• Applied Chemistry for Engineering
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• v.7 no.2
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• pp.237-244
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• 1996

Liquid-liquid extractions by use of microporous hollow fiber modules are fast compared with conventional extraction equipment because of the large surface area per volume. In these modules, the extractant and feed can be contacted at high speed and two flows are completely independent, so there are no problems with loading and channeling. In this paper, it was investigated the extraction selectivities for liquid-liquid extraction of Fe(II) and Ni(II) from dilute aqueous solution into TOA (tri-n-octylamine) and EHPNA (bis(2-ethylhexyle)hydrogenphosphite) as organic extractants by using the hydrophobic hollow fiber module. To determine the rate controlling step for mass transfer in hollow fibers, we also examined the effect of inside and outside flow rates of the hollow fiber module. From these experiments, we identified for the extraction of system with high partition coefficient in hydrophobic hollow fibers, mass transfer in the inside aqueous feed dominated the overall mass transfer, and in this paper, correlation between $K_w$ and $v_t$ was obtained as $K_w{\frac{d}{D}}=6.22\(\frac{d^2v_t}{LD}\)^{1/3}$ On the other hand, for the system with low partition coefficient, the resistance in the inside of hollow fibers was much less than membrane resistance because the extraction was not simple in the micropore. Thus, for systems with high partition coefficients, hydrophobic hollow fibers would be a better choice.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2014.10a
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• pp.581-584
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• 2014

In this paper, a micro-scale photovoltaic(PV) energy harvesting system is proposed where an MPPT(Maximum Power Point Tracking) control is implemented using an energy distribution technique. Miniature PV cells output very low energy and low voltages, and thus, they cannot be used to directly power the MPPT controller. In the proposed system, a start-up circuit boosts an internal Vcp, and the boosted Vcp is used to operate the internal MPPT control block. When the Vcp reaches a predefined value, a detector circuit makes the start-up block turn off and provide a power converter with the energy from the PV cell. When the Vcp decreases such that the MPPT controller can not be operated, the energy transferred to the power converter is blocked and the start-up circuit is reactivated. In this way, the MPPT function is achieved by alternately operating the start-up circuit and the power converter using the energy distribution technique, and the harvested energy is transferred to a load through a PMU(Power Management Unit). The proposed circuit is designed in a 0.35um CMOS process and its functionality has been verified through extensive simulations. The designed chip area including pads is $1430um{\times}1110um$.

• Proceedings of the Korean Information Science Society Conference
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• 2001.10c
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• pp.391-393
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• 2001

이동컴퓨팅 환경에서 호스트의 이동성으로 야기되는 멀티미디어 데이터전송 문제 해결에 관한 연구가 활발히 진행되고 있다 . 멀티캐스트는 멀티미디어 데이터가 차지하는 많은 네트워크 트래픽을 수신자에게 효율적으로 분배함으로써 네트워크 트래픽을 줄일수 있다. 그러나 이동 호스트를 대상으로 하는 멀티캐스트는 무선자원의 효율적 사용을 위해 셀 반경이 작아짐에 따라 빈번하게 그룹의 멤버와 위치를 변화시키기 때문에 라우팅 경로의 최적화, 투명성 제공, 잦은 핸드오프로 인한 등록지연에 따른 서비스 단절과 패킷손실의 증가에 대한 명확한 대책이 제시되지 못하고 있다. 또한 멀티캐스트를 지원하지 않는 영역으로 이동했을 때의 데이터전송에 관한 문제점도 내포하고 있다. 본 논문에서는 이러한 문제의 해결방안으로 이동컴퓨팅환경에서 Hop Counter로 정의된 서비스 범위를 하나의 그룹이라 정의하고 그룹기반의 멀티캐스트 라우팅 방법을 제안한다. 제안 방법은 셀이 마이크로화됨에 따라 나타나는 Hop 증가에 따른 전송 오버로드와 터널링 문제를 해결하고, 광역 네트워크에서의 멀티캐스팅을 담당하는 에이전트의 부하를 감소시킴으로써 성능 향상을 기대할 수 있다. 또한 호스트가 이동한 FA가 멀티캐스트를 지원하지 않을 때 MA가 그룹의 특정 호스트로부터 보낸 데이터를 받기 위해서 주변에 인접해 있는 MA중 멀티캐스트를 지원하고 가장 작은 Hop을 갖은 MA를 터널의 대리자로 등록해 놓음으로써 멀티캐스팅이 지원되지 않은 환경에서의 멀티캐스팅이 이루어질 수 있다.

• The Journal of the Korea Contents Association
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• v.9 no.3
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• pp.288-295
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• 2009

This study empirically analyzed how the organizational fairness perceived by revenue officers affect the empowerment and employee efforts. The result of the analysis revealed that as for job fairness, distribution fairness and interaction fairness, with the exception of process fairness, have significant influence on the empowerment while the empowerment, in turn, has significant influence on the employee efforts. This finding confirms that a high level of organizational fairness perceived by revenue officers in their job processes results in a high level of empowerment, which then produces heightened employee efforts, eventually contributing to the efficiency of revenue officers' job performance and the improvement of satisfaction with service quality. Therefore, it is necessary that administrators of revenue offices allow their subordinates to develop their potentials by empowering the employees and delegating authority.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.4
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• pp.297-302
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• 2011

According to the standards for district heating substation established by Korea District Heating Corporation, water heating supply systems at over 150 Mcal/h capacity must employ the 2-stage heat exchanger that improves the system efficiency by reusing the heat included in the return water of district heating system already used for space heating. In this paper, the operating characteristics of the system in accordance with the load distribution of two heat exchangers for pre-heating and re-heating cold city water are investigated. The results including mass flow rate, return temperature etc. help to manage district heating system economically.

• Journal of Korea Game Society
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• v.16 no.1
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• pp.83-92
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• 2016

An online game is a huge distributed system comprised of servers and untrusted clients. In such circumstances, cheaters may employ abnormal behaviors through client modification or network packet tampering. Client-side detection methods have the merit of distributing the burden to clients but can easily be breached. In the other hand, server-side detection methods are trustworthy but consume tremendous amount of resources. Therefore, this paper proposes a security reinforcement method which involves both the client and the server. This method is expected to provide meaningful security fortification while minimizing server-side stress.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.7
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• pp.603-611
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• 2013

In this paper, we propose a new frame structure and the underlying dynamic resource control mechanism to support an integrated service, including a real-time (RT) service that requires to serve the end-to-end delay performance, as well as non-real-time (NRT) service, using Self-Organizing Time Division Multiple Access (SO-TDMA)-based MAC protocol in a multi-hop ad-hoc maritime communication network. The underlying frame structure is dynamically configured by resource allocation to guarantee the average target outage performance of the real-time service. Toward this end, we analyze the average outage probability and its performance is verified for the proposed frame structure by simulation.

• Proceedings of the KIEE Conference
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• 2000.07d
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• pp.2962-2964
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• 2000

최근 웹의 사용이 일반화되면서 인터넷의 사용자가 급속히 증가하고 있어서. 기존의 단일 웹서버 방식에서는 막대한 접속 트래픽의 수용과 유연한 시스템 확장 등의 문제점이 예상되고 있다. 이와 함께 business-critical한 작업의 경우, 웹서버의 안정성 및 가용성 문제가 가장 중요한 문제로 지적되고 있어서 이러한 문제를 해결할 수 있는 웹전용 서버를 개발이 절대적으로 필요하다. 본 연구에서는 이를 위해. 급격한 트래픽 변화의 수용 및 웹서버의 확장성이 용이한 가상머신 개념과 고신뢰성의 시스템 운영을 위한 고장포용(fault-tolerant)기법을 적용하여 클러스터링 웹전용 서버를 구축하고, 특히 클러스터 웹서버의 부하를 분배해주는 로드밸런서의 고가용성 보장을 위해 heartbeat, fake, mon등의 기법을 이용하여 백업(backup)을 구현한다. 또한 구현된 시스템의 고성능 및 고가용성을 극대화하고. 시스템의 고장시 데이터 손실의 최소화와 이의 복구를 위해 고장 검출 및 진단 기법에 대한 방안을 제시한다.

• Proceedings of the Korea Information Processing Society Conference
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• 2014.11a
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• pp.118-121
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• 2014

격자 양자 색역학(Lattice Quantum ChromoDynamics; Lattice QCD)은 자연계에 존재하는 중력, 전자 기력, 약한 핵력, 그리고 강한 핵력 등의 기본적인 상호작용 중 강한 핵력의 상호작용을 이해하기 위한 핵물리 분야의 이론이다. 이 물리 역학은 몬테 카를로(Monte Carlo) 기법을 이용하여 대규모 수치 연산을 필요로 하고, 수행시간 단축을 위하여 병렬처리가 필요하다. 본 논문에서는 격자 양자 색역학에서 요구되는 대규모 수치 연산에 대하여 마이크로프로세서와 성능가속기에 최적의 작업부하 분배를 통한 이기종 병렬처리 방법을 제안하고 성능가속기반을 사용한 방법과 제안 방법의 성능을 비교한다.

• Journal of IKEEE
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• v.23 no.1
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• pp.173-180
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• 2019

There is a case where the output of renewable energy(RE) is curtailed due to an increase in the share of RE. Typically, wind power(WP) is curtailed due to oversupply and low load at midnight. However there is a case where the output of WP is limited during daytime due to the increase in share of photovoltaic(PV). In current electricity market, as the share of PV is increased, the curtailments of WP will be increased further, which will add to the difficulties of wind farm operators. In this paper, we propose a method to distribute the power limit of RE according to the criterion based on the priority constraint of the energy source which is difficult to operate the power system.