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MVPN 서비스 제공을 위한 효율적이고 안전한 핸드오버 메커니즘
우현제(Hyunje Woo),김경민(Kyoungmin Kim),이미정(Meejeong Lee) 한국정보과학회 2007 정보과학회논문지 : 정보통신 Vol.34 No.1
MVPN(Mobile Virtual Private Network)은 이동단말을 사용하는 이동근무자가 지역적 제한없이 VPN 서비스를 제공받을 수 있도록 하는 기술이다. 이동 VPN 사용자에게 지속적인 VPN 서비스를 제공하기 위해서는 이동성을 제공하기 위한 MIP(Mobile IP) 프로토콜과 IPsec 기반 VPN 기술의 공존이 필요하다. 그런데 MIP와 IPsec 기반 VPN GW(Gateway)를 함께 사용하게 되면 등록 실패나 빈번한 IPsec 터널 재 설립과 같은 문제가 발생한다. IETF에서는 이와 같은 문제를 해결하기 위해 VPN GW의 외부에 홈 에이전트(x-HA)를 사용하는 방안을 제시하였고, 이를 기반으로 동일한 외부네트워크 내에서의 이동에 대한 핸드오버 지연을 줄이기 위한 방안으로 MN(Mobile Node)이 위치한 외부네트워크 내에 x-HA를 동적으로 할당하는 방안도 제안되었다. 그러나 동적으로 x-HA를 할당하는 방안은 세션 키의 노출이나 네트워크 간 이동 시의 긴 핸드오버 지연 발생과 같은 문제를 가진다. 이에 본 논문은 이동 VPN 사용자의 핸드오버 지연시간을 최소화하고 핸드오버로 인한 데이타 손실을 줄이면서 보안을 강화하는 새로운 MVPN 프로토콜을 제안하고, 시뮬레이션을 통해 기존에 제안된 방안과 비교하였다. Mobile Virtual Private Network (MVPN) provides VPN services without geographical restriction to mobile workers using mobile devices. Coexistence of Mobile IP (MIP) protocol for mobility and IPsec-based VPN technology are necessary in order to provide continuous VPN service to mobile users. However, Problems like registration failure or frequent IPsec tunnel re-negotiation occur when IPsec-based VPN Gateway (GW) and MIP are used together. In order to solve these problems, IETF proposes a mechanism which uses external home agent (x-HA) located external to the corporate VPN GW. In addition, based on the IETF proposal, a mechanism that assigns x-HA dynamically in the networks where MN is currently located was also proposed with the purpose to reduce handover latency as well as end-to-end delay. However, this mechanism has problems such as exposure of a session key for dynamic Mobility Security Association (MSA) or a long latency in case of the handover between different networks. In this paper, we propose a new MVPN protocol in order to minimize handover latency, enhance the security in key exchange, and to reduce data losses cause by handover. Through a course of simulation, the performance of proposed protocol is compared with the existing mechanism.
CuO hollow nanosphere-catalyzed cross-coupling of aryl iodides with thiols
Woo, Hyunje,Mohan, Balaji,Heo, Eunjung,Park, Ji Chan,Song, Hyunjoon,Park, Kang Hyun Springer 2013 Nanoscale research letters Vol.8 No.1
<P>New functionalized CuO hollow nanospheres on acetylene black (CuO/AB) and on charcoal (CuO/C) have been found to be effective catalysts for C-S bond formation under microwave irradiation. CuO catalysts showed high catalytic activity with a wide variety of substituents which include electron-rich and electron-poor aryl iodides with thiophenols by the addition of two equivalents of K<SUB>2</SUB>CO<SUB>3</SUB> as base in the absence of ligands.</P>
Woo, Hyunje,Kim, Daeho,Park, Ji Chan,Kim, Ji Woong,Park, Sungkyun,Lee, Jae Myung,Park, Kang Hyun The Royal Society of Chemistry 2015 Journal of Materials Chemistry A Vol.3 No.42
<▼1><P>We report a one-pot synthesis of hybrid nanocomposites of Cu-doped Pd–Fe3O4<I>via</I> controlled thermal decomposition of Fe(CO)5 and reduction of Pd(OAc)2 and Cu(acac)2.</P></▼1><▼2><P>We report a one-pot synthesis of hybrid nanocomposites of Cu-doped Pd–Fe3O4<I>via</I> controlled thermal decomposition of Fe(CO)5 and reduction of Pd(OAc)2 and Cu(acac)2. Sodium oleate, used as a capping agent, affected both the morphologies and surface areas of the Cu-doped Pd–Fe3O4 nanocomposites. To the best of our knowledge, these magnetically recyclable hybrid nanocomposites are a new class of nanocatalysts, and the tandem synthesis of 2-phenylbenzofuran from 2-iodophenol with phenylpropiolic acid catalyzed by heterogeneous nanocatalysts has not been reported in the literature. Moreover, Cu-doped Pd–Fe3O4 nanocatalysts are superior to previously reported catalysts for this tandem reaction.</P></▼2>
Woo, Hyunje,Park, Junha,Kim, Jiwoong,Park, Sungkyun,Park, Kang Hyun ELSEVIER 2017 CATALYSIS COMMUNICATIONS Vol.100 No.-
<P><B>Abstract</B></P> <P>We report a one-pot synthesis of hierarchical MnO/Pd-Fe<SUB>3</SUB>O<SUB>4</SUB> and CoO/Pd-Fe<SUB>3</SUB>O<SUB>4</SUB> nanocomposites containing scrolled multilayered nanosheets by controlled thermal decomposition of Fe(CO)<SUB>5</SUB> and reduction of metal precursors [Pd(OAc)<SUB>2</SUB>]. During the synthetic process, particles of amorphous MnO and CoO are immobilized on the Pd-Fe<SUB>3</SUB>O<SUB>4</SUB> support. These hierarchical nanocomposites follow a stepwise growth mechanism, initially forming Pd-Fe<SUB>3</SUB>O<SUB>4</SUB> seeds aggregated from nuclei, followed by growth to produce multilayered MnO/Pd-Fe<SUB>3</SUB>O<SUB>4</SUB> or CoO/Pd-Fe<SUB>3</SUB>O<SUB>4</SUB> structures. To the best of our knowledge, this is the first report on the hydroboration of styrene with bis(pinacolato)diboron using heterogeneous nanocatalysts. Among these catalysts, CoO/Pd-Fe<SUB>3</SUB>O<SUB>4</SUB> nanocomposites showed excellent performance due to the presence of a dual Pd and CoO catalytic system.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A one-pot synthesis of hierarchical MnO/Pd-Fe<SUB>3</SUB>O<SUB>4</SUB> and CoO/Pd-Fe<SUB>3</SUB>O<SUB>4</SUB> nanocomposites was reported. </LI> <LI> Hierarchical nanocomposites exhibit a stepwise growth mechanism. </LI> <LI> CoO/Pd-Fe<SUB>3</SUB>O<SUB>4</SUB> nanocomposites showed excellent performance for the hydroboration of styrene. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Salt-dilution 방법을 이용한 산지소하천의 유량과 유속 관계 분석
양현제 ( Hyunje Yang ),이성재 ( Sung-jae Lee ),임상준 ( Sangjun Im ) 한국산림과학회(구 한국임학회) 2018 한국산림과학회지 Vol.107 No.2
산지하천의 평균유속을 정확하게 추정하는 것은 하천의 수리적 흐름을 이해하고, 사방댐과 같은 사방구조물 최적 설계를 위해 중요하다. 산지하천의 평균 유속에 대한 연구는 부족한 실정이나 최근에는 상대적으로 자료 확보가 용이한 유량 자료를 이용하여 유량과 평균유속의 관계를 파악하는 연구들이 많이 진행되고 있다. 이 연구에서는 8개소의 서로 다른 산지소하천에서 조사된 87회의 유량과 평균 유속 자료를 분석하였다. 산지하천의 유량과 평균유속을 측정하기 위해 salt-dilution 방법을 사용하였으며, 평균유속은 도달 시간의 조화 평균을 적용하여 구하였다. 하천의 거칠기 높이를 이용하여 유량과 유속과의 무차원 관계식을 도출하였다. 거칠기 높이는 하상재료의 D<sub>50</sub>, D<sub>84</sub>와 하상변위의 σ<sub>pro</sub>, IPR<sub>90</sub>를 이용하였으며, σ<sub>pro</sub>와 IPR<sub>90</sub>의 정확성이 더 높게 나타났다. 일반적으로 유량과 평균 유속은 지수함수 관계를 보였다. Reach-average velocity prediction in steep mountain streams is important for understanding fluvial processes and practical applications of erosion control in mountain streams. little studies have been conducted in reach-average velocity, but hydraulic researches have been carried out to examine the relationship between discharge and reach-average velocity in torrent reaches using a relatively large amount of discharge data. In this study, a total of 87 data were measured in 8 torrent reaches. Salt-dilution method was used to estimate discharge. Reach-average velocity was calculated from harmonic mean of travel time that were measured by salt-dilution technique. In order to exlpore the hydraulic relation, both discharge and velocity were non-dimensionalized by using D<sub>50</sub>, D<sub>84</sub>, σ<sub>pro</sub> and IPR<sub>90</sub>. It also indicated that σ<sub>pro</sub> and IPR<sub>90</sub> were good variables as roughness height for develop the relationship between non-dimensional discharge and velocity in mountain streams. Generally, reach-average velocity could increase exponentially as discharge increases.