Journal of Northeastern University(Natural Science)

Estimation of Lower Limb Continuous Movements Based on sEMG and LSTM

WANG Fei， WEI Xiao-tong， QIN Hao

2020, 41 (3): 305-311. DOI: 10.12068/j.issn.1005-3026.2020.03.001

Abstract ( 851 )

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A scheme of continuous motion estimation based on surface electromyography (sEMG) and long-short-term memory (LSTM)network is proposed for the control of lower limb assisted exoskeleton. The mapping relationship between EMG and motion is trained and analyzed by LSTM. The number of principal components (dimensionality reduction) for principal component analysis (PCA) algorithm are obtained based on the error algorithm of singular value decomposition eigenvalue matrix. The continuous motion estimation of three lower limb joints in sagittal plane is realized， and the real-time performance of the continuous motion estimation is improved. In comparison of the training results of LSTM network with those of traditional networks such as support vector machine (SVM) and back propagation(BP) neural network， the superiority of LSTM network in continuous motion prediction of lower limbs is proved.

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Multicarrier Modulation of UWA Communication Based on Combined Frequency Division Multiplexing

FU Xiao-mei， MA Peng-yu， HAN Guang-yao

2020, 41 (3): 311-315. DOI: 10.12068/j.issn.1005-3026.2020.03.002

Abstract ( 642 )

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The orthogonal frequency division multiplexing (OFDM)， widely applied in underwater acoustic (UWA) communication， is an efficiently multicarrier modulation technique. But OFDM requires the subcarriers to be orthogonal and is very sensitive to frequency offset. The Doppler compensation or adding the subcarrier filter is mainly used to combat Doppler shift in UWA communication， but the implementation is complicated. This paper investigates the method of reducing intercarrier interference (ICI) from a new perspective， that is， increasing the spacing between subcarriers. The combined frequency division multiplexing (C-FDM) is proposed and several OFDM subcarrier blocks are combined into one new C-FDM subcarrier block， and the same frequency subcarrier near each other to construct new C-FDM subcarriers is arranged. Assuming the symbol lengths of C-FDM and OFDM are equal and the subcarrier spacing of C-FDM is larger，the anti-Doppler shifting capability is effectively improved without complex compensation algorithms. The simulation results showed that C-FDM technology has better BER performance in UWA channel.

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Reversible Data Hiding Algorithm Based on Adaptive Histogram Modification for 3D Mesh Models

ZHANG Qi-long， WEN Tao， SONG Xiao-ying， SUN Wei

2020, 41 (3): 316-321. DOI: 10.12068/j.issn.1005-3026.2020.03.003

Abstract ( 703 )

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Reversible data hiding， as a special information hiding technology， is very useful in many fields， such as medicine， military and law. This paper proposes a reversible data hiding algorithm based on adaptive histogram modification for 3D mesh models. At first， the local similarity of model shapes is used to predict vertex positions in order to obtain the prediction error sequence with a steep histogram. Then， according to the distribution characteristics of the prediction error histogram， two groups of prediction errors are specified in embedding region for data embedding，which reduce the auxiliary date transfer. In addition， to reduce the model distortion， proper embedding regions are selected based on the payload size to avoid moving more prediction errors. The experimental results demonstrate that the proposed algorithm maintains high visual quality after data embedding and is applicable to low-capacity reversible data hiding.

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Ensemble Learning Based Recognition Method for Bundle Branch Block

XU Jiu-qiang， ZHANG Jin-peng， JIA Yu-qi， SHAO Jian-xin

2020, 41 (3): 321-326. DOI: 10.12068/j.issn.1005-3026.2020.03.004

Abstract ( 539 )

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In order to improve the automatic diagnosis performance of left and right bundle branch block based on electrocardiogram(ECG)， an ensemble learning method was proposed，while a combination of multi-lead electrocardiogram and convolution neural network model served as the basic learner. Firstly， effective diagnostic lead data is extracted from the clinical 12-lead synchronous static electrocardiogram and divided into slices of multi-lead single heart beat data. Secondly， the bootstrapping method is used to extract multiple data subsets. Each subset would be perturbed and input to the base learner. Afterwards， the corresponding prediction models are obtained. Then， the Bayesian method is used as the combined strategy of ensemble learning to fuse multiple prediction models. Finally， the diagnosis is provided by voting combined with the classification results of multiple beats in an ECG. The experimental results show that the method has high sensitivity and specificity， which has clinical application value.

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Knee MRI Segmentation Algorithm Based on Chaotic Moth-Flame Optimization

WANG Hai-fang， QI Chao-fei， ZHANG Yao， ZHU Ya-kun

2020, 41 (3): 326-331. DOI: 10.12068/j.issn.1005-3026.2020.03.005

Abstract ( 539 )

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The moth-flame optimization (MFO) algorithm may show shortcomings such as the local optimum and convergence stagnation when solving the practical optimization problem. Therefore， aiming at the problem that MRI (magnetic resonance imaging) images are difficult to segment， this paper proposes a chaotic moth-flame optimization(CMFO) algorithm. In order to help doctors read the MRI films and improve the efficiency and accuracy of diagnosis， the knee MRI images are selected as research objects during the experiments. Then，CMFO algorithm and maximum threshold entropy are combined and applied into multi-threshold segmentation. In order to present the advantages of the CMFO algorithm proposed， SOA， BFOA and MFO algorithms are introduced under the same condition for comparative experiments. The experimental results show that CMFO can effectively improve the optimal performance of MFO， and has better applicability and advantages for knee MRI image segmentation.

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Generating Algorithm of Medical Image Simulation Data Sets Based on GAN

MENG Lu， ZHONG Jian-ping， LI Nan

2020, 41 (3): 332-336. DOI: 10.12068/j.issn.1005-3026.2020.03.006

Abstract ( 1162 )

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Based on generative adversarial networks (GAN)， a deep learning algorithm for generating diseased liver CT image data sets was proposed. Firstly， the CT image data file was formatted and saved as an image file in PNG format. Then the liver lesion area was uniformly marked as white， and the liver CT original image was combined to form a paired picture. Finally， diseased liver image was generated using a pix2pix architecture that created an anti-network. In order to quantitatively analyze and compare the generated image with the target image， the peak signal-to-noise ratio and structural similarity were used to evaluate the model. The results showed that the average peak signal-to-noise ratio of the simulated CT diseased liver image generated by the proposed algorithm is 64.72dB and the average structural similarity is 0.9973， thus proving these simulated image data have very high trueness.

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Research on Cloud Storage Integrity of Wireless Body Area Network Data Based on Blockchain Technology

GAO Yan-fang， YAO Lan， MA Yan-song， LI Feng-yun

2020, 41 (3): 337-342. DOI: 10.12068/j.issn.1005-3026.2020.03.007

Abstract ( 744 )

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Aiming at the security problems in cloud storage of the data in wireless body area network (WBAN for short)， an access control framework based on blockchain was designed. The framework controlled user’s access requests by combining blockchain technology with the digital signature. It used blocks to store access requests and digital signatures of the access requests， and utilized the improved Raft algorithm to ensure the consistency of each node’s blockchain. Then， an ordered array combined with Merkle tree was designed to store WBAN data. A Hash table is combined with Merkle tree to store the access requests of the WBAN data. Thirdly， on the basis of access control framework， the storage mode of the WBAN data and the access requests of the WBAN data， and the integrity verification scheme for the WBAN data was proposed. Finally， experiments were carried out on the consistency of blockchain and the data integrity verification scheme. The experimental results showed that the proposed framework enables each user node to control the access request cooperatively， and the proposed scheme supports each user node to verify the integrity of data.

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Dynamic Modeling and Vibration Analysis of Rolling Bearings with Local Fault

MA Hui， LI Hong-fei， YU Kun， ZENG Jin

2020, 41 (3): 343-348. DOI: 10.12068/j.issn.1005-3026.2020.03.008

Abstract ( 821 )

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A two-dimensional explicit finite element (FE) model of healthy cylindrical roller bearings based on ANSYS/LS-DYNA software was established， and the availability of model was verified from the perspective of bearing kinematics. The FE model of cylindrical roller bearing with local spalling fault was developed by introducing local spalling fault into healthy inner and outer raceway， among which the local spalling was simulated by circumferential rectangle. The equivalent stress of the edge element of fault zone and the process of rolling through the local fault zone were analyzed. Comparing the simulation results with the experimental ones， the correctness of the FE model was confirmed. On this basis， the influence of smoothness of the local fault on the vibration characteristics of the rolling bearing was studied. The smoother the fault area， the smaller the vibration response. These results can provide some reference for the fault diagnosis of rolling bearings.

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Anthropopathic Robotic Hand Design and Hardness Recognition Research

ZHANG Ying， ZHAO Chang-sheng， YUAN Wen-bo， HAO Li-na

2020, 41 (3): 349-355. DOI: 10.12068/j.issn.1005-3026.2020.03.009

Abstract ( 727 )

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The manipulator plays an important role in improving the intelligence and execution ability of the robot. Hardness， as one of the important physical properties of an object， affects partly the intelligent grasping control of a manipulator. In order to make it possible for the manipulator to improve characteristics of good adaptability， integration and lightweight， an anthropopathic robotic hand based on 3D printing technology was designed. The manipulator worked via the wire ropes pulled by micro-motor screws， and the micro-motor screws were embedded in the palm of the hand. Thus the bending motion of four fingers and the bending and swinging motion of the thumb can be realized. Based on the platform， this work focuses on the object hardness recognition on the basis of current sensor feedback only， without using additional external sensors.It makes up for the disadvantage that most manipulators cannot directly distinguish the hardness of objects. By integrating the robotic hand with a soft arm， the classification for rotten fruits and fresh fruits with different hardness is realized.

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A Fast Tracking Strategy for Uncalibrated Visual Servo System

MA Shu-jun， JIN Tie-zheng， WANG Ying-lei， BAI Xin-hui

2020, 41 (3): 355-360. DOI: 10.12068/j.issn.1005-3026.2020.03.010

Abstract ( 660 )

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In order to improve the tracking efficiency of manipulator tracking dynamic target， this paper proposed a fast tracking strategy of uncalibrated visual servo systems. On the one hand， by predicting the joint angle of the manipulator motion， the controller’s calculating behavior can be carried out in parallel with the manipulator’s moving behavior. On the other hand， the strategy uses the latest image information to calculate the joint angle， which improves the real-time performance of the system. In the simulation and physical experiments， two uncalibrated visual servo systems with different tracking strategy algorithms are constructed to track dynamic target. Finally， the fast， real-time and anti-jamming performance of the strategy are verified by comparing tracking time and tracking path.

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Research on the Dynamic Characteristics of Metal Chain Continuously Variable Transmission

ZHANG Lei， ZHAO Xin

2020, 41 (3): 361-366. DOI: 10.12068/j.issn.1005-3026.2020.03.011

Abstract ( 594 )

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The transmission mechanism and axial compression principle of the V-shaped structure of the metal chain continuously variable transmission (CVT) were studied in depth. By studying the relationship of clamping force and thrust for the cone disk， the mathematical model of dynamic characteristics were established， the theoretical loading curve of the compression mechanism was derived and simulated， and the experiment of corresponding dynamic characteristics was carried out to obtain the thrust ratio. It was concluded that the change rate of speed ratios has a negative effect on the acceleration of the vehicle， and the thrust ratio cannot be completely relied on to adjust the speed ratio. The relationship between the thrust ratio and the speed ratio at high and low chain speeds is slightly different. Thus， it may lay a foundation for the development of reliable axial clamping force control structure and system.

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Optimal Placement of Strain Sensors for Urban Rail Vehicles Based on Information Entropy

ZHANG Zi-fan， LI Qiang， LIU Han-wen， DING Ran

2020, 41 (3): 367-374. DOI: 10.12068/j.issn.1005-3026.2020.03.012

Abstract ( 521 )

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In view of the concentration of measurement points in the traditional sensor optimization method with a large number of configurations， the relationship between optimization results and prediction errors was analyzed based on the information entropy theory， and an improved optimization method considering prediction errors was proposed. The reciprocal of the sum of normalized modal strain energy was used as the principal diagonal element of the prediction error covariance matrix， and the non-diagonal element was expressed by an exponential correlation equation combining the distance of measurement points and the response level. Aiming at maximizing the determinant of Fisher information matrix， the forward sequential sensor placement method was used to obtain the optimal location of measurement points. The finite element analysis results of the urban rail vehicle frames showed that the improved sensor optimization method is superior to the classical method in the performance of three evaluation criteria， and significantly reduces the concentrating effect of measurement points， which proves the effectiveness of the improved method in the configuration of bogie frame strain sensors.

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Study on the Process and Performance of Variable Thickness Cladding Layer Deposition

XIN Bo， ZHOU Xian-xin， GONG Ya-dong

2020, 41 (3): 374-379. DOI: 10.12068/j.issn.1005-3026.2020.03.013

Abstract ( 511 )

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In order to reduce the step-effect caused by uniform thickness cladding layers， the variable scanning speed and height-varying overlapping methods were proposed to form variable thickness cladding layers. Based on the raster scanning path， the geometric model with variable thickness slices was established. The surface quality， hardness and microstructure distribution of the ramp cuboids were observed， compared with uniform thickness cladding layer deposition. The results showed that the process of variable thickness cladding layers can dramatically improve geometric precision. The variation of grain growth direction at the longitudinal section of the formed samples is revealed. Moreover， in the scanning and overlapping direction， the maximum hardness value appears near the high end.

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Experiment on the Macro-morphology and Residual Stress of 316L by Hybrid Additive and Subtractive Manufacturing

YANG Yu-ying， GONG Ya-dong， QU Shuo-shuo， CAI Ming

2020, 41 (3): 380-386. DOI: 10.12068/j.issn.1005-3026.2020.03.014

Abstract ( 740 )

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In order to investigate the influence of laser power (P)， powder feeding rate (f) and scanning speed (v_f) on the macroscopic quality of cladding layers during the laser melting deposition， the orthogonal experiment was conducted to study the single pass laser cladding layer. The shape factor (ξ) was used as the evaluation index. The influence rule of P， f and v_f on the geometry morphology was concluded and the range analysis was adopted. The results indicate that f has the greatest influence on the shape factor ξ. The optimized process parameters of P， f and v_f are 1kW， 0.7g/min and 600mm/min， respectively. The superficial residual stresses in the thin-wall ring specimen of 316L by hybrid additive and subtractive manufacturing were measured by the X-ray diffraction method. The measurement results showed that the top and bottom of the samples are tensile stresses and the middle part is compressive stress. Moreover， the milling process can release part of the residual stress.

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Study on the Milling Surface Quality of GH4169 Alloy Based on Graphene-Enhanced MQL Method

LI Ming， YU Tian-biao， ZHANG Rong-chuang， WANG Wan-shan

2020, 41 (3): 387-392. DOI: 10.12068/j.issn.1005-3026.2020.03.015

Abstract ( 549 )

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In order to improve the surface quality of GH4169 alloy during the milling process， the graphene nanoparticle was added to the vegetable-oil-based cutting fluid to enhance the cooling and lubrication performances based on MQL(minimum quantity lubrication). The effects of the graphene nanoparticle concentration， cutting fluid flow rate and gas pressure on the surface roughness were studied by the range analysis and variance analysis based on the orthogonal experimental scheme. Besides， the optimal parameter combination was obtained. The results showed that the effect of the graphene nanoparticle concentration on the surface roughness is the most significant， followed by the cutting fluid flow rate， and finally the gas pressure. Meanwhile， the optimal surface roughness is 0.406μm， and the optimal parameter combination is graphene nanoparticle concentration 0.1%， cutting fluid flow rate 60mL/h， and gas pressure 0.6MPa. It could be concluded that appropriate MQL parameters can significantly improve the cooling and lubrication state in the cutting zone during the MQL milling of GH4169 alloy， thereby improving the surface quality and reducing the surface roughness.

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Workpieces’ Surface Material Removal Mechanism of Disc Grinding

SUN Cong， LI Qing-liang， XIU Shi-chao， LIU Hong-wei

2020, 41 (3): 393-398. DOI: 10.12068/j.issn.1005-3026.2020.03.016

Abstract ( 975 )

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In terms of the uneven removal and substandard flatness on the workpiece’s surface in disc grinding， a calculation method with multiple grits’ removal rate was proposed. Firstly， a mathematic model for the disc wheel’s grits’ distribution was established considering the grits’ sizes and the positions. Then， the multiple grits’ dynamic trajectory equation was deduced. Meanwhile， the workpiece’s removal rate model was established on this basis. The rationality of the model was further validated by the experiment of disc grinding. The results show that the removal effect appears to be uneven on the workpieces’ surfaces of disc grinding. It is the lower removal rate that leads to the embossment phenomenon in the central location. Moreover， the height difference of ground workpieces’ surface profile goes up with the increase of the speed ratio. Therefore， it is advisable to reduce the speed ratio so as to improve the consistency of the ground workpieces’ surface.

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CFD-Based Evaluation of Back Pressure Resistance of Steam Ejectors

WANG Xiao-dong， SUN Hao， NING Jiu-xin， SUN Hao-lin

2020, 41 (3): 399-402. DOI: 10.12068/j.issn.1005-3026.2020.03.017

Abstract ( 614 )

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The back pressure resistance of the steam ejector was evaluated by the kinetic energy e of the unit volume of the steam ejector’s throat outlet section. The influence of geometric parameters of the ejector including throat diameter d， mixing chamber angle θ and nozzle exit position s on the steam ejector’s back pressure resistance and the relationship between e and the steam ejetor’s back pressure resistance were studied by using the computational fluid dynamics(CFD) method. The results showed that as d or θ decreases， or s increases， e and the back pressure resistance of steam ejector increase. When d， θ and s change， e can be used as a standard for evaluating the capability to resist the back pressure of steam ejectors.

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Numerical Simulation on Overlying Strata Movement Law in Underground Mining of Cuyu Gold Mine

GUAN Shou-an， LI Hao， JIN Chang-yu， LIU Dong

2020, 41 (3): 402-407. DOI: 10.12068/j.issn.1005-3026.2020.03.018

Abstract ( 573 )

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The numerical simulation on the stratum movement law during the downward filling-mining process of steep and extremely narrow orebody in Cuyu gold mine was carried out. The joint strike and spacing is determined through on site investigation. The Hoek-Brown strength criterion was used to determine the numerical calculation parameters， and the boundary conditions of numerical calculation was obtained by the neural network. was used to optimize the neural network to obtain the boundary conditions of numerical calculation. The stratum movement law during underground mining of steep and extremely narrow orebody was carried out by three different numerical calculation methods. The research showed that the settlement of the rock mass on the upper part of the orebody is obvious， and the settlement area of the overburden rock in the orebody is cylindrically collapsed. According to the calculation results of FLAC3D and 3DEC， there is no settlement area on the surface in Cuyu gold mine. The No. 2 shaft， the newly-built concentrator and the staff dormitory bath are all located outside the rock transfer belt based on the calculation results of random medium method. Compared with FLAC3D and 3DEC calculation， the random medium method is more suitable for simulating the rock strata movement caused by the steep and extremely narrow orebody mining.

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Growth Mechanism of α-Fe₂O₃Nanopolyhedra Synthesized from Pyrite by Cu²⁺Inducement

ZHOU Peng-fei， ZHANG Wei， ZHAO Si-kai， SHEN Yan-bai

2020, 41 (3): 408-412. DOI: 10.12068/j.issn.1005-3026.2020.03.019

Abstract ( 528 )

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Taking pyrite as the iron source， Fe³⁺ leaching solution was obtained through roasting， chemical leaching and impurity removal. Then，α-Fe₂O₃ nanopolyhedra was synthesized by hydrothermal method via Cu²⁺ inducement. The structure and morphology of α-Fe₂O₃ nanopolyhedra were characterized by X-ray diffraction (XRD)， scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) to investigate their nucleation and crystal growth. The results showed that α-Fe₂O₃ nanopolyhedra with a hexagonal structure was about 500nm in grain size. Based on the morphology observation of the as-prepared products synthesized at different hydrothermal times and the analysis result of solution chemistry calculations， it is concluded that the formation of α-Fe₂O₃ nanopolyhedra is followed by the precipitation， dissolution and recrystallization. The presence of Cu²⁺ mainly induces the crystal nucleus of α-Fe₂O₃ so as to form nanopolyhedra structure in the process of growth.

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Processing a Gold Ore from Hainan Province Using Knelson Gravity Concentration-Flotation

CHEN Qiao，YANG Hong-ying，TONG Lin-lin

2020, 41 (3): 413-418. DOI: 10.12068/j.issn.1005-3026.2020.03.020

Abstract ( 920 )

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The experimental study of Knelson gravity concentration-flotation technology of a quartz-vein type gold ore in Hainan Province was carried out. The GRG(gravity recoverable gold) test showed that the gold content in the gold ore is 80.88%. The optimal technological conditions of Knelson gravity concentration-flotation for the ore were determined by condition test to be a grinding size of 80% powder below 74μm， a relative centrifugal force of 60g， a fluidizing water pressure of 16kPa， a feed slurry mass fraction of 40%， a dosage of amyl xanthate of 200g/t and a flotation time of 5min. A gold concentrate with grade of 230g/t and recovery of 80.30% can obtained from the raw ore(9.8g/t) by gravity separation， and a gold concentrate with grade of 57.3g/t and recovery of 75.66% can be obtained from the gravity separation tailing by a flotation process of one roughing， one cleaning and three scavengings. The gold grade of final tailings is 0.5g/t and the total gold recovery in the Knelson gravity concentration-flotation process is 95.21%.

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Simulation on the Internal Flow Field Characteristics of Deep-Cone Thickener

WANG Xue-tao， CUI Bao-yu， WEI De-zhou， SONG Zhen-guo

2020, 41 (3): 418-423. DOI: 10.12068/j.issn.1005-3026.2020.03.021

Abstract ( 536 )

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Based on the independent validation on mesh quality， the single phase flow field of a lab-scale deep-cone thickener with 4 L capacity was numerically simulated by using the turbulence model of Reynolds stress. The influence of the feed flow rate on the characteristics of velocity， shear and turbulence intensity was systemically investigated. The numerical results showed that the velocity field of the thickener distributes symmetrically along the shaft. The up-down circuit flow is formed in the axial direction. The counterflow and discharging flow is formed in radial direction. The axial velocity increases by about 0.02m·s^-1 with every 1.8L/min increase rate of feed flow. The shear intensity in the feedwell is higher than that in any other region of the thickener， and takes on positive correlation to the feed flow rate.The region of high turbulence intensity distributes at the edge of the shelf as well as in the contractile region of the feedwell. A feed flow rate of 1.8L/min in this case presents better dissipation performance of turbulence kinetic energy. The feed flow rate has little effect on the reflux ratio of the feedwell with a deflector.

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Experiment of Shear Properties on the Interface Between Gravelly Sand and Concrete Pipe

ZHAO Wen， LI Tian-liang， HAN Jian-yong， CHENG Cheng

2020, 41 (3): 424-430. DOI: 10.12068/j.issn.1005-3026.2020.03.022

Abstract ( 658 )

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Based on the digital image correlation (DIC) technology， the mechanical properties on the interface between garvelly sand and concrete pipe were studied systematically under a constant normal stress condition by using a self-developed visual direct shear container. The experimental results showed that the initial shear modulus of the interface between gravelly sand and concrete pipe increases with the increase of normal stress. When D_r=0.8， the friction coefficient of the interface increases about 17.5% compared with that when D_r=0.4， and when the relative density increases by 0.2， the friction angle increases by 2° on average. The softening degree of the shear stress vs. shear displacement curve of the interface is gradually reduced with the increase of normal stress， and the hardening degree is gradually obvious. In addition， the shear displacement of the soil increases with the increase of the distance away from the interface. The shear deformation mainly occurs in the shear zone， and the thickness of shear band is 3D₅₀.

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Identification of Optimal Tourmaline Powders for Filtration Enhancement

ZHENG Jia-wen， HE Wei-dong， GUO Ying-he， LIU Jing-xian

2020, 41 (3): 430-437. DOI: 10.12068/j.issn.1005-3026.2020.03.023

Abstract ( 541 )

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The effects of different particle size purified tourmaline powder samples on the filtration performance of air filter materials from Xinjiang， Hebei and Guilin were studied. Electrode performance of various tourmaline powder samples was carried out by piezoelectric experiments and pyroelectric experiments to identify the preferred polarization characterization. The results show that the electrode of the 0.074mm pure grade tourmaline has the best performance. The highest grade of three tourmaline powders is attached to the filter surface for the whole dust efficiency experiment. The 0.074mm pure grade of tourmaline in Guilin has the highest filtration efficiency. The most significant improvement is obtained. Using the Rietveld method， the XRD pattern of tourmaline powder is refined to obtain the crystal structure. The calculation of the intrinsic electric dipole moment proves that the electrostatic adsorption caused by the spontaneous polarization of tourmaline is the main reason for improving the filtration performance of the filter material.

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Rainfall Infiltration Characteristics of Double-Layered Soil Slope Covered by a Highly Permeable Stratum

WANG Shu-hong， HE Jian， WANG Shuai， NGUYEN Vantuan

2020, 41 (3): 438-444. DOI: 10.12068/j.issn.1005-3026.2020.03.024

Abstract ( 676 )

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In order to study the rainfall infiltration characteristics of double-layered soil slope covered by a highly permeable stratum， the soil column and slope model of homogeneous silt and sand-soil were established respectively， and the governing equations according to the matric suction and water content were used to analyze the effect of permeability， ground water level and slope angle on the formation of saturated zone. The results showed that the formation of saturated zone in sand-soil column is caused by the water accumulation under the sand layer due to the permeability difference， and the dramatically decrease of seepage velocity in the surface of the silt layer. The saturated zone is initially formed in the interface of the soil layer in the sand-soil slope and develops along the interface till to the upper boundary of the slope. In the meanwhile， it gradually develops into the soil layers and up to the interface of layers in the longitudinal direction. The extension length along the soil interface gradually increases with the increase of the groundwater table， but when the groundwater table is 2m and 1m， the extension of the saturated zone is reduced with the increases slope angle. The initial saturation degree is affected by groundwater table and slope angle.

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Effect of Data Mode from Stress-Strain Curve on Forming Limit of Aluminum Alloy Sheets

CAI Zhong-yi， LI Li， SUN Li-rong， MENG Fan-xiang

2020, 41 (3): 445-451. DOI: 10.12068/j.issn.1005-3026.2020.03.025

Abstract ( 848 )

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In order to analyze sheet formability more realistically， a new approach based on the M-K theory was proposed， which predicted the forming limit of aluminum alloy sheets by using different modes of data from the measured stress-strain curve. The forming limits of 6016-T4 and 7075-T6 aluminum alloy sheets were theoretically analyzed using three modes of data， which were the original data of the measured stress-strain curve， the power exponential fitted data and polynomial fitted data of the stress-strain curves， respectively. According to the stress-strain data from tensile test， the ultimate strains were calculated and the theoretical forming limit curves (FLC) were plotted. After comparing the theoretically predicted FLC with experimental data from the bulging test， the results indicate that the predicted forming limits using the data of the original stress-strain curve is the best one， while the forming limits using the data from the power exponential fitted curve has a certain deviation from the experimental one.

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Theory of Droplet Formation and Cell Encapsulation for T-Shaped Microfluidics Chip

HU Sheng， LIAO Zi-wei， CAI Lu， JIANG Xiao-xiao

2020, 41 (3): 452-456. DOI: 10.12068/j.issn.1005-3026.2020.03.026

Abstract ( 622 )

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The velocity values of the continuous phase and the discrete phase are the key factors affecting the droplets generated by the T-shaped microfluidic chip. The droplet encapsulation and encapsulation of cells in T-shaped microfluidic channels become hot topics for gene sequencing. Therefore， the dynamic transport relative to both droplet size and blood cell encapsulation is studied by combining level set method with hydrodynamics. The water and n-dodecane oil as objective is simulated in the T-shaped microfluidics， in which the width of discrete and continuous channel is 50μm and 80μm， respectively. The results indicate that the capillary number (C_a) from 0.008 to 0.1 can result in decreasing droplet size and increasing generation frequency when there are the initial velocity of aqueous solution 0.012m/s， the interfacial tension 5mN/m and contact angle 165°. Meanwhile， the encapsulated efficiency can be decreased， so that the blood cell with diameter of 5μm moves straightway nearby the wall due to viscosity force greater than surface tension.

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