• Architectural research
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• 제15권3호
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• pp.151-158
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• 2013

Offshore oil and gas process plants are exposed to hazardous accidents such as explosion and fire, so that the structural components should resist such accidental loads. Given the possibilities of thousands of different scenarios for the occurrence of an accidental hazard, the best way to predict a reasonable size of a specific accidental load would be the employment of a probabilistic approach. Having the fact that a specific procedure for probabilistic accidental hazard analysis has not yet been established especially for explosion and fire hazards, it is widely accepted that engineers usually take simple and conservative figures in assuming uncertainties inherent in the procedure, resulting either in underestimation or more likely in overestimation in the topside structural design for offshore plants. The variation in the results of a probabilistic approach is determined by the assumptions accepted in the procedures of explosion probability computation, explosion analysis, and structural analysis. A design overpressure load for a sample offshore plant is determined according to the proposed probabilistic approach in this study. CFD analysis results using a Flame Acceleration Simulator, FLACS_v9.1, are utilized to create an overpressure hazard curve. Moreover, the negative impulse and frequency contents of a blast wave are considerably influencing structural responses, but those are completely ignored in a widely used triangular form of blast wave. An idealistic blast wave profile deploying both negative and positive pulses is proposed in this study. A topside process module and piperack with blast wall are 3D FE modeled for structural analysis using LS-DYNA. Three different types of blast wave profiles are applied, two of typical triangular forms having different impulse and the proposed load profile. In conclusion, it is found that a typical triangular blast load leads to overestimation in structural design.

• 한국작물학회지
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• 제51권1호
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• pp.89-94
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• 2006

Traditionally fatty acid composition used to be analysed by a GC and the sample preparation process includes lipid extraction from sample and subsequent methyl esters preparation, which are time-consuming and cumbersome. As an alternative, simultaneous extraction/methylation methods are being developed for rapid and simplified sample preparation. To optimize one-step extraction/methylation method for analysis of fatty acid composition in brown rice, various reaction factors such as sample to reaction solution ratio, reaction time and temperature, shaking intensity were changed and resultant fatty acid composition data were evaluated in comparison with previous reports. The ratio of sample weight to reaction solution volume was the most critical factor in that higher sample to reaction solution ratio caused overestimation of palmitic acid and linoleic acid composition, resulting in underestimation of oleic acid. Lower reaction temperature also induced overestimation of linoleic acid and underestimation of oleic acid. Reaction duration and the intensity of shaking prior to and during the reaction, however, caused no significant changes in analysis results. In conclusion, the optimum condition was mixing 5 grains (about 0.2 g) of brown rice with $680{\mu}L$ of extraction/methylation mixture and $400{\mu}L$ of heptane, followed by reaction at $80^{\circ}C$ for 2 hours.

• 한국정보과학회논문지:시스템및이론
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• 제32권4호
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• pp.148-159
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• 2005

CPU의 수행과 병행하여 I/O가 수행되도록 DMA 방식을 채택한 실시간 시스템의 스케줄 가능성을 보장하기 위해서는 CPU 태스크 뿐만 아니라 I/O 요구의 스케줄 가능성도 반드시 검증되어야 한다. 본 논문에서는 CPU에게 최상위 우선순위가 할당된 고정우선순위 버스 프로토콜을 기반으로 CPU와 다수의 DMA 컨트롤러가 시스템 버스를 공유하는 환경에서 DMA I/O 요구의 최악 응답시간을 분석하는 기법을 제안한다. 제안하는 분석 기법의 첫 번째 단계에서는 CPU 상에서 수행 중인 각 CPU 태스크별로 최악 버스 요구 패턴을 구한다. 두 번째 단계에서는 이들 CPU 태스크의 최악 버스 요구 패턴을 모두 통 차해 CPU 전체의 최악 버스 요구 패턴을 구한다. 최종 세 번째 단계에서는 CPU의 최악 버스 요구 패턴으로부터 DMA 컨트롤러의 버스 가용량을 구하고 DMA I/O 요구의 최악 응답시간을 산출한다. 모의 실험을 통해 제안하는 분석 기법이 일반적인 DMA 전송량에 대해 $20\%$ 오차 범위 이내에서 안전한 응답시간을 산출하며, DMA 전송량이 증가할수록 오차가 점차 감소함을 보였다

• 대한방사선기술학회지:방사선기술과학
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• 제45권5호
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• pp.397-405
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• 2022

Computed radiography (CR) systems, which convert an analog signal recorded on a cassette into a digital image, combine the characteristics of analog and digital imaging systems. Compared to digital radiography (DR) systems, CR systems have presented difficulties in evaluating system performance because of their lower detective quantum efficiency, their lower signal-to-noise ratio (SNR), and lower modulation transfer function (MTF). During the step of energy-storing and reading out, a baseline offset occurs in the edge area and makes low-frequency overestimation. The low-frequency offset component in the line spread function (LSF) critically affects the MTF and other image-analysis or qualification processes. In this study, we developed the method of baseline correction using mathematical morphology to determine the LSF and MTF of CR systems accurately. We presented a baseline correction that used a morphological filter to effectively remove the low-frequency offset from the LSF. We also tried an MTF evaluation of the CR system to demonstrate the effectiveness of the baseline correction. The MTF with a 3-pixel structuring element (SE) fluctuated since it overestimated the low-frequency component. This overestimation led the algorithm to over-compensate in the low-frequency region so that high-frequency components appeared relatively strong. The MTFs with between 11- and 15-pixel SEs showed little variation. Compared to spatial or frequency filtering that eliminated baseline effects in the edge spread function, our algorithm performed better at precisely locating the edge position and the averaged LSF was narrower.

• Journal of the korean society of oceanography
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• 제33권3호
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• pp.53-63
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• 1998

The Princeton ocean model (POM) with free surface in sigma-coordinate, governed by primitive equations, is used to examine the response of sea water in Deukryang Bay to a typhoon. The model reproduces reasonably well the main features in the wind-driven dynamics due to passing of a typhoon. In response to the wind, the coastal jet develops and the upwelling(or downwelling) occurs dominantly in both sides of the bay. This result implies that there should be an overturn in the bay water with the passing of typhoons. Numerical results of POM are also compared to those of a depth-averaged model. From the comparison, it is postulated that the bottom drag coefficient conventionally used for the two-dimensional flow models is inadequate due to overestimation of the computed current field.

• Structural Engineering and Mechanics
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• 제11권3호
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• pp.287-299
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• 2001

Columns in multi-storey frames are presently categorised as either braced or unbraced, usually by means of the stability index criterion, for estimating their effective length ratios by design aids such as 'alignment charts'. This procedure, however, ignores the transition in buckling behaviour between the braced condition and the unbraced one. Hence, this results in either an overestimation or an underestimation of effective length estimates of columns in frames that are in fact 'partially braced'. It is shown in this paper that the transitional behaviour is gradual, and can be approximately modelled by means of a 'fuzzy logic' based technique. The proposed technique is simple and intuitively agreeable. It fills the existing gap between the braced and unbraced conditions in present codal provisions.

• Asian Journal of Innovation and Policy
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• 제4권1호
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• pp.35-54
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• 2015

The purpose of this study is to compare the valuation of technology firms in the KOSPI and KOSDAQ. This study analyzed 224 market reports for KOSDAQ firms and 602 reports for KOSPI firms. We compare the two markets under 3 definitions on the accuracy of stock price forecasting. Findings are as follows: Although PER multiples is the most used method of valuation, KOSDAQ valuation more heavily relies on the method than KOSPI valuation. In stock market, the period of earnings forecasting is mostly 2-3 years. Multiples of KOSDAQ is generally higher than those of KOSPI. Even for technology firms, valuation in KOSPI mostly relies on earnings of the company, but that in KOSDAQ mostly relies on relative price. In stock price forecasting, generally overestimation prevails. Moreover, forecasting of KOSPI reports is more accurate than that of KOSDAQ reports. ROE and COE of KOSDAQ firms are generally higher than those of KOSPI firms.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2005년도 춘계 학술발표회 논문집
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• pp.456-463
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• 2005

An analytical procedure to analyze reinforced concrete (RC) beams subject to monotonic loadings is proposed on the basis of the moment-curvature relations of RC sections. Unlike previous analytical models which result the overestimation of stiffnesses and underestimation of structural deformations induced from ignoring the shear deformation and assuming perfect-bond condition between steel and concrete, the proposed relation considers the rigid-body-motion due to anchorage slip at the fixed end. The advantages of the proposed relation, compared with the previous numerical models, are on the promotion in effectiveness of analysis and reflection of influencing factors which must be considered in nonlinear analysis of RC beam by taking into account the nonlinear effects into the simplifying moment-curvature relation. Finally, correlation studies between analytical and experimental results are conducted to establish the applicability of the proposed model to the nonlinear analysis of RC structures.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2008년도 정기 학술대회
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• pp.350-355
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• 2008

This paper addresses vibration comfort evaluation on suspension bridge subjected to moving vehicles. The moving load method is commonly employed for the analysis, even though it is less accurate than the moving mass approach which considers vehicle-bridge interaction effects and roughness of the pavement. In this study, a parametric study on modeling method by means of the moving load technique, such as the number of modes included in the analysis, types of moving loads, and length of the stiffening girder, is carried out. The numerical result indicated that use of the triangular pulse load may result in significant overestimation on vibration discomfortness.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 가을 학술발표논문집(II)
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• pp.245-250
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• 1998

The Elastic modulus depends on the elastic property of composition materials, the gravity of aggregate, the bond strength of binder, the usage and quantity of admixture, curing and measuring method, etc. Accordingly, the aim of this study, by manufacturing concrete of practical high strength range(600~ 1000kg/$\textrm{cm}^2$) with the specific cement and mineral admixtures, is to compare elastic modulus with the existing equations and also to estimate elastic property of use materials. As a result, it could be confirmed that the existing equations which were proposed by the ACI 363, CEB-FIP Code, and New-RC have a tendency to the overestimation in general. However, it could be confirmed that the KCI-96 and Norwegian NS 3473 equations are closed to measuring results, and that the elastic modulus property have a different tendency due to types of cements.