• 한국전기전자재료학회논문지
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• 제23권10호
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• pp.788-792
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• 2010

The yttrium-barium-copper-oxide (YBCO) coated conductor, which supplement the fault of the existing superconducting current-limit materials YBCO thin film, bismuth-strontium-calcium-copper-oxide(BSCCO) wire and bulk, has been improved its mechanical weakness and has high index; hence, after quench YBCO coated conductor could limit the fault current effectively because of fast resistance occurrence speed. Furthermore, it has wide applicable area as an current limit material because it shows different resistance occurrence tendency by the thickness and kind of stabilization material sputtered on the superconducting layer. Therefore, many researchers are carrying out the study of application of YBCO coated conductor to superconducting fault current limiter (SFCL) for making high quality current limit element, based on resistance type. On the other hand, the study for other type except resistance type has been rarely conducted for the application of YBCO coated conductor to SFCL as an current limit element. Consequently, in this study, YBCO coated conductor with different stabilization layer Cu and Stainless steel, is applied to SFCL using iron core and coil, and examine the many index points as an current limit element, such as current limit characteristic, the tendency of resistance occurrence, response time, the temperature trend for stability.

• 조명전기설비학회논문지
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• 제29권1호
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• pp.57-63
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• 2015

The incidence of fires caused by electrical factors has increased with the growth in domestic electrical consumption. According to the national fire data system of national emergency management agency, electrical fires accounted for 20% of all domestic fires in the last 10 years. Electrical fires are mainly caused by short circuit, leakage current, defect in an electrical equipment, over load, utility fault, etc. The fault current can be several times larger than the nominal current, thereby exceeding the rated current of cable. Consequently, the cable conductor, typically copper wire, heats up to a temperature that ignites surrounding combustibles. This paper describes the transient characteristics of the 0.6/1kV, TFR-8 cable have been investigated, and analyzed under the over current conditions for reduce the risk of electrical fire by experimental and FEM analysis. The experimental and FEM(Finite Element Method) analysis results of temperature and resistance variation according to the over current in copper wires were analyzed. The experimental results coincide well with the FEM analysis.

• 정보처리학회논문지A
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• 제8A권2호
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• pp.81-90
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• 2001

인터넷의 급속한 확산으로 인하여, 컴퓨터 시스템의 규모 및 복잡도가 점차 증가하고 있으며, 컴퓨터 시스템에 대한 높은 수준의 가용도 요구 조건을 충족시키기 위해, 하드웨어적.소프트웨어적 결함 허용 기법에 대한 연구가 활발하다. 소프트웨어 재활 기법은 서버에 탑재된 소프트웨어의 장시간 가동에 따른 소프트웨어 노화 현상을 다루고 있으며, 서버에서 실행중인 소프트웨어의 수행을 고의적으로 멈춘 후에 결함 발생 가능성이 낮은 초기 상태에서 이를 다시 가동시키는 소프트웨어적 결함 예방 방법의 일종이라 볼 수 있다. 본 연구에서는 주-여분 서버 시스템에서의 작업전이 시간이 소프트웨어 재활에 미치는 영향을 연구하였으며, 가용도 분석을 통해서 작업전이 시간이 재활 정책을 결정함에 있어서 중요한 요소임을 발견하였다.

• 한국멀티미디어학회논문지
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• 제24권8호
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• pp.1101-1113
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• 2021

The rapid growth of sense-and-respond applications and the emerging cloud computing model present a new challenge: providing publish/subscribe middleware as a scalable and elastic cloud service. The publish/subscribe interaction model is a promising solution for scalable data dissemination over wide-area networks. In addition, there have been some work on the publish/subscribe messaging paradigm that guarantees reliability and availability in the face of node and link failures. These publish/subscribe systems are commonly used in information-centric networks and edge-fog-cloud infrastructures for IoT. The IoT has an edge-fog cloud infrastructure to efficiently process massive amounts of sensing data collected from the surrounding environment. In this paper. we propose a quorum-based hierarchical fault-tolerant publish/subscribe systems (QHFPS) to enable reliable delivery of messages in the presence of link and node failures. The QHFPS efficiently distributes IoT messages to the publish/subscribe brokers in fog overlay layers on the basis of proposing extended stepped grid (xS-grid) quorum for providing tolerance when faced with node failures and network partitions. We evaluate the performance of QHFPS in three aspects: number of transmitted Pub/Sub messages, average subscription delay, and subscritpion delivery rate with an analytical model.

• 한국진공학회:학술대회논문집
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• 한국진공학회 1999년도 제17회 학술발표회 논문개요집
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• pp.188-188
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• 1999

The embedded atom method (EAM) of Daw and Baskes as a semiempirical method, has been successfully applied to the fcc or nearly filled d-band transition metals due to its computational feasibility and its methodological simplicity. Then Baskes modified the EAM (MEAM) to include directional bonding and applied it to metals, semiconductors, and diatomic gases, all of which have different types of bondings. Here, we present a detailed study of the energetics of adsorption on the fcc(111) surfaces and binary system within the framework of MEAM. In adsorption on fcc(111) surfaces, there are two energetically favored sites, so called, fcc site and hcp site, which may trigger stacking fault in the growth of films and might switch growth mode between 3D growth and layer by layer growth. We scrutinized the role of the hcp sites, which would offer dynamic growth pathways although the dynamics are not yet clear within the limited experimental resolution. Featuring these transient motions in the atomic level should contribute to the understanding the growth mechanisms on fcc(111) surface. And we also applied MEAM for initial stage energetics at the Cr coverage of sub- monolayer on W(110). We hope that recently observed extraordinary growth behavior at the Cr coverage of 0.7 monolayer, self- organized nano-scale lines, can be resolved in this MEAM binary system calculation.

• 대한안전경영과학회지
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• 제1권1호
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• pp.7-17
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• 1999

As the loss from break-downs and errors, which became more frequent with the growth of elaborateness, complexity and in scale of the plant and equipments, are enormous, the improvement in the reliability, maintenance, safety, and qualify become to have interest. The fault diagnosis is a systematic and unified method to find errors, which is based on the interpretation that data, subconsciously, have noises. But, as most of the methods are inferences based on binomial logic, the uncertainty is not correctly reflected. In this study, we suggest, to manage the uncertainty in the system efficiently on the point of predictive maintenance, We should use fuzzy expert system, which make the decision considering uncertainty possible by taking linguistical variable and fixed quantity by using the fuzzy theory concepts on the basis of an expert's direct observation and experience.

• 한국표면공학회지
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• 제36권2호
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• pp.135-140
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• 2003

The difference in lattice parameter and thermal expansion coefficient between GaN and Si which results in many defects into the grown GaN is larger than that between GaN and sapphire. In order to obtain high quality GaN films on Si substrate, it is essential to understand growth characteristics of GaN. In this study, GaN layers were grown on Si(111) substrates by MOCVD at three different GaN growth temperatures ($900^{\circ}C$, $1,000^{\circ}C$ and $1,100^{\circ}C$), using AlN and LT-GaN buffer layers. Using TEM, we carried out the comparative investigation of growth characteristics of GaN by characterizing lattice coherency, crystallinity, orientation relationship and defects formed (transition region, stacking fault, dislocation, etc). The localized region with high defect density was formed due to the lattice mismatch between AlN buffer layer and GaN. As the growth temperature of GaN increases, the defect density and surface roughness of GaN are decreased. In the case of GaN grown at $1,100^{\circ}$, growth thickness is decreased, and columns with out-plane misorientation are formed.

• 한국주조공학회지
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• 제17권2호
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• pp.188-194
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• 1997

The effects of solidification condition and vibration on structure refinement were investigated for unidirectionally solidified $Al-CuAl_2$ eutectic composites. Eutectic composites were unidirectionally solidified under vibration with different growth rates (R) and thermal gradient(G). The lamellar structure was varied according to growth condition (G/R ratio). For the structure refinement the effect of G/R was found out to be greater than that of vibration. The interlamellar spacing(${\lambda}$) in this materials was varied with the growth rates(R) with "${\lambda}^2R$=Constant" relationship.

• 한국재료학회지
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• 제3권3호
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• pp.230-236
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• 1993

Si(111) 표면위에 Si을 homepitaxial 성장시킬때 중간 금속인 Ag, Sn등을 흡착시키지 않을 경우와 흡착시킬 경우 RHEED(Reflection High Energy Electron Diffraction)상의 경면반사점(specular spot)강도의 주기적 변화를 관찰함으로써 두 경우의 Si결정성장 과정의 차이점을 관찰하였다. 중간금속을 흡착하지 않을 경우 성장 초기에는 흡착Si원자가 Si(111) $7{\times}7 $구조의 Stacking Fault층을 먼저 채우고난 후 정상적인 충상성장을 하기 때문에 성장초기에는 불규칙적인 진동을 나타내다가 약 6ML정도부터 주기적인 진동으로 바뀜이 관찰되었다. 그러나, 중간금속인 Ag, Sn을 Si(111)위에 1ML흡착시키면 Ag의 경우 300~$600^{\circ}C$, Sn의 경우 190~$860^{\circ}C$의 시료온도에서 표면구조가 ${\sqrt}{3}{\times}{\sqrt}{3}$구조로 바뀜이 RHEED상으로 관찰되었다. 그리고 난 후에 Si을 흡착시킬 경우 RHEED 상의 경면반사점 강도는 초기부터 주기적일 변화를 가짐이 관찰되었으며${\sqrt}{3}{\times}{\sqrt}{3}$구조는 변함이 없었다. 또한 보다 낮은 시료 온도에서 많은 진동이 관찰되었다. 이는 중간금속이 성장표면쪽으로 편석하면서 흡착원자 Si의 표면확산에 대한 활성호 에너지를 감소시켜 주기 때문이라 생각된다.

• 응용통계연구
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• 제23권3호
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• pp.573-584
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• 2010

This paper considers the differences in the software execution environments in the testing phase and the operational phase to determine the optimal release time and warranty period of software systems. We formulate equations for the total expected software cost until the end of the software life cycle based on the NHPP. In addition, we derive the optimal release time that minimizes the total expected software cost for an imperfect debugging software reliability model. Finally, we analyze the sensitivity of the optimal testing and maintenance design related to variation of the cost model parameters based on the fault data observed in the actual testing process, and discuss the quantitative properties of the proposed model.