• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.3
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• pp.207-214
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• 2009

Crossover of nitrogen from cathode to anode is inevitable in typical membranes used in PEM fuel cells. This crossovered nitrogen normally accumulates in the hydrogen recirculation system at anode side channels. Excessive buildup of nitrogen in the anode side lowers the relative hydrogen concentration and finally affects the performance of fuel cell stack. So it is very important to analysis the nitrogen gas crossover at various operating conditions. In this study, characterization of nitrogen gas crossover in PEM fuel cell stack was investigated. The mass spectroscopy (MS) has been applied to measure the amount of the crossovered nitrogen gas at the anode exit. Results show that nitrogen gas crossover rate was affected by current density, anode and cathode stoichiometric ratio and operating pressure. Current density, anode stoichiometric ratio and anode operating pressure do not affect nitrogen crossover rate but anode exit concentration of nitrogen. Cathode pressure and stoichiometric ratio largely affect the nitrogen crossover rate.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 2002.12a
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• pp.375-378
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• 2002

In this paper we propose parallel GA to optimize mutation rate and crossover rate using server-client model. The performance of GA depend on the good choice of crossover and mutation rates. Although many researcher has been study about the good choice, it is still unsolved problem. proposed GA optimize crossover and mutation rates trough evolving subpopulation. In virtue of the server-client model, these parameters can be evolved rapidly with relatively low-grade

• 한국전기화학회:학술대회논문집
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• 2003.04a
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• pp.56-56
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• 2003

• 제어로봇시스템학회:학술대회논문집
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• 1997.10a
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• pp.512-515
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• 1997

In this paper the fuzzy-genetic controller for path-tracking of WMRs is proposed. Fuzzy controller is implemented to adaptive adjust the crossover rate and mutation rate, and genetic algorithm is implemented to adaptive adjust the control gain during the optimization. The computer simulation shows that the proposed fuzzy-genetic controller is effective.

• Macromolecular Research
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• v.16 no.6
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• pp.524-531
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• 2008

The mitigation or elimination of methanol crossover for perfluorosulfonic acid fuel cell membranes has been investigated extensively for direct methanol fuel cell applications with the aim of increasing the electrochemical performance and enhancing the utilization rate of methanol. Self-assembly modifications by applying an oppositely charged polyelectrolyte to Nafion membranes were attempted in order to block or reduce methanol crossover while maintaining the other advantageous properties of Nafion membranes. It was reported that anionic polyallylamine hydrochloride (PAH) was the most efficient polyelectrolyte in reducing methanol crossover, and considerable cell performance was obtained even at a methanol feed concentration of 10 M.

• Korean Chemical Engineering Research
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• v.47 no.4
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• pp.441-445
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• 2009

Effect of temperature on membrane degradation in PEMFCs was studied. After cell operation at different temperatures($60{\sim}90^{\circ}C$) under accelerating degradation conditions(OCV, anode dry, cathode RH 65%) for 144 h, cell performance decreased from 12 to 35%. The results of FER in effluent water showed that this decrease in cell performance was caused by membrane degradation by the attack of $H_2O_2$ or oxygen radicals(${\cdot}OH$, $HO_2{\cdot}$) and that resulted in increase in gas crossover for radical formation. Radical formation on the electrode was confirmed by ESR. Activation energy of 66.2 kJ/mol was obtained by Arrhenius plot used to analyze the effect of temperature on membrane degradation. Increase of cell temperature enhanced gas crossover rate, radical formation rate and membrane degradation rate.

• Korean Chemical Engineering Research
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• v.56 no.2
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• pp.151-155
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• 2018

Degree of membrane degradation in Proton Exchange Membrane Fuel Cells (PEMFC) is mainly evaluated by the hydrogen crossover current density. The hydrogen crossover current density is measured by linear sweep voltammetry (LSV), which differs from the DOE protocol and the NEDO protocol. In this study, two protocols were compared during PEMFC operation and accelerated stress test. In the LSV method by the DOE method, the scan rate change affects the hydrogen crossover current density, but the NEDO method does not affect the hydrogen crossover current density. In the course of 15,000 cycles of polymer membrane wet/dry cycle, the DOE method was sensitive to membrane degradation, but the NEDO method was less sensitive to membrane degradation than the DOE method.

• Industrial Engineering and Management Systems
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• v.10 no.4
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• pp.247-254
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• 2011

In this paper, we study a single-machine scheduling problem with deteriorating processing time of jobs and multiple rate-modifying activities which reset deteriorated processing time to the original processing time. In this situation, the objective function is to minimize total completion time. First, we formulate an integer programming model. Since the model is difficult to solve as the size of real problem being very large, we design an improved genetic algorithm called adaptive genetic algorithm (AGA) with spontaneously adjusting crossover and mutation rate depending upon the status of current population. Finally, we conduct some computational experiments to evaluate the performance of AGA with the conventional GAs with various combinations of crossover and mutation rates.

• Journal of Ginseng Research
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• v.42 no.2
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• pp.144-148
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• 2018

Background: Panax ginseng is a well-known immune modulator, and there is concern that its immune-enhancing effects may negatively affect patients with rheumatoid arthritis (RA) by worsening symptoms or increasing the risk of adverse effects from other drugs. In this randomized, crossover clinical trial, we evaluated the impact of Korean Red Ginseng (KRG) on disease activity and safety in RA patients. Methods: A total of 80 female RA patients were randomly assigned to either the KRG (2 g/d, n = 40) treatment or placebo (n = 40) groups for 8 wk, followed by crossover to the other treatment group for an additional 8 wk. The primary outcome was the disease flare rate, defined as worsening disease activity according to the disease activity score 28 joints-erythrocyte sedimentation rate (DAS28-ESR). The secondary outcomes were development of adverse events (AEs) and patient reported outcomes. Outcomes were evaluated at baseline and 8 wk and 16 wk. The outcomes were compared using the Chi-square test. Results: Of the 80 patients, 70 completed the full study. Their mean age was 51.9 yr, and most exhibited low disease activity (mean DAS28-ESR $3.5{\pm}1.0$) at enrollment. After intervention, the flare rate was 3.7% in each group. During KRG treatment, 10 AEs were reported, while five AEs were developed with placebo; however, this difference was not statistically significant (p = 0.16). Gastrointestinal- and nervous system-related symptoms were frequent in the KRG group. Conclusion: KRG is not significantly associated with either disease flare rate or the rate of AE development in RA patients.

• Korean Chemical Engineering Research
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• v.51 no.3
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• pp.325-329
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• 2013

The membrane and electrode were degraded coincidentally at real PEMFC(Proton Exchange Membrane Fuel Cells) operation condition. But the interaction membrane degradation between electrode degradation has not been studied. The effect of membrane degradation on electrode degradation was studied in this work. We compared electrode degradation after membrane degradation and electrode degradation without membrane degradation. I-V performance, hydrogen crossover current, impedance and TEM were measured after and before degradation of MEA. Membrane degradation enhanced hydrogen crossover, and then Pt particle growth rate was reduced. Increase of hydrogen crossover by membrane degradation reduced the electrode degradation rate.