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RISS 인기검색어
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- 저자 : Woonsup Choi (검색결과 6 건)
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Climate Change and Nighttime Heat Stress: Tales of Two Cities in the US Midwest
Woonsup Choi 건국대학교 기후연구소 2018 기후연구 Vol.13 No.3
This study explores nighttime heat stress in two Midwestern regions in the United States, encompassing the cities of Minneapolis and Milwaukee. Daily minimum temperature data were obtained from the MACAv2-METDATA dataset at a 4-km resolution. The dataset was downloaded both for the historical (1950-2005) and Representative Concentration Pathways (RCP) 4.5 (2006-2099) simulations from 11 global climate models. MODIS land cover data at a 5´×5´ resolution were used to delineate urban and non-urban areas. Heat stress was indicated by the occurrence of hot nights in two criterions. First, the number of days with daily minimum temperatures above 300K (27°C) was counted to calculate decadal frequency. Second, the 95th percentile of daily minimum temperatures in the historical period was used as a threshold to calculate the duration of hot nights. The study finds that (1) hot nights (> 300K) are practically non-existent in the historical simulation but are likely to occur typically 2-3 times per decade with the RCP4.5 simulations; (2) the frequency of such events in the future can exceed 25 per decade in urban areas whereas it can be just about 1 per decade in non-urban areas depending on models; and (3) hot nights (> 95th percentile threshold) are likely to last longer in the future simulations. Overall, heat stress is projected to increase both in frequency and duration, and the urban heat island effect in terms of heat stress is projected to intensify in the future.
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Choi, Mihwa,Ahn, Chi-Yeong,Lee, Hyunjoon,Kim, Jong Kwan,Oh, Seung-Hyeon,Hwang, Wonchan,Yang, Seugran,Kim, Jungsuk,Kim, Ok-Hee,Choi, Insoo,Sung, Yung-Eun,Cho, Yong-Hun,Rhee, Choong Kyun,Shin, Woonsup Elsevier 2019 Applied Catalysis B Vol.253 No.-
<P><B>Abstract</B></P> <P>Formic acid is a chemical with a simple molecular structure containing hydrogen. This liquid at room temperature is easy to handle and has a low toxicity, and is thus in the spotlight as a fuel. In particular, formic acid is an excellent fuel candidate because it can be operated at low temperatures when applied as a fuel in fuel cells with a high theoretical open-circuit voltage (1.48 V). However, it has a drawback in that the electrode catalyst is deactivated due to the generation of CO intermediates when formic acid is oxidized during cell operation. Therefore, to prevent this, an irreversibly adsorbed Bi on Pt catalyst is applied to a direct formic acid fuel cell (DFAFC) anode because it is easy to synthesize and economical. Physical analyses such as transmission electron microscopy (TEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA) were conducted, and electrochemical evaluations were performed through half-cell and single-cell level tests. The results revealed that the formic acid oxidation reaction activity of the Bi-modified Pt/C was 13 times higher than that of the conventional catalyst at 0.58 V. Further, a DFAFC stack was fabricated using the Bi-modified Pt/C, which yielded a power of 300 W. These results suggest that a simple synthesis method can be applied to fabricating industrially available DFAFC stacks.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Bi-modified Pt catalyst is applied to a direct formic acid fuel cell (DFAFC) anode. </LI> <LI> Bi was irreversibly adsorbed on Pt catalyst by a simple synthetic strategy. </LI> <LI> Bi-modified Pt/C showed significantly high formic acid oxidation reaction activity. </LI> <LI> A DFAFC stack fabricated using Bi-modified Pt/C yielded a power of 300 W. </LI> <LI> The simple synthetic strategy can be applied to achieving DFAFC stacks commercially. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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Early Summer Dissolved Oxygen Characteristics in Restored Streams in Seoul
Casey Thoenen,Woonsup Choi(최운섭),Jinmu Choi(최진무) 대한지리학회 2013 대한지리학회지 Vol.48 No.3
This paper presents an evaluation of stream restoration projects in Seoul with a focus on dissolved oxygen. Five test sites across four streams were measured for dissolved oxygen (DO) in late May to early June in 2012 and compared against a set of minimum and maximum thresholds. Only one test site, Hwarang-cheon, showed measurements below 6 ㎎/l DO. Towards the upper limit, the Hwarangcheon site was the only tested stream which was not at risk of DO supersaturation. The Danghyeon-cheon site had the highest probability of supersaturation, with DO saturation exceeding 130% expected 86.5% of the time. When measured every hour during daytime, DO levels showed diurnal variations, peaking in the afternoon. However, they showed inconsistent results along transects of the streams. Overall, the streams are rich in DO. To maintain the streams in good standing, nutrient loading should be addressed to prevent potential algal bloom induced hypoxic events down the line.
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Local-scale variability in groundwater resources: Cedar Creek Watershed, Wisconsin, U.S.A.
Han, Weon Shik,Graham, J.P.,Choung, S.,Park, Eungyu,Choi, Woonsup,Kim, Young Sug Elsevier 2018 JOURNAL OF HYDRO-ENVIRONMENT RESEARCH Vol.20 No.-
<P>The steady-state simulation revealed that groundwater head in general was decreased toward the Lake Michigan with local variation caused by stream networks. In response to 2012 drought event, groundwater drawdown was not rehabilitated until spring 2013, implying that the aquifer required approximately 3-4 months until responding to meteorological drought. Additionally, variation in recharge caused to change in groundwater table throughout the entire aquifer simultaneously, but the effect of Lake Michigan stage on groundwater table was relatively minimal. Finally, a certain portion of streams in the Cedar Creek Watershed could be ephemeral. Switching from the RIVER to the DRAIN package for the implementation of ephemeral river and stream cells resulted in significant reduction of both groundwater head and flux, implying that realistic distribution of present groundwater head would resemble one simulated between RIVER and DRAIN packages.</P>
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