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SWAT모형을 이용한 유량 및 유사 예측 정확성 평가 및 최적관리 기법 효과 분석
이지민,류지철,강현우,강형식,금동혁,장춘화,최중대,임경재,Lee, Ji-Min,Ryu, Ji-Chul,Kang, Hyun-Woo,Kang, Hyeong-Sik,Kum, Dong-Hyuk,Jang, Chun-Hwa,Choi, Joong-Dae,Lim, Kyoung-Jae 한국농공학회 2012 한국농공학회논문집 Vol.54 No.1
Soil erosion and sediment from agricultural farmland has caused various negative impacts on environment in recent years. The effect of rice straw mat on soil erosion has been investigated by many researchers these days. In this study, the SWAT model was applied to Hongcheon watershed to evaluate SWAT flow and sediment, and the effect of rice straw mat on sediment yield at watershed outlet was evaluated. The Nash-Sutcliffe model efficiency (NSE) and coefficient of determination ($R^2$) values for flow simulation (calibration period) were 0.66 and 0.67, and the NSE values for sediment was 0.90. The calibrated parameters were used to analyze the reduction of sediment yield in the farmland with rice straw mat. Average daily sediment yield without rice straw mat was 49.8 ton/day and sediment yield with rice straw mat was 25.5 ton/day, and the reduction rate was 38.7 %. Also, average daily sediment yield with/without rice straw mat were 97.5 ton/day and 190.7 ton/day during the rainy season (Jun. 2008 - Aug. 2009), with the reduction rate 46.3 %.
이지민,한종주,송영범,함진희,김홍규,황병철,Lee, Ji-Min,Han, Jong-Ju,Song, Young-Beum,Ham, Jin-Hee,Kim, Hong-Kyu,Hwang, Byoungchul 한국재료학회 2018 한국재료학회지 Vol.28 No.8
This paper presents a study of the microstructure and mechanical properties of commercial high-hardness armor (HHA) steels tempered at different temperatures. Although the as-received specimens of all the steels exhibit a tempered martensite structure with lath type morphology, the A steel, which has the smallest carbon content, had the lowest hardness due to reduced solid solution hardening and larger lath thickness, irrespective of tempering conditions. As the tempering temperature increases, the hardness of the steels steadily decreases because dislocation density decreases and the lath thickness of martensite increases due to recovery and over-aging effects. When the variations in hardness plotted as a function of tempering temperature are compared with the hardness of the as-received specimens, it seems that the B steel, which has the highest yield and tensile strengths, is fabricated by quenching, while the other steels are fabricated by quenching and tempering. On the other hand, the impact properties of the steels are affected by specimen orientation and test temperature as well as microstructure. Based on these results, the effect of tempering on the microstructure and mechanical properties of commercial high-hardness armor steels is discussed.
이지민,Lee, Jimin 한국농촌계획학회 2018 농촌계획 Vol.24 No.3
In countries and regions population plays an important role. Recently the importance of population migration increased as population growth slowed. Researches on population migration are mainly focused on the analysis of the population movement factors and the regional structure analysis using the network analysis method. Analysis of regional structure through population movement is not enough to explain the phenomenon of migration of small cities and rural regions. In this study, to overcome the limit of previous studies the characteristics of the population movement rate according to the size of the population were analyzed. Also network analysis using the population movement OD (Origin and Destination) and population movement rate OD were conducted and the results of them were compared. As the results of analysis by the regional population scale, the population movement by population size showed a big difference in the areas with more than 100 thousand people and less than 100 thousand people. Migration to the outside of the province was the most frequent in regions with 30,000~50,000 people. The population migration rate network analysis result showed that the new area with large population inflow capacity was identified, which could not be found in the population movement network analysis because population movement number is small. The population movement rate irate is expected to be used to identify the central regions of the province and to analyze the difference in resident attractiveness.
오스템퍼링 시간에 따른 초고강도 나노 베이나이트강의 미세조직과 기계적 특성
이지민,황병철,Lee, Ji-Min,Hwang, Byoungchul 한국재료학회 2020 한국재료학회지 Vol.30 No.2
This study deals with the effects of austempering time on the microstructure and mechanical properties of ultra-high strength nanostructured bainitic steels with high carbon and silicon contents. The steels are composed of bainite, martensite and retained austenite by austempering and quenching. As the duration of austempering increases, the thickness of bainitic ferrite increases, but the thickness of retained austenite decreases. Some retained austenites with lower stability are more easily transformed to martensite during tensile testing, which has a detrimental effect on the elongation due to the brittleness of transformed martensite. With increasing austempering time, the hardness decreased and then remained stable because the transformation to nanostructured bainite compensates for the decrease in the volume fraction of martensite. Charpy impact test results indicated that increasing austempering time improved the impact toughness because the formation of brittle martensite was prevented by the decreased fraction and increased stability of retained austenite.
등온 열처리에 따른 중탄소 베이나이트강의 미세조직과 기계적 특성
이지민,이상인,임현석,황병철,Lee, Ji-Min,Lee, Sang-In,Lim, Hyeon-Seok,Hwang, Byoungchul 한국재료학회 2018 한국재료학회지 Vol.28 No.9
This study investigates the effects of isothermal holding temperature and time on the microstructure, hardness and Charpy impact properties of medium-carbon bainitic steel specimens. Medium-carbon steel specimens with different bainitic microstructures are fabricated by varying the isothermal conditions and their microstructures are characterized using OM, SEM and EBSD analysis. Hardness and Charpy impact tests are also performed to examine the correlation of microstructure and mechanical properties. The microstructural analysis results reveal that granular bainite, bainitic ferrite, lath martensite and retained austenite form differently in the specimens. The volume fraction of granular bainite and bainitic ferrite increases as the isothermal holding temperature increases, which decreases the hardness of specimens isothermally heat-treated at $300^{\circ}C$ or higher. The specimens isothermally heat-treated at $250^{\circ}C$ exhibit the highest hardness due to the formation of lath martensite, irrespective of isothermal holding time. The Charpy impact test results indicate that increasing isothermal holding time improves the impact toughness because of the increase in volume fraction of granular bainite and bainitic ferrite, which have a relatively soft microstructure compared to lath martensite for specimens isothermally heat-treated at $250^{\circ}C$ and $300^{\circ}C$.
Seismicity of the 2016 ML 5.8 Gyeongju earthquake and aftershocks in South Korea
이지민,류용규,박순천,Young Mo Ham,Jong Soo Park,김명수,Sang Mi Park,Hyen Geom Cho,Keun Su Lee,In Sun Kim,Hye Su Kim,Sunhee Bae 한국지질과학협의회 2018 Geosciences Journal Vol.22 No.3
Since the modern seismograph network by the Korea Meteorological Administration (KMA) had been operated from 1978, the largest earthquake (ML 5.8) occurred in Gyeongju, South Korea on 12 September 2016. ML 5.1 and 5.8 earthquakes occurred successively and damaged mostly old building structures around Gyeongju. Aftershocks continued to occur, clustering around the epicenters of the two events. Number of observed aftershocks with ML ≥ 0.1 was 3,376 from 12 September 2016 to 31 March 2017 and these aftershocks were located by manual procedure. Since the origin time of the ML 5.8 earthquake, 339 and 672 aftershocks (ML ≥ 0.1) occurred on 12 and 13 September 2016, respectively. The occurrence rate of aftershocks decreased exponentially with time after 16 September. It is observed that the seismicity of the 2016 Gyeongju earthquake and aftershock sequences is dominant in the Yangsan Fault System. The distribution of aftershocks is NNE-SSW direction along the Yangsan Fault System, which agrees with the fault plane solutions of main shock and foreshock showing the strike-slip faulting. These aftershocks concentrate within the epicentral distance of 5 km from main shock and the depth distribution of aftershocks is mainly around 11–15 km with vertical trends. With regard to the seismicity of the 2016 Gyeongju earthquake’s aftershocks the full catalog with ML ≥ 1.2 based on Mc is suggested in this study. Finally the distribution of aftershock sequence correlated to the focal mechanisms can provide specific seismicity in the Gyeongsang Basin.
사마륨-코발트 자성 섬유 제조를 위한 환원 거동 연구 및 환원-확산 공정의 최적화
이지민,김종렬,좌용호,Lee, Jimin,Kim, Jongryoul,Choa, Yong-Ho 한국분말야금학회 2019 한국분말재료학회지 (KPMI) Vol.26 No.4
To meet the current demand in the fields of permanent magnets for achieving a high energy density, it is imperative to prepare nano-to-microscale rare-earth-based magnets with well-defined microstructures, controlled homogeneity, and magnetic characteristics via a bottom-up approach. Here, on the basis of a microstructural study and qualitative magnetic measurements, optimized reduction conditions for the preparation of nanostructured Sm-Co magnets are proposed, and the elucidation of the reduction-diffusion behavior in the binary phase system is clearly manifested. In addition, we have investigated the microstructural, crystallographic, and magnetic properties of the Sm-Co magnets prepared under different reduction conditions, that is, $H_2$ gas, calcium, and calcium hydride. This work provides a potential approach to prepare high-quality Sm-Co-based nanofibers, and moreover, it can be extended to the experimental design of other magnetic alloys.