http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
장기간 접속 단절된 이동 클라이언트를 위한 효과적 캐시 유지 기법
박광진(Kwangjin Park),송문배(Moonbae Song),강상원(Sangwon Kang),황종선(Chongsun Hwang) 한국정보과학회 2005 정보과학회논문지 : 데이타베이스 Vol.32 No.3
접근 빈도가 높은 데이타를 클라이언트의 캐시에 저장하여 사용하는 것은 한정된 무선 대역폭을 사용하는 이동 컴퓨팅 환경에서 매우 중요한 이슈이다. 그러나 클라이언트의 접속 단절이 빈번하게 발생하는 무선환경에서 캐시 데이타의 일관성을 보장해주기 위해서는 적지 않은 노력이 필요하다. 최근에는 캐시 데이타의 일관성 검사를 위하여 서버의 주기적인 무효화보고(Invalidation Report, IR) 기법을 이용한 연구가 활발하게 진행되고 있다. 하지만 클라이언트가 오랜 접속 단절이 발생할 경우 모든 캐시 데이타를 버려야 하므로, 성능에 큰 장점을 얻을 수 없게 된다. 이에 본 논문에서는 이동 컴퓨팅 환경에서 빈번한 접속 단절로 인하여 오랫동안 무효화 보고를 받지 못하더라도 유효한 캐시 데이타를 최대한 유지시킬 수 있는 기법들을 제안한다. 먼저 클라이언트가 접속 단절 후 첫 재접속이 되었을 경우, 자신의 접속 단절 시간을 전송하도록 하여 서버가 동적으로 IR에 포함될 이전 일정 주기를 결정하도록 하였다. 이에 반하여 두 번째 기법에서는 서버가 특정 기간 동안의 IR 정보를 저장하도록 하여, 오랜 접속 단절 후에도 클라이언트가 직접 캐시 데이타의 일관성 검사를 요청할 수 있도록 하였다. 제안한 기법에 의해 현저히 줄어드는 클라이언트의 캐시 손실률과 그에 따른 업링크수의 감소, 그리고 질의에 대한 응답시간의 감소로 인한 시스템 성능 향상은 시뮬레이션을 통해 확인된다. In the mobile computing environment, caching data at the client's side is a useful technique for improving the performance. For caching to be effective, the cache contents must be consistent with those stored in the server. That is, unfortunately, difficult to enforce due to the frequent disconnection and mobility of clients. In the literature, the basic approach adopted is for the server to periodically broadcast invalidation reports(IRs) that contain information about objects that have been updated recently. However IR-based cache maintenance scheme has a main drawback. Any client who has been disconnected longer than w seconds has to discard all cached items even some of them may still be valid. In this paper, we propose two main schemes which can adapt clients' losing IR messages by long disconnection. First, the client sends its disconnection time when connection is re-established, and the server uses this information to decide the size of broadcast window w dynamically. Second, the server maintains IR messages for a given period of time and a client who has been disconnected longer than w seconds can verify its cache consistency individually. Compared to previous IR-based schemes, our schemes can significantly reduce cache missing and uplink request and improve the throughput by reducing response time.
박광진(Kwangjin Park),정재화(Jaehwa Jeong),김정현(Jung Hyun Kim),배중면(Joongmyeon Bae) 대한기계학회 2007 大韓機械學會論文集A Vol.31 No.12
This study focuses on the corrosion problems of STS316(stainless steel 316) tube for the cooling system of PEMFC (Proton Exchange Membrane Fuel Cell) operation. Deionized water which is highly corrosive is used especially for cooling agent of PEMFC to eliminate electrical conductivity. The tensile stress analysis was performed to check the change of mechanical strength of cooling line and pH of the water was monitored for the observation of extent of corrosion at simulated PEMFC operating condition. When STS316 tube was exposed to deionized water for 500 hours, substantial cracks were found on the surface and the pH of water was decreased from 6.8 to 5.8. For prevention of corrosion problems, the STS316 was coated by three kinds of fluororesin such as PTFE, FEP and ETFE. Among the coating materials, PTFE was the most protective in corrosive environment and was maintained the mechanical strength. To lower the cost, the same experimental analyses were carried out for iron tubes and the result will be discussed in detail.
박광진(Kwangjin Park),정재화(Jaehwa Jeong),김정현(Jung Hyun Kim),배중면(Joongmyeon Bae) 한국자동차공학회 2007 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
This study focuses on the corrosion resistance of STS316(stainless steel 316) line for the cooling system of PEMFC (Proton Exchange Membrane Fuel Cell) operation. The deionized water which is highly corrosive was used especially for cooling water of PEMFC to eliminate electronic conductivity. The tensile experiment was performed to check the change of mechanical strength of line and pH of water was measured for the observation of extent of corrosion after experiment. When STS316 line was exposed to deionized water for 500 hours, cracks were found on the surface and the pH of water was decreased from 6.8 to 5.8. For protection of corrosion, the STS316 was coated by three kinds of fluororesin such as PTFE, FEP and ETFE. Among the coating materials, the PTFE was the most protective in environment of corrosion and was maintained the mechanical strength.
박광진(Kwangjin Park),정재화(Jaehwa Jeong),김정현(Jung Hyun Kim),배중면(Joongmyeon Bae) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10
This study focuses on the corrosion problems of STS316(stainless steel 316) and iron tube for the cooling system of PEMFC operation. Among the coating materials of fluororesin, PTFE was the most protective in corrosive environment and was maintained the mechanical strength. To lower the cost, the same experimental analyses were carried out for iron tubes and the result will be discussed in detail.
박광진(Kwangjin Park),김정현(Jung Hyun Kim),정재화(Jaehwa Jeong),배중면(Joongmyeon Bae) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5
This study focuses on the hydrogen embrittlement of iron tube for fuel line of PEMFC (Proton Exchange Membrane Fuel Cell). PEMFC is operated by feed of hydrogen as a reactant and steam for proton conductivity of membrane. However, the environment with hydrogen and steam occur the hydrogen-induced degradation in BOP system. When iron tube was exposed to hydrogen and steam condition for 24 hours, the oxide layer on the surface was decreased by reduction. When the ambient temperature was 90℃, micro cracks were found on the surface than any other temperature. The mechanical strength of iron tube was 3% lower than that of non-experiment tube. Maximum tensile stress was decreased 8%.
중ㆍ저온형 고체산화물 연료전지에서 연료로 공급되는 CO 와 H₂ 가 성능에 미치는 영향
박광진(Kwangjin Park),배중면(Joongmyeon Bae) 대한기계학회 2008 大韓機械學會論文集B Vol.32 No.12
The performance behavior of solid oxide fuel cell using H2 and CO as fuels was investigated. The power densities and impedance results showed a little variation as the ratio of H₂ and CO changed. However, when the pure CO was used as a fuel, area specific resistance (ASR), especially low frequency region, was increased. This might be due to carbon deposition on anode. The maximum power density was 60% lower using CO than using H₂. Carbon deposition reduced after constant current was applied. The SOFC performance was recovered from the carbon deposition after applying constant current during 100h.