• 대한원격탐사학회지
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• 제24권2호
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• pp.99-106
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• 2008

영상 레이다(SAR)는 주야간, 일조량에 관계없이 전천후로 영상획득이 가능하여 군사용으로는 물론 과학 민수용으로 광범위하게 활용된다. SAR 시스템에서는 고도, 운용 주파수, PRF 등의 다양한 시스템설계 파라미터로부터 생성된 임펄스 응답 함수(impulse response function)를 분석하여 공간해상도, PSLR, ISLR 등 영상품질 성능 파라미터의 추정이 가능하다. 그러나 모델링된 임펄스 응답 특성은 주변 클러터 환경이 고러되지 않은 이상적인 경우이므로 실제 주변 클러터 환경을 고려한 SAR 영상품질 분석 기법이 필요하다. 본 논문에서는 먼저 주요 SAR시스템 파라미터를 기반으로 SAR 점표적 원시 데이터를 생성하고, 거리-도플러 알고리듬(range-Doppler algorithm)을 이용하여 임펄스 응답 데이터를 형성한다. 그리고 실제 SAR영상의 일부분을 추출하여 주변 배경 클러터 환경 데이터를 형성한 후, 임펄스 응답 데이터를 삽입한다. 형성된 응답 데이터는 영상품질의 정확도를 향상시키고자 확장보간법을 도입하여 분석하고, 이에 대한 효과를 주요 도플러 파라미터인 방위 FM율 오차에 따른 성능분석을 수행함으로써 확인한다.

• 대한전자공학회논문지TC
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• 제42권9호
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• pp.19-28
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• 2005

본 논문에서는 실제 아파트 환경에서 2000번의 주파수 응답에 의한 통계적 UWB 실내 채널 모델을 연구하였다. 측정은 서로 다른 방, 서로 다른 위치에서 이루어 졌으며, 실험 결과를 통해 채널의 전파특성을 이론적으로 설명하였다. Time-domain상에서 측정할 수 있는 channel impulse response (CIR)와 frequency-domain상에서 측정할 수 있는 channel transfer function (CTF) 측정방법을 제안하였다. 측정데이터를 통해서 CIR과 CTF를 비교하여 분석하였고, 통계적 경로손실 모델 또한 제안하였다. 신호 대역은 10MHz에서 8.010Hz까지 사용하였다. 측정결과를 통해 time-domain상에서 확인할 수 있는 maximum excess delay, mean excess delay, ms delay spread를 나타내었다. 송신기와 수신기에는 전방향의 biconical 안테나를 사용하였다. 또한 제안된 아파트 환경에서의 채널 모델은 UMB용 안테나 특성이 포함된 결과이다.

• 한국식생활문화학회지
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• 제19권6호
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• pp.630-639
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• 2004

Korean households' expenditures on foodservices are on the steady increase. This paper aims to examine the foodservice expenditures of salary and wage earners's households by income decile group. This is analysed through comparing foodservice expenditures with private education expenditures because households' expenditures are likely to be weighted in favor of eating-out rather than private education. We also model the consumption function in terms of income and price, examining the responsiveness of private education demand and eating-out demand to changes in income and price using econometric methods such as regression, rolling regression and impulse response. This paper show that foodservice demand increases more than the private education does in the long-run. The result indicates that households are likely to evaluate the desire for foodservice more important than private education contrary to our expectations in the long-run. The impulse response analysis, however, suggests that households tend to increase private education expenditures rather than eating-out expenditures in the short-run.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1994년도 Proceedings of the Korea Automatic Control Conference, 9th (KACC) ; Taejeon, Korea; 17-20 Oct. 1994
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• pp.742-745
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• 1994

In this paper we show the performance of neural Chandrasekhar filtering which is a special case for the new method of neural filtering using the artificial neural network systems developed recently for the filtering problems of linear and nonlinear, stationary and nonstationary stochastic signals. The neurofilter developed has either the finite impulse response(FIR) structure or the infinite impulse response(IIR) structure. The neurofilter differs from the conventional linear digital FIR and IIR filters because the artificial neural network system used in the neurofilter has nonlinear structure due to the sigmoid function. Numerical studies for the estimation of a second order Butterworth process are performed by changing the structures of the neurofilter in order to evaluate the performance indices under the changes of the output noises or disturbances. In the numerical studies both Chandrasekhar filtering estimates and true signals are used as the training signals for the neurofilter. The results obtained from the studies verified the capabilities which are essentially necessary for on-line filtering of various stochastic signals.

• 소음진동
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• 제10권4호
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• pp.679-685
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• 2000

A procedure is presented for calculating the magnitude and shape of impact pulses in a vibro-impact system when an arbitrary input force is applied to a point in the system. The procedure utilizes the condition that the displacements of two contacting point in the primary and secondary system are the same during a contacting period. The displacements of those points are calculated numerically through the convolution integral which involve the impulse response functions and applied forces. The validity of the calculation procedure is demonstrated by using it to calculated the impact forces of a simple system where a theoretical solution is known and also of systems for which other researchers have published results. The agreement between the results derived by the numerical method and the theoretical and also some published results is good.

• 통상정보연구
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• 제10권3호
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• pp.459-474
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• 2008

Under violent competition to secure international raw materials, safe supply and demand of crude oil that only relies on import among main raw materials is an important task for Korean economic development. Therefore, this study aims to analyze the impact of price change of international crude oil on merchandise balance. It also presents political suggestions in preparation for national economic development and safety and develops an organized and long-term overseas resources development program. As the time-series data which had the 1st difference contribute to dismissal of the null hypothesis successfully, we carry out a multivariate cointegration test developed by Johansen (1988) and find that at least one cointegration vector exists. And, when Impulse Response Function is introduced, as the crude oil import price shows a negative impact from Step 2, then an extreme change, a positive impact since Step 13, is maintained and a safe result appears.

• 한국통신학회논문지
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• 제23권9A호
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• pp.2240-2247
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• 1998

본 논문은 이진 사운딩시퀀스를 이용하여 채널 임펄스응답을 측정하는 새로운 방법에 대하여 기술하였다. 이 새로운 방법은 한개의 상관기를 이용하는 대신에 세 개의 상관기를 이용하나 이상적인 채널 임펄스응답을 얻을 수 있다. 본 세안 방법에서 이용되는 사운딩 시퀀스의 부류는, GSM에 기반을 둔 디지틀 셀루리 이동전화 시스템에서 사용하는 채널 임펄스응답측정 이진부호로서 0 지연과 중간 지연을 제외한 모든 지연에서 자기상관함수 값이 영의 값을 갖는 채널응답측정을 위한 트레이닝 시퀀스이다. 또한 본 논문에서는 0 지연과 중간 지연을 제왼한 모든 지연에서 자기상관함수 값이 영이 되는 이진부호를 탐색하는 효과적인 방법을 제시한다.

• 전기학회논문지
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• 제60권11호
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• pp.2097-2102
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• 2011

Discharge analysis technique for dielectric liquid was presented by using the Finite Element Analysis (FEA) under a lightning impulse incorporating two-phase flow phenomena which described gas and liquid phases in discharge space. Until now, the response of step voltage has been extensively explored, but that of lightning impulse voltage was rarely viewed in the literature. We, therefore, developed an analyzing technique for dielectric liquid in a tip-sphere electrode stressed by a high electric field. To capture the bubble phase, the Heaviside function was introduced mathematically and the material functions for the ionization, dissociation, recombination, and attachment were defined in liquid and bubble, respectively. By using this numerical setup, the molecular dissociation and ionization mechanisms were tested under low and high electric fields resulted from the lightning impulse voltage of 1.2/50 ${\mu}s$. To verify our numerical results, the velocity of electric field wave was measured and compared to the previous experimental results which can be viewed in many papers. Those results had good agreement with each other.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2003년도 ICCAS
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• pp.2298-2303
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• 2003

In this paper, very simple methods based on the exponential analysis are presented by which transfer function models for processes can easily be obtained. These methods employ step responses or impulse responses of the processes. These can also give a more precise transfer function model compared to the well-known graphical methods. Transfer functions are determined based on Prony method, which is one of the oldest and the most representative methods in the exponential analysis. Here, the method is reformed and applied to obtain the so-called low-order transfer function with pure time delay from the data of the step response. The effectiveness of the proposed method is examined through several numerical examples and experiments of the 2-tank level control process.

• International Journal of Naval Architecture and Ocean Engineering
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• 제3권1호
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• pp.53-64
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• 2011

The present study considers multi-level approach for the analysis of parametric roll phenomena. Three kinds of computation method, GM variation, impulse response function (IRF), and Rankine panel method, are applied for the multi-level approach. IRF and Rankine panel method are based on the weakly nonlinear formulation which includes nonlinear Froude-Krylov and restoring forces. In the computation result of parametric roll occurrence test in regular waves, IRF and Rankine panel method show similar tendency. Although the GM variation approach predicts the occurrence of parametric roll at twice roll natural frequency, its frequency criteria shows a little difference. Nonlinear roll motion in bichromatic wave is also considered in this study. To prove the unstable roll motion in bichromatic waves, theoretical and numerical approaches are applied. The occurrence of parametric roll is theoretically examined by introducing the quasi-periodic Mathieu equation. Instability criteria are well predicted from stability analysis in theoretical approach. From the Fourier analysis, it has been verified that difference-frequency effects create the unstable roll motion. The occurrence of unstable roll motion in bichromatic wave is also observed in the experiment.