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김영철,차명훈,이상민,김영균,Kim, Y.C.,Cha, M.H.,Lee, S.M.,Kim, Y.K. 한국전자통신연구원 2009 전자통신동향분석 Vol.24 No.4
가상화는 클라우드 컴퓨팅 서비스를 제공하기 위한 기반 기술로 서버, 스토리지, 네트워크 등과 같은 컴퓨팅 자원을 통합 관리하면서 필요에 따라 자원을 할당함으로써 자원 활용률을 높이고 운영 비용을 절감할 수 있도록 한다. 또한 가상화된 자원에 대한 높은 확장성과 안정성을 제공할 수 있다. 최근에 클라우드 컴퓨팅에서 제공하는 스토리지 서비스는 이러한 가상화 기술 중에서 스토리지 가상화 기술을 기반으로 한다. 본 고에서는 클라우드 컴퓨팅 서비스에서 요구하는 스토리지 가상화 기술과 클라우드 스토리지 서비스에 대해 살펴본다.
김영철,박근태,이상민,김홍연,김영균,Kim, Y.C.,Park, K.T.,Lee, S.M.,Kim, H.Y.,Kim, Y.K. 한국전자통신연구원 2007 전자통신동향분석 Vol.22 No.6
최근에 블로그, UCC, IPTV 등 사용자 중심의 인터넷 서비스와 언제 어디서나 웹을 통해 서비스를 받을 수 있는 유비쿼터스 컴퓨팅 환경으로의 변화는 대용량 저장 공간과 빠르고 안정된 서비스를 제공할 수 있는 대규모 클러스터 시스템 플랫폼을 필요로 한다. 그리고 이러한 대규모 클러스터 시스템 플랫폼을 효율적으로 관리하고 이용할 수 있는 클러스터 파일 시스템은 필수적이다. 본 고에서는 최근에 연구 개발되고 있는 클러스터 파일 시스템들을 소개하고 기술 동향에 대해 살펴본다.
김영철,박근우,윤영,민만기,최영돈,Kim, Y. C.,Park, G. W.,Youn, Y.,Min, M. K.,Choi, Y, D, 대한설비공학회 2001 설비공학 논문집 Vol.13 No.3
A system simulation program was developed for a multi-type inverter heat pump. Electronic expansion valve(EEV) was used to extend the capacity modulating range of the heat pump as expansion device. The program was also developed to calculate actual system performance with the building load variation with climate during a year. The performance variation of a multi-type hat pump with two EEV and an inverter compressor was simulated with compressor speed, capacity, and flow area of the EEV. As a result, the optimum operating frequency of the compressor and openings of the expansion device were decided at a given load. As compressor speed increased, he capacity of heat pump increased, the capacity of heat pump increased. Therefore flow area of EEV should be adjusted to have wide openness. Thus the coefficient of performance(COP) of the heat pump decreased due to increasement of compressor power input. The maximum COP point at a given load was decided according to the compressor speed. And under the given specific compressor speed and the load, the optimum openings point of EEV was also decided. Although the total load of indoor units was constant, the operating frequency increased as the fraction of load in a room increased. Finally ad the compressor power input increased, the coefficient of performance decreased.
질소 열처리에 따른 $RuSr_2(EuCe)Cu_2O_z$ 계의 구조 및 자기적 특성
이호근,김용일,김영철,Lee, H.K.,Kim, Y.I.,Kim, Y.C. 한국초전도학회 2012 Progress in superconductivity Vol.13 No.3
Two $RuSr_2(EuCe)Cu_2O_z$ samples (as prepared and after $N_2$ treatment) have been investigated by thermogravimetric (TC) analysis, high-resolution x-ray powder diffraction and magnetization measurements. TG measurements which were carried out in $H_2/Ar$ atmosphere showed that the $N_2$ treatment of the as-prepared sample at $650^{\circ}C$ for 2h leads to a decrease in the oxygen content z by about 0.25. This oxygen depletion was accompanied by an increase in the magnetic transition temperature from 54.0 K to 114.9 K. This magnetic behavior is discussed in connection with the results of Rietveld analysis of the x-ray diffraction data which showed that the $N_2$ treatment resulted in both a significant increase in the rotation angle of the $RuO_6$ octahedra and a decrease in c-lattice parameter of the sample.
범 밀도함수론을 이용한 정방정계-HfO<sub>2</sub>/Si의 계면 층 구조 연구
김대희,서화일,김영철,Kim, D.H.,Seo, H.I.,Kim, Y.C. 한국진공학회 2009 Applied Science and Convergence Technology Vol.18 No.1
본 연구는 정방정계-$HfO_2$/Si 초격자의 계면 층 구조를 범밀도함수론 (density functional theory)을 이용하여 계산하였다. 입방정계-$HfO_2$는 Si 기판과 에피택시 접합을 위하여 a와 b축의 길이가 증가되면 c축의 길이가 2% 감소하여 정방정계 구조가 되었다. 정방정계-$HfO_2$와 Si 기판의 말단층에 따라서 8 개의 계면 층 모델이 생성되었다. 정방정계-$HfO_2$ (004)$_{1/4}$/Si $(004)_{3/4}$ 초격자구조가 에너지 관점에서 가장 안정하였고, 정방정계-$HfO_2$ $(004)_{1/4}$/Si (002) 초격자구조는 가장 불안정하였다. 에너지 관점에서 가장 불안정한 구조의 경우, 정방정계-$HfO_2$의 계면에 존재하는 2 개의 산소 원자가 Si 기판으로 이동하여 정방정계-$HfO_2$ 초격자구조에 2 개의 산소 공공이 생성되었다.
김홍,이부영,이준호,김영철,Kim H,Lee B. Y,Lee J. H,Kim Y. C 한국초전도학회 2004 Progress in superconductivity Vol.6 No.1
The policrystalline$SmBa_2$$Cu_2$$O_{y}$ was synthesized by the solid state reaction method. The dependence of AC susceptibility on temperature and applied ac field was studied. The critical temperature $T_{c}$ is about 92 K. As the ac field is increased, the slope and the value of real part of susceptibility become smaller and the peak position of imaginary part $T_{P}$ was shifted to a lower temperature with peak broadening. Using Bean's model, we determined intergrain critical current density $J_{c}$ and obtained $44 A/{cm}^2$ at 75 K. From the relation of the $J_{c}$ (T)=($1-T/T_{c}$ )$^{\beta}$ we obtained $\beta$=0.8 and found that the Josephson junction type of the $SmBa_2$$Cu_2$$O_{y}$ is SIS junction. The peak of the imaginary part shifts to higher temperature with increasing frequency, f. from Arrhenius plot, we obtained the activation energy of about 0.96 eV.
김영철(Y.C.Kim),이현우(H.W.Lee) 전력전자학회 1998 전력전자학술대회 논문집 Vol.- No.-
A large number of soft switc hing topologies included a resonant circuit have been proposed. But these circuits increase number of switch in circuit and complicate sequence of switching operation. In this paper, the authors propose power conversion system, DC-AC inverter of high efficiency and high power factor with soft switching mode by partial resonant method. The switching devices in a proposed circuits are operated with soft switching by the partial resonant method, that is, PRS²MPC (Partial Resonant Soft Switching Mode Power Converter). The result is that the switching loss is very low and the efficiency of system is high. And the snubber condenser used in partial resonant circuit makes charging energy regenerated at input power source for resonant operation.
김영철 ( Y C Kim ),김도현 ( Do Hyun Kim ) 한국항공운항학회 2012 한국항공운항학회지 Vol.20 No.4
This paper is part of the research about the selection and justification of Jeju international airport as an aircraft category ``F`` alternative airport, which is the results of an weather analysis based on meteorological statistics. As the results of the study, it has been only 1 day per year (58minutes) that weather conditions of Incheon and Jeju international airports, from January 2006 to June 2011, are below landing weather minimums of each airport at the same times. This means that these airports are not within the same meteorological region, which is against the current orthodoxy. In addition, it is very rare that weather conditions of Jeju international airports are below landing weather minimums when Incheon international airport is below landing weather minima. It shows that the meteorological characteristics of these regions differ widely and the designation of Jeju international airport as an alternative airport is scientifically reasonable.
할로우 캐소드 방전에 의한 금속소결부품의 질화처리에 관한 연구
김영철 ( Y C Kim ),한창석 ( C S Han ) 한국열처리공학회 2012 열처리공학회지 Vol.25 No.2
An apparatus was constructed to nitrify small metallic sintered components by using a hollow-cathode discharge plasma method. A stainless steel basket, which contains a sintered part to be nitrified, is potentially grounded and serves as hollow-cathode electrode. Hollow-cathode plasma was produced by supplying the positive voltage to the anode. In this study sintered carbon iron and stainless steel were used as testing specimens. It was shown that an effective nitrifying took place by controlling the total pressure of nitrogen and hydrogen gas and applied voltage.