• Proceedings of the Membrane Society of Korea Conference
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• 1997.10a
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• pp.85-86
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• 1997

1. 서론 : Nanofiltration(NF)은 분자량이 200-1000인 유기물과 음이온 및 다가 이온등을 일가 이온으로부터 선택적으로 분리함으로써 유기물의 농축과 이온의 선택적인 분리를 동시에 행할 수 있는 분리 공정이며, 순수의 제조, 과일과 야채주스의 농축, 저알콜 맥주와 와인의 제조, 낙농 산업에서 유제품의 농축, 섬유공업에서 염료와 이온의 분리 및 제지공업의 폐수 처리 등에 응용되고 있다. NF용 막재료로는 셀룰로오스 계열의 고분자나 폴리아미드, 폴리술폰, PAN등이 연구되어 왔으며 최근에는 친수성이 좋고 가교를 하지 않고도 이온 결합에 의하여 강도를 유지할 수 있다는 아이오노머의 성질을 이용하여 아이오너마를 Nanofiltration용 막재료로 이용하려는 연구가 이루어지고 있다.[1-3] 그러나 아이오노머의 미세구조와 유기물의 분리특성간의 관계에 관한 연구는 미흡한 실정이다. 따라서 본 연구에서는 분리막의 성형성을 향상시키고자 알킬메타크릴레이트가 도입된 아이오너머를 합성하고 알킬기의 길이나 이온의 함량 등 고분자의 구조에 따른 아이오노머막의 분리특성을 연구하여 아이오노머막의 NF용막으로서의 응용가능성을 살펴보았다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37B no.12
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• pp.1128-1137
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• 2012

In this paper, we propose an improved MPR selection method considering mobility and density of nodes for ad-hoc networks. In Optimized Link State Routing(OLSR), a node selects 1-hop Multi-Point Relay(MPR) nodes to cover all 2-hop neighbor nodes. In a high population area, many nodes are likely to be selected as MPR nodes by their neighbors. This leads to increase in contention among MPR nodes and may decrease overall performance of the network. In addition, when an MPR node leaves the communication range of its MPR selector node, it can no longer perform as the MPR node and the performance of the network may also decrease. In this paper, we propose an MPR selection method which measures the mobility and density of nodes by exchanging the hello messages and gives the priorities to the nodes for MPR selection. Performance evaluation results using OPNET show that the proposed method is superior to OLSR or the MPR candidate method in terms of connectivity and throughput.

• Journal of Korea Society of Industrial Information Systems
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• v.14 no.5
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• pp.1-9
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• 2009

Relay-assisted multiple input technique has become a promising candidate for next generation broadband wireless communications. In this paper, we propose channel selective relay-based multiple input transmission system. In the proposed system, single carrier frequency division multiple access (SC-FDMA) and orthogonal frequency division multiple access (OFDMA) are adopted for uplink and downlink transmissions, respectively. The performance of relay-based system can be improved by using the subcarriers selectively based on the channel condition between relay station (RS) and mobile station, or between RS and base station. Simulation results show that the proposed relay-based system considerably outperforms the conventional relay-based system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.4A
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• pp.291-301
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• 2009

In this paper, the effect of ISI(Inter-Symbol Interference) and ICI(Inter-Carrier Interference) due to time difference of arrival on OFDMA-based mobile multi-hop relay (MMR) systems is analyzed. Analyses are performed for the ISI caused by the previous OFDMA symbol transmitted from neighboring macro or relay cell as well as the ISI caused by the next OFDMA symbol transmitted from neighboring macro or relay cell. Then, an effective SINR(Signal to Interference plus Noise Ratio) estimation method and a path selection method considering time difference of arrival are proposed to minimize the effect of ISI and ICI. It is shown by simulation that the performance degradation caused by time difference of arrival can be significantly mitigated when the proposed path selection method is applied to the uplink of OFDMA-based MMR systems.

• Journal of KIISE:Databases
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• v.35 no.4
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• pp.307-318
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• 2008

One of the primary issues confronting XML message brokers is the difficulty associated with processing a large set of continuous XPath queries over incoming XML seams. This paper proposes a novel system designed to present an effective solution to this problem. The proposed system transforms multiple XPath queries before their run-time into a new region-based data structure, called an XP-table, by sharing their common constraints. An XP-table is matched with a stream relation (SR) transformed from a target XML stream by a SAX parser. This arrangement is intended to minimize the runtime workload of continuous query processing. Also, system performance is estimated and verified through a variety of experiments, including comparisons with previous approaches such as YFilter and LazyDFA. The proposed system is practically linear- scalable and stable for evaluating a set of XPath queries in a continuous and timely fashion.

• Polymer(Korea)
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• v.28 no.6
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• pp.445-454
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• 2004

The requirement for a much finer line width circuits on semiconductors needs new developers such as supercritical fluid to prevent the collapse of the photoresist micro-patterns. The copolymers contain t-butyl methacrylate having an acid-cleavable t-butyl group and supercritical fluid $CO_2$ soluble perfluorinated decyl methacrylate segments. The supercritical fluid $CO_2$-philic properties of the photoresist changed to supercritical fluid $CO_2$-phobic properties after the deprotection reaction by exposure, which made the exposed resist insoluble in the supercritical fluid $CO_2$ developer. The synthesized copolymers containing more than 30% of perfluorinated decyl methacrylate were found to be soluble in supercritical fluid $CO_2$. The variation of film thickness before and after exposure was largest when the mole ratio of perfluorinated decyl methacrylate in the copolymer was 30%.

• Journal of KIISE:Databases
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• v.29 no.5
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• pp.347-357
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• 2002

Graphs have provided a powerful methodology to solve a lot of real-world problems, and therefore there have been many proposals on the graph representations and algorithms. But, because most of them considered only memory-based graphs, there are still difficulties to apply them to large-scale problems. To cope with the difficulties, this paper proposes a graph representation and graph algorithms based on the well-developed relational database theory. Graphs are represented in the form of relations which can be visualized as relational tables. Each vertex and edge of a graph is represented as a tuple in the tables. Graph algorithms are also defined in terms of relational algebraic operations such as projection, selection, and join. They can be implemented with the database language such as SQL. We also developed a library of basic graph operations for the management of graphs and the development of graph applications. This database approach provides an efficient methodology to deal with very large- scale graphs, and the graph library supports the development of graph applications. Furthermore, it has many advantages such as the concurrent graph sharing among users by virtue of the capability of database.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.7A
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• pp.523-529
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• 2009

This paper provides closed form expressions for the evaluation of the end-to-end outage probability, symbol error rate, bit error rate and average capacity of the partial-based Decode-and-Forward (DF) relay selection scheme with an arbitrary number of relays. In a comparison with the performance of systems that exploit Amplify-and-Forward (AF), it can be seen that the performance of our proposed protocol converges to that of partial-based AF relay selection in high SNR regime. We also perform Monte-Carlo simulations to validate the analysis.

• Journal of Intelligence and Information Systems
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• v.4 no.2
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• pp.85-102
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• 1998

현재의 시스템 개발 프로젝트에서 대부분의 기업은 관계형 데이터베이스를 목표 환경으로 채택하고 있지만 설계자들은 기존의 파일 시스템이나 계층형 데이터베이스의 설계 방식을 관계형 데이터베이스 설계 시에도 그대로 적용하려는 경향이 있다. 또한 모델링 시 시스템 특성과는 무관한 업무 중심의 엔티티 관계도를 작성함으로써 구현 시에 모델을 상당 부분 변경하거나 추가해야 하는 오버헤드가 발생하기도 한다. 관계형 데이터베이스의 경우 구조를 어떻게 설계하느냐에 따라 효율의 차이가 크게 나타나므로 성능 향상을 위한 데이터 모델링 기법이 중요한 이슈로 등장하게 되었다. 본 논문에서는 관계형 데이터베이스 성능과 관련하여 이미 연구되고 실험된 내용을 여러 문헌과 자료를 참고하여 조사하였다. 성능 항상을 위한 모델링 기법들을 테이블, 릴레이션쉽, 인덱스 등의 객체별로 분류하여 정리하였고, 조사된 내용 중에서 몇 가지를 선택하여 Oracle DBMS 환경에서 실제로 실험을 실시하였다. 대용량 테이블에 대한 질의를 수행하여 소요되는 시간을 측정하고 그 결과를 분석하였다. 실험을 통해 검증된 결과를 토대로 제안되는 모델링 방법을 제시한다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.2
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• pp.989-992
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• 2005

본 연구에서는 JXTA 기반의 P2P 컴퓨팅 기술을 J2ME 와 MIDP의 기술과 접목하여 새로운 JXTA 기반의 모바일 P2P 솔류션 구현을 가능하도록 한다. MIDP에서 제공하는 API는 무선 JXTA피어를 창조하는데 기초 역할을 수행하지만 그럼에도 불구하고, MIDP의 제한된 라이브러리, XML 파서 부족등의 한계가 있다. 그래서 이러한 자원의 한계를 극복하기 위해 중간에 릴레이 서버를 두어 제한된 환경에서 서비스 제공을 담당한다. JXTA의 가장 중요한 설계 선택중의 하나는 피어에 의해 사용되는 운영체제나 개발언어를 가정하지 않는 것이다. JXTA프로토콜 규격은 명시적으로 네트워크 피어가 소규모 임베디드 장치에서 대규모 슈퍼컴퓨터 클러스터에 이르는 모든 종류의 장치가 될 수 있다. 이러한 기술에 J2ME의 모바일 기능을 추가한 JXTA를 사용하여 기존의 제한된 메시지 전달방법을 탈피하여 JXTA 기반의 P2P 시스템을 만드는데 있다.