Table of Content

29 July 2011, Volume 45 Issue 07 Previous Issue    Next Issue

Automation Technique, Computer Technology

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Simulation and Analysis of Low Emitting Diode Illumination Uniformity for 2-D Bar Code Identification on Cutting Tool Cylindrical Surface WANG Hong-Xiao, HE Wei-Ping, LEI Lei, LIN Qing-Song 2011, 45 (07):  945-948.  Abstract ( 3400 )   Save To predict the illumination uniformity of the lighting design for 2-dimensional bar code image collection on cutting tool, this paper analyzed the practical low emitting diode(LED) light source model, its luminescence properties and the light intensity distribution based on a computer aided optical illumination software, built a light source simulation model, and designed a development model according to the practical application requirement. It also simulated and analyzed the three key factors on the impact of LED illumination uniformity, implemented experiments based on simulation, contrasted the simulation and experimental results by fitting the curve. The experimental results show that the simulation can correctly predict the actual uniformity of illumination. The research can help the optical system design for identifying 2-dimensional bar code directly marked on cylindrical surface of cutting tool. References | Related Articles | Metrics

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Quick Startup Control of a Platoon of Vehicles Based on Optimal Theory XIE Qiang-De-a, YANG Ming-a, WANG Bing-a, WANG Chun-Xiang-b 2011, 45 (07):  949-953.  Abstract ( 3884 )   Save A coordination methodology based on optimal control was proposed for platoons of vehicles to reduce the time passing through the intersection. The linear model of the platoon was derived and can be of overlapping interconnected subsystem. By decomposing the original system model via an appropriate input/state expansion, an expand system model was obtained. By applying the optimal output tracking control algorithm to the expand system model and by choosing the weight matrixes according to the safe distance, the optimal control rate was acquired, and then the original system control rate was obtained by contracting back. The method can have the platoon achieve the target cruising speed as soon as possible and guarantee the safety of vehicles. The application results of the controller illustrate the effectiveness of the proposed methodology. References | Related Articles | Metrics

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A Time Step Alterable and Predicative Electronic Reconnaissance Satellite Guiding Scheduling Technique WANG Hui-Lin, RAN Cheng-Xin, HUANG Wei, MA Man-Hao 2011, 45 (07):  954-960.  Abstract ( 4486 )   Save To solve the problem of electronic reconnaissance satellites(ERS) guiding scheduling with area prior information, a time step alterable and predicative electronic reconnaissance satellites guiding scheduling mechanism was put forward, in which the realtime satellites reconnoitering information is used to guide the following detecting actions in the limited and alterable future time step. With the continuously data downloading, the rolling impellent guiding scheduling windows are driven to form. An updating method based on Bayesian rule for forecasting the area state was presented, and the universal multiobjective scheduling model in the rolling alterable time step scheduling windows was brought forward. According to the characteristics of the model, an improved multiobjective ant colony algorithm(IMOACA) was designed to compute the pareto optimal solutions. The comparative experiments prove that the proposed mechanism, model and algorithm can effectively deal with the ERS guiding scheduling problem and the performance is good. References | Related Articles | Metrics

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Weather Optimal Dynamic Positioning Control of Fully Actuated Autonomous Underwater Vehicles with Current GE Hui, JING Zhong-Liang 2011, 45 (07):  961-965.  Abstract ( 4292 )   Save The weather optimal dynamic positioning control was brought out for the fully actuated autonomous underwater vehicles(AUV) with the influence of current. The AUVs are controlled under certain position and posture with the antidirection of the current and holding the determinate distance. Then the current influence are cancelled out by the main thrusters without the help of other thrusters, at the same time, fuel consumption is reduced. Considering the unmatched uncertainties in the dynamic system for the reason of current, the adaptive backstepping control based on the neural network was used. The simulation proved the effectiveness of the dynamic positioning controller. References | Related Articles | Metrics

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Genetic Algorithm to Solve Optimization Problem with Equality Constrains HU Kuan-1, 2 , CHANG Xin-Long-1, SONG Bi-Feng-2, ZHANG Lin-3, LONG Bing-1, YU Yan-Feng-1 2011, 45 (07):  966-969.  Abstract ( 6531 )   Save Aiming at difficultly solving optimization with equality constraint in genetic algorithm, based on independence analysis of design variables, a descending dimension method was used to deal with equality constraint. In this way, not only equality constraints can be strictly satisfied during optimization, but also there are only inequality constrains in optimization. Furthermore, referring to the multiobjective idea, individuals was ranked through violation degree and violation times simultaneously, which is more in accord with practice. Finally, three numerical examples were used to examine the proposed method, satisfying results were achieved, which indicates the method is valid and feasible. References | Related Articles | Metrics

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Unimodal Biometric System Based on Subspace Learning Method LIU Huan-Xi-１, WU Zhe-１, ZHU Jun-2, LI Xiong-1, LIU Yun-Cai-1 2011, 45 (07):  970-974.  Abstract ( 3207 )   Save This paper built a unimodal biometric system that is suitable for most individual modalities, e.g., face and gait. We first preprocess each raw datum into unit and then obtain a new biometric data set. Then we determine the intrinsic low-dimensional subspace of preprocessed data by local topology structure preserving projections (LTSPP). Finally we perform the classification in the determined subspace using the intra-class distance sum. In the proposed system, LTSPP is a novel subspace algorithm. Compared with other subspace methods, LTSPP possesses more discriminant abilities and is more suitable for biometric recognition. In addition, both preprocessing each raw datum into unit and performing the classification using the intra-class distance sum are helpful to improve the recognition rates. The experimental results demonstrate the effectiveness of our unimodal biometric system. References | Related Articles | Metrics

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Real-Time Optimization Based on Chance-Constrained Programming for Plant-Wide Processes ZHANG Yan-1, DING Mao-Sen-1, MAO Hong-Yan-2 2011, 45 (07):  975-979.  Abstract ( 3629 )   Save A dynamic real-time optimization (RTO) scheme based on chanceconstrained programming (CCP) was presented for a class of plant-wide processes. Chance-constrained programming is employed in the optimization problem, in which the constraints containing economic and model uncertainties are guaranteed to be satisfied at a high level of probability. The real-time optimizer based on product quality model determines the optimal setpoint for each sub-process by solving joint probability constrained problem. Simulation studies for furnace temperature setpoints optimization problem of the walking beam reheating furnace were illustrated to verify the effectiveness and practicality of the proposed method. References | Related Articles | Metrics

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Representing Bounded Petri Nets by Process Calculi DONG Zhen-Hua-a, b , DONG Xiao-Ju-a, b 2011, 45 (07):  980-984.  Abstract ( 3416 )   Save A formal encoding method was given to represent bounded Petri nets by CCS which is one kind model of process calculi for researching the relationship between Petri nets and process calculi. A Place/Transition net could be encoded to a finite process by this method. The process and the original net satisfy the operational and observational correspondence. In this view, they have the same behaviors. It shows that the encoding method is fully abstract with respect to the labeled bisimulation, which is an equivalence relation between nets. References | Related Articles | Metrics

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Collision Detection and Optimization of Dual-Arm Mobile Robot Based on Node Tree of VRML LIU Zhong, CAO Qi-Xin, ZHU Xiao-Xiao, WANG Wen-Shan 2011, 45 (07):  985-989.  Abstract ( 4279 )   Save A large number of non-convex models exist in three-dimensional simulation environment for dual-arm mobile robots, it is impossible to realize accurate real-time collision detection. This paper proposed a method to implement convex decomposition of non-convex models based on node tree of VRML. Pass vertexes returned by convex decomposition to Quickhull algorithm to create convex polyhedron that used for V-Clip collision detection algorithm to realize accurate real-time collision detection. In order to improve the efficiency of collision detection to enhance real-time simulation, bounding box is used. The results show that this method can make real-time collision detection and has great precision. References | Related Articles | Metrics

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On Self-organized Collaboration Behavior in  Multi-modular Mobile Robots FEI Yan-Qiong-a, b , ZHU Yue-Liang-a, b , SONG Li-Bo-a, b 2011, 45 (07):  990-994.  Abstract ( 3185 )   Save  A new modular mobile robot was designed, which consists of four basic modules. For the selforganized collaboration behavior of multi-modular mobile robots in the complex environment, this paper presented three motion strategies. The direction selected rules of the goal were analyzed in the multimodular mobile robots. The multi-obstacle avoidance strategy that based on the “perception-action” was described. So robots can avoid the obstacle continuously and reach the assigned goal. The coordination strategy in multi-modular robots was shown, by which they can cooperate with others to carry the heavy or climb over a step that a single robot cannot complete. At last, the 3D simulation proves the validity of the strategy in the multi-obstacle environment. References | Related Articles | Metrics

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Design of an Active Safety Collision Avoidance System Based on Adaptive Warning Area CHEN Ping-a, WANG Chun-Xiang-a, YANG Ming-b, WANG Bing-b 2011, 45 (07):  995-999.  Abstract ( 3199 )   Save To improve vehicle driving safety in urban environment, an active safety collision avoidance system was presented and implemented. A distributed architecture was adopted in the lowlevel system, uC/OSII employed as the realtime operational system of the bottom software. The communication system was realized by CANopen protocol. Since the road curvature always changes drastically in urban environment, an adaptive  warning area based collision detecting method was proposed using scanning laser radar. The stability of the system and the validity of the proposed method were proved by the real experiments. References | Related Articles | Metrics

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Research of Predicting Machine’s Remaining Useful Life Based on Statistical Pattern Recognition and Auto-regressive and Moving Average Model LIAO Wen-Zhu-1, PAN 尔Shun-2, WANG Ying-2, XI Li-Feng-2 2011, 45 (07):  1000-1005.  Abstract ( 4105 )   Save Considering the important applications of predictive maintenance (PdM) today, it becomes essential to acquire machine’s condition and its deterioration process. A machine’s remaining useful life (RUL) model was proposed in which a statistical pattern recognition (SPR) method is developed to estimate machine’s health index (HI) and an autoregressive and moving average (ARMA) model is used to predict machine’s RUL based on HI information, which greatly supports PdM planning. Through a case study, the computational results show that the proposed model is efficient and practical. References | Related Articles | Metrics

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Design and Optimized Implementation of Rainbow Table with GPU JIN Quan-a, GU Da-Wu-a, ZHAO Jian-Jie-b 2011, 45 (07):  1006-1011.  Abstract ( 3916 )   Save This paper proposed a new implementation of Rainbow table algorithm on GPU. Utilizing the GPU’s powerful SIMT capacity, the algorithm greatly improves the performance of Rainbow chain generation by dispatching the pre-computation of Rainbow chain to each GPU thread and accelerates the execution efficiency of online attack through the newly introduced pre-computation chain. The running time of pre-computation on GPU (Tesla C1060) outperforms that on CPU (Core2 Duo 2.8 GHz) by 41.2 times, that is 110×106 times DES encryptions per second; and the running time of online attack, 3.52 times faster. Based on the new hardware system, we obtain the 40 bits keys of DES in 2.73 seconds on average with successful rate of 46% by using 1.3 GB hard disk space. References | Related Articles | Metrics

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Multi-sensor Fusion Based Vehicle Detection and Tracking Method MAI Xin-Chen-a, YANG Ming-a, WANG Chun-Xiang-b, WANG Bing-a 2011, 45 (07):  1012-1016.  Abstract ( 3597 )   Save To fulfill real-time vehicle detection and track in city environment, a method based on laser radar and vision was presented. By perspective transform, vehicle hypothesis is done through laser radar. For vehicle recognition aspect, a method based on multi-dimension space Mahalanobis distance is presented, which extracts feature vector in ROI, and using the Mahalanobis distance between it and standard vector as presence probability. In vehicle tracking, the system uses Kalman filter to fulfill target tracking, at the mean time, to improve robustness, a particle-filter method based on Kalman filter is presented, it could realize more precise target state estimation when laser radar data does not work well. The experiment shows this method can achieve better vehicle tracking in general city environment. References | Related Articles | Metrics

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The Performance Optimization of the Articulated-Tracked Pipe-Inspected Robot for Obstacle Negotiation CHEN Zong-Yao, YAN Guo-Zheng, WANG Kun-Dong, ZHAO Zhong-Hua 2011, 45 (07):  1017-1020.  Abstract ( 3758 )   Save Aiming at the special requirement of pipe-inspection, this paper presented the design of a compact articulated-tracked robot. Based on the structure design of the robot, several mathematical models describing the relationship between the posture and the capacity of the robot’s obstacle negotiation were established. And the effect of posture regulation on the performance of the robot’s obstacle negotiation was also investigated. Using an optimization technology, this paper gave the calculation results for the max-imum step height and the adaptive moving posture during the process of obstaclenegotiation. The Matlab simulation of the model and the experiment verify the improvement of the robot performance by the design and optimization presented in this paper. References | Related Articles | Metrics

Radiao Electronics, Telecommunication Technology

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Joint Optimization of Rate Allocation and Network  Cost in Distributed Wireless Sensor Networks TAN Chong-1, ZOU Jun-Ni-1, WANG Min-1, XIONG Hong-Kai-2 2011, 45 (07):  1021-1030.  Abstract ( 3355 )   Save The limitation and the inappropriate allocation of network resource would be critical in wireless sensor networks. Considering both network flow control and transmission cost, this paper defined the subtraction between source utility and transmission cost as the net utility of the sensor network. By formulating the rate allocation and the transmission control based on multipath network coding as the optimization problem, a decentralized algorithm was proposed to solve it through the convex optimization and the Lagrange dual approach. And the network utility is maximized and the transmission cost is minimized at the same time. The performance of the proposed algorithm was validated through numerical experiments. References | Related Articles | Metrics

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TR-TC Associated Test Cost Mathematical Model in SoC Using Controllable Multi-Scan-Enable ZHANG Jin-Yi-a, b , c , HUANG Xu-Hui-b, CAI Wan-Lin-b, WENG Han-Yi-a, c 2011, 45 (07):  1026-1030.  Abstract ( 3156 )   Save Based on the scan chain structure of SoC（System-on-Chip）, this paper described a method of multi-Scan-Enable DFT for at-speed testing to improve the transition fault coverage. A TR-TC (Test Resources-Test Coverage) associated test cost mathematical model was built. The results show that the TR-TC model can effectively control the complexity of at-speed DFT and establish the optimization number of Scan-Enable, which provides a reliable target control value in multi-Scan-Enable at-speed DFT. References | Related Articles | Metrics

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A New Corner Detection Algorithm Based on Barycenter Finding TU Yan-Xin, ZHU Yi, DU Zheng-Chun 2011, 45 (07):  1031-1034.  Abstract ( 5309 )   Save  A new algorithm was presented for the detection of corners of digital contour profiles based on barycenter. Firstly the length of curve on two sides of the each point on the contour profile is calculated to determine the support area, of which the end point is obtained with interpolation technique. Next an intersected polygons method is employed to calculate the barycenter of support area with given length. And then the distance between each point in the support area and its corresponding barycenter is used as feature strength to determine the feature point candidates. Finally the points with local maximum feature strength are chosen as corner point. The experiments show that the new algorithm is more accurate for corner detection and has stronger noisetolerant capacity than the other algorithms.   References | Related Articles | Metrics

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Fabrication of Dry Electroencephalography Electrode Using Flexible Substrate MEMS Technique WU Cheng-a, CHEN Di-a, HU Rui-Jun-a, CHEN Jing-Dong-a, CHEN Xiang-a, WANG Xiao-Wei-b, 吕Bao-Liang-b , c 2011, 45 (07):  1035-1040.  Abstract ( 4424 )   Save A novel dry electroencephalography (EEG) electrode was fabricated for the vigilance analysis based on EEG signal acquisition, which is conventionally acquired by wet electrodes. Flexible substrate MEMS fabrication technique was applied to fabricate the flexible dry micro-needle electrode array, which is chemical stable and bio-compatible. Featuring its cantilever structured micro-needles, the electrode was fabricated by wet etching of Cu sacrificial layer process. The electrodes were then released from substrate by PDMS lift-off process and packaged by polyimide, and finally fabricated a threedimensional electrode array by multi-layer assembly. Ni was electroplated to fabricate the micro-needles, the wire and the pads of the dry electrode to obtain mechanical strength while Au was electroplated on the surface of micro-needles for bio-compatibility. The performance of the dry electrode was tested by the amplifier of EEG acquisition, Neuroscan. The impedance of dry electrode was approximately 10 kΩ, and the similarity between the performances of dry and wet electrodes was proved by comparison of their time domain and frequency domain signals. With the advantage of high yield, small size, simple assembly, fine shielding, good reliability and mechanical strength, the dry electrode is capable of convenient and painless EEG signal acquisition. References | Related Articles | Metrics

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Research of the Integrity Algorithm on Multi-receivers Local Airport Monitor System WANG Zhi-Peng, ZHANG Jun, ZHU Yan-Bo, XUE Rui 2011, 45 (07):  1041-1045.  Abstract ( 4393 )   Save The existing local airport monitor (LAM) with single receiver is not robust, and its integrity is not good enough. Based on multi-receivers local airport monitor (MLAM) concept, its integrity was discussed on both ground monitor station and airborne user. For ground monitor station, the multi-receivers pseudorange corrections verifying method was studied. Through using least monitor protection level principle to choose the optimal visible satellites combination, the computation complex is reduced. As to the airborne user, under the premise of system integrity, continuity and availability, the missed detection coefficient was computed to estimate airborne user protection level and thus improve the system performance. The experimental results demonstrate that, compared to the LAM, the accuracy and integrity of the MLAM are all improved. References | Related Articles | Metrics

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Research on Robust GMD-Based Vector Precoding WU Da-Wei, HE Chen, JIANG Ling-Ge 2011, 45 (07):  1046-1049.  Abstract ( 4368 )   Save A robust vector-precoding (VP) algorithm based on geometric mean decomposition (GMD) method was proposed for multiple input multiple output (MIMO) system with imperfect channel state information (CSI). By exploiting statistical information of CSI and minimizing the mean square error of signal vectors transmitted and received, the optimal perturbation vector and precoding matrix based on GMD method were got. The simulation results show that the proposed robust GMD-VP scheme outperforms the existing methods. The performance gain is at least 2dB at high SNRs. References | Related Articles | Metrics

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Linear Precoder Design for Amplify-and-Forward MIMO Relay Systems with Channel Estimation Errors ZOU Jun-1, LIU Wei-1, LUO Han-Wen-1, YU Hui-1, MA Ji-Peng-2 2011, 45 (07):  1050-1053.  Abstract ( 3485 )   Save  A linear relay precoder design scheme was proposed for the amplifyandforward MIMO relay system with channel estimation errors modeled as Gaussian random variables. The closedform solution was derived based on the minimum mean squared error (MMSE) criterion. The numerical results show that compared with other schemes that do not consider channel estimation errors, our scheme achieves better performance in terms of both mean squared error (MSE) and bit error rate (BER). References | Related Articles | Metrics

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Greedy Antenna Selection Algorithm for MIMO Relay System LIU Shi-1, DING Ming-1, 2 , LIU Wei-1, LUO Han-Wen-1 2011, 45 (07):  1054-1057.  Abstract ( 3523 )   Save  To improve the capacity of multi-input multi-output (MIMO) relay systems with relay selection, a greedy capacity maximization antenna selection algorithm was proposed. By taking noise at relay nodes into account, the proposed algorithm selects the backward and forward sub-channel gradually according to the closed form expression of capacity when one more antenna pair is added. The simulation results show that the proposed scheme outperforms the existing selection algorithms in terms of ergodic capacity. References | Related Articles | Metrics

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An Algorithm for Phase Noise Mitigation in High-Frequency OFDM DU Wen, JIANG Ling-Ge, HE Chen 2011, 45 (07):  1058-1062.  Abstract ( 3474 )   Save The increasing of phase noise in high-frequency orthogonal frequency division multiplexing wireless communication system degrades the system performance. A joint channel transfer function and phase noise estimation algorithm with low pilot consumption was proposed to resolve the conflict. By analyzing the characteristics of channel transfer function and phase noise, the algorithm is divided into two steps: on OFDM pilot time-slot, estimate channel transfer function and phase noise; on pilot sub-carriers, estimate phase noise continuously to eliminate inter-carrier interference caused by it, assuming the channel is constant. The simulation results show that the proposed algorithm can eliminate phase noise effectively in a heavy phase noise condition.   References | Related Articles | Metrics

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Impossible Differential Cryptanalysis of ARIA ZHANG Lei, GUO Jian-Sheng 2011, 45 (07):  1063-1067.  Abstract ( 3566 )   Save This paper studied the security of the block cipher ARIA against impossible differential cryptanalysis. By analyzing the property of the diffusion transformation, a new kind of nontrivial 6-round impossible differential was presented. Generally, considering the weigh of differential, these two different kinds of impossible differential structures and the count were proposed. Based on this, we can give out all the number of these two kinds 6-round impossible differential in theory. It is shown that, when guessing the input-and-output differential weight of 10, there are only two kinds of impossible differential and all of them can be used to attack the 6-round ARIA with the best result by now: the data complexity is 2120 chosen plaintexts, and the time complexity is 294.5 encryptions of 6-round ARIA. References | Related Articles | Metrics

Communication and Transportation

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Active Control of Energy-Regenerative Electromagnetic Suspension Based on Energy Flow Analysis HUANG Kun, YU Fan, ZHANG Yong-Chao 2011, 45 (07):  1068-1073.  Abstract ( 3975 )   Save The mathematical model for the developed electromagnetic actuator was established and a main/inner-loop control structure was proposed for its active control. The physical constraints of control current and the energy flow states of the inner-loop system were analyzed and a two-mode controller which respectively emphasizes on vibration control and energy regeneration was designed for the main-loop. Simulations were carried out with different road inputs and the results demonstrate that the former mode can improve vehicle ride comfort by more than 30% with battery energy consumption while in the latter mode the ride comfort can be improved by up to 10% with battery charged by regenerated energy. References | Related Articles | Metrics

Aeronautics & Astronautics

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Modeling and PID Controller Designing for  Pressure Control System of Cabin Function Test HAN Ye-Fei, FANG Gang, HU Yong-Xiang, YAO Zhen-Qiang 2011, 45 (07):  1074-1079.  Abstract ( 4413 )   Save Aiming at the problem that it is not allowed to debug pressure control system parameters of cabin function test directly in the airplane cabin, the model of pressure control system in cabin function test was built. The model contains the effects caused by the dynamic characteristics of pneumatic valve components and the pressure variation process of pipeline, which makes the design of the control system objective and analytical. The model linearization and model reduction were applied to design PID controller for pressure control system in the cabin function test. The simulation results of pressure control system show the PID controller  obtained by analytical method can meet the technical requirements of airplane cabin function test. References | Related Articles | Metrics

Environmental Science

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Application of Genetic Algorithm in Site Selection of Municipal Sewage Sludge Treatment and Disposal Projects HOU Xiao-Feng-1, XUE Hui-Feng-1, 2 2011, 45 (07):  1080-1084.  Abstract ( 4271 )   Save Aiming at solving the problems of site selection for sewage sludge treatment and disposal projects in bigger cities, this paper established a mathematical model which is in accordance with the principle of minimum cost for project and analyzed the solution of objective function. By taking the example of site selection process of Xi’an sewage sludge treatment and disposal projects which have adopted the technology of sintering brickmaking by using sewage sludge, it simplifies and optimizes the alternative plans of site selection process through the theory of genetic algorithm. On the basis of traditional methods of decisionmaking, it selects 1-5 sites of sewage sludge treatment and disposal projects out of the 15 alternative sites which include the site selection, corresponding scale of production, transportation fees and path etc. Finally, the paper suggests setting up 3 sewage sludge treatment and disposal projects which can provide scientific basis for the site selection. References | Related Articles | Metrics

Mathematics

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Uniqueness of the Entropy Solutions to Cauchy Problem for a Degenerate Parabolic-Hyperbolic Equation HAO Xing-Wen-1, 2 , WANG Qin-1 2011, 45 (07):  1085-1090.  Abstract ( 2869 )   Save  Kuznetsov’s method is a useful tool to establish the error estimate between numerical solutions and entropy weak solution for hyperbolic equation. This paper uses this method to prove the uniqueness to the Cauchy problem of a special example of second order degenerate parabolic-hyperbolic equation, Meanwhile, the paper obtained that entropy solutions are continuous at t=0 in the sense of L1 norm by the double variable device. References | Related Articles | Metrics

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Existence and Uniqueness of Positive Solutions of a Class of Nonlinear Differential Equations of Fractional Order LI Xiao-Yan, JIANG Wei 2011, 45 (07):  1091-1094.  Abstract ( 3122 )   Save By using the fixed point theorem and contraction mapping principle on a  cone in a real Banach space, the existence and uniqueness of positive solutions of nonlinear fractional differential equations in which the inhomogeneous term depends on the fractional derivative of lower orders were investigated respectively. Based on the expression of the solutions for this type equation, sufficient conditions for the existence of positive solutions for this type equation were obtained, also for the uniqueness. Meanwhile two examples were presented to demonstrate the main results. References | Related Articles | Metrics