• Journal of the Korean Data and Information Science Society
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• 제24권4호
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• pp.919-929
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• 2013

We compared two basic methods, combine-accumulate method and accumulate-combine method, using the past quality information in multivariate quality control procedure for monitoring mean vector of multivariate normal process. When small or moderate shifts have occurred, accumulate-combine method yields smaller average run length (ARL) and average time to signal (ATS) than combine-accumulate method. On the other hand, we have found from our numerical results that combine-accumulate method has better performances in terms of switching behavior than accumulate-combine method. In industry, a quality engineer could select one of the two method under the comprehensive consideration about the required time to signal, switching behavior, and other physical factors in the production process.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1996년도 Proceedings of the Korea Automatic Control Conference, 11th (KACC); Pohang, Korea; 24-26 Oct. 1996
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• pp.18-18
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• 1996

This paper reviews some of the most prominent and promising areas of chemical process control both in relations to batch and continuous processes. These areas include the modeling, optimization, control and monitoring of chemical processes and entire plants. Most of these areas explicitly utilize a model of the process. For this purpose the types of models used are examined in some detail. These types of models are categorized in knowledge-driven and datadriven classes. In the areas of modeling and optimization, attention is paid to batch reactors using the Tendency Modeling approach. These Tendency models consist of data- and knowledge-driven components and are often called Gray or Hybrid models. In the case of continuous processes, emphasis is placed in the closed-loop identification of a state space model and their use in Model Predictive Control nonlinear processes, such as the Fluidized Catalytic Cracking process. The effective monitoring of multivariate process is examined through the use of statistical charts obtained by the use of Principal Component Analysis (PMC). Static and dynamic charts account for the cross and auto-correlation of the substantial number of variables measured on-line. Centralized and de-centralized chart also aim in isolating the source of process disturbances so that they can be eliminated. Even though significant progress has been made during the last decade, the challenges for the next ten years are substantial. Present progress is strongly influenced by the economical benefits industry is deriving from the use of these advanced techniques. Future progress will be further catalyzed from the harmonious collaboration of University and Industrial researchers.

• 대한조선학회논문집
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• 제55권6호
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• pp.505-513
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• 2018

Main engine failures in ship operations can lead to a major damage in terms of the vessel itself and the financial cost. In this respect, monitoring of a vessel's main engine condition is crucial in ensuring the vessel's performance and reducing the maintenance cost. The collection of a huge amount of vessel operational data in the maritime industry has never been easier with the advent of advanced data collection technologies. Real-time monitoring of the condition of a vessel's main engine has a potential to create significant value in maritime industry. This study presents a case study on the establishment of upper control limit to detect vessel's main engine failures using multivariate control chart. The case study uses sample data of an ocean-going vessel operated by a major marine services company in Korea, collected in the period of 2016.05-2016.07. This study first reviews various main engine-related variables that are considered to affect the condition of the main engine, and then attempts to detect abnormalities and their patterns via multivariate control charts. This study is expected to help to enhance the vessel's availability and provide a basis for a condition-based maintenance that can support proactive management of vessel's main engine in the future.

• Journal of the Korean Data and Information Science Society
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• 제28권2호
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• pp.451-459
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• 2017

There are many researches showing that when a process change has occurred, variable sampling intervals (VSI) control chart is better than the fixed sampling interval (FSI) control chart in terms of reducing the required time to signal. When the process engineers use VSI control procedure, frequent switching between different sampling intervals can be a complicating factor. However, average number of samples to signal (ANSS), which is the amount of required samples to signal, and average time to signal (ATS) do not provide any control statistics about switching performances of VSI charts. In this study, we evaluate numerical switching performances of multivariate VSI EWMA chart including average number of switches to signal (ANSW) and average switching rate (ASWR). In addition, numerical study has been carried out to examine how to improve the performance of considered chart with accumulate-combine approach under several different smoothing constant and sample size. In conclusion, process engineers, who want to manage the correlation coefficients of related quality variables, are recommended to make sample size as large and smoothing constant as small as possible under permission of process conditions.

• Asian Pacific Journal of Cancer Prevention
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• 제14권10호
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• pp.6109-6114
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• 2013

Aim: To determine whether beta-blockers (BBs) improve the overall survival (OS) of patients with metastatic non-small cell lung cancer (NSCLC). Materials and Methods: The medical charts of 107 patients with metastatic NSCLC were retrospectively assessed. Thirty-five patients (BB group) using BBs during chemotherapy (CT) were compared with 72 controls [control=(C) group] who did not use BBs following the diagnosis of NSCLC. The histological tumor subtype, performance status (ECOG), age, gender, smoking status, comorbidities, other medications and chemotherapeutics that were received in any line of treatment were recorded. We compared the overall survival (OS) of the patients in the BB and C groups. Results: The mean age of the patients was 61 years (range 42-81 years) and all patients were administered CT. The BB group was more likely to have HT and IHD and was more likely to use RAS blockers (p<0.01 for all) compared with the C group, as expected. The mean follow-up time was 17.8 months (range 1-102 months) for the entire group. The most commonly prescribed BB agent was metoprolol (80% of cases). At the time of the analysis, 74 (69%) of all patients had died. In the univariate analysis the median overall survival (OS) was 19.25 (${\pm}2.87$) months (95%CI: 13.62-24.88) in the BB group and 13.20 (${\pm}2.37$) months (95%CI: 8.55-17.85) in the C group (p=0.017). However, the benefit of BBs on survival disappeared in the multivariate analysis. Conclusions: The use of BBs during CT may be associated with an improved OS for patients with metastatic NSCLC.

• Journal of the Korean Data and Information Science Society
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• 제26권6호
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• pp.1353-1366
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• 2015

공정의 안정성을 평가하기 위해 사용되는 Shewhart 관리도 기법은 최근 다양한 분야에서 널리 응용되고 있지만, 품질 특성치에 대한 엄격한 확률분포를 가정한다. 하지만 현업에서 수집되고 있는 데이터의 확률분포는 알려진 경우가 많지 않으며, 다변량 데이터로 확장될수록 확률분포를 결정하는데 더 큰 어려움이 따른다. 이러한 문제점을 해결하기 위해 다양한 비모수 관리도 기법이 연구되었는데, 최근 연구되고 있는 비모수 관리도 기법 중 하나인 RBF (Radial Basis Function) 커널 기반의 SVDD (Support Vector Data Description) 관리도는 관리상태 하의 데이터 영역에 대한 경계를 결정함으로써 공정의 이상상태를 탐지하는 기법으로 K 관리도로 불리우며, 다양한 분야에서 적용되고 있다. 그런데 K 관리도를 적용하기 위해서는 관리도의 성능을 결정짓는 커널모수 등의 선택이 중요하며, 관리도를 작성하기 전에 미리 결정되어야 한다. 이를 위해 기존의 연구들은 격자 탐색법 등을 활용하여 모수를 결정하고 있지만, 선택 가능한 범위에 대한 반복적인 계산으로 최적값을 선택하고 있어 계산 비용이 커지고 또 시간 등의 문제로 실제 문제에 적용하기 어려운 점이 있다. 따라서 본 연구에서는 데이터의 구조에 따라 모의실험을 통해 선택 가능한 영역에서의 효율성을 비교 검토하고, 이를 바탕으로 쉽게 적용할 수 있는 새로운 모수 선택 방법을 제안하고자 한다. 이를 통해 데이터 구조에 대해 강건함을 보이는 모수의 선택과 K 관리도의 구성을 논의하고 실제 자료에 적용해 보았다.

• 한국산학기술학회논문지
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• 제12권11호
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• pp.5094-5101
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• 2011

위암 완치수술을 받은 환자들의 재발수준과 재발에 미치는 영향을 파악하고자 2010년 9월부터 2011년 5월까지 한 대학병원에서 위암으로 진단받고 수술받은 환자 386명을 대상으로 조사하였다. 이들의 의무기록지와 병원암등록 자료에서 인구사회학적 특성, 생화학적 검사치, 임상병리학적 특성 등을 조사하였으며, 통계학적 검증으로 카이스퀘어 검정과 로지스틱 회귀분석을 실시하였다. 전체 조사대상자의 위암 재발률은 2.6%이었고, 성별 재발률은 남자에서 3.45%, 여자는 0.89%로 남자가 여자보다 약 4배정도 높았다. 단변량 로지스틱 회귀분석에서 재발이 발생할 위험은 림프전이가 있을수록 8.793배, 헬리코박터 파이로니균에 감염시 6.495배, 총콜레스테롤이 비정상일 때 14.333배 높았다. 다변량 로지스틱 회귀분석에서 림프전이와 헬리코박터 파이로니 감염이 재발에 중요한 요인으로 작용하였다. 결론적으로 위암의 재발에는 림프전이, 헬리코박터 파이로니 감염과 총콜레스테롤을 관리하고, CEA 및 CRP와 같은 생화학적 물질을 모니터링하여 재발을 조기에 발견하기 위한 노력이 함께 필요할 것으로 보인다.