• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 춘계학술대회논문집
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• pp.408-413
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• 2003

The frequency response function(FRF) of each substructure is used for the transfer function synthesis method(TFS). The dynamic characteristics of the full system are obtained by synthesizing FRFs of each substructure. The validation of TFS depends on accuracy for FRF of each substructure. Impact hammer testing Is widely used to obtain the modal characteristics of structures However. the FRF obtained from impact hammer testing contains bias errors, such as finite record length error and leakage error of which characteristic depends on data acquisition time which we call record length. In this paper, a method to remove hose errors is proposed so as to enhance results of TFS. Numerical and experimental examples show that the FRF of full structure can be predicted nearly exactly by the method proposed in this paper.

• 대한기계학회논문집
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• 제19권3호
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• pp.623-630
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• 1995

The impulse response functions (force-strain relations) for Euler-Bernoulli and Timoshenko beams are considered. The response of a beam to a transverse impact force is numerically obtained with the convolution approach using the impulse response function obtained by Laplace transform. Using this relation, the impact force history is determined in the time domain and results are compared with those from Hertz's contact law. The parameters of timpact force model are identified using the recovered force and compared with the Hertz's contact model. In order to verify the proposed algorithm, measurements were done using an impact hammer and a steel ball drop test and these results are also compared with the simulated values.

• 제어로봇시스템학회논문지
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• 제21권9호
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• pp.807-810
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• 2015

In this paper, a finite impulse response(FIR) fixed-lag smoother is proposed for discrete-time nonlinear systems. If the actual state trajectory is sufficiently close to the nominal state trajectory, the nonlinear system model can be divided into two parts: The error-state model and the nominal model. The error state can be estimated by adapting the optimal time-varying FIR smoother to the error-state model, and the nominal state can be obtained directly from the nominal trajectory model. Moreover, in order to obtain more robust estimates, the linearization errors are considered as a linear function of the estimation errors. Since the proposed estimator has an FIR structure, the proposed smoother can be expected to have better estimation performance than the IIR-structured estimators in terms of robustness and fast convergence. Additionally the proposed method can give a more general solution than the optimal FIR filtering approach, since the optimal FIR smoother is reduced to the optimal FIR filter by setting the fixed-lag size as zero. To illustrate the performance of the proposed method, simulation results are presented by comparing the method with an optimal FIR filtering approach and linearized Kalman filter.

• 경영과학
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• 제25권3호
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• pp.13-26
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• 2008

We investigate the effect of government and public sector R&D Investment at IT Industry on the amount of Production, export and nongovernment R&D Investment at IT Industry. We, firstly, examine the stationarity of each variable by the unit root t-test and perform the co-integration test for the pairs of variables. We use YECM(Vector Error Correction Model) according to the results of co-integration test for the examination of Granger-causality between variables. It is found that there exist an Granger-causality between public sector R&D Investment and nongovernment R&D investment and also between public sector R&D Investment and export. Secondly, we analyze the impulse response of government and public sector R&D Investment at IT Industry on the amount of production, export and nongovernment R&D investment at IT Industry based on VECM model. It is found that the response of the amount of production is highest at 3th period and is lowest at 8th period and that of export shows similar pattern.

• Wind and Structures
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• 제7권6호
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• pp.421-447
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• 2004

This paper presents a time domain approach for predicting buffeting response of long suspension bridges under skew winds. The buffeting forces on an oblique strip of the bridge deck in the mean wind direction are derived in terms of aerodynamic coefficients measured under skew winds and equivalent fluctuating wind velocities with aerodynamic impulse functions included. The time histories of equivalent fluctuating wind velocities and then buffeting forces along the bridge deck are simulated using the spectral representation method based on the Gaussian distribution assumption. The self-excited forces on an oblique strip of the bridge deck are represented by the convolution integrals involving aerodynamic impulse functions and structural motions. The aerodynamic impulse functions of self-excited forces are derived from experimentally measured flutter derivatives under skew winds using rational function approximations. The governing equation of motion of a long suspension bridge under skew winds is established using the finite element method and solved using the Newmark numerical method. The proposed time domain approach is finally applied to the Tsing Ma suspension bridge in Hong Kong. The computed buffeting responses of the bridge under skew winds during Typhoon Sam are compared with those obtained from the frequency domain approach and the field measurement. The comparisons are found satisfactory for the bridge response in the main span.

• Journal of Korea Trade
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• 제23권5호
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• pp.87-101
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• 2019

Purpose - This paper examines the effectiveness of the foreign exchange risk insurance system in the promotion of SME exports in Korea. The purpose of this study is to analyze the short-term and long-term responses of SME exports to foreign exchange risk insurance support policies. Based on these empirical studies, we would like to present some operational improvements to the operation of the foreign exchange risk insurance system. Design/methodology - In order to analyze the effect of exchange risk insurance on the exports of SMEs, a VAR model consisting of foreign exchange risk insurance underwriting values, export relative price, and domestic demand pressure, including export volume, was established. The study began with tests of the stationarity of time series data. The unit root tests showed that all concerned variables were non-stationary. Accordingly, the results of the cointegration test showed that the tested variables are not cointegrated. Finally, an impulse response function and variance decomposition analysis were conducted to analyze the impulse of foreign exchange risk insurance on exports of SMEs. Findings - As a result of estimating the VAR (1) model, foreign exchange risk insurance was found to be significant at a 1% significance level for SME' export promotion. In the impulse response analysis, SMEs' export response to the impulse of foreign exchange risk insurance showed that exports gradually increased until the third quarter, and then slowed down. However, the impulse did not disappear, and appeared continuously. Originality/value - This study analyzed the effect of foreign exchange insurance on exports of SMEs by applying the VAR model. In particular, this study is the first to analyze the short-term and long-term effects of foreign exchange risk insurance on exports of SMEs. The empirical evidence in the current study have a policy implication for the policy authority to support and promote the foreign exchange risk insurance in the effect of exchange rate volatility on Korea' export SMEs.

• ETRI Journal
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• 제38권4호
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• pp.634-644
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• 2016

Channel-based radio-frequency fingerprinting such as a channel impulse response (CIR), channel transfer function (CTF), and frequency coherence function (FCF) have been recently proposed to improve the accuracy at the physical layer; however, their empirical performance, advantages, and limitations have not been well reported. This paper provides a comprehensive empirical performance evaluation of RF location fingerprinting, focusing on a comparison of received-signal strength, CIR-, CTF-, and FCF-based fingerprinting using the weighted k-nearest neighbor pattern recognition technique. Frequency domain channel measurements in the IEEE 802.11 band taken on a university campus were used to evaluate the accuracy of the fingerprinting types and their robustness to human-induced motion perturbations of the channel. The localization performance was analyzed, and the results are described using the spatial and temporal radio propagation characteristics. In particular, we introduce the coherence region to explain the spatial properties and investigate the impact of the Doppler spread in time-varying channels on the time coherence of RF fingerprint structures.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2011년도 춘계학술대회
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• pp.310-312
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• 2011

복합 잡음 환경에서 원 신호의 음성이나 영상신호를 획득하거나, 전송 및 저장을 위해서 디지털필터가 사용되고 있다. 디지털필터는 크게 FIR 필터와 IIR 필터로 나눌 수 있다. FIR 필터 중에서 창함수는 선형위상의 특성을 가지고 있고 손쉽게 통과대역, 차단주파수 등을 설정할 수 있다. 본 논문에서는 기존의 창함수를 변형하여 설계한 후 필터 특성을 확인하기 위해 Peak side-lobe와 주파수 천이특성 등을 사용하여 기존의 방법들과 비교하였다.

• 서비스연구
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• 제6권1호
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• pp.83-95
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• 2016

본 논문은 한국은행 경제통계시스템에서 제공한 서비스업생산지수와 서비스업도소매지수를 가지고 상호간의 연관성을 분석하였다. 분석을 위한 통계분석 기간은 2000년 1월부터 2015년 9월까지 15년 9개월간의 월별자료 189개를 사용하였고, 분석도구로는 E-Views 6을 이용하여 VAR 모형을 통한 그랜저 인과관계분석(Granger Causality test)과 충격반응분석(Impulse Response Function) 및 분산분해(Variance Decomposition)를 실시하였다. 주요 분석결과는 다음과 같다. 첫째, 그랜저 인과관계 분석결과(Granger Causality test) 상승률과 변동성에 있어서 서비스업생산지수와 서비스업도소매지수 상호간에 예측력이 있음을 알 수 있었다. 둘째, 충격반응함수(Impulse Response Function)분석결과 서비스업생산지수와 서비스업도도소매지수에 사이에 충격이 존재하여 일정시차까지 영향을 미치다가 사라짐을 알 수 있었다. 이는 다른 산업뿐만 아니라 서비스업산업에 있어서도 생산량은 어느 정도 도소매업체의 판매량을 예측할 수 있다는 것으로 해석할 수 있다. 마지막으로 분산분해(Variance Decomposition) 분석결과 서비스업도소매지수는 일정시차동안 73.65%~65.59%의 서비스업생산지수에 의하여 영향을 받는 것으로 나타났다. 하지만 서비스업생산지수는 일정시차동안 0.97%~1.92%의 서비스업도소매지수에 영향을 받는 것으로 나타나 영향력이 미미함을 알 수 있었다. 본 연구는 다양한 지수를 대상으로한 상호간의 가격발견을 통한 상호연관성을 분석한 기존의 연구방법을 확장하여 서비스업생산지수와 서비스업도소매지수와의 가격발견 기능을 파악하는데 기여하였다고 사료된다. 이와 같은 연구결과는 물가지수를 관리하고 있는 정부에게 물가정책을 수립하는데 의미를 부여하고, 각종 지수를 관리하고 있는 한국은행 및 통계청에게 의미 있는 시사점을 제공할 것으로 판단된다. 본 연구에 대한 한계점으로는 물가지수를 이용한 선행연구가 많지 않아서 좀 더 체계적인 분석이 부족하다는 점과 구조변화 시점을 구분하여 분석하지 못했다는 점이다. 따라서 다양한 물가지수를 활용한 후속연구와 구조변화를 전후를 대상으로 한 추가연구가 필요하다고 사료된다.

• 한국전자통신학회논문지
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• 제16권4호
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• pp.591-598
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• 2021

디지털 위상 고정 루프는 위상 동기화를 위해 사용되는 회로로 일반적으로 통신, 회로분야 등 다양한 분야에서 사용된다. 디지털 위상 고정 루프를 설계 시 상태추정기를 사용하는 경우 보통 칼만 필터와 같은 무한 임펄스 응답 상태추정기를 활용해왔다. 일반적으로 무한 임펄스 응답 상태추정기 기반 디지털 위상 고정 루프의 성능은 우수하지만, 초기값의 부정확, 모델 오차, 외란 등의 예상하지 못하는 상황에서 급격한 성능저하가 발생할 수 있다. 본 논문에서는 새로운 디지털 위상 고정 루프를 설계 하기 위해 최적의 측정값 구간 길이를 갖는 최소 공분산 유한 임펄스 응답 필터를 제안한다. 제안된 유한 임펄스 응답 필터의 중요 파라미터인 측정값 구간 길이를 구하기 위해 수치적 방법을 소개하며, 필터의 이득을 얻기 위해 비용함수로 오차의 공분산 행렬을 설정하고, 이를 최소화 하기 위하여 선형 행렬 부등식을 사용하였다. 제안된 디지털 위상 동기 루프의 우수성과 강인성을 검증하기 위해 노이즈 정보가 부정확한 상황에서 기존 방법과의 비교 및 분석을 위한 시뮬레이션을 수행하였다.