• 소성∙가공
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• 제30권2호
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• pp.74-82
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• 2021

Stretch-flangeability, which is the ability of sheet steels to be deformed into complex shapes, is a critical formability property in automobile body parts. In this study, the center-hole for hole expansion test, which is normally used to evaluate the stretch-flangeability of sheet steels, was prepared by both punching and electrical discharge machining (EDM) methods. Hole expansion ratio (HER) of punched hole was far lower than the HER of EDM drilled hole because of damage/crack in hole-edge due to punching process. The effect of hole-edge condition on HER was quantified by mechanical, fractographic and geometric factors. Based on these factors, the empirical equation used to determine HER for various sheet steels was derived using non-linear regression.

• Journal of the Korean Data and Information Science Society
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• 제24권2호
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• pp.267-275
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• 2013

데이터 마이닝 기법들 중에서도 연관성 규칙은 가장 최근에 개발된 기법으로 대용량 데이터베이스에서 각 항목들 간의 관련성을 찾아내며, 두 항목간의 관계를 명확히 수치화함으로써 두 개 이상의 항목간의 관련성을 표시하여 주기 때문에 현장에서 직접 적용이 가능하다. 일반적으로 연관성 규칙 생성 여부를 판단할 때, 각 항목간의 연관성을 반영하는 기준인 지지도, 신뢰도, 향상도 등의 흥미도 측도를 활용하게 된다. 실제적으로 연관성 규칙의 수를 결정하기 위해서는 이들 흥미도 측도들의 평가기준을 정하기 위해 반복적으로 조정 과정을 거쳐야 한다. 본 논문에서는 이러한 문제를 해결하기 위해 연관성 평가기준 모두를 일반적으로 많이 활용되고 있는 비선형 회귀모형에 적용하여 연관성 규칙의 수를 추정하는 방안을 강구하였다. 또한 분산팽창계수를 이용하여 다중공선성 문제를 진단하는 동시에 분산분석 결과와 수정 결정계수를 이용하여 각 모형의 기여도를 비교하여 가장 바람직한 회귀 모형을 구하였다.

• 한국안전학회지
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• 제35권5호
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• pp.15-21
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• 2020

Quantitative risk assessment (QRA) is used as a legal or voluntary safety management tool for the hazardous material industry and the utilization of the method is gradually increasing. Therefore, a leak frequency analysis based on reliable generic data is a critical element in the evolution of QRA and safety technologies. The aim of this paper is to derive the leak frequency function that can be applied more flexibly in QRA based on OGP report with high reliability and global utilization. For the purpose, we first reviewed the data on the 16 equipments included in the OGP report and selected the predictors. And then we found good equations to fit the OGP data using non-linear regression analysis. The various expectation functions were applied to search for suitable parameter to serve as a meaningful reference in the future. The results of this analysis show that the best fitting parameter is found in the form of DNV function and connection function in natural logarithm. In conclusion, the average percentage error between the fitted and the original value is very small as 3 %, so the derived prediction function can be applicable in the quantitative frequency analysis. This study is to contribute to expand the applicability of QRA and advance safety engineering as providing the generic equations for practical leak frequency analysis.

• 실천공학교육논문지
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• 제12권2호
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• pp.265-273
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• 2020

본 논문에서는 비전공자들을 위한 교양과목으로 적용할 수 있는 기초 데이터과학 실습 커리큘럼을 제안하고, 엑셀(스프레드시트) 데이터 분석 도구를 활용한 교육 방법을 제안하였다. 데이터 수집, 데이터 가공 및 데이터 분석을 위한 도구에는 엑셀, R, 파이썬, SQL(Structured Query Language) 등이 있다. R, 파이썬 및 SQL은 데이터 과학을 실습하는 데 있어, 프로그래밍 언어와 자료구조를 이해해야 한다. 반면에, 엑셀 도구는 비전공자들에게도 친숙한 데이터 분석도구로서, 프로그래밍 언어에 대한 학습 부담이 없다. 그리고 기초적인 데이터과학 실습을 엑셀로 진행하면, 데이터과학 이론을 습득하는 데 집중할 수 있는 장점이 있다. 본 논문에서는 한 학기 분량의 기초 데이터과학 실습 커리큘럼과 주별 엑셀 실습 내용을 제안하였다. 그리고, 교육 내용 실체를 실증하기위해, 엑셀 데이터분석 도구를 활용하여, 선형 회귀 분석(Linear Regression Analysis) 예제들을 제시하였다.

• Industrial Engineering and Management Systems
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• 제8권3호
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• pp.148-154
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• 2009

In recent days, large-sized flat-panel display (FPD) has been increasingly applied to computer monitors and TVs. Mura defects, appearing as low contrast or non-uniform brightness region, sometimes occur in manufacturing of the Thin-Film Transistor Liquid-Crystal Displays (TFT-LCD). Implementation of automatic Mura inspection methods is necessary for TFT-LCD production. Various existing Mura detection methods based on regression diagnostics, surface fitting and data transformation have been presented with good performance. This paper proposes an efficient Mura detection method that is based on a regression diagnostics using studentized residuals for automatic Mura inspection of FPD. The input image is estimated by a linear model and then the studentized residuals are calculated for filtering Mura regions. After image dilation, the proposed threshold is determined for detecting the non-uniform brightness region in TFT-LCD by means of monitoring the every pixel in the image. The experimental results obtained from several test images are used to illustrate the effectiveness and efficiency of the proposed method for Mura detection.

• 한국시스템다이내믹스연구
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• 제8권2호
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• pp.253-273
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• 2007

To measure the effect of school zone on housing cost, Linear Regression Model is widely used, and school zone is known as a key determinant of housing cost in Korea. However, when the Hierarchical Linear Model (HLM) is applied with the same data, school effect on housing cost becomes statistically non-significant. It is because HLM effectively separates the effect of individual housing's attributes from the group effect. In sum, the housing cost of Kangnam, where good public schools are located, is apparently is higher than that of Kangbuk. However, the school effect on housing cost (Level 2) becomes non-significant when individual housing's attributes (Level 1) are controlled with HLM.

• Journal of the Korean Statistical Society
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• 제28권2호
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• pp.225-234
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• 1999

We consider the following semi-parametric non-linear mixed effect regression model : y\ulcorner=f($\chi$\ulcorner;$\beta$)+$\sigma$$\mu$($\chi$\ulcorner)+$\sigma$$\varepsilon$\ulcorner,i=1,…,n,y*=f($\chi$;$\beta$)+$\sigma$$\mu$($\chi$) where y'=(y\ulcorner,…,y\ulcorner) is a vector of n observations, y* is an unobserved new random variable of interest, f($\chi$;$\beta$) represents fixed effect of known functional form containing unknown parameter vector $\beta$\ulcorner=($\beta$$_1$,…,$\beta$\ulcorner), $\mu$($\chi$) is a random function of mean zero and the known covariance function r(.,.), $\varepsilon$'=($\varepsilon$$_1$,…,$\varepsilon$\ulcorner) is the set of uncorrelated measurement errors with zero mean and unit variance and $\sigma$ is an unknown dispersion(scale) parameter. On the basis of finite-sample, small-dispersion asymptotic framework, we derive an absolute lower bound for the asymptotic mean squared errors of prediction(AMSEP) of the regular-consistent non-linear predictors of the new random variable of interest y*. Then we construct an optimal predictor of y* which attains the lower bound irrespective of types of distributions of random effect $\mu$(.) and measurement errors $\varepsilon$.

• Journal of Korean Medical Science
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• 제33권53호
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• pp.322.1-322.14
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• 2018

Background: Osteoprotegerin (OPG) plays protective roles against the development of vascular calcification (VC) which greatly contributes to the increased cardiovascular events in patients with chronic kidney disease (CKD). The present study aimed to find the non-traditional, kidney-related cardiovascular risk factors correlated to serum OPG and the effect of serum OPG on the arterial stiffness measured by brachial ankle pulse wave velocity (baPWV) in patients with the pre-dialysis CKD. Methods: We cross-sectionally analyzed the data from the patients in whom baPWV and the serum OPG were measured at the time of enrollment in a prospective pre-dialysis CKD cohort study in Korea. Results: Along with traditional cardiovascular risk factors such as age, diabetes mellitus, pulse pressure, and baPWV, non-traditional, kidney-related factors such as albuminuria, plasma level of hemoglobin, total $CO_2$ content, alkaline phosphatase, and corrected calcium were independent variables for serum OPG in multivariate linear regression. Reciprocally, the serum OPG was positively associated with baPWV in multivariate linear regression. The baPWV in the 3rd and 4th quartile groups of serum OPG were higher than that in the 1st quartile group after adjustments by age, sex and other significant factors for baPWV in linear mixed model. Conclusion: Non-traditional, kidney-related cardiovascular risk factors in addition to traditional cardiovascular risk factors were related to serum level of OPG in CKD. Serum OPG level was significantly related to baPWV. Our study suggests that kidney-related factors involved in CKD-specific pathways for VC play a role in the increased secretion of OPG into circulation in patients with CKD.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권11호
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• pp.5392-5418
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• 2017

The primary aim of this paper is to propose a non-linear regression based technique for mapping different network Quality of Service (QoS) factors to an integrated end-user Quality of Experience (QoE) or Mean Opinion Score (MOS) value for an online video streaming service on a mobile phone. We use six network QoS factors for finding out the user QoE. The contribution of this paper is threefold. First, we investigate the impact of the network QoS factors on the perceived video quality. Next, we perform an individual mapping of the significant network QoS parameters obtained in stage 1 to the user QoE based upon a non-linear regression method. The optimal QoS to QoE mapping function is chosen based upon a decision variable. In the final stage, we evaluate the integrated QoE of the system by taking the combined effect of all the QoS factors considered. Extensive subjective tests comprising of over 50 people across a wide variety of video contents encoded with H.265/HEVC and VP9 codec have been conducted in order to gather the actual MOS data for the purpose of QoS to QoE mapping. Our proposed hybrid model has been validated against unseen data and reveals good prediction accuracy.

• 한국터널지하공간학회 논문집
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• 제10권3호
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• pp.233-243
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• 2008

터널 건설시 조사 및 설계 단계에서 예측한 터널의 거동은 지반의 지질 구조 및 재료 특성의 복잡함 등으로 인해 실제 시공 중의 거동과 일치하지 않는 경우가 많다. 따라서 시공 중에는 관찰과 계측을 통하여 지반과 지보재의 거동을 확인하고 위험이 예상될 경우 신속히 굴착 방법 및 보강 방법 등을 변경하므로써 터널의 안정성을 확보해야 한다. 그리고 이러한 목적을 위해서는 가급적 굴착 초기 단계에서 터널의 변형 거동을 파악하고 이로부터 최종적인 변위를 예측하는 과정이 필요하다. 본 연구에서는 NATM 방식에 의해 시공 중인 국내 두 곳의 도로터널 현장에서 수집한 변위 계측 data를 분석하여 굴착 초기 측정 내공변위량과 최종 내공변위량과의 관계를 통계적으로 유도하였다. 이 때 굴착 후 계측 전 까지 미측정 내공변위량을 추정하기 위하여 기존의 근사함수식을 수정하여 회귀분석하는 방법과 본 연구에서 제안하는 막장거리 1D(D:터널직경)까지의 계측 data를 이용하여 현장에서 용이하게 적용할 수 있는 간단한 선형 회귀분석을 이용하는 방법을 적용하였다. 최종적으로, 계측 전 변위량을 포함한 굴착 초기 내공변위와 최종 내공변위와의 관계를 통계적 방법을 통해 선형관계식으로 근사적으로 표현할 수 있었으며, 이 때 계측 전 변위량 추정방법으로 지수함수를 이용한 경우와 선형 회귀분석을 이용한 경우에 대해서 결과의 차이는 그다지 크지 않은 것으로 나타났다.