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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. Department of Physics, Key Laboratory for Quantum Information and Measurements, tsinghua Univer- sity, beijing 100084, china 2. {4. for Atomic and Molecular NanoSciences, tsinghua University, beijing 100084, 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.

TEXTURE DETERMINATION OF THIN FILM ZrO_2 BY ELECTRON DIFFRACTION

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Acta Metallurgica Sinica(English Letters) 1993年第12期6卷 472-473页

作者： WANG Yinghua tsinghua University,beijing,china Department of Materials Science and Engineering,tsinghua University,{4. tsinghua Univ Beijing China

A method for semi-quantitative determination of thin film texture using electron diffrac- tion is *** texture state of a zirconia thin film with a cubic structure has been determined in this way and is presented as an... 详细信息

关键词： texture thin film electron diffraction ZrO_2

CM elliptic curves and p-adic valuations of their L-series at s=1

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Progress in Natural Science:Materials International 2002年第10期12卷 67-70页

作者： QIU Derong(center for Advanced Study, tsinghua University, beijing 100084, {4.) Tsing Hua Univ Ctr Adv Study Beijing 100084 Peoples R China

For rational integers γ and λ, consider two families of elliptic curves y2 = x3 - D1γx and y2 = x3 - 24.3D2λ over fields (?) ( (-1)~1/2) and (?) ((- 3)1/2) respectively. General formulae expressed by Weierstrass (?)-functions are given for special values of Hecke L-series attached to such elliptic curves. The uniform lower bounds of 2-adic and 3-adic valuations of these values of Hecke L-series as well as global criteria for reaching these bounds are obtained. Moreover, when γ = 2 and λ = 2, 4. further results of 2-adic and 3-adic valuations are obtained for the corresponding curves in more general case of D1 and some restricted D2 respectively. These results are consistent with the predictions of the conjecture of Birch and Swinnerton-Dyer, and greatly develop and generalize some results in recent literature for more special cases.

关键词： elliptic curve L-series complex multiplication Birch and Swinnerton-Dyer conjecture.

Development of silicon-based microelectrode array

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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, china 2 tsinghua National Laboratory for Information Science and Technology, beijing 100084, china 3 Yangtze Delta Region Institute of tsinghua University, Jiaxing 314.50, china 4.State Key Laboratory of Transducer Technology, Chinese Academy of Sciences, Shanghai 200050 china 5 Department of Biomedical Engineering, tsinghua University, beijing 100084, china 1. Institute of Microelectronics Tsinghua University Beijing 100084 China 2. tsinghua National Laboratory for Information Science and Technology Beijing 100084 China 3. Yangtze Delta Region Institute of tsinghua University Jiaxing 314050 China 4. State Key Laboratory of Transducer Technology Chinese Academy of Sciences Shanghai 200050 China 5. Department of Biomedical Engineering Tsinghua University Beijing 100084 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

Gas kinetic algorithm for flows in Poiseuille-like microchannels using Boltzmann model equation

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Science china(Physics,Mechanics & Astronomy) 2005年第4期48卷 496-512页

作者： LI Zhihui1,2, ZHANG Hanxin1 & FU Song2 ⒈ National Laboratory for CFD, Hypervelocity Aerodynamics Institute,china Aerodynamics Research and Development center,Mianyang 621000,china 2.Department of Engineering Mechanics,tsinghua University,{4. 1. National Laboratory for CFD Hypervelocity Aerodynamics Institute China Aerodynamics Research and Development Center 621000 Mianyang China 2. Department of Engineering Mechanics Tsinghua University 100084 Beijing China

The gas-kinetic unified algorithm using Boltzmann model equation have been extended and developed to solve the micro-scale gas flows in Poiseuille-like micro-channels from Micro-Electro-Mechanical Systems (MEMS). The numerical modeling of the gas kinetic boundary conditions suitable for micro-scale gas flows is presented. To test the present method, the classical Couette flows with various Knudsen numbers, the gas flows from short microchannels like plane Poiseuille and the pressure-driven gas flows in two-dimensional short microchannels have been simulated and compared with the approximate solutions of the Boltzmann equation, the related DSMC results, the modified N-S solutions with slip-flow boundary theory, the gas-kinetic BGK-Burnett solutions and the experimental data. The comparisons show that the present gas-kinetic numerical algorithm using the mesoscopic Boltzmann simplified velocity distribution function equation can effectively simulate and reveal the gas flows in microchannels. The numerical experience indicates that this method may be a powerful tool in the numerical simulation of micro-scale gas flows from MEMS.

关键词： Boltzmann model equation, discrete velocity ordinate method, finite-difference scheme, Couette flow, Poiseuille flow, gas flow in short-microchannel.

A preliminary study on vegetation-erosion dynamics and its applications

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Science china Earth Sciences 2005年第5期48卷 689-700页

作者： WANG Zhaoyin 1,2 , WANG Guangqian 1 , LI Changzhi 1 & WANG Feixin 1 1. Department of Hydraulic Engineering, tsinghua University, beijing 100084, china 2. International Research and Training {4. on Erosion and Sedimentation, beijing 100084, china 1. Department of Hydraulic Engineering Tsinghua University 100084 Beijing China 2. International Research and Training center on Erosion and Sedimentation 100084 Beijing China

Vegetation-erosion dynamics is a new interdisciplinary science, studying the laws of evolution of watershed vegetation under the action of various ecological stresses. Introducing a qualitative expression of ecological stresses in this paper, the present authors establish the cou- pled differential equations for the vegetation-erosion process and derive a theoretical solution. The model is applied to the Anjiagou watershed on the Loess Pateau and the Xiaojiang water- shed and its sub-watersheds on the Yunnan Plateau. The calculated results agree well with the vegetation development processes. Abstracted from the differential equations the so-called vegetation-erosion chart is worked out, with which we can predict the development trend of vegetation under no human stresses. It is demonstrated that the erosion control is important for vegetation development and reforestation must be a long-term strategy. On the Yunnan Plateau with relatively high precipitation and temperature, vegetation can be greatly improved if erosion is controlled. On the dry and cold Loess Pateau suffering from high rate of soil erosion, however, vegetation can effectively control erosion but erosion reduction exhibits low effectiveness on vegetation development. Vegetation in the area is not stable and management is always needed to maintain the vegetation.

关键词： vegetation-erosion dynamics, human activities, coupled differential equations, erosion control, vigor ofvegetation.

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. {4. Xian Ke ZHANG Department of Mathematical Sciences, tsinghua University, beijing 100084, P. R. {4. center for Advanced Study Tsinghua University Beijing P. R. China Department of Mathematical Sciences 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

The correlation timescale of the X-ray flux during the outbursts of soft X-ray transients

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Science china(Physics,Mechanics & Astronomy) 2010年第S1期53卷 161-167页

作者： WU YuXiang1,2,YU WenFei1 & LI TiPei2 1 Shanghai Astronomical Observatory,Shanghai 100012,china 2 Department of Engineering Physics & center for astrophysics,tsinghua University,{4. Shanghai Astron Observ Shanghai 100012 Peoples R China tsinghua Univ Dept Engn Phys Beijing 100084 Peoples R China tsinghua Univ Ctr Astrophys Beijing 100084 Peoples R China

Recent studies of black hole and neutron star low mass X-ray binaries(LMXBs) show a positive correlation between the X-ray flux at which the low/hard(LH)-to-high/soft(HS) state transition occurs and the peak flux of the following HS *** analyzing the data from the All Sky Monitor(ASM) onboard the Rossi X-ray Timing Explorer(RXTE),we show that the HS state flux after the source reaches its HS flux peak still correlates with the transition flux during soft X-ray transient(SXT) *** studying large outbursts or flares of GX 339-4.Aql X-1 and 4. 1705-4.,we have found that the correlation holds up to 250,4.,and 50 d after the LH-to-HS state transition,*** time scales correspond to the viscous time scale in a standard accretion disk around a stellar mass black hole or a neutron star at a radius of-104.5 Rg,indicating that the mass accretion rates in the accretion flow either correlate over a large range of radii at a given time or correlate over a long period of time at a given *** the accretion geometry is a two-flow geometry composed of a sub-Keplerian inflow or outflow and a disk flow in the LH state,the disk flow with a radius up to-105 Rg would have contributed to the nearly instantaneous non-thermal radiation directly or indirectly,and therefore affects the time when the state transition occurs.

关键词： accretion disks black hole physics star:individual(Aquila X-1 GX 339-4 4. 1705-4.)

Torsion theories of pseudo-regular S -systems

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Progress in Natural Science:Materials International 2002年第2期12卷 68-70页

作者： QIU Derong(center for Advanced Study, tsinghua University, beijing 100084, {4.) Tsing Hua Univ Ctr Adv Study Beijing 100084 Peoples R China

The concept of pseudo-regular S-system is introduced. A torsion theory τu = ( Us, Us) with its torsion class Us consisting of pseudo-regular S-systems is constructed. Its corresponding quasi-filter is completely described. A number of results on the relations between τu and two special torsion theories, the stable and Lambek torsion theories, are obtained.

关键词： pseudo-regular S-system torsion theory quasi-filter stable torsion theory Lambek torsion theory.