• 대한수학회논문집
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• 제10권3호
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• pp.653-659
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• 1995

We prove that two essentially normal elements of a type $II_{\infty}$ factor von Neumann algebra are unitarily equivalent up to the compact ideal if and only if they have the identical essential spectrum and the same index data. Also we calculate the spectrum and essential spectrum of a non-unitary isometry of von Neumann algebra.

• 한국수자원학회논문집
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• 제38권6호
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• pp.439-448
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• 2005

본 논문은 수문시계열에서 나타나는 주기성 및 경향성 등을 평가하기 위한 방법으로 Fourier Transform을 개선한 Wavelet Transform방법을 제시하고 이에 대한 타당성 및 적용성을 월강수량 및 연강수량 자료와 대표적인 기상인자인 남방진동지수(SOI)와 해수면온도(SST)를 대상으로 평가해 보았다. Fourier Transform은 시간적인 특성을 파악하지 못하는 반면에 Wavelet Transform은 수문시계열이 갖는 시간적인 특성을 유지하면서 빈도에 대한 스펙트럼을 보다 효율적으로 평가할 수 있었다. Wavelet Transform을 이용하여 분석한 결과 국내 월강수량은 1년을 중심으로 강한 스펙트럼을 나타내고 있으며 연강수량은 2-8년 주기에서 통계적으로 유의한 주기를 확인할 수 있었다. SOI와 SST에서는 2-8년 주기가 지배적임을 확인할 수 있었다.

• 한국광학회지
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• 제7권4호
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• pp.357-362
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• 1996

스핀 코팅으로 제작한 MNA/PMMA 고분자박막의 두께 및 굴절율과 소광계수를 결정하였다. 타원해석 스펙트럼을 분석하여 박막의 두께 및 투과영역에서의 굴절율을 결정하고 광흡수 스펙트럼으로부터 흡수영역에서의 소광계수 스펙트럼을 역방계산하였다. 이 소광계수 스펙트럼을 가장 잘 나타내는 고전적 Lorentz 진동자 상수들과 양자역학적 진동자 상수들을 각각 구하고 이들 진동자에 의한 복소굴절율 스펙트럼들을 비교하였다. 이 방법은 대부분의 고분자박막의 두께 및 굴절율과 소광계수 스펙트럼을 구하는데 적용될 수 있으며 고분자박막의 광학적 특성을 규정짓는데 매우 유용하게 사용될 수 있겠다.

• 한국광학회:학술대회논문집
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• 한국광학회 1991년도 제6회 파동 및 레이저 학술발표회 Prodeedings of 6th Conference on Waves and Lasers
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• pp.203-208
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• 1991

We present an analytic equation for the reflectivity spectrum of a Bragg reflector in terms of the front mirror reflectivity, due to the refractive index difference between the refractive index of outside medium and the average refractive index of Bragg reflector structures, and the reflectivity of a Bragg reflector calculated by the coupled wave method. We show that even Fresnel reflection causes the reflectivity spectrum of a bragg reflector to be very different from that of Bragg reflectors calculated by the coupled wave method. The reflectivity spectrum of a Bragg reflector is dramatically changed because the interference effect between the reflected wave from the front facet and that from the Bragg reflector is changed due to the difference of a phase change from a Bragg reflector when the sequence of layers in a Bragg reflector is changed.

• Journal of Communications and Networks
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• 제11권2호
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• pp.134-147
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• 2009

Tracking and exploiting instantaneous spectrum opportunities are fundamental challenges in opportunistic spectrum access (OSA) in presence of the bursty traffic of primary users and the limited spectrum sensing capability of secondary users. In order to take advantage of the history of spectrum sensing and access decisions, a sequential decision framework is widely used to design optimal policies. However, many existing schemes, based on a partially observed Markov decision process (POMDP) framework, reveal that optimal policies are non-stationary in nature which renders them difficult to calculate and implement. Therefore, this work pursues stationary OSA policies, which are thereby efficient yet low-complexity, while still incorporating many practical factors, such as spectrum sensing errors and a priori unknown statistical spectrum knowledge. First, with an approximation on channel evolution, OSA is formulated in a multi-armed bandit (MAB) framework. As a result, the optimal policy is specified by the wellknown Gittins index rule, where the channel with the largest Gittins index is always selected. Then, closed-form formulas are derived for the Gittins indices with tunable approximation, and the design of a reinforcement learning algorithm is presented for calculating the Gittins indices, depending on whether the Markovian channel parameters are available a priori or not. Finally, the superiority of the scheme is presented via extensive experiments compared to other existing schemes in terms of the quality of policies and optimality.

• 전기학회논문지
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• 제58권6호
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• pp.1078-1086
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• 2009

This paper presents a Fourier based algorithm for estimating the parameters of the low frequency oscillating modes. The proposed methods estimates various parameters(frequency, damping factor, mode magnitude, phase) by fitting Fourier spectrum and phase with a damped exponential cosine function. Dominant frequency is selected by taking frequency corresponding to the peak spectrum, and damping factor is estimated using the left/right spectra of Fourier spectrum. In addition, mode magnitude is calculated by the normalized peak spectrum, and phase is estimated from spectrum phase. Also, we introduce an accuracy index in order to determine the accuracy of the estimated parameters, and the index is calculated using the deviations of the peak spectrum and the left/right spectra. The parameter estimation methods proposed in this paper include very simple arithmetical processes, so the algorithms are simple and the calculation speed is very fast. The proposed methods are applied to test functions with two dominant modes. The results show that the proposed methods are highly applicable to low frequency parameter estimation.

• 천문학회지
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• 제37권5호
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• pp.315-322
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• 2004

Several arguments have been presented in the literature to support the connection between radio halos and cluster mergers. The spectral index distributions of the halos in A665 and A2163 provide a new strong confirmation of this connection, i.e. of the fact that the cluster merger plays an important role in the energy supply to the radio halos. Features of the spectral index (flattening and patches) are indication of a complex shape of the radiating electron spectrum, and are therefore in support of electron reacceleration models. Regions of flatter spectrum are found to be related to the recent merger. In the undisturbed cluster regions, instead, the spectrum steepens with the distance from the cluster center. The plot of the integrated spectral index of a sample of halos versus the cluster temperature indicates that clusters at higher temperature tend to host halos with flatter spectra. This correlation provides further evidence of the connection between radio emission and cluster mergers.

• 대한의용생체공학회:의공학회지
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• 제28권6호
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• pp.750-755
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• 2007

The linear SEF (Spectral Edge Frequency) parameter and spectrum analysis method can not reflect the non-linear of EEG. This method can not contribute to acquire real time analysis and obtain a high confidence in the clinic due to low discrimination. To solve the problems, the development of a new index is carried out using the bispectrum analyzing the EEG including the non-linear characteristic. At the bispectrum analysis of the 2 dimension, the most significant's power spectrum density peaks appeared much at the specific area in awake and anesthesia state. Because many peaks are showed at the specific area in the frequency coordinate, these points are used to create the new index. Range of the index is 0-100. At the anesthesia, the index is 20-50 and at the awake, the index is 90-60. New index can discriminate the awake and anesthesia state.

• 한국광학회지
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• 제14권3호
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• pp.266-271
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• 2003

수 $\mu\textrm{m}$ 이상의 두께를 가지는 비교적 두꺼운 박막의 경우 박막에 의한 간섭효과로 인하여 나타나는 반사율 스펙트럼에서의 진동주기로부터 막의 두께를 얻는다. 대개 빠른 데이터 처리를 위해서 고속 푸리에 변환(Fast Fourier Transformation, FFI)을 사용하여 진동주기(또는 진동수)를 구한다. 본 연구에서는 반사율 또는 투과율 스펙트럼을 빛의 에너지 축상에서 푸리에 변환하는 종래의 방법을 개선하여 박막의 굴절률 분산을 반영하는 수정된 고속 푸리에 변환 방법을 최초로 도입하였다. 이 새로운 방법은 굴절률 분산에서 유래하는 유효굴절률 결정에서의 오차를 줄여주고 푸리에 변환 피크의 폭 넓어짐을 막아줌으로써 막 두께 결정의 정밀도를 크게 향상시킨다. 수정된 고속 푸리에 변환방법을 80 $\mu\textrm{m}$의 덮게층과 13 $\mu\textrm{m}$의 사이층이 있는 시료의 반사 스펙트럼에 적용하여 고 타당성을 확인하였다.

• Applied Microscopy
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• 제46권1호
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• pp.27-31
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• 2016

It has been investigated what kind of characteristic X-ray in electron probe micro-analyzer (EPMA) is effective for the determination of compounds of Si series materials. After comparing the characteristic X-rays among the primary and secondary lines in $K_{\alpha}$ and $K_{\beta}$ obtained from the Si series standard samples, it was found that the secondary line of $K_{\alpha}$ exhibited the most informative spectrum although the intensity was considerably weak. As a result of analyzing the spectrum shapes of the Si series standard samples, the spectrum shape of the secondary line of $K_{\alpha}$ for SiC was different from those for other Si compounds. To grasp the characteristics of the shape, a line was perpendicularly drawn from the peak top to base line in order to divide a spectrum into two areas. The area ratio of right to left was defined to call as the asymmetry index here. As a result, the asymmetry index value of the SiC was greater than one, while those of other Si compounds were less than one. It was found from the EPMA analysis that identification of SiC became successful to distinguish from other Si compounds and this method was applicable for micro-sized compounds in a practical composite material.