• Journal of Korea Water Resources Association
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• 제36권2호
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• pp.315-324
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• 2003

Stream flow data was analyzed for determining the lowflow which is the standard for river maintenance flow. Lowflow quantiles were estimated based on the parametric and nonparametric methods and two methods were compared by Monte Carlo simulation study. As the results of the parametric method, three probability distributions such as gamma-2, lognormal-2 and Weibull-2, are selected as appropriate models for stream flow data of 13 stations in Han River Basins. According to simulation results, relative bias (RBIAS) and relative root mean square error (RRMSE) of the lowflow quantiles are the smallest when the applied and population models are the same. The fame statistical properties from the nonparametric models are good within the interpolation range. Among 7 bandwidth selectors used in this study, the RRMSEs of the Park and Marron method (PM) are the smallest while those of the Shoaler and Jones method (SJ) are the largest.

• Journal of the Korean Association of Geographic Information Studies
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• 제23권4호
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• pp.16-41
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• 2020

Geospatial input setting to represent the reality of spatial distribution or quantitative property within model has become a major interest in earth system simulation. Many studies showed the variation of grid resolution could lead to drastic changes of spatial model results because of insufficient surface property estimations. Hence, in this paper, the authors proposed Monte Carlo Integration (MCI) to apply spatial probability (SP) in a spatial-sampling framework using a three-dimensional point cloud (3DPC) to keep the optimized spatial distribution and area/volume property of buildings in urban area. Three different decision rule based building identification results were compared : SP threshold, cell size, and 3DPC density. Results shows the identified building area property tend to increase according to the spatial sampling grid area enlargement. Hence, areal building property manipulation in the sampling frameworks by using decision rules is strongly recommended to increase reliability of geospatial modeling and analysis results. Proposed method will support the modeling needs to keep quantitative building properties in both finer and coarser grids.

• Proceedings of the Korea Water Resources Association Conference
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• 한국수자원학회 2016년도 학술발표회
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• pp.158-158
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• 2016

본 연구에서는 극치 분포의 오른쪽 꼬리 부분 예측 시 안정적인 확률수문량 산정하는 확률분포형과 매개변수 추정 방법을 평가하기 위해 Monte Carlo 모의를 수행하였다. 수문자료의 빈도해석에 적합한 것으로 알려진 generalized extreme value (GEV), Gumbel (GUM), generalized logistic (GLO), gamma3 (GAM3), normal (NOR), log-normal3 (LN3) 총 6개의 확률분포형을 바탕으로 오른쪽 꼬리 부분의 확률수문량 추정 성능을 모의 실험을 통해 평가하고자 한다. 30년 이상 자료를 보유한 기상청 지점의 지속기간별 연최대값 자료를 분석한 결과를 바탕으로 모분포를 GEV분포로 선정하였으며 평균이 1.0, 표준편차 0.5, 왜곡도 계수는 0.5, 1.0, 2.0, 3.0, 4.0이 되도록 가정하였다. 또한 자료 길이에 따른 성능 평가를 위해 표본 크기 20, 50, 100, 150, 200개에 대해 분석을 수행하였다. 위와 같은 가정으로 총 25종류(왜곡도계수 5개 ${\times}$ 표본 크기 5개)의 발생된 모분포에 6가지의 확률분포형과 3가지의 매개변수 추정방법(모멘트법, 최우도법, 확률가중모멘트법)을 조합한 18가지의 모델을 비교 분석해보았다. 평가방법으로는 평균 제곱근 오차(Root Mean Square Error, RMSE), 편의(bias), 평균 상대오차(Mean Relative Difference, MRD), 평균 절대 상대오차(Mean Absolute Relative Difference, MARD)를 사용하여 적용 모델의 성능을 비교 분석하였다.

• Journal of radiological science and technology
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• 제38권4호
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• pp.477-482
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• 2015

Workers in nuclear medicine have performed various tasks such as production, distribution, preparation and injection of radioisotope. This process could cause high radiation exposure to wokers' hand. The purpose of this study was to investigate shielding effect for r-rays of 140 and 511 keV by using Monte-carlo simulation. As a result, it was effective, regardless of lead thickness for radiation shielding in 140 keV r-ray. However, it was effective in shielding material with thickness of more than only 1.1 mm in 511keV r-ray. And also it doesn't effective in less than 1.1 mm due to secondary scatter ray and exposure dose was rather increased. Consequently, energy of radionuclide and thickness of shielding materials should be considered to reduce radiation exposure.

• Journal of the Korean Geosynthetics Society
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• 제18권4호
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• pp.193-204
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• 2019

Reliability analyses of sixteen domestic design cases of open cell caisson breakwaters against circular sliding failure were conducted in this study. For the reliability analyses, uncertainties of parameters of soils, mound, and concrete cap were assessed. Bishop simplified method was used to obtain load and resistance of open cell caisson breakwater for randomly generated open cell caisson breakwater. Sufficient number of Monte Carlo simulations were conducted for randomly generated open cell caisson breakwaters, and statistical analysis was conducted on loads and resistances collected from the large number of Monte Carlo simulations. Probability of failure produced from Monte Carlo simulation has a nonconvergence issue for very low probability of failure; therefore, First-Order Reliability Method (FORM) was conducted using the statistical characteristics of loads and resistances of open cell caisson breakwaters. In addition, effects of safety factor, uncertainties of load and resistance, and correlation between load and resistance on reliability of open cell caisson breakwaters against circular sliding failure were examined.

• Progress in Medical Physics
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• 제16권3호
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• pp.138-147
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• 2005

The Monte Carlo method cannot have been used for routine treatment planning because of heavy time consumption for the acceptable accuracy. Since calculation time is proportional to particle histories, we can save time by decreasing the number of histories. However, a small number of histories can cause serious uncertainties. In this study, we proposed Monte Carlo dose computation time and uncertainty reduction method using specially designed filters and adaptive denoising process. Proposed algorithm was applied to 6 MV photon and 21 MeV electron dose calculations in homogeneous and heterogeneous phantoms. Filtering time was negligible comparing to Monte Carlo simulation time. The accuracy was improved dramatically in all situations and the simulation of 1 $\%$ to 10$\%$ number of histories of benchmark in photon and electron dose calculation showed the most beneficial result. The empirical reduction of necessary histories was about a factor of ten to fifty from the result.

• Journal of Radiation Protection and Research
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• 제29권2호
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• pp.105-115
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• 2004

The Monte Carlo simulation requires very much time to obtain a result of acceptable accuracy. Therefore we should know the optimum number of history not to sacrifice time as well as the accuracy. In this study, we have investigated the effects of statistical uncertainties of the photon dose calculation. BEAMnrc and DOSXYZnrc systems were used for the Monte Carlo dose calculation and the case of mediastinum was simulated. The several dose calculation result from various number of histories had been obtained and analyzed using the criteria of isodose curve comparison, dose volume histogram comparison(DVH) and root mean-square differences(RMSD). Statistical uncertainties were observed most evidently in isodose curve comparison and RMSD while DVHs were less sensitive. The acceptable uncertainties $(\bar{{\Delta}D})$ of the Monte Carlo photon dose calculation for the radiation therapy were estimated within total 9% error or 1% error for over than $D_{max}/2$ voxels or voxels at maximum dose.

• The Journal of the Korea Contents Association
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• 제16권8호
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• pp.477-483
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• 2016

The effect of dose enhancement was evaluated using Snyder head phantom, dependence on size of gold nanoparticle and material concentration in megavoltage X, ${\gamma}$-ray. Monte Carlo simulation using MCNPX was used for 4, 6, 10, 15 MV and Co-60 ${\gamma}$-ray. Described the tumor in Snyder head phantom, gold nanoparticle of 25, 75, 125nm diameter was inserted inside tumor. Concentration of dose enhancement material was used for 5, 15, 25 mg/g and dose enhancement factor was calculated on the basis of the no dose enhancement material. The lower incident energy and the higher concentration of material were that high dose enhancement factor is indicated. The size of gold nanoparticle had relatively high dependence on lower incident energy and higher concentration of material. It will increase dose inside the tumor, and be additional effect of use of gold nanoparticles in radiation therapy.

• Proceedings of the Korea Water Resources Association Conference
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• 한국수자원학회 2005년도 학술발표회 논문집
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• pp.90-94
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• 2005

본 연구의 목적은 현 국내 홍수 예경보시스템에 사용되고 있는 저류함수모형의 매개변수 변화에 따른 유량해석의 불확실성을 평가하는데 있다. 적용 대상지점으로는 개진을 출구로 하는 낙동강 회천유역($747.5km^2$)이며 비교적 양호한 수문자료를 가지고 있는 단일 호우사상을 선정하였다. 불확실성 평가에 사용된 매개변수는 관측수문곡선을 비교적 정확하게 모의하는 경험적인 값을 기준으로 Monte Carlo 기법을 이용하여 각각의 매개변수(K, P, $T_{1},\;f_{l},\;R_{sa}$)에 대한 정규분포를 가지는 100개의 난수를 발생시켜 저류함수 모형으로 모의되는 유량 앙상블을 평가하였다. 최적화된 매개변수를 이용하여 유량해석을 실시한 결과, 각각의 매개변수가 유출해석에 미치는 영향을 파악할 수 있었으며, 그 중 저류상수 K와 포화누가우량 Rsa가 불확실성이 제일 큰 매개변수로 나타났고, 이들의 혼합 앙상블 유출결과도 매우 큰 불확실성을 내포하는 것으로 나타났다.

• Proceeding of EDISON Challenge
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• 제6회(2017년)
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• pp.64-74
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• 2017

본 연구에서는 동역학 격자기반 대정준 Monte Carlo (Kinetic Lattice Grand Canonical Monte Carlo, KLGCMC) 모의실험 방법과 Poisson-Nernst-Planck (PNP) 계산 방법을 이용하여 이온채널의 전하분포, 채널 반지름, 그리고 이온의 농도와 이온의 크기가 이온전류와 이온전도도에 미치는 영향과, 이온 간 상관관계 (correlation)가 이온전류와 이온전도도에 미치는 영향을 조사하였다. 이로부터 이온 간 상호작용에 의해 이온 이동에 제약이 가해지는 이온 간 상관관계 효과는 채널 내 이온 수가 증가할수록 커지는 것을 알 수 있었다. 또한, 평균장 이론에 기반한 PNP 이론은 이온 간 상관관계 효과를 적절하게 기술하지 못하며, 이온 간 상관관계 효과가 중요해지는 이온 채널 관련 결맞음 공명 (coherence resonance) 등 특이 현상을 연구하기 위해서는 이온 간 상관관계를 기술할 수 있는 KLGCMC 모의실험 방법이 필요함을 알 수 있었다.