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Tsinghua Science and Technology

Issue 4 • Date Dec. 2000

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Displaying Results 1 - 25 of 29
  • [Front cover]

    Publication Year: 2000 , Page(s): c1
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    Freely Available from IEEE
  • Contents

    Publication Year: 2000 , Page(s): 1
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    Freely Available from IEEE
  • Dynamic modeling and parameter identification of power systems

    Publication Year: 2000 , Page(s): 408
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    Open Access
  • Development of the field of flexible AC transmission systems (FACTS)

    Publication Year: 2000 , Page(s): 413
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    Open Access
  • Atomic ionization by electron impact

    Publication Year: 2000 , Page(s): 339 - 342
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (911 KB)  

    The field of atomic ionization by electron impact is several decades old. In that period of time significant progress has been made in several aspects of the problem and we have learned a lot about ionizing collisions as a result of this work. Over the years both the experiments and theories have improved dramatically. Experiments are now able to measure absolute triple differential cross sections for both in-plane or out-of-plane geometries. Theories have been getting better and better at including all the 3-body interactions in the wavefunction for the system. However during the history of the field experiment has been ahead of theory and it is just very recently that theory has started to catch up. In this paper we will show that theory is now able to accurately predict the results of electron impact ionization of hydrogen for intermediate and higher energies. View full abstract»

    Open Access
  • Spin effects in collisions of electrons with atoms and molecules

    Publication Year: 2000 , Page(s): 343 - 353
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (2408 KB)  

    Some recent experimental and theoretical work on spin-dependent electron-atom and electron-molecule collisions is reviewed. The spin is involved in such collisions by explicit spin-dependent interactions such as the spin-orbit interaction of the continuum electron — Mott scattering but also by exchange which in conjunction with the Pauli principle gives rise to observable spin exchange effects. We present results for Mn and Na atoms and experiments in which electron dichroism with chiral molecules has been studied. View full abstract»

    Open Access
  • One-dimensional anisotropic band gap structure

    Publication Year: 2000 , Page(s): 354 - 359
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1060 KB)  

    The band gap structure of one-dimensional anisotropic photonic crystal has been studied by means of the transfer matrix formalism. From the analytic expressions and numeric calculations we see some general characteristics of the band gap structure of anisotropic photonic crystals each band separates into two branches and the two branches react to polarization sensitively. In the practical case of oblique incidence gaps move towards high frequency when the angle of incidence increases. Under some special conditions the two branches become degenerate again. View full abstract»

    Open Access
  • Mathematical model of extrinsic blood coagulation cascade dynamic system

    Publication Year: 2000 , Page(s): 360 - 364
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (964 KB)  

    The blood coagulation system is very important to life. This paper presents a mathematical blood coagulation model for the extrinsic pathway. This model simulates clotting factor VIII which plays an important role in the coagulation mechanism. The mathematical model is used to study the equilibrium stability orbit structure attractors and global stability behavior with conclusions in accordance with the physiological phenomena. Moreover the results provide information about blood related illnesses which can be used for further study of the coagulation mechanism. View full abstract»

    Open Access
  • Wavelet-galerkin method for the singular perturbation problem with boundary layers

    Publication Year: 2000 , Page(s): 365 - 369
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (955 KB)  

    A Wavelet-Galerkin method is proposed to solve the singular perturbation problem with boundary layers numerically. Because there are boundary layers in the solution of the singular perturbation problem the approximation spaces with different scale wavelets and boundary bases are chosen. In addition the computation of the inner integrals is transformed to an eigenvalue problem. Therefore a high accuracy method with reasonable computation is obtained. On the other hand there is an explicit diagonal preconditioning which makes the condition number of the stiff matrix become bounded by a constant. The error estimate of the Wavelet-Galerkin method and the analysis of the computation complexity are given. The numerical examples show that the method is feasible and effective for solving the singular perturbation problem with boundary layers numerically. View full abstract»

    Open Access
  • Lower bound for ideal class numbers of real quadratic function fields

    Publication Year: 2000 , Page(s): 370 - 371
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (465 KB)  

    In this paper the theory of continued fractions of algebraic functions will be used to give a general theorem on lower bounds for class numbers of real quadratic function fields K = k (\sqrt {D}) . The bounds are given more explicitly for six types of real quadratic function fields. As a consequence six classes of real quadratic function fields with ideal class number greater than one are given. View full abstract»

    Open Access
  • Ideal class groups and subgroups of real quadratic function fields

    Publication Year: 2000 , Page(s): 372 - 373
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (455 KB)  

    In this paper we study the real quadratic function fields K = k (\sqrt {D}) , given a necessary and sufficient condition for the ideal class group H K of any real quadratic function field K to have a cyclic subgroup of order n and obtained eight series of such fields. The ideal class numbers h(Ok) of K in the series all have a factor n. View full abstract»

    Open Access
  • Nonlinear time series model for shape classification using neural networks

    Publication Year: 2000 , Page(s): 374 - 377
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (812 KB)  

    A complex nonlinear exponential autoregressive CNEAR model for invariant feature extraction is developed for recognizing arbitrary shapes on a plane. A neural network is used to calculate the CNEAR coefficients. The coefficients which constitute the feature set are proven to be invariant to boundary transformations such as translation rotation scale and choice of starting point in tracing the boundary. The feature set is then used as the input to a complex multilayer perceptron C-MLP network for learning and classification. Experimental results show that complicated shapes can be accurately recognized even with the low-order model and that the classification method has good fault tolerance when noise is present. View full abstract»

    Open Access
  • Determination of mechanical properties of micromembranes with compressive residual stress

    Publication Year: 2000 , Page(s): 378 - 382
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1246 KB)  

    A novel model of a load-deflection method to determine the mechanical properties of micromembranes with compressive residual stress is described. Since thin film structures are frequently used in micro devices characterisation of mechanical properties of thin films is desired by the design and fabrication of micromachines. In this paper the mechanical properties of thin micromembranes under compressive stress are characterised which are fabricated by bulk micromachining. The relation between the center deflection and the load pressure on a square membrane is deduced by modelling the membrane as an elastic plate having large deflection with clamped boundaries. According to the model whether the membrane has initial deflection or not has no effect on the measurement result. The Young s modulus and residual stress are simultaneously determined. The mechanical properties of siliconoxide silicon nitride membranes and composite membranes of polysilicon with silicon nitride are measured. View full abstract»

    Open Access
  • Optimal nesting for continuous shape stamping processes

    Publication Year: 2000 , Page(s): 383 - 390
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1441 KB)  

    This paper discusses the optimal nesting problem for minimizing the scrap in continuous shape stamping processes. The shape sliding technique is used to propose a new approach OVERLAP-and-ESCAPE to solve the problem of continuously nesting shapes onto a metal coil of fixed or selectable width. The approach is used to construct the objective function of the mathematical model of the problem using the Simulated Annealing Algorithm to determine the globally minimal configurations for the nesting problems. Some representative cases are studied and the results are encouraging. An automatic nesting software package for manufacturing bicycle chain link blanks is also described. View full abstract»

    Open Access
  • Numerical investigation of separated plug nozzle flow

    Publication Year: 2000 , Page(s): 391 - 394
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1177 KB)  

    Modern analysis techniques that provide improved viability have enabled further investigation of plug nozzle rocket engines as advanced launch vehicle concepts. A plug nozzle for future single-stage-to-orbit vehicles in China has been designed and the flow field in the plug nozzle has been studied numerically for different ambient pressures. Calculations were performed by solving the Navier-Stokes equations for an ideal gas. Turbulence is modelled using the k-∊ turbulence model. The advantages of the plug nozzles are the external expansion which automatically adapts to external pressure variations and the short compact design for high expansion ratios. Expansion waves compression shocks and the separated base flow dominate the flow structures and affect the plug nozzle rocket engine performance. View full abstract»

    Open Access
  • Numerical investigation of dynamic effects on unsteady flow measurements using a two-dimensional probe

    Publication Year: 2000 , Page(s): 395 - 399
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1121 KB)  

    The dynamic effects in measurements of unsteady flow when using a probe with quasi-steady calibration curves has been investigated in this paper by numerical simulation of the compressible flow around a fixed two-dimensional 3-hole probe. The unsteady velocity and pressure distributions as well as the hole-pressures are calculated for high frequency flow variations. The measurement errors caused by the dynamic effects indicate that considerable measurement errors may occur for high frequency flow fluctuation e. g. 2000 Hz especially when the flow around the probe head approaches separation. This work shows how numerical simulation can be used to investigate and correct for the dynamic effects. View full abstract»

    Open Access
  • Numerical investigation of the influence of reynolds number on probe measurements

    Publication Year: 2000 , Page(s): 400 - 403
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (895 KB)  

    The influence of Reynolds number Re on probe measurements was investigated numerically including the effects of the pressure holes and their geometry to obtain accurate hole-pressures. The results indicate that Re influences the probe measurements and cannot be neglected for Re larger than 105 and that the influence increases with Mach number Ma. The calculations show that the pressures in the downwind holes are influenced more by Re than those of the upwind and central holes when the probe is at an angle. Thus 7-hole probes may be more suitable for measurements at different Re than 5-hole probes. View full abstract»

    Open Access
  • Luminous flame temperature distribution measurement using the emission method

    Publication Year: 2000 , Page(s): 404 - 408
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (947 KB)  

    Flame temperature distribution is one of the most important characteristic parameters in combustion research. The emission method is a good way to measure the luminous flame temperature field. The maximum entropy method is introduced to the temperature distribution measurement of a luminous flame using the emission method. A simplified mathematical model was derived by combining the thermal radiation theory reconstruction algorithm and maximum entropy method. Suitable parameters were selected in the computing process. Good experimental results were obtained with pulverized coal flames. View full abstract»

    Open Access
  • Principle and implementation of an MC4044-based phase locked loop for constant speed control

    Publication Year: 2000 , Page(s): 409 - 413
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1098 KB)  

    An inexpensive MC4044-based phase locked loop for constant speed control of a DC motor is discussed. It operates on a principle similar to that of a frequency synthesizer. The paper introduces the system configuration with a detailed description of its operating principle some practical design considerations are discussed with an experimental study to test the control performance of the newly designed system. The experimental result shows that the phase locked control system can regulate the speed of a DC torque motor with a precision up to 0. 0022 %.1σ View full abstract»

    Open Access
  • A new method for dressing fine grain diamond wheels the soft-elastic elastic dressing method

    Publication Year: 2000 , Page(s): 414 - 418
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1041 KB)  

    This paper describes a completely new dressing technique the soft-elastic dressing method which can effectively dress fine grain diamond wheels. A rotating and vibrating abrasive belt is used in the soft-elastic dressing method. The principle of the new dressing technique and the soft-elastic dressing equipment are presented. Factors that influence the truing efficiency truing precision and sharpening quality are carefully investigated. The grinding surface roughness after soft-elastic dressing is performed is investigated experimentally. The dressing and grinding experiments both prove that the soft-elastic dressing method has high truing efficiency high truing precision and good sharpening quality. View full abstract»

    Open Access
  • Optimization method for turbine airfoil designing using genetic algorithms — CFD and parallel computing

    Publication Year: 2000 , Page(s): 419 - 423
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (991 KB)  

    An optimization method to design turbine airfoils using a Genetic Algorithm • GA design shell coupled directly with a viscous CFD Computational Fluid Dynamics analysis code is proposed in this paper. The blade geometry is parameterized and the optimization method is used to search for a blade geometry that will minimize the loss in the turbine cascade passage. The viscous flow prediction code is verified by the experimental data of cascade which is typical for a gas turbine rotor blade section. A comparative study of the blades designed by the optimization technique and the original one is presented View full abstract»

    Open Access
  • Condensation-induced steam bubble collapse in a pipeline

    Publication Year: 2000 , Page(s): 424 - 427
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1134 KB)  

    Steam bubbles often occur in pipelines due to the pipeline structure or operational errors. The water hammer force induced by the steam bubble collapse is a hidden safety concern. This paper experimentally and numerically investigates the conditions for steam bubble formation and collapse. A series of video pictures taken in the laboratory show that steam bubbles form and collapse over several cycles. The pressure history of the steam bubbles is measured in conjunction with the pictures. In the experiment' the liquid column cavitated at the low pressures and then the cavities collapsed due to condensation causing high pressure pulses. The process was also simulated numerically. The results suggest that coolant pipeline design and operation must include procedures to avoid steam bubble formation. View full abstract»

    Open Access
  • Induction of apoptosis in protoplasts and suspension cultures of plant cells

    Publication Year: 2000 , Page(s): 428 - 431
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1587 KB)  

    Many studies have showed that apoptosis exists in plants. Our study shows that (1) menadione-VK3 induces apoptosis in suspension cultures of carrot celis; (2) heat shock induces apoptosis in suspension cultures of tobacco cells; and (3) ethrel induces apoptosis in carrot protoplasts. Some important indications of apoptosis were observed including DNA laddering TUNEL-positive reaction condensation and degradation of nuclei. View full abstract»

    Open Access
  • Feasibility of using chitosan in nerve repair

    Publication Year: 2000 , Page(s): 432 - 435
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (2505 KB)  

    The chemical composition and microstructure of a biocompatible material prepared from chitosan were evaluated using FTIR and SEM techniques. Its mechanical and physical properties were also tested. The materials nerve cell affinity and peripheral nerve repair feasibility were also evaluated. In vitro cytotoxicity tests indicated that both cerebral cortex cells and endothelial cells ECs can attach to the surface and grow well. These results indicate that chitosan has the necessary properties for an artificial nerve conduit material and may be a promising candidate for the design of a bioactive biodegradable nerve conduit. View full abstract»

    Open Access
  • Direct promotion of collagen calcification by alkaline phosphatase

    Publication Year: 2000 , Page(s): 436 - 438
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (680 KB)  

    Alkaline phosphatase promotes hydrolysis of phosphate containing substrates causes a rise in inorganic phosphate and therefore enhances calcification of biological tissues. In this work the calcification of collagen in a model serum was used as a model of collagenous tissue biomaterials to study the possible calcification promotion mechanism of alkaline phosphatase. In the enzyme concentration range of 0.1–0.5 mg/mL the enzyme shows a direct calcification promoting effect which is independent of the hydrolysis of its phosphate containing substrates but proportional to the enzyme concentration. Potassium pyrophosphate somewhat inhibits the calcification promotion. View full abstract»

    Open Access

Aims & Scope

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.

Full Aims & Scope