• Polymer(Korea)
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• v.32 no.5
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• pp.440-445
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• 2008

The failure mechanism and failure morphology of linear low density polyethylene (LLDPE) tubing under hydrostatic pressure were investigated. Microscopic observations using video microscope and scanning electron microscope indicate that the failure mode is a brittle fracture including cracks propagated from inner wall to outer wall. In addition, oxidation induction time and Fourier transform infrared spectroscopy results show the presence of exothermic peak and the increase in carbonyl index on the surface of fractured LLDPE tubing, due to thermal-degradation. An accelerated life test methodology and testing system for LLDPE tubing are developed using the relationship between stresses and life characteristics by means of thermal acceleration. Statistical approaches using the Arrhenius model and Weibull distribution are implemented to estimate the long-term life time of LLDPE tubing under hydrostatic pressure. Consequently, the long-term life time of LLDPE tubing at the operating temperature of $25^{\circ}C$ could be predicted and also be analyzed.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.59 no.4
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• pp.467-472
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• 2010

In this study, an analysis of the used RCD's condition is conducted to assess the effect on environment of installation area, terms of use, corrosion, contamination etc. According to KS C 4613, the used RCDs were tested to get date which is the RCD's life time. And then, the date is analysed using Minitab which is a statistical program for reliability analysis. As a result, The RCD's MTTF for the all samples is $12.7{\pm}0.23$ years. and the MTTF of RCDs which are used indoor area is $12.9{\pm}0.34$ years, the MTTF of RCDs which are used outdoor area is $11.9{\pm}0.30$ years. Futhermore, the MTTF of RCDs which are used in dry area is a $13.1{\pm}0.26$ years, the MTTF of RCDs which are used in dust area is $13.0{\pm}0.57$ years, the MTTF of RCDs which are used in moisture area is $8.4{\pm}0.77$ years.

• Journal of Families and Better Life
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• v.18 no.1
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• pp.67-84
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• 2000

The purpose of this study was to analyze interrelationship among the degree of leisure activity the level of leisure needs and the satisfaction of leisure life of the elderly in the urban areas and to identify the factors which have effects on them. The sample were composed of 421 elderly over 60 years old living in Seoul. The data were analyzed by the statistical methods such as the frequency percentile mean standard deviation cronbach'a coefficient pearson's correlation stepwise multiple regression analysis path analysis utilizing SPSS/WIN. It intended to help the elderly to make advantage of their leisure time more effectively and to increase their the satisfaction of leisure life eventually to improve the quality of their lives.

• The Journal of the Korea Contents Association
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• v.21 no.7
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• pp.601-608
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• 2021

This study was conducted using data from the 2019 National Statistical Office's Life Time Survey, It was to investigate the effect of time-perception on the time-use pattern of 594 single middle-aged women in the city. This study found that there were differences of time management for daily behaviors between the insufficiently-percieved group and the sufficiently-percieved group. The both spent the most time with personal management. Secondly, the sufficiently-perceived group spent the more time with leisure activities than the insufficiently one did; the insufficiently-perceived one did the more work than the sufficiently-perceived one. The founding suggested the difference of time-use pattern by time-perception of the middle-aged women in the city. Also, the leisure activities and work were key factors to understand the daily life of the city-living middle-aged women.

• Korean Journal of Human Ecology
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• v.8 no.3
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• pp.487-497
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• 1999

The purpose of this study was to investigate the relationship between the adjustment to life(school life, personal relations, home life, economic problem and time management), the clothing attitudes(status symbolism, fashionability, aesthetics, modesty, conformity, comfort aspect) and the clothing satisfaction. The questionnaires were administered to 456 university students in Chongju city to measure the demographic information, the adjustment to life and the clothing attitudes. As statistical analysis, frequencies, t-test, ANOVA, and correlation were used. The results were as follows: 1. The university students showed average state on the adjustment to their life. The adjustment to their home life and family was showed higher than other aspects, otherwise that to school life was showed lower than the others. 2. There were partially significant differences according to demographic variables of students on each aspect of the adjustment to life. 3. The university students showed moderate interest toward clothing attitudes. In the clothing attitudes, the interest toward comfort aspect was showed higher than other aspects, otherwise that toward conformity aspect was showed lower than the others. 4. There were partially significant differences according to demographic variables of students on each variable of the clothing attitudes. 5. There were partially significant correlations between each aspect of the adjustment and the clothing attitudes aspects.

• Journal of Families and Better Life
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• v.21 no.1
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• pp.37-48
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• 2003

The major purpose of this study is to examine how korean elderly people spend their leisure time in a day In order to do this, we analysed the time dairy which were collected through the national investigation made by Korea National Statistical Office in 1999 and executed the frequency analysis, the One-way ANOVA and the Duncan's post hoc test. Major findings are as follows; First, Korean elderly people spent their leisure time passively and negatively Especially, they spent their most leisure time watching TV. Second, Those who were male elderly people, had their spouses and their own cars, and lived in an urban area etc, spend their leisure time executing positive leisure activity such as self-development activity and sports activity.

• The Korean Journal of Applied Statistics
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• v.9 no.2
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• pp.119-134
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• 1996

Accelerated life testing (ALT) of a system is commonly used to reduce time and cost. ALT is achieved by subjecting the test systems to more severe conditions than the normal ones to obtain estimates of life distribution under normal condition. The major interest of this research is to use a model of incorporating the common environmental effect on the components serially linked into a system-so called frailty model for the system life time distribution under each stress and to discuss the related data analysis and comparison of the model with the generally used one. The profile likelihood is used to get an initial values required to compute maximum likelihood estimates and simulation is carried for comparison.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1406-1411
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• 2005

The creep rupture data for type 316LN stainless steels were collected through literature survey or experimental data produced in KAERI. Using these data, polynomial equations for predicting creep life were obtained by Larson-Miller (L-M), Orr-Sherby-Dorn (O-S-D) and Manson-Haferd (M-H) etc. time-temperature parametric (TTP) methods. Standard error of estimate (SEE) values for the each parameter was obtained with different temperatures through the statistical process of the creep data. The results of L-M, O-S-D and M-H methods showed good creep-life prediction, but M-H method showed better agreement than L-M and O-S-D methods. Especially, it was found that SEE values of M-H method at $700^{\circ}C$ were lower than that of L-M and O-S-D methods.

• Journal of the military operations research society of Korea
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• v.22 no.1
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• pp.114-128
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• 1996

In this paper, a life distribution fitting method based on generalized phase-type distributions(GPH) is presented. By fitting the life distribution to a GPH, we can utilize various useful properties of the GPH. Two different approaches are used according to the properties of the given failure time data. One is an approximation to a GPH through the piecewise Weibull failure rate(PWF) model and the other is a direct approximation to a GPH using the empirical distribution function. Two numerical examples are also presented. In the first example, both of the two approaches are utilized and compared for an incomplete data set. And in the second example, the direct approximation method from an empirical distribution is utilized for the analysis of a complete data set. In both cases, we could confirm the validity of the proposed method.

• International Journal of Reliability and Applications
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• v.3 no.4
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• pp.185-198
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• 2002

In the traditional life testing model, it is assumed that a certain number of identical items are tested under identical condition. This is due to statistical rather than practical considerations. The proportional hazards model can be used to develop a realistic approach to determine the performance of an item. That is also capable of modeling the failure rates of accelerated life testing when the covariates are applied stresses. The proportional hazards model is typically applied for a group of items to assess the importance of factors that may influence the reliability of an item. In this paper we considered the interarrival times of an item rather than the time to first failure for grouped items and provided the availability estimation for the determination of maintenance policy and overhaul time. In order to demonstrate the proposed approach, an example is presented.