• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.6A
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• pp.449-456
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• 2011

Spacing factor proposed by Power is a concept of averaging air void spacing composed of geometric models. Thus, there's a limitation on simulating actual air void characteristics in concrete. This study presents SDI(spacing distribution index) to overcome the limitation of spacing factor. SDI is also evaluated through comparing SDI with SF(spacing factor). In this study, it was confirmed that SF decreased due to increasing air-entrainer content but SDI increased. This occurs because SDI is the area of spacing distribution curve and SDI increases with increasing the frequency of spacing. SDI is evaluated to have better coverage below $300{\mu}m$ of SF so that determination of critical point of SDI above 80% of durability index can be easily obtained with more reliability. SDI is the area of spacing distribution curve and reflects actual air void characteristics in concrete. A comparative study of SDI and results of freeze-thaw test will be performed later.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.6
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• pp.276-286
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• 2013

SVD-based deconvolution algorithm has been known as the most effective technique for CT perfusion image analysis. In this algorithm, in order to reduce noise effects, SVD coefficients smaller than a certain threshold are removed. As the truncation threshold, either a fixed value or a variable threshold yielding a predetermined OI (oscillation index) is frequently employed. Each of these two thresholding methods has an advantage to the other either in accuracy or efficiency. In this paper, we propose a Monte Carlo simulation method to evaluate the accuracy of the two methods. An extension of the proposed method is presented as well to measure the effects of image smoothing on the accuracy of the thresholding methods. In this paper, after the simulation method is described, experimental results are presented using both simulated data and real CT images.

• The Journal of the Korea Contents Association
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• v.6 no.2
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• pp.34-43
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• 2006

This paper shows modeling methods for VBR video trace. It is well known that VBR video trace is characterized as longterm correlated and highly intermittent burst data. To analyze this, we attempt to model it using neural network with auxiliary linear structures derived from residual threshold. For testing purpose, we generate VBR video trace from chaotic nonlinear function combined with the geometric random noise. The modeling result of the generated data shows that the attempted method represents more accurately than the traditional neural network. However, we also found that combining hRU to the attempted modeling method can yield a closer agreement to statistical features of the generated data than the attempted modeling method alone.

• Tunnel and Underground Space
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• v.18 no.3
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• pp.194-201
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• 2008

In order to investigate the characteristics in tensile strength of transversely isotropic rock, a new anisotropic tensile failure function was suggested. According to the function, the tensile strength is minimum in the normal direction to a weakness plane and rises exponentially to its maximum on a plane perpendicular to the weakness plane. The anisotropic function is defined in terms of three strength parameters which can be identified trom direct tensile tests of transversely isotropic rocks. By incorporating the suggested function into the critical plane approach, a numerical procedure which enables to search the tensile strength and the direction of critical plane at failure was presented. The validity of the suggested numerical procedure was checked through the simulation of direct tensile tests reported in a literature. The numerical results from the simulation were in good agreements with those from the laboratory tests.

• Journal of the Korean Magnetics Society
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• v.25 no.6
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• pp.180-184
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• 2015

We have investigated the magnetization reversal behavior in ferromagnetic $Co_{0.5}Fe_{0.5}$ alloy films using the magneto-optical Kerr microscope capable of the direct observation of time-resolved domain patterns. Interestingly enough, as the sample thickness increases the magnetization reversal behavior becomes changed from a single domain wall motion to the random nucleations of domains. Also, from the stochastic analysis of the domain jump sizes during the domain wall motion, it was found that the magnetization reversal behavior in the samples shows the critical scaling behavior with the critical exponent of ${\tau}{\sim}1.33$.

• Atmosphere
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• v.20 no.4
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• pp.467-482
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• 2010

In this study, characteristics of various stability indexes (SI) and environmental parameters (EP) for the lightning are analysed by using 5 upper air observatories (Osan, Gwangju, Jeju, Pohang, and Baengnyeongdo) for the years 2002-2006 over South Korea. The analysed SI and EP are the lifted index, K-index, Showalter stability index, total precipitable water, mixing ratio, wind shear and temperature of lifting condensation level. The lightning data occurred on the range of -2 hr~+1 hr and within 100 km based on the launch time of rawinsonde and observing location are selected. In general, summer averaged temperature and mixing ratio of lower troposphere for the lightning cases are higher about 1 K and $1{\sim}2gkg^{-1}$ than no lightning cases, respectively. The Box-Whisker plot shows that the range of various SI and EP values for lightning and no lightning cases are well separated but overlapping of SI and EP values between lightning and no lightning are not a little. The optimized threshold values for the detection of lightning are determined objectively based on the highest Heidke skill socre (HSS), which is the most favorable validation parameter for the rare event, such as lightning, by using the simulation of SI and EP threshold values. Although the HSS is not high (0.15~0.30) and the number and values of selected SI and EP are dependent on geographic location, the new threshold values can be used as a supplementary tool for the detection or forecast of lightning over South Korea.

• 한국경영정보학회:학술대회논문집
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• 2008.06a
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• pp.141-148
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• 2008

각종 인공지능 기법들을 활용하여, 주식시장의 흐름을 예측하려는 연구가 지금까지 많은 인공지능 및 금융공학의 연구자들에 의해 시도되어 왔으며, 그 결과 다양한 인공지능 기법들이 예측 방법론으로 제시되어 왔다. 이런 가운데 서로 다른 예측모형들이 산출하는 예측결과를 종합 - 보완하는 결합기법에 관련된 연구가 90년대 후반부터 오늘날까지 꾸준하게 발표되고 있다. 본 연구 역시 유전자 알고리즘 기반의 새로 인공지능 예측모형간 결합기법을 제시하고 있다. 다만, 기존의 연구모형들이 각 개별모형 결과의 상대적 가중치에 초점을 맞추고 있었다면, 본 연구의 제안모형은 등락을 판단하는데 활용되는 임계치까지 유전자 알고리즘을 이용해 동시에 최적화하도록 설계되어 있다는 점에서 차별화된다. 제안모형의 유용성을 검증하기 위해, 본 연구에서는 지난 1998년부터 2007년까지의 KOSPI 지수 등락 예측을 위해 구축된 로지스틱 회귀모형, 인공신경망, SVM모형의 결과들을 제안모형을 이용해 결합하였다. 그 결과, 예측력 향상에 본 연구의 제안모형이 기여 할 수 있음을 확인 할 수 있었다.

• Proceedings of the Korean Information Science Society Conference
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• 2002.04a
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• pp.892-894
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• 2002

본 논문은 유한 체 GF(/2 sup m/)상에서 A$B^2$연산을 위해 AOP(All One Polynomial)에 기반한 새로운 MSB(Most Significant bit) 유선 알고리즘을 제시하고, 제시한 알고리즘에 기반하여 병렬 입출력 세미시스톨릭 구조를 제안한다. 제안된 구조는 표준기저(standard basis)에 기반하고 모듈라(modoular) 연산을 위해 다항식의 계수가 모두 1인 m차의 기약다항식 AOP를 사용한다. 제안된 구조에서 AND와 XOR게이트의 딜레이(deray)를 각각 /D sub AND$_2$/와/D sub XOR$_2$/라 하면 각 셀 당 임계경로는 /D sub AND$_2$+D sub XOR/이고 지연시간은 m+1이다. 제안된 구조는 기존의 구조보다 임계경로와 지연시간 면에서 보다 효율적이다. 또한 구조 자체가 정규성, 모듈성, 병렬성을 가지기 때문에 VLSI 구현에 효율적이다. 더욱이 제안된 구조는 유한 체상에서 지수 연산을 필요로 하는 Diffie-Hellman 키 교환 방식, 디지털 서명 알고리즘 및 EIGamal 암호화 방식과 같은 알고리즘을 위한 기본 구조로 사용할 수 있다. 이러한 알고리즘을 응용해서 타원 곡선(elliptic curve)에 기초한 암호화 시스템(Cryptosystem)의 구현에 사용될 수 있다.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.19 no.3
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• pp.54-60
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• 2011

The purpose of this study is verification of threshold of the aircraft turbulence index and icing index using PIREPs and KWRF on Korean peninsula, to operational weather support. There is improvement in new threshold value made of the pilot weather report data and the turbulence and icing index from KWRF model result, using the ROC Diagram method. the accuracy is up to 0.6 compared with the precedent study result 0.5. Through this study, It is founded on the research and development of the Korean peninsula aircraft turbulence and icing.

• Science of Emotion and Sensibility
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• v.1 no.1
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• pp.171-179
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• 1998

스피커의 음질을 평가하기 위해서 가장 많이 측정하는 것은 주파수 응답이다. 그러나 주파수 응답으로부터 바로 스피커의 성능을 평가하기는 어려운데, 이는 인간의 청각특성이 주파수나 음압에 대해 선형적인 관계를 가지지 않기 때문이다. 본 논문에서는 인간의 청각특성 중 24개의 임계대역과 라우드니스 등을 이용하여 스피커의 성능을 평가하는 방법을 제안한다. 본 논문에서 제안하는 방법은 지향서을 고려하여 스피커의 주파수 응답을 구한 후 이를 이상적인 스피커의 주파수 응답과 임계대역-라우드니스 영역에서 비교하여 음질평가지수를 산출한다. 제안된 방법에 의한 스피커의 성능 평가법은 신뢰도가 가장 큰 문제가 되므로 청취평가를 수행하여 그 결과와 비교하고 상관관계를 보였다. 제안된 방법에 의한 결과와 청취평가의 결과는 0.9765의 높은 상관관계를 가졌는데, 이는 본 논문에서 제안하는 방법이 청취평가 대용으로 훌륭히 사용될 수 있음을 의미한다.