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Park, Sangwon,Park, Chulho,Na, Youngsang,Kim, Hyoung-Seop,Kang, Namhyun Elsevier 2019 JOURNAL OF ALLOYS AND COMPOUNDS Vol.770 No.-
<P><B>Abstract</B></P> <P>In this study, we investigated the influence of (W, Cr) carbide on the hardness and tensile properties of friction stir welds (FSWs) for CoCrFeMnNi high entropy alloys. FSW without cracks or voids were achieved for rotational speeds of 400–1000 rpm. As the rotational speed increased, the thinning of the weld thickness compared to the thickness of the base metal was increased. Specifically, an abnormal tornado-shaped region was observed in the stir zone at rotation speeds of 600 rpm and above. The tensile strength increased as the rotation speed increased from 400 to 800 rpm and decreased at a rotation speed of 1000 rpm. The abnormal region with a fine (W, Cr) carbide of 0.5 μm or less was dispersed in the grain boundaries. At a rotation speed of 800 rpm, the dispersion of fine (W, Cr) carbide was optimized to produce grain refinement and maximum tensile strength. However, at 1000 rpm, (W, Cr) carbide coarsened due to high heat input, and the number of carbide particles per unit area decreased, thereby decreasing the hardness and tensile strength.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Friction stir welds without crack or void were achieved for CoCrFeMnNi alloy. </LI> <LI> Fine (W, Cr) carbides of 0.5 μm or less were dispersed in the grain boundaries. </LI> <LI> Dispersion of fine carbides produced grain refinement and maximum tensile strength. </LI> <LI> High heat input decreased the number of carbides per unit area. </LI> <LI> High heat input coarsened (W, Cr) carbides, thereby decreasing the tensile strength. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Photovoltaic effect in a few-layer ReS<sub>2</sub>/WSe<sub>2</sub> heterostructure
Park, Chulho,Duong, Ngoc Thanh,Bang, Seungho,Nguyen, Duc Anh,Oh, Hye Min,Jeong, Mun Seok The Royal Society of Chemistry 2018 Nanoscale Vol.10 No.43
<P>Two-dimensional transition-metal dichalcogenides (TMDCs) are notable materials owing to their flexibility, transparency, and appropriate bandgaps. Because of their unique advantages, TMDC p-n diodes have been studied for next-generation electronics and optoelectronics. However, their efficiency must be increased for commercialization. In this study, we demonstrated a heterostructure composed of few-layer ReS2 and WSe2. This few-layer ReS2/WSe2 heterostructure exhibits a p-n junction and an n-n junction in different gate-bias regimes. In the p-n junction regime, the heterostructure shows outstanding rectification behavior. Additionally, we identify three carrier-transfer mechanisms − direct tunneling, Fowler-Nordheim tunneling, and the space charge region − depending on the drain bias. Furthermore, the photovoltaic effect is observed in this few-layer ReS2/WSe2 heterostructure. As a result, a high fill factor (≈ 0.56), power conversion (≈ 1.5%), and external quantum efficiency (≈ 15.3%) were obtained. This study provides new guidelines for flexible optoelectronic devices.</P>
( Jonghoon Park ),( Yeonhee Park ),( Youngjun Lee ),( Jungwoo Lee ),( Seunghee Lee ),( Chulho Shin ),( Eun-sook Sung ) 한국운동영양학회 2021 Physical Activity and Nutrition (Phys Act Nutr) Vol.25 No.4
[Purpose] This study analyzed data from the 7<sup>th</sup> Korean National Health and Nutrition Examination Survey (2016-2018) to compare the differences in energy intake and physical activity (PA) levels in middle-aged Korean men aged 40-59 years according to household type and the presence of metabolic syndrome (MetS). [Methods] Data from 2,266 young adults (aged >39 years and <60 years) were obtained from the KNHANES. We analyzed the differences in energy intake and PA levels according to household type and MetS. The presence or absence of MetS was determined by measuring waist circumference, blood pressure, fasting blood glucose, triglyceride, and HDL-C levels. [Results] Regarding total nutritional intake, no relationship with MetS was observed regardless of household type (interaction between MetS and household type: p = 0.875). No differences in total PA were observed between multiple- and single-person households (interaction between MetS and household type: p = 0.122). The relationship between MetS and MetS components according to nutritional intake showed that participants with a higher energy intake had a 27% lower prevalence of low high-density lipoprotein cholesterol (HDL-C) (p < 0.05) and a 36% higher prevalence of high blood pressure (p < 0.01). The relationship between MetS and MetS components according to the PA level showed significantly reduced prevalence of MetS by approximately 39%, 35%, and 43% (p < 0.01, 0.01, and 0.001) in subjects who were somewhat active, active, and very active, respectively, compared to inactivity. [Conclusion] Middle-aged men showed no difference in nutritional intake and PA between multiple- and single- person households. However, the risk of MetS was significantly higher in participants with approximately 1.5 times the energy intake compared to the group with the lowest energy intake. Moreover, higher levels of PA had a marked positive effect on the risk factors and prevalence of MetS. Therefore, we suggest that reducing the total energy intake and increasing total PA are important for preventing MetS in middle-aged men regardless of household type.
박철호(Chulho Park),홍성수(Sungsoo Hong),심재홍(Jaehong Sim) 한국정보과학회 1993 한국정보과학회 학술발표논문집 Vol.20 No.2
PCCs(Piecewise Circular Curves)는 기하학적 모델링에서 곡선과 곡면의 교선이나 곡선과 곡선의 교선(intersection) 혹은 곡면과 임의의 점까지의 최단거리를 쉽게 계살할 수 있는 효과적인 알고리즘을 제안한다. 본 논문은 곡면 분할법(subdivision)과 깊이 우선 탐색법(depth first search)을 사용하여 PCCs 곡면간의 교선을 검색할 수 있는 알고리즘을 제안한다. 제시된 알고리즘을 사용하면 곡면과 곡면간의 만나는 교선 전체길이를 쉽게 구할 수 있다.
박철호(Chulho Park),한준(Joon Han),구지선(Jisun Ku),이상훈(Sanghoon Lee),이학연(Hakyeon Lee) 대한산업공학회 2017 대한산업공학회지 Vol.43 No.1
This paper proposes an R&D project selection methodology for green technology centered on developing country-oriented technology commercialization. Eight selection criteria are derived from the R&BD logic model : technology needs of developing countries, effectiveness of green technology, technological potentials, domestic technological capability, commercialization feasibility, economic benefits, business feasibility, and spillover effects of developing countries. 21 qualitative and quantitative indicators are then defined for each criterion. The analytic hierarchy process is conducted to produce relative importance of evaluation indicators and to set final priority scores of R&D project candidates. The working of the proposed methodology is provided with the help of a case study example of Green Technology Center. The proposed methodology is expected to be effectively utilized for policy practices of R&D project selection in the field of green technology.