• 한국신뢰성학회지:신뢰성응용연구
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• 제18권1호
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• pp.80-86
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• 2018

Purpose: This article provides a mathematical model for the accelerated degradation test when the performance degradation characteristic follows the lognormal distribution. Method: For developing test plans, the total number of test units and the test time are determined based on the minimization of the asymptotic variance of the q-th quantile of the lifetime distribution at the use condition. Results: The mathematical model for the accelerated degradation test is provided. Conclusion: Accelerated degradation test method is widely used to evaluate the product lifetime within a resonable amount of cost and time. In this article. a mathematical model for the accelerated degradation test method is newly developed for this purposes.

• Communications for Statistical Applications and Methods
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• 제24권1호
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• pp.29-41
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• 2017

The estimation problem of expected time to failure of units is studied in a discrete set up. A simple step-stress accelerated life testing is considered with a Type-I censored sample from geometric distribution that is a commonly used distribution to model the lifetime of a device in discrete case. Maximum likelihood estimators as well as the associated distributions are derived. Exact, approximate and bootstrap approaches construct confidence intervals that are compared via a simulation study. Optimal confidence intervals are suggested in view of the expected width and coverage probability criteria. An illustrative example is also presented to explain the results of the paper. Finally, some conclusions are stated.

• Communications for Statistical Applications and Methods
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• 제23권2호
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• pp.119-129
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• 2016

A new sampling method is introduced based on the idea of a ranked set sampling scheme in which taken samples in each set are dependent on previous ones. Some theoretical results are presented and distribution-free confidence intervals are derived for the quantiles of any continuous population. It is shown numerically that the proposed sampling scheme may lead to 95% confidence intervals (especially for extreme quantiles) that cannot be found based on the ordinary ranked set sampling scheme presented by Chen (2000) and Balakrishnan and Li (2006). Optimality aspects of this scheme are investigated for both coverage probability and minimum expected length criteria. A real data set is also used to illustrate the proposed procedure. Conclusions are eventually stated.

• Wind and Structures
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• 제16권6호
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• pp.541-560
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• 2013

The aim of the paper is to use optimization and advanced numerical computation of a sail fiber-reinforced composite model to increase the performance of a yacht under wind action. Designing a composite-shell system against the wind is a very complex problem, which only in the last two decades has been approached by advanced modeling, optimization and computer fluid dynamics (CFDs) based methods. A sail is a tensile structure hoisted on the rig of a yacht, inflated by wind pressure. Our objective is the multiple criteria optimization of a sail, the engine of a yacht, in order to obtain the maximum thrust force for a given load distribution. We will compute the best possible yarn thickness orientation and distribution in order to minimize the total fiber volume with some displacement constraints and in order to leave the most uniform stress distribution over the whole structure. In this paper our attention will be focused on computer simulation, modeling and optimization of a sail-shape mathematical model in different regatta and wind conditions, with the purpose of improving maneuverability and speed made good.

• 보건교육건강증진학회지
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• 제26권1호
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• pp.81-92
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• 2009

Objectives: This study set out to investigate the relationship among the factors of metabolic syndrome diagnosis criteria, their risk factors including general characteristics, and the distribution of the diagnosis criteria and risk among the adult residents of a rural community. Methods: Among 1,968 residents, those who had three or more of the risk factors of metabolic syndrome, which include blood pressure, blood glucose, triglyceride, abdominal obesity, and HDL-C, were categorized as the metabolic syndrome group. And their correlations were analyzed. Results: As for the risk ratio with five factors of the metabolic syndrome diagnosis criteria, it was high according to age and smoking. In addition, the results show that body fat percentage, hs-CRP, insulin, BMI, PP2, total cholesterol, and W/Ht also had much impact on increasing the risk ratio of the metabolic syndrome diagnosis criteria. It turned out that metabolic syndrome was affected by the body mass index(BMI), insulin, waist to height ratio(W/Ht), and hs-CRP. It was 2.51 times crude odds ratio that BMI over the 25kg/m2 in the ratio of the fact of metabolic syndrome and adjusted for sex odds ratio 2.50times and W/Ht was 3.31times, adjusted for sex odds ratio 3.25 times. Conclusion: BMI, W/Ht and smoking of the general characteristics seem to have close relationships with high correlations between the metabolic syndrome diagnosis criteria and the risk factors. Thus there is an urgent need to evaluate them and take interventions and monitoring measures for the clustering of risk factors.

• 한국환경보건학회지
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• 제21권2호
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• pp.1-6
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• 1995

Authors investigated the size distribution and mass fraction of dusts in work environment of Changwon industrial complex. Size distribution of suspended dusts in welding and grinding processes were evaluated using ambient cascade impactors. The mass median diameters of dusts were 0.25 to $0.60 \mu m$ at welding sites and 1.20 to $1.92 \mu m$ at grinding sites. Respirable mass fractions were 63.68 to 73.50% at welding sites and 43.24 to 51.47% at grinding sites. Respirable fractions were calculated from the size distribution data for the ACGIH criteria by the respirable particle mass. In case of dust removal system, electrostatic precipitator and bag filter were appropriate for welding process and grinding process, respectively.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문집
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• pp.605-610
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• 2002

Eigenvalues are taken as performance criteria for structural damping design using viscoelastic material. Given material properties, optimal distribution of damping material is sought based on eigenvalue sensitivity. For eigenanalysis of frequency dependent viscoelastic material treated structures, Golla-Mushes-McTavish (GHM) model is used and some dominant modes are chosen for consideration. To avoid the intensity of computation caused by increased problem size, an alternative approximate method is proposed which uses elastic modes and can be applied under small damping assumption. A cantilever beam treated with unconstrained viscoelastic layer is tested and optimal distribution of thickness of the layer is illustrated. Partial coverage configurations are compared with the one-sided full coverage case.

• Communications for Statistical Applications and Methods
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• 제29권3호
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• pp.373-391
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• 2022

The distribution of observations in most econometric studies with spatial heterogeneity is skewed. Usually, a single transformation of the data is used to approximate normality and to model the transformed data with a normal assumption. This assumption is however not always appropriate due to the fact that panel data often exhibit non-normal characteristics. In this work, the normality assumption is relaxed in spatial mixed models, allowing for spatial heterogeneity. An inference procedure based on Bayesian mixed modeling is carried out with a multivariate skew-elliptical distribution, which includes the skew-t, skew-normal, student-t, and normal distributions as special cases. The methodology is illustrated through a simulation study and according to the empirical literature, we fit our models to non-life insurance consumption observed between 1998 and 2002 across a spatial panel of 103 Italian provinces in order to determine its determinants. Analyzing the posterior distribution of some parameters and comparing various model comparison criteria indicate the proposed model to be superior to conventional ones.

• 토지주택연구
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• 제7권4호
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• pp.251-259
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• 2016

공간구조가 다핵분산형으로 전환되면서 도시 간 네트워크적 연계를 통한 경쟁력 강화가 중요한 이슈로 등장하고 있다. 이에 따라 지역거점으로서의 신도시 역할, 특히 적절한 산업기능의 확보가 필요하지만 현행 신도시의 경제적 기준은 규모에 따른 일괄적 기준을 제시하고 있어 권역 내 신도시의 위상을 반영하지 못하는 한계가 있다. 이에 본 연구는 기존 신도시에 대한 네트워크 분석을 통해 신도시 유형을 구분하고 이러한 유형과 규모에 따른 경제적 자족성 계획기준을 검토하였다. 연구방법으로는 국 내외 신도시 산업용지에 대한 사례 분석 및 1, 2기 신도시에 대한 네트워크 분석방법을 적용하였다. 네트워크 특성은 다양한 지표로 나타나는 바, 본 연구는 연결중심성, 근접중심성 지표를 활용하여 신도시의 네트워크적 위상에 따른 유형을 단핵집중형, 분산집중형, 모도시종속형으로 구분하였다. 이와 같은 유형구분을 바탕으로 신도시 규모별 자족시설용지 확보기준을 재검토하였다. 본 연구결과는 지속가능한 신도시계획기준 및 택지개발업무처리지침의 개선 및 개발계획 수립 변경을 위한 자료로 활용할 수 있다.

• 한국항해항만학회지
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• 제37권5호
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• pp.453-461
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• 2013

본 논문에서는 소형 해상 부유체의 위기 평가를 위한 확률기반 위기평가기법(PET)에서 표본 데이터에 최적인 누적분포함수(CDF) 추정에 관한 평가절차와 실험결과를 기술하였다. CDF는 PET에서 부유체의 위기수준을 평가하기 위한 위기허용기준의 참조 값을 제공하기 위한 것으로, 부유체 모델의 롤(Roll), 피치(pitch), 히브(Heave) 등의 운동응답함수에 대한 표본 데이터에서 추정할 수 있다. 본 연구에서는 여덟가지 정형화된 분포함수와 최대우도추정기법을 적용하여 표본 데이터에 대해서 최대우도를 갖는 CDF들을 평가하였다. 분포함수들의 적합도 검정 실험을 통해서, 베타 분포가 롤과 피치 표본 데이터에 대해서 평균 확률오차 $\bar{\delta}(0{\leq}\bar{\delta}{\leq}1.0)$가 가장 작은 0.024와 0.022로 최적임을 나타냈고, 히브 표본 데이터에 대해서는 감마 분포가 $\bar{\delta}$가 가장 작은 0.027로 최적임을 나타냈다. 본 연구에서 제안한 방법은 표본 데이터의 최적분포 추정을 위한 다양한 분야에 적용 가능할 것으로 기대된다.