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    25 August 2013, Volume 41 Issue 8
    Power & Electrical Engineering
    Liao Yan- fen Zeng Cheng- cai Ma Xiao- qian Song Jing- hui
    2013, 41(8):  1-8.  doi:10.3969/j.issn.1000-565X.2013.08.001
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    TGA was employed to investigate several kinds of typical biomass materials (namely,eucalyptus bark,eucalyptus leaves,eucalyptus branches,straw,bagasse and sugarcane leaves) in South China through pyrolysis and combustion experiments.The results show that (1) as compared with wood- based materials (eucalyptus barks,eucalyptus leaves,eucalyptus branches),herbal materials(straw,bagasse and sugarcane leaves)are of better per-formance in the ignition process and the liberation of volatile compounds due to their simple material structure; (2) herbal materials,however,have a short burnout time in terms of the fixed carbon and the residue,with a low com-bustion loss which accounts for only 20% of the overall weight loss and a greatly decreasing combustion intensity in the later stage; (3) three types of eucalyptus materials are found to be of different combustion characteristics due to their different compositions; (4) eucalyptus leaves are easy to ignite and their more crude protein and crude fat bring about a wider combustion temperature range and a lower combustion intensity; (5) eucalyptus branches have advantage in terms of the combustion intensities of the volatiles and the fixed carbon,indicating that they are of more stable combustion in the furnace; (6) eucalyptus barks have a long combustion duration but possess no advantage in terms of the ignition and the combustion intensity; and (7) bagasse and sugarcane leaves possess a short combustion duration but show a good synthetic combustion performance.In addition,a non- isothermal kinetic analysis method (Coats- Redfern) is adopted to evaluate the pyrolysis and combustion processes of all the materials,thus obtaining the corresponding kinetic parameters.

    Ouyang Sen Shi Yi- li Pan Wei Feng Tian- rui
    2013, 41(8):  9-14.  doi:10.3969/j.issn.1000-565X.2013.08.002
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    Proposed in this paper is a new method to evaluate the voltage sag sensitivity (VSS) of the sensitive load by combining several probability density function models,which can fully describe the randomness of the load sen-sitivity.First,five typical probability density functions are deeply analyzed and are used to respectively establish the mathematical model of the voltage tolerance curve of the sensitive load,and the VSS of the sensitive load in the uncertainty region is evaluated respectively by the five models.Then,the weighted sum of the results of the fivemodels is calculated by means of the unbiased variance method.Finally,the rationality and effectiveness of the pro-posed method are verified by simulation results.

    Zeng Jiang Gu Zhi- peng Chen Chang- ming Zhang Xiang- hua
    2013, 41(8):  15-20,27.  doi:10.3969/j.issn.1000-565X.2013.08.003
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    Metal halide lamp,a kind of high- intensity gas discharge lamp with the circuit containing the arc, is widely used in stadium lighting.Its negative resistance characteristics bring about harmonic current,and the corre-sponding electronic ballasts,which are the main harmonic sources,also generate a large number of electrical harmonics.In this paper,the piecewise linearization method and the polynomial curve fitting method are used to establish an electrical model of 2500W metal halide lamp and a model of three- level electronic ballasts on PSCAD/EMTDC.The proposed models are then employed to analyze the grid- side harmonic current,and the simulation results are compared with the measured data of the lighting circuits of the venues for Shenzhen 26th Summer Univer-siade.The accuracy of the proposed models is thus verified.

    Electronics, Communication & Automation Technology
    Hou Yue- en Li Wei- guang Rong Ai- qiong Ye Guo- qiang
    2013, 41(8):  21-27.  doi:10.3969/j.issn.1000-565X.2013.08.004
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    As the current sparse representation tracking algorithms are of low real- time performance,this paper puts forward a tracking algorithm of the block sparse representation with background information.In the algorithm,first,candidate targets are selected through a fast algorithm in the framework of particle filtering.Then,images are divid-ed into blocks with different weights to reduce the disturbance of occlusions and noises.Finally,the background in-formation is fused into the template dictionary,and the sparse solution of the candidate targets is calculated through the collaborative representation of the targets and the background.The proposed algorithm is compared with the oth-er two algorithms by using four videos on the Matlab platform.The results show that the proposed algorithm is of a higher calculation speed and a stronger robustness.

    Ma Xiang Huo Jun- yan Yang Xu Ren Guang- liang Chang Yi- lin
    2013, 41(8):  28-33.  doi:10.3969/j.issn.1000-565X.2013.08.005
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     In order to improve the coding efficiency of the I frame of depth maps,a macro- block (MB) mode skip coding method is proposed.This method fully considers the features of the depth map,namely,large flat areas and strong correlation among the modes of spatial adjacent MBs in the flat areas.On this basis,the modes of spatial ad-jacent coded MBs are used to predict the current MB mode,and the current MB mode coding is skipped when the predicted mode is equal to the current MB mode.Moreover,an intra MB skip coding method is put forward,which can skip both the MB mode and the quantized residual coefficients of the MBs in the flat areas and can reduce the involved redundancy in the process of coding the coefficients.The two proposed methods have no effect on the qua-lity of the reconstructed frame because they are adopted in the MB coding stage after the MB mode decision.Experi-mental results show that the two proposed methods bring about bit- rate reduction respectively by 7.83% and 8.93%.

    Xu Yu- ge Song Ya- ling Luo Fei Zhang Yong- tao Cao Tao
    2013, 41(8):  34-40.  doi:10.3969/j.issn.1000-565X.2013.08.006
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    In this paper,an energy- saving optimization control strategy of the biochemical process of wastewater is proposed to determine the optimal setting values of the control variables based on the artificial immune algorithm.First,two PI controllers respectively for the dissolved oxygen concentration of the aerobic tank and the nitrate nitro-gen concentration of the anoxic tank are established on the benchmark simulation platform BSM1,which is used in describing the biochemical treatment process of the pre- denitrification activated sludge wastewater system.Next,a control scheme is presented to meet the effluent standards with minimal aeration and pumping energy consumption.Then,the optimal setting values of the PI controllers are evaluated by using the artificial immune algorithm of global optimization,and both the oxygen transfer coefficient and the internal flow rate are controlled by making the contro-ller follow the setting values.Finally,simulation experiments are conducted by using the data of the influent flow rate under three kinds of weather conditions.The results show that the proposed algorithm is effective and robust.

    Xu Yu- bin Chen Jia- mei Ma Lin
    2013, 41(8):  41-46,60.  doi:10.3969/j.issn.1000-565X.2013.08.007
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    In wireless heterogeneous networks,the access control mechanism plays a vital role in ensuring the net-work performance.This paper proposes a Q- learning- based network selection algorithm for the access control of wireless heterogeneous networks.In the algorithm,the agent takes advantage of the past experience to implement a Q- learning algorithm by means of value iteration,thus obtaining the optimal strategy.Moreover,before the system makes decisions,the statuses of the wireless heterogeneous network of WLAN/WIMAX are analyzed in detail from a new perspective,thus providing accurate input bottom layer parameters for the Q- learning algorithm.Simulation results show that the proposed algorithm outperforms the traditional Markov Decision Process (MDP) algorithm in terms of the call- blocking probability and the system reward.

    Ye Jin- hua Li Di Ye Feng
    2013, 41(8):  47-54.  doi:10.3969/j.issn.1000-565X.2013.08.008
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    In this paper,a design method of the global finite- time stabilization controller is proposed for the uncer-tain n- dimensional nonholonomic single chain system.In this method,the single chain system is divided into a first-order subsystem and an (n -1)- order subsystem,and they are decoupled by means of the input- state- scaling tech-nique.Then,the controller of each subsystem is separately designed by means of the finite- time Lyapunov function method,thus guaranteeing the stability and finite- time convergence of the uncertain system.Moreover,the recur-sive design method is also adopted in the controller design of the (n -1)- order subsystem,and the switching con-trol strategy is used to eliminate the singularity of the (n -1)- order subsystem,thus ensuring the global stability of the controller.Finally,the controller is applied to a kind of uncertain nonholonomic wheeled mobile robot.Simula-tion results show that the controller is effective.

    Yu Wei Pi You- guo
    2013, 41(8):  55-60.  doi:10.3969/j.issn.1000-565X.2013.08.009
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    Based on the fact that the actual inductance and capacity are essentially of fractional- order,this paper establishes a fractional- order model of the permanent magnet synchronous motor (PMSM).Then,the pseudoran-dom binary sequence is taken as the external excitation signal of the PMSM to implement an identification experi-ment.Based on the experimental data,the fractional- order model is identified by using the output- error identifica-tion algorithm.Finally,according to the same criteria,two PI controllers are designed respectively for the identified fractional- order model and the traditional integer- order one.From the comparative experiment of the two PI contro-llers,it is found that in terms of accuracy,the proposed fractional- order model is superior to the traditional integer-order one in describing the PMSM.

    Xu Wei- wei Jiang Rong- xin Chen Yao- wu
    2013, 41(8):  61-66,73.  doi:10.3969/j.issn.1000-565X.2013.08.010
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    Video transmission in unstable networks suffers packet loss and bit error.In order to solve this problem,a low- complexity error- concealment algorithm is proposed for the spatial multiple description coding (MDC).In the algorithm,different error concealment strategies are employed to treat the regions with different features.Moreover,the texture difference of adjacent frames and the residual energy of complementary description are used to estimate the spatial and motion differences of the lost description,based on which the region of lost macro- blocks is divided and different methods are adopted to implement error concealment.Experimental results show that,as compared with the traditional MDC error concealment algorithm,the proposed algorithm achieves better subjective and objec-tive quality of error concealment in most sequences.

    Traffic & Transportation Engineering
    Hu Jun- liang Yu Xiao- lin Zheng Heng- bin Chen Zhou Yan Quan- sheng
    2013, 41(8):  67-73.  doi:10.3969/j.issn.1000-565X.2013.08.011
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    The traditional model updating methods based on sensitivity analysis can not determine the appropriate design parameters to be updated,and most of the model updating methods independent of sensitivity analysis are complex with large computation.In this paper,a model updating method based on parameters is adopted,and a BP neural network optimized by genetic algorithm is introduced.Then,with the structural dynamic eigen vector as the input,the updated design parameters are directly obtained.The parameters are then used to obtain the structural dynamic eigen vector error of the updated finite element model,and the error minimization is taken as the objective function to implement iterative resolution,thus determining the final updated design parameters.Finally,a 3- span continuous beam model is tested.The results prove that the proposed method is accurate and effective.

    2013, 41(8):  74-79,86.  doi:10.3969/j.issn.1000-565X.2013.08.012
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    In this paper,a resistant torque model of the steering wheel in a steady- steering status at different vehi-cle velocities is established by means of the force analysis of the steering system.Then,a parameterized model de-scribing the ideal steering wheel torque for the driver is put forward.Based on the parameterized model,the design mechanism of the assist characteristic curve of EPS (Electric Power Steering) is investigated,and a viewpoint is presented,that is,the assist characteristic curves should be separately designed according to the vehicle velocity and the designer should take into consideration the relationships between the ideal steering wheel torque for the driver and three parameters,namely,the vehicle velocity,the steering wheel angle and the lateral acceleration.Fi-nally,the geometric features of the EPS assist characteristic curve are expounded in detail.The result show that the basic form of EPS assist characteristic curve should be down concave and the curve is not completely straight linear or broken linear or curvilinear.

    2013, 41(8):  80-86.  doi:10.3969/j.issn.1000-565X.2013.08.013
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    The handling stability control of vehicles plays a vital role in their active safety.This paper deals with the handling stability control of the electric vehicle based on the anti- directional Bi- rotary motor.First,a model of the vehicle in an ideal status is established to estimate the yaw rate and the side- slip angle,and the phase plane method is used to design the stability criteria of the vehicle,so as to detect the driving situation.Next,a fuzzy yaw moment controller is employed to estimate the compensatory yaw moment according to the instability situation of the vehicle.Then,the slip rate of the target wheel is estimated by using a slip rate controller and is adjusted to a re-quired value by means of the PID control,the fuzzy control,and the fuzzy PID control of both the brake system and the anti- directional Bi- rotary motor.Finally,the vehicle is analyzed by using the simulation software Vedyna.The effectiveness of the proposed control strategy is thus verified.

    2013, 41(8):  87-92,98.  doi:10.3969/j.issn.1000-565X.2013.08.014
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    At present,overtaking accidents on highway frequently occur with serious consequences.Aiming at this problem,a warning model is proposed for preventing overtaking safety.First,the main factors influencing the safety of overtaking are analyzed.Next,overtaking collisions are categorized and overtaking scenario is developed.Then,by describing overtaking trajectories and by using a kinematic model of vehicles,a warning model of preventing o-vertaking collisions is established,which includes a critical longitudinal safety spacing model and a time- spa- cing model.Finally,the effectiveness of the model is verified by using two instances,namely,constant- velocity overtaking and specific- acceleration overtaking.

    Qian Zhe Xu Jian- min
    2013, 41(8):  93-98.  doi:10.3969/j.issn.1000-565X.2013.08.015
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    The identification of the oversaturted traffic conditions at the signal control intersection helps to control traffic congestion.In the investigation,based on the detection data of inductive loop detectors,the traffic wave theory is utilized to identify the oversaturated traffic condition from two aspects,namely,the retention queue length at the end of the green light at an intersection and the overflow of the downstream intersection.Aiming at the first aspect,the queuing dissipated coefficient is defined to identify the oversaturated traffic condition at the intersection.Aiming at the second aspect,the overflow retardation coefficient is defined to reveal the oversaturated overflow phenome-non.Case study results show that oversaturated traffic condition can be accurately and effectively identified by cal-culating the queue dissipation coefficient and the overflow retardation coefficient based on the loop detection data.

    Mechanics
    2013, 41(8):  99-102.  doi:10.3969/j.issn.1000-565X.2013.08.016
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    Based on the dynamic experiment of split- Hopkinson pressure bar (SHPB) and the static compression experiment of Instron at the room temperature,a dynamic Johnson- Cook constitutive equation of polycarbonate is proposed by using the least square and parameter identification methods to fit the corresponding constitutive parame-ters.It is found that the theoretical values accord well with the experimental ones at lower strain rates while they ac-cord well with each other only at yield points at higher strain rates.In addition,the model is employed to simulate the aircraft windshield under bird impact by using the nonlinear finite element software LS- DYNA3D.The results show that the deformations of the bird and the windshield as well as the history curve of the windshield displacement in the simulation accords well with those in the experiments.

    Yao Xiao- hu Chen Da Ou Zhi- cheng Sun Yu- gang
    2013, 41(8):  103-108,114.  doi:10.3969/j.issn.1000-565X.2013.08.017
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    Aiming at the problem of the axially- compressed buckling of the small- scale carbon nanotubes in multi-physical fields,a mechanical model for the coupled fields is proposed based on the nonlocal elasticity theory.First,a buckling governing equation of the multi- walled carbon nanotubes subjected to thermo- electro- mechanical loadings is obtained based on the nonlocal elasticity theory and by using the elastic shell model,which considers the van der Waals forces between adjacent nanotubes and the effects of the surrounding elastic medium.Then,the analytical solution to the axially critical buckling load of double- walled carbon nanotubes is derived.Finally,the small- scale effects on the axially critical buckling load are discussed by means of numerical analysis.It is found that,with a large coefficient of the small- scale effects,the critical buckling load based on the nonlocal elasticity theory is markedly different from that based on the classical elasticity theory,which indicates that the classical elasticity theory is no longer applicable in a small- scale range.

    Zhao Chuan- yu Huang Pei- yan Luo Yi
    2013, 41(8):  109-114.  doi:10.3969/j.issn.1000-565X.2013.08.018
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    Semi- elliptic surface crack is a common defect in metal structures,which is easy to propagate under the effects of external factors and may even result in the damage of the structures.The service life of the damaged struc-tures can be greatly extended by using the fiber- reinforced polymer (FRP) to strengthen and repair them.In this paper,the finite element software Abaqus is employed to numerically analyze the stress intensity factor (SIF) of the semi- elliptic surface crack in the X80 steel plate strengthened with FRP under tensile load,and the semi- empirical expression of the SIF is obtained.The results show that,under the uniform tensile load,the crack shape ratio has a greater effect on the SIF as well as on the reinforcement effect,and the relative crack depth also affects them to a certain degree.

    Peng Chong- mei Zhang Qi- wei Li Yuan- bing
    2013, 41(8):  115-119,126.  doi:10.3969/j.issn.1000-565X.2013.08.019
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    It is difficult to employ the parallel model or the steel strand model based on the assumption of parallel wire to analyze the mechanical properties of the semi- parallel cable due to its helical characteristics and special structure.In this paper,a nonlinear equation of multilayered semi- parallel cable under the static tensile load is de-rived based on the theory of Love's curved bar and by considering the effects of the bending moment,the torque and the Poisson effect.Moreover,the effects of the helical angle on the axial force,the torsion,the axial stiffness and the distribution of the tensions between wire layers are discussed in detail.Numerical results show that,with the in-crease of the helical angle,both the axial force and the axial stiffness increase,the torque first increases and then decreases,and the distribution of the tensions between wire layers tends to be uniform.

    Chai Sheng- bo Xiao Ru- cheng
    2013, 41(8):  120-126.  doi:10.3969/j.issn.1000-565X.2013.08.020
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    In the double- main cable suspension bridge system,the sags of the main cables change with the defor-mation of the pylon and the elastic extension of the main cables.Based on the assumption that the hangers of the top and bottom cables are inextensible,the vertical displacements of the top and bottom cables are equal when the de-formation of the pylon and the elastic extension of the main cables jointly play their roles.According to the above principle,this paper derives the expression of the longitudinal restraint stiffness of the bridge to the pylon as well as the relationship between the load transfer on the top and the bottom cables and the deformation of the pylon.Then,the solution method of the deflection of the load span under the uniform single- span load is investigated,and the corresponding analytical expression is obtained.Finally,all the formulas are verified by establishing a finite ele-ment model.It is found that the formulas accord well with the model.

    Physics
    Peng Jian- xin Wang Jun- dong
    2013, 41(8):  127-130,144.  doi:10.3969/j.issn.1000-565X.2013.08.021
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    Two room impulse responses with flat reverberation frequency characteristics and different reverberation time in low and medium frequency domains were obtained in a listening position of a classroom model through acoustical simulation.Then,the Chinese syllable recognition performances of two groups of children in differentages were evaluated under white noise and low- frequency noise conditions via an auralization method,and the re-sults were finally compared with those of adults.It is found that (1) the Chinese syllable recognition scores of chil-dren in low- frequency noise are lower than those in white noise; (2) no matter what the frequency condition of noise is,the Chinese syllable recognition scores of children are lower than those of adults at the same signal- to- noise ratio and reverberation time; and (3) the Chinese syllable recognition scores are positively related to children’ s age.

    Liu Yang Xie Bo- sun
    2013, 41(8):  131-138.  doi:10.3969/j.issn.1000-565X.2013.08.022
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    The head- related transfer functions (HRTFs) which can be measured through experiments,usually dis-tribute in discrete directions,and the other HRTFs in unmeasured directions,have to be estimated by means of spatial interpolation.The commonly- used interpolation methods include the adjacent linear interpolation,the global interpolation,the bilinear interpolation,and the spherical- triangular interpolation.In practice,potential subjects' head movements in the HRTF measurement may result in error,thus influencing the accuracy and stability of the spatial interpolation.In this paper,the errors caused by slight head movements in the HRTF measurement are eva-luated,and the effects of the head movements on the above four kinds of spatial interpolation are compared by calcu-lating the signal- to- distortion ratio.The results indicate that,the global interpolation outperforms the others before and after the head movements,and is of excellent performance in a certain frequency band range of HRTF and with appropriate head movements.Due to the similarity of the HRTF spatial interpolation to the signal panning or mixing methods for the multi- channel sound,the proposed methods and the corresponding results are extended to analyze the stability of the sound image reproduced from the sound field signal mixing with 6 or 8 horizontal uniformly-arranged loudspeakers below 1.5kHz.

    Chen Xi He Yong- hou Chen Long- sheng
    2013, 41(8):  139-144.  doi:10.3969/j.issn.1000-565X.2013.08.023
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    BiFe1-xMnxO3 ( 0≤ x ≤0.3)  crystal powders were synthesized via the sol- gel method,and the effects of Mn doping on the structure and magnetic properties of the product were investigated.XRD and Raman spectroscopy analyses reveal that Mn doping changes the crystal structure and vibration mode of BiFeO3.Rietveld refinement re-sults indicate that the substitution of Mn at Fe- site brings about a structural phase transition from the rhombohedral R3c to the orthorhombic Pbnm around x =0.1.Magnetic measurement results demonstrate that,with the increase of the Mn dosage x,the remanent magnetization gradually increases and reaches its maximum near the phase transition point.In addition,the enhanced magnetization of BiFe1-xMnxO strongly correlates with the variations of the crystal structural,which indicates that it is mainly attributed to the Dzyaloshinskii- Moriya interaction.

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