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효과적인 시계열 데이터 분류를 위한 동적시간왜곡 기반의 시계열 길이 변환
이환철,허선 대한산업공학회 2020 대한산업공학회지 Vol.46 No.4
Time series data produced from various sensors are mostly different from each other in length due to various environment of collection. Most time series classification methods, however, assume that the lengths of time series data are the same. There is no alternative, moreover, for variant-length time series classification except DTW and DTW-related methods and few researches on transformation of time series length can be found in direct ways. In this paper, we propose a length transformation method for effective variant-length time series classification. Proposed method is a similarity-preserving transformation and the restoration is possible. To evaluate the proposed method, experiments are conducted to compare the classification performance by applying well-known methods to the time series data before and after the transformation. The classification using the dataset transformed by the proposed method shows better performance on almost all measurements.
Exploring the Future Direction of Math Education in AlgeoMath
이환철 영남수학회 2019 East Asian mathematical journal Vol.35 No.4
The Korea Foundation for the Advancement of Science and Creativity(KOFAC) developed AlgeoMath, a dynamic geometry software, with support from the Ministry of Education and 17 municipal and provincial education offices. Starting Nov. 7, 2018, AlgeoMath can be used for free by anyone. This study summarizes various discussions on the future direction of math education. The four aspects of the curriculum, textbook, teaching and learning, and assessment were explored on how AlgeoMath could contribute in realizing the future direction of math education. We confirmed that AlgeoMath can faithfully fulfill its role as a tool for changing math education, and we looked at what should be emphasized more and what should be complemented.
이환철,양재웅,안재우 대진대학교 1995 大眞論叢 Vol.3 No.-
The etching characteristics of r.f.-sputtered permalloy magnetic thin films using ion beam apparatus are investigated. The process parameters investigated during ion beam etching are accelerating voltage, beam voltage and beam current. The etch rate of the permalloy films is proportion to the beam current, but it is not directly related to the accelerating voltage and beam voltage. The dependence of etch rate on the process parameters can be explained by the ion beam current density. It is found that the ion beam etching is on effective method in obtaining well-developed micropatterns on the permalloy thin films.
이환철,이재헌,Hwan Cheol Lee,Jae-Heon Lee 한국플랜트학회 2023 플랜트 저널 Vol.18 No.4
In this study, to increase the methane content of biogas supplied from Nanji Water Regeneration Center and to purify impurities, a three-stage membrane purification process was designed and installed to demonstrate operation. The methane concentration of biomethane produced in the 2 Nm3/h purification process was set to three cases: 95%, 96.5%, and 98%, and the membrane area ratio of the membrane was 1:1, 1:2, 1:1:1, The optimum conditions for the membrane area of the separator were derived by changing to five of 1:2:1 and 1:2:2. 3 stage separation membrane process of 30 Nm3/h was installed to reflect the optimum condition of 2 Nm3/h, and biomethane production of 98% or more of methane concentration was demonstrated. As a result of the operation of the 2 Nm<sup>3</sup>/h refining device, the methane recovery rate at the 98% methane concentration was 95.6% when the membrane area ratio was 1:1 as the result of the two-stage operation of the separator, and the recovery rate of methane at 1:2 was increased to 96.8%. The methane recovery rate of the membrane three-stage operation was highest at 96.8% when the membrane area ratio was operated at 1:2:1. The carbon dioxide removal rate was 16.4 to 96.4% and the 2:2 to 95.7% film area ratio in the two-step process. In the three-step process, the film area ratio was 1:2:1 to 95.4%, and the two-step process showed higher results than the three-step process. In the 30 Nm3/h scale biogas purification demonstration operation, the methane concentration after purification was 98%, the recovery rate of methane was 97.1%, the removal rate of carbon dioxide was 95.7%, and hydrogen sulfide, the cause of corrosion, was not detected, and the membrane area ratio was 1:2:1 demonstration operation, biomethane production with a methane concentration of 98% or higher was possible.