explained by thermal explosion ***,the ignition distance of supersonic combustion is predicted according to the ignition time obtained in a Semenov system,which is very reasonable.

关键词： ignition time thermal explosion detailed reaction mechanism Semenov system supersonic combustion

Molecular architecture and engineering of spider dragline silk protein

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Progress in Natural Science:Materials International 2005年第9期15卷 769-776页

作者： zhang Hengmu and LIU Jinyuan(department of Biological {2. and Biotechnology, Tsinghua University, beijing 100084, china) department of Biological sciences and Biotechnology Tsinghua University Beijing 100084 China

Spider dragline silk, which is produced in spider major ampullate gland, is a composite proteinacious fiber with highly repetitive Ala-Gly-rich domain. The unique combination of both high tensile strength and high elasticity makes spider dragline silk superior to almost any other natural or synthetic fibers. Cloning of the genes reveals that the silk is composed of at least two major proteins. Each protein component contains multiple repeats of modular structures that alternate between Ala-rich domains and Gly-rich domains. Molecular engineering not only opens a door to the production of spidroins but also provides a valuable experimental system to test and further establish the relationship between modular structures and mechanical properties. Here, based on our own studies, we review the latest progress of the modular structure and genetic engineering and outline the future prospects.

关键词： spider dragline silk protein modular structure molecular engineering.

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

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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 {2. of Computer Science and Technology, Tsinghua University, {2., china 2.Tsinghua National Laboratory for Information Science and Technology, Tsinghua University, {2., china 1. department of Computer Science and Technology Tsinghua University Beijing 100084 China2. Tsinghua National Laboratory for Information Science and Technology Tsinghua University Beijing 100084 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 37%. 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

Explicit Classification for Torsion Subgroups of Rational Points of Elliptic Curves

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Acta Mathematica Sinica,English Series 2002年第3期18卷 539-548页

作者： De Rong QIU Center for Advanced Study, Tsinghua University, beijing 100084. P. R. china Xian Ke {2. department of mathematical sciences, Tsinghua University, beijing 100084, P. R. china Center for Advanced Study Tsinghua University Beijing P. R. China department of mathematical {2. Tsinghua University Beijing P. R. China

We study the classification of elliptic curves E over the rationals Q according to the torsion subgroups E_(tors)(Q). More precisely, we classify those elliptic curves with E_(tors)(Q) being cyclic with even orders. We also give explicit formulas for generators of E_(tors)(Q). These results, together with the recent results of K. Ono for the non-cyclic E_(tors)(Q), completely solve the problem of the explicit classification and parameterization when E has a rational point of order 2.

关键词： Elliptic curve Rational point Torsion group Mordell group Parameterization

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

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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, {2. 2. department of Hydraulic Engineering, Tsinghua University, beijing 100084, {2. 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.