• Transactions of the Korean hydrogen and new energy society
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• v.28 no.1
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• pp.30-39
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• 2017

Interests in fuel cell based power generation systems are on the steady rise owing to various advantages such as high efficiency, ultra low emission, and potential to achieve a very high efficiency by a synergistic combination with conventional heat engines. In this study, the performance of a hybrid system which combined a molten carbonate fuel cell (MCFC) and an indirectly fired micro gas turbine adopting carbon dioxide capture technologies was predicted. Commercialized 2.5 MW class MCFC system was used as the based system so that the result of this study could reflect practicality. Three types of ambient pressure hybrid systems were devised: one adopting post-combustion capture and two adopting oxy-combustion capture. One of the oxy-combustion based system is configured as a semi-closed type, while the other is an open cycle type. The post-combustion based system exhibited higher net power output and efficiency than the oxy-combustion based systems. However, the semi-closed system using oxy-combustion has the advantage of capturing almost all carbon dioxide.

• Macromolecular Research
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• v.16 no.3
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• pp.218-223
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• 2008

In order to obtain crosslinked poly(butylene succinate) (PBS) foams with a closed-cell structure, a commercial-grade PBS was first modified in the melt using two different branching agents to increase the melt viscosity. The rheological properties of the branched and crosslinked PBS were examined by varying the amount of the branching agents. The complex viscosity of the crosslinked PBS increased with increasing amount of the branching agent. However, it decreased with increasing frequency. When 2 phr of the branching agent was added to PBS, the storage modulus (G') was higher than the loss modulus (G") throughout the entire frequency range, showing that the addition of a branching agent increases the melt viscosity and elasticity of PBS effectively. Closed-cell PBS foams were prepared by mixing the chemical blowing agent with the crosslinked PBS. The effect of the foaming conditions such as temperature and time, and the amount of the crosslinking agent on the structure of the expanded PBS foams were also investigated.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.10a
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• pp.289-292
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• 2001

Aluminium foams, having a closed cell structure, fabricated by applying the powder compact method and an induction heating were studied. The powdered A6061 mixed with the powdered titanium hydride as a foaming agent was hot pressed into a foamable precursor. The resulting precursor was foamed by induction heating up to desired temperature. The effects of the titanium hydride content ($0.3{\~}1.5 wt.\%$), pressing pressure of the foamable precursor material (50-150kN), the forming temperature ($610{\~}690^{\circ}C$) and heating rate during foaming on the expansion behavior of the foam were investigated.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.5
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• pp.2524-2528
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• 2013

Cell opening characteristics dependent on the cell openers for the conventional formulation of a closed-cell polyurethane foam (PUF) was studied using 1-butanol and lithium salt of 12-hydroxystearic acid (Li-12HSA) as the reactive cell opening agents. While cell openining content of only 10.5 % was obtained for the sample with 4 phr of 1-butanol as the single reactive cell opener, that of 98.0% could be obtained for the sample with 2 phr of Li-12HSA as the reactive co-cell opener. As the results, it showed that a fully open-cell rigid PUF could be obtained by introducing a novel reactive cell opener, having a functional group able to form a bulky side-chain on the urethane networks, without severe loss of mechanical properties of the closed-cell PUF like cell size, bulk density, and thermal conductivity.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.1
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• pp.50-61
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• 2014

Operating small cell with existing macro cell is of interest in wireless communication technology to enhance network capacity. Closed-access small cell allows the access of users registered in it and causes severe interference to nearby users connected to macrocell. We propose a dynamic channel allocation for small cells in the same building that first aim to minimize call-drop of the nearby macrocell users, and then want to reduce interferences between the small cells. Since the interference effect of small cells on the nearby macrocell users mainly depends on the small cells' position, the proposed algorithm includes a self-configuration to flexibly allocate frequency channels according to the variation of downlink quality of the macrocell users. Furthermore the algorithm is very simple and practical, which is main contribution of this paper. We observe that the proposed algorithm provides 82-94% of maximum achievable throughput.

• Elastomers and Composites
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• v.38 no.3
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• pp.251-261
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• 2003

The flame retardancy and foaming properties of NBR foams containing waste ground tire rubber (GTR) were studied. When the composition ratios of NBR/GTR were ranged in $100/0{\sim}80/20$ (w/w) and rubbers/flame retardants were in the range of $1/1.95{\sim}3.70 wt%$, the considerably optimized foam for flame retardancy was obtained with high limiting oxygen indices (LOI, $29.4{\sim}40.0$), low heat release rate(HRR), closed/semi-closed cell of uniformity, and reasonable expandability ($215{\sim}300 %$). The LOI was increased and the heat release rate was decreased with increasing the amount of GTR content.

• Proceedings of the Korean Ceranic Society Conference
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• 2004.04b
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• pp.43.3-43.3
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• 2004

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.2
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• pp.54-61
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• 2004

The engine-out flow is highly transient and hot, and may place tremendous thermal and inertial loads on a closed-coupled catalyst. Therefore, time-dependent and detailed flow and thermal field simulation may be crucial. The aim of this study is to develop combined chemical reaction and multi-dimensional fluid dynamic mathematical model and to study the effect of unsteady pulsating thermal and flow characteristics on thermal reliability of closed-coupled catalyst. The effect of cell density on the conversion performance under real running condition is also investigated. Unlike previous studies, the present study focuses on coupling between the problems of pulsating flow pattern and catalyst thermal response and conversion efficiency. The results are expressed in terms of temporal evolution of flow, pollutant and temperature distribution as well as transient characteristics of conversion efficiency. Fundamental understanding of the flow and thermal phenomena of closed-coupled catalyst under real running condition is presented. It is shown that instants of significantly low values of flow uniformity and conversion efficiency exist during exhaust blowdown and the temporal varaition of flow uniformity is very similar in pattern to one of conversion efficiency. It is also found that the location of hot spot in monolith is directly affected by transient flow pattern in closed-coupled catalyst.

• Journal of Satellite, Information and Communications
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• v.6 no.2
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• pp.26-34
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• 2011

In Femtocell that provides high quality of indoor communications with low transmitted power, there are two typical Access modes; Closed Access mode and Open Access mode. In this paper, we propose resource allocation scheme, which mitigates difference of performance between Access modes and improves overall cell performance, according to Access mode. We give more wireless resources to Open Access mode Femtocell, which improves performance of other users, than Closed Access mode Femtocell. If Open Access mode Femtocell uses more resource, there is trade-off between improvement of user using Open Access mode Femtocell and increase of interference that other users receive. So, we solve the optimal value for resource allocation and analyze performance of conventional scheme and proposed scheme applying the optimal value. Eventually, proposed scheme can improve overall cell performance relative to conventional scheme.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 1993.06a
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• pp.1078-1081
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• 1993

The Objective of this paper is to provide fuzzy control designers with a design tool for stable fuzzy logic controllers. Given multiple sets of data disturbed by vagueness uncertainty, we generate the implicative rules that guarantee stability and robustness of closed-loop fuzzy dynamic systems. We propose the cell-state transition method which utilizes Hsu's cell-to-cell mapping concept [1]. As a result, a generic and implementable design methodology for obtaining a fuzzy feedback gain K, a fuzzy hypercube [2], is provided and illustrated with simple examples.