• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2014년도 추계학술대회 논문집
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• pp.544-544
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• 2014

Energy harvesting technology, which scavenges electric power from ambient, otherwise wasted, energy sources, has been explored to develop self-powered wireless sensors and possibly eliminate the battery replacement cost for wireless sensors. Among ambient energy sources, vibration energy can be converted into electric power through a piezoelectric energy harvester. For the last decade, although tremendous advances have been made in design methodology to maximize harvestable electric power under a given vibration condition, the research in reliability assessment to ensure durability has been stagnant due to the complicated nature of the multiple failure modes of a piezoelectric energy harvester, such as the interfacial delamination, fatigue failure, and dynamic fracture. Therefore, this study presents the first-ever system reliability analysis for multiple failure modes of a piezoelectric energy harvester using the Generalized Complementary Intersection Method (GCIM), while accounts for the energy conversion performance. The GCIM enables to decompose the probabilities of high-order joint failure events into probabilities of complementary intersection events. The electromechanically-coupled analytical model is implemented based on the Kirchhoff plate theory to analyze its output performances of a piezoelectric energy harvester. Since a durable as well as efficient design of a piezoelectric energy harvester is significantly important in sustainably utilizing self-powered electronics, we believe that technical development on system reliability analysis will have an immediate and major impact on piezoelectric energy harvesting technology.

• 한국농림기상학회지
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• 제22권3호
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• pp.152-163
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• 2020

실제적인 산사태 대응조치 단계 이전에 산사태위험지수를 통하여 산사태 발생 위험도를 모니터링하고 예측하기 위하여, LAMP의 고해상도 강우와 토양수분 예측 자료를 DB화 하고, 산사태 연구자들의 연구대상 지역에 적합한 지도 투영법과 공간해상도로 변환하는 절차를 ArcGIS를 이용하여 마련하였다. 이를 위하여 ERA5 재분석 강수와 농촌진흥청 10m 깊이 토양수분자료를 이용하여 LAMP 모델 강수 및 토양수분 자료를 정량적 그리고 정성적으로 평가하여 모델의 특성을 파악하였다. 또한, LAMP 강우, 토양수분, 증발산 등의 결과 자료를 10m 초고해상도 ArcGIS 포맷 자료로 변환하는 과정을 실무적으로 상세히 기술하여, 국내 지역에서 WRF 모델의 NetCDF 자료를 ArcGIS로 이용자들이 손쉽게 변환할 수 있도록 기술적 편의를 제공하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권4호
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• pp.1406-1423
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• 2014

Multi-mode device which combines multiple access technologies into a device will offer more cost-effective solution than a sole access implementation. Its concurrent multipath transfer (CMT) technology can transmit media flows over multiple end-to-end paths simultaneously, which is essential to select at least two paths from all available paths. At real networks, different paths are likely to overlap each other and even share bottleneck, which can weaken the path diversity gained through CMT. Spurred by this observation, it is necessary to select multiple independent paths as much as possible to avoid underlying shared bottleneck between topologically joint paths. Recent research in this context has shown that different paths with shared bottleneck can weaken the path diversity gained through CMT. In our earlier work, a grouping-based multipath selection (GMS) mechanism is introduced and developed. However, how to estimating the selection is still to be resolved. In this paper, we firstly introduce a Selection Correctness Index (SCI) to evaluate the correctness of selection results in actual CMT experiment. Therefore, this metric is helpful to discuss and validate the accuracy of the output paths. From extensive experiments with a realized prototype, the proposed scheme provides better evaluation tool and criterion in various network conditions.

• 산업클러스터
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• 제2권1호
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• pp.44-60
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• 2008

본 연구에서는 국내 주요 7개 산업클러스터에 대해 자료포락분석(DEA)을 통한 상대적 효율성과 생산구조를 비교.평가하였다. 2004년 혁신클러스터로 지정된 울산, 창원, 구미, 원주, 반월시화, 광주, 군산 7개 지역을 대상으로 분석한 결과 울산, 원주를 제외한 5개 지역이 모두 산업클러스터 도입이후 효율적인 상태로 개선되어가고 있음을 보이고 있다. 또한 과거의 비효율성의 원인은 모두 투입과 산출의 물리적인 관계를 나타내는 기술적 요인이 아닌 생산규모의 적절성을 나타내는 규모의 요인에 의한 것임을 알 수 있었다. 또한 노동과 성장, 자본과 성장, 연구개발과 성장간의 포지셔닝 분석을 통해 각 산업클러스터별 생산구조를 비교.평가한 결과 상대적으로 반월시화 클러스터와 구미클러스터의 생산구조가 노동, 자본, 연구개발 면에서 모두 우수한 것으로 나타났다. 반면 원주와 울산, 군산클러스터의 경우 상대적으로 노동, 자본 면에서 생산구조가 취약한 것으로 평가되었다.

• Structural Engineering and Mechanics
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• 제43권2호
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• pp.179-197
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• 2012

This study presents the findings of the structural health monitoring and the real time system identification of one of the first large scale building instrumentations in Turkey for earthquake safety. Within this context, a thorough review of steps in the instrumentation, monitoring is presented and seismic performance evaluation of structures using both nonlinear pushover and nonlinear dynamic time history analysis is carried out. The sensor locations are determined using the optimal sensor placement techniques used in NASA for on orbit modal identification of large space structures. System identification is carried out via the stochastic subspace technique. The results of the study show that under ambient vibrations, stocky buildings can be substantially stiffer than what is predicted by the finite element models due to the presence of a large number of partitioning walls. However, in a severe earthquake, it will not be safe to rely on this resistance due to the fact that once the partitioning walls crack, the bare frame contributes to the lateral stiffness of the building alone. Consequently, the periods obtained from system identification will be closer to those obtained from the FE analysis. A technique to control the validity of the proportional damping assumption is employed that checks the presence of phase difference in displacements of different stories obtained from band pass filtered records and it is confirmed that the "proportional damping assumption" is valid for this structure. Two different techniques are implemented for identifying the influence of the soil structure interaction. The first technique uses the transfer function between the roof and the basement in both directions. The second technique uses a pre-whitening filter on the data obtained from both the basement and the roof. Subsequently the impulse response function is computed from the scaled cross correlation between the input and the output. The overall results showed that the structure will satisfy the life safety performance level in a future earthquake but some soil structure interaction effects should be expected in the North South direction.

• Journal of Chest Surgery
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• 제25권1호
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• pp.49-56
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• 1992

Total 20 cases of reoperation for mitral vavular disease, which had been performed during the period from May 1983 till October 1991, were reviewed. This study contained 1 case of previous balloon valvuloplasty and 1 case of death with bleeding from right ventricle during sternal reenrty. The average time intervals between reoperation and previous operation was 19 years in closed mitral commissurotomy[n=4], 7 years and 2 months in mitral valve replacement[n=10], 1 year and 8 months in mitral valvuloplasty[n=4], 3 years and 10 months in open mitral commissurotomy [n=2]. The cause of reoperation in closed mitral commissurotomy was progression of the disease, and residual stenosis with progression was the cause in open mitral commissurotomy cases. Technical failure might be the cause in the cases of valvuloplasty. In prosthetic valve replacement group the causes of reoperation were primary failure. Also two cases of suggested valve thrombosis and one case of failure of tricuspid annuloplasty was noted in prosthetic valve replacement group. The used valves for reoperation were Ionescue-Shiley in 3 cases, Bjork-Shiley in 6 cases, St. Jude Medical in 2 cases and CarboMedics in 8 cases. The mortality rate was 20%[n=4] and the causes of death were low output syndrome in 1 case, multiple organ failure in 2 cases and bleeding in 1 case during sternal reentry. During follow up 1 case of sudden death was observed.

• 한국산학기술학회논문지
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• 제10권6호
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• pp.1304-1316
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• 2009

본 연구는 효율성에 기초한 환산지수의 도입 가능성을 알아보기 위한 기초 연구로 시도되었다. DEA 효율성지표와 환산지수가 전공의 수련교육을 실시하고 있는 60 개 병원을 그룹화하는데 얼마나 유용하게 사용될 수 있는가를 고찰하였다. 이러한 목적을 달성하기 위해 자료수집이 가능한 표본병원의 환산지수와 AHP 개념을 도입해 DEA 모형의 투입변수와 산출변수를 선정하였다. 그 결과 병상규모가 클수록 규모적 비효율성이 큰 것으로 나타났으며 기술적으로 또는 규모적으로 비효율적인 병원일수록 환산지수가 더 큰 것으로 나타났다. 환산지수와 효율성지표는 수련병원을 병원의 종별에 따라 종합전문병원과 종합병원으로 구분하는데 유용하게 사용될 수 있었다. 또한 DEA 효율성을 구하는 과정에서 독립변수로 사용된 투입 산출변수를 판별함수에 도입하였음에도 불구하고 환산지수와 효율성지표는 판별함수를 구성하는 주요 변수로 작용함을 확인하였다. 따라서 만약 모집단을 대표할 수 있는 많은 표본을 기초로 보다 명확한 결과를 얻을 수 있다면 건강보험의 수가계약제 하에서 효율성 개념을 바탕으로 한 환산지수계약의 도입을 신중하게 고려해 볼 수 있다.

• 전기학회논문지
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• 제67권8호
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• pp.1024-1030
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• 2018

Recently, the large scaled energy storage system(ESS) which has various functions such as peak saving, demand management, output stabilization of renewable energy and frequency regulation(FR) is being energetically installed and operated. Especially, as the use case of frequency regulation ESS, the KEPCO has demonstrated the total of 376[MW] ESS since 2014. However, there are no operational experiences and international technical standards on frequency regulation application in ESS. Therefore, this paper propose the evaluation algorithm for power system performance of ESS by considering the frequency characteristics between governor of existing generator and frequency regulation ESS, in order to verify the power system performance of ESS. And also, this paper propose an evaluation modeling for small scaled power system including the existing generator, frequency control ESS and customer loads based on the PSCAD/EMTDC S/W. From the simulation results in 360[MW] model power system, it is confirmed that frequency regulation ESS has better performances than conventional generators.

• Smart Structures and Systems
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• 제22권4호
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• pp.413-424
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• 2018

The factors affecting the shear strength of the angle shear connectors in the steel-concrete composite beams can play an important role to estimate the efficacy of a composite beam. Therefore, the current study has aimed to verify the output of shear capacity of angle shear connector according to the input provided by Support Vector Machine (SVM) coupled with Firefly Algorithm (FFA). SVM parameters have been optimized through the use of FFA, while genetic programming (GP) and artificial neural networks (ANN) have been applied to estimate and predict the SVM-FFA models' results. Following these results, GP and ANN have been applied to develop the prediction accuracy and generalization capability of SVM-FFA. Therefore, SVM-FFA could be performed as a novel model with predictive strategy in the shear capacity estimation of angle shear connectors. According to the results, the Firefly algorithm has produced a generalized performance and be learnt faster than the conventional learning algorithms.

• 한국기계가공학회지
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• 제16권5호
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• pp.69-77
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• 2017

This paper introduces an optical encoder using the reflection in the slit. The digital optical encoder is a sensor to generate a pulse according to the displacement. An optical encoder is composed of 3 parts: light source, slit plate and light-receiving element. In a conventional encoder, one slit produces one signal. The resolution of the digital optical encoder is determined by the number of slits in the encoder plate. The small slit size is most important among the factors that determine the resolution in a generic-type optical encoder. However, a small slit has low productivity and technical difficulties, so analog optical encoders have emerged as an alternative. Nonetheless, this alternative requires additional circuitry and equipment because of the noise and drafts in the analog signals. A new sensor is presented in this paper with a high resolution and a slit of the same size using the reflection in the slit. Then, the path of the light that passes through the slit ccording to the shape was analyzed, and some paths were expressed in the mathematical expressions. In addition, the optical paths were analyzed in the rectangular, octagonal, and circular encoders, and shown the obtained number of signals per slit by using them. Thus, we confirm that this method has the best performance in circle-shaped slits.