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Ha-Linh Quach,Thai Quang Pham,Ngoc-Anh Hoang,Dinh Cong Phung,Viet-Cuong Nguyen,Son Hong Le,Thanh Cong Le,Dang Hai Le,Anh Duc Dang,Duong Nhu Tran,Nghia Duy Ngu,Florian Vogt,Cong-Khanh Nguyen 대한의료정보학회 2022 Healthcare Informatics Research Vol.28 No.4
Objectives: Online misinformation has reached unprecedented levels during the coronavirus disease 2019 (COVID-19) pandemic. This study analyzed the magnitude and sentiment dynamics of misinformation and unverified information about public health interventions during a COVID-19 outbreak in Da Nang, Vietnam, between July and September 2020. Methods: We analyzed user-generated online information about five public health interventions during the Da Nang outbreak. We compared the volume, source, sentiment polarity, and engagements of online posts before, during, and after the outbreak using negative binomial and logistic regression, and assessed the content validity of the 500 most influential posts. Results: Most of the 54,528 online posts included were generated during the outbreak (n = 46,035; 84.42%) and by online newspapers (n = 32,034; 58.75%). Among the 500 most influential posts, 316 (63.20%) contained genuine information, 10 (2.00%) contained misinformation, 152 (30.40%) were non-factual opinions, and 22 (4.40%) contained unverifiable information. All misinformation posts were made during the outbreak, mostly on social media, and were predominantly negative. Higher levels of engagement were observed for information that was unverifiable (incidence relative risk [IRR] = 2.83; 95% confidence interval [CI], 1.33–0.62), posted during the outbreak (before: IRR = 0.15; 95% CI, 0.07–0.35; after: IRR = 0.46; 95% CI, 0.34-0.63), and with negative sentiment (IRR = 1.84; 95% CI, 1.23–2.75). Negatively toned posts were more likely to be misinformation (odds ratio [OR] = 9.59; 95% CI, 1.20–76.70) or unverified (OR = 5.03; 95% CI, 1.66–15.24). Conclusions: Misinformation and unverified information during the outbreak showed clustering, with social media being particularly affected. This indepth assessment demonstrates the value of analyzing online “infodemics” to inform public health responses.
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Novel Single-State PWM Technique for Common-Mode Voltage Elimination in Multilevel Inverters
Nguyen, Nho-Van,Quach, Hai-Thanh,Lee, Hong-Hee The Korean Institute of Power Electronics 2012 JOURNAL OF POWER ELECTRONICS Vol.12 No.4
In this paper, a novel offset-based single-state pulse width modulation (PWM) method for achieving zero common-mode voltage (CMV) and reducing switching losses in multilevel inverters is presented. The specific active switching state of the zero common-mode (ZCM) voltage that approximates the reference voltage can be deduced from the switching state sequence of the reduced CMV phase disposition PWM (CMV PD PWM) method. From the reference leg voltages for the zero common-mode voltage, an N-to-2-level transformation defines a virtual two-level inverter and the corresponding nominal leg voltage references. The commutation process of the reduced CMV PD PWM method in a multilevel inverter and its outputs can be simply followed in a nominal switching time diagram for the virtual inverter. The characteristics of the reduced CMV PD PWM and the single-state PWM for zero common-mode voltage are analyzed in detail in this paper. The theoretical analysis of the proposed PWM method is verified by experimental results.
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Novel Single-State PWM Technique for Common-Mode Voltage Elimination in Multilevel Inverters
Nho-Van Nguyen,Hai-Thanh Quach,Hong-Hee Lee 전력전자학회 2012 JOURNAL OF POWER ELECTRONICS Vol.12 No.4
In this paper, a novel offset-based single-state pulse width modulation (PWM) method for achieving zero common-mode voltage (CMV) and reducing switching losses in multilevel inverters is presented. The specific active switching state of the zero common-mode (ZCM) voltage that approximates the reference voltage can be deduced from the switching state sequence of the reduced CMV phase disposition PWM (CMV PD PWM) method. From the reference leg voltages for the zero common-mode voltage, an N-to-2-level transformation defines a virtual two-level inverter and the corresponding nominal leg voltage references. The commutation process of the reduced CMV PD PWM method in a multilevel inverter and its outputs can be simply followed in a nominal switching time diagram for the virtual inverter. The characteristics of the reduced CMV PD PWM and the single-state PWM for zero common-mode voltage are analyzed in detail in this paper. The theoretical analysis of the proposed PWM method is verified by experimental results.
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Carrier Based Single-State PWM Technique for Minimizing Vector Errors in Multilevel Inverters
Nguyen Van Nho,Quach Thanh Hai,Hong-Hee Lee 전력전자학회 2010 JOURNAL OF POWER ELECTRONICS Vol.10 No.4
In this paper, a novel analysis of a carrier based PWM method for multilevel inverters is presented. The space vector PWM and carrier based PWM correlations in multilevel inverters are investigated in a nominal two-level switching diagram. The obtained results can be applied to design various carrier PWM techniques. In this paper, a carrier based single-state PWM technique, which reduces the switching number and optimizes the active voltage errors, is presented. This PWM technique can be advantageous if there are a large number of levels. The proposed method is mathematically formulated and demonstrated by simulations and experimental results.
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Carrier Based Single-State PWM Technique for Minimizing Vector Errors in Multilevel Inverters
Nho, Nguyen Van,Hai, Quach Thanh,Lee, Hong-Hee The Korean Institute of Power Electronics 2010 JOURNAL OF POWER ELECTRONICS Vol.10 No.4
In this paper, a novel analysis of a carrier based PWM method for multilevel inverters is presented. The space vector PWM and carrier based PWM correlations in multilevel inverters are investigated in a nominal two-level switching diagram. The obtained results can be applied to design various carrier PWM techniques. In this paper, a carrier based single-state PWM technique, which reduces the switching number and optimizes the active voltage errors, is presented. This PWM technique can be advantageous if there are a large number of levels. The proposed method is mathematically formulated and demonstrated by simulations and experimental results.
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