• Earthquakes and Structures
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• 제19권4호
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• pp.287-301
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• 2020

Fragility as one of the most effective methods to evaluate seismic performance, which is greatly affected by damage index. Taking a multi span continuous rigid frame offshore bridge as an example. Based on fragility and reliability theory, considering coupling effect of time-varying durability damage of materials and time-varying attenuation effect of damage index to analyze seismic performance of offshore bridges. Results show that IDA curve considering time-varying damage index is obviously below that without considering; area enclosed by IDA of 1# pier and X-axis under No.1 earthquake considering this effect is 96% of that without considering. Area enclosed by damage index of 1# pier and X-axis under serious damage with considering time-varying damage index is 90% of that without considering in service period. Time-varying damage index has a greater impact on short pier when ground motion intensity is small, while it has a great impact on high pier when the intensity is large. The area enclosed by fragility of bridge system and X-axis under complete destruction considering time-varying damage index is 165% of that without considering when reach designed service life. Therefore, time-varying attenuation effect of damage index has a great impact on seismic performance of bridge in service period.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 추계학술대회 논문집 전력기술부문
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• pp.9-11
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• 2006

This paper suggests a revision method for historical fault data using Proportional Aging Reduction(PAR) to consider maintenance effect in time-varying failure rate. In order to product time-varying failure rate, the historical fault data are necessary. However, the maintenance record could be left out in historical data by spot operator's mistake. In this case, the failure rate is produced less than the average failure rate for increasing equipments' life-time by maintenance effect. Hence, it is necessary for new time-varying failure rate to extract maintenance effect from the existing fault data. In this paper, the revision method to reduce equipments' life-time, adversely using PAR among three techniques to consider maintenance effect.

• Journal of Communications and Networks
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• 제11권5호
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• pp.473-479
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• 2009

Conventional frequency domain equalization (FDE) schemes were originally devised for quasi-static channels. Thus, such equalization schemes could suffer from significant performance degradation in fast-fading channels. This paper proposes a frequency domain equalization algorithm to mitigate the effect of fast time-varying fading. First, a mathematical expression is derived to quantify the total interference resulting from the time variation of the channel. Then, the proposed approach attempts to eliminate the effect of time-variations of the channel. This cancellation allows efficient use of the classical FDE structures in fast time-varying fading environments, although they are built upon the quasi-static channel model. Simulation results of bit-error-rate performance are provided to demonstrate the effectiveness of the proposed algorithm.

• 제어로봇시스템학회논문지
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• 제7권5호
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• pp.393-398
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• 2001

This paper presents a new method with time-varying boundary layer and input gain, variated by Fuzzy Logic Control(FLC) by means of the system state in Sliding Mode Control (SMC). In addition to the time-varying boundary layer, the time-varying range of the fuzzy membership function has an effect on not only chattering reduction but also fast response characteristics. On the basis of SMC with time-varying boundary and FLC with time-varying input and output range, a computer simulation for inverted pendulum results in elimination of the chattering phenomenon and fast response.

• 조명전기설비학회논문지
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• 제23권8호
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• pp.14-20
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• 2009

본 논문에서는 배전 시스템을 구성하는 기기들에 대한 설치 현황자료와 고장 자료 및 전국 지점을 대상으로 한 설문조사 자료를 이용하여 기후별 고장률을 예측하였다. 같은 종류의 배전 설비라 하더라도 그 설비가 설치되어 있는 기후 상태에 따라서 고장률은 다르게 나타날 수 있다. 그러므로 배전기기의 고장률을 설비관리나 최적 투자 계획의 운용에 사용하기 위해서는 대상 설비가 설치된 기후 특성을 고려해야 하며 이를 위해 기후 특성을 고려한 고장률 예측이 요구된다고 할 수 있다. 기후특성분석을 위하여 한국전력공사의 전국지점을 대상으로 기후 특성(호우, 낙뢰, 강풍, 해일, 특징 없음)으로 구분하여 설문조사를 실시하였고 기후 특성에 따른 영향도를 분석하였고 고장률 추정 알고리즘을 제안하였다.

• Communications for Statistical Applications and Methods
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• 제21권5호
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• pp.387-393
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• 2014

Recurrent gap times are analyzed with diverse methods under several assumptions such as a marginal model or a frailty model. Several resampling techniques have been recently suggested to estimate the covariate effect; however, these approaches can be applied with a time-fixed covariate. According to simulation results, these methods result in biased estimates for a time-varying covariate which is often observed in a longitudinal study. In this paper, we extend a resampling method by incorporating new weights and sampling scheme. Simulation studies are performed to compare the suggested method with previous resampling methods. The proposed method is applied to estimate the effect of an educational program on traffic conviction data where a program participation occurs in the middle of the study.

• 제어로봇시스템학회논문지
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• 제19권3호
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• pp.183-189
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• 2013

This paper presents a stabilization method for NCS (Networked Control Systems) with two additive time-varying delays. Each time delay component between the plant and the controller has different characteristics depending on communication network, and has the upper and lower bounds. The time delay occurring from the controller to the plant has an effect on the time delay occurring from the plant to the controller, and the relationship between two delays is taken into account on the stability analysis. Based on the two additive delay components and the bound conditions, the appropriate Lyapunov-Krasovskii functional and the LMI (Linear Matrix Inequality) method derive the stability condition and the $H_{\infty}$ norm constraint for time-varying delayed NCS. Simulation results are finally given to demonstrate the effectiveness of the proposed method.

• Journal of electromagnetic engineering and science
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• 제15권3호
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• pp.134-141
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• 2015

The effect of a 60 Hz time-varying electric field was studied using a facing-electrode device (FED) and a coplanar-electrode device (CED) for further investigation of the genotoxicity of 60 Hz time-varying magnetic field (MF) from preceding research. Neither a single 30-minute exposure to the CED or to the FED had any obvious biological effects such as DNA double strand break (DSB) and apoptosis in cancerous SCC25, and HeLa cells, normal primary fibroblast IMR90 cells, while exposures of 60 Hz time-varying MF led to DNA damage with induced electric fields much smaller than those used in this experiment. Nor did repetitive exposures of three days or a continuous exposure of up to 144 hours with the CED induce any DNA damage or apoptosis in either HeLa or IMR90 cells. These results imply that the solitary electric field produced by time-varying MF is not a major cause of DSBs or apoptosis in cancer or normal cells.

• The Journal of Asian Finance, Economics and Business
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• 제7권10호
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• pp.513-521
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• 2020

In this paper, we have developed a Fama - French five factor model (FF5 model) from Fama & French (2015) by using concept of time-varying coefficient. For a data set, we have used monthly data form Kenneth R. French home page, it include Japan portfolios (classified by using size and book-to-market) and 5 factors from July 1990 to April 2020. The first analysis, we used Augmented Dickey-Fuller test (ADF test) for the stationary test, from the result, all Japan portfolios and 5 factors are stationary. Next analysis, we estimated a coefficient of Fama - French five factor model by using a generalized additive model with a thin-plate spline to create the time-varying coefficient Fama - French five factor model (TV-FF5 model). The benefit of this study is TV-FF5 model which can capture a different effect at different times of 5 factors but the traditional FF5 model can't do it. From the result, we can show a time-varying coefficient in all factors and in all portfolios, for time-varying coefficients of Rm-Rf, SMB, and HML are significant for all Japan portfolios, time-varying coefficients of RMW are positively significant for SM, and SH portfolio and time-varying coefficients of CMA are significant for SM, SH, and BM portfolio.

• Journal of Platform Technology
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• 제11권4호
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• pp.62-70
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• 2023

이 논문은 농수산물 생산자가 도매시장에 상품을 출하하는 시기와 양을 결정하는 것을 돕기 위한 시스템을 구축하기 위한 일련의 과정 중 일부이다. 기존 농수산물 출하모델에서 사용하지 않은 품질변화효과를 모델링하고, 그 통계적 유의성을 확인한 후, 시스템에 도입하는 것이 이 연구의 목적이다. 이를 위해 연구자는 품질변화효과를 측정할 수 있는 네 가지 모델을 개발하였다. 시간이 지남에 따라 1) 품질이 일정하게 떨어지는 경우, 2) 품질이 처음에 급속히 떨어지다가 나중에는 천천히 떨어지는 경우, 3) 품질이 처음에 천천히 떨어지다가 나중에는 급속히 떨어지는 경우, 4) 품질이 낮았다가 시간이 흐른 후 높아지다가 다시 감소하는 경우를 모델링하였다. 각 모델의 품질변화효과가 출하량에 미지는 영향을 2014-2021년 사이에 가락도매시장에서 거래된 사과를 대상으로 실증분석 해 본 결과에 따르면 네 모델 모두 품질변화효과에 유의성을 발견하였다. 그리고 네 모델 간 설명력에 유의한 차이는 없었다. 따라서 네 개 모델 중 어느 하나를 선택해서 사과에 대한 출하시기의사결정시스템에 적용시킬 수 있는 것으로 나타났다.