• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.1A
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• pp.122-131
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• 2000

In this paper, we propose a cell scheduling algorithm for input queueing ATM switch. The input queueing architecture is attractive for building an ultra-high speed ATM (Asynchronous Transfer Mode) switch. We proposea WMUCS (Weighted Matrix Unit Cell Scheduler) based on the MUCS which resolves HOL blocking and outputport contention. The MUCS algorithm selects an optimal set of entries as winning cells from traffic matrix (weightmatrix). Our WMUCS differs from the MUCS in generating weight matrices. This change solves the starvationproblem and it reduces the cell loss variance. The performance of the proposed algorithm is evaluated by thesimulation program written in C++. The simulation results show that the maximum throughput, the average celldelay, and the cell loss rate are significantly improved. We can see that the performance of WMUCS is excellentand the cost-effective implementation of the ATM switch using proposed cell scheduling algorithm.

• Journal of electromagnetic engineering and science
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• v.10 no.3
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• pp.86-91
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• 2010

In this paper, a double-layered frequency selective surface(FSS) superstrate was built and tested. The unit cell of the proposed FSS consists of a ring slot and a dipole-shaped structure and shows a complementary frequency response. Each unit cell is printed on two sides of a substrate. By using these double-layered structures, the first resonant frequency of the pass-band can be lowered. As a result, the size of the unit cell is minimized and the spacing between the other cells is reduced. The proposed FSS-dipole composite antenna is designed for the gain enhancement of wide-band code division multiple access(WCDMA) frequency bands(1.92~2.17 GHz) with a low quality factor(Q=0.17). To verify the gain enhancement performance of the FSS, an FSS-dipole composite antenna was created. Although the FSS layer enhances the gain of the primary radiation source of the dipole antenna, the FSS-dipole complex antenna cannot show a uniform gain over the entire desired frequency band. The experimental results show a gain enhancement of 3 dBi with an FSS superstrate in the WCDMA frequency band.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.20 no.5
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• pp.31-37
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• 2020

In this paper, we propose a novel sub-wavelength unit cell metamaterial absorber using multi-layer structure. The proposed absorber consists of 4 layers, and each layer has a spiral resonator connected by a via hole. This structure increases inductance of the unit cell, and therefore the resonant frequency can shift to lower frequency. We optimized the proposed absorber, and the electrical size of the unit cell is dramatically reduced to 0.013 times of the wavelength. The performance of the proposed absorber is demonstrated with full-wave simulation and measurement results. An absorption rate exceeding 97% is achieved at 1.74GHz. In addition, the proposed absorber attains a high absorption rate of 90% for different polarization and incident angles.

• Transactions of the Korean hydrogen and new energy society
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• v.13 no.4
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• pp.313-320
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• 2002

The characteristics of the AISI bipolar plates have been investigated to replace the expensive graphite bipolar plates. It was found from the contact resistance evaluation of graphites, composites, and AISI that the contact resistance of AISI was the lowest, but it could approach to that of composites at higher compression forces. The single cell operation using the AISI bipolar plates revealed that the lower performance of the AISI single cell compared to the graphite one was due to not only the higher contact resistance but the flooding effect caused by high wettability of AISI. The performance of the AISI single cell could be improved if the channels were modified appropriately. The large size AISI single cell was operated to investigated the size effect on the performance.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3423-3428
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• 2007

This paper shows that inlet humidity condition at cathode side is one of dominant parameters affecting the performance of PEMFC. To investigate effects of inlet humidity condition, the performance measurements were conducted for a single PEMFC with two operating variables : cathode relative humidity and dry condition in anode dry. The fuel cell employed for the experiments is a unit PEMFC with a 25$Cm^2$, Nafion$^(R)$112 membrane. As a result of this study, the cell performance is getting higher by increasing inlet humidity condition at cathode side. The cell performance is different from each operating temperature an it has maximum30% higher than dry condition at 60$^{\circ}C$ operating temperature with 80% relative humidity.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.9
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• pp.749-755
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• 2017

In this paper, a wideband microwave absorber for X-band(8~12 GHz) applications is proposed. The structure of the proposed absorber unit cell consists of a resonator with a slot and slit, a backing ground plate, and a Taconic RF-30(${\varepsilon}_r=3$, $tan{\delta}=0.0014$) substrate with a dimension of $8.5{\times}8.5{\times}0.5mm^3$. The proposed absorber has a dual resonance at 9.83 and 10.37 GHz. To demonstrate the operating principle of the proposed absorber structure at each resonance frequency, the simulated current distributions on the unit cell are analyzed. To verify the performance of the proposed absorber, a prototype absorber was fabricated with a planar array of $20{\times}20$ unit cells. The measured results exhibit two absorptivity peaks stronger than 99 % and full-width at half-maximum(FWHM) bandwidth of 1.1 GHz(9.51~10.61 GHz).

• Proceedings of the KIPE Conference
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• 2018.07a
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• pp.356-357
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• 2018

Fuel-cell powered Railway Vehicle Propulsion Systems (RVPSs) are highly desirable due to environment friendly characteristics, and high efficiency of fuel cell (FC). Among various types, the faster start-up and optimality to frequent starts and stops of Polymer electrolyte membrane fuel cell (PEMFC) makes it well suited for propulsion systems. A comprehensive model of PEMFC with reflection of multi-physics behavior required to identify and validate its performance in real RVPSs. Thus this paper will model and simulate the PEMFC unit cell model: a detailed reflection of governing laws and account of dynamic conditions.

• Macromolecular Research
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• v.10 no.4
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• pp.181-186
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• 2002

The displacement of carbon black to polypyrrole as a catalyst supporter in the fuel electrode of a direct methanol fuel cell was investigated. Polypyrrole was obtained as a black powder by the chemical polymerization of pyrrole with three different oxidants. The synthesized polypyrroles were pasted on carbon paper and transformed to the fuel electrodes with electrochemically deposited platinum. The prepared fuel electrode was assembled and mounted in a unit cell using a membrane and cathodic electrode film. In comparison with the carbon black fuel electrode, the performance of the unit cell was analyzed in relation to the state of the catalyst, the type of oxidant, and the morphology of the polypyrrole powder.

• Electrical & Electronic Materials
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• v.8 no.6
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• pp.768-773
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• 1995

We describe a manufacturing method and characteristics on components of molten carbonate fuel cell. Cr, Al, AI$_{2}$O$_{3}$, Co, MgO powder were mixed with Ni powder for anode components and NiO was used for cathode electrode. The electrolyte plate consisted of LiAIO$_{2}$ and carbonate (Li$_{2}$CO$_{3}$/K$_{2}$CO$_{3}$=62/38) and these three were manufactured by doctor-blade method. As a result, open circuit voltage was 1.05[VI at Ni-10Cr anode and porosity was above 60[%].

• Journal of the Korean Ceramic Society
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• v.44 no.12
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• pp.703-709
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• 2007

We evaluate and compare the power generating characteristics of the anode supported SOFCs which have been fabricated from KIST and FZ-Julich in Germany. The performance and electrochemical property of each unit cell was characterized at the temperature range of $650-850^{\circ}C$ under same operating conditions and its microstructural property was thoroughly investigated via SEM after the performance test. According to the investigation, KIST- and FZJ SOFC showed different power generating characteristics in their temperature dependances due to their different design of electrode microstructure, especially the cathode microstructure. FZJ SOFC showed better performance at high temperature while showed lower performance at lower temperature. From the investigation about the correlation between microstructure and electrochemical property, we found that the superior performance of FZJ SOFC at high temperature was mainly due to its lower cathodic polarization resistance whereas better performance of KIST SOFC at lower temperature was mostly attributed to the lower ohmic resistance.