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Tsinghua Science and Technology

Issue 3 • Date June 2002

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Displaying Results 1 - 25 of 28
  • [Front cover]

    Page(s): c1
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    Freely Available from IEEE
  • Contents

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    Freely Available from IEEE
  • Boltzmann equations with quantum effects (1): Long time behavior of spatial decay solutions

    Page(s): 215 - 218
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (348 KB)  

    The Boltzmann equations for Fermi-Dirac particles and Bose-Einstein particles, both in the absence of external force fields, are combined into a more general form called the Boltzmann equation with quantum effects (BQE). It is assumed that the initial data f(x, v, 0) satisfies 0 ≤ f(x, v, 0) < cΦ(x, v, 0) for a positive constant c and certain types of control functions Φ(x, v, t). Then within a given function space B(Φ), we prove that f(x + tv, v, t) uniformly converges to f = (x, v) in a certain norm where f = (x, v) = limf(x + tv, v, t) and different initial data determines different long time limits. View full abstract»

    Open Access
  • Boltzmann equations with quantum effects (2): Entropy identity, existence and uniqueness of spatial decay solutions

    Page(s): 219 - 222
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    A previous study[l] is continued by investigating the Boltzmann equation for particles with quantum effects (BQE). First, the corresponding entropy identity is proved, then if the initial data f(x, v, 0) satisfies 0 ≤ f(x, v, 0) ≤ CΦ (x, v, 0) for a constant 0 < C < ∞ and function Φ(x, v, t), we prove the existence and uniqueness of spatial decay solutions of the BQE within a given function space B(Φ) using fixed point theory. Moreover, if there is a continuous function F(x, v) which belongs to a function set, then there exists a mild solution f(x, v, t) of the BQE such that f∞(x, v) = limf(x+ vt, v, t) = F(x, v). t→=∝ View full abstract»

    Open Access
  • Two ARCH models and their limitations as diffusion processes

    Page(s): 223 - 227
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    Two typical ARCH models: the ASDARCH model and the APARCH model are analyzed. Let Yk, and σ2k denote the log returns and the volatility. When the time interval h goes to zero, (Yk; σ2k), as a discrete time Markov chain system, weakly converges to a continuous time diffusion process. The continuous time approximation of the ASDARCH model is done using two different methods. With some transformation, these two results are equivalent to high frequency data. The continuous time approximation of the APARCH model is obtained by a different procedure. View full abstract»

    Open Access
  • Mixed finite element method and higher-order local artificial boundary conditions for exterior 3-D Poisson equation

    Page(s): 228 - 234
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (502 KB)  

    The mixed finite element method is used to solve the exterior Poisson equations with higher-order local artificial boundary conditions in 3-D space. New unknowns are introduced to reduce the order of the derivatives of the unknown to two. The result is an equivalent mixed variational problem which was solved using bilinear finite elements. The primary advantage is that special finite elements are not needed on the adjacent layer of the artificial boundary for the higher-order derivatives. Error estimates are obtained for some local artificial boundary conditions with prescibed orders. A numerical example demonstrates the effectiveness of this method. View full abstract»

    Open Access
  • Generalization of Hopf functional equation

    Page(s): 235 - 242
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    This paper generalizes the Hopf functional equation in order to apply it to a wider class of not necessarily incompressible fluid flows. We start by defining characteristic functionals of the velocity field, the density field and the temperature field of a compressible field. Using the continuity equation, the Navier-Stokes equations and the equation of energy we derive a functional equation governing the motion of an ideal gas flow and a van der Waals gas flow, and then give some general methods of deriving a functional equation governing the motion of any compressible fluid flow. These functional equations can be considered as the generalization of the Hopf functional equation. View full abstract»

    Open Access
  • RCC arch dam structure on the Taxi River and Water storage measure during construction

    Page(s): 243 - 250
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (628 KB)  

    The new structure of roller compacted concrete (RCC) arch dams is presented for extremely cold and earthquake prone areas. The influence of construction plans and improved materials on the stresses in the Taxi River dam is also given. Earlier impoundment of water is shown to not only benefit the engineering design but also improve the stresses during construction in winter. Low cement content in the concrete and artificial short joints improved the monolithic structure and the transmitted forces. The concrete plug installed in the first cooled part of the arch dam provides excellent force transmission in the arch, which increases the monolith of the earlier arch, reduces the increasing thermal stresses that occur later, and improves the deformation flexibility of the dam. View full abstract»

    Open Access
  • Experimental study of turbulent wake behind a sine shaped Island in a Shallow-Water layer layer

    Page(s): 251 - 253
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    A series of experiments is conducted to study shallow-water flow in the wake of a sine shaped island. Digital particle imaging velocimetry (DPIV) is used to measure velocities in the turbulent wake behind a sine shaped island for different characteristic coefficients S. Flow streamlines are given for the wake flows. The measured results show that the characteristic coefficient S is uniquely related to the flow pattern around a sine shaped island in a shallow water layer. An S value of approximately 0.20 is the critical value for transition from a vortex street to unsteady flow and a value of approximately 0. 40 is the critical value for transition from unsteady flow to steady flow. View full abstract»

    Open Access
  • Stochastic boundary element analysis of concrete gravity dam

    Page(s): 254 - 257
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (331 KB)  

    Stochastic boundary integral equations for analyzing large structures are obtained from the partial derivatives of basic random variables. A stochastic boundary element method based on the equations is developed to solve engineering problems of gravity dams using random factors including material parameters of the dam body and the foundation, the water level in the upper reaches, the anti-slide friction coefficient of the dam base, etc. A numerical example shows that the stochastic boundary element method presented in this paper to calculate the reliability index of large construction projects such as a large concrete gravity dam has the advantages of less input data and more precise computational results. View full abstract»

    Open Access
  • Dimensional synthesis design of novel parallel machine tool

    Page(s): 258 - 262
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    This paper presents dimensional synthesis design theory for a novel planar 3-DOF (degrees of freedom) parallel machine tool. Closed-form solutions are developed for both the inverse and direct kinematics. The formulation of the dexterity and the definitions of the theoretical workspace and the valid workspace are used to analyze the effects of the design parameters on the dexterity and workspace. The analysis results are used to propose an approach to satisfy the platform motion requirement while realizing orientation capability, dexterity and valid workspace. A design example is given to illustrate the effectiveness of this approach. View full abstract»

    Open Access
  • Optimal nonlinear filter for INS alignment

    Page(s): 263 - 269
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    All the methods to handle the inertial navigation system (INS) alignment were sub-optimal in the past. In this paper, particle filtering (PF) as an optimal method is used for solving the problem of INS alignment. A sub-optimal two-step filtering algorithm is presented to improve the real-time performance of PF. The approach combines particle filtering with Kalman filtering (KF). Simulation results illustrate the superior performance of these approaches when compared with extended Kalman filtering (EKF). View full abstract»

    Open Access
  • Experimental and theoretical study of Young modulus in micromachined polysilicon films

    Page(s): 270 - 275
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    The elastic modulus is a very important mechanical property in micromachined structures. Several design issues such as resonant frequencies and stiffness in the micromachined structures are related to the elastic modulus. In addition, the accuracy of results from finite element models is highly dependent upon the elastic modulus. In this study, the Young modulus of micromachined thin polysilicon films has been investigated with a new tensile test machine using a magnetic-solenoid force actuator with linear response, low hysteresis, no friction and direct electrical control. The tensile test results show that the measured average value of Young modulus for a typical sample, (164 ± 1. 2) GPa, falls within the theoretical bounds of the texture model. These results will provide more reliable design of polysilicon microelectromechanical systems (MEMS). View full abstract»

    Open Access
  • Casimir force correction between parallel polysilicon plates

    Page(s): 276 - 280
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (494 KB)  

    Both the size of the components and the separation between them in some microelectromechanical systems (MEMS) are already in the sub-micrometer regime, where quantum mechanical effects such as the Casimir effect will need to be considered. This paper theoretically analyzes the roughness, electrical conductivity, and temperature corrections due to the Casimir force between two parallel polysilicon plates. The theoretical results show that the combined effects of roughness, conductivity and temperature cause a maximum relative error of the Casimir force per unit area of 26.2% between parallel polysilicon plates separated by 1 p.m. Therefore, the surface roughness and finite conductivity corrections should be taken into account when calculating precise Casimir forces with separations on the order of 1 μm. View full abstract»

    Open Access
  • Optimal configuration of a redundant robotic arm: Compliance approach

    Page(s): 281 - 285
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (361 KB)  

    Applications of robots in tasks where the robot's end-effector bears loads, such as manipulating or assembling an object, picking-and-placing loads, grinding or drilling, demand precision. One aspect that improves precision is the limitation, if not elimination, of manipulator compliance. This paper presents a manipulator compliance optimization approach for determining an optimal manipulator configuration for a given position in the robot's task space. A numerical solution for minimal compliance, a nonlinear constrained optimization problem, is presented for an arbitrary position and illustrated by an example, using a model developed on ADAMS software and using MATLAB optimization tools. Also, this paper investigates the optimal value function for robot tasks in which the tool-point is subjected to applied force as it generates an important trajectory such as in grinding processes. The optimal value function is needed for optimal configuration control. View full abstract»

    Open Access
  • Numerical simulation model of laminar hydrogen/air diffusion flame

    Page(s): 286 - 290
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    A numerical simulation model is developed for a laminar hydrogen/air diffusion flame. Nineteen species and twenty chemical reactions are considered. The chemical kinetics package (CHEMKIN) subroutines are employed to calculate species thermodynamic properties and chemical reaction rate constants. The flow field is calculated by simultaneously solving a continuity equation, an axial momentum equation and an energy equation in a cylindrical coordinate system. Thermal diffusion and Brownian diffusion are considered in the radial direction while they are neglected in the axial direction. The results suggest that the main flame is buoyancy-controlled. View full abstract»

    Open Access
  • Acoustic signal feature extraction of vehicle targets

    Page(s): 291 - 293
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (218 KB)  

    Acoustic signal feature extraction is an important part of target recognition. The mechanisms for producing acoustic signals and their propagation are analyzed to extract the features of the radiated noise from different targets. Analysis of the acoustic spectra of typical vehicle targets acquired outdoors shows that the vehicles can be classified based on the acoustic spectra and amplitudes. View full abstract»

    Open Access
  • Modeling of a cooperation environment in a virtual enterprise

    Page(s): 294 - 298
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (377 KB)  

    Virtual enterprises (VEs) are the most promising structure for future enterprises. The cooperative environment of VEs is investigated in this paper. The cooperation in a VE is a process and the depth of the cooperation and the information transparency change in different phases of the cooperation. A tri-layered cooperative structure pattern is discussed with a tri-layered cooperative process model which includes the conceptual cooperation model, the detailed cooperation model, and the executive cooperation model. Analysis of the tri-layered process modeling provides a foundation for the cooperation environment. View full abstract»

    Open Access
  • Hierarchical least squares identification and its convergence for large scale multivariable systems

    Page(s): 299 - 304
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (413 KB)  

    The recursive least squares identification algorithm (RLS) for large scale multivariable systems requires a large amount of calculations, therefore, the RLS algorithm is difficult to implement on a computer. The computational load of estimation algorithms can be reduced using the hierarchical least squares identification algorithm (HLS) for large scale multivariable systems. The convergence analysis using the Martingale Convergence Theorem indicates that the parameter estimation error (PEE) given by the HLS algorithm is uniformly bounded without a persistent excitation signal and that the PEE consistently converges to zero for the persistent excitation condition. The HLS algorithm has a much lower computational load than the RLS algorithm. View full abstract»

    Open Access
  • Dispersion compensation of 180-km 10-Gb/s transmission system using chirped fiber grating

    Page(s): 305 - 308
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (375 KB)  

    Many methods have been suggested to reduce dispersion in optical fiber communication. Among these methods, chirped fiber grating (CFG) is a promising scheme. This paper describes a linearly chirped fiber grating with 95% reflectivity and 0. 3 nm bandwidth written using a double exposure method with a uniform phase mask. The CFG resonant wavelength is 1554. 5 nm and dispersion is 1700 ps/nm. Dispersion compensation in a 10-Gb/s optical transmission system has been demonstrated using this chirped fiber grating. The power penalty induced by the dispersion compensation after 180-km transmission is 1 dB. This is the first report describing dispersion compensation of 180 km at 10-Gb/s optical transmission now-return to zero (NRZ) system in China. View full abstract»

    Open Access
  • Bi-spectrum scattering model for conducting randomly rough surface

    Page(s): 309 - 316
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    A scattering model is developed to predict the scattering coefficient of a conducting randomly rough surface by analyzing the randomly rough surface in the spectral domain using the bi-spectrum method. For common randomly rough surfaces without obvious two-scale characteristics, a scale-compression filter can divide the auto-correlation spectrum into two parts with different correlation lengths. The Kirchhoff approximation and the small perturbation method are used to obtain the surface field, then a bistatic scattering model, the bi-spectrum model (BSM), is used to derive an explicit expression from the surface field. Examples using the integral equation model (IEM), finite difference of the time domain (FDTD) method, and BSM show that the BSM accuracy is acceptable and its range of validity is similar to IEM. BSM can also be extended to a scattering model for dielectric randomly rough surfaces. View full abstract»

    Open Access
  • Image mosaicing algorithm for rolled fingerprint construction

    Page(s): 317 - 321
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1492 KB)  

    Fingerprint identification is one of the most important biometric authentication methods. However, current devices for recording digital fingerprints can only capture plain-touch fingerprints. Rolled fingerprints have much more information for recognition, so a method is needed to construct a rolled fingerprint from a series of plain-touch fingerprints. This paper presents a novel algorithm for image mosaicing for real time rolled fingerprint construction in which the images are assembled with corrections to create a smooth, non-fragmented rolled fingerprint in real time. Experimental results demonstrate its effectiveness by comparing it with other conventional algorithms. View full abstract»

    Open Access
  • In-plane elastic buckling of arch

    Page(s): 322 - 325
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (318 KB)  

    The in-plane elastic buckling behavior of arches is investigated using a new finite-element approach for the nonlinear analysis. The linear buckling, nonlinear primary buckling, and secondary bifurcation buckling behavior of arches are compared taking into account the large deformation and the effects of initial geometric imperfections or perturbations. The theoretical investigation emphasizes the nonlinear secondary bifurcation buckling behavior for a full span uniformly distributed load. The efficiency of compact method for tracing secondary buckling path is shown through several examples. Finally, a new structural design, which prevents the secondary bifurcation buckling by adding some crossed cables across the arch, is proposed to improve the limit load carrying capacity. View full abstract»

    Open Access
  • Large eddy simulation of flow field in vector flow clean-room

    Page(s): 326 - 330
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (428 KB)  

    The turbulent large eddy simulation (LES) technique and the finite element method (FEM) of computational fluid dynamics (CFD) are used to predict the three-dimensional flow field in a vector flow clean-room under empty state and static state conditions. The partly expanded Taylor-Galerkin (TG) discretization scheme is combined with implicit stream-upwind diffusion in the finite element formulation of the basic equations with Gauss filtering. The vortex viscosity subgrid model is used in the numerical simulation. The numerical results agree well with the available experimental data, showing that the LES method can more accurately predict the size and location of large eddies in clean-rooms than the standard k-∊ two equation model. View full abstract»

    Open Access
  • Open Access

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Tsinghua Science and Technology (Tsinghua Sci Technol) aims to highlight scientific achievements in computer science, electronic engineering, and other IT fields. Contributions all over the world are welcome.

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