• 콘크리트학회논문집
• /
• 제18권2호
• /
• pp.233-238
• /
• 2006

본 연구에서는 염해환경에 노출되어 있는 철근콘크리트 구조물의 수명예측에 있어서 철근덮개 파괴시간 예측을 위하여, 유한요소해석을 통한 방법을 제시하였다. 또한 본 연구에서는 인공세공용액중의 철근 부식속도로부터 콘크리트 중의 철근 부식속도를 유도하는 방법을 제시하였으며, 철근 부식의 분포에 따른 철근덮개의 파괴시간을 비교하여, 철근덮개 파괴시간을 합리적으로 예측하기 위한 방법을 제시하였다. 국부부식을 고려한 경우 균일한 부식을 가정한 경우보다 최대 약 40%정도 철근덮개 파괴시간이 짧아짐을 알 수 있다. 따라서, 철근덮개의 파괴시간 예측을 위한 유한요소해석에 있어서 국부부식을 고려하는 것이 합리적인 결과를 제시할 수 있을 것으로 사료된다.

• 한국기술혁신학회:학술대회논문집
• /
• 한국기술혁신학회 2011년도 춘계 학술대회 논문집
• /
• pp.161-173
• /
• 2011

• 대한간호학회지
• /
• 제49권6호
• /
• pp.701-712
• /
• 2019

Purpose: Despite the high drinking rates and the complexity of drinking behaviors in adolescents, insufficient attention has been paid to their drinking patterns. Therefore, we aimed to identify patterns of adolescent drinking behaviors and factors predicting the distinct subgroups of adolescent drinking behaviors. Methods: We analyzed nationally representative secondary data obtained in 2017. Our final sample included 24,417 Korean adolescents who had consumed at least one glass of alcohol in their lifetime. To investigate patterns of drinking behaviors, we conducted a latent class analysis using nine alcohol-related characteristics, including alcohol consumption levels, solitary drinking, timing of drinking initiation, and negative consequences of drinking. Furthermore, we investigated differences in demographics, mental health status, and characteristics of substance use across the latent classes identified in our study. To do so, we used the PROC LCA with COVARIATES statement in the SAS software. Results: We identified three latent classes of drinking behaviors: current non-drinkers (CND), binge drinkers (BD), and problem drinkers (PD). Compared to the CND class, both BD and PD classes were strongly associated with higher academic year, lower academic performance, higher levels of stress, suicidal ideation, lifetime conventional or electronic cigarette use, and lifetime use of other drugs. Conclusion: Health professionals should develop and implement intervention strategies targeting individual subgroups of drinking behaviors to obtain better outcomes. In particular, health professionals should consider different characteristics across subgroups of adolescent drinking behaviors when developing the interventions, such as poor mental health status and other substance use among binge and problem drinkers.

• 대한간호학회지
• /
• 제46권4호
• /
• pp.552-561
• /
• 2016

Purpose: The purpose of this study was to investigate factors influencing lifetime smoking and current smoking among adolescents in South Korea. Methods: Hierarchical logistic regression was conducted based on complex sample analysis using statistics from the 10th (2014) Korea Youth Risk Behavior Web-Based Survey. The study sample comprised 72,060 adolescents aged 12 to 18. Results: The significant factors influencing adolescent lifetime smoking were female gender, older age, higher stress, higher weekly allowance, lower economic status, living apart from parents, parental smoking, sibling smoking, peer smoking, observation of school personnel smoking, and coed school compared to boys' school. The significant factors influencing adolescent current smoking were female gender, older age, higher stress, higher weekly allowance, both higher and lower economic status compared to middle economic status, living apart from parents, parental smoking, sibling smoking, peer smoking, observation of school personnel smoking, and coed school compared to boys' school. Conclusion: Factors identified in this study need to be considered in programs directed at prevention of adolescent smoking and smoking cessation programs, as well as policies.

• 한국결정성장학회지
• /
• 제9권2호
• /
• pp.157-161
• /
• 1999

초크랄스키 실리콘 기판의 뒷면에 형성된 기계적 손상이 미치는 효과에 대하여 고찰하였다. 기계적 손상의 정도는 레이저 여기/극초단파 반사 광전도 감쇠법에 의한 소수반송자 재결합 수명, 습식산화/선택적 식각 방법, 표면 부위 미소 결함 및 X-선 단면 측정 분석으로 평가하였다. 그 결과, 웨이퍼 뒷면에 가해지는 기계적 손상의 세기가 강할수 록 소수반송자 재결합 수명은 짧아지고, 표면 부위 미소 결함 밀도는 비례적으로 증가하였으며, 산화 유기 적충 결함 밀 도와도 상호 일치하였다. 그래서, 표면 부위 미소 결함 기술은 산화 유기 적층 결함을 측정하는데 있어서 통상적인 부식 방법과는 별도로 사용될 수 있다.

• 한국전기전자재료학회논문지
• /
• 제30권9호
• /
• pp.551-557
• /
• 2017

It is extremely important to improve methodologies for the lifetime assessment of porcelain insulators. While there has been a considerable amount of work regarding the phenomena of lifetime distributions, most of the studies assume that aging distributions follow the Weibull distribution. However, the true underlying distribution is unknown, giving rise to unrealistic inferences, such as parameter estimations. In this article, we review several distributions that are commonly used in reliability and survival analysis, such as the exponential, Weibull, log-normal, and gamma distributions. Some properties, including the characteristics of failure rates of these distributions, are presented. We use a Bayesian approach for model selection and parameter estimation procedures. A well-known measure, called the Bayes factor, is used to find the most plausible model among several contending models. The posterior mean can be used as a parameter estimate for unknown parameters, once a model with the highest posterior probability is selected. Extensive simulation studies are performed to demonstrate our methodologies.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
• /
• pp.720-723
• /
• 2004

This study is intended to propose a systematic approach for determining optimum Life-Cycle Cost (LCC)-effective seismic design for continuous PSC bridges considering lifetime expected seismic risks. In the paper, a set of cost function for LCC analysis of bridges is proposed. The total LCC functions consist of initial cost and direct/indirect damage costs considering repair/replacement costs, human losses and property damage costs, road user costs, and indirect socio-economic losses. The damage costs are expressed in terms of Park-Ang median global damage indices (Park and Ang, 1985) and lifetime damage probabilities. The proposed approach is applied to model bridges of both moderate seismicity regions like Korea and high seismicity regions like Japan. Since, in case of bridges, a number of parameters may have an influence on optimal target reliability, various sensitivity analyses are performed in this study. It may be expected that the proposed approach can be effectively utilized for the development of cost-effective performance criteria for design and upgrading of various types of bridges as well as continuous PC bridges.

• Smart Structures and Systems
• /
• 제4권5호
• /
• pp.641-653
• /
• 2008

This paper proposes a practical and realistic method to establish an optimal lifetime maintenance strategy for deteriorating bridges by considering the life-cycle performance as well as the life-cycle cost. The proposed method offers a set of optimal tradeoff maintenance scenarios among other conflicting objectives, such as minimizing cost and maximizing performance. A genetic algorithm is used to generate a set of maintenance scenarios that is a multi-objective combinatorial optimization problem related to the lifetime performance and the life-cycle cost as separate objective functions. A computer program, which generates optimal maintenance scenarios, was developed based on the proposed method using the life-cycle costs and the performance of bridges. The subordinate relation between bridge members has been considered to decide optimal maintenance sequence and a corresponding algorithm has been implemented into the program. The developed program has been used to present a procedure for finding an optimal maintenance scenario for steel-girder bridges on the Korean National Road. Through this bridge maintenance scenario analysis, it is expected that the developed method and program can be effectively used to allow bridge managers an optimal maintenance strategy satisfying various constraints and requirements.

• 설비공학논문집
• /
• 제19권4호
• /
• pp.313-320
• /
• 2007

In this paper, the experimental study has been carried out to investigate the reliability lifetime of two bearing units based on the oil temperature. Measurements for the oil temperature as well as the bearing temperature during normal operation were performed to study the effects of oil viscosity and oil submergence percentages in the two bearing units. The optimal lubrication condition to increase the lifetime of the bearing unit A was found that its viscosity and submergence percentage were VG32 and 25%, respectively. For the bearing unit B, when the oil viscosity and submergence percent were VG32 and 75%, the lubrication condition was the most efficient. Finally, the adjusted rating times of both the bearing units were calculated to be over 28,000 h, which is greater than the minimum adjusted rating times of 25,000 h. Therefore, they satisfied the regulated lifetime of API 610.

• Communications for Statistical Applications and Methods
• /
• 제24권4호
• /
• pp.325-337
• /
• 2017

In this paper, we proposed a new long-term lifetime distribution with four parameters inserted in a risk competitive scenario with decreasing, increasing and unimodal hazard rate functions, namely the Weibull-Poisson long-term distribution. This new distribution arises from a scenario of competitive latent risk, in which the lifetime associated to the particular risk is not observable, and where only the minimum lifetime value among all risks is noticed in a long-term context. However, it can also be used in any other situation as long as it fits the data well. The Weibull-Poisson long-term distribution is presented as a particular case for the new exponential-Poisson long-term distribution and Weibull long-term distribution. The properties of the proposed distribution were discussed, including its probability density, survival and hazard functions and explicit algebraic formulas for its order statistics. Assuming censored data, we considered the maximum likelihood approach for parameter estimation. For different parameter settings, sample sizes, and censoring percentages various simulation studies were performed to study the mean square error of the maximum likelihood estimative, and compare the performance of the model proposed with the particular cases. The selection criteria Akaike information criterion, Bayesian information criterion, and likelihood ratio test were used for the model selection. The relevance of the approach was illustrated on two real datasets of where the new model was compared with its particular cases observing its potential and competitiveness.