Table of Content

20 September 2004, Volume 40 Issue 5

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Using Data Processing Methods to Improve the Accuracy of Strap-down North Finder for Vehicles

SONG Chunlei,XIE Ling,CHEN Jiabin

2004, 40(5):  844-848. 

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The data processing methods are applied to improve the accuracy of strap-down north finder for vehicles when north finder is subject to some external disturbances. The north-seeking principles of strap-down north finder and reasons for causing errors by external disturbances are analyzed in detail. Low pass filtering method and two types of statistical subsection methods are presented. The experimental data and simulation results show that the methods presented are very practical and effective to reject some external disturbances and to improve the accuracy of strap-down north finder.

Robust Stabilization for a Class of Uncertain Nonlinear Systems: LMI Approach

OUYANG Hua

2004, 40(5):  722-728. 

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The robust stabilization of a class of nonlinear systems in the frame of LMI is studied especially the case of system stabilization via output feedback. The problem of robust stabilization of a class of nonlinear systems is induced into a problem of bilinear matrix inequality(BMI), and then transferred it to an LMI problem by adding constraint. The case of interconnected systems is also discussed. In addition, the validity of this method is verified by numerical example.

Congruences on Some Quasi-Completely Regular Semirings

SUN Yongli,YU Jianping,LI Shizheng,ZHANG Yufen

2004, 40(5):  683-686. 

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Congruences on some quasi-completely regular semirings have been studied, it has shown theses congruences can be characterized by their additive semigroups.

The Null Dirac Structure on Product Poisson Manifolds

WANG Lan

2004, 40(5):  687-695. 

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The null Dirac structures on the product Poisson manifold are characterized by their characteristic triples and discussed in detail.

Nonparametric Estimation of Value-at-Risk of Chinese Stock Market

WU Guangxu ,CHENG Qiansheng,PAN Jiazhu

2004, 40(5):  696-701. 

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Continues-time finance model are discussed and modified for the purpose of estimating value-at-risk. Kernel method are applied to estimate price density and VaR of Shanghai Stock Index VaR. Comparing with VaR estimated from Black-Scholes geometric Brownian Motion hypothesis, the modified model is better.

On the Lower Confidence Limits for the Structure Reliability

CHEN Jiading,LI Ji

2004, 40(5):  702-711. 

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Let X₁, X₂,…，X_n be independent and identically distributed random variables. X₁ is distributed as N(μ, σ²), where μ and σ are unknown parameters satisfying μ>0 and σ/μ≤c₀(c₀ is known). Given t_i>0(i=1,…,n). Suppose that the observation data is Z=(Z₁,…，Z_n)，in which Z_i=1 or 0 according as X_i is bigger than t_i or not. R(t₀)=P(X₁>t₀) is so-called structure reliability. A method seeking the lower confidence limit R_L of R(t₀) based on the data Z is given. Especially, the accurate computational method is obtained in the case of no failure (i.e.Z_i≡1).

The Ellipsoidal Inhomogeneity with Imperfect Interface

ZHAO Yingtao,GAO Yang,WANG Minzhong

2004, 40(5):  712-721. 

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Presents an exact solution to the problem of an ellipsoidal inhomogeneity embedded in an infinitely extended body with imperfect interface subject to uniform shear stress at infinity. A kind of new boundary condition similar to the dislocation-like model is used. The tractions are assumed continuous across the interface, and the displacements may be discontinuous from one side to the other. With the help of Lamé functions, Papkowich-Neuber displacement potential functions are introduced. In the end, the displacements fields inside and outside the ellipsoid are obtained in explicit form, respectively. Then the stress field in the whole do main will be concluded relevantly.

Impact on Planar Multi-Rigid-Body Systems with Friction

YAO Wenli,CHEN Bin

2004, 40(5):  729-734. 

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The impulsive dynamics of planar multi-rigid-body systems with friction is studied. When impact applies on a planar multi-rigid-body system in which one of the constraints is a constant constraint with coulomb friction, the phenomenon of slip-stick and slip-reversal at the frictional applied point can cause the change of frictional force and make it impossible to integrate the frictional force over the impact interval according to the traditional impulsive dynamics of multi-rigid-body systems. Under considering slip-stick and slip-reversal phenomena and keeping the traditional approximate assumptions of impact, the method of piecewise analysis during the finite region of impulse is used and the theoretical solution of the impact problem of planar multi-rigid-body systems with friction is obtained, i.e., the dynamic response after the impact can be obtained according to initial conditions before the impact and geometry properties of the system by using the formulation provided. The example here validates the rationality of the expressions.

Ideal Load of Bilateral Constraint

ZHAO Zhen,JIN Hai,CHEN Bin

2004, 40(5):  735-741. 

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One of ideal methods that deal with variable structure system is treating variable structure problem as load or relieving of constraints. The simplest instance is ideal load of bilateral constraints, which means that there is only ideal constraint force during load. From the point of view of analytical mechanics, the theory of ideal load of bilateral constraint is given. The advantage of the theory is that it reveals mechanical mechanism of ideal load of bilateral constraint and it is more convenient for extension.

Stability and Performance to Bounded Disturbance of Linear Neutral Time-Delay Systems

YIN Shanshan,HAO Fei

2004, 40(5):  742-751. 

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By using Lyapunov-Krasovskii functional method, the delay-independent stability and delay-dependent stability of linear neutral time-delay system is studied. Sufficient conditions of the stability and performance to bounded disturbance of the given systems are given in terms of linear matrix inequalities(LMI). Numerical examples are presented to illustrate the feasibility of the results.

Adaptive Controller for Active Queue Management

WU Baoyu,WANG Long

2004, 40(5):  752-759. 

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Proportional-Integral(PI) control is a successful active queue management(AQM)scheme in dealing with relatively smooth traffic. However, in the face of changeful traffic, the performance of such a fixed PI controller degrades. A remedy to this problem: adaptive PI controller is proposed. By estimating the active flow number multiplexed on the congested link, the controller adjusts its parameters to achieve a much expeditious response speed in tracking the change of load condition in the network. Simulation results show an improvement in performance.

Characteristics of Ekman Vertical Velocity of the Atmospheric Boundary Layer Calculated with a New Ekman Pumping Formula

YANG Lei,TAN Benkui

2004, 40(5):  766-773. 

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Ekman vertical velocity of atmospheric boundary layer was calculated by using GCM data and the new Ekman Pumping formula given by Tan(2000), in which complex boundary was included for stratified atmosphere. The results show: (1) the vertical velocity of atmospheric boundary layer in most areas is about 10^-３m/s, but the velocity over Tibetan Plateau can reach 10^-２m/s; (2) the distribution of vertical velocity over Tibetan Plateau during winter is significantly different from that in summer, which is closely related to the dominant winds over this area. The characteristics of the Ekman vertical velocity obtained here with the new Ekman Pumping formula are compared with those obtained with the classic formula.

Robust Control of Time-Delay Systems with Mixed Uncertainties

DONG Hairong,GENG Zhiyong,HUANG Lin

2004, 40(5):  760-765. 

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The robust stability of the time-delay system with mixed uncertainties is discussed, which has a wide-representative sense in practice. It is supposed that the linear part in the forward loop is of parametric uncertainties described by interval perturbation mode, and that the non-linear part in the feedback loop is characterized by an integral quadratic constraint(IQC). The infinite stability checking problem of the systems with mixed uncertainties can be converted to finite or one dimensional stability checking for different structures of the IQC multipliers.

Numerical Simulation of Dynamic and Thermal Field over 2-D Urban Street Canyon

WANG Baomin,SUN Xiangming,LIU Huizhi,SANG Jianguo

2004, 40(5):  774-780. 

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The dynamic sub model ARPS is improved to simulate the flow field over two-dimensional street canyons. An energy budget sub model coupled with the modified ARPS is developed to compute the thermal structure. The dynamic sub model is capable of describing those characteristic flows around the buildings, including vortices between buildings and lee vortices, etc., while the coupling model can be used to simulate the diurnal variations of energy budget of different facades and temperature. These cases studies indicate that the above model systems can be used for investigating the wind and thermal environment and the processes of air pollutant transportation and diffusion over a street canyon or a group of buildings.

The Characteristics of Dissipation Rates of Turbulent Variance over Damxung Area in the TIbetan Plateau

LI Fuyu,ZHANG Hongsheng,LI Shiming,ZHOU Mingyu,CHEN Jiayi,XU Xiangde,LIU Huizhi,HU Fei

2004, 40(5):  781-787. 

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The turbulent data obtained from Damxung site during TIPEX in 1998 were used to study the characteristics of dissipation rates of turbulent kinetic energy, temperature variance and humidity variance in the middle area of Tibetan Plateau. The results indicate that the dimensionless dissipation rates of turbulent energy are 20% less than the energy produced by velocity shear, and the dimensionless temperature and humidity variances are also 20% less than the variances produced by temperature and humidity gradients. These deficits appear to increase with the increasing of the absolute stability parameter. Moreover, the effects of turbulent transportation and pressure variance, which are related with the stability parameter, persist throughout the whole stability region. The differences between these results and some previous studies show the underlying-surface-dependant characteristics of the dissipation rates of turbulent energy, temperature variance and humidity variance.

Interdecadal Variations of Droughts in Northeastern China

SUN Yonggang,BAI Renhai,XIE An

2004, 40(5):  806-813. 

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Based on observed temperatures and precipitation from 26 surface stations in Northeastern China (including the east of Inner Mongolia), the tendency and interdecadal variations of droughts in the past fifty years were analyzed. The result showed that interdecadal variations of dry/wet years are clearly even though themain tendency is towards to more dry years. Annual increases in temperature play a major role in the tendency of drought development but the interdecadal variationsof precipitation are the main player in the interdecadal variations of droughts, especially in 12-year and 25-year periods of low-frequency oscillations. These low-frequency oscillations connected with the interdecadal variations of regional averaged westerly circulation indices in mid- and high latitudes of Eastern Asia with a good counter-phase relationship. The precipitation and regional averaged meridianal circulation indices, however, vary in the same phase. All these relations, however, are not as good in the second part of time as in the first part of time for the past fifty years. It may relate with the weak Eastern Asian monsoon due to the different degrees of global warming in higher and lower latitudes areas.

Multiuser Detection Algorithm Based on Belief Propagation in Multiple-Input Multiple-Output Systems with M-QAM Modulation Scheme

JIANG Wei,XIANG Haige

2004, 40(5):  814-822. 

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This paper focuses on the appliance of multiuser detection algorithm based on belief propagation (BP) in MIMO systems with M-QAM(Quadrature Amplitude Modulation) modulation scheme. Because of the characteristics of M-QAM modulation, this paper introduces a preprocess to eliminate the correlation between the elements of receiving signal vector, proposes to take a conditional probability vector as the measurement of “belief” of transmitting signal, deduces the corresponding formulae of belief-updating and thus constructs the BP-Based MUD algorithms in MIMO systems with M-QAM modulation scheme. The algorithm proposed in this paper has a computation complexity proportional to the square of transmitting antenna number while it outperforms the conventional linear MMSE multiuser detector. Simulation results are given to prove this.

Using the Fast Multipole Method to Analyze Monostatic RCS of Electrically Large 3-D Multi-Conducting Bodies

TAN Yunhua,ZHOU Lezhu

2004, 40(5):  823-829. 

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A fast algorithm—fast multipole method and conjugate gradient method (FMM-CG)is developed to analyze electromagnetic scattering by electrically large three-dimensional multi-conducting bodies in this paper. Two methods are also presented to accelerates the solution of RCS: surface electric current approximation of physical optics (PO) and phase-corrected succession iterative method. This algorithm obviously reduces the computing complexity and memory requirement. It is fast and accurate, just fit for analysis of interactions between electrically large multi-conducting bodies. Finally, the accuracy and efficiency of the method are verified by 3-D numerical examples.

Decision-Directed Feedback Amplitude Estimate for BPSK/QPSK Signal

PAN Shenfu,LI Zhendong,LIANG Qinglin

2004, 40(5):  830-834. 

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After the derivation of Cramer-Rao Bound (CRB) for amplitude estimation in AWGN channel, a decision directed feedback amplitude estimation algorithm for BPSK/QPSK signal is proposed, followed by its performance analysis and simulation. The simulation results show that the variance of the algorithm is very close to the CRBat high signal-to-noise ratio in decision directed feedback mode.

Multi-Antenna Adaptive OFDM System

LI Zhendong,PAN Shenfu,SHI Haiyang,LIANG Qinglin

2004, 40(5):  840-843. 

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Adaptive OFDM(Orthogonal Frequency Division Multiplexing) system can allocate the data rates and transmit power among subcarriers adaptively, it has better BER(Bit Error Rate) performance than the traditional OFDM system in frequency selective fading channel. This article combines the adaptive OFDM system with MIMO(Multiple-input Multiple-output) technology, and utilizes the channel state information known at the transmitter, thus proposes a multi-antenna adaptive OFDM system. The simulation result shows that the system outperforms the multi-antenna OFDM system in BER performance.