• Issue 5,2019 Table of Contents
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    • >Special Column: National Young Scholar/Local Science Foundation
    • Structural analysis and optimum design of ECM machine tool based on variable density method

      2019, 40(5):371-378. DOI: 10.7535/hbkd.2019yx05001

      Abstract (1144) HTML (0) PDF 4.13 M (1364) Comment (0) Favorites

      Abstract:In order to improve the precision and quality of electrochemical machining of complex surface/cavity parts, the design of horizontal electrochemical machine tool which can realize the compound feeding motion of straight line and rotation is carried out. In this paper, UG software is used to build three-dimensional model of horizontal machine tool, and the simplified model is imported into ANSYS Workbench software for static analysis. The structural stiffness of the machine tool is analyzed based on deformation and stress distribution nephograms. The first six natural frequencies and modes of motion platform are determined by modal analysis, and the optimal design is carried out by using the variable density topology optimization method. Finally, the design is redesigned on the basis of considering the technological characteristics of the structure, and the lightweight design goal of the machine tool is achieved. The developed electrochemical machining machine has sufficient stiffness and stability, which can satisfy the requirements of actual machining. The research results have certain reference value to the design and application of electrochemical machining tool.

    • >Chemistry and Chemical Industry
    • Optimization and improvement of the synthesis method of terbutaline sulfate

      2019, 40(5):379-384. DOI: 10.7535/hbkd.2019yx05002

      Abstract (1339) HTML (0) PDF 315.58 K (1082) Comment (0) Favorites

      Abstract:In order to obtain high yield and product quality of terbutaline sulfate, the synthetic method of terbutaline sulfate is studied. Terbutaline sulfate is synthesized from 3,5-dibenzyloxyacetophenone by bromination, alkylation reaction, carbonyl reduction and catalytic hydrodebenzylation. The reaction conditions and parameters are optimized and improved. Bromination is optimized,with tetrahydrofuran and methanol as solvents,tetrabutylammonium tribromide is used instead of liquid bromide and copper bromide as bromination reagent, n(3,5-dibenzyloxyacetophenone)∶n(tetrabutyl ammonium bromide)=1∶1.3,the reaction time could be reduced to 6 hours, and the yield is up to 99.1%.In condensation reaction, with benzyl tert-butylamine instead of tert-butylamine,n(3, 5-dibenzyloxy-alpha-Bromoacetophenone)∶n(benzyl tert-butylamine)=1∶3, the yield is 69.9%. In catalytic hydrodebenzylation, the amount of Raney Ni is 15% in solvent methanol, the pressure is 1.0 MPa,temperatuer is 40 ℃,and the yield is up to 90.2%. Under the optimized conditions,the total yield is 62.4%,and the purity is 99.90%(by HPLC), the impurities are less than 0.1%. The structures of the target compound are confirmed by 1H-NMR and 13C-NMR. The improved synthesis process with mild reaction conditions, simple operation, and high yield is more suitable for industrial production.

    • >Mechanical, Electronics and Information Science
    • Kinematics analysis and dynamics co-simulation of permanent magnet three-DOF motor

      2019, 40(5):385-396. DOI: 10.7535/hbkd.2019yx05003

      Abstract (1025) HTML (0) PDF 1.98 M (880) Comment (0) Favorites

      Abstract:In order to solve the problems of low precision and low motion control of multi-degree-of-freedom motor in three-dimensional space, under the rigid mechanical system, based on the characteristics of strong coupling and nonlinearity of complex mechanical systems, a three-degree-of-freedom motor capable of linkage control can be designed. The motor's rotation motion control strategy is used to analyze the stress distribution and deformation degree of the motor during the rotation. The dynamic model of the hybrid drive motor is established and three axial torques are applied as the driving force. The motor is based on the three-degree-of-freedom motion of hybrid drive, and the dynamic joint simulation interface of the machine-controlled integrated motor is built and designed. The results show that by activating the effective mode, the motor structure under the rigid-flexible coupling system can be optimized to obtain a small eccentric displacement. The intelligent control scheme of the multi-degree-of-freedom motor can freely design the parameter changes of the controlled object, reduce the sensitivity of the disturbance, and make the control system have better robustness. Combining the dynamic mathematical model of the three-degree-of-freedom motor to build a joint simulation platform based on the sliding mode control system, the trajectory tracking of the three axial angular velocities of the motor can be realized. The tracking effect can be achieved during the whole dynamics joint simulation period, which provides a theoretical basis for the subsequent manufacture and testing of the physical prototype.

    • Simulation research on UAV recognition method based on convolutional neural network

      2019, 40(5):397-403. DOI: 10.7535/hbkd.2019yx05004

      Abstract (1170) HTML (0) PDF 1.37 M (906) Comment (0) Favorites

      Abstract:In order to improve the accuracy of identifying the target image while the drone is sailing, a hybrid model combining convolutional neural network (CNN) and probabilistic neural network (PNN) is proposed. The model uses CNN to extract multi-layer image representations and uses PNN extraction features to classify images. In order to improve the generalization and robustness of CNN, CNN-PNN model replaces BP neural network inside CNN with PNN, and trains the model by mean square error and gradient reduction method. The pre-processed image is transmitted to the CNN-PNN model to classify and identify the texture and contour of the image, and the simulation results of this model are compared with the results of convolutional neural network model and convolutional neural network-support vector machine model. The simulation results show that the CNN-PNN model has better accuracy compared with the two models, and the recognition rate is as high as 96.30%. The improved model improves the generalization and robustness of CNN, and can enhance the accuracy of image recognition in all aspects, and has high real-time performance.

    • Application-layer DDoS attack defense detection model based on Web access path

      2019, 40(5):404-413. DOI: 10.7535/hbkd.2019yx05006

      Abstract (1087) HTML (0) PDF 568.38 K (849) Comment (0) Favorites

      Abstract:In order to improve the effectiveness and timeliness of defense against distributed denial of service (DDoS) attacks in application layer, the evolution and mode of application-layer DDoS attacks, as well as the attack path and behavior of attackers are explored in depth. A defense detection model based on Web access path is proposed, according to access path trajectory, attack behavior characteristics and website link rules, five anomaly detection models including request path, request distribution, path loop, behavior slot and path length are established. By calculating the normal value of legitimate users accessing websites and the deviation degree of real-time outliers of users with aggressive behavior, it can determine whether it is attacked by application-layer DDoS. In order to improve the accuracy of detection, the defense module chooses the best defense strategy according to the size of user's illegal value, resists application-layer DDoS attacks, and achieves website data security and computer security. The experiment is trained with real log data, launch five different types of application-layer DDoS attacks on experimental website, the result show that the defense detection model can accurately identify users with aggressive behavior in a short time, it combines with defense module to defend the application-layer DDoS to a specific website, realizes real-time detection and real-time defense, and the false alarm rate is significantly reduced.

    • Dynamic step BI-RRT UAV path planning algorithm

      2019, 40(5):414-422. DOI: 10.7535/hbkd.2019yx05005

      Abstract (1402) HTML (0) PDF 1.60 M (1009) Comment (0) Favorites

      Abstract:To solve the problems of traditional RRT algorithm, such as slow convergence and long path length, the dynamic step BI-RRT algorithm is proposed. The sampling efficiency of the RRT algorithm is improved by using a target-oriented sampling strategy. The dynamic step algorithm improves the local smoothness of the path in the obstacle environment. A new tree cutting strategy is proposed to make the growth trend of random trees more obvious and improve the convergence rate of the algorithm. For the initial path, the path nodes are filtered by applying greedy algorithm to reduce the invalid nodes and path length of the unmanned aerial vehicle (UAV). Finally, a feasible smooth path is obtained by using B-Spline. The simulation maps in 2D and 3D environment are built to verify the effectiveness of the algorithm. Compared to the segmentated optimization RRT algorithm, the dynamic step BI-RRT algorithm proposed in this paper improves the convergence rate and reduces the path distance, while ensuring that the number of path nodes is optimal. This path planning algorithm has some advantages such as good real-time performance and smoothness of path.

    • Improved feature matching strategy for 3D reconstruction

      2019, 40(5):423-430. DOI: 10.7535/hbkd.2019yx05007

      Abstract (1055) HTML (0) PDF 2.27 M (1070) Comment (0) Favorites

      Abstract:In order to get the feature points in the image more quickly and improve the stability of feature matching results, an improved matching strategy is proposed. First, the image is subsampled, matched by a low-resolution image, and the matching pair that matches the failure is quickly filtered out, and then the matched ones that succeed are matched with the corresponding original images, so as to achieve the purpose of acceleration. In addition, the matching result of SIFT and the matching result of SURF are merged, and the fusion result is applied to the 3D reconstruction technology, which effectively improves the accuracy of the 3D point cloud. The algorithm is tested by using self-acquired data set and public data set, and the experimental data is analyzed. The results show that the improved feature matching strategy improves the running speed of 3D reconstruction by 40% and greatly increases the number of 3D points. Therefore, the proposed method can not only reduce the computational burden of feature matching process, but also improve the stability of 3D reconstruction, so it has certain reference value in the research of 3D reconstruction.

    • >Material Science
    • Research on joining mechanism and fracture mode of Al-Cu alloy joint by refill friction stir spot welding

      2019, 40(5):431-437. DOI: 10.7535/hbkd.2019yx05008

      Abstract (1054) HTML (0) PDF 2.99 M (996) Comment (0) Favorites

      Abstract:In order to increase the joint strength, RFSSW is used to weld 2524-T3 aluminum alloys of aircraft skin. The joint Connection Mechanism is studied through the analysis of its appearance and microstructure by SM and metallographic microscope, The mechanical properties of the joint is investigated by tension-shear test and cross-tension test, and the fracture is analyzed by SEM. The experiment results show that the RFSSW joint has a good forming and defect-free on the surface, and with the action of thermo-mechanical, the cross-section of the joint can be divided into four zones in grain structure. The mechanical performance of RFSSW joints is generally higher than that of riveting joints. The tension-shear performance of welding joints reaches 7.233 kN, which is 113.4% higher than that of riveting joints. The tension-shear performance of welding joints reaches 3.172 kN, which is 6.16% higher than that of riveting joints. There are two types of joint fracture modes: nugget debonding fracture and plug fracture. When the plunge depth of sleeve is relatively small and the internal agitation of joint is insufficient enough, it can result in the nugget debonding fracture. With the increase of plunge depth of sleeve, plug fracture make gradually changes, the transition from plug fracture (fracture in the upper sheet) to plug fracture (fracture in the lower sheet). Ductile fracture is observed in both tension-shear test and cross-tension test with the nugget debonding fracture. The mechanical properties of refilled friction stir spot welding joints are analyzed, which provides theoretical and technical basis for the application of RFSSW in aerospace structural components.

    • Design of 3D printing feeding system and extrusion system based on fused deposition modeling (FDM) technology with

      2019, 40(5):438-445. DOI: 10.7535/hbkd.2019yx05009

      Abstract (1138) HTML (0) PDF 1.00 M (849) Comment (0) Favorites

      Abstract:Mostly filamentous thermoplastic materials processed from granular thermoplastic materials are used by FDM 3D printers, which has high material cost, and it is difficult to reach uniform mixing due to the filamentary geometry of the material itself, so Multicolor FDM 3D printing technology has been limited,and it is difficult to realize Multi-color mixed printing. For the above questions, according to the traditional extrusion technology combined with the characteristics of fused deposition modeling(FDM) technology, the granular FDM 3D printing equipment feeding and extrusion system is designed, the granular plastics as raw material is directly selected, and multiple inlets, storage bins and exhaust screw are designed, the material is controlled by the hole-drilling. the reasonable ratio of different colors and different feed rate of granular plastic can be realized by the design result. The exhaust screw related to fully melt, pressurize, homogenize, vent, re-homogenize and extrude the granular plastic is designed. The 3D printing process of homogeneous material and the Multi-color mixed color printing process are realized. The design proposed in the paper can be directly used for 3D printing by using granule, which not only reduces the material production cost and cycle, but also realizes the effective utilization of waste materials, providing a reference basis for the development of 3D printing technology.

    • >Food Science and Biological Science
    • Advances in research on analysis methods and stability of folic acid in food

      2019, 40(5):446-453. DOI: 10.7535/hbkd.2019yx05010

      Abstract (1412) HTML (0) PDF 317.09 K (1009) Comment (0) Favorites

      Abstract:It is urgently and practically significant to optimize the sample pretreatment, and to establish accurate detection of folic acid content in food and the presence of folic acid, in order to promote the in-depth research of various aspects of folic acid. In the paper, the molecular structure of folic acid and its main forms, as well as the content of folic acid in common foods are introduced. The sample pretreatment methods such as chemical method and enzymatic hydrolysis method are described. It is indicated that the enzymatic hydrolysis method is more suitable for the determination of folic acid in foods such as beans and grains, so that the folic acid combined with protein, starch and the like is fully hydrolyzed by using a combination of protease and amylase. The common methods for detecting folic acid, such as microbial method, fluorescence analysis method and high performance liquid chromatography (HPLC), are reviewed. HPLC is characterized by high efficiency and precision, especially ultra-performance liquid chromatography-mass spectrometry/-mass spectrometry (UPLC-MS/MS), which can quickly determine different forms of folic acid. Factors affecting the stability of folic acid and measures to increase folic acid intake and stability are explored.It shows that the measures to increase folic acid intake and stability includes adding folic acid in staple crops, packaging folic acid with protein capsule, facilitating the combination of folic acid and protein, etc.

    • Advances in microbial antimicrobial peptides expression system and transformation strategy

      2019, 40(5):454-460. DOI: 10.7535/hbkd.2019yx05011

      Abstract (1029) HTML (0) PDF 448.44 K (947) Comment (0) Favorites

      Abstract:In this paper, a review on antimicrobial peptides, including the bioactivity, recombinant expression system and molecular transformation strategy, is provided. The main problems in the fields of antimicrobial peptides are put out,including low antibacterial activity, small productivity, and weak selectivity. It is considered that molecular structure modification is a valid strategy to enhance its antibacterial activity and selectivity. Optimization of recombinant expression system would be the key way to improve productivity. On one hand, the research and development on antibacterial peptides will strengthen the knowledge on the relationship between structure and function, including selectivity, antibacterial activity and toxicity, and the regulation strategies on gene expression system, both of which show significant scientific importance. On the other hand, antimicrobial peptides seldom shows drug resistance because of its antibacterial mechanism, and the research and development on antibacterial peptides will promote greatly its application in the fields of food, pharmaceuticals, cosmetics, and feed industry, etc.

Editor in chief:朱立光


International standard number:ISSN 1008-1542

Unified domestic issue:CN 13-1225/TS

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