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최재석,유대석,최연희,연규환,홍경식,이병회,김혜진,김현기,김은주,노성환,정영철,김영섭,유시용,Choi, Jae-Seok,Yoo, Dae-Seok,Choi, Yeon-Hee,Yon, Gyu-Hwan,Hong, Kyung-Sik,Lee, Byung-Hoe,Kim, Hye-Jin,Kim, Hyun-Ki,Kim, Eun-Ju,Roh, Seong-Hwan,Jeong 한국생약학회 2007 생약학회지 Vol.38 No.2
We investigated the contents of crude saponin in the decoctions of Platycodi Radix prepared by the different extraction processes. Each lyophilized decoctions prepared by the different protocol were suspended in water and partitioned with ethylacetate (EtOAc) and n-butanol (BuOH), which gave the EtOAc fraction, BuOH fraction and the remaining water fraction, respectively. The content of crude saponin, which was estimated as the amount of BuOH fraction, and the HPLC profiles of the BuOH fraction were analyzed, and compared each others. The crude saponin content in the decoctions were increased proportionally to the increment of the extraction time, amount of water, extraction temperature and the number of repetition for extraction. Consequently, the optimized conditions were deduced to be suitable and recommendable for the preparation of Platycodi Radix ; the water amount needed for the extraction be 15-20 volumes to crude material, temperature for extraction be optimal at $85{\sim}100^{\circ}C$, extraction time be more than 5 hours and the repetition of extraction was 2 times.
데이터마이닝을 이용한 학자금 대출 부실 고위험군 예측모형 개발
최재석,한준태,김면중,정진아,Choi, Jae-Seok,Han, Jun-Tae,Kim, Myeon-Jung,Jeong, Jina 한국데이터정보과학회 2015 한국데이터정보과학회지 Vol.26 No.6
We develop the high risk group predictive model for loan default by utilizing the direct loan data from 2012 to 2014 of the Korea Student Aid Foundation. We perform the decision tree analysis using the data mining methodology and use SAS Enterprise Miner 13.2. As a result of this model, subject types were classified into 25 types. This study shows that the major influencing factors for the loan default are household income, national grant, age, overdue record, level of schooling, field of study, monthly repayment. The high risk group predictive model in this study will be the basis for segmented management service for preventing loan default. 본 연구는 한국장학재단의 2012-2014년간 일반 학자금 대출 자료를 활용하여 부실채권 보유 및 신용유의자로 분류될 수 있는 위험요인들을 파악하고, 부실 고위험군 예측모형을 개발했다. 예측모형 개발은 데이터마이닝 방법 중 의사결정나무 분석을 적용하였으며, 분석 패키지는 SAS Enterprise Miner 13.2를 활용했다. 개발된 모형은 25가지의 그룹으로 세분화 했으며, 부실 위험군에 영향을 미치는 주요 요인은 소득분위, 국가장학금 수혜유무, 나이, 연체계좌 보유 이력, 대학구분 (학부/대학원), 전공 계열, 월평균 상환액이 주요 요인으로 나타났다. 본 연구에서 개발된 부실 고위험군 예측모형은 장기연체로 인한 부실채권 발생 및 신용유의자 발생 예방을 위한 세분화된 관리서비스 제공을 위한 기초자료가 될 수 있을 것이다.
최재석(Jae Seok Choi),유정훈(Jeonghoon Yoo) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11
Eddy current is usually generated in material with high conductivity by time-varying source such as AC current and also is induced in the moving source with relative velocity. The contactless magnetic brakes make use of the braking force from the eddy current generated by moving source and currently used for the secondary brakes of heavy trucks, buses and rail vehicles. This study aims to design the magnetization pattern of a permanent magnet type eddy current brake system to maximize the braking force. The analysis of the brake system is based on the two-dimensional finite element analysis. We use the sequential linear programming as the optimizer and the adjoint variable method for the sensitivity analysis.
최재석(Jae Seok Choi),유정훈(Jeonghoon Yoo),홍상준(Sang-Joon Hong),김태현(Tae-Hyun Kim),이성진(Sung Jin Lee) 한국자동차공학회 2005 한국자동차공학회 Symposium Vol.- No.-
Generally, Johnsen-Rahbek(J-R) type electrostatic chuck(ESC) generates higher attractive force than Coulomb type ESC. The attractive force in J-R type ESe is caused by the high electrical resistance which occurs in contact region between semiconductor wafer and dielectric layer. This research tries the simple geometrical modeling of contact surface and simulates contact resistance, attractive force and response time according to the variation of contact surface shape. In the latter half of this research, the simulation for pin chuck is accomplished using similar surface modeling and the comparison between pin chuck and general flat chuck is made in aspects of the attractive force and the response time.
최재석(Jae Seok Choi),유정훈(Jeonghoon Yoo) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
This study tries to design Halbach magnet array using numerical optimization techniques based on the two-dimensional finite element analysis. Optimization problems with various objectives are introduced and design variables are defined as the magnetization direction of each element in the design domain. It is interesting that the base magnet array of all optimized results is equivalent to the Halbach array without any exception. The optimal magnet arrays composed of two linear magnet layers are investigated to maximize the magnetic force between magnet layers. The optimization procedure is constructed by using the sequential linear programming and the adjoint variable method.