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THEORY OF MUM FOR METAL SPHERICAL ROTOR WITH CONTACTLESS SUSPENSION

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Chinese Journal of Mechanical Engineering 2004年第2期17卷 243-246页

作者： He Xiaoxia Gao Zhongyu Wang Yongliang department of Precision Instruments and Mechinery,tsinghua university,beijing 100084, China department of Precision Instruments and Machinery Tsinghua University Beijing 100084 China

Based on the motion equations of an unbalanced spherical rotor withcontactless suspension, three methods of MUM (mass unbalance measurement) are put forward to measurethe total mass unbalance, radical mass unbalance and radical mass unbalance of the rotor. Totalmass unbalance is obtained when the unbalanced rotor plays as a simple pendulum in static *** pendulant period and pendulant midpoint indicate magnitude and direction of total massunbalance of the rotor respectively. Analysis of the motion equations by using the averaging methodyields that the rotor will do a special side oscillation when an auxiliary system makes the rotorspin about its pole axis which is orientating toward the local vertical. The radical mass unbalancecan be obtained by building a proper displacement sensor to sense the amplitude of the sideoscillation. Necessary analysis of the motion equations also shows that when the rotor spins at asmall angular velocity and the rotary axis is perpendicular to the vertical, the pole axis of therotor will precess slowly about the vertical by virtue of the axial mass unbalance. The axial massunbalance can be estimated from the time history of the spin vector of the rotor. Finally,measurement precision of the three methods is compared and how the external torque affects themeasurement precision for the three methods are examined.

关键词： Mass unbalance measurement Radical mass unbalance Axial mass unbalance Static balancing Averaging method

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

Constraints on Cardassian universe from Gamma ray bursts

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Science China(Physics,Mechanics & Astronomy) 2010年第9期53卷 1720-1725页

作者： WANG TaiShan1 & LIANG Nan2 1 department of Physics & Center for Astrophysics,tsinghua university,beijing 100084,China 2 department of Astronomy,beijing Normal university,beijing 100875.China tsinghua university Department of Physics &amp Center for Astrophysics Beijing China (GRID:grid.12527.33) (ISNI:***) beijing Normal university Department of Astronomy Beijing China (GRID:grid.20513.35) (ISNI:***)

Constraints on the original Cardassian model and the modified polytropic Cardassian model are examined from the recently derived 42 gamma-ray bursts(GRBs) data calibrated with the method that can avoid the circularity *** results show that GRBs can be an optional observation to constrain the Cardassian *** the GRBs data with the newly de-rived size of baryonic acoustic oscillation peak from the Sloan Digital Sky Survey(SDSS),and the position of the first acoustic peak of the Cosmic Microwave Background radiation(CMB) from Wilkinson Microwave Anisotropy Probe(WMAP),we find Ωm0=0.27+0.02-0.02,n=0.06+0.07-0.08(1σ) for the original Cardassian model,and Ωm0=0.27+0.23-0.02,n=-0.09+0.23-1.91,β=0.82+2.10-0.62(1σ) for the modified polytropic Cardassian model.

关键词： Cardassian Gamma ray burst Cosmic Microwave Background baryonic acoustic oscillation

Numerical exploration of new features on three-dimensional transition of a cylinder wake

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Science China Mathematics 2004年第z1期47卷 69-80页

作者： LING Guocan, XIONG Jun & ZHU KeqinState Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of sciences, beijing 100080, China department of Engineering Mechanics, tsinghua university, beijing 100084, China State Key Laboratory of Nonlinear Mechanics Institute of Mechanics Chinese Academy of Sciences Beijing China department of Engineering Mechanics Tsinghua University Beijing China

The three-dimensional transition of the wake flow behind a circular cylinder is studied in detail by direct numerical simulations using 3D incompressible N-S equations for Reynolds number ranging from 200 to 300. New features and vortex dynamics of the 3D transition of the wake are found and investigated. At Re = 200, the flow pattern is characterized by mode A instability. However, the spanwise characteristic length of the cylinder determines the transition features. Particularly for the specific spanwise characteristic length linear stable mode may dominate the wake in place of mode A and determine the spanwise phase difference of the primary vortices shedding. At Re = 25. and 300 it is found that the streamwise vortices evolve into a new type of mode "dual vortex pair mode" downstream. The streamwise vortex structures switch among mode A, mode B and dual vortex pair mode from near wake to downstream wake. At Re = 25., an independent low frequency fm in addition to the vortex shedding frequency fs is identified. Frequency coupling between fm and fs occurs. These result in the irregularity of the temporal signals and become a key feature in the transition of the wake. Based on the formation analysis of the streamwise vorticity in the vicinity of cylinder, it is suggested that mode A is caused by the emergence of the spanwise velocity due to three dimensionality of the incoming flow past the cylinder. Energy distribution on various wave numbers and the frequency variation in the wake are also described.

关键词： cylinder, wake, 3D transition, Fourier-spectral-spectral-element method, direct numerical simulation (DNS).

ELASTO-PLASTICITY ANALYSIS BASED ON COLLOCATION WITH THE MOVING LEAST SQUARE METHOD

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Acta Mechanica Solida Sinica 2003年第2期16卷 162-170页

作者： Song Kangzu Zhang Xiong Lu Mingwan (department of Engineering Mechanics,tsinghua university,beijing 100084,China) department of Engineering Mechanics Tsinghua University Beijing 100084 China

A meshless approach based on the moving least square method is developed for elasto-plasticity analysis,in which the incremental formulation is *** this approach,the dis- placement shape functions are constructed by using the moving least square approximation,and the discrete governing equations for elasto-plastic material are constructed with the direct collo- cation *** boundary conditions are also imposed by *** method established is a truly meshless one,as it does not need any mesh,either for the purpose of interpolation of the solution variables,or for the purpose of construction of the discrete *** is simply formu- lated and very efficient,and no post-processing procedure is required to compute the derivatives of the unknown variables,since the solution from this method based on the moving least square approximation is already smooth *** examples are given to verify the accuracy of the meshless method proposed for elasto-plasticity analysis.

关键词： meshless method elasto-plasticity collocation method moving least square incremental formulation

New Monotonicity Formulae for Semi-linear Ellipti and Parabolic Systems

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Chinese Annals of Mathematics,Series B 2010年第3期31卷 411-432页

作者： Li MA Xianfa SONG Lin ZHAO department of mathematical sciences Tsinghua University Beijing 100084 China. department of Mathematics Tianjin University Tianjin 300072 China.

The authors establish a general monotonicity formula for the following elliptic system △ui＋fi（x,ui,…,um）=0 in Ω,where Ω belong to belong to R^n is a regular domain, （fi（x, u1,... ,um）） = △↓F（x,→↑u）, F（x,→↑u ） is a given smooth function of x ∈ R^n and →↑u = （u1,…,um） ∈ R^m. The system comes from understanding the stationary case of Ginzburg-Landau model. A new monotonicity formula is also set up for the following parabolic systemδtui-△ui-fi（x,ui,…,um）=0 in（ti,t2）×R^n,where t1 〈 t2 are two constants, （fi（x,→↑u ） is given as above. The new monotonicity formulae are focused more attention on the monotonicity of nonlinear terms. The new point of the results is that an index β is introduced to measure the monotonicity of the nonlinear terms in the problems. The index β in the study of monotonieity formulae is useful in understanding the behavior of blow-up sequences of solutions. Another new feature is that the previous monotonicity formulae are extended to nonhomogeneous nonlinearities. As applications, the Ginzburg-Landau model and some different generalizations to the free boundary problems are studied.

关键词： Elliptic systems Parabolic system Monotonicity formula Ginzburg-Landau model

A secure multi-party computation solution to intersection problems of sets and rectangles

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Progress in Natural Science:Materials International 2006年第5期16卷 538-545页

作者： LI Shundong, DAI Yiqi, WANG Daoshun and LUO Ping (department of Computer Science and Technology, beijing Normal university, beijing 100875. China department of Computer Science and Technology,{5., beijing 100084, China) department of Computer Science and Technology Beijing Normal University Beijing 100875 China 2. department of Computer Science and Technology Tsinghua University Beijing 100084 China

Secure multi-party computation (SMC) is a research focus in international cryptographic community. At present, there is no SMC solution to the intersection problem of sets. In this paper, we first propose a SMC solution to this problem. Applying Cantor encoding method to computational geometry problems, and based on the solution to set-intersection problem, we further propose solutions to points inclusion problem and intersection problem of rectangles and further prove their privacy-preserving property with widely accepted simulation paradigm. Compared with the known solutions, these new solutions are of less computational complexity and less communication complexity, and have obvious superiority in computational and communication complexity.

关键词： Cantor encoding secure multi-party computation set-intersection rectangle-intersection computational complexity.

On (2~m + 1)-variable symmetric Boolean functions with submaximum algebraic immunity 2^(m-1)

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Science China Mathematics 2009年第1期52卷 17-28页

作者： LIAO QunYing1, LIU Feng2 & FENG KeQin2 1 College of Mathematics and Software sciences, Sichuan Normal university, Chengdu 610066, China 2 department of mathematical sciences, tsinghua university, beijing 100084, China College of Mathematics and Software sciences Sichuan Normal University Chengdu China department of mathematical sciences Tsinghua University Beijing China

All (2m +1)-variable symmetric Boolean functions with submaximal algebraic immunity 2m-1 are described and constructed. The total number of such Boolean functions is 32 ·22m-3 +3m-2 · 24 - 2 for m≥2.

关键词： symmetric Boolean function algebraic immunity cryptography

Mapping and overlapping based carrier frequency searching technique for rapid GNSS long PN-code acquisition

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Science China(Information sciences) 2010年第12期53卷 2642-2652页

作者： LI Hong ,LU MingQuan & FENG ZhenMing department of Electronic Engineering,tsinghua university,beijing 100084,China department of Electronic Engineering Tsinghua University

In global navigation satellite systems(GNSS),because of the long period and high chip rate of long pseudo-noise(PN) code,the rapid acquisition is hard to *** speed up search process,in the paper,a mapping and overlapping based carrier frequency searching technique is *** mapping incoming signals of the same interval to different carrier frequency cells and overlapping together the mapped incoming signals that correspond to the same code phase,the technique reduces the number of the cells to be *** effect of the technique on detection and mean acquisition time performance is *** is shown that the technique reduces the cells to be searched and shortens mean acquisition time at the expense of degrading detection *** technique is fit to the previously published acquisition methods and is capable of improving their mean acquisition time *** and simulation results validate the analysis.

关键词： carrier frequency cells mapping overlapping acquisition performance