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15 June 2018, Volume 39 Issue 6 Previous Issue    Next Issue
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Information & Control

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New Algorithm of DOA Estimation Based on the Twice Reconstruction of Pseudo Data Correlation Matrix LIU Xiao-zhi， SONG Mu-ye， LI Hong-ru 2018, 39 (6):  761-766.  DOI: 10.12068/j.issn.1005-3026.2018.06.001 Abstract ( 688 )   HTML   PDF (471KB) ( 819 )   Due to the problem that the traditional direction of arrival (DOA) estimation algorithm can hardly estimate the weak signal when the strong signal is adjacent and it will fail when the signals are coherent， the covariance matrix was reconstructed by corresponding transformation for the received data matrix of array elements on the basis of theoretical derivation and analysis of traditional estimation algorithms. Then the pseudo data correlative matrix was constructed by rearranging the larger eigenvalues of the reconstructed covariance matrix. Finally combined with the MUSIC spectrum to search spectral peaks， the DOA estimation of strong and weak adjacent coherent signals were finished. By simulation， the results show that the coherence of signals could be eliminated by the proposed algorithm without reducing the array aperture. Whats more， the DOA of strong and weak adjacent signals could be estimated accurately. References | Related Articles | Metrics

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Extended Tabu Search Algorithm for Schedule Risk Control of IT Outsourcing Project LU Fu-qiang， BI Hua-ling， HUANG Min， JIN Meng-meng 2018, 39 (6):  766-770.  DOI: 10.12068/j.issn.1005-3026.2018.06.002 Abstract ( 664 )   HTML   PDF (553KB) ( 857 )   With the rapid development of IT outsourcing projects in recent years， the schedule risk control has also become one of the urgent issues to be solved. Based on the optimization problems of schedule risk control in IT outsourcing projects， a two-level mathematical model was built. For the NP hard and hierarchical structure of the optimization problem， the basic tabu search algorithm was improved in generating initial solution with heuristic methods and constructing dynamic tabu list. According to the result of simulation experiment， the improved algorithm was analyzed in reliability， convergence and effectiveness. In addition， the simulation results were also compared with traditional tabu search algorithm， and the value of the improved tabu search is verified. References | Related Articles | Metrics

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Non-guillotine Cutting Algorithm of Rectangular Items Based on Five-Homogeneous-Block Mode ZHANG Rui-you， PAN Wei-ping， LIU Shi-xin 2018, 39 (6):  771-775.  DOI: 10.12068/j.issn.1005-3026.2018.06.003 Abstract ( 654 )   HTML   PDF (383KB) ( 908 )   A type of non-guillotine cutting problem of rectangular items was studied based on the use of five-homogeneous-block mode. According to the idea of dynamic programming and implicit enumeration， a five-homogeneous-block cutting algorithm for an unconstrained non-guillotine cutting problem was designed. The comparative experiments with existing non-guillotine cutting algorithms indicated that optimal solutions of the problem could be quickly given by this algorithm， and both the difficulty of plate cutting process and the sorting cost of rectangular items could be reduced. Furthermore， comparisons with another experiment with two guillotine cutting algorithms show the benefits of “non-guillotine”. References | Related Articles | Metrics

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PIR-based Indoor Localization Method Combined with Human Behavior-based Map YANG Dan， XU Bin 2018, 39 (6):  776-780.  DOI: 10.12068/j.issn.1005-3026.2018.06.004 Abstract ( 820 )   HTML   PDF (786KB) ( 1078 )   Aiming to human localization method for elder people assisting in smart home， a method was proposed to realize the indoor localization by pyroelectric infrared sensor (PIR) combined with human behavior-based map. PIRs were used for collecting body motion signal to localize the subject’s raw position in the room. One inertial measurement unit (IMU) was used to collect 3D motion data for human daily body activity recognition such as lying， sitting， and standing. The other IMU was used for velocity and direction estimation. The related behavior-based maps were built by human habits observation. Particle filters method was presented to fuse the data from PIR and IMU，and took into account these prior behavior-based maps to get more accurate localization. Experimental results showed that the proposed approach has the advantage of protecting the privacy while maintaining high accuracy and stability of indoor localization. References | Related Articles | Metrics

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Automatic Control Method and Performance Analysis of Platoon Vehicles ZHAO Hai， GUO Hong-ye， SI Shuai-zong， ZHU Jian 2018, 39 (6):  781-786.  DOI: 10.12068/j.issn.1005-3026.2018.06.005 Abstract ( 582 )   HTML   PDF (566KB) ( 1008 )   The leader vehicle broadcast the information included motion parameters and driving behavior to followers is necessary in the control of platoon vehicles. To ensure the stability and robustness of platoon， an adaptive control method of vehicles was proposed， in which the motion information of leader and adjacent front vehicle became inputs of control system. The H∞ control theory was used to solve the optimal control gain function， for closed-loop linear system contained vehicles dynamics subsystem and control subsystem， and the string stability conditions were presented that the system transfer function matrix and spacing error function satisfied. This method was used to acquire the dynamic trajectory of motion parameters and spacing error function， and was compared with the control method based on front vehicle. The numerical results showed that the asymptotic following effect of vehicles and guarantee string stability and safety of platoon could be improved by using the proposed method. References | Related Articles | Metrics

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Blind Source Separation Based on Grouping Simplified Particle Swarm Optimization Algorithm JI Ce， SHAN Chang-fang， SHA Yi， ZHOU Rong-kun 2018, 39 (6):  787-791.  DOI: 10.12068/j.issn.1005-3026.2018.06.006 Abstract ( 555 )   HTML   PDF (755KB) ( 757 )   Traditional algorithm of blind source separation (BSS)is easy to fall into partial optimum value， and the convergence precision is low. In view of these disadvantages， the BSS method based on improved simplified particle swarm optimization algorithm was proposed， by which the whole particle swarm could be divided into several groups. Each particle was optimized while optimizing the whole area， and the difference between particles was increased. What’s more， premature convergence was avoided effectively. The negative entropy was taken as the objective function in the proposed algorithm， and the separation matrix was adjusted to separate each signal component from each other， so as to accomplish the blind source separation of instantaneous mixed signals. The simulation results show that the proposed algorithm is effective in avoiding premature convergence， and further improving convergence accuracy and algorithm stability compared with the basic particle swarm algorithm. References | Related Articles | Metrics

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Adaptive Random Sampling Algorithm Based on the Balance Maximization DONG Li-yan， WANG Yue-qun， LI Yong-li， ZHU Qi 2018, 39 (6):  792-796.  DOI: 10.12068/j.issn.1005-3026.2018.06.007 Abstract ( 637 )   HTML   PDF (557KB) ( 624 )   The problem on the classification algorithm of imbalanced datasets was analyzed. Common methods of balancing data， including improvement of datasets and the improved algorithm， were summarized. Then a novel algorithm called adaptive random sampling algorithm was put forward based on balance maximization. The classification effect of random forest algorithm was further optimized. Experiments show that the proposed algorithm performs well with the imbalanced data， the new data are fitted with the original data， and it could improve the ability of classifier to deal with the imbalanced data. References | Related Articles | Metrics

Materials & Metallurgy

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Effect of Extension Length of Catheter on Properties of TC4 Powder Prepared by Electrode Induction Melting Gas Atomization GUO Kuai-kuai， LIU Chang-sheng， DONG Huan-huan， CHEN Sui-yuan 2018, 39 (6):  797-802.  DOI: 10.12068/j.issn.1005-3026.2018.06.008 Abstract ( 677 )   HTML   PDF (2871KB) ( 847 )   TC4 titanium alloy powder was prepared by electrode induction melting gas atomization(EIGA). The atomization flow field was simulated， and the effects of extension length of the catheter on powder morphology， powder size distribution， hollow ball rate， apparent density and flow ability were investigated. The results showed that with the increase of extending length of the catheter， the negative pressure zone increases and the atomization powder is broken more fully.When the extending length is 3mm， negative pressure zone splits into two independent small zones， and the bulk powder and hollow spheres increase. When atomization pressure， the melting power and the extending length are 6.0MPa， 60kW and 2mm， respectively， the negative pressure area， which is large and inverted triangular， fills the lower part of the whole catheter while the atomization is more complete. The printable powder production rate is 51.60%. Apparent density is 2.870g/cm3， flow ability is 22.23s/50g and hollow ball rate is below 3%. TC4 powder prepared by EIGA is more suitable for laser direct deposition. References | Related Articles | Metrics

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Element Enrichment Behavior of Cold-Rolled IF Steel Plate Surface and Its Influence on Corrosion Resistance CHEN Hong-xing， LI Jian-zhong， YU Zi-han， LIU Chang-sheng 2018, 39 (6):  803-807.  DOI: 10.12068/j.issn.1005-3026.2018.06.009 Abstract ( 690 )   HTML   PDF (1212KB) ( 857 )   Cold-rolled IF steel plate has been widely used in automobile and other industries， but the corrosion resistance of the surface is very poor. The effects of the surface element enrichment behavior on corrosion resistance of the cold-rolled IF steel plate were investigated by GDS， XPS and SEM in the experiments with different processing conditions. The results showed that the element enrichment on the surface of cold rolled plate has obvious influences on the corrosion resistance. The corrosion resistance decreases with the increase of Mn enriched on the surface of cold rolled plate. The enrichment of Mn on the cold-rolled plate surface can be effectively reduced with the increase of the plate-passing speed and the dew point temperature during the continuous annealing process. The corrosion resistance of the cold-rolled plate can be effectively improved by increasing the inlet temperature of the quenching tank. References | Related Articles | Metrics

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Effect of Liquid Zinc Chamfer on Electromagnetic Force in Vertical Electromagnetic Sealing Process HUA Fu-an， HOU Shuai， LI Jian-ping 2018, 39 (6):  808-812.  DOI: 10.12068/j.issn.1005-3026.2018.06.010 Abstract ( 647 )   HTML   PDF (1929KB) ( 609 )   In studies of the technology of vertical hot galvanizing， it was reported that the liquid zinc area is ideal rectangular， however the actual shape of zinc liquid boundary is curved. In order to understand clearly the force distribution in zinc liquid， it is assumed in this paper that liquid zinc area is the rectangular region with chamfer. The experimental was carried out when liquid zinc dimensionless vertical height was 7.375~7.625， exciting current frequency was 3~7 Hz， dimensionless chamfer distance was 0.25， 0.5 and 0.75. The results showed that the electromagnetic force of zinc liquid decreases with increasing chamfer distance. Peak electromagnetic force of zinc liquid decreases with frequency increasing. Electromagnetic force becomes smoothly with the frequency increasing. The greater the chamfer of liquid zinc， the bigger the difference of the peak electromagnetic force and valley electromagnetic force. References | Related Articles | Metrics

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Effects of Y on Microstructure and Properties of Ag-based Alloy Targets ZHANG De-sheng， ZHANG Qin， YU Yun-he， YANG Hong-ying 2018, 39 (6):  813-817.  DOI: 10.12068/j.issn.1005-3026.2018.06.011 Abstract ( 693 )   HTML   PDF (4539KB) ( 767 )   The influence of different addition amounts of element Y on the microstructure and properties of Ag-based alloy targets was studied by using optical microscope (OM)， scanning electron microscope (SEM)， energy diffraction spectrum (EDS)， hardness tests， electrical conductivity tests and sulfidation resistance tests. The results indicated that when Y content added to the Ag-based alloy target is small， Y mainly exists in form of solid solution and plays an important role in grain refinement. However， adding excess Y leads to the precipitation of the second phase. The Ag-based alloy targets with 0.1wt% Y addition demonstrates the superior properties: higher hardness， lower electrical conductivity and the most optimal sulfidation resistance. References | Related Articles | Metrics

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Simulation on Desulfurization of Molten Iron with Bottom Blown-Mechanical Stirring Coupled WANG Kun， LIU Yan， ZHANG Ting-an 2018, 39 (6):  818-822.  DOI: 10.12068/j.issn.1005-3026.2018.06.012 Abstract ( 666 )   HTML   PDF (1523KB) ( 796 )   To understand the interaction between bubble and melt in desulfurization of hot metal pretreatment with bottom blown-mechanical stirring coupled， the CFD commercial software Fluent 15.0 and physical simulation method were used to study on desulfurization process of 120t bottom blown ladle. The influence of impeller structure， rotation speed， gas flow rate， eccentricity on the mixing effect of molten steel in ladle was investigated from the aspects of flow field and gas volume distribution. The results showed that， under the conditions of using the SSB-D impeller， the rotation speed of 200r/min， the gas flow rate of 1.5m3/h and the eccentricity of 0.4， the flow field distribution in the molten iron is more uniform while the magnesium vapor bubbles are more dispersed and refined in the molten iron. The gas-liquid contact area of magnesium vapor and hot metal is increased to improve the desulfurization efficiency of magnesium vapor. References | Related Articles | Metrics

Mechanical Engineering

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Theoretical and Experimental Study of the Tension String-Permanent Magnet Dynamic Vibration Absorber YAO Hong-liang， GAO Ying-hua， LI Wen-long， WEN Bang-chun 2018, 39 (6):  823-827.  DOI: 10.12068/j.issn.1005-3026.2018.06.013 Abstract ( 588 )   HTML   PDF (1212KB) ( 754 )   In order to eliminate the vibration of the rotor system， a tension string-permanent magnet dynamic vibration absorber is designed for the rotating machinery. The frequency adjustability of the vibration absorber is realized by using the adjustable tension-stiffness feature of the tension string， and the structure of the vibration absorber is separated from the rotor system by a stiffness institution which is made with permanent magnets. In this paper， the dynamical model and the simulation analysis of the rotor-dynamic vibration absorber is built，the operating characteristic of the vibration absorber is studied， and the correctness of the theoretical research is proved by the experimental study. The results proved that the vibration absorber has good effect on eliminating the vibration of the rotor system， and the absorbing function becomes better and more stable as the inter-distance of the magnets is set closer. References | Related Articles | Metrics

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Simulation of Temperature Field for Bulk Metallic Glass in Micro-scale Grinding LIU Yin， GONG Ya-dong， SUN Yao， ZHANG Huan 2018, 39 (6):  828-833.  DOI: 10.12068/j.issn.1005-3026.2018.06.014 Abstract ( 580 )   HTML   PDF (1119KB) ( 707 )   The orthogonal cutting model of single grain and constitutive equation of glass metal are established， and the micro grinding temperature field of bulk metallic glass is simulated using the finite element simulation system. The grinding temperature of bulk metallic glass and the temperature change trend in micro grinding process are acquired， and then the relationship between the grinding temperature and the glass transition temperature of bulk metallic glass is observed. Consequently， the simulation of the grinding temperature of the bulk glass metal can effectively predict the crystallizing procedure of the grinding surface. With various micro grinding parameters， the temperature variation trend of the grinding zone of bulk metallic glass is observed. The simulation results show that the highest grinding temperature of bulk metallic glass occurs in the contact area between the abrasive rake surface and the grinding chips， i.e. the secondary deformation zone. References | Related Articles | Metrics

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Adaptive Analytical Model of Thermal Error Prediction for the Ball Screw Feed Drive Systems in CNC Machine Tools LI Tie-jun， ZHAO Chun-yu， ZHANG Yi-min 2018, 39 (6):  834-839.  DOI: 10.12068/j.issn.1005-3026.2018.06.015 Abstract ( 619 )   HTML   PDF (1296KB) ( 1055 )   This paper presents an analytical model of thermal error prediction for the ball screw based on temperatures measured on the surfaces of the heat sources. First， the analytical solution of one dimensional heat conduct equation for the screw shaft is derived based on the variable separation method. Consequently， the two bearings are considered to be fixed heat sources， and the nut is divided into a few of moving heat sources distributed continually. The temperature distribution formula on the screw shaft excited by each heat source is given， and the temperature distribution equation is acquired based on the superposition principle of heat sources. The curve fitting parameters of relation functions of temperature difference between the heat source center and the measured surface point are obtained using FEM calculation data. Then an analytical model is proposed to predict the thermal error distribution of the ball screw shaft on line. Finally， the effectiveness is verified by the experiments. References | Related Articles | Metrics

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Optimization Method for the Runner Crown Shape of a Low Specific Speed Francis Turbine WEN Zhe-nan， ZHANG Ying-li， BA De-chun， YUE Xiang-ji 2018, 39 (6):  839-843.  DOI: 10.12068/j.issn.1005-3026.2018.06.016 Abstract ( 623 )   HTML   PDF (533KB) ( 961 )   The turbine efficiency was aimed to be improved through the optimization design of the runner crown shape in the Francis turbine. Based on ISIGHT software platform， a method which combined GAMBIT with ANSYS FLUENT16.0 software was presented. In this method， 80 sets of the sample points were generated using the optimal Latin hypercube (OLH) of the experiment design， whose performances were evaluated through ANSYS FLUENT16.0 software. The turbine efficiency in the design condition was used as the objective function， the approximate model was used based on the response surface method (RSM)， and the optimization result was finally obtained using particle swarm optimization (PSO). The proposed method was applied for the optimization design of the runner crown shape of a model Francis turbine. The results indicated that the hydraulic efficiency of the Francis turbine increased by 0.35% through the optimization process. This method provided a reasonable and effective approach to the optimization design of the runner crown of Francis turbine. References | Related Articles | Metrics

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Design Method of Reaming Pneumatic Impactors Based on Its Cuttings Removal Performance XU Hai-liang， ZHOU Yong-xing， XU Cong， ZHAO Hong-qiang 2018, 39 (6):  844-849.  DOI: 10.12068/j.issn.1005-3026.2018.06.017 Abstract ( 518 )   HTML   PDF (1151KB) ( 613 )   In order to improve the cuttings removal performance of reaming pneumatic impactors in hard layers， the computational fluid mechanics theory and Fluent simulation software were employed to find out a design method based on the critical velocity principle of cutting particles， which is related to the cuttings removal performance of reaming pneumatic impactors and then it was applied to the back-reaming pneumatic impactor. The speed distribution regularities of gas phase， the change of cutting particles’ velocity and trajectory， and the concentration distribution of cutting particles in the flow field of the back-reaming pneumatic impactor were obtained. The results showed that the cutting particles’ critical velocity of the back-reaming pneumatic impactor in the cuttings flow field is 6.02m/s. The design method related to cuttings removal performance can effectively strengthen the cuttings removal performance of the back-reaming pneumatic impactor， and the velocity of gas phase increases to 10m/s in the flow field. The time when cutting particles remain in the flow field is shortened， and the value of particle concentration distribution range in the flow field decreases from 0~100kg/m3 to 0~4kg/m3. References | Related Articles | Metrics

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Fatigue Reliability Analysis of Aviation Bearings Based on ANN JIN Yan， LIU Shao-jun 2018, 39 (6):  850-855.  DOI: 10.12068/j.issn.1005-3026.2018.06.018 Abstract ( 602 )   HTML   PDF (583KB) ( 841 )   An intelligent method is proposed to complete the contact fatigue reliability analysis of aviation bearings. The temperature field is approximated using quadratic polynomial with intercrossing term， and the stress model under thermal elastohydrodynamic lubrication (EHL) is set up. Considering the randomness of the thermal EHL， material properties and fatigue strength correction factors， the probabilistic reliability analysis model is established using artificial neural network (ANN)， and the reliability sensitivity analysis is completed based on the advanced first order second moment (AFOSM). The numerical example shows that the established probabilistic reliability analysis model could correctly reflect the effect of the thermal EHL on contact fatigue of aviation bearings， and the proposed intelligent method has an excellent global search capability as well as a highly efficient computing performance compared with the traditional Monte Carlo method， and then the results are verified with the fatigue life test of rolling bearings considering the non-interacting variance analysis. References | Related Articles | Metrics

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On the Vibration Reduction of Mistuned Blisks by Hard Coating GAO Feng， SUN Wei 2018, 39 (6):  856-861.  DOI: 10.12068/j.issn.1005-3026.2018.06.019 Abstract ( 511 )   HTML   PDF (720KB) ( 665 )   A vibration reduction method by hard coating was proposed to improve the working reliability of mistuned blisks (integrally bladed disks)， and the mistuned blisk with depositing NiCoCrAlY+YSZ hard coating on both sides of the blades was taken as an example to conduct the vibration investigation. Firstly， the ROM (reduced-order model) of the hard-coated blisk， which can improve the computational efficiency under the premise of ensuring the computational precision， was established by using an improved fixed-IDSMSM (fixed interface dynamic stiffness modal synthesis method). Secondly， the modal analysis of the hard-coated blisk was achieved based on the proposed ROM， and the results were compared with those of the FOM (full-order FEM). Finally， the influence of hard coating on mistuned blisks was studied. The results revealed that the NiCoCrAlY+YSZ hard coating has a good damping effect on mistuned blisks， and can suppress remarkably the resonant response of mistuned blisks. References | Related Articles | Metrics

Resources & Civil Engineering

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Modified Mechanism of Asphalt by Nickel-Ferrous Slag Fiber LIU Jie， NIE Qiao-qiao， HAN Yue-xin， TIAN Ze-feng 2018, 39 (6):  862-867.  DOI: 10.12068/j.issn.1005-3026.2018.06.020 Abstract ( 881 )   HTML   PDF (941KB) ( 699 )   Nickel-ferrous slag fiber was used as modifier to produce road modified asphalt， and the performances of modified asphalt were evaluated by penetration， softening point and penetration index. The mechanism of modified asphalt by nickel-ferrous slag fiber was analyzed by means of scanning electron microscopy (SEM)， infrared spectroscopy(IR) and differential scanning calorimetry(DSC). The results showed that the high-temperature performance， low-temperature performance and temperature-sensitive performance of asphalt can be improved by nickel-ferrous slag fiber. The reason for the good effect of nickel-ferrous slag fiber on asphalt performance is to adjust the relative proportions of light components of asphalt composition under the foundation of physical blending， which leading the colloid type of the matrix asphalt to be more “sol-gel” type. References | Related Articles | Metrics

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Simulation of Heavy Metal Pollutants Migration in Soil Based on Finite Volume Method WANG Zhong-kang， GU Xiao-wei， XIE Ting， XU Xiao-chuan 2018, 39 (6):  867-871.  DOI: 10.12068/j.issn.1005-3026.2018.06.021 Abstract ( 729 )   HTML   PDF (542KB) ( 669 )   Aiming at the migration and diffusion of heavy metal pollutants in soil， the finite volume method is used to discretize the basic equations that heavy metal pollutants transport in two-dimensional steady water flow， and then the calculation model for migration in saturated soil is obtained. The dynamic process of heavy metal pollutants transporting in different conditions is simulated by Matlab to study the migration laws of heavy metal pollutants. The research shows that the concentration contours of heavy metal pollutants gradually changes from central parabolic into peripheral elliptical over time， and concentration decreases continuously in both horizontal and vertical directions， when the source of pollution always exists; however， the concentration contours of heavy metal pollutants mainly presents elliptical over time， and pollution range gradually becomes larger with concentration decreasing continuously and the maximum concentration at the ellipse center， when the source of pollution lasts for only 10 days. References | Related Articles | Metrics

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Characteristics of Partial Nitrification and N2O Emissions Through Aerobic Granular Sludge Treating Livestock Wastewater ZHANG Ming-chuan， XU Xin-yang， WANG Lin 2018, 39 (6):  872-876.  DOI: 10.12068/j.issn.1005-3026.2018.06.022 Abstract ( 663 )   HTML   PDF (506KB) ( 626 )   Aerobic granular sludge can achieve partial nitrification due to the special anaerobic/aerobic space structure. However， the greenhouse gas N2O could emit through partial nitrification and aerobic granular structure. In this study， performance of partial nitrification in an aerobic granular sludge reactor treating livestock wastewater was investigated， and its characteristics of N2O emissions were quantified by sensitive N2O micro-sensors. In the steady-state， the average COD and ammonium removal rates were 76.8% and 94.4%， respectively. The partial nitrification efficiency reached 88.9%. According to the results of micro-sensors and gas chromatography， the proportion of N2O generation from anaerobic and aerobic stage in the aerobic granular sludge system was 46.4% and 53.6%， respectively， but the N2O emissions from the partial nitrification system were mainly caused by air stripping in aeration phase. The ratio of N2O-N emissions was 2.1% of the influent nitrogen loading from this system. It showed N2O emissions were not significantly enhanced by the aerobic granular sludge. References | Related Articles | Metrics

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Effect of Carbon Source on Nitrogen Removal and N2O Generation in Subsurface Wastewater Infiltration System LI Hai-bo， LI Ying-hua， XU Xin-yang， WANG Si-qi 2018, 39 (6):  877-881.  DOI: 10.12068/j.issn.1005-3026.2018.06.023 Abstract ( 604 )   HTML   PDF (541KB) ( 617 )   Domestic wastewater was infiltrated through a subsurface wastewater infiltration system (SWIS) for depth denitrification treatment after precipitation. Influence of carbon source addition on nitrogen removal， denitrification microbial activity， N2O generation and conversion rate was analyzed. The results showed that carbon source was conductive to the promotion of microbial denitrification， but adding excess would promote substantial growth of other bacterial groups and inhibit the advantages of denitrification activity and nitrogen removal efficiency. When the organic content increased from 2.0% to 9.5%， removal efficiency for COD， NH+4-N and TN decreased by 10.9%， 19.5% and 24%， respectively and N2O generation and conversion rate declined. Correlation analysis showed that the nitrifier and denitrifier quantity exhibited significantly positive and negative correlation with N2O conversion (R2=0.994 and 0.959)， respectively， suggesting that N2O production was the result of the interaction of nitrification and denitrification， and mainly derived from nitrification process in upper layer. References | Related Articles | Metrics

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Preparation of Dust Removal Felt Filter with Nanofibers Membrane GUO Ying-he， HE Wei-dong， TIAN Xin-jiao， LIU Jing-xian 2018, 39 (6):  881-885.  DOI: 10.12068/j.issn.1005-3026.2018.06.024 Abstract ( 641 )   HTML   PDF (1345KB) ( 670 )   The polyester nanofiber membrane used in the field of dust removal was prepared by electrospinning. The fiber membrane microstructures were characterized by scanning electron microscopy. The optimum spinning conditions were determined. The nanofiber membrane under the optimum spinning conditions was attached to the filter surface， and the resistance characteristics test， the classification efficiency test and dynamic filtration performance test were applied to the nanofiber membrane filter. The results indicated that 15kV spinning voltage， 21cm receiving distance and 18% spinning solution concentration are the optimum spinning conditions. The nanofiber filter prepared under the optimum spinning conditions has low resistance and good cleaning performance. The filtration efficiency of fine particles below 3μm is over 99.99%， the filtration efficiency is improved obviously， which can effectively control the fine particles. References | Related Articles | Metrics

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Study on Hydrogen Fire and Explosion Accident in Battery Charging Area Based on WBS-RBS-BN WANG Yan-tong， XU Kai-li， LI Li， ZHANG Jin-jia 2018, 39 (6):  886-891.  DOI: 10.12068/j.issn.1005-3026.2018.06.025 Abstract ( 670 )   HTML   PDF (662KB) ( 972 )   Through field tests， the distribution of hydrogen concentration in the battery charging area was clarified. Based on the WBS-RBS analysis method， the coupling matrices of the risk events of the hydrogen fire and explosion accident in the battery charging area were obtained. Then， the fault tree of hydrogen fire and explosion accident was obtained. After then the fault tree was transformed into a Bayesian network. Thus the probability of the hydrogen fire or explosion accident in the battery charging area calculated by the GeNIe is 2.688e-4. Through the bidirectional reasoning function of the Bayesian network， the posterior probability of the basic events under the condition of hydrogen fire and explosion accident was calculated. The safety technology or management weaknesses leading to the occurrence of the accident are: electrostatic discharge， operator smoking， metal collision， battery overcharging， battery rupture and mechanical exhaust system failure. The corresponding countermeasures are clarified to reduce the hydrogen fire and explosion accident risk of the battery charging area. References | Related Articles | Metrics

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Simulation on Granular Material Collapse and Research on Its Characteristics FAN Yun-yun， WU Feng-yuan， LIANG Li， CUI Xin-reng 2018, 39 (6):  892-896.  DOI: 10.12068/j.issn.1005-3026.2018.06.026 Abstract ( 677 )   HTML   PDF (928KB) ( 682 )   The behavioral characteristics of granular materials are the theoretical basis for many technologies and natural phenomena research. In order to study the characteristics of the collapse of granular material， the numerical simulation was realized by using the discrete element numerical method， and the results of which were verified through experimental data showing the correctness and effectiveness of the simulation. Based on the numerical simulation， the processes and characteristics of two typical granular collapses were studied and analyzed. At last， the regular curves of the static core area under different collapse conditions were obtained and analyzed. References | Related Articles | Metrics

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Comprehensive Assessment of Rock Slope Stability Based on Spatial Block Identification ZHANG Zi-shan， WANG Shu-hong， WANG Fei-li 2018, 39 (6):  896-901.  DOI: 10.12068/j.issn.1005-3026.2018.06.027 Abstract ( 581 )   HTML   PDF (666KB) ( 664 )   A comprehensive assessment on rock slope stability was carried out by combining the key block theory with the fuzzy method. Based on typical slope of strip mine in Fushun， the physical and mechanical parameters were measured and a block identification system—GeoSMA-3D (Geotechnical Structure and Model Analysis-3D) was developed to identify the key blocks and to calculate the factors of safety. The assessment factors were detemined based on the characteristics of the spatial blocks. According to the information acquired， a fuzzy comprehensive assessment method based on AHP was applied to assess the stability of the slopes in an objective and quantitative way. Finally， an visualizaion plantform is established to visulize the terrain and total safety factors of the slope， which provides a reliable basis for disaster control and reinforcement on the slopes. References | Related Articles | Metrics

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Risk Assessment Method on Multi-disaster Coupled Hazard for Urban Utility Tunnel WANG Shu-hong， ZHANG Ze， HOU Wen-shuai， WANG Fei-li 2018, 39 (6):  902-906.  DOI: 10.12068/j.issn.1005-3026.2018.06.028 Abstract ( 854 )   HTML   PDF (352KB) ( 975 )   The risk assessment method of multi-disaster coupled hazard was studied in view of the shortcomings in the aspect of disaster prevention for utility tunnel， and a comprehensive risk analysis on the hazards of urban utility tunnel in Baotou Xindu central district was carried out. First， the single disaster risk assessment indicators for the potential disaster in utility tunnel was set up. Then， the coupled model regarding on multi-disaster in the utility tunnel was established in order to get the coupling relationship between multiple disasters. Finally， a risk assessment method was proposed for the multi-disaster coupled hazard. The risk assessment method proposed can be used to evaluate the safety of the urban utility tunnel under various disasters， which is of great significance to policy making and comprehensive planning of urban utility tunnel. References | Related Articles | Metrics

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Experimental Research on Overloaded Damaged Reinforced Concrete Beams Strengthened with Near Surface Mounted CFRP Strips YANG Jia， WANG Lian-guang 2018, 39 (6):  907-912.  DOI: 10.12068/j.issn.1005-3026.2018.06.029 Abstract ( 549 )   HTML   PDF (803KB) ( 680 )   In order to investigate the performance of damaged reinforced concrete beams strengthened with near surface mounted (NSM) carbon fiber reinforced polymer (CFRP) strips under overloading， the bending test of five reinforced concrete beams was carried out. The overloading state was simulated， and the failure mode， capacity and stiffness were studied. The influences of the overload cycle number and overload amplitude on the performance of reinforced concrete beams were also evaluated. The results show that embedding CFRP strips can enhance the capacity of overloaded damaged reinforced concrete beams to about 16% to 27%. The cycle number and overload amplitude affect the yield and ultimate load and stiffness in different ways. The yield and ultimate load decrease with the increase of cycle number and overload amplitude. The stiffness decreases with the increase of cycle number. The formula of ultimate bearing capacity is established， and the calculated results agree well with the experimental results. References | Related Articles | Metrics