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Your search keyword '"Ma, Chunqing"' showing total 124 results
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124 results on '"Ma, Chunqing"'

26. Effects of Hydrogen Bonds between Polymeric Hole-Transporting Material and Organic Cation Spacer on Morphology of Quasi-Two-Dimensional Perovskite Grains and Their Performance in Light-Emitting Diodes

Author

Guan, Zhiqiang, primary, Shen, Dong, additional, Li, Menglin, additional, Ma, Chunqing, additional, Chen, Wen-Cheng, additional, Cui, Xiao, additional, Liu, Bin, additional, Lo, Ming-Fai, additional, Tsang, Sai-Wing, additional, Lee, Chun-Sing, additional, and Zhang, Wenjun, additional

Published
2020
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27. Quantitative fault analysis of roller bearings based on a novel matching pursuit method with a new step-impulse dictionary

Author

Na Wu, Huaqing Wang, Lingli Cui, and Ma Chunqing

Subjects
0209 industrial biotechnology, Accuracy and precision, Engineering, Speech recognition, Aerospace Engineering, 02 engineering and technology, Impulse (physics), 01 natural sciences, law.invention, 020901 industrial engineering & automation, law, 0103 physical sciences, Fault analysis, 010301 acoustics, Civil and Structural Engineering, Bearing (mechanical), business.industry, Mechanical Engineering, Matching pursuit algorithms, Matching pursuit, Computer Science Applications, Stuck-at fault, Control and Systems Engineering, Signal Processing, business, Algorithm
Abstract

A novel matching pursuit method based on a new step-impulse dictionary to measure the size of a bearing׳s spall-like fault is presented in this study. Based on the seemingly double-impact theory and the rolling bearing fault mechanism, a theoretical model for the bearing fault with different spall-like fault sizes is developed and analyzed, and the seemingly double-impact characteristic of the bearing faults is explained. The first action that causes a bearing fault is due to the entry of the roller element into the spall-like fault which can be described as a step-like response. The second action is the exit of the roller element from the spall-like fault, which can be described as an impulse-like response. Based on the quantitative relationship between the time interval of the seemingly double-impact actions and the fault size, a novel matching pursuit method is proposed based on a new step-impulse dictionary. In addition, the quantitative matching pursuit algorithm is proposed for bearing fault diagnosis based on the new dictionary model. Finally, an atomic selection mechanism is proposed to improve the measurement accuracy of bearing fault size. The simulation results of this study indicate that the new matching pursuit method based on the new step-impulse dictionary can be reliably used to measure the sizes of bearing spall-like faults. The applications of this method to the fault signals of bearing outer-races measured at different speeds have shown that the proposed method can effectively measure a bearing׳s spall-like fault size.

Published
2016

28. Quantitative diagnosis of fault severity trend of rolling element bearings

Author

Feibin Zhang, Ma Chunqing, Lingli Cui, and Huaqing Wang

Subjects
Engineering, Bearing (mechanical), Artificial neural network, business.industry, Network packet, Mechanical Engineering, Condition monitoring, Control engineering, Hardware_PERFORMANCEANDRELIABILITY, Fault severity, Industrial and Manufacturing Engineering, Wavelet packet decomposition, law.invention, Wavelet, Control theory, law, Entropy (information theory), business
Abstract

The condition monitoring and fault diagnosis of rolling element bearings are particularly crucial in rotating mechanical applications in industry. A bearing fault signal contains information not only about fault condition and fault type but also the severity of the fault. This means fault severity quantitative analysis is one of most active and valid ways to realize proper maintenance decision. Aiming at the deficiency of the research in bearing single point pitting fault quantitative diagnosis, a new back-propagation neural network method based on wavelet packet decomposition coefficient entropy is proposed. The three levels of wavelet packet coefficient entropy(WPCE) is introduced as a characteristic input vector to the BPNN. Compared with the wavelet packet decomposition energy ratio input vector, WPCE shows more sensitive in distinguishing from the different fault severity degree of the measured signal. The engineering application results show that the quantitative trend fault diagnosis is realized in the different fault degree of the single point bearing pitting fault. The breakthrough attempt from quantitative to qualitative on the pattern recognition of rolling element bearings fault diagnosis is realized.

Published
2015

33. Diagnosis of Roller Bearings Compound Fault Using Underdetermined Blind Source Separation Algorithm Based on Null-Space Pursuit

Author

Ma Chunqing, Lingli Cui, Huaqing Wang, and Chunguang Wu

Subjects
Engineering, Bearing (mechanical), Article Subject, Underdetermined system, Series (mathematics), business.industry, Mechanical Engineering, Geotechnical Engineering and Engineering Geology, Condensed Matter Physics, Fault (power engineering), Differential operator, Signal, Blind signal separation, lcsh:QC1-999, law.invention, Overdetermined system, Mechanics of Materials, law, business, Algorithm, lcsh:Physics, Civil and Structural Engineering
Abstract

In order to solve the problem of underdetermined blind source separation (BSS) in the diagnosis of compound fault of roller bearings, an underdetermined BSS algorithm based on null-space pursuit (NSP) was proposed. In this algorithm, the signal model of faulty roller bearing is firstly used to construct an appropriate differential operator in null space. With the constructed differential operator, the mixed signals collected by the vibration sensor are decomposed into a series of stacks of narrow band signal containing the characteristics of faulty bearing. Finally, the underdetermined problem is transformed to an overdetermined problem by combining the narrow band signals and the original mixed signals into a new group of observed signals. In this way, the separation of the mixed signals can be realized. Experiments and engineering data analyses show that the problem of underdetermined BSS can be solved effectively by this approach, and then the compound fault of the roller bearing can be separated.

Published
2015

36. Magnetic-field-induced dielectric behaviors and magneto-electrical coupling of multiferroic compounds containing cobalt ferrite/barium calcium titanate composite fibers

Author

Zhang, Deqing, primary, Cheng, Junye, additional, Chai, Jixing, additional, Deng, Jiji, additional, Ren, Ran, additional, Su, Yang, additional, Wang, Hao, additional, Ma, Chunqing, additional, Lee, Chun-Sing, additional, Zhang, Wenjun, additional, Zheng, Guang-Ping, additional, and Cao, Maosheng, additional

Published
2018
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44. The application of matching pursuit to extract vibration signalfeature

Author

Na Wu, Lingli Cui, and Ma Chunqing

Subjects
Vibration, Engineering, Signal processing, business.industry, Pattern recognition, Artificial intelligence, Impulse (physics), business, Matching pursuit
Abstract

It has become the main direction equipment fault diagnosis to extract the signal character from the fault vibration signals using signal processing methods in the field of mechanical. This paper compares and analyzes the matching pursuit methods based on the Impulse Time-frequency Dictionary for bearing faults, using the Impulse Time-frequency Single Dictionary (ITSD) and the Impulse Time-frequency Composite Dictionary (ITCD) for decomposition of vibration signal measured by acceleration sensors, respectively. Firstly, two kinds of dictionaries are constructed based on the generation mechanism and characteristics of fault vibration signals of bearing. Then, the analysis results of simulation signals indicated the effectiveness of ITCD, and the impulse or harmonic characteristic components could be separately extracted.

Published
2015

48. Direct observation of cation-exchange in liquid-to-solid phase transformation in FA1−xMAxPbI3 based perovskite solar cells.

Author

Xie, Yue-Min, Yu, Binbin, Ma, Chunqing, Xu, Xiuwen, Cheng, Yuanhang, Yuan, Shuai, Wang, Zhao-Kui, Chandran, Hrisheekesh Thachoth, Lee, Chun-Sing, Liao, Liang-Sheng, and Tsang, Sai-Wing

Abstract

Mixed-organic-cation FA1−xMAxPbI3 perovskites are currently attracting intensive attention for their high photovoltaic performance. However, FA1−xMAxPbI3 usually has an undesired non-perovskite phase leading to a compromised efficiency, and a facile strategy to achieve pure-phase FA1−xMAxPbI3 has been rarely reported. Here, we demonstrate a facile approach to form δ-phase free FA1−xMAxPbI3 using a non-stoichiometric precursor solution. It is found that a small amount of excess methylammonium iodide (MAI) added to the precursor solution has a profound effect on perovskite crystallization during the liquid-to-solid phase transformation. Using an in situ photoluminescence spectroscopy measurement, it is found that the excess MAI can promote the formation of FA1−xMAxPbI3 and facilitate the cation-exchange between organic FA+ and MA+ during the film formation. Based on the optimized pure-phase FA1−xMAxPbI3, the perovskite solar cells exhibit an encouraging power conversion efficiency (PCE) of 17.40%. This study demonstrates a facile method to achieve high performance FA dominating mixed-organic-cation perovskite devices while providing insight into the ion-exchange process during perovskite crystallization. [ABSTRACT FROM AUTHOR]

Published
2018
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49. Air-processed mixed-cation Cs0.15FA0.85PbI3 planar perovskite solar cells derived from a PbI2–CsI–FAI intermediate complex.

Author

Xu, Xiuwen, Ma, Chunqing, Xie, Yue-Min, Cheng, Yuanhang, Tian, Yameng, Li, Menglin, Ma, Yuhui, Lee, Chun-Sing, and Tsang, Sai-Wing

Abstract

Developing facile strategies that enable high-performance perovskite solar cell (PSC) fabrication in ambient air is appealing yet challenging for low-cost and large-scale industrial deployment. However, attempts in this regard are still limited to methylammonium lead triiodide (CH3NH3PbI3), which lags significantly behind the rapid development of the state-of-the-art formamidinium (FA) based mixed perovskites. Here, a PbI2–(CsI)0.15–(FAI)x intermediate complex is proposed to unlock the processing limitation and efficiently facilitate the growth of high-quality mixed-cation Cs0.15FA0.85PbI3 perovskite films in ambient air with relative humidity (RH) as high as 70 ± 10%. It is found that the PbI2–(CsI)0.15–(FAI)x (x = 0.2 to 0.4) intermediate complex consisting of a mixture of composites is favorable for the conversion of PbI2 to high-quality Cs0.15FA0.85PbI3 perovskite. Eventually, it reduces the required FAI concentration deposited on the intermediate for the conversion of PbI2 to perovskite, which allows the strong hygroscopic FAI to be processed in ambient air. With the PbI2–(CsI)0.15–(FAI)0.3 intermediate complex, a low-temperature air-processed planar Cs0.15FA0.85PbI3 PSC achieves a champion power conversion efficiency (PCE) of 15.56% with superior thermal-stability and photo-durability, demonstrating its great potential for the large scale development of PSCs. [ABSTRACT FROM AUTHOR]

Published
2018
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