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Yu, Xiaomei,Wang, Yunfei,Kim, Ansoon,Kim, Yu Kwon Elsevier 2017 Chemical physics letters Vol.685 No.-
<P>TiO2-supported Pt catalysts were prepared for the study of CO oxidation kinetics at reaction conditions of pressures (1-100 Torr) and temperatures (300-500 K). We find two distinct temperature ranges with different reaction kinetics distinguished by an abrupt slope change at around 380 K in the Arrhenius plot only with the excess O-2, not with the stoichiometric O-2/CO ratio. We propose that Pt oxides are formed during the catalytic reactions with increasing temperatures under the oxidizing condition and the origin of the slope change is due to the changes in the reaction pathways of CO oxidation due to the Pt oxide formation. (C) 2017 Elsevier B.V. All rights reserved.</P>
An Improved SPWM Strategy to Reduce Switching in Cascaded Multilevel Inverters
Xiucheng Dong,Xiaomei Yu,Zhiwen Yuan,Yankun Xia,Yu Li 전력전자학회 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.2
The analysis of the switch status of each unit module of a cascaded multi-level inverter reveals that the working condition of the switch of a chopper arm causes unnecessary switching under the conventional unipolar sinusoidal pulse width modulation (SPWM). With an increase in the number of cascaded multilevel inverters, the superposition of unnecessary switching gradually occurs. In this work, we propose an improved SPWM strategy to reduce switching in cascaded multilevel inverters. Specifically, we analyze the switch state of the switch tube of a chopper arm of an H-bridge unit. The redundant switch is then removed, thereby reducing the switching frequency. Unlike the conventional unipolar SPWM technique, the improved SPWM method greatly reduces switching without altering the output quality of inverters. The conventional unipolar SPWM technique and the proposed method are applied to a five-level inverter. Simulation results show the superiority of the proposed strategy. Finally, a prototype is built in the laboratory. Experimental results verify the correctness of the proposed modulation strategy.
An Improved SPWM Strategy to Reduce Switching in Cascaded Multilevel Inverters
Dong, Xiucheng,Yu, Xiaomei,Yuan, Zhiwen,Xia, Yankun,Li, Yu The Korean Institute of Power Electronics 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.2
The analysis of the switch status of each unit module of a cascaded multi-level inverter reveals that the working condition of the switch of a chopper arm causes unnecessary switching under the conventional unipolar sinusoidal pulse width modulation (SPWM). With an increase in the number of cascaded multilevel inverters, the superposition of unnecessary switching gradually occurs. In this work, we propose an improved SPWM strategy to reduce switching in cascaded multilevel inverters. Specifically, we analyze the switch state of the switch tube of a chopper arm of an H-bridge unit. The redundant switch is then removed, thereby reducing the switching frequency. Unlike the conventional unipolar SPWM technique, the improved SPWM method greatly reduces switching without altering the output quality of inverters. The conventional unipolar SPWM technique and the proposed method are applied to a five-level inverter. Simulation results show the superiority of the proposed strategy. Finally, a prototype is built in the laboratory. Experimental results verify the correctness of the proposed modulation strategy.
Graphitization of graphene oxide films under pressure
Chen, Xianjue,Deng, Xiaomei,Kim, Na Yeon,Wang, Yu,Huang, Yuan,Peng, Li,Huang, Ming,Zhang, Xu,Chen, Xiong,Luo, Da,Wang, Bin,Wu, Xiaozhong,Ma, Yufei,Lee, Zonghoon,Ruoff, Rodney S. Elsevier 2018 Carbon Vol.132 No.-
<P><B>Abstract</B></P> <P>Lightweight, flexible graphite foils that are chemically inert, high-temperature resistant, and highly electrically and thermally conductive can be used as component materials in numerous applications. “Graphenic” foils can be prepared by thermally transforming graphene oxide films. For this transformation, it is desirable to maintain a densely packed film structure at high heating rates as well as to lower the graphitizing temperatures. In this work, we discuss the pressure-assisted thermal decomposition of graphene oxide films by hot pressing at different temperatures (<I>i.e.</I>, 300 °C, 1000 °C, or 2000 °C). The films pressed at 1000 °C or 2000 °C were subsequently heated at 2750 °C to achieve a higher degree of graphitization. The combination of heating and pressing promotes the simultaneous thermal decomposition and graphitic transformation of G-O films. Films pressed at 2000 °C as well as films further graphitized at 2750 °C show high chemical purity, uniformity, and retain their flexibility. For films pressed at 2000 °C and then further heated at 2750 °C, the mechanical performances outperform the reported values of the “graphite” foils prepared by calendering exfoliated graphite flakes; the electrical conductivity is ∼3.1 × 10<SUP>5</SUP> S/m and the in-plane thermal conductivity is ∼1.2 × 10<SUP>3</SUP> W/(m·K).</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>