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- 저자 : Xiaoxin Wu (검색결과 6 건)
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Narrowing the gap: a Chinese experience of teacher rotation
Wu Xiaoxin 서울대학교 교육연구소 2020 Asia Pacific Education Review Vol.21 No.3
In an effort to equalize the quality of teacher resources across all state schools in the compulsory education sector of China and eliminate the school choice phenomenon, the Chinese government has launched a nationwide program of rotating principals and teachers. This study has revealed mixed results to date. While the rotation of teachers has helped to narrow the gap in teacher quality between the low-performing and high-performing schools, the study has revealed some important issues that need to be addressed, such as conflict of goals, ineffective incentives, and rotation for rotation’s sake. Whether such a Robin Hood method of “robbing the rich in order to help the poor” can consistently raise the quality of teacher resources and improve the overall quality of education across the whole country remains to be seen.
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Model-free predictive current control for IPMSMs with multiple current difference updating technique
Wu, Xiaoxin,Zhu, Zhihao,Liu, Xing,Yu, Feng The Korean Institute of Power Electronics 2021 JOURNAL OF POWER ELECTRONICS Vol.21 No.3
This paper proposes a model-free predictive current control (MFPCC) for interior permanent magnet synchronous motors (IPMSMs) with a multiple current difference updating (MCDU) technique. Firstly, to improve robustness against machine parameter variations and reduce the computational burden, current difference-based prediction that only requires accumulation operation is implemented, which avoids the model-based complex calculations in traditional model predictive current control (MPCC). Secondly, a MCDU technique is conducted with the characteristic of updating the current differences associated with voltage vectors in opposite directions. Thus, the updating frequency of the current difference can be significantly increased. Finally, the effectiveness of the proposed method is verified by simulation and experimental results.
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An Improved Model Predictive Direct Torque Control for Induction Machine Drives
Wenxiang Song,Shengkang Le,Xiaoxin Wu,Yi Ruan 전력전자학회 2017 JOURNAL OF POWER ELECTRONICS Vol.17 No.3
The conventional model predictive direct torque control (MPDTC) method uses all of the voltage vectors available from a two level voltage source inverter for the prediction of the stator flux and stator current, which leads to a heavy computational burden. This paper proposes an improved model predictive direct torque control method. The stator flux predictive controller is obtained from an analysis of the relationship between the stator flux and the torque, which can be used to calculate the desired voltage vector based on the stator flux and torque reference. Then this method only needs to evaluate three voltage vectors in the sector of the desired voltage vector. As a result, the computational burden of the conventional MPDTC is effectively reduced. The time delay introduced by the computational time causes the stator current to oscillate around its reference. It also increases the current and torque ripples. To address this problem, a delay compensation method is adopted in this paper. Furthermore, the switching frequency of the inverter is significantly reduced by introducing the constraint of the power semiconductor switching number to the cost function of the MPDTC. Both simulation and experimental results are presented to verify the validity and feasibility of the proposed method.
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An Improved Model Predictive Direct Torque Control for Induction Machine Drives
Song, Wenxiang,Le, Shengkang,Wu, Xiaoxin,Ruan, Yi The Korean Institute of Power Electronics 2017 JOURNAL OF POWER ELECTRONICS Vol.17 No.3
The conventional model predictive direct torque control (MPDTC) method uses all of the voltage vectors available from a two level voltage source inverter for the prediction of the stator flux and stator current, which leads to a heavy computational burden. This paper proposes an improved model predictive direct torque control method. The stator flux predictive controller is obtained from an analysis of the relationship between the stator flux and the torque, which can be used to calculate the desired voltage vector based on the stator flux and torque reference. Then this method only needs to evaluate three voltage vectors in the sector of the desired voltage vector. As a result, the computational burden of the conventional MPDTC is effectively reduced. The time delay introduced by the computational time causes the stator current to oscillate around its reference. It also increases the current and torque ripples. To address this problem, a delay compensation method is adopted in this paper. Furthermore, the switching frequency of the inverter is significantly reduced by introducing the constraint of the power semiconductor switching number to the cost function of the MPDTC. Both simulation and experimental results are presented to verify the validity and feasibility of the proposed method.
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Zuo, Chaohui,Xia, Man,Liu, Jingshi,Qiu, Xiaoxin,Lei, Xiong,Xu, Ruocai,Liu, Hanchun,Li, Jianliang,Li, Yongguo,Li, Qinglong,Xiao, Hua,Hong, Yuan,Wang, Xiaohong,Zhu, Haizhen,Wu, Qunfeng,Burns, Michael,Li Asian Pacific Journal of Cancer Prevention 2015 Asian Pacific journal of cancer prevention Vol.16 No.1
Objectives: Intrahepatic recurrence is the major cause of death among patients with hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC) after curative surgical resection. Several approaches have been reported to decrease the recurrence rate. The objective of our study was to compare the clinical effects of transcatheter arterial chemoembolization (TACE) combined with interferon-alpha (IFN-${\alpha}$) therapy on recurrence after hepatic resection in patients with HBV-related HCC with that of TACE chemotherapy alone. Methods: We retrospectively analyzed the data from 228 patients who were diagnosed with HBV-related HCC and underwent curative resection between January 2001 to December 2008. The patients were divided into TACE (n = 126) and TACE-IFN-${\alpha}$ (n = 102) groups for postoperative chemotherapy. The TACE regimen consisted of 5-fluorouracil (5-FU), cisplatin (DDP), and the emulsion mixed with mitomycin C (MMC) and lipiodol. The recurrence rates, disease-free survival (DFS), overall survival (OS), and risk of recurrence were evaluated. Results: The clinicopathological parameters and adverse effects were similar between the 2 groups (P > 0.05). The median OS for the TACE-IFN-${\alpha}$ group (36.3 months) was significantly longer than that of the TACE group (24.5 months, P < 0.05). The 3-and 5-year OS for the TACE-IFN-${\alpha}$ group were significantly longer than those of the TACE group (P < 0.05) and the recurrence rate was significantly lower (P < 0.05). The TACE and IFN-${\alpha}$ combination therapy, active hepatitis HBV infection, the number of tumor nodules, microvascular invasion, liver cirrhosis, and the BCLC stage were independent predictors of OS and DFS. Conclusions: The use of the TACE and IFN-${\alpha}$ combination chemotherapy after curative hepatic resection safely and effectively improves OS and decreases recurrence in patients with HBV-related HCC who are at high risk. Our findings can serve as a guide for the selection of postoperative adjuvant chemotherapy for patients with HBV-related HCC who are at high risk of recurrence.
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