Table of Content

    20 February 2012
    Volume 42 Issue 1
    A method for critical core mining based on network capital evaluation
    HUANG Jin-cai, CHENG Qing, LIU Yan-jun, QIAO Shi-dong
    Abstract ( 247 )   PDF (1332KB) ( 1388 )   Save
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    To solve the problem of multiple critical nodes mining in the network, the definitions of network capital and critical core were  proposed. In addition,  the influence function and attenuation function were used to calculate network capital, and  the change of network capital was used  to characterize the change of network performance. Inspired by the inputoutput analysis, a complete correlated mode was proposed to mine the critical core, which was the node(set) and whose removal with its links decreased the network performance to a certain degree. Experimental results showed  that the dynamic failure method could mine the critical core with fewer nodes than the ranked failure method when the network performance decreased to 30%.This method was more accurate and efficient in mining the critical core.

    A kind of iterative improvement based ant colony optimization algorithm for the traveling salesman problem
    CAI Rong-ying, WANG Li-jin, WU Chao, ZHONG Yi-wen*
    Abstract ( 330 )   PDF (1026KB) ( 1711 )   Save
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    Classical ant colony optimization algorithms build solutions by starting with an empty initial solution, and unconditionally accepting selected components. This has become a natural restriction of its intensification ability. To overcome this shortage, an iterative improvement based ant colony optimization algorithm was  presented for the traveling salesman problem. In the process of constructing the solution, the ant always memorizes a complete solution; and it adopts a candidate city only when such an adoption can improve the solution. Reconstructing of a partial solution was used to keep the diversity of swarm and avoid premature convergence. Simulation results showed that the proposed algorithm can obtain better solutions within less iteration numbers.

    A path planning method using two-stage particle swarm optimization
    LIU Bin, ZHANG Ren-jin
    Abstract ( 312 )   PDF (1498KB) ( 1470 )   Save
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     Multiple short curves are joined to a long curve in path planning, which usually could only realize C1 continuity and could cause the second order derivative to be discontinuous in the joint of adjacent short curves. To resolve this problem, the cubic B-spline curve with the feature of C2 continuity was used to implement path planning carried out by a two-stage particle swarm optimization. Control vertexes of the B-spline curve were determined at the first stage of two-stage particle swarm optimization, and then the optimal path was searched for at the second stage. To ensure the particles effectiveness, the particles initialization was improved according to the characteristic of the Bspline curve. The length of the path and collision detection reflected on the arc length factor and collision factor respectively in the fitness function. The global optimum was gradually approached with the loop by the particles. Experimental results indicated that the improved initialized particles were closer to the actual path and that the C2 continuous path could be achieved by two-stage particle swarm optimization.

    A learning to rank approach based on ranking positions
    LIN Yuan, LIN Hong-fei*, ZHANG Ping
    Abstract ( 378 )   PDF (960KB) ( 1859 )   Save
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    Designing effective ranking functions is a core problem for information retrieval since the ranking functions directly impacted the relevance of the search results. Learning ranking functions from preference data in particular have recently attracted much interest. The ranking algorithms were often evaluated using information retrieval measures. The main difficulty in direct optimization of these measures was that they depended on the ranks of documents. So it was important to optimize the ranking positions of relevant documents in the result list. Specifically, the roles of preference were investigated between the relevant documents and irrelevant documents in the learning process. To remedy this, a new input sample named one-group sample was constructed by a relevant document and a group of irrelevant documents according to a given query. The new sample could effectively distinguish the relevance of documents.  With the new samples a new position based loss function was also developed to improve the performance of learned ranking functions. Experimental studies were conducted using the Letor30 data set which improved ranking accuracies by 2% and demonstrated the effectiveness of the proposed method.

    Two-dimensional Otsu image thresholding based on second order generalized probability
    ZHANG Xin-ming, MAO Wen-tao, LI Zhen-yun
    Abstract ( 369 )   PDF (1658KB) ( 1275 )   Save
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    Aiming at the problems of inaccurate segmentation and bad universality in traditional twodimensional (2-D) Otsu thresholding methods, a fast 2-D Otsu image thresholding method based on the second order generalized probability (SOGP) was proposed. First, a 2-D histogram was created with the improved neighborhood and the two-variable probability distribution of it was modified to the second order generalized probability to obtain better segmentation performance. Then, the values of objects area and background area in the 2-D histogram main-diagonal district in the Otsu method were precisely calculated to get a more accurate threshold, and the parameter of SOGP was selected to improve the method’s universality. Finally, a 2-D histogram was analyzed to get Otsu computing features, and a new recursive algorithm was inferred with the features to reduce the computational complexity. Experimental results showed that the proposed method could not only achieve more accurate segmentation results and more applicability, but also required much less memory space and running time, compared to the current 2-D Otsu thresholding methods.

    A co-evolution model integrated with an immune mechanism
    YAN Xuan-hui, ZENG Qing-sheng*, SHU Cai-liang
    Abstract ( 365 )   PDF (1931KB) ( 1227 )   Save
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    To solve the problems of traditional evolutionary algorithms in computational efficiency, a co-evolution model integrated with an immune mechanism was proposed by referring the idea of co-evolution algorithm. The model maintained the diversity of a population through the respective evolution of multiple sub-populations. During the evolution in each iteration, each sub-population selected the elite antibodies individually and carried out the immune memory operation. Then every sub-population independently mutated with a variety of the algorithm. If the mutation reduced the fitness of the antibody, the antibody was guided by the elite ones. Group collaboration included randomized crossover of a number of individual between sub-populations and large-scale migration among sub-populations. Final the immune metabolism operation removed the weak antibodies in the population. The above operations were repeated until the algorithm reached the established goals or intended loop iterations. Simulation experiments with 13 benchmark functions showed that the optimal solution or satisfactory solution of the model obtained from the search was better than traditional evolutionary algorithms, and its optimization efficiency was also greatly improved.

    A visual servoing algorithm based on rotation matrix decomposition
    LI Guo-dong, ZHAO Wei, TIAN Guo-hui*, XUE Ying-hua
    Abstract ( 393 )   PDF (1975KB) ( 2244 )   Save
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    To avoid the target being lost from the camera views in the application of traditional visual servoing methods, a new characteristic vector was derived from the rotation axis and a rotation angle decomposing from the rotation matrix connecting the current camera frame and the desired camera frame, as well as the Jacobian matrix representing the relationship between the time variation of the characteristic vector and the camera velocity. The proposed characteristic vector could be efficiently applied to control the camera’s orientation so that the task function was constructed, and a decoupled control scheme was designed using the second Lyapunov method. Experimental results showed that the failures of visual servoing tasks for home environments could be avoided by using the rotation matrix decomposition method.

    Image acquisition and transmission system for a hospital inspection robot
    ZHANG Kai, TIAN Guo-hui*, ZHOU Feng-yu, SONG Bao-ye
    Abstract ( 494 )   PDF (3099KB) ( 1224 )   Save
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    To meet the requirements of a hospital inspection robot for image collection and transmission, an image acquisition and transmission system based on WLAN was designed and developed. A method of combining an embedded device and industrial control computer was proposed to decrease the calculation burden of a robot. The embedded device was responsible for image acquisition and compression, and the industrial control computer completed transmission. The occupancy ratio of the network bandwidth was effectively reduced by applying the algorithm of JPEG. A communication protocol based on UDP was designed. It made image transmission quick and steady in the WLAN. The improved parallel transmission increased the real-time ability by applying multithreading technology. Experiments demonstrated that the system of image capture and transmission for the hospital inspection robot had high stability and real-time ability, which could complete the task of capturing the image of the environment and transmission when the hospital inspection robot visited wards.

    Path planning of a mobile robot based on fixed-length real number encoding mechanism
    YAN Xuan-hui, XIAO Guo-bao*
    Abstract ( 460 )   PDF (1489KB) ( 1031 )   Save
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     Aimed at the path planning problem of a mobile robot, a novel fixed-length real number encoding mechanism was proposed. The first step was to make a new map between starting-point and goal-point through coordinate system transferring. Then the encoding mechanism was introduced to search for an optimized path in which the robot gets close to the target. Then a valid region for the robot was mapped out according to the location of obstacles, which could reduce the search space and further improve the efficiency. An immune simulated annealing algorithm by combining an immune optimization algorithm with simulated annealing algorithm was developed. The simulation result demonstrated that the proposed algorithm had strong global and local search ability, which could help  the robot to quickly find the optimized path.

    Compressible dynamic virtual window algorithm based on sequential picking strategy
    WU Ying-ying, WU Yao-hua*, SHEN Chang-peng
    Abstract ( 436 )   PDF (2167KB) ( 1300 )   Save
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     To shorten the length of the virtual window and reduce the order picking time, the picking device was improved and a compressible dynamic virtual window algorithm was proposed. A gravity buffer and a flashboard were added to each dispenser. The items were launched to the gravity buffer in which the gap between each other was at fiost compressed, and then merged to the conveyor from the gravity buffer. Therefore the items were close to each other on the conveyor and the length of the virtual window was shortened. A model of the compressible dynamic virtual window algorithm was built based on the sequential picking strategy. The simulation with 3 sets of data collected from a tobacco distribution center showed that the picking time could be reduced by 87.45%~87.77%, and the picking time was decreased when the launching time of the dispenser and the merging time of the gravity buffer increased.

    The adaptive neighborhood selection strategy of the parallel Clarke-Wright algorithm
    FU Lian-ning1, CUI Wen2, ZENG Hua1
    Abstract ( 412 )   PDF (1472KB) ( 1841 )   Save
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    In order to improve the operation efficiency of the parallel saving algorithm, the reasonable neighborhood selection strategy and data structure were  used to reduce the space and time complexity of the algorithm. A new scheme of the adaptive neighborhood selection strategy was adopted to improve the rationality of neighborhood selection through optimizing the neighborhood radius and data structure, with the data dimensions and customer distribution condition of VRP as the breakthrough point with comprehensive consideration of the relationship among the neighborhood range of the customer, distance, dimensions and distribution. Comparing the proposed scheme with other non-adaptived schemes, the results showed that the former had obvious advantages on concentrated VRP by significantly reducing computation time and storage space while guaranteeing the operation quality. Taking the rl5915 as an example, its operation time was 50% less than other non-adaptived strategies. Theory research and experimental results showed that adaptive neighborhood selection strategy could  improve the operation efficiency of the saving algorithm.

    The precursor law of inrush of clay and water  in a high-risk karst tunnel and its application
    XIE Dong-sheng1,2, SHI Shao-shuai3, CHEN Shi-lin4, LI Li-ping3,5, ZHOU Zong-qing3, HU Cong3
    Abstract ( 404 )   PDF (1597KB) ( 1480 )   Save
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    Tunnel inrush of clay and water,which has become the key technology that needs to be solved for the construction of high risk karst tunnels, brings huge security risks and economic losses. On the basis of many examples of karst water inrush and sudden mud of tunnels, ground water, petrofabric, geological structure surface structures, attitude of rocks, deposition of ancient erosion surface, topography and geomorphology and rainfall were the main geological influence factors on water inrush and sudden mud. The response characteristics of karst water and unfavorable geological condition in the geophysical field have been researched. That is the particular type of precursor signal information when the seismic waves and electromagnetic waves encounter the karst water and unfavorable geological condition in its propagation process. The response characteristics of the karst aquifer and unfavorable geological body in the geophysical information field were interpreted. The precursor signal information that led to the disaster was recognized. This was successfully applied in the tunnel construction and was significant in the prediction of water inrush and sudden mud of tunnels.

    Test study on soil dynamic stress diffusion of a waste iron slag embankment during dynamic consolidation
    MENG Xiang-bin1, YAO Kai2*, WU Qing-dong3, LIU Ji-shan3, DOU Zhi-gang2
    Abstract ( 440 )   PDF (1943KB) ( 1456 )   Save
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     A large field test was conducted in the project of the Qing-Lin Expressway. Forty-eight soil pressure cells were embedded in the test section of the road. Different classes of tamping energy(2000, 2250, 2500, 2800kN·m) were used in this test. A dynamic strain gauge was used to record the dispersion and decay of the stress caused by dynamic compaction. The results showed that the reinforce effect on the waste iron slag embankment and the dynamic stress were both obvious. The dynamic stress decayed very fast and increased with the tamping energy. The vertical influence distance of dynamic stress was larger than that of the horizontal, and the dynamic stress was more than 10kPa at 8m under the rammer. The critical dynamic stress of the effective impacting depth was about 20kPa. The decay speed of the horizontal dynamic stress was faster than that in the vertical. The effective horizontal impacting distance was about 3m. With the compaction numbers increased, the dynamic stress in the reinforced range obviously increased and tended to be stable after about the third hit.

    The influence of capillary water action on the embankment stability of a silt embankment
    ZHU Deng-yuan1, 2, GUAN Yan-hua1*
    Abstract ( 464 )   PDF (2248KB) ( 1278 )   Save
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    The influence of capillary water action on the embankment stability of a silt embankment was studied. Based on experiment, the relationships between the height of capillary action and water content, the water content and modular of silt, the water content and shear strength were obtained, and then the equation about the height of capillary action and the modular of silt was fitted. The test results indicated that capillary water had great influence on stiffness and strength of the silt embankment. The finite element method software, Abaqus, was applied to simulate the influence of capillary water action on the silt embankment stability. The strength reduction method was adopted to calculate the safety factors for the silt embankment with deferent water level under standard loads. The discipline about the height of capillary action and the silt embankment stability was obtained. The foundation could provide the basis for the design and construction of silt embankments.

    Research on the frequency dispersion curve of the Rayleigh wave in the foundation with an obstacle
    BIAN Peng1, WANG Yuan2, WANG Du-qiang2
    Abstract ( 304 )   PDF (1755KB) ( 1082 )   Save
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    It is difficult to identify the frequency dispersion curve of the Rayleigh wave when obstacles exist in the foundation. For this situation, displacement curves of half space foundation were calculated using the finite element method, and were transformed into the frequency dispersion curve of the Rayleigh wave. Then its characteristics were acquired when there were sewage pipes in the half space foundation. The results showed that the reflected wave was received in front of the obstacles but not behind it, and the location and space of sensors had great influence on the calculated result. The results could provide reference for the identification of dispersion curves and the layout of sensors.

    Properties of concrete containing recycled clay brick powde
    GE Zhi1, WANG Hao2*, ZHENG Li1, MAO Hong-lu1
    Abstract ( 375 )   PDF (1394KB) ( 1885 )   Save
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    The effect of replacing cement with recycled clay brick powder on concrete mechanical properties was studied, including compressive strength, rupture strength and shrinkage. The strength of concrete with recycled clay brick powder was close to or even higher than that of normal concrete. Recycled clay brick powder reduced the shrinkage. Experimental results showed that recycled clay brick powder could be used as partial replacement of cement in concrete.

    Investigation on the properties of plastic mortar
    GE Zhi1, WANG Hao2, ZHANG Kun1, LI Peng-cheng1
    Abstract ( 372 )   PDF (1391KB) ( 797 )   Save
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    A simple and effective method to recycle waste polyethylene terephthalate (PET) bottles to produce plastic mortar  was discussed. The effects of PET-to-sand ratio, curing time, and addition of asphalt on physical and mechanical properties of plastic mortar were investigated. According to the results, plastic mortar had the characteristics of low water absorption and fast strength growth. As the sand content increased, the compressive and flexural strength of plastic mortar increased.  At the room temperature, plastic mortar could attain over 90% of its ultimate compressive strength within 3 hours. Adding a small amount of asphalt could improve the plastic mortar’s flexural strength.

    Simulation and experimental verification of residual stress in hard turning of AISI 52100 using the 2D finite element method
    WANG Zhong-qiu1,3, ZHOU Shan2, LI Jian-feng3, SUN Jie3
    Abstract ( 322 )   PDF (2874KB) ( 1539 )   Save
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    High-speed, small feed rate and hard turning is an important tendency in the machining of bearing steel. In order to investigate the residual stress after hard turning under a small feed rate condition, a 2D FEM simulation of AISI 52100 hard turning processes was carried out and the residual stress was obtained. Based on the user subroutine named Konti-Cut, the steady state of the cutting process was simulated and the cutting forces and residual stresses in this time were investigated. The residual stresses distribution predicted by the FEM model showed good consistency with experimental data. In addition, a relatively large compressive residual stress was formed in the depth of 0.02~0.06mm under the machined surface.

    Flow stress determination of aluminum alloy 7050-T7451 using cutting experiment inverse analysis methods
    WANG Hong-ru1, WANG Zhong-qiu1, 3*, ZHANG Qian2, LI Jian-feng3, SUN Jie3
    Abstract ( 343 )   PDF (1877KB) ( 1741 )   Save
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     Based on the Oxley slip-line theory, two-dimensional orthogonal cutting experiments in conjunction with an analyticalbased computer code were used to determine Johnson-Cook flow stress data of aluminum alloy 7050-T7451 in metal cutting. The strain range was 0.61~1.12, the strain rate range was 10263~69941, and the temperature range was 95~248,which were covered by the model. In order to verify the flow stress model, cutting experiments were done in the same cutting parameter range used in determining the flow stress. By comparing the results obtained by experiments and FEM using the flow stress model as input, the maximum error between cutting forces simulated obtained by FEM and obtained by experiments were less than 15%, and the maximum error of temperature was less than 11%.

    Biomimetic fabrication of 2D photonic Y2O3:Eu3+ phosphor templated from butterfly wing scales
    YU Kui-long, FAN Tong-xiang*
    Abstract ( 327 )   PDF (2536KB) ( 1531 )   Save
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    Using the natural intricate and delicate structures in biology as templates, i.e. biotemplation, the artificial analogue could be fabricated for improving the properties of novel materials. The green wing scales of the butterfly Papilio epiphorbas with intricate two dimensional photonic crystal (2D PhC) structure were adopted as templates to fabricate the 2D PhC Y2O3:Eu3+ phosphor through the aqueous sol-gel method. Field emission scanning electron microscopy (FESEM) demonstrated that the biomimetic Y2O3:Eu3+ could well duplicate the 2D PhC structure of butterfly scales. Emission spectra of the biomimetic Y2O3:Eu3+ tested via Laser-focused Raman microspectrometer confirmed that Eu3+ was efficiently dopped into the Y2O3 matrix and the target biomimetic material was obtained. The experimental contrast of fabrication routes with aqueous solgel precursor and water solution precursor indicated the advantages of the aqueous sol-gel method in fabricating delicate materials through biotemplation and thus could provide significant reference.

    Synthesis and release behavior of emodin intercalated into Mg-Zn-Al layered double hydroxide
    DAI Xiao-nan, WANG Qi-peng*, ZHU Zheng, DUAN Ran-ran
    Abstract ( 318 )   PDF (1654KB) ( 1090 )   Save
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    The drug emodin was first intercalated into the layers of Mg-Zn-Al layered double hydroxides (Mg-Zn-Al-LDHs) by the re-assemble method. The emodin/LDHs nanohybrids could be used to extend the action duration and reduce the side effect of emodin. Then the effect of the temperature T and the mass ratio R of emodin to LDHs on drug loading were discussed. The XRD spectra indicated that the interlayer distance of Mg-Zn-Al-LDHs increased from 0.48 nm to 3.42 nm with the increase of drug loading. The determination results of the drug release showed that the drug release rate from the emodin/LDHs nanohybrids was much slower than that of the corresponding physical mixture with the pH of solution of either 4.8 or 7.5. Analysis showed that the mechanism of the pH 7.5 release was primarily through ion-exchange with the ions in the buffer solution, while that of the pH4.8 release was primarily through the dissolution of LDHs.

    Statistical analysis of delay spread in distributed antenna systems
    SHI Hai-dong, HU Dong-mei, WANG Xiao-dong
    Abstract ( 323 )   PDF (2552KB) ( 1317 )   Save
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    The statistical properties of delay spread in a two-path distributed antenna system were analyzed, of which each path was characterized by Rayleigh fading and lognormal shadowing. As a special case, the statistical properties of delay spread in single scale alone fading environments were also obtained. Finally, a Monte Carlo simulation model was constructed using the channel parameters under typical urban environments, and the derived expressions were validated by simulation results. Because  the root mean square of delay spread depended on many parameters,  the effect of one specified parameter was considered under the condition of other parameters being fixed according to the practical scenarios.