Table of Content

20 September 2006, Volume 42 Issue 5

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Design and Implementation of Digital Down Converter for Homenet

CUI Xiaoxin,YU Dunshan,SHENG Shimin,CUI Xiaole

2006, 42(5):  690-696. 

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Based on the classical system design flow, a custom digital down converter (DDC) was designed and implemented for Homenet wireless communication system. At the system level, the behavior model of DDC was constructed with the assistant of system modeling tool MATLAB. At the circuit level, considering implementation complexity, a large number of digital filter optimizing schemes such as CSD and RAG were adopted; in our design, numerically controlled oscillators (NCO) was based on a new hybrid scheme, which combines the respective advantages of LUT and CORDIC algorithm. Homenet system verification flat including our custom digital down converter was implemented with Xilinx VirtexII XC2V1000-4FG256 FPGA.

Fast Marker-Controlled Interactive Mesh Segmentation

LI Chengjun,ZHANG Chi,WANG Guoping

2006, 42(5):  662-667. 

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A fast 3D mesh segmentation method was introduced. Different from most of the others, the method provided segmentations in respect of the mesh face set, and the curvatures were estimated between two adjacent faces. Based on watersheds algorithm, the method completes the segmentation using interactive markers as indicators, thus over-segmentation and noising problems were avoided. At the same time minima rule was adopted to achieve a much reasonable result according to human's subjective perception. Experimental results show that the process is fast enough for interactive applications.

Seamless 2D-3D Texture Mapping

LI Xiaolan,ZHA Hongbin

2006, 42(5):  674-680. 

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Wavelete decomposition was performed to classify the source images into two types: the edge-riched image and the smooth image. Based on the Human Visual System theory, different combination techniques, the image stitching and the image blending methods, were selected to deal with different source images. A new algorithm was proposed to find an optimized stitching path in the overlapped area of Partial Texture Maps. View dependent weight was added into the ordinary blending weight, which made the generated texture map reveal some geometric properties of the 3D model. The experimental results verify the validity of the methods.

Evaluation on Shelter Effect of Porous Windbreak Fence through Wind Tunnel Test

CHEN Kai,ZHU Fengrong,NIU Zhennan

2006, 42(5):  636-640. 

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The flow field of a large storage yard with windbreak was investigated in the wind tunnel under three dominant wind directions. The wind speed was measured by the so-called "omnidirectional surface wind sensor", and the qualitative flow pattern was visualized by tuft method. According to the experimental results, the shelter effect of the porous windbreak fence was evaluated. It was found that the wind speed significantly decreased behind the windbreak, by 80% at most. However, at some wind direction a large bubble appeared behind the fence due to the low porosity of 30%. Thus its necessary to improve the design of the windbreak fence. In addition, it was verified that the shelter effect for a certain storage yard was related to the local terrain and accordingly the given conditions should be taken in consideration.

Professor Li Xianzhi's Works on Studies of Meteorological Disasters and Their Effects

LI Zengzhong

2006, 42(5):  569-577. 

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The late Prof. Li Xianzhi (Dr.Sjan-zsi Li) was a professor with Peking University and a famous meteorologist in China. In his youth, he took part in The Scientific Expedition to China's Northwestern Provinces during 1927-1930. He observed the movement of a strong outbreak of cold air masses in late Oct. 1928, in Qinghai Province. This event had an important influence on Li Xianzhi's life. Between 1930 and 1936, he studied and then worked in Berlin University. He published his famous papers "A Study on the Outbreak of cold air in East Asia" and "A Study on Typhoon" in 1934 and 1936 respectively. He got a Doctor's Degree in 1934 and came back to his motherland in 1936. He devoted himself to the teaching of meteorological sciences in China's famous institutions of higher learning i.e., Tsinghua and Peking universitie, and to meteorological studies. He wrote quite a number of initiative works. He discovered that cold air coming from the North Pole region can sweep across the Equator and then reach the Southern Hemisphere, and lead to precipitation and drops in temperature over there. At the same time, he pointed out that the outbreak of cold air coming from Australasia can lead to the generation of typhoon in the northwestern Pacific when the cold air crosses the Equator and reaches the lower latitude regions of the Northern Hemisphere. In the later part of his life, Li Xianzhi presented a new concept of "Microscopical System between two Hemispheres". He pointed out that the heavy rainfall and flood disasters on the Chinese mainland are closely connected with the weather systems coming from the Southern Hemisphere. This theory points a new way to the monitoring and prediction of heavy rainfall and flood disasters in China. This paper presents a comprehensive study and comment on Prof. Li Xianzhi's principal research results and his viewpoint on the study of meteorological disasters, and shows his influence and his contribution.

Possible Impact of Stratospheric Polar Ozone Depletion on Tropospheric Climate

HU Yongyun

2006, 42(5):  561-568. 

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It has become a public concern that ozone depletion in the stratosphere would lead to increasing ultraviolet radiation on the surface. That stratospheric polar ozone depletion likely has important impacts on atmospheric circulations and climate has also been one of important topics in climate research in the past few years. Observational studies showed that in the seasons with severe ozone depletion in stratospheric polar regions, surface air temperatures have a significant tendency of warming in the past few decades, that is, surface air temperatures demonstrate warming trends over the high-latitude Europe-Asia continent during February-March and over the Antarctic Peninsula during December-May. The warming is not due to direct radiative effect of ozone depletion, instead, it is throughout dynamic processes, such as wave-mean flow and stratosphere-troposphere interactions. There have been a lot of numerical simulations on this problem. Some simulations show consistent results with observations, while others point out that the impact of ozone depletion alone is too weak, and that other forcings are also important. The author reviews the progress in this field in the past few years, summarizes these observational and simulation results, interprets the physical mechanism of stratospheric polar ozone depletion impacting on the troposphere, and clarifies controversies.

Implicitization of Rational Curves and Surfaces

YU Jianping,SUN Yongli,MA Yujie

2006, 42(5):  578-583. 

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The implicitization of rational curves and surfaces was studied. The methods are based on Bezout's Matrix theory.

A High Resolution Low Power Sample and Hold Module Dedicated to a Pipelined ADC

JIN Rui,ZHANG Tianyi,YANG Xin

2006, 42(5):  685-689. 

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A high performance sample-and-hold(S/H) circuit dedicated to a high resolution analog to digital converter is designed and implemented in 0.25μm CMOS process. The sampling rate of this proposed S/H module is 20MHz with a bandwidth of 10MHz, the full scale of the sampled fully differential signal is 2V with the 2.5V power supply. Instead of the traditional charge transfer architecture, a fully differential flip-around architecture is used to reduce the power consumption. In order to improve the signal to noise ratio(SNR), a bootstrapped switch is implemented in two places. Hspice simulation shows that it achieves a SFDR of 92.4dB for 5MHz input signal. This circuit is integrated to one 14bit 20MHz pipelined ADC.

Causal Inference in the Models with Hidden Variables and Selection Bias

ZHAO Hui,ZHENG Zhongguo,XU Jing

2006, 42(5):  584-589. 

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In the presence of unobserved hidden variables and selection bias, Bayesian networks may not correctly represent causal relationships among the observed variables. Using maximal ancestral graph models, this paper characterizes the independencies and causal structure of the observed variables and provides an algorithm for causal inference using observational data.

Difference Sets in Groups of Order 4p⁴

WAN Zhaoze,LI Jian

2006, 42(5):  590-597. 

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Let G be a group of order 4p⁴ with Dihedral image D_4p², by investigating the intersection numbers, it is concluded that there is no Menon difference set in G if p≥5 (where p is a prime).

Experimental Research on the Chaos Characteristics during Reverse Transition

ZHANG Zhen,YAN Dachun

2006, 42(5):  624-627. 

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Nonlinear dynamics parameters, such as correlation dimension, maximum Lyapunov exponent and Kolmogorov entropy, which reflect the chaos characteristics of flow field are calculated with the time series of instantaneous velocity during reverse transition. Computational results show that chaos exists during reverse transition. Contrary to transition, the flow regimes during reverse transition experience the process of turbulence-chaos-laminar flow.

A Calibration Method for Far-Field Photogrammetry and Its Application

YU Yongsheng,BI Weitao

2006, 42(5):  628-631. 

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In displacement measurements by far-field photography, the scale between object and image has to be calibrated. The calibration can be carried out by placing a rule at the position of the object. In practice, however, this is usually not possible. Especially the orientation of the rule is difficult to set precisely. In this research, a calibration method is proposed by use of equilateral polygon, which can be the hat of a bolt. The authors prove the equilateral polygons that have the same front projection are congruent. Therefore, the size of the equilateral polygon can be uniquely extracted by its front-projection image and the photogrammetric calibration can be done accordingly. This calibration method is successfully implemented in a field measurement of the wind-induced vibration of a structure.

Solution and Potential Function for Boussinesq Problem of Transversely Isotropic Piezoelectric Media

LI Xiangyong,WANG Minzhong

2006, 42(5):  632-635. 

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Based on the symmetry properties of the material constants, the Boussinesq solution in analytic form was obtained by Fourier transforms for a transversely isotropic piezoelectric half-space submitted with a normal point force and a point charge. The associated potential function was also discussed. By Fourier transforms method, the boundary value problem of partial differential equations was transformed to algebraic equations. Then by the principle of superposition and solving two sets of algebraic equations, the interaction between the point force and the point charge was uncoupled. Compared with the tentative semi-inverse method, the method in this paper is direct and effective.

Associated Dynamical Equation on Wobble and Nutation of Fluid Core Earth Model

ZHANG Hanwei,XU Houze,ZHOU Xuhua

2006, 42(5):  641-645. 

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Based on classical dynamical equation on rotation of Earth with elasticity's mantle and fluid core, the associated dynamical equation containing both nutation and wooble of Earth rotation were detuced through introducing motion of nutation frame system with respect to inertial spatial frame. The primary contents consist of: (1) considering influence of high order precession-nutation moment on Earth rotation; (2) introducing influence of other disturbing mechanism (atmosphere, ocean and surface water distributing, et al.) on Earth rotation, which periods satisfy relations of T≤2/3d and T≥2d; (3) establishing theoretical relations between polar motion of rotational axis, polar motion and precession-nutation of either celestial sphere reference axis; (4) presenting the associated dynamical equation containing wobble and nutation of fluid core Earth model, trying investigated wobble and nutation with unitive method. Deduced formulae can provide a reference and gist for research of dynamical geodey and arstrogeodynamics.

A Semantic Security Policy Language for Distributed Computing Environment

LIU Peng,HU Jianbin,CHEN Zhong

2006, 42(5):  646-657. 

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A semantic security policy language, called SSPL, was proposed for distributed computing environment. SSPL is represented in OWL DL. SSPL supports basic concepts of security policy-positive and negative authorization and obligation, privilege delegation and revocation, policy conflict resolution. Furthermore, SSPL supports rule-style policy, which enhances the expressiveness of SSPL. This paper also demonstrates the reasoning of SSPL policy. DL-safe rule and courteous logic program were introduced for the formal semantic of SSPL. The transformation from SSPL policy to courteous DL-safe program and the query answering procedure of the result courteous DL-safe program are presented.

The Optimum Symbol Length Design for Wireless OFDM over Fast Fading Channels

MA Meng,YANG Yuli,JIAO Bingli

2006, 42(5):  658-661. 

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The analysis of OFDM system over time-variant channel is often performed under the assumption that the channel remains constant within one symbol period, however this is not always true for any situations. With the higher carrier frequency, faster movement speed and longer symbol duration, the Inter-Carrier Interference (ICI) caused by Doppler spread will be increased. The authors analyze the Maximum Achievable Data Rate (MADR) and SINR (Signal to Interference and Noise Ration) for time-frequency selective fading channels when the orthogonality of sub-carriers is destroyed by the Doppler spread. The authors also find out the optimal symbol durations to maximize the MADR and SINR. Numerical results corroborate the theoretical findings.

GATEST: A Validation Platform of Automatic Simulation Vectors Generation Using Genetic Algorithms

YI Jiangfang,TONG Dong,CHENG Xu

2006, 42(5):  668-673. 

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The approaches of simulation-based validation need a large amount of simulation-vectors for verifying the corner cases of VLSI designs. The authors developed a validation platform of automatic simulation vectors generation based on the path coverage metric using genetic algorithm for RT-level designs. Given the critical signals, it used techniques of data flow analysis to acquire the critical path set and choose the critical path coverage to be the fitness function used in the GA. The authors performed experiments on some functional modules of Unity-863 SoC. The relationship between the final results and the control factors were also analyzed in detail. The results show that GATEST is effective and efficient.

A Novel Latched Comparator with Low Kickback Noise

ZHANG Xin,YU Dunshan,SHENG Shimin

2006, 42(5):  681-684. 

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A new latched comparator architecture was proposed. Because of its very low kickback noise feature, it is especially suitable for differential analog-to-digital converters (ADCs). Simulated results of the proposed circuit in a 0.35μm standard CMOS technology show that this comparator achieves a sampling speed of 400 Ms/s at 3.3V supply, with a kickback noise 88% lower than conventional schemes.

Existence of Renormalized Solutions for an Evolution Equation with Small Measure

XU Meng

2006, 42(5):  619-623. 

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The existence of the renormalized solutions for the initial-boundary value problem of parabolic equation with small measure is established.

Relative Value-at-Risk: A New Kind of Coherent Risk Measure

HU Dekun,DONG Gang,XU Jicheng

2006, 42(5):  598-603. 

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A new coherent risk measure called Relative Value-at-risk(RVaR) was proposed. As a intuitional and meaningful index in insurance and risk control, RVaR has many good properties and is consistent with several often used orders. We offer a criterion to determine the value of parameter ρ and RVaR. Based on the criterion, RVaR is identical with VaR for the normal-distributed risk, bigger than VaR for the fat-tail risk and smaller than VaR for the thin-tail risk. We also prove the representation formula of RVaR and illuminate its purport. Finally, RVaR is applied in risk exchange model and capital allocation model.

An Efficient Salt-and-Pepper Noise Removal

DONG Yiqiu,XU Shufang

2006, 42(5):  604-612. 

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A more efficient two-phase salt-and-pepper noise removal method is proposed. In the first phase, adaptive median filter is used to detect noisy pixels. In the second phase, a minimization problem is solved by global Barzilai and Borwein (GBB) method. Through the improvement on edge-preserving regularization in the second phase, no regularization coefficient need to be chosen, and the parameter α of the edge-preserving potential function, φ(t)=|t|^α, can create adaptively. Comparing the results of removing noise, our method is better with much less running time, especially when the noise ratio is high.

A Note to the Lorenz Curve and Gini Coefficient

CHEN Qizhi,CHEN Jiading

2006, 42(5):  613-618. 

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Most general definition of the Lorenz curve and Gini coefficient are given. Under the general condition, the usual estimators of Lorenz curve and Gini coefficient are proved to possess strong consistency respectively.