• 품질경영학회지
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• 제24권2호
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• pp.65-76
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• 1996

In general, most industrial products exhibit bath-tub shaped curve for their failure rate functions. This distributional life model can be obtained by the Piecewise Weibull distribution. The least squares, maximum likelihood, and mixed methods of estimating the parameters of the Piecewise Weibull distribution are compared. The comparison is made by using the empirical mean squared errors of (a) the parameter estimates and (b) the estimated change-points, to summarize the results of 1000 simulated samples of three sizes - each 100, 150 and 200. The results are that the mixed method estimation comes to be the best as the sample sizes increase.

• 한국음향학회지
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• 제36권5호
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• pp.338-344
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• 2017

본 논문에서는 머리전달함수 보간 알고리즘을 제안하며, 특히 작은 크기의 측정 데이터를 다루는 경우를 고려한다. 제안하는 알고리즘은 머리전달함수의 음향학적 모델링에 기초하며, 모델링 계수를 추정함으로써 머리전달함수를 보간한다. 이 때 측정 위치의 개수가 부족할 경우 모델링 계수를 추정하는 것은 매우 어려우며, 따라서 본 알고리즘은 벡터-기반 크기 패닝 기법을 이용하여 데이터를 확장함으로써 이러한 문제를 해결하려고 한다. 본 알고리즘은 벡터-기반 크기 패닝 기법 기반의 데이터 확장 단계와, 최소자승법 기반의 모델링 계수 추정 단계의 두 단계로 이루어져 있다. 제안하는 알고리즘의 성능을 확인하기 위하여 CIPIC(Center for Image Processing and Integrated Computing) 머리전달함수 데이터베이스의 측정 데이터 중 일부를 이용한 시뮬레이션을 진행하였으며, 시뮬레이션 결과 약 1.5 dB ~ 4 dB의 최소 자승 오차가 감소됨을 확인할 수 있었다.

• Smart Structures and Systems
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• 제23권2호
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• pp.195-205
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• 2019

An accurate non-model-based method for delamination identification of laminated composite plates is proposed in this work. A weighted mode shape damage index is formulated using squared weighted difference between a measured mode shape of a composite plate with delamination and one from a polynomial that fits the measured mode shape of the composite plate with a proper order. Weighted mode shape damage indices associated with at least two measured mode shapes of the same mode are synthesized to formulate a synthetic mode shape damage index to exclude some false positive identification results due to measurement noise and error. An auxiliary mode shape damage index is proposed to further assist delamination identification, by which some false negative identification results can be excluded and edges of a delamination area can be accurately and completely identified. Both numerical and experimental examples are presented to investigate effectiveness of the proposed method, and it is shown that edges of a delamination area in composite plates can be accurately and completely identified when measured mode shapes are contaminated by measurement noise and error. In the experimental example, identification results of a composite plate with delamination from the proposed method are validated by its C-scan image.

• The Journal of the Acoustical Society of Korea
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• 제14권1E호
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• pp.56-64
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• 1995

최소평균사승 적응알고리즘은 추정오차의 평균사승값을 최소화하는 추정경도방법 가운데 하나이다. 알고리즘의 잠재적인 여러 장점에도 불구하고, 이 알고리즘은 현재 기존의 최소평균자승 알고리즘 보다 실제 적게 주목받고 있다. 그 이유는 최소평균사승 알고리즘의 수렴특성에 관한 통계적 분석이 최소평균자승 알고리즘에 비해 매우 어렵고, 따라서 아직 알고리즘에 대해 모르는 분분이 많이 때문으로 보인다. 본 논문에서는 적응필터의 입력신호가 평균이 영이고 시불변 가우시안 랜덤신호일 경우 최소평균사승 적응알고리즘의 통계적인 수렴특성에 대하여 연구하였다. 이를 위해, 시스템인지 모드에서 알고리즘의 평균 및 평균자승 특성을 나타내는 일련의 관계식을 유도하였다. 그리고 알고리즘의 평균특성이 수렴하기 위한 조건을 찾았는데, 여기서 최소평균사승 적응알고리즘의 수렴특성이 초기치의 선택에 크게 좌우됨을 알 수 있었다. 또한 최소 평균사승 알고리즘의 성능을 기존의 최소평균자승 알고리즘과 실험적으로 비교하였고, 두개의 알고리즘이 정상상태에서 같은 값의 평균자승추정오차를 갖을 때 최소평균사승 알고리즘이 치소평균자승 알고리즘에 비해 매우 빠른 수렴속도를 갖을수 있음을 확인하였다.

• 품질경영학회지
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• 제23권4호
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• pp.28-41
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• 1995

We consider the problem of identifying multiple outliers in linear model. The available regression diagnostic methods often do not succeed in detecting multiple outliers because of the masking and swamping effect. Recently, among the various robust estimator of reducing the effect of outliers, LMS(Least Meadian Square) estimator has been to be a suitable method proposed to expose outliers and leverage points. However, as you know it, the data analysis method with LMS estimator is to be taken the median of the squared residuals in the sample which is extracted the sample space. Then this model causes the trouble, for the number of the chosen sample is nCp, i.e. as the size of sample space n is increasing, the number is increasing fastly. And the covariance matrix may be the singular matrix, so that matrix is approching collinearity. Thus we propose a procedure ELMS for the resampling in LMS method and study the size of the effective elementary set in this algorithm.

• 전기학회논문지
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• 제62권4호
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• pp.554-561
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• 2013

In this paper, we introduce a modeling and a process simulator developed with the aid of pRBFNNs for activated sludge process in the sewage treatment system. Activated sludge process(ASP) of sewage treatment system facilities is a process that handles biological treatment reaction and is a very complex system with non-linear characteristics. In this paper, we carry out modeling by using essential ASP factors such as water effluent quality, the manipulated value of various pumps, and water inflow quality, and so on. Intelligent algorithms used for constructing process simulator are developed by considering multi-output polynomial radial basis function Neural Networks(pRBFNNs) as well as Fuzzy C-Means clustering and Particle Swarm Optimization. Here, the apexes of the antecedent gaussian functions of fuzzy rules are decided by C-means clustering algorithm and the apexes of the consequent part of fuzzy rules are learned by using back-propagation based on gradient decent method. Also, the parameters related to the fuzzy model are optimized by means of particle swarm optimization. The coefficients of the consequent polynomial of fuzzy rules and performance index are considered by the Least Square Estimation and Mean Squared Error. The descriptions of developed process simulator architecture and ensuing operation method are handled.

• 한국수자원학회논문집
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• 제33권2호
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• pp.263-276
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• 2000

본 논문은 인천지방에서의 확률강우량과 확률강우강도식을 유도하기 위하여 인천기상대에서 관측된 자료로부터 강우 지속기간 10분 ~ 6시간까지의 연최대강우량을 선정하였다. 12개 강우지속기간별 확률강우량을 추정하기 위하여 11개 확률분포형을 적용하였으며 Chi-square 검정방법, Kolmogorov-Smirnov 검정방법, Cramer Von Mises 검정방법으로 적합도 검정과 함께 도시적 해석법으로 가정 적합한 분포형을 결정하였다. 확률강우도식은 최소자승법을 사용하여 Talbot 형, Sherman 형, Japanese 형의 3가지로 분석하고, 최소자승법과 함께 시산법을 사용하여 통합형I과 통합형II의 형태로 결정하였다. 표준제곱근오차와 계산된 강우강도와 추정된 강우강도와의 차이를 분석하여 단기 강우 지속기간에 관한 통합형I의 확률강우강도식을 인천지방 강우강도공식으로 제안하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권7호
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• pp.1792-1801
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• 2012

Symbol timing error amounts to a major degradation in the system performance. Conventionally, timing error is estimated by predefined preamble on both transmitter and receiver. The maximum of the correlation result is considered the start of the OFDM symbol. Problem arises when the prime path is not the strongest one. In this paper, we propose a new combined time and channel estimation method for multi-band OFDM ultra wide-band (MB-OFDM UWB) systems. It is assumed that a coarse timing has been obtained at a stage before the proposed scheme. Based on the coarse timing, search interval is set (or time candidates). Exploiting channel statistics that are assumed to be known by the receiver, we derive a maximum a posteriori estimate (MAP) of the channel impulse response. Based on this estimate, we discern for the timing error. Timing estimation performance is compared with the least squares (LS) channel estimate in terms of mean squared error (MSE). It is shown that the proposed timing scheme is lower in MSE than the LS method.

• 응용통계연구
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• 제18권1호
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• pp.43-56
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• 2005

본 연구에서는 AR(1) 과정을 따르는 시계열 모형에서 가산적 이상치(Additive Out-lier)가 존재하는 경우, 1차 자기상관계수에 대한 로버스트 추정방법으로 Rupport 와 Carroll (1980)에 의해 회귀모형에서 제안된 L-추정법 형태의 절사최소제곱추정 (PE 추정)방법을 제안하였다. 더불어 X축의 이상치에 대한 비중강하(down-weight)의 방법으로 Mallows의 가중함수를 고려한 유계영향 절사최소제곱 (bounded influence PE, BIPE)추정량을 제안하였으며 모의 실험을 통하여 각 추정량의 효율성을 비교하였다. 모의실험 결과, 다양한 자료의 오염률상에서 일반화 LAD추정치를 예비 추정치로 고려한 BIPE(LAD)-추정량의 효율이 좋은 것으로 나타났다.

• Journal of Electrical Engineering and Technology
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• 제11권4호
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• pp.974-986
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• 2016

Reversible image watermarking, a type of digital data hiding, is capable of recovering the original image and extracting the hidden message with precision. A number of reversible algorithms have been proposed to achieve a high embedding capacity and a low distortion. While numerous algorithms for the achievement of a favorable performance regarding a small embedding capacity exist, the main goal of this paper is the achievement of a more favorable performance regarding a larger embedding capacity and a lower distortion. This paper therefore proposes a reversible data hiding algorithm for which a novel piecewise 2D auto-regression (P2AR) predictor that is based on a rhombus-embedding scheme is used. In addition, a minimum description length (MDL) approach is applied to remove the outlier pixels from a training set so that the effect of a multiple linear regression can be maximized. The experiment results demonstrate that the performance of the proposed method is superior to those of previous methods.