• 경영과학
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• 제29권3호
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• pp.121-134
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• 2012

In this study, we consider a component procurement planning problem where the procurement amounts of components are determined under assemble-to-order systems with demand uncertainty. In the problem, procurement amount of each component is decided before the demands of finished products are known and after the demands are identified the assembly amounts of the finished products are decided. In this study, the objective function of the problem is minimizing the total costs which are composed of purchase and inventory costs of the components and the backorder costs of the finished products. We assume that the uncertain demand information is given as multiple scenarios of the demands, and we propose procurement planning methods based on stochastic models which considering the multiple demand scenarios. To evaluate the performances of the proposed methods, computational experiments were carried out on the proposed methods as well as benchmarks including a method based on deterministic mathematical model and a heuristic. From the results of the computational tests, the superiorities of the proposed methods were shown.

• 한국대기환경학회지
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• 제22권6호
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• pp.922-928
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• 2006

An absolute absorption cross section of benzene was measured with a spectrometer system including a mono-chrometer and a grating in the wavelength region of $240{\sim}280nm$ under the atmospheric pressure and room temperature in the laboratory. A certificated reference benzene gas ($98{\mu}mol/mol$ in $N_2$) was used to measure its absorption cross section. A 710 mm cell with a quartz window and a 150 W Xe arc lamp were employed. The magnitude of absorption cross section of $1.41{\times}10^{-18}cm^2$ was lower than that of the reference spectra ($2.5{\times}10^{-18}cm^2$) of high resolution spectrometer, Total measurement uncertainty was estimated to be 4.0%.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2006년도 춘계 학술발표회 논문집
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• pp.988-997
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• 2006

In this paper, a reliability-groundwater flow program is developed by coupling the 3-D finite element numerical groundwater flow program with first and second order reliability program. The numerical groundwater program developed called DGU-FLOW is verified by solving the examples of groundwater flow through the underground excavation and comparing the results with those of commercial MODFLOW 3D programs. Reliability routine of the program is also verified by comparing the probability of failure of the flow model from FORM/SORM with that of Monte-Carlo Simulation. The difference of out-flux and total head calculated near the bottom of the excavation using the deterministic 3D groundwater flow and the commercial programs was negligible. The reliability analysis of the groundwater flow showed that the probability of failure from the first and second order reliability method are quite close that of Monte-Carlo Simulation. Therefore, the developed program is considered effective for analyzing the groundwater flow with uncertainty in hydraulic conductivity of the soils.

• 한국대기환경학회지
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• 제18권6호
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• pp.465-474
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• 2002

In order to reflect variability due to exposure factors as well as to assess uncertainty associated with cancer risk posed by airborne trace metals, a Monte Calro analysis has been made in this study. Input parameters for Monte Carlo analysis were developed or adjusted using body weight, lifetime, and exposure frequency of Koreans. Ambient distributions of toxic metals were founded to be lognormal distributions for most of them using goodness-of-fit tests. Thus, the 95% UCL and 95% LCL of carcinogenic metals were estimated by H-statistic method for lognormal distribution, respectively. The results of Monte Carlo analysis of 95% UCL showed that the 95th percentile risks for men and women were 1.2 and 1.1 times higher than an acceptable risk of 10$^{-5}$ , respectively. The probabilities which those risks exceed the acceptable risk were estimated to be 8% and 6%, respectively, while to be 95% and 94%, respectively on the basis of the minimum acceptable risk of 10$^{-6}$ , respectively. Approximately 90% of total cancer risk came from human carcinogens such as arsenic and hexavalent chromium. Therefore, it is necessary to properly manage both arsenic and hexavalent chromium emissions in the study area.

• 한국지진공학회논문집
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• 제17권4호
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• pp.181-186
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• 2013

The construction costs for nonstructural systems such as mechanical/electrical equipment, ceiling system, and piping system occupy a significant proportion of the total cost. These nonstructural systems can also cause considerable economic losses and loss of life during and after an earthquake. Therefore, reduction of seismic risk of nonstructural components has been emerging as a key aspect of research in recent year. The primary objective of this study was to evaluate the seismic performance of a single-story and multi-story piping system installed in low-rise building and to identify the seismic vulnerability of the current piping systems. The seismic performance evaluation of the piping systems was conducted with 5 different earthquakes to account for the ground motion uncertainty and the preliminary results demonstrated that the maximum displacements of each floor in the multi-story piping system increased linearly with increasing floor level in the building system. This study revealed that the current design piping systems are significantly sensitive to the effect of floor height, which stress the necessity to improve the seismic performance of the current piping systems by, for example, strengthening with seismic sway bracing using transverse/longitudinal bracing cables or hangers.

• Nuclear Engineering and Technology
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• 제53권10호
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• pp.3449-3459
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• 2021

With the increasing availability of high-performance computing (HPC) platforms, uncertainty quantification (UQ) and sensitivity analyses (SA) can be efficiently leveraged to optimize design parameters of complex engineering problems using modeling and simulation tools. The workflow involved in such studies heavily relies on HPC resources and hence requires pre-processing and post-processing capabilities of large amounts of data along with remote submission capabilities. The NEAMS Workbench addresses all aspects of the workflows involved in these studies by relying on a user-friendly graphical user interface and a python application program interface. This paper highlights the NEAMS Workbench capabilities by presenting a semiautomated coupling scheme between Dakota and any given package integrated with the NEAMS Workbench, yielding a simplified workflow for users. This new capability is demonstrated by running a SA of a turbulent flow in a pipe using the open-source Nek5000 CFD code. A total of 54 jobs were run on a HPC platform using the remote capabilities of the NEAMS Workbench. The results demonstrate that the semiautomated coupling scheme involving Dakota can be efficiently used for UQ and SA while keeping scripting tasks to a minimum for users. All input and output files used in this work are available in https://code.ornl.gov/neams-workbench/dakota-nek5000-study.

• 아태비즈니스연구
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• 제11권1호
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• pp.27-44
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• 2020

Purpose - This study examines the factors that influence the performance of contract farming by agricultural cooperatives from the agency theory and resource-based view of the firm. Design/methodology/approach - This study collected 1,090 data related to a sample of contract information between agricultural cooperatives and producers from national agricultural cooperatives federation. In order to examine the performance of contract farming, we use the multiple regression analysis. Findings - Incentives may reduce agency problems by increasing producers' motivation and discouraging their opportunistic behavior. Total asset size and education expenses function like resources that lessen the risks coming from environment uncertainty, and also facilitate the contract farming between producers and agricultural cooperatives. Research implications or Originality - By analyzing the factors that influence on the performance of contract farming between producers and agricultural cooperatives, we propose that incentives, and resources may improve the performance of contract farming between agricultural cooperatives and producers. Overall, the contract farming can co-create the economic efficiency and effectiveness while minimizing risks and uncertainty.

• 수산해양기술연구
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• 제59권2호
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• pp.145-154
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• 2023

In this study, to control the heading angle of a ship, which is constantly subjected to various internal and external disturbances during the voyage, an LADRC (linear active disturbance rejection control) design that focuses more on improving the disturbance removal performance was proposed. The speed rate of change of the ship's heading angle due to the turn of the rudder angle was selected as a significant factor, and the nonlinear model of the ship's maneuvering equation, including the steering gear, was treated as a total disturbance. It is the similar process with an LADRC design for the first-order transfer function model. At this time, the gains of the controller included in LADRC and the gains of the extended state observer were tuned to RCGAs (real-coded genetic algorithms) to minimize the integral time-weighted absolute error as an evaluation function. The simulation was performed by applying the proposed GA-LADRC controller to the heading angle control of the Mariner class vessel. In particular, it was confirmed that the proposed controller satisfactorily maintains and follows the set course even when the disturbances such as nonlinearity, modelling error, uncertainty and noise of the measurement sensor are considered.

• 아태비즈니스연구
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• 제14권1호
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• pp.351-364
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• 2023

Purpose - This study examines the effects of Dubai oil price and the volatility on the asymmetry of domestic gasoline price adjustment. Additionally, the study investigates the effects of "Altteul" gas-station and tax-cut policies on asymmetry. Design/methodology/approach - Firstly, the study calculates proxies for asymmetry and volatility of each window(every 3-month) by error-correction model and GARCH(1, 1) using daily domestic gas price and Dubai oil price from 2008/04/15 to 2022/12/31. Secondly, the study investigates the effects of the increasing rate of Dubai oil price, volatility, "Altteul" gas-station and tax-cut policies on asymmetry. The autoregressive distributed lag regression model is employed for estimations. Findings - The study finds that changes in the increasing rate of Dubai oil price and both types of volatility of Dubai oil price increase asymmetry. While "Altteul" gas-station and tax-cut policies decrease asymmetry. Additionally, the study fails to find that asymmetry in the Korean gasoline market in the estimation with total observations. Research implications or Originality - An increase in Dubai oil price volatility means an increase in cost uncertainty for gas-station owners. Since cost uncertainty is a kind of financial risk, the increase in volatility reinforces the asymmetry. The study provides supporting evidence for the idea.

• Mass Spectrometry Letters
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• 제5권2호
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• pp.57-61
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• 2014

A gravimetric standard addition method combined with internal standard calibration has been successfully developed for the accurate analysis of total arsenic in a laver candidate reference material. A model equation for the gravimetric standard addition approach using an internal standard was derived to determine arsenic content in samples. Handlings of samples, As standard and internal standard were carried out gravimetrically to avoid larger uncertainty and variability involved in the volumetric preparation. Germanium was selected as the internal standard because of its close mass to the arsenic to minimize mass-dependent bias in mass spectrometer. The ion signal ratios of $^{75}As^+$ to $^{72}Ge^+$ (or $^{73}Ge^+$) were measured in high resolution mode ($R{\geq}10,000$) to separate potential isobaric interferences by high resolution ICP/MS. For method validation, the developed method was applied to the analysis of arsenic content in the NMIJ 7402-a codfish certified reference material (CRM) and the result was $37.07mg{\cdot}kg^{-1}{\pm}0.45mg{\cdot}kg^{-1}$ which is in good agreement with the certified value, $36.7mg{\cdot}kg^{-1}{\pm}1.8mg{\cdot}kg^{-1}$. Finally, the certified value of the total arsenic in the candidate laver CRM was determined to be $47.15mg{\cdot}kg^{-1}{\pm}1.32mg{\cdot}kg^{-1}$ (k = 2.8 for 95% confidence level) which is an excellent result for arsenic measurement with only 2.8 % of relative expanded uncertainty.