• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.5A
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• pp.397-401
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• 2005

A different alternative method for simulating bit error rate(BER) performance of Satellite Digital Multimedia Broadcasting(DMB) in tunnel environments is presented. The method based on a channel model obtained by ray-tracing is able to support BER estimation over the channel presents arbitrary statistics that are difficult to fit to an analytic expression. The BER performance for System E over the tunnel fading channel that obtained by ray-tracing is predicted by the monte-carlo method. It can be observed that the BER performance for a straight tunnel channel is better than that for a line-of-sight(LOS) area in curved tunnel. Also, the BER performance for LOS areas in a curved tunnel outperforms that for non-line-of-sight(NLOS) areas in a curved tunnel. The BER performances for straight, curved LOS and curved NLOS tunnel channels are better than that for a Rayleigh channel(K=0) and less than that for a Rician channel with K=3. Moreover, for BER=10-3, it can be seen that there is approximately a $1{\sim}1.5\;dB$ difference between those three types of tunnel channels and a Rayleigh channel.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.5
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• pp.607-617
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• 2014

This paper proposed the M&S(Modeling & Simulation) method of channel characterization of satellite communication in the operating area of satellite OTM(On-The-Move) terminal. In M&S, received signal profile was acquired by HTZ warfare software which uses 3 dimensional map including building, road information and geographical features, and then was analyzed statistically. And a received signal profile and its statistics from M&S data were compared with those from measured data. The research showed that the simulated received signal profile matched the measured one about 74.8 percent and simulated statistics matched well as roadside trees were excluded.

• Journal of the Korean Data and Information Science Society
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• v.25 no.1
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• pp.155-167
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• 2014

This study uses a continuous autoregressive (CAR) model to analyze daily average temperature in six Korean metropolitan cities. Data period is Jan. 1, 1954 to Dec. 31, 2010 covering 57 years. Using a relative long time series reveals that the linear time trend components are all statistically significant in the six cities, which was not shown in previous studies. Particularly the plus sign of its coefficient implies the effect on Korea of the global warming. Unit-root test results are that the temperature time series are stationary without unit-root. It turns out that CAR(3) is suitable for stochastic component of the daily temperature. Since developing suitable continuous stochastic model of the underlying weather related variables is crucial in pricing the weather derivatives, the results in this study will likely prove useful in further future studies on pricing weather derivatives.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.181.1-181.1
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• 2010

기후변화의 주요인이 되는 온실가스 감축을 목표로 화석연료를 대체하기 위한 대체 에너지 개발을 위한 많은 노력이 진행되고 있다. 풍력 에너지와 같은 신재생에너지는 이러한 하나의 해결 수단이 될 수 있으며 풍력 에너지 사업의 활성화를 위해서는 정확한 풍력 정보 제공이 우선이다. 풍력-기상자원지도는 풍력 발전에 유용한 정보 제공을 위한 목적으로 중규모 수치 모델을 이용하여 작성된다. 본 연구에서는 중규모 수치 모델의 정확도 향상을 위한 자료동화 방법으로써 Four-Dimensional Data Assimilation (FDDA) 방법을 이용한다. 풍력-기상자원지도는 공간분해능 1 km 해상도로 개발된다. 풍력-기상자원지도는 1998-2008년까지의 평균적인 상태에 대하여 모의를 하기 위하여 통계적인 방법으로 11년 기간의 평균과 유사한 기간을 선정하였다. 풍력-기상자원지도는 연 평균, 월 평균 풍속과 주 풍향, 주풍향 발생 비율 등의 정보를 제공한다. 우리나라 풍속의 평균 분포는 내륙 산악지역, 남해안, 제주도에서 강풍이 발생하며 주 풍향은 대체로 북서풍이다. 주 풍향의 발생비율은 산악 지역과 남 동해안에서 높아 풍력 발전의 최적지 정보를 제공한다. 1 km 해상도의 모델과 관측의 오차는 서해안 등의 해안지역보다 강원 산악지역에서 오차가 더욱 증가하였다. 이러한 산악 지역의 오차는 복잡한 지형에서는 1km 미만의 수 백 m 해상도 수치모의가 필요함을 지시한다. 따라서 본 연구에서는 WRF-LES 모형을 이용하여 333m 해상도의 기상자원지도를 개발한다. 333m 해상도의 자원지도 영역은 강원도 지역에 대하여 모의되었다. 333m 해상도의 풍속 분포는 1km 해상도의 풍속 분포와 비교하였을 때 풍속의 분포가 보다 세밀하게 표현되었다. 정량적인 검증을 하였을 때 관측소에 따라 차이는 있었으나 1km 해상도에서 과대 모의된 풍속의 분포가 현저히 개선이 되었으며, 시간적인 경향도 잘 일치함을 보였다.

• Journal of Radiation Protection and Research
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• v.26 no.2
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• pp.113-117
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• 2001

The energy band method for NaI spectrum calculates only the exposure rate due to natural radiation because it calculates exposure rate using energy spectrum of $1300{\sim}3000keV$. However, the total energy method includes in its calculation the exposure rate due to man-made radiation because it uses the energy spectrum of $150{\sim}3400keV$. Therefore, the resulting difference of extracting the exposure rate calculated by the energy band method from the exposure rate calculated by the total energy method is apparently the exposure rate due to man-made radiation. In this study, we measured the NaI spectrum during the period of significant changes of the exposure rate in the area without a man-made radiation. As the results, we found the exposure rates calculated by those two methods are equal within the statistical variation of ${\pm}0.3{\mu}R\;h^{-1}$. Consequently, if the difference between the exposure rates calculated by the two methods exists, it may be due to the man-made radiation exposure rate.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.98-98
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• 2013

태양의 활동영역에서 관측할 수 있는 흑점은 주로 흑점군으로 관측되며, 태양폭발현상의 발생을 예보하기 위한 중요한 관측 대상 중 하나이다. 현재 태양 폭발을 예보하는 모델들은 McIntosh 흑점군 분류법을 사용하며 통계적 모델과 기계학습 모델로 나누어진다. 컴퓨터는 흑점군의 형태학적 특성을 연속적인 값으로 계산하지만 흑점군의 형태적 다양성으로 인해 McIntosh 분류법과 일치하지 않는 경우가 있다. 이러한 이유로 컴퓨터가 계산한 흑점군의 형태학적인 특성을 예보에 직접 적용하는 것이 필요하다. 우리는 흑점군을 검출하기 위해 최소신장트리(Minimum spanning tree : MST)를 이용한 계층적 군집화 기법을 수행하였다. 그래프(Graph)이론에서 최소신장트리는 정점(Vertex)과 간선(Edge)으로 구성된 간선의 가중치의 합이 최소인 트리이다. 우리는 모든 흑점을 정점, 그들의 연결을 간선으로 적용하여 최소신장트리를 작성하였다. 또한 최소신장트리를 활용한 계층적 군집화기법은 초기값에 따른 군집화 결과의 차이가 없기 때문에 흑점군 검출에 있어서 가장 적합한 알고리즘이다. 이를 통해 흑점군의 기본적인 형태학적인 특성(개수, 면적, 면적비 등)을 계산하고 최소신장트리를 통해 가장 면적이 큰 흑점을 중심으로 트리의 깊이(Depth)와 차수(Degree)를 계산하였다. 이 방법을 2003년 SOHO/MDI의 태양 가시광 영상에 적용하여 구한 흑점군의 내부 흑점수와 면적은 NOAA에서 산출한 값들과 각각 90%, 99%의 좋은 상관관계를 가졌다. 우리는 이 연구를 통해 흑점군의 형태학적인 특성과 더불어 예보에 직접적으로 활용할 수 있는 방법을 논의하고자 한다.

• Journal of the Korean Society of Groundwater Environment
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• v.1 no.2
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• pp.90-99
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• 1994

Heterogeneous hydraulic conductivity in a flow domain is generated under the assumption that it is a random variable with a lognormal, spatially-correlated distribution. The hydraulic head and the conductivity in a groundwater flow system are represented as a stochastic process. The method of Monte Carlo Simulation (MCS) and the finite element method (FEM) are used to determine the statistics of the head and the logconductivity. The second moments of the head and the logconductivity indicate that the cross-covariance of the logconductivity with the head has characteristic distribution patterns depending on the properties of sources, boundary conditions, head gradients, and correlation scales. The negative cross-correlation outlines a weak-response zone where the flow system is weakly responding to a stress change in the flow domain. The stochastic approach has a potential to quantitatively delineate the zone of influence through computations of the cross-covariance distribution.

• Journal of Korea Multimedia Society
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• v.14 no.2
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• pp.288-294
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• 2011

In this paper we define the probability models for determining the disparity map given stereo images and derive the methods for solving the problem, which is proven to be equivalent to an energy-based stereo matching. Under the assumptions the difference between the pixel on the left image and the corresponding pixel on the right image and the difference between the disparities of the neighboring pixels are exponentially distributed, a recursive approach for estimating the MRF regularizing parameter is proposed. The proposed method alternates between estimating the parameters with the intermediate disparity map and estimating the disparity map with the estimated parameters, after computing it with random initial parameters. Our algorithm is applied to the stereo matching algorithms based on the dynamic programming and belief propagation to verify its operation and measure its performance.

• Journal of the Korean Institute of Gas
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• v.10 no.2 s.31
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• pp.7-13
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• 2006

In order to evaluate the fire and explosion involved and to ensure the safe and optimized operation of chemical processes, it is necessary to know combustion characteristics. The explosion limit, the heat of combustion, flame temperature and temperature dependence of the lower explosive limit are the major combustion characteristics used to determine the fire and explosion hazards of the flammable substances. The aim of this study is to investigate interrelationship of explosion characteristics and the temperature dependence of the lower explosion limit at elevated temperature for akylketones. By using the reference data, the empirical equations which describe the interrelationships of explosion properties of akylketones have been derived. Also, the new equations using the mathematical and statistical methods for predicting the temperature dependence of lower explosion limits of akylketones on the basis of the literature data are proposed. The values calculated by the proposed equations agreed with literature data within a few percent. From the given results, using the proposed methodology, it is possible to predict the explosion limits of the other flammable substances.

• The KIPS Transactions:PartB
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• v.15B no.2
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• pp.171-178
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• 2008

Foreign word transliterations are not consistently used in documents, which hinders retrieving some important relevant documents in exact term matching information retrieval systems. In this paper, a meta search method is proposed, which expands and refines relevant variant queries from an original input foreign word transliteration query to retrieve the more relevant documents. The method firstly expands a transliteration query to the variants using a statistical method. Secondly the method selects the valid variants: it queries each variant to the retrieval systems beforehand and checks the validity of each variant by counting the number of appearance of the variant in the retrieved document and calculating the similarity of the context of the variant. Experiment result showed that querying with the variants produced at the first step, which is a base method of the test, performed 38% in average F measure, and querying with the refined variants at the second step, which is a proposed method, significantly improved the performance to 81% in average F measure.