• Proceedings of the Korean Society of Computer Information Conference
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• 2015.01a
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• pp.155-158
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• 2015

클라우드 컴퓨팅 기술의 발전과 맞물려서 이를 위한 많은 플랫폼들이 제안되고 있다. Amazon이나 Google 등의 세계적인 기업들을 이미 자신들 만의 플랫폼을 구축하여 안정적으로 서비스를 제공하고 있으며 오픈소스 커뮤니티들이 주도 하는 오픈 플랫폼들도 속속 등장하여 발전을 거듭하고 있다. 본 논문에서는 가장 대표적이고 널리 사용되는 오픈소스 기반의 클라우드 컴퓨팅 플랫폼들을 분석하고 그 기능들을 서로 비교해서 사용자가 자신의 요구사항에 가장 적합한 플랫폼을 선택할 수 있게 한다.

• Annual Conference of KIPS
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• 2016.10a
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• pp.66-67
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• 2016

최근 수많은 국 내외 글로벌 기업들이 클라우드 자원의 제공자 겸 소비자 역할을 하는 프라이빗 IaaS 클라우드 환경을 구축하고 있는 추세이며 이를 위해 오픈소스 클라우드 플랫폼인 오픈스택(OpenStack)이 많이 사용되고 있다. 이 논문에서는 대규모 빅데이터 처리를 위해 오픈스택 클라우드 환경의 가상머신 라이브 마이그레이션 기법을 사용할 경우 발생할 수 있는 문제점을 분석한다. 이러한 문제점에 대하여 가상머신에서 빅데이터 연산 처리 시 스토리지 병목현상을 해결하기 위한 마이그레이션 기법을 제시한다.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 2004.05a
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• pp.115-118
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• 2004

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.5 s.335
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• pp.5-12
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• 2005

Establishment of bandwidth and effective traffic processing are required to treat various traffics according to a rapid increase in Internet traffic. A wavelength based transferring method was introduced to support a broadband bandwidth according to this requirement, and consequently, a label processing procedure has been investigated to treat various traffics. This paper introduces a regular shape of stack structure in order to solve the present MPLS label stack processing unit, and analyzes the relationship to label merging, which is initiated between label merging inside and outside the LSP tunnel. By applying an adaptive label structure and merging point a hierarchical label, which is aroused in the GMPLS, can be uniformly simplified and improved from the perspective of cost and processing time at a node

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.9
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• pp.54-62
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• 2015

Although NAND flash-based SSD (Solid-State Drive) provides superior performance in comparison to HDD (Hard Disk Drive), it has a major drawback in write endurance. As a result, the lifetime of SSD is determined by the workload and thus it becomes a big challenge in current technology trend of such as the shifting from SLC (Single Level Cell) to MLC (Multi Level cell) and even TLC (Triple Level Cell). Most previous studies have dealt with wear-leveling or improving SSD lifetime regarding hardware architecture. In this paper, we propose the optimal configuration of host I/O stack focusing on file system, I/O scheduler, and link power management using JEDEC enterprise workloads in terms of WAF (Write Amplification Factor) which represents the efficiency perspective of SSD life time especially for host write processing into flash memory. Experimental analysis shows that the optimum configuration of I/O stack for the perspective of SSD lifetime is MinPower-Dead-XFS which prolongs the lifetime of SSD approximately 2.6 times in comparison with MaxPower-Cfq-Ext4, the best performance combination. Though the performance was reduced by 13%, this contributions demonstrates a considerable aspect of SSD lifetime in relation to I/O stack optimization.

• Journal of the Korean Ceramic Society
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• v.41 no.10 s.269
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• pp.777-782
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• 2004

In this research, $5\times5cm^2$ unit cells were fabricated via liquid condensation process and uniaxial pressing followed by the screen printing of electrolyte and cathode layer. The SOFC stack was assembled with unit cells, gasket-type sealant and metal interconnect. The stack was designed to have a single column with internal-manifold and cross-flow type gas-channels. The SOFC stack produced 15 W, which is $50\%$ of the maximum power being expected from the maximum power density of the unit cell. Controlling factors for the proper operation of the SOFC stack and other designing factors of stack manifold and gas channels were discussed.

• Applied Chemistry for Engineering
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• v.28 no.1
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• pp.118-124
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• 2017

An air cooling, open cathode type polymer electrolyte membrane fuel cell (PEMFC) has the advantages of system simplification and cost effectiveness. Open cathode PEMFC could suffer from reduced performance due to the membrane dehydration in low humidity of air. Effects of the cathode air flow rate, anode purge interval and long term storage on PEMFC performance were investigated in this work. Fan voltage is an important factor on air cooling PEMFC performance because the cathode air flow rate and stack temperature were controlled by fan voltage. The dead ended anode (DEA) method was applied to increase hydrogen usage. Periodical purge was used to discharge accumulated water and gas. The influence of long term non-operating condition on PEMFC performance degradation due to the membrane dehydration was also studied and the quick recovery method was developed.

• Journal of KIISE:Software and Applications
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• v.30 no.1_2
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• pp.81-92
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• 2003

Generalized LR parsing is one of the enhanced LR parsing methods so that it overcome the limit of one-way linear stack of the traditional LR parser using graph-structured stack, and it has been playing an important role of a firm starting point to generate other variations for NL parsing equipped with various mechanisms. In this paper, we propose a conditional Action Model that can solve the problems of conventional probabilistic GLR methods. Previous probabilistic GLR parsers have used relatively limited contextual information for disambiguation due to the high complexity of internal GLR stack. Our proposed model uses Surface Phrasal Types representing the structural characteristics of the parse for its additional contextual information, so that more specified structural preferences can be reflected into the parser. Experimental results show that our GLR parser with the proposed Conditional Action Model outperforms the previous methods by about 6-7% without any lexical information, and our model can utilize the rich stack information for syntactic disambiguation of probabilistic LR parser.

• Composites Research
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• v.36 no.6
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• pp.422-428
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• 2023

The electrical contact resistance between the bipolar plate (BP) and the carbon felt electrode (CFE), which are in contact by the stack clamping pressure, has a great impact on the stack efficiency because of the relatively low clamping pressure of the vanadium redox flow battery (VRFB) stack. In this study, a polyethylene (PE) composite-CFE hybrid bipolar plate structure is developed through a local heat welding process to reduce such contact resistance and improve cell performance. The PE matrix of the carbon fiber composite BP is locally melted to create a direct contact structure between the carbon fibers of CFE and the carbon fibers of BP, thereby reducing the electrical contact resistance. Area specific resistance (ASR) and gas permeability are measured to evaluate the performance of the PE composite-CFE hybrid bipolar plate. In addition, an acid aging test is performed to measure stack reliability. Finally, a VFRB unit cell charge/discharge test is performed to compare and analyze the performance of the developed PE composite-CFE hybrid BP and the conventional BP.

• KIISE Transactions on Computing Practices
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• v.24 no.3
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• pp.129-137
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• 2018

NVMe(Non-Volatile Memory Express) SSD(Solid State Drive) is a high-performance storage that makes use of flash memory as a storage cell, PCIe as an interface and NVMe as a protocol on the interface. It supports multiple I/O queues which makes it feasible to process parallel-I/Os on multi-core environments and to provide higher bandwidth than SATA SSDs. Hence, NVMe SSD is considered as a next generation-storage for data-center and cloud computing system. However, in the virtualization system, the performance of NVMe SSD is not fully utilized due to the bottleneck of the software I/O stack. Especially, when it uses I/O stack of the hypervisor or the host operating system like Xen and KVM, I/O performance degrades seriously due to doubled-I/O stack between host and virtual machine. In this paper, we propose a new I/O engine, called Direct-AIO (Direct-Asynchronous I/O) engine, that can access NVMe SSD directly for I/O performance improvements on QEMU emulator. We develop our proposed I/O engine and analyze I/O performance differences between the existed I/O engine and Direct-AIO engine.