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Science china(Technological Sciences) 2007年第4期50卷 385-401页

作者： ZHANG HanXin1,2,3, ZHANG Zhao1,3, YUAN XianXu1,2, LIU Wei1, XIE YuFei1,2 & YE YouDa1,2 1 china Aerodynamics research and Development center, Mianyang 621000, china 2 National Laboratory for Computational Fluid Dynamics, beijing university of Aeronautics and Astronautics, beijing 100083, china 3 School of Aerospace, tsinghua university, beijing 100084, china china Aerodynamics research and Development center School of Aerospace Tsinghua University National Laboratory for Computational Fluid Dynamics Beijing University of Aeronautics and Astronautics

Analytical methods of nonlinear dynamics and numerical simulations for the cou-pling equations of Navier-Stokes and flight mechanics are used to study the dynamic behaviour of pitching motions of reentry capsules with the variation of Mach number, and rocking motions of swept wings with the variation of angle of attack. Conditions under which the dynamic instability, Hopf bifurcation and saddle-node bifurcation occur are obtained. The node-saddle-node topological structure in the phase portrait, i.e. the state of bi-attractors (attracting basins) is described. The evolving process of dynamic behaviour and flow fields are given. The theories are compared with some numerical simulations conducted by the authors. Besides, some verifiable experi-mental results are cited. The agreement between them is very well.

关键词： physical analysis numerical simulation pitching oscillation rocking motion bifurcation

Dynamics and control of a solar collector system for near Earth object deflection

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research in Astronomy and Astrophysics 2011年第2期11卷 205-224页

作者： Shen-Ping Gong,Jun-Feng Li and Yun-Feng Gao School of Aerospace,tsinghua university,beijing 100084,china School of Aerospace Tsinghua University

A solar collector system is a possible method using solar energy to deflect Earth-threatening near-Earth *** investigate the dynamics and control of a solar collector system including a main collector （MC） and secondary collector （SC）.The MC is used to collect the sunlight to its focal point,where the SC is placed and directs the collected light to an *** the relative position and attitude of the two collectors should be accurately controlled to achieve the desired optical ***,the dynamical equation of the relative motion of the two collectors in the vicinity of the asteroid is ***,the nonlinear sliding-mode method is employed to design a control law to achieve the desired configuration of the two ***,the deflection capability of this solar collector system is compared with those of the gravitational tractor and solar sail gravitational *** results show that the solar collector is much more efficient with respect to deflection capability.

关键词： minor planets asteroids -- techniques: miscellaneous -- solar collector

Numerical simulation of channel pattern changes Part Ⅱ:Application in a conceptual channel

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International Journal of Sediment research 2010年第4期25卷 380-390页

作者： Hong WANG1, Gang ZHOU2, and Xuejun SHAO31 Ph.D., Associate Professor, State Key Laboratory of Hydroscience and Engineering, tsinghua university, beijing 100084, china. 2 Graduate student for a Ph.D. degree (at the time of this research work), State Key Laboratory of Hydroscience and Engineering, tsinghua university, beijing 100084, china. Presently: Post-doctoral research fellow, Chinese research Academy of Environmental Sciences, beijing 100012, china 3 Ph.D., Professor, State Key Laboratory of Hydroscience and Engineering, tsinghua university, beijing 100084, china. Ph.D. Associate Professor State Key Laboratory of Hydroscience and Engineering Tsinghua University Beijing 100084 China Graduate student for a Ph.D. degree (at the time of this research work) State Key Laboratory of Hydroscience and Engineering Tsinghua University Beijing 100084 China. Presently: Post-doctoral research fellow Chinese Research Academy of Environmental Sciences Beijing 100012 China Ph.D. Professor State Key Laboratory of Hydroscience and Engineering Tsinghua University Beijing 100084 China

This paper presents simulated channel patterns for various scenarios in a conceptual alluvial valley by an improved two-dimensional (2-D) mathematical model described in the companion paper. Starting from the same initial channel, different channel patterns have been simulated over a real time period of 250 days for varied boundary and initial conditions, including the inlet water discharge and sediment load, initial valley slope, and erodibility of river banks. Impacts of these control factors are discussed, in terms of the longitudinal bottom profiles of simulated fluvial channels, the geometry of channel cross sections, and the water surface profiles in the conceptual river valley. Results suggest that the upper and lower parts of the same channel may have different planforms because the sediment transport conditions of the two parts differ greatly. Simulated causal relationship between control variables and channel patterns agrees qualitatively with known channel pattern theories.

关键词： Channel pattern changes Numerical simulation Resistance to bank erosion Sediment transport Braided channel

Scan chain design for shift power reduction in scan-based testing

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Science china(Information Sciences) 2011年第4期54卷 767-777页

作者： LI Jia 1,HU Yu 2 & LI XiaoWei 2 1 The School of Software,tsinghua university,beijing 100084,china 2 The Institute of Computing Technology,Chinese Academy of Sciences,beijing 100190,china The School of Software Tsinghua University The Institute of Computing Technology Chinese Academy of Sciences

Test power of VLSI systems has become a challenging issue *** scan shift power dominates the average test power and restricts clock frequency of the shift phase,leading to excessive thermal accumulation and long test *** paper proposes a scan chain design technique to solve the above *** on weighted transition metric (WTM),the proposed extended WTM (EWTM) that is utilized to guide the scan chain design algorithm can estimate the scan shift power in both the shift-in and shift-out ***,the wire length overhead of the proposed scan chain design can also be reduced by the proposed distance of EWTM (DEWTM) *** results confirm that the proposed approach can significantly reduce scan shift power with low wire length overhead.

关键词： low power DfT scan-based testing test power reduction scan chain design

Arbitrarily long distance quantum communication using inspection and power insertion

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Chinese Science Bulletin 2009年第1期54卷 158-162页

作者： WANG WanYing1,2,WANG Chuan1,2,ZHANG GuangYu1,3 & LONG GuiLu1,2 1 Department of Physics,tsinghua university,beijing 100084,china 2 tsinghua National Laboratory for Information Science and Technology,tsinghua university,beijing 100084,china 3 College of Applied Science,Harbin university of Science and Technology,Harbin 150080,china Department of Physics Tsinghua University Beijing 100084 China tsinghua National Laboratory for Information Science and Technology Tsinghua University Beijing 100084 China College of Applied Science Harbin University of Science and Technology Harbin 150080 China

The biggest obstacle for long distance quantum communication is the channel loss and the channel noise on photons. In this paper,a method to solve this problem was analyzed using inspection and power insertion (IPI). It is proved that quantum communication may be established over arbitrarily long distance using this technology. The amount of resources required is a polynomial function of the dis-tance. IPI is proposed as a general technique to prolong quantum secure direct communication where secret messages are transmitted directly over a quantum channel.

关键词：长距离量子通信量子安全通信量子密匙分布噪声

An analysis of seismic attenuation in random porous media

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Science china(Physics,Mechanics & Astronomy) 2010年第4期53卷 628-637页

作者： LIU Jiong1, BA Jing2, MA JianWei1 & YANG HuiZhu1 1 Institute of Seismic Exploration, School of Aerospace, tsinghua university, beijing 100084, china 2 research Institute of Petroleum Exploration & Development, Petrochina, beijing 100083, china tsinghua university Institute of Seismic Exploration School of Aerospace Beijing China (GRID:grid.12527.33) (ISNI:***) Petrochina Research Institute of Petroleum Exploration &amp Development Beijing China (GRID:grid.453058.f) (ISNI:***)

The attenuation of seismic wave in rocks has been one of the interesting research topics, but till now no poroelasticity models can thoroughly explain the strong attenuation of wave in rocks. In this paper, a random porous medium model is designed to study the law of wave propagation in complex rocks based on the theory of Biot poroelasticity and the general theory of stochastic process. This model sets the density of grain, porosity, permeability and modulus of frame as random parameters in space, and only one fluid infiltrates in rocks for the sake of better simulation effect in line with real rocks in earth strata. Numerical simulations are implemented. Two different inverse quality factors of fast P-wave are obtained by different methods to assess attenuation through records of virtual detectors in wave field (One is amplitude decay method in time domain and the other is spectral ratio method in frequency domain). Comparing the attenuation results of random porous medium with those of homogeneous porous medium, we conclude that the attenuation of seismic wave of homogeneous porous medium is far weaker than that of random porous medium. In random porous media, the higher heterogeneous level is, the stronger the attenuation becomes, and when heterogeneity σ = 0.15 in simulation, the attenuation result is consistent with that by actual observation. Since the central frequency (50 Hz) of source in numerical simulation is in earthquake band, the numerical results prove that heterogeneous porous structure is one of the important factors causing strong attenuation in real stratum at intermediate and low frequency.

关键词： the theory of stochastic process the theory of Biot poroelasticity the attenuation of seismic wave inverse quality factor

Micro-computed tomography for small animal imaging: Technological details

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Progress in Natural Science:Materials International 2008年第5期18卷 513-521页

作者： Hao Li, Hui Zhang , Zhiwei Tang, Guangshu Hu Department of Biomedical Engineering, tsinghua university, beijing 100084, china Department of Biomedical Engineering Tsinghua University Beijing 100084 China

The high-resolution micro-computed tomography (micro-CT) system has now become an important tool for biological research. The micro-CT system enables a non-invasive inspection to screen anatomical changes in small animals. The promising advantages include high-spatial resolution, high sensitivity to bone and lung, short scan time and cost-e ectiveness. The dose received by the small animal might be a critical concern in the research. In this article, the choice of the components, fundamental physical problems, the image recon- struction algorithm and the representative applications of micro-CT are summarized. Some results from our research group are also pre- sented to show high-resolution images obtained by the micro-CT system.

关键词： Micro-computed tomography Small animal X-ray

Remarks on the bounds for cryptanalysis of low private key RSA

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Progress in Natural Science:Materials International 2009年第10期19卷 1327-1331页

作者： Haijian Zhou a,Ping Luo b,Daoshun Wang a,Yiqi Dai a a Department of Computer Science and Technology,tsinghua university,beijing 100084,china b School of Software,tsinghua university,beijing 100084,china Department of Computer Science and Technology Tsinghua University Beijing 100084 China School of Software Tsinghua University Beijing 100084 China

Boneh and Durfee have developed a cryptanalytic algorithm on low private key *** algorithm is based on lattice basis reduction and breaks RSA with private key d < N0:*** on,an improved version by Blmer and May enhan... 详细信息

Boneh and Durfee have developed a cryptanalytic algorithm on low private key *** algorithm is based on lattice basis reduction and breaks RSA with private key d 277 for ordinary RSA systems with a 1024-bit public key eN;eT.

关键词： RSA Cryptanalysis Low private key Lattice basis reduction

research Development of Endocrine Disrupting Chemicals(EDCs) in Water in china

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Biomedical and Environmental Sciences 2003年第1期16卷 62-67页

作者： HONG ZHOU, XIAO-JIAN ZHANG, AND ZHAN-SHENG WANGDepartment of Environmental Sciences and Engineer, tsinghua university, beijing 100084, china Department of Environmental Sciences and Engineer Tsinghua University Beijing 100084 Chin

More and more importance has been attached to the problem of endocrine disrupting chemicals (EDCs) since 1960s. This article elaborates the recent research progress of EDCs in water and the trends in the near future i... 详细信息

关键词： Endocrine disrupting chemicals Source water Alkylphenols Phthalates Atrazine

A SOLUTION PROCEDURE FOR LOWER BOUND LIMIT AND SHAKEDOWN ANALYSIS BY SGBEM

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Acta Mechanica Solida Sinica 2001年第2期14卷 118-129页

作者： Zhang Xiaofeng Liu Yinghua Cen Zhangzhi (Department of Engineering Mechanics,tsinghua university,beijing 100084,china) ***

The symmetric Galerkin boundary element method (SGBEM) instead ofthe finite element method is used t perform lower bound limit andshakedown analysis of structures. The self-equilibrium stress fieldsare constructed by a linear combination of several basicself-equilibrium stress fields with parameters to be *** basic self-equilibrium stress fields are expressed as elasticresponses of the body to im- posed permanent strains and obtainedthrough elastic-plastic incremental analysis.

关键词： limit and shakedown analysis SGBEM self-equilibrium stress