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Objective Bayesian Approach to Step Stress Accelerated Life Tests
김달호,Sang Gil Kang,Woo Dong Lee 한국통계학회 2006 Journal of the Korean Statistical Society Vol.35 No.3
This paper considers noninformative priors for the scale parameter ofexponential distribution when the data are collected in step stress acceler-ated life tests. We nd the Jereys' and reference priors for this model andshow that the reference prior satises rst order matching criterion. Also, weshow that there exists no second order matching prior in this problem. Somesimulation results are given and we perform Bayesian analysis for proposedpriors using some data.AMS 2000 subject classications.Primary 62F15; Secondary 62F25.Keywords. Accelerated life tests, Jereys' prior, matching prior, reference prior, stepstress.1. IntroductionIn many reliability studies, the life tests were made under various environ-mental conditions. But for extremely reliable units it is in general impossible tomake life tests under the usual conditions because the life times of units underthe usual conditions may tend to be large and then the testing time may be verylong. As a common approach to overcome this problem, the accelerated life tests(ALTs) are widely used, in which samples of units are subjected to conditions ofgreater stress than the usual conditions. For example, accelerated test conditionsinvolve higher than usual temperature, voltage, pressure, vibration, cycling rate,load,etc., or some combination of them.Received June 2006; accepted July 2006.yThis research was supported by Kyungpook National University Research Team Fund, 2003.1Corresponding author. Department of Statistics, Kyungpook National University, Daegu702-701, Korea (e-mail: dalkim@knu.ac.kr)
김달호,Sang Gil Kang,주용성 한국통계학회 2010 Journal of the Korean Statistical Society Vol.39 No.3
The paper develops some objective priors for the common mean in the one-way random effects model with heterogeneous error variances. We derive the first and second order matching priors and reference priors. It turns out that the second order matching prior matches the alternative coverage probabilities up to the second order, and is also an HPD matching prior. However, derived reference priors just satisfy a first order matching crite-rion. Our simulation studies indicate that the second order matching prior performs better than the reference prior and the Jeffreys prior in terms of matching the target coverage probabilities in a frequentist sense. We also illustrate our results using real data.
Noninformative priors for linear combinations of normal means with unequal variances
김달호,이우동,강상길,김용구 한국통계학회 2018 Journal of the Korean Statistical Society Vol.47 No.4
For normal populations with unequal variances, we develop matching priors and reference priors for a linear combination of the means. Here, we find three second-order matching priors: a highest posterior density (HPD) matching prior, a cumulative distribution function (CDF) matching prior, and a likelihood ratio (LR) matching prior. Furthermore, we show that the reference priors are all first-order matching priors, but that they do not satisfy the second-order matching criterion that establishes the symmetry and the unimodality of the posterior under the developed priors. The results of a simulation indicate that the secondorder matching prior outperforms the reference priors in terms of matching the target coverage probabilities, in a frequentist sense. Finally, we compare the Bayesian credible intervals based on the developed priors with the confidence intervals derived from real data.
김달호,우남교,조준우,Kim, Dal Ho,Woo, Namkyo,Jo, Junwoo 한국데이터정보과학회 2016 한국데이터정보과학회지 Vol.27 No.6
본 연구는 소상공인과 임차상인 보호정책을 지원하고, 권리금 분쟁소송 등에 참고자료로 활용할 뿐만 아니라 상가권리금 현황 파악을 위한 최초 조사를 실시하기 위한 표본설계 연구이다. 개별 임차 사업체 단위로 발생하는 권리금의 특성상 통계청의 전국사업체조사를 모집단으로 활용 하였으며, 우선적인 정보 제공이 필요한 7개 도시지역을 반영하였다. 전체 표본수는 8,000개로 하였으며, 7개 도시지역을 부차모집단으로 하고 지역별 상권별 표본수는 비례배분 하였으며, 상권내 업종은 제곱근비례배분 하였다. 목표오차를 활용하여 최종 표본수를 조정 하였으며, 표본설계가중치를 이용한 권리금 평균 추정량과 추정오차, 구간추정 공식을 유도하였으며, 이를 통해 도시별 상권별 및 업종별 통계 추정과 추정의 정도에 대한 평가를 가능하게 하였다. In this paper, we study a sample design for survey on goodwill in retail properties to provide a protecting policy for small traders and tenants, to use basic data for a dispute case related to goodwill. Since goodwill in retail properties is occurred by individual rent company, we use the census on establishments from the Statistics Korea as population. First of all, we consider preferentially seven metropolitan cities in which there are more than half of population. Total sample size is decided as 8,000. We allocate the sample size for markets as stratum in each city using proportional formula and the sample size for industrial classifications in each market using root proportional formula. Also we compute survey weights and calculate estimators, standard errors and interval of estimators for each characteristic such as type of establishments and market in seven metropolitan cities.
A Note on the Two Dependent Bernoulli Arms
김달호,차영준,이재만,Kim, Dal-Ho,Cha, Young-Joon,Lee, Jae-Man The Korean Data and Information Science Society 2002 한국데이터정보과학회지 Vol.13 No.2
We consider the Bernoulli two-armed bandit problem. It is well known that the my optic strategy is optimal when the prior distribution is concentrated at two points in the unit square. We investigate several cases in the unit square whether the my optic strategy is optimal or not. In general, the my optic strategy is not optimal when the prior distribution is not concentrated at two points in the unit square.
김달호,김지헌,황연희,신재우,박재근 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.3
We investigated the dependencies of a polymer photovoltaic (PV) cell on the thicknesses of its 8-hydroxy-quinolinato lithium (Liq) layer. The power conversion efficiency (PCE) of the polymer PV cell shows a similar trend to the fill factor (FF) but not to the open-circuit voltage (V<SUB>oc</SUB>) and short-circuit current (J<SUB>sc</SUB>) for various Liq layer thicknesses. This trend is likely associated with the series resistance of the polymer PV cell depending on the thickness of the Liq layer. As a result, to enhance the PCE of polymer PV cells fabricated with the Liq layer, a specific thickness (in our experiment, ∼1.0 nm) should be used for the Liq layer. In addition, we suggest that the electron injection mechanism of the Liq layer between the small-molecular hole/exciton blocking layer (in our experiment, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)) and metal cathode (in our experiment, Al) strongly influences the PCE of polymer PV cells.
김달호,박재근 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.4
We investigated the device characteristics of polymer photovoltaic (PV) cells based on the poly(3-hex-ylthiophene) (P3HT) and [6,6]-phenylC61 butyric acid methyl ester (PCBM) bulk heterojunction with a cathode buffer layer of thermally evaporated bis (2-methyl-8-quninolinato)-4-phenylphenolate (BAlq).A power conversion efficiency (PCE) of 2.46% was obtained with the insertion of a 4 nm-thick BAlq, which increased ~118 % over the cell without BAlq layer under Air Mass 1.5 Global (AM 1.5G) illumination, 100 mW/cm<SUP>2</SUP>. Moreover, we examined the charge carrier transport property, showing hole mobility enhancement of the cell due to the insertion of BAlq layer with a thickness of less than 4 nm, which accounted for the improvement in the photocurrent and fill factor (FF) due to the better balance of charge carriers. Finally, the BAlq buffer layer was also demonstrated as an optical spacer to improve the optical absorption of the P3HT:PCBM layer, which accounted for the J<SUB>sc</SUB> enhancement of the device.