• 한국철도학회논문집
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• 제12권1호
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• pp.135-143
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• 2009

대부분의 개발 프로젝트는 목표 비용과 일정을 $40{\sim}200%$ 초과한다. 이러한 초과 현상은 계획시 업무를 과소 평가하거나 재작업을 고려하지 않음으로써 발생한다. 현재 국내에서 사용되는 대표적인 일정 계획/관리 기법(Gantt Chart, PERT/CPM 등)들은 재작업을 반영할 수 없다. 이 논문은 일정 계획시 보다 현실적인 일정 계획 값을 예측하기 위해서 재작업을 고려하는 방법을 고안하구 또한 과업의 과소평가를 방지하기 위해 수행시간의 불확실성을 확률변수로 나타내어 다루기 위해서 시뮬레이션을 수행하여 최종 완료 날짜의 예상치와 분산도를 계산하는 방법을 제안한다.

• 한국신뢰성학회지:신뢰성응용연구
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• 제13권4호
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• pp.241-252
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• 2013

Because of financial and safety concerns, there are needs for more accurate prediction of bridge behavior. Underestimation of the bridge load carrying capacity can have serious economic consequences, as deficient bridges must be repaired or rehabilitated. Therefore, the knowledge of the actual bridge behavior under live load may lead to a more realistic calculation of the load carrying capacity and eventually this may allow for more bridges to remain in service with or without minor repairs. The presented research is focused on the reliability evaluation of the actual load carrying capacity of existing bridges based on the field testing. Seventeen existing bridges were tested under truck load to confirm their adequacy of reliability. The actual response of existing bridge structures under live load is measured. Reliability analysis is performed on the selected representative bridges designed in accordance with AASHTO codes for bridge component (girder). Bridges are first evaluated based on the code specified values and design resistance. However, after the field testing program, it is possible to apply the experimental results into the bridge reliability evaluation procedures. Therefore, the actual response of bridge structures, including unintentional composite action, partial fixity of supports, and contribution of nonstructural members are considered in the bridge reliability evaluation. The girder distribution factors obtained from the tests are also applied in the reliability calculation. The results indicate that the reliability indices of selected bridges can be significantly increased by reducing uncertainties without sacrificing the safety of structures, by including the result of field measurement data into calculation.

• Structural Engineering and Mechanics
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• 제4권3호
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• pp.257-276
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• 1996

In North America, a large number of concrete old slab-on-steel girder bridges, classified noncomposite, were built without any mechanic connections. The stablizing effect due to slab/girder interface contact and friction on the steel girders was totally neglected in practice. Experimental results indicate that this effect can lead to a significant underestimation of the load-carrying capacity of these bridges. In this paper, the two major components-concrete slab and steel girders, are treat as two deformable bodies in contact. A finite element procedure with considering the effect of friction and contact for the analysis of concrete slab-on-steel girder bridges is presented. The interface friction phenomenon and finite element formulation are described using an updated configuration under large deformations to account for the influence of any possible kinematic motions on the interface boundary conditions. The constitutive model for frictional contact are considered as slip work-dependent to account for the irreversible nature of friction forces and degradation of interface shear resistance. The proposed procedure is further validated by experimental bridge models.

• Nuclear Engineering and Technology
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• 제49권2호
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• pp.295-305
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• 2017

This paper reviews current status of the unified approach known as integrated safety assessment (ISA), as well as the associated SCAIS (simulation codes system for ISA) computer platform. These constitute a proposal, which is the result of collaborative action among the Nuclear Safety Council (CSN), University of Madrid (UPM), and NFQ Solutions S.L, aiming to allow independent regulatory verification of industry quantitative risk assessments. The content elaborates on discussions of the classical treatment of time in conventional probabilistic safety assessment (PSA) sequences and states important conclusions that can be used to avoid systematic and unacceptable underestimation of the failure exceedance frequencies. The unified ISA method meets this challenge by coupling deterministic and probabilistic mutual influences. The feasibility of the approach is illustrated with some examples of its application to a real size plant.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2008년도 International Symposium on Remote Sensing
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• pp.285-288
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• 2008

We analyzed evaporation data in the Japanese Ocean Flux Data Sets with Use of Remote Sensing Observations (J-OFURO) Ver.2. There exists huge evaporation in Gulf Stream, Kuroshio Extension, the ocean dessert and the southern part of the Indian Ocean. The temporal variation of evaporation is overwhelmingly large, of which the standard deviation is more than 120(mm), in the Kuroshio Extension region. Also, the result of harmonic analysis gives that this large variation is closely related to annual variation. In addition, the first EOF mode shows long-term variation showing the maximum amplitude between 1992 and 1994 and remarkable decrease after 1994, and large amplitude in the equatorial region and northeast of Australia. The second and third modes were strongly influenced by El Nino. Moreover, we compared J-OFURO2 evaporation product with other products. We used six kinds of data sets (HOAPS3 and GSSTF2 of satellite data, NRA1, NRA2, ERA40 and JRA25 of reanalysis data) for comparison. Most products show underestimation in the most regions, in particular, in the northern North Pacific, mid-latitudes of the eastern South Pacific, and high-latitudes of the South Pacific compared with J-OFUR02. On the other hand, JRA25 and NRA2 show large overestimation in the equatorial regions. RMS difference between NRA2 and J-OFURO2 in the Kuroshio Extension was significantly large, more than 120(mm).

• Asian-Australasian Journal of Animal Sciences
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• 제15권5호
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• pp.745-750
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• 2002

The effects of recording interval (1, 2, 3, 4, 5, 10, 15, 20 and 30 min) on the estimation of some grazing behavior variables in beef cows and calves (<4 months old) were investigated in a daytime grazing (7 h) system utilizing a bahiagrass (Paspalum notatum Flugge) pasture (a 1.1 ha paddock and a 0.4 ha resting area). Recording intervals of 10-30 min tended to underestimate the time spent grazing and ruminating and overestimate the time spent resting by animals, whereas intervals of 1-5 min resulted in almost constant estimates. In all grazing activities, the errors of estimation became larger when the recording interval exceeded 5 min. The accuracy of estimation was higher for grazing time>rumination time>resting time. An increase in recording interval always decreased estimates of the distance walked by animals. It was concluded that recording intervals of 1-5 min provide reliable estimates of the time spent grazing, ruminating and resting. It was also concluded that positioning of animals at 1 min intervals may provide estimates of walking distance with acceptable bias toward underestimation.

• 한국대기환경학회지
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• 제28권1호
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• pp.52-58
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• 2012

In this study, the effect of standard phase difference in calibration of carbonyl compounds (CC) was evaluated by using their standards prepared in both gaseous and liquid phase. For this analysis, standards in both phases were prepared for 6 different CCs (formaldehyde (FA), acetaldehyde (AA), propionaldehyde (PA), butyraldehyde (BA), isovaleraldehyde (IA) and valeraldehyde (VA)) at similar concentration levels. Their gaseous standard was calibrated after derivatization with three types of DNPH cartridge, and their calibration results were compared against liquid-phase standards. Although there was a strong compatibility between 2 phases for CCs with lower molecular weights (e.g., formaldehyde and acetaldehyde), it was not the case for the heavier CCs. The results of our analysis indicate that the analytical bias of the heavier CCs can be significantly large (by more than a few tens of %). As a result, underestimation of hevier CCs can be significant, if their gaseous samples are quantified by liquid phase standard.

• 보험의학회지
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• 제26권
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• pp.31-39
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• 2007

Background and main issue: In the Korean insurance market, an outstanding issue is the decrease of margin of risk ratio. This affects the solvency and profitability of insurance companies. Insurance medicine, which has been developed in Western countries, is so-called medical risk selection or medical underwriting. Medical risk selection is based on clinical follow-up study and mortality analysis methodology. Unfortunately, there have been few clinical follow-up studies, and no intercompany disease analysis system is available in the Korean insurance market. In practice, we use underwriting guidelines, which were developed by some global reinsurance companies. However, these guidelines were developed under clinical follow-up studies performed abroad. So, we cannot rule out underestimation of excess mortality factors such as mortality ratio, excess death rate, and life expectancy. It is necessary to perform medical assessment in claims administration. Comparing the insured's statement by medical records with products' benefit according to this procedure, we can make sound claim decisions and participate in the role of sound underwriting. We can call this scientific procedure as the verification of medical claims review. Another area of medical claims review is medical counsel for claims staff. Result: There is another insurance medicine in addition to medical risk selection. Independent medical assessment by medical records of insured is medical claims review. Medical claims review is composed of verification and counsel.

• 한국조사연구학회:학술대회논문집
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• 한국조사연구학회 2000년도 춘계학술대회 조사연구의 방법론적 쟁점
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• pp.1-14
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• 2000

사회.경제조사에서 흔히 발생하는 무응답에 대한 통계적 대처 방안을 고찰하였다. 항목 무응답이 발생했을 때 무응답 데이터를 포함하지 않는 완전 데이터를 만드는 방법으로 무응답 대체 방법이 널리 이용되고 있다. 본 논문에서는 여러 가지 대체 방법을 소개하고 각 방법의 장.단점을 비교.설명하였다. 또한 대체된 데이터를 응답 데이터인 것처럼 활용했을 때 발생하는 문제점들을 지적하였다. 무응답을 대체하면 대체된 값들 때문에 대체 후 추정량의 분산은 대체 분산만큼 증가하는 반면, 대체된 데이터에 기초한 통상적인 분산추정량은 대체 분산을 추정하지 못하므로 결과적으로 대체 후 추정량의 분산을 과소추정하게 된다. 이러한 분산의 과소추정의 원인을 이론적으로 고찰하였고, 모의실험을 통하여 그 결과의 심각성을 설명하였다. 마지막으로 분산의 과소 추정 문제를 해결하는 몇 가지 수정된 분산추정 방법을 소개하고 토의하였다.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2007년도 Proceedings of ISRS 2007
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• pp.278-281
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• 2007

The purpose of this study is to develop snow and sea ice detection algorithm in Communication, Ocean and Meteorological Satellite (COMS) meteorological data processing system. Since COMS has only five channels, it is not affordable to use microwave or shortwave infrared data which are effective and generally used for snow detection. In order to estimate snow and sea ice coverage, combinations between available channel data(mostly visible and 3.7 ${\mu}m$) are applied to the algorithm based on threshold method. As a result, the COMS snow and sea ice detection algorithm shows reliable performance compared to MODIS products with channel limitation. Specifically, there is partial underestimation over the complicated vegetation area and overestimation over the area of high level clouds such as cirrus. Some corrections are performed by using water vapor and infrared channels to remove cloud contamination and by applying NDVI to detect more snow pixels for the underestimated area.