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퍼지논리를 이용한 수평 머시닝 센터의 열변형 오차 모델링
이재하,이진현,양승한,Lee, Jae-Ha,Lee, Jin-Hyeon,Yang, Seung-Han 대한기계학회 2000 大韓機械學會論文集A Vol.24 No.10
As current manufacturing processes require high spindle speed and precise machining, increasing accuracy by reducing volumetric errors of the machine itself, particularly thermal errors, is very important. Thermal errors can be estimated by many empirical models, for example, an FEM model, a neural network model, a linear regression model, an engineering judgment model, etc. This paper discusses to make a modeling of thermal errors efficiently through backward elimination and fuzzy logic strategy. The model of a thermal error using fuzzy logic strategy overcomes limitation of accuracy in the linear regression model or the engineering judgment model. It shows that the fuzzy model has more better performance than linear regression model, though it has less number of thermal variables than the other. The fuzzy model does not need to have complex procedure such like multi-regression and to know the characteristics of the plant, and the parameters of the model can be mathematically calculated. Also, the fuzzy model can be applied to any machine, but it delivers greater accuracy and robustness.
이재하(Lee Jae Ha) 한국지역개발학회 1994 韓國地域開發學會誌 Vol.6 No.2
The central government of Korea in 1994 promotes the consolidation of city(Shi) and county(Gun) which are separate local administrative district. The consolidation of such administrative district has a profound effect upon daily life of residents, equity of administration, regional balanced development, and conservation of natural environment in a administrative region. From this point of view, this paper examines the consolidation of city and county from the perspective of related urban and regional development theories such as growth center, agropolitan development, optimal size of city as well as urban and regional sustainable development, and discusses its reasonable alternative. It is evaluated that the simple consolidation of city and county without consideration of size and function of each administrative district has a negative effect upon equity of administration, regional balanced development and conservation of natural environment. As an alternative, it is suggested that the desirable consolidation of city and county should be accomplished between cities of less than population 200,000 and counties of less than 100,000.
이재하 ( Lee Jae Ha ),한덕희 ( Han Deog Hui ) 한국파생상품학회 2002 선물연구 Vol.10 No.2
This study explores hedging strategies that use the KTB futures to hedge the price risk of the KTB spot portfolio. The study establishes the price sensitivity, risk-minimization, bivariate GARCH(1,1) models as hedging models, and analyzes their hedging performances. The sample period covers from September 29, 1999 to September 18, 2001. Time-matched prices at 11:00(11:30) of the KTB futures and spot were used in the analysis. The most important findings may be summarized as follows. First, while the average hedge ration of the price sensitivity model is close to one, both the risk-minimization and GARCH model exhibit hedge ratios that are substantially lower than one. Hedge rarios tend to be greater for daily data than for weekly data. Second, for the daily in-sample data, hedging effectiveness is the highest for the GARCH model with time-varying hedge ratios, but the risk-minimization model with constant hedge ratios is not far behind the GARCH model in its hedging performance. In the case of out-of-sample hedging effectiveness, the GARCH model is the best for the KTB spot portfolio, and the risk-minimization model is the best for the corporate bond portfolio. Third, for daily data, the in-sample hedge shows a better performance than the out-of-sample hedge, except for the risk-minimization hedge against the corporate bond portfolio. Fourth, for the weekly in-sample hedges, the price sensitivity model is the worst and the risk-minimization model is the best in hedging the KTB spot portfolio. While the GARCH model is the best against the KTB +corporate bond portfolio, the risk-minimization model is generally as good as the GARCH model. The risk-minimization model performs the best for the weekly out-of-sample data, and the out-of-sample hedges are better than the in-sample hedges. Fifth, while the hedging performance of the risk-minimization model with daily moving window seems somewhat superior to the traditional risk-minimization model when the trading volume increased one year after the inception of the KTB futures, on the average the traditional model is better than the moving-window model. For weekly data, the traditional model exhibits a better performance. Overall, in the Korean bond markets, investors are encouraged to use th simple risk-minimization model to hedge the price risk of the KTB spot and corporate bond portfolios.