Table of Content

20 September 2005, Volume 41 Issue 5

Previous Issue    Next Issue

On Hamilton Sequences of Extremal Teichmüller Mappings

YAO Guowu

2005, 41(5):  663-666. 

Asbtract ( )  

Related Articles | Metrics

The following question is answered negatively: Let φ be holomorphic in the unit disk Δ. If an extremal Teichmüller mapping f on Δ has complex dilatation μ_f=kφ/|φ|, can one say that μ_f has a Hamilton sequence such as {φ(t_nz)/‖φ(t_nz)‖:lim_n→∞t_n=1, t_n∈(0,1)}?

Clifford Algebra-Valued Admissible Wavelets Associated with Admissible Group

ZHAO Jiman

2005, 41(5):  667-670. 

Asbtract ( )  

Related Articles | Metrics

The Clifford algebra-valued admissible wavelets are studied. An explicit characterization of the admissibility condition in terms of Fourier transform is given. Some properties of this kind of admissible wavelet transform are proved, and a characterization of the admissible group is presented.

1-Level Correlation Functions of Disturbed Unitary Ensembles

YAN Kuihua,HU Zhiguang

2005, 41(5):  671-678. 

Asbtract ( )  

Related Articles | Metrics

In the random matrix theory, the 1-level correlation functions R¹_nβ(x) ( β is generally called Dyson's index) can be explained as the distribution density of energy levels which can be found nearby x. As yet, its limit behavior is still remarkably noticed by many mathematicians and physicists. In the case of unitary ensemble (i.e. β=2), the 1-level correlation functions R¹_n2(x) is closely related to the weight function μ(x) in the classical orthogonal polynomial theory. For the simplication of statement, only the Gaussian unitary ensemble case is considered. The authors find that in weak sense, the limit behavior of R¹_n2(x) is not disturbed by appending a "good" nontrivial multiplicative factor to μ(x).

Dynamic Simulation and Kinetic Description of Revolute Joint with Spatial Clearance

YU Lixiao,LIU Caishan

2005, 41(5):  679-687. 

Asbtract ( )  

Related Articles | Metrics

This paper is focused on the modeling of revolute joints with spatial clearance based on Hertz contact theory and Coulomb's friction law. The effects of friction, damping and link flexibility on the system dynamic responses are considered. Two mass points are approximately taken for the contact points. The authors consider the real potential contact points on the boundary of the bodies. Kinetic relationship between two potential contact points is obtained through the geometric relations between the two moving bodies. An example demonstrates the reliability of the proposed method. Different clearance size, friction coefficient, damping and flexible coefficient are given to the model.

The Effect of Periodic Disturbance to the Hierarchical Structure in Turbulent Boundary Layer

CHENG Xueling,HU Fei

2005, 41(5):  688-694. 

Asbtract ( )  

Related Articles | Metrics

Artificial periodic disturbances are introduced to the outer field of turbulent boundary layer in an closed-circuit open water channel. Statistical method is employed for analyzing the velocity-fluctuation-time-series. The effect of the disturbance to turbulent structure in boundary layer is studied. The result indicates the She-Leveque hierarchical similarity exists among high frequency turbulence.

Dynamics of Discrete System with Friction and Multiple-Point Impact

YAO Wenli,CHEN Bin,ZHAO Zhen,YU Lixiao

2005, 41(5):  695-700. 

Asbtract ( )  

Related Articles | Metrics

The purpose is to study the solution of impulsive dynamics of planar discrete system with friction and multiple-point impact. When impact applies on a discrete system in which one of constraints is a constant with coulomb friction, the phenomenon of slip-stick at the point can cause the change of friction and the integration for frictional force during infinitesimal impulsive interval becomes impossible according to traditional impulsive dynamics of discrete systems. By introducing a new dimensional time parameter, first-order momentum-impulse differential equations are obtained and the discussion over infinitesimal impulsive interval is transformed into a piece-wise study on the finite region of impulse. An algorithm for response of impact and an example are given.

Four-Dimensional Variational Assimilation of AWS Precipitation Data

SHAO Mingxuan,CHEN Min,TAO Zuyu,CHEN Lu

2005, 41(5):  701-709. 

Asbtract ( )  

Related Articles | Metrics

Four-dimensional variation data assimilation (4D-VAR) is a logical and rigorous mathematical method to obtain the "best" estimate of the model initial conditions from observations and a priori knowledge of the atmospheric state. It is one of the most advanced data assimilation methods today. Automation weather station (AWS) precipitation data is assimilated by 4D-VAR in experiments. Experiment results show that, due to addition of information of AWS precipitation data, the initial field of test is enhanced in meso-scale information, and it matches the model better in thermo-dynamical mechanism. After assimilation, the simulation is improved. The precipitation during the start period in simulation is increased, and the situation of simulating precipitation matches real situation better. The "spin-up" problem of the model is weakened. Experiment results also show that temporal information of AWS precipitation data is very important for assimilation.

Study on In Situ Annealing Superconducting MgB₂ Films Prepared by Pulsed Laser Deposition

REN Guoli,ZHANG Xieqiu,NIE Ruijuan,WANG Shouzheng,WANG Furen

2005, 41(5):  710-714. 

Asbtract ( )  

Related Articles | Metrics

In Situ annealed superconducting thin films are acquired by pulsed laser deposition method. With SEM, X-ray diffraction analysis, magnetic measurement (by Magnetic Property Measurement System), the effects of growth and annealing conditions are analyzed. It indicats that the growth temperature, annealing temperature and time greatly affects the quality of MgB₂ films. The films grown at 200℃, annealed for 5min at different temperatures ranged from 280℃ to 820℃ are carefully compared to study the effect of annealing temperature. The film acquired at the highest T_c of 33K grows at 200℃, annealed at 670, 720℃ for 5min, X-ray analysis shows that it has c axis orientation. The films which were grown at 200℃ and annealed at 670℃ for different time are compared to study the effect of annealing temperature. The films grown at different temperatures but all annealed at 670℃ for 5min are also compared to study the effect of growth temperature.

Superconductivity of Mesoscopic Superconductor

XIONG Mingyuan,GAN Zizhao

2005, 41(5):  722-730. 

Asbtract ( )  

Related Articles | Metrics

The development of micro-fabrication technologies in the last years has resulted in an increasing interest in the research of superconducting property of mesoscopic samples. Because most researches on this subject use numerical approach, an analytical method is developed to investigate the property of mesoscopic superconductor.

The Annealing Effects of MgB₂ and Experimental Study on Thermostability of MgB₂

ZHANG Xieqiu,REN Guoli,NIE Ruijuan,WANG Shouzheng,WANG Furen

2005, 41(5):  715-721. 

Asbtract ( )  

Related Articles | Metrics

The effects of annealing on superconducting transition and the thermostability of MgB₂ have been investigated. MgB₂ is fabricated on boron flakes by annealing in the magnesium atmosphere at different temperatures and period of times. The temperature range from 700 to 1000℃ is appropriate to prepare MgB₂ in the experiments. At higher temperature shorter time is needed to get relatively high T_c. The thermostability experiments show that after the heat treatment in the atmosphere without Mg, MgB₂ is stable below 700℃ and begins to decompose from 800℃ until the complete loss of superconductivity. The lower temperature is needed to form MgB₂ phase when using Mg-B film precursor instead of boron flakes.

A Study of the Microwave Radiance and Lightning Characters of Mesoscale Convective Systems

CAO Zhiqiang,LIU Huizhi,LI Wanbiao,TONG Ke,NIU Xiaolei

2005, 41(5):  731-739. 

Asbtract ( )  

Related Articles | Metrics

Through the analysis of 11 typical mesoscale convective systems occurring at China continent and adjacent ocean on June, July and August, 1998, it is found that 10.65GHz_ V channel and 19.35GHz_ V channel can well response to the absorbability and emission of liquid water in cloud and precipitation, and that 85.5GHz_ V channel and 37.00GHz_ V channel can response to the ice scatting in cloud well. Based on these characters of MCS, the relationship between 85.50GHz polarization-corrected temperatures (T_PC) and lightening is further discussed. The results show that large events density occurred within the contour of 220K, and that during 220--260K, the events density is sharply reduced. At T_PC higher than 260K, there is almost no events observed.

The Wobble and Precession-Nutation on CIP of Elastic Earth

ZHANG Hanwei,XU Houze,WANG Aisheng

2005, 41(5):  740-745. 

Asbtract ( )  

Related Articles | Metrics

Based on classical dynamical equation on elastic oarth rotation, an associated dynamical equation containing both nutation and wooble of earth rotation has been deduced through introducing motion of nutation frame with respect to inertial spatial frame. Therefore, the theoretical definition of CIP and its dynamical equation on wobble and precession-nutation are given. Considering precession-nutation moment up to 5^th order, the authors present the expression of precession-nutation of CIP. Theoretical result shows that odd order's precession-nutation moment causes out-of-phase longitude and obliquity nutation (namely, there are cos term in longitude nutation, and sin term in obliquity nutation). Moreover, it proves that the expression of precession is independent of Earth model. The deduced formulae can serve as a reference and gist in dynamical geodesy and astrogeodynamics' research.

A Modified AEDA Algorithm for Sound Source Localization and Tracking

LI Chengzhi,QU Tianshu,WU Xihong

2005, 41(5):  809-814. 

Asbtract ( )  

Related Articles | Metrics

Sound source localization and tracking has turned to be one of hotspots in acoustic signal processing area in recent years. It is widely adopted in a lot of applications, such as multimedia conference, intelligent robot, speech enhancement, etc. Adaptive Eigenvalue Deposition Algorithm (AEDA) is one of the effective methods for its robustness performance of noise and reverberation. However, AEDA is suffered from its slowness in tracking variation of time delay of arrival (TDOA) as well as its sensitivity to initial value. Faced with such problems, a Modified Adaptive Eigenvalue Decomposition Algorithm (MAEDA) for time delay estimation is proposed, based on which an emulation system is developed. Experimental results show that the proposed new algorithm works well in sound source location and moving sound source tracking, meanwhile, it overcomes the drawbacks of the traditional AEDA algorithm.

A Study to the Trigger Mechanism and Unstable Conditions of Spring Heavy Rainfall with Numerical Simulation

ZHANG Chunxi,ZHU Peijun,ZHENG Yongguang,ZHUO Hong,SHAO Mingxuan,TAN Xiaoguang,YU Xiaoding

2005, 41(5):  746-753. 

Asbtract ( )  

Related Articles | Metrics

A mesoscale convective system (MCS) which happened around Shangdong Province in the middle spring 2003 induced heavy rainfall. In the unstable large scale atmosphere, trigger conditions determine when and where the convections come into being. However, these conditions lie in boundary level above ground with small scales, and the general surface and rawinsonde data can not reveal them. A method of numerical simulation and sensitivity simulation together with objective analysis are conducted, and its trigger mechanism can be diagnosed. The results of diagnosis indicate that two developments of MCS bring up this heavy rain. The first can be called a typical Huabei MCS, whose initial convections are arisen by terrain forced climb; the second initial convections are arisen by boundary convergence lines in the afternoon, meantime the lower level cold air from Huabei Plain also contributes to their formation. So the maximum convective available potential energy (MCAPE) is able to give right information on where the initial convections will occur.

Design Features of a High Throughput RSA Cryptoprocessor

LIU Qiang,MA Fangzhen,TONG Dong,CHENG Xu

2005, 41(5):  754-763. 

Asbtract ( )  

Related Articles | Metrics

Montgomery multiplication algorithm is optimized for large-bit modular multiplication and VLSI implementation. It is combined with the R-L (Right to Left) binary method to achieve speed improvement. Special efforts are focused on the problems with long-bit modular arithmetic. A Carry-Save-Adder architecture, which is implemented by redesigned (4:2) compressors, is used in the multiplier to avoid the long carry propagation. A signal-backup strategy is used to resolve the problem of signal broadcasting. Using a multiplexer-based method, the datapath of the multiplier is reconfigurable to perform either one 1024-bit-multiplication or two 512-bit multiplications in parallel. The Chinese Remainder Theorem (CRT) increases the decryption data rate by a factor of 3.8.

Research and Implement on General Multimedia Digital Rights Management System

SI Duanfeng,WANG Yidong,PAN Aimin,YE Zhiyuan

2005, 41(5):  792-799. 

Asbtract ( )  

Related Articles | Metrics

To protect the interest of multimedia data owners, dealers and consumers, the author proposes a general architecture of multimedia data and implements a real DRM topology system called sDRM. It can protect the local and on-line play of multimedia data files. It uses XrML as its rights expression language which achieves the standardization of the rights expression. User name and password, USB device, smart card and finger mark are used in the system to identify the user. As a result, the key problem in DRM of multimedia data is resolved. An experiment is implemented to demonstrate the efficiency of our DRM system.

Hardware Adaptive Copyright Protection Mechanism for Digital Contents

YU Yinyan,TANG Zhi

2005, 41(5):  800-808. 

Asbtract ( )  

Related Articles | Metrics

Binding digital license to a unique identification of hardware configuration of the rendering device is the most popular strategy adopted in current digital rights management. But the main drawback of this scheme is that the protected content cannot be rendered any more once the user replaces any part of the hardware. By encrypting the digital content, splitting the decryption key into multiple pieces and binding them each to different hardware components of the machine, the authors propose a hardware adaptive copyright protection mechanism for digital contents. With this scheme, a buyer can change the hardware configuration of his machine within a determinate range without influencing the use of the bought digital content. Meanwhile, copyright of the content is properly protected.

Electrical Transport Studies of Sodium Titanate Nanowires

SUN Zhonghua,LIANG Xuelei,CAO Jianjun,CHEN Qing,ZHANG Zhiyong,PENG Lianmao

2005, 41(5):  764-768. 

Asbtract ( )  

Related Articles | Metrics

Individual sodium titanate nanowire-based device is fabricated via e-beam lithography techniques. The authors measure their electrical transport properties in air and in vacuum respectively and find that the electrical transport of sodium titanate nanowires devices is affected. This is attributed to oxygen adsorption on the surface of nanowire. In addition, the authors study ultraviolet (UV) light response of sodium titanate nanowire-based devices and find that UV light may induce a large photoconductivity. The work shows that sodium titanate nanowires may be used potentially as gas sensors and photoelectric sensors.

Design of Field-Effect Nano-Transistors and Measurement of Their Electrical Property

DENG Nan,ZHANG Qifeng,LI Pingjian,SHEN Ziyong,HOU Shimin,WU Jinlei

2005, 41(5):  769-773. 

Asbtract ( )  

Related Articles | Metrics

Structure design of metal nano-electrode for nano-electronic device is investigated. It is found that the height of the metal electrode, the distance between the source and drain electrodes, the thickness of the SiO₂ insulation layer and the materials of the nano-electrode play important roles in the electrical property of the nano electronic device. A single-walled carbon nanotubes bundle based on field-effect transistor is fabricated accordingly, and its I-V characteristic is measured.

Field Emission from a Non-Aligned ZnO Nanowire Array

CHEN Liang,ZHANG Gengmin,WANG Mingsheng

2005, 41(5):  774-779. 

Asbtract ( )  

Related Articles | Metrics

An array of non-aligned monocrystalline zinc oxide nanowires (ZnO NWs) is fabricated on a silicon substrate by thermal evaporation. The non-aligned ZnO NWs in the array are approximately 10～20 nm in diameter. During the fabrication, the temperature around the substrate is lower 500℃, which is conducive to practical application. Field emission is available from these ZnO NWs. The electric field that extracts 10μA·cm^-2 current density is measured to be 5.5V·μm^-1. Moreover, the emission site distribution (ESD) is also studied and the field emission is found from the whole sample surface, suggesting that the screen effect is almost avoided.

The Adaptive Algorithm Based on Minimum Average BER Criterion in OFDM System

LI Zhendong,SHI Shuangning,LIANG Qinglin

2005, 41(5):  780-785. 

Asbtract ( )  

Related Articles | Metrics

Adaptive OFDM (Orthogonal Frequency Division Multiplexing) system can allocate the data rates and transmit power among subcarriers adaptively. This article proposes the adaptive algorithm based on equal SNR (Signal Noise Ratio), and applies it in adaptive OFDM system. In frequency selective fading channel, compared with the traditional OFDM system based on equal power allocation, the system outperforms in BER (Bit Error Ratio) performance.

Improving the Subcell-FDTD Simulation Accuracy of the Currents in Conducting Thin-Wire

TIAN Fang,GONG Zhonglin

2005, 41(5):  786-791. 

Asbtract ( )  

Related Articles | Metrics

The round contour integration method is proposed to accurately simulate the currents on conducting thin-wire by using the subsell technique in the Finite Difference Time Domain (FDTD) method. Through calculating the characteristic impedance of coax, the scattering current in a conducting thin-wire for E type plane wave incidence and the input admittance of cylindrical monopole antenna, it is testified that the proposed method is more accurate than the conventional square contour integration method.

Design and Implementation of a Tool Supporting Contract-based Design for Testability of Components

SHAN Jinhui,JIANG Ying,LIU Jianghong,XIN Guomao,HOU Shanshan

2005, 41(5):  815-819. 

Asbtract ( )  

Related Articles | Metrics

New characteristics in component technology bring new challenges to component testing. Design by contract is an important approach to design for testability of software. Contract-based design for test ability of components provides effective means to component testing. A new tool to support design by contract is designed and implemented, which is named PKUJDBCT and can be used to support design for testability of components, and provide a basis for our future research on methods of contract-based design for testability of components.

Statistical Distributions of MIMO Channels over Flat Fading

XUE Jinyin,ZHU Xiaolong,JIAO Bingli

2005, 41(5):  820-824. 

Asbtract ( )  

Related Articles | Metrics

The authors discuss the statistical distributions of multiple-input multiple-output (MIMO) channels over flat Rayleigh fading via the order statistics analysis. Simplified expressions are derived for expectations of the vector energies when the column (or row) number is equal to 1 and 2, which is followed by the upper and lower bounds when the antenna number at one side approaches infinite. Finally, some applications of the analysis, such as the computation of antenna selection and diversity gain, are discussed.