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Zheng Feng Bai,Yu Qiang Liu,Yi Sun 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.2
The effects of clearance on dynamic responses of dual-axis positioning mechanism of a satellite antenna are investigated using a computationalmethodology. Considering clearances in joints, the clearance is defined and the mathematical model of revolute joint withclearance is presented. The normal contact force model and tangential friction model in clearance joint are established using nonlinearcontinuous contact force model and Coulomb friction model, respectively. Then numerical simulation is used to investigate the dynamicresponses of dual-axis positioning mechanism with joint clearance. The results show that clearance has significant effects on dynamicresponses of mechanism, and the investigation of the work can predict the dynamic responses of dual-axis positioning mechanism withclearance preferably, which is the basis of mechanism design, precision analysis and control system design.
Reducing undesirable vibrations of planar linkage mechanism with joint clearance
Zheng Feng Bai,Xin Jiang,Fei Li,Ji Jun Zhao,Yang Zhao 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.2
An optimization design method is presented to reduce the undesirable vibrations caused by clearance for planar linkage mechanism. A clearance joint is defined and considered a contact/impact force constraint. Contact and impact force models for the clearance joint are established using a normal contact force model based on Hertz model with energy loss and a tangential friction model based on modified Coulomb model with dynamic friction coefficient, respectively. In view of the clearance joint, dynamic equations and optimization method for a planar four-bar mechanism are then presented as an application example. The optimization aims to minimize the maximum absolute acceleration peaks of the mechanism by determining the link lengths of the planar linkage mechanism. Finally, the optimization design is solved by a generalized reduced gradient algorithm. Results show evident decrease in vibration peaks of the mechanism and obvious reduction in the contact forces in the clearance joint, which contribute to a good performance of planar linkage mechanism systems.
A FREE BREATHING IMPEDANCE RHEOGRAM APPARATUS MADE OF MICROPROCESSOR
Hua, Feng Jian,Chao, Zhang Xin,Wei, Zheng,Xuan, Jin Pei,Qiou, Bai Yan 대한전자공학회 1992 HICEC:Harbin International Conference on Electroni Vol.1 No.1
The impedance rheogram is a modern non-invasive method used to observe the disease of each part of the body such as heart, liver and lung etc. Because of the breathing interference effect, the patients have to hold their breathing when they are being tested by conventional impedance rheogram apparatus. It is not convenient to observe those patients who are difficult to cooperate with doctor such as children and poor-function-heart patients. Therefore, we have developed the free breathing impedance rheogram apparatus by using microprocessor, it can effectively eliminate the interference of the breathing to impedance rheogram, so that patients can be tested in the free breathing. By this way, it can not only much improve measuring accuracy, and also extend clinical service extant. The digital filtering system that we have developed by using microprocessor is used for automatically tracking variation of rhythm of the heart by specific program and filtering interference of the breathing by in-phase superposing-averaging the impendance signal of the lung in free breathing. The present artical introduces the hardware structure and main technical targets of the free breathing impedance rheogram apparatus, and provides application results for grown-up healthful persons and the patients having heart or lung problems in clinical service. The results show that the effect filtering interference of the breathing to impedance rheogram is very obvious. This technique can be used In impedance rheogram of heart and liver etc, and lays down a foundation for developing monitor in clinical service. In addition, it can also be used in studying of sport-medicine and space-medicine. This result has gotten United States Patent on Jun. 25,1991.
Effect of postharvest dehydration on the microstructure and anthocyanin content of grapes
Wancai Zheng,Aygul Alim,Yujia Bai,Zuoshan Feng,Jianmei Zhang,Na Xia,Zeren Ding 한국원예학회 2021 Horticulture, Environment, and Biotechnology Vol.62 No.3
Postharvest dehydration temperature is important for the quality of grapes, especially the content of anthocyanin. Therefore,this article investigated the changes in the contents of total phenolic and anthocyanin compounds as well as the tissue microstructureof grapes. Furthermore, the correlation between the drying temperature and the total phenolic and anthocyanincompounds was analyzed. The results showed that the total phenol content was 1188.25 ± 37.32 mg/kg in the control groupand 998.13 ± 52.28 mg/kg and 886.00 ± 12.33 mg/kg in the groups treated at 25 °C and 45 °C, respectively, with 60% massloss. The microstructure of the grape peel showed shrinkage, rupture, and collapse with the disappearance of fi ne structuresduring dehydration at diff erent temperatures. The drying temperature was positively correlated with the dehydration rate( p < 0.01, sig = 0.781), which was negatively correlated with the total phenolic content ( p < 0.01, sig = − 0.985). Overall, theresults provide a reliable scientifi c basis for the extraction and utilization of anthocyanins in grapes.
Xinliang Zheng,Juan Feng,Jiarui Zhang,Hongna Xing,Jiming Zheng,Mingzi Wang,Yan Zong,Jintao Bai,Xinghua Li 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2016 NANO Vol.11 No.3
High-quality neodymium oxychlorides nanocrystals with cubic shape were synthesized by a nonhydrolytic thermolysis route. The morphology and crystal structure of the neodymium oxychlorides nanocubes were characterized by transmission electron microscopy at the nanoscale. Transmission electron microscope (TEM) image shows that the neodymium oxychlorides nanocrystals are nearly monodispersed with cube-like shape. X-ray diffraction (XRD) and selected area electron diffraction (SAED) patterns of numerous neodymium oxychlorides nanocubes suggest a pure crystal phase with tetragonal PbFCl matlockite structure. HRTEM image of individual neodymium oxychlorides nanocubes indicate that each nanocubes have a singlecrystalline nature with high quality. Unlike the anti-ferromagnetism of the bulk, the neodymium oxychlorides nanocubes show clearly anomalous ferromagnetic characteristic at room temperature. This finding provides a new platform for the exploration of diluted magnetic semiconductors, rare earth-based nanomaterials and so on.
Jun Duan,Feng Deng,Wan-Shan Li,Xue-Lei Li,Lei-Lei Zheng,Gui-Yuan Li,Yan-Jie Bai 대한치과교정학회 2015 대한치과교정학회지 Vol.45 No.4
Objective: To compare the positions of the mandibular premolars in Angle Class I subjects according to vertical facial type. The results will provide a theoretical basis for predicting effective tooth movement in orthodontic treatment. Methods: Cephalometric parameters were determined using cone-beam computed tomography in 120 Angle Class I subjects. Subjects were categorized as short, normal, and long face types according to the Frankfort mandibular angle. Parameters indicating the position of the mandibular right premolars and the mandible were also measured. Results: The angle between the mandibular first premolar axis and buccal cortex, the distance between the root apex and buccal cortex, angle of vestibularization, arc of vestibularization, and root apex maximum movable distance were significantly greater in the short face type than in the long and norm face types. The angle between the mandibular second premolar axis and buccal cortex, the distance from root apex to buccal cortex, and the arc of vestibularization were significantly greater in the short face type than in the normal face type. Conclusions: There are significant differences in the mandibular premolar positions in Class I subjects according to vertical facial type.
Juan Liu,Feng Gao,Yan Xing,Wenqi Zheng,Yun Bai 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.11
The engineering rock mass is a multi-fracture body crisscrossed by geologic structure planes, and its safety is affected by the rock joints' mechanical properties and morphological features. The joint roughness coefficient (JRC) is a vital characterization method to describe joint surface roughness. Its precise quantization is a crucial factor in predicting shear strength. However, JRCin recent research did not reflect the directional effect of the joint morphology. A new 3D roughness parameter WAD (weighted apparent dip) was proposed to estimate JRC based on the apparent dip angle of the contact unit. The proposed parameter comprehensively reflects the contribution of shear direction and asperity features to the roughness. Based on the ten standard roughness profiles, we investigated the directionality of the WAD and studied the influence of the sampling interval (Sai) on WAD and their correlation with JRC. And the practicability of WAD in evaluating JRC was well verified by the comparison between the indoor test and calculated results with different roughness and shear directions, and the results showed that WAD could accurately estimate the shear strength of the joint rock.