• Computational Structural Engineering : An International Journal
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• 제1권2호
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• pp.81-87
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• 2001

A framework for reliability analysis of structural components and systems under conditions of statistical and model uncertainty is presented. The Bayesian parameter estimation method is used to derive the posterior distribution of model parameters reflecting epistemic uncertainties. Point, predictive and bound estimates of reliability accounting for parameter uncertainties are derived. The bounds estimates explicitly reflect the effect of epistemic uncertainties on the reliability measure. These developments are enhance-ments of second-moment uncertainty analysis methods developed by A. H-S. Ang and others three decades ago.

• 한국전산구조공학회논문집
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• 제27권6호
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• pp.605-613
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• 2014

신뢰성 해석을 수행할 때 정보부족으로 인해 발생하는 인식론적 불확실성(epistemic uncertainty)은 고유의 변동성에 의해 존재하는 내재적 불확실성(aleatory uncertainty)보다 더 중요하게 다뤄야 한다. 그러나 그동안 개발된 확률이론은 주로 내재적 불확실성을 모델링하는데 이용된 반면, 인식론적 불확실성의 모델링에 대해서는 아직 확실한 접근법이 없었다. 최근 이를 위해 probability theory를 포함한 여러 접근법들이 제시되고 있지만 이들은 서로 다른 통계적 이론들을 바탕으로 도출되었기 때문에, 각 방법들의 결과들을 이해하는데 어려움이 있었다. 본 연구에서는 고장 확률을 계산하는 문제를 가지고 이러한 방법들이 인식론적 불확실성을 어떻게 다루는지를 비교, 분석하였다. 이를 위해 probability method, combined distribution method, interval analysis method 그리고 evidence theory를 대상으로 신뢰도 분석문제에 대해 각 방법들의 특징들을 비교하였으며, 그 결과는 다음과 같다. 입력변수의 확률분포 형태를 알 수 있다면 probability method가 가장 우수하나, 이를 전혀 모르면 interval method를 사용해야 한다. 그러나 계산비용 면에서는 두 방법이 유사하므로 결국 입력변수의 확률특성 정보가 얼마나 있느냐에 따라 방법을 선택한다. Combined distribution method는 failure probability의 평균만 제공하므로 사용하지 않는 것이 좋다. 다만 이 방법은 계산비용이 매우 적게 드는 장점이 있다. Evidence theory는 probability와 interval 방법의 중간에 해당하며, 구간별 probability assignment를 세분화 할수록 probability결과에 접근한다. 이 방법은 계산비용이 가장 높은 것이 문제이다.

• Nuclear Engineering and Technology
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• 제35권1호
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• pp.64-79
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• 2003

In the risk and reliability analysis of complex technological systems, the primary concern of formal uncertainty analysis is to understand why uncertainties arise, and to evaluate how they impact the results of the analysis. In recent times, many of the uncertainty analyses have focused on parameters of the risk and reliability analysis models, whose values are uncertain in an aleatory or an epistemic way. As the field of parametric uncertainty analysis matures, however, more attention is being paid to the explicit treatment of uncertainties that are addressed in the predictive model itself as well as the accuracy of the predictive model. The essential steps for evaluating impacts of these model uncertainties in the presence of parameter uncertainties are to determine rigorously various sources of uncertainties to be addressed in an underlying model itself and in turn model parameters, based on our state-of-knowledge and relevant evidence. Answering clearly the question of how to characterize and treat explicitly the forgoing different sources of uncertainty is particularly important for practical aspects such as risk and reliability optimization of systems as well as more transparent risk information and decision-making under various uncertainties. The main purpose of this paper is to provide practical guidance for quantitatively treating various model uncertainties that would often be encountered in the risk and reliability modeling process of complex technological systems.

• 한국추진공학회지
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• 제22권2호
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• pp.131-137
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• 2018

엔진 당량비의 제어오차가 요구범위를 불만족할 확률을 분석하였다. 당량비의 제어오차는 무작위 불확실요소와 인식론적 불확실요소로부터 동시에 영향을 받는다. 무작위 불확실요소는 일반적으로 확률 분포가 주어지므로 민감도 기반의 신뢰성 해석기법을 이용해 쉽게 해석이 가능하다. 확률분포를 알기 어려운 인식론적 불확실요소를 다루기 위해서는 새로운 접근법이 필요하다. 무작위 불확실요소에 대한 신뢰성 해석결과를 베이지안 추론에 이용함으로서 엔진 당량비의 제어오차가 요구범위를 불만족할 확률에 대한 확률분포를 구할 수 있었다. 이러한 접근은 무작위 불확실요소와 인식론적 불확실 요소가 동시에 존재하는 공학시스템 해석에 유용하게 사용될 수 있다.

• 비교문화연구
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• 제25권
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• pp.649-678
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• 2011

The purpose of this work is to explain categorial correlations between indirect evidentiality and epistemic modality on the basis of semantic, pragmatic usages of Russian so-called non-specialized lexical markers of evidentiality, such as kazhetsja, naverno, vidimo, poxozhe, dolzhno byt' etc. To do this, firstly I concentrated on the parameter of internal functional variation of a given parenthetic word. Secondly, I approached this topic from a typological perspective. Thirdly, I accepted Sweeter(1990)'s methodological assumption that etymological prototype of a given word plays a great role in grammatical, semantic, pragmatic changes. As a result, I could postulate general tendencies of grammaticalizations (or semantic, pragmatic, funtional changes) in the direction from epistemic modality to indirect evidentialty, which consists of inferentives, presumptives, and quotatives. For example, such a parenthetic word as kazhetsja can functions not only as a marker of epistemic modality of uncertainty, but also as inferentives. Besides, it is very interesting that this word lately has started to function as quotatives, too. This kind of functional variations are very characteristic in these spheres.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2008년도 정기 학술대회
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• pp.602-607
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• 2008

A technique for reliability-based design optimization(RBDO) is developed based on the Bayesian approach, which can deal with the epistemic uncertainty arising due to the limited number of data. Until recently, the conventional RBDO was implemented mostly by assuming the uncertainty as aleatory which means the statistical properties are completely known. In practice, however, this is not the case due to the insufficient data for estimating the statistical information, which makes the existing RBDO methods less useful. In this study, a Bayesian reliability is introduced to take account of the epistemic uncertainty, which is defined as the lower confidence bound of the probability distribution of the original reliability. In this case, the Bayesian reliability requires double loop of the conventional reliability analyses, which can be computationally expensive. Kriging based dimension reduction method(KDRM), which is a new efficient tool for the reliability analysis, is employed to this end. The proposed method is illustrated using a couple of numerical examples.

• 한국어학
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• 제77권
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• pp.331-357
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• 2017

The purpose of this paper is to identify the workings of intonation realized in the endings through the spoken language. To achieve this objective, this paper has analyzed 300 minutes of spontaneous speech by women from Seoul and discussed the meanings of modality and their relationship with intonation. Intonation functions significantly in polysemous modal endings in epistemic and act modality. Epistemic modality is usually expressed through indirect and soft intonations such as L:, M: and LH, whereas act modality is expressed through direct and strong intonations such as H, HL and LHL. Intonation appears to be related to the Certainty degree of information, rather than classification of modality, Lengthening relate to indirectness, H with uncertainty, L with statements or affirmation, and HL and LHL relates to assertive attitude. This paper is significant as it has overcome the abstractness of existing modality studies and has engaged in objective and comprehensive analysis with actual spontaneous speech data.

• Nuclear Engineering and Technology
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• 제51권2호
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• pp.607-617
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• 2019

Global warming and climate change are increasing the intensity of typhoons and hurricanes and thus increasing the risk effects of typhoon and hurricane hazards on nuclear power plants (NPPs). To reflect these changes, a new NPP should be designed to endure design-basis hurricane wind speeds corresponding to an exceedance frequency of $10^{-7}/yr$. However, the short typhoon and hurricane observation records and uncertainties included in the inputs for an estimation cause significant uncertainty in the estimated wind speeds for return periods of longer than 100,000 years. A logic-tree framework is introduced to handle the epistemic uncertainty when estimating wind speeds. Three key parameters of a typhoon wind field model, i.e., the central pressure difference, pressure profile parameter, and radius to maximum wind, are used for constructing logic tree branches. The wind speeds of the simulated typhoons and the probable maximum wind speeds are estimated using Monte Carlo simulations, and wind hazard curves are derived as a function of the annual exceedance probability or return period. A logic tree decreases the epistemic uncertainty included in the wind intensity models and provides reasonably acceptable wind speeds.

• 한국학교수학회논문집
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• 제19권3호
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• pp.261-275
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• 2016

많은 학생들이 수학에는 하나의 정답이 존재하며, 수학 수업은 교사로부터 문제를 푸는 방법을 전달받는 수동적 과정이라는 이원론적 신념을 가지고 있다. 이 연구는 인식론적 신념의 개념화와 발달에 대한 교육심리학의 여러 연구를 고찰하고, 이를 바탕으로 수학적 사실 및 절차를 절대적이고 확실한 것으로 제시하며 학생의 오류도 절대적인 방식으로 다루는 통상적인 수학 교수 관행의 인식론적 한계를 살펴보고 그에 대한 대안을 탐색하였다. Langer와 Piper(1987)의 실험 및 Oliveira 외(2012) 등의 교실 관찰 연구는 교사가 지식을 불확실성을 허용하는 조건부적 언어로 제시하고 논의하는 것이 학생들의 인식론적 신념을 생산적인 방향으로 유도할 수 있다는 가능성을 제시하고 있다. 한편, 학생의 오류에 대한 교실 의사소통의 초점과 패턴의 변화는 수학 교실을 지배하는 이원론적 신념의 극복에 도움이 될 수 있다. 이상의 논의는 수학 수업이 암묵적으로 전달하는 인식론적 메시지의 분석 및 학생들의 인식론적 신념 발달을 자극하는 교수 전략을 탐색하는 데 토대를 제공할 수 있을 것이다.

• Structural Engineering and Mechanics
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• 제62권4호
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• pp.507-517
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• 2017

Due to the discontinuous nature of uncertainty quantification in conventional evidence theory(ET), the computational cost of reliability analysis based on ET model is very high. A novel ET model based on fuzzy distribution and the corresponding combination rule to synthesize the judgments of experts are put forward in this paper. The intersection and union of membership functions are defined as belief and plausible membership function respectively, and the Murfhy's average combination rule is adopted to combine the basic probability assignment for focal elements. Then the combined membership functions are transformed to the equivalent probability density function by a normalizing factor. Finally, a reliability analysis procedure for structures with the mixture of epistemic and aleatory uncertainties is presented, in which the equivalent normalization method is adopted to solve the upper and lower bound of reliability. The effectiveness of the procedure is demonstrated by a numerical example and an engineering example. The results also show that the reliability interval calculated by the suggested method is almost identical to that solved by conventional method. Moreover, the results indicate that the computational cost of the suggested procedure is much less than that of conventional method. The suggested ET model provides a new way to flexibly represent epistemic uncertainty, and provides an efficiency method to estimate the reliability of structures with the mixture of epistemic and aleatory uncertainties.