• Smart Structures and Systems
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• 제2권2호
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• pp.141-154
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• 2006

Recently, the Hilbert-Huang transform (HHT) has gained considerable attention as a novel technique of signal processing, which shows promise for the system identification and damage detection of structures. This study investigates the effectiveness and accuracy of the HHT method for the system identification and damage detection of structures through a series of experiments. A multi-degree-of-freedom (MDOF) structural model has been constructed with modular members, and the columns of the model can be replaced or removed to simulate damages at different locations with different severities. The measured response data of the structure due to an impulse loading is first decomposed into modal responses using the empirical mode decomposition (EMD) approach with a band-pass filter technique. Then, the Hilbert transform is subsequently applied to each modal response to obtain the instantaneous amplitude and phase angle time histories. A linear least-square fit procedure is used to identify the natural frequencies and damping ratios from the instantaneous amplitude and phase angle for each modal response. When the responses at all degrees of freedom are measured, the mode shape and the physical mass, damping and stiffness matrices of the structure can be determined. Based on a comparison of the stiffness of each story unit prior to and after the damage, the damage locations and severities can be identified. Experimental results demonstrate that the HHT method yields quite accurate results for engineering applications, providing a promising tool for structural health monitoring.

• Smart Structures and Systems
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• 제24권4호
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• pp.525-539
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• 2019

In this study, vibration characteristics of a gravity-based caisson-foundation breakwater system are investigated for ambient and geometric parameters such as various waves, sea levels, and foundation conditions. To achieve the objective, following approaches are implemented. Firstly, operational modal analysis methods are selected to identify vibration modes from output-only dynamic responses. Secondly, a finite element model of an existing caisson-foundation breakwater system is established by using a structural analysis program, ANSYS. Thirdly, forced vibration analyses are performed on the caisson-foundation system for two types of external forces such as controlled impacts and wave-induced dynamic pressures. For the ideal impact, the wave force is converted to a triangular impulse function. For the wave flow, the wave pressure acting on the system is obtained from wave field analysis. Fourthly, vibration modes of the caisson-foundation system are identified from the forced vibration responses by combined use of the operational modal analysis methods. Finally, vibration characteristics of the caisson-foundation system are investigated under various waves, sea levels, and foundations. Relative effects of foundation conditions on vibration characteristics are distinguished from that induced by waves and sea levels.

• 수산해양교육연구
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• 제28권1호
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• pp.198-210
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• 2016

This study firstly aims to estimate a leading-price of Jeju flounders with various price-classes by fish weight and secondly plans to provide policy implications of flounder purchase projects by understanding dynamic changes and interactions among flounder producer price-classes caused by price impulses in the market. This study applies an unit root test for stability of data, uses a Granger causality test to estimate the leading-price among producer prices by fish weight, employs the vector autoregressive model to analyze statistical impacts among t-1 variables used in models, and finally utilizes impulse response analyses and forecast error variance decomposition analyses to understand dynamic changes and interactions among change rates of the producer prices caused by price impulses in the market. The results of the study are as follows. Firstly, KPSS, PP, and ADF tests show that the change rate of Jeju flounder monthly producer prices by fish weight differentiated by logarithm is stable. Secondly, the Granger causality test presents that the change rate of the 1kg flounder producer price strongly leads it of 500g, 700g, and 2kg flounder producer prices respectively. Thirdly, the vector autoregressive model indicates that the change rate of the 1kg producer price in t-1 period statistically, significantly influences it of own weight in t period and also slightly affects price change rates of other weights in t period. Fourthly, the impulse response analysis indicates that impulse responses of structural shocks for the change rate of the 1kg producer price are relatively more powerful in its own weight and in other weights than shocks emanating from price change rates of other weights. Fifthly, the variance decomposition analysis points out that the change rate of the 1kg producer price is relatively more influential than it of 500g, 700g, and 2kg producer prices respectively. In conclusion, the change rate of the 1kg Jeju flounder producer price leads the change rates of other ones and Jeju purchase projects need to be targeted to the 1kg Jeju flounder producer price as the purchase project implemented in 2014.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2011년도 정기 학술대회
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• pp.531-538
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• 2011

멤브레인형 LNG 탱크의 구조적 안전성을 확보하기 위해서는 슬로싱에 의한 작용 압력과 구조응답을 정확히 평가할 수 있어야 한다. 탱크 방열구조에 작용하는 슬로싱 충격하중은 매우 불규칙적이며 이로 인한 구조 응답 역시 유탄성 거동을 포함하는 매우 복잡한 물리 현상이기 때문에 최신의 이론적 실험적 접근 방법을 동원하더라도 정확한 평가가 어렵다. 본 연구에서는 실험이나 수치해석으로부터 얻어진 슬로싱 압력 시계열을 이용하여 탱크 방열 구조의 구조응답을 간편하게 해석할 수 있는 방안을 제안하였다. 이 간이 해석법은 기본적인 삼각형 impulse 형태의 충격 압력에 대한 구조응답을 시간영역에서 과도응답해석법으로 계산한 후, 이렇게 구해진 구조물의 삼각형 응답함수를 조합하여 임의 형상의 압력 시계열에 대한 구조 응답을 구하는 방식이다. 여러 가지 예제 해석을 통하여 제안된 해석법의 타당성을 검토하였고, 이를 이용하여 실제 모형실험에서 얻어진 압력시계열을 바탕으로 구조응답을 계산하고 그 결과를 고찰하였다.

• 복식문화연구
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• 제22권2호
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• pp.346-359
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• 2014

Black Friday, a biggest holiday shopping season in the United States, has been regarded as a great opportunity that fashion retailers can dramatically increase their sales. However, there has been a lack of attention to consumers' shopping experiences on Black Friday from the consumer perspectives. The objective of this study is to explore consumer shopping experiences on Black Friday, in terms of consumer responses toward the experiences, shopping values, and any possible factors influencing the experiences. The method of critical incident technique was used with 198 critical incidents extracted from 165 responses of university students in the United States. As results, the shopping experiences on Black Friday were categorized into positive vs. negative shopping experiences. After that, the positive and negative experiences were respectively divided into two common themes: utilitarian shopping value vs. hedonic shopping value. In addition to the common themes, 12 categories were also emerged. Among positive experiences, utilitarian shopping experiences includes two categories of off-price shopping and shopping for expensive products, whereas hedonic shopping experiences includes three categories of impulse buying, holiday atmosphere, and shopping for the latest or luxury brand products. Among negative experiences, utilitarian shopping experiences includes four categories of modest discounts, out of stock, time-consuming queues, and fatigue of holiday shopping, while hedonic shopping experiences includes three categories of crowded environments, compulsive buying, and poorly managed stores. In conclusion, it is notable that consumer can undergo negative as well as positive shopping experiences on Black Friday. Implications and suggestions are also discussed.

• 디지털융복합연구
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• 제17권10호
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• pp.127-139
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• 2019

본 연구의 목적은 소비자정보로서의 유튜브 1인 미디어에 대한 대학생들의 인상적인 경험을 긍정적, 부정적 측면에서 탐색하고, 유용한 소비자정로보서의 1인 미디어의 개선점을 모색하는 것이다. 대학생 44명을 연구대상으로 선정하고 소비 맥락에서의 유튜브 이용 경험에 관한 자료를 결정적 사건기법을 적용하여 수집 및 분석하였다. 연구 결과, 1인 미디어에 대한 긍정적 반응으로는 'C2C 정보력 강화', '소비자 중심적 사용성', '매력적인 정보 크리에이터', '공감대와 동류의식 형성', '신선하고 유희적인 정보'가 도출되었고, 부정적 반응으로는 '유해정보의 확산', '정보 크리에이터에 대한 불신', '과도한 광고와 충동구매 유발', '미디어 중독', '상대적 박탈감'이 도출되었다. 대학생들은 1인 미디어 개선을 위해 '법 정책적 규제 도입', '미디어 리터러시 강화', '소비자 지향적 UI 개선'이 요구된다고 제안하였다. 본 연구는 1인 미디어에 대한 소비자의 인식과 경험을 이해하는 기초자료로 활용될 수 있으며, 소비자 지향적인 1인 미디어의 방향을 제언한다는 점에서 의의를 가진다.

• 한국세라믹학회지
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• 제50권1호
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• pp.82-86
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• 2013

A poled lead zirconate titanate (PZT) cube specimen is subjected to impulse-type compressive stress with increasing magnitude in parallel to the poling direction at four room and high temperatures. During the ferroelastic domain switching induced by the compressive stress, electric displacement in the poling direction and longitudinal and transverse strains are measured. Using the measured responses, linear material properties, namely, the piezoelectric and elastic compliance coefficients, are evaluated by a graphical method, and the effects of stress and temperature are analyzed. Finally, the dependency of the evaluated linear material properties on relative remnant polarization is analyzed and discussed.

• 노동경제논집
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• 제21권2호
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• pp.17-46
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• 1998

In this paper, I pursue an empirical analysis of different patterns of employment and wage adjustments to demand changes for the US and Japan. Analyzed are the data in the 70's and 80's, the period that the two countries are believed to show most conspicuous diverging patterns. Using the framework of cointegration and error correction, I establish that in the US it is employment level, while in Japan it is wages, that is more responsive to output fluctuations both in the long run and the short run. All the comparisons on the long run relationships are estimated and tested based on the system cointegrating regressions, and the transition from the short run to the long run responses are investigated using impulse response analysis of the error correction models. I also study differences across genders and establishment sizes within each country. For males and females in Japan, the adjustments are significantly different both in the long run and the short run, but for the firms of different sizes they diverge only in the short run. In contrast to some of the earlier work, the gender effect turns out to be insignificant in the US.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2005년도 추계종합학술대회
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• pp.447-450
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• 2005

Multi-channel artificial reverberation algorithm to control perceived direction and distance is described in this paper. In conventional algorithms using IIR filters, reverberation time is the only parameter to be controlled. Moreover, since the convolution-based conventional algorithms apply only same impulse responses, but not considering sound localization, it was not realistic enough. The new algorithm proposed in this paper utilizes early reflections segmented according to the azimuth from which direct sound comes and controls perceived direction by panning the direct sound, and controls perceived distance by adjusting Energy Decay Curve (EDC) of reverberation and gain of the direct sound. In addition, the algorithm enhances Listener Envelopment(LEV) to make late reverberation incoherent among channels.

• 펄프종이기술
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• 제36권5호
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• pp.11-20
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• 2004

In this work the Model Algorithmic Control (MAC) method is applied to control the grade change operations in paper mills. The neural network model for the grade change operations is identified first and the impulse model is extracted from the neural network model. Results of simulations for MAC control of grade change operations are compared with plant operation data. The major contribution of the present work is the application of MAC in the industrial plants based on the identification of neural network models. We can confirm that the proposed MAC method exhibits faster responses and less oscillatory behavior compared to the plant operation data in the grade change operations.