• 융합신호처리학회논문지
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• 제5권2호
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• pp.119-125
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• 2004

방향 성분은 소벨(sobel)과 FFT 방법 등을 주로 사용한다. 소벨을 이용한 방법은 소벨 마스크의 복잡한 처리 과정과 대표 방향 성분을 추출하고자 할 때 픽셀별로 단위 벡터를 만들어 누적시킬 경우 낮은 대비 영상이나 높은 대비 영상이나 같은 값이 나오므로 기울기 크기를 누적할 수 없어 대표 방향을 설정하기 어렵다. FFT를 변환을 이용한 방법은 융선이 정확한 방향 성분을 가지는 경우에만 방향성 추출이 가능하며 별도의 방향 필터를 사용해야 한다. 본 논문에서는 위의 단점을 보완하기 위하여 이진화 된 영상을 세선화 한 후 픽셀 단위로 방향 성분을 추출하며, 8${\times}$8 픽셀크기의 블록 내에 존재하는 픽셀이 가지는 방향 성분 중 가장 많은 방향 성분을 융선의 대표 방향으로 추출하는 새로운 방법을 제안한다.

• 한국지진공학회논문집
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• 제24권6호
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• pp.253-266
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• 2020

The extended slip-weakening model was investigated by using a compiled set of source-spectrum-related parameters, i.e. seismic moment M_o, S-wave velocity V_s, corner-frequency f_c, and source-controlled high-cut frequency fmax, for 113 shallow crustal earthquakes (focal depth less than 25 km, M_W 3.0~7.5) that occurred in Japan from 1987 to 2016. The investigation was focused on the characteristics of stress drop, radiation energy-to-seismic moment ratio, radiation efficiency, and fracture energy release rate, G_c. The scaling relationships of those source parameters were also investigated and compared with those in previous studies, which were based on generally used singular models with the dimensionless numbers corresponding to f_c given by Brune and Madariaga. The results showed that the stress drop from the singular model with Madariaga's dimensionless number was equivalent to the breakdown stress drop, as well as Brune's effective stress, rather than to static stress drop as has been usually assumed. The scale dependence of stress drop showed a different tendency in accordance with the size category of the earthquakes, which may be divided into small-moderate earthquakes and moderate-large earthquakes by comparing to M_o = 10¹⁷~10¹⁸ Nm. The scale dependence was quite similar to that shown by Kanamori and Rivera. The scale dependence was not because of a poor dynamic range of recorded signals or missing data as asserted by Ide and Beroza, but rather it was because of the scale dependent V_r-induced local similarity of spectrum as shown in a previous study by the authors. The energy release rate G_c with respect to breakdown distance D_c from the extended slip-weakening model coincided with that given by Ellsworth and Beroza in a study on the rupture nucleation phase; and the empirical relationship given by Abercrombie and Rice can represent the results from the extended slip-weakening model, the results from laboratory stick-slip experiments by Ohnaka, and the results given by Ellsworth and Beroza simultaneously. Also the energy flux into the breakdown zone was well correlated with the breakdown stress drop, ${\tilde{e}}$ and peak slip velocity of the fault faces. Consequently, the investigation results indicate the appropriateness of the extended slip-weakening model.

• 환경정책연구
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• 제12권4호
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• pp.71-92
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• 2013

보편적인 공공투자사업과는 달리, 환경관련 투자사업은 사업추진으로 인한 비용과 편익의 부담주체가 동일하지 않다. 비용의 큰 비중은 현재세대가 부담하지만 그 편익은 미래세대가 더 많이 누리는 구조인 것이다. 이러한 특성을 고려하지 않은 채 일률적인 사회적할인율을 적용하는 것은 환경투자사업의 경제성 평가과정에서 미래 세대의 편익이 상대적으로 과소평가되는 문제를 발생시키는 것으로 인식된다. 이에 미래 세대의 편익이 경제성 평가과정에서 보다 적절히 반영될 수 있는 사회적할인율과 그 적용방법을 모색해 보았다. 최근의 경제상황 변동을 고려한 사회적할인율을 추정해 본 결과, 적정 사회적할인율은 2.9%에서 4.9% 사이의 범위를 갖는 것으로 나타났다. 또한 기 수행된 실제 예비타당성조사 자료를 분석하여 환경투자사업의 전형적인 편익발생 패턴을 분석해 보았으며, 사회적할인율을 다양한 방식으로 적용해 보았을 때, 이의 조정이 경제성 평가결과에 어떠한 영향을 미칠 수 있는지를 살펴보았다. 사회적 할인율이 현행 수준보다 1%p. 가량 인하조정될 경우 사업의 편익/비용 비율은 약 6%가량 개선될 수 있는 것으로 분석되었으며, 이때 미래 세대의 편익을 보다 적절하게 고려하기 위해서는 분석기간별로 차등적인 사회적할인율을 적용하는 것이 바람직함을 지적하였다. 이러한 방법은 편익추정과정에서 발생할 수 있는 추정위험 등의 기술적 요인도 보완해줄 수 있는 효과적인 방안이라 평가된다.

• 정보처리학회논문지D
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• 제13D권7호
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• pp.889-900
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• 2006

센서 네트워크는 애플리케이션 분야에 따라 데이터 특성과 사용자의 요구사항이 다양함에도 불구하고, 현존하는 스트림 데이터 축소 연구는 데이터의 본질적인 특징보다 특정 축소 기법의 성능 향상 측면에 중점을 두고 있다. 이 논문은 계층/분산형 센서 네트워크 구조와 데이터 모델을 소개하고, 선택적으로 축소 기법을 적용하기 위해 데이터 특성과 사용자의 요구에 적합한 다변량 데이터 축소 기법을 비교 평가한다. 다변량 데이터 축소 기법의 성능을 비교 분석하기 위해, 우리는 웨이블릿, HCL(Hierarchical Clustering), SVD(Singular Value Decomposition), 샘플링과 같은 표준화 된 다변량 축소 기법을 이용한다. 실험 데이터는 다차원 시계열 데이터와 로봇 센서 데이터를 사용한다. 실험 결과 SVD와 샘플링 기법이 상대 에러 비율과 수행 성능 측면에서 웨이블릿과 HCL기법에 비해 우수하였다. 특히 각 데이터 축소 기법의 상대 에러 비율은 입력 데이터 특성에 따라 다르기 때문에 선택적으로 데이터 축소 기법을 적용하는 것이 좋은 성능을 보였다. 이 논문은 다차원 센서 데이터가 수집되는 센서 네트워크를 디자인하고 구축하는 응용 분야에 유용하게 활용될 것이다.

• 전산구조공학
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• 제6권2호
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• pp.95-102
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• 1993

노후 구조물의 안전진단을 위하여 동적재하시험을 수행하고 그 결과를 유한요소모델과 같은 해석적 모델과 결합하여 기존구조물의 강성평가 및 파손부위 색출에 적용하고 있는데 측정점의 제한성과 유한요소모델의 많은 자유도가 측정데이타를 유한요소모델과 연계하는데 커다란 문제점으로 대두된다. 본 연구에서는 유한요소모델과 같이 많은 자유도를 갖는 구조계의 해석적 모델을 측정데이타와 결합하기 위하여 축약된 좌표계에서 구조계의 동강성행렬(dynamic stiffness matrix)표현방법을 제시하였다. 유한요소모델로부터 좌표계를 축약시 필연적으로 발생되는 주파수의존성(frequency dependency)을 고려하기 위하여 주파수영역에서 Chebyshev다항식으로 축약된 동강성행렬을 표시하였고 특이점에서 발생되는 악조건(ill-condition)을 극복하기 위하여 특이해분리(singular value decomposition)기법을 사용하였다. 제시된 방법의 검증을 위하여 간단한 구조계에 대하여 시뮬레이션을 수행하였으며 본 방법으로 수립된 구조계의 동적모델은 축약이전의 전체계에 대한 동적특성을 비교적 정확히 유지하고 있고 일반적으로 사용되는 정적축약 형태의 수학적 모델보다 우수함을 알 수 있었다.

• Korea-Australia Rheology Journal
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• 제15권3호
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• pp.131-150
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• 2003

A new numerical algorithm of finite element methods is presented to solve high Deborah number flow problems with geometric singularities. The steady inertialess planar 4 : 1 contraction flow is chosen for its test. As a viscoelastic constitutive equation, we have applied the globally stable (dissipative and Hadamard stable) Leonov model that can also properly accommodate important nonlinear viscoelastic phenomena. The streamline upwinding method with discrete elastic-viscous stress splitting is incorporated. New interpolation functions classified as rational interpolation, an alternative formalism to enhance numerical convergence at high Deborah number, are implemented not for the whole set of finite elements but for a few elements attached to the entrance comer, where stress singularity seems to exist. The rational interpolation scheme contains one arbitrary parameter b that controls the singular behavior of the rational functions, and its value is specified to yield the best stabilization effect. The new interpolation method raises the limit of Deborah number by 2∼5 times. Therefore on average, we can obtain convergent solution up to the Deborah number of 200 for which the comer vortex size reaches 1.6 times of the half width of the upstream reservoir. Examining spatial violation of the positive definiteness of the elastic strain tensor, we conjecture that the stabilization effect results from the peculiar behavior of rational functions identified as steep gradient on one domain boundary and linear slope on the other. Whereas the rational interpolation of both elastic strain and velocity distorts solutions significantly, it is shown that the variation of solutions incurred by rational interpolation only of the elastic strain is almost negligible. It is also verified that the rational interpolation deteriorates speed of convergence with respect to mesh refinement.

• International Journal of Contents
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• 제9권4호
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• pp.1-10
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• 2013

The electroencephalogram (EEG) time series is a measure of electrical activity received from multiple electrodes placed on the scalp of a human brain. It provides a direct measurement for characterizing the dynamic aspects of brain activities. These EEG signals are formed from a series of spatial and temporal data with multiple dimensions. Missing data could occur due to fault electrodes. These missing data can cause distortion, repudiation, and further, reduce the effectiveness of analyzing algorithms. Current methodologies for EEG analysis require a complete set of EEG data matrix as input. Therefore, an accurate and reliable imputation approach for missing values is necessary to avoid incomplete data sets for analyses and further improve the usage of performance techniques. This research proposes a new method to automatically recover random consecutive missing data from real world EEG data based on Linear Dynamical System. The proposed method aims to capture the optimal patterns based on two main characteristics in the coevolving EEG time series: namely, (i) dynamics via discovering temporal evolving behaviors, and (ii) correlations by identifying the relationships between multiple brain signals. From these exploits, the proposed method successfully identifies a few hidden variables and discovers their dynamics to impute missing values. The proposed method offers a robust and scalable approach with linear computation time over the size of sequences. A comparative study has been performed to assess the effectiveness of the proposed method against interpolation and missing values via Singular Value Decomposition (MSVD). The experimental simulations demonstrate that the proposed method provides better reconstruction performance up to 49% and 67% improvements over MSVD and interpolation approaches, respectively.

• Structural Engineering and Mechanics
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• 제27권5호
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• pp.625-638
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• 2007

The damage detection process may appear difficult to be implemented for truss structures because not all degrees of freedom in the numerical model can be experimentally measured. In this context, the damage locating vector (DLV) method, introduced by Bernal (2002), is a useful approach because it is effective when operating with an arbitrary number of sensors, a truncated modal basis and multiple damage scenarios, while keeping the calculation in a low level. In addition, the present paper also evaluates the noise influence on the accuracy of the DLV method. In order to verify the DLV behavior under different damages intensities and, mainly, in presence of measurement noise, a parametric study had been carried out. Different excitations as well as damage scenarios are numerically tested in a continuous Warren truss structure subjected to five noise levels with a set of limited measurement sensors. Besides this, it is proposed another way to determine the damage locating vectors in the DLV procedure. The idea is to contribute with an alternative option to solve the problem with a more widespread algebraic method. The original formulation via singular value decomposition (SVD) is replaced by a common solution of an eigenvector-eigenvalue problem. The final results show that the DLV method, enhanced with the alternative solution proposed in this paper, was able to correctly locate the damaged bars, using an output-only system identification procedure, even considering small intensities of damage and moderate noise levels.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2003년도 한국우주과학회보 제12권2호
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• pp.82-82
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• 2003

It is well known that electromagnetic (EM) waves are mode converted to electrostatic (ES) waves in inhomogeneous plasmas. We examine this issue in a three-dimensional multi-fluid numerical model. First, we derive a set of coupled linear wave equations when a one-dimensional inhomogeneous density profile is assumed in a cold and collisionless plasma. The massive ions are considered as fixed because we are interested in high frequency waves in plasmas. It is shown that the EM mode satisfies the 0th order modified Bessel equation near the resonant region where the frequency matches the local electron plasma frequency. It is expected that the EM waves are coupled and damped to the ES waves owing to the logarithmic singular behavior at such resonances. Second, we numerically test the same case in a 3-D multi-fluid model. An impulsive input is assumed to excite EM waves in the inhomogeneous 3-D box model. The wave spectra of electric and magnetic fields are presented and compared with the analytical results. Our results suggest that the EM energy is irreversibly converted into the ES energy wherever the resonant condition is satisfied. Finally we discuss how the mode conversion appears in both electric and magnetic fields by analyzing time histories of each component. We also compare our results with MHD wave coupling. It is numerically confirmed in this study that the coupling of EM and ES waves is similar to that of compressional and transverse MHD waves.

• 대한한의학원전학회지
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• 제27권1호
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• pp.99-109
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• 2014

Objectives : The concepts of many Korean medicine terms have changed for a long time and cumulatively been recorded in later medicine literatures. And, the same terms have very often been used for different meanings depending on context. Methods : This study was performed so that conceptual magnitude of Korean medicine terms could intuitively be recognized for the purpose of quantization. Results : This study was performed under the premise that terms used in old literatures of Korean medicine are related mostly to treatments that could immediately be reverted to types of medical herbs used. Through this, conceptual magnitude of terms was quantified by the method that frequency of medical herbs used for treatment was changed to numerical values. For this, data of "Compilation of Formulas and Medicinals Addendum" were used. First, after 'specificity' of each medicine herb corresponding to representative disease symptoms was calculated, medians in the set were selected, and 'values of conceptual magnitude' for representative disease symptoms were calculated. Conclusions : As a result, if disease symptoms are diverse, concept range is diachronically changed greatly, and specific disease symptoms of great conceptual difference are included, value of conceptual magnitude was great. Meanwhile, if disease factor and treatment are singular or limited to several types, and many medical herbs with high specificity are used, value of conceptual magnitude was less.