Table of Content

30 September 2002, Volume 20 Issue 3

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Articles

Research on the Algorithm of Hole Repairing in Mesh Surfaces

ZHANG Li-yan, ZHOU Ru-rong, ZHOU Lai-shui

2002, 20(3):  221-224. 

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Triangular mesh surfaces are widely used in a variety of situations. Unfortunately, there often exist unwanted holes in many mesh surfaces. The existence of these holes makes it difficult for us to carry out some operations on mesh surfaces, such as rapid prototyping, finite element analysis, etc. It is therefore necessary to repair the holes. In this paper, we put forward a hole repairing algorithm. By iteratively searching the adjacent edges which have the smallest angle, new triangles are constructed, and the hole polygon are refreshed until the newly generated triangles completely fill the holes. In the algorithm, the character plane of the hole polygon is introduced for the validity verification of the new generated triangles. Practical examples show that the proposed algorithm is effective.

Calibration and Rapid Optimizing of Imaging Model for a Two-camera Vision System

HENG Wei

2002, 20(3):  225-229. 

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On the basis of the analysis of the imaging vision processing in a two camera 3D vision system, an imaging model including lens' distortion parameters is setup. The derivation for solving imaging model parameters and the realization for calibrating are described. A novel technique of parameters optimizing parameters rapidly for calibration in the two camera system is also proposed. Experimental results show that our approach can effectively increase the precision of both cameras' imaging models and the precision of the 3D data captured by the two-camera vision system. Experimental results also show that the optimizing processing converges rapidly.

A Novel Approach to Channel Estimation for WCDMA Downlink

SHENG Bin, YOU Xiao-hu

2002, 20(3):  230-233. 

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A novel scheme is proposed for channel estimation of WCDMA down link where a pilot channel is simultaneously combined with a data traffic channel. The proposed scheme exploits channel information in both pilot and data traffic channels by combining channel estimates from these two-channels. The computer simulation results show that the performance of the Rake receiver is improved effectively.

Performance Comparison Between Space-time Spreading and Space-time Transmit Diversity in cdma2000

WU Gang, CHENG Shi-xin

2002, 20(3):  234-238. 

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Space-time spreading (STS) is considered as a transmit diversity scheme in the current cdma2000 standard. Space-time transmit diversity (STTD) has been adopted in the current WCDMA standard. In this paper, the performance of STS and STTD have been compared and simulated in forward link cdma2000 systems. The performance analysis and simulation results show that these two schemes have approximately the same performance on the frame error ratio in the multipath fading channel even with imperfect channel estimation. However, compared with STTD, STS has more implementation complexity and higher peak to average power ratio.

Optimum Decoding of Trellis-coding Scheme with Large Free Distances and Iterative Decoding of DAPSK

SAYHOOD Khalid Hassan, WU Le-nan

2002, 20(3):  239-245. 

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A new receiver for convolutionally coded and differential amplitude phase shift keying modulation using iterative decoding is proposed. Performance close to that of coherent detection over an additive white Gaussian noise channel is demonstrated. Also, an optimum decoding of the trellis-code encoded by the schemes proposed by Lin, et al outperforms their suboptimum decoding, even though the decoding delay of each of their schemes and this decoder are longer than that of a conventional trellis coded modulation or convolutional codes.

Improvement of the Design of Inter leaver Based on Quadratic Congruence Mapping

TANG Chao-jing, LIU Dong-hua

2002, 20(3):  246-250. 

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The principle of algebraic quadratic congruence mapping is analysed, and then limitation of odd-even protection and shift computation are added to the mapping of interleaver, and then a new improved algorithm for interleaver design is obtained. It is proved that the performance of the new algorithm is well by simulation.

Evolutionary Computation-based MMI Training in Speech Recognition

MAO Xiao-quan, HU Guang-rui, TANG Bin

2002, 20(3):  251-253. 

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This paper proposes a hybrid MMI/EC architecture to be embedded in the training of HMMs. Each individual in evolutionary computation represents a set of HMMs, while the fitness value of each individual represents the maximum mutual information. Since evolutionary computation is noted for its global search and population-based operations, the globally optimal solutions (or the sub-optimal solutions) can be obtained. Experiments indicate that the system trained with the proposed method is superior to the one trained with the traditional gradient based training method.

An Improved Real-time Two-dimension Near-zone to Far-zone Transformation

XU Feng, HONG Wei

2002, 20(3):  254-257. 

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Near-zone to far-zone transformation in the finite-difference time-domain (FDTD) method can be performed by the integral of the equivalent electric and magnetic currents originated from scattered electric and magnetic fields on a surface enclosing the object. There are two kinds of near-zone to far-zone transformation, one is in the frequency domain and the other is in time-domain. Because the integral for time is included in the 2-D time domain Green function, the calculation of 2-D far-zone time-domain fields is more difficult than that of 3-D far-zone time-domain fields. However, by quantifying the positions of equivalent sources and arranging the time series, the calculations of the time integrals of equivalent sources are converted in to the calculation of matrix multiplying. Besides, by using the analytic method, the abnormal integral for the time is obtained accurately.

An Isomorphism Testing Algorithm for Directed Graphs: the In-degree and Out-degree Sequence Method

LI Feng, SHANG Hui-liang

2002, 20(3):  258-262. 

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In this paper, a new isomorphism testing algorithm for directed graphs——the in-degree and out-degree sequence method——is presented. The algorithm can be used in many pattern recognition problems that can be described by directed graphs.

Order Reduction Methods Based on Step Response and Impulse Response

TANG Wei, SHI Song-jiao, WANG Meng-xiao

2002, 20(3):  263-266. 

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By applying the basic principles of step response modeling and moment modeling, two classes of order reduction methods-the graphical method and the moment method-are obtained respectively. A detailed analysis of and comparison between the approximating abilities of the low models resulting from the two proposed order reduction methods is made by a large number of simulations.

A Two-channel Relay and Its Application——The SISO Case

WANG Xue-lei, SHAO Hui-he

2002, 20(3):  267-271. 

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The two-channel relay feedback of SISO systems is analyzed in-depth. With the use of the describing function method and Nyquist stability criterion, the existence and stability conditions for-corresponding limit cycle oscillation are presented. Furthermore, the relation between the information of the limit cycle and the frequency characteristic of the forward path is built. On the basis of these conclusions, two ways to apply two-channel relay feedback——extracting multi point frequency characteristics in multiple quadrant and closed-loop performance monitoring——are given. Simulations show satisfying results and verify the method presented in this paper.

The Decoupling Problem of Stochastic Nonlinear Systems: Differential Geometry Method

FU Yu-sun, TIAN Zuo-hua, SHI Song-jiao

2002, 20(3):  272-274. 

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This paper investigates the decoupling problem of stochastic nonlinear systems. It is showed that the decoupling problem of stochastic nonlinear systems can be resolved only if the problem of the deterministic systems can be resolved. The sufficient and necessary condition for the problem is given.

A Study of the Multi-objective Optimization Theory Based on the Generalized Satisfactory Degree Principle

YAO Xin-sheng, HUANG Hong-zhong, ZHOU Zhong-rong, TIAN Zhi-gang, LI Hai-bin

2002, 20(3):  275-281. 

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In this paper, the short comings of the usual optimization theory is analysed, the background for bringing forward satisficing criteria is discussed, and current researches on the satisfactory degree is described. In view of the limitation of the present research work in the satisficing domain, some concepts of the generalized satisfactory degree are defined and characterized, and the multi objective optimization theory based on the generalized satisfactory degree theory are explored and applied to the optimization design of transportation capability of railway-network. The analysis of the example shows that the theory and method in this paper is effective and applicable.

Dynamics Analysis and Computer Simulation of RV12L-6R Welding Robot

LIU Cheng-liang, ZHANG Kai, FU Zhuang, CAO Qi-xin, YIN Yue-hong

2002, 20(3):  282-286. 

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In order to satisfy the requirement of the real time control, the dynamics equation that combines Lagrangian method and recursion Newton-Euler method to solve inverse dynamics is proposed. The trajectory plan of welding robot is made for the purpose of realizing the predefined track by using the joint space method and Cartesian space method. The real-time simulation is given. The results reveal that the different initial angular of joints may lead to the discontinuity acceleration of joints and cause the system to vibrate. Finally, a practical method to avoid the unstable situation is suggested.

Research on the Function Approximation Capabilities of Fuzzy Backpropagation Neural Networks

WANG Shi-tong, ZHU Xiao-ming

2002, 20(3):  287-290. 

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This paper studies the function approximation capabilities of FBP. The results here show the ordered monotony property, the continuous mapping theorem and the non-function approximation theorem. It is proved that although FBP still retain the continuous mapping property, their capabilities to approximate function are worse when compared with traditional neural networks.

Several Theoretical Problems in the Measurements of Ultrafast Electromagnetic Radiation Pulses with Electro-optic Sampling Detection

JIANG Yu-xi, CHENG Dong-fang, ZHAO Leng-zhu, LI Jiao

2002, 20(3):  291-295. 

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This paper discusses the relationship between ultrafast electromagnetic radiation pulses E₀ (t)(THz radiation field) and the value of electro-optic sampling E_m (t).The influence of group-velocity-mismatching on the THz radiation field and fs optical probe pulses and the effects of self dispersive propagation in radiation field are also analysed.

Discussion by Using Molecular Orbital Theory on the Mechanism of the Negative Resistance Phenomenon in MIM Junction

ZHOU Li-xin, MIAO Jiang-ping, CHEN Wei, WU Zong-han, SUN Cheng-xiu

2002, 20(3):  296-300. 

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In this paper, we discuss the reason of the negative resistance phenomenon(NRP) existing in a MIM(metal-insulator-metal) light emission tunnel junction's I-V character by using orbital hybridization theory for the first time. Combining with chemical calculation and our experimental results, a theoretical explanation of the NRP is proposed.

Parameter Optimization of Low Power BIST

HU Chen, YANG Jun, SHI You-hua

2002, 20(3):  301-304. 

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With the fast growing portable-electronics market and stricter requirement of the wafer test, the power consumption problem of built-in self-test (BIST) has attracted more and more attention. In this paper, a parameter optimization algorithm that can lower the peak power during test application has been proposed. Experiment results show that peak power is reduced considerably with no extra silicon overhead of test logic on the condition that fault coverage is guaranteed.

The Behavior of Pulse Heat Flux Wave Propagation in a Fine Round Ceramic Bar

HU Xue-gong, LIU Deng-ying, ZHOU Ding-wei

2002, 20(3):  305-308. 

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The effect of a volumetric heat source induced by pulse laser heating in the temperature fields of a fine round ceramic bar was investigated experimentally and theoretically. Experimental results show that non-Fourier heat conduction phenomena such as temperature waves exist on the end surface of the fine round ceramic bar. Hyperbolic heat conduction equation was used to model the non-Fourier heat conduction process and the theory about thermal energy wave propagation was introduced to explain it. The experimental evidence for thermal energy wave propagation was obtained. The paper makes it clear that thermal relaxation time f is mainly responsible for rapid transient heat transfer processes in heterogeneous materials.

The Network for Fast Prediction of Mechanical Properties of Cast Iron

XIA Shan-mu, LI Da-yong

2002, 20(3):  309-312. 

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The artificial neural network for fast prediction of mechanical properties of cast iron has been studied. Matlab is used to create and train a predicting network. Meanwhile some efficient methods have been adopted to promote the performance of the network. The testing result shows that the network has a fine ability of generalization and can predict mechanical properties of cast iron precisely and quickly.

Experimental Study on the Metal Ceramic Thermal Couple for Continuous Measuring of the Temperature of Hot Metal

WANG Xue-song, WANG Jian-jun, ZHOU Li

2002, 20(3):  313-315. 

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Experiment had proved feasible that two different metal ceramic rods used as thermal couple electrodes were immersed directly into hot metal to measure temperature continuously. Thermal couple electrodes made up of two different metal ceramic rods had merits of high resistance corrosion by hot metal and slag, higher export emf, ideal linear relationship between measuring temperature and thermal emf at the range of melting temperature.

An Application of Fuzzy Reliability Theory in the Reliability Analysis of Mechanism Movement

DONG Yu-ge, CHEN Xin-zhao, CHO Hyun-deog, KWON Jong-wan

2002, 20(3):  316-320. 

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This paper discusses the common method of analysing the fuzzy reliability of mechanism movement and the method to analyze fuzzy reliability by transforming a fuzzy reliability problem into a general reliability problem. Finally, this paper explains the applications of above methods in the reliability analysis of slider crank mechanism.

Filling Simulation of Gas-assisted Injection Molding

ZHOU Hua-min, ZHANG Yi-sheng, LI De-qun

2002, 20(3):  321-325. 

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The characteristics of gas-assisted injection molding have been investigated, and the mathematical model of the filling simulation is thus established. Aiming at solving the gas penetration interface, which is the key problem in the implementation of the simulation, a detailed calculation model is presented. The simulation results based on this model seem to agree well with the experimental results.

Design and Performance Analysis of a Novel Two-stage Fast Code Acquisition Scheme

WANG Jia-yong, CHEN Yin-jian, LIANG Xu-wen, YANG Gen-qing

2002, 20(3):  326-330. 

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A novel two-stage code acquisition scheme for direct-sequence spread-spectrum communication is presented in this paper. The acquisition scheme uses a passive matched filter as an acquisition-aiding device in the first stage. The matched filter has rapid search capability but the hardware is always excessive. In order to reduce the hardware requirement,the 1-bit quantization method is used. In the second stage, a bank of active and mutual independent correlators are employed, and the long active correlators contribute to decision reliability. In addition, the bank of mutual independent active correlators solve the problem of engaged correlators which usually exist in the traditional two-stage scheme. An analytical model based on queuing and detection theory is developed and optimization of the scheme is treated. Finally, the numerical results of theoretical performance are presented. This code acquisition scheme can be used in burst direct-sequence spread-spectrum communication, especially in mobile satellite burst communication.