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김동욱,천지훈,Kim, Donguk,Chun, Jihun 한국통계학회 2016 응용통계연구 Vol.29 No.7
시간의 흐름에 따라 관측되는 경시적(longitudinal) 자료의 경우, 경시적 자료와 생존(survival) 자료가 종종 동시에 수집된다. 이 때 경시적 자료에서 발생하는 결측이 생존자료와의 연관성으로 인해 발생한 무시할 수 없는 결측(non-ignorable missing)이라면, 경시적 자료분석 방법만으로는 두 자료 간의 연관성을 고려하지 않아 독립변수에 대한 효과는 편향된 결과를 얻게 된다. 이러한 문제를 해결하기 위해서 결측의 원인이 생존시간과 연관되어 있으므로 생존모형을 고려하여 불편추정량을 얻기 위해 경시적 자료와 생존자료의 결합모형에 대한 연구가 이루어져 왔다. 본 논문은 경시적 자료의 형태가 영이 많이 존재하는 영과잉 가산자료(zero-inflated count data)와 생존자료의 결합모형을 연구하였다. 경시적 영과잉 가산자료와 생존자료는 각각 허들모형(hurdle model)과 비례위험모형(proportional hazards model)의 부 모형을 적용하였고, 두 부 모형들의 변량효과가 다변량 정규분포를 따른다는 가정을 통하여 결합하였다. 모수의 최우추정법으로 EM 알고리즘을 활용하였고, 추정된 표준오차를 계산하기 위해 프로파일 우도(profile likelihood)를 이용하였다. 최종적으로 모의실험을 통해 두 부 모형의 변량효과 간 상관관계가 존재하는 경우 결합모형이 개별적 모형보다 편의와 포함확률(coverage probability)의 측면에서 더 우수함을 보였다. Both longitudinal data and survival data are collected simultaneously in longitudinal data which are observed throughout the passage of time. In this case, the effect of the independent variable becomes biased (provided that sole use of longitudinal data analysis does not consider the relation between both data used) if the missing that occurred in the longitudinal data is non-ignorable because it is caused by a correlation with the survival data. A joint model of longitudinal data and survival data was studied as a solution for such problem in order to obtain an unbiased result by considering the survival model for the cause of missing. In this paper, a joint model of the longitudinal zero-inflated count data and survival data is studied by replacing the longitudinal part with zero-inflated count data. A hurdle model and proportional hazards model were used for each longitudinal zero inflated count data and survival data; in addition, both sub-models were linked based on the assumption that the random effect of sub-models follow the multivariate normal distribution. We used the EM algorithm for the maximum likelihood estimator of parameters and estimated standard errors of parameters were calculated using the profile likelihood method. In simulation, we observed a better performance of the joint model in bias and coverage probability compared to the separate model.
김동욱(Donguk Kim),이웅근(Woonggeun Lee),박상철(Sangchul Park) (사)한국CDE학회 2020 한국CDE학회 논문집 Vol.25 No.1
Presented in the paper is the framework of an intelligent boiler management system in thermal power generation industry which accounts for more than 60% of the domestic power generation. The power plant boiler is very large in size and very expensive in cost. Even a small damage to the boiler may cause a big disruption to the whole operation of the power plant which may lead to significant economic losses as well as to casualties. Because of this reason, the prognostics and health management of a power plant boiler is very important. For the intelligent management of a boiler, we propose the framework of a software system supporting the health management of a power plant boiler. The propose framework uses a CAD drawing for the intuitive user interface, and supports ten different diagnostic methods. The framework has been implemented and applied to various examples.
AHP기법을 이용한 천연가스 발전소의 최적가용기술의 중요도 선정
김동욱 ( Donguk Kim ),권순길 ( Soongil Kwon ),황용우 ( Yongwoo Hwang ),김영운 ( Youngwoon Kim ) 한국전과정평가학회 2020 한국전과정평가학회지 Vol.21 No.1
최근 국내에서 환경오염시설의 통합관리에 관한 법률이 시행되었다. 통합관리에 따라 사업장의 환경인허가는 2017년 시행된 통합법에 따라 사업장 환경관리수준평가를 통하여 인허가 기간을 5∼8년까지 갱신하게 된다. 이 과정에서 최적가용기법의 적용률을 평가하게 되는데, 높은 평가점수를 받기 위해서 반드시 필요한 부분이다. 하지만 최적가용기법을 평가하는데 있어 사업장의 상황을 고려하지 않는 문제점이 있다. 적용 가능한 최적가용기법을 국내 기준서와 EU 기준서를 조사하여 사업장의 상황에 맞게 전문가들을 대상으로 AHP분석을 실시하여 우선적으로 적용할 기법을 선정하여 우선순위를 마련하였다. Recently, the Act on the Integrated Management of Environmental Pollution Facilities was implemented in Korea. Under the integrated management, the license period of the workplace will be renewed by five to eight years through the assessment of the level of environmental management of the workplace in accordance with the integrated law implemented in 2017. In this process, the application rate of the optimal use technique is evaluated, which is essential to obtain a high evaluation score. However, there is a problem in assessing optimal use techniques without considering the situation at the workplace. An AHP analysis was conducted on experts according to the situation of the workplace by examining the applicable optimal use techniques and the EU standards, and the priority was prepared by selecting the techniques to be applied first.
프로톤 전도성 페로브스카이트 산화물 기반 전기화학전지 개발
김동욱(Donguk Kim),이태경(Tae Kyeong Lee),한승우(Seungwoo Han),최민기(Mingi Choi),이원영(Wonyoung Lee) 한국세라믹학회 2023 세라미스트 Vol.26 No.1
Protonic ceramic cells (PCCs) are environmentally friendly energy conversion devices that operate in the intermediate temperatures due to their high ionic conductivity. This can resolve the drawbacks of solid oxide cells, such as thermochemical, physical, and thermal degradation caused by high operating temperatures. To effectively utilize PCCs as a next generation energy source, the development and optimization of PCC electrolyte materials and manufacturing process of electrochemical device are essential. This review summarizes the current progress, approaches, and challenges of PCCs and offers guidance on material design and manufacturing processes to overcome these difficulties.
김동욱(Donguk Kim) (사)한국CDE학회 2017 한국CDE학회 논문집 Vol.22 No.2
Delaunay refinement algorithm is a classical method to generate quality triangular meshes when point cloud and/or constrained edges are given in two- or three-dimensional space. It computes the Delaunay triangulation for given points and edges to obtain an initial solution, and update the triangulation by inserting steiner points one by one to get an improved quality triangulation. This process repeats until it satisfies given quality criteria. The efficiency of the algorithm depends on the criteria and point insertion method. In this paper, we propose a method to accelerate the Delaunay refinement algorithm by applying geometric hashing technique called bucketing when inserting a new steiner point so that it can localize necessary computation. We have tested the proposed method with a few types of data sets, and the experimental result shows strong linear time behavior.