• Proceedings of the KIEE Conference
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• 2002.07b
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• pp.796-798
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• 2002

In these days, the interruption capability of some circuit breakers, which are installed in the transmission systems, is getting lower than the magnitude of the fault current because of continuous increase of power demand and relatively short power line which was installed in forms of mesh network As a result of these situations, fault current limiters (FCLs) are strongly necessary. There are various types which is investigated around the world, and new power apparatuses that have been newly considered and developed by many manufactures. In this paper, we considered resistive superconducting fault current limiters with YBCO thin films. The resistive limiters utilize a transition of YBCO films from superconducting to normal state caused by exceeding the critical current. By means of newly occurred impedance, the fault current will be limited effectively. Generally, a few current path patterns are available for YBCO films to enhance the current limiting performance of YBCO films. In this paper. the meander-type and the bi-spiral-type were used for current paths of YBCO flims. When YBCO films are quenched into the normal state, bubbles could be observed on the surface of YBCO films. Using our high-speed camera, the number of bubbles and the size of bubbles could be visualized and the relation between bubbles and current density was analyzed. By means of moving pictures of bubbles, we observed how the quench extended or how the heat was conducted in films.

• Journal of the Korean institute of surface engineering
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• v.49 no.5
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• pp.416-422
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• 2016

We have investigated the effects of applied potential, deposition time and electrolyte types on shapes and physical properties of Cu dendrites by potentiostatic electrodeposition. Finer shape of dendrites was observed at less cathodic potential by 100mV than at the limiting current, due to 'effective overpotential'. The shape of copper dendrite is related to the deposition time, too. The dendrite depositing for 10 min showed the finest shape. The finer dendrite has the less apparent density and the larger specific surface area. Dendrite from chloride solution has the lowest density and the largest surface area among three plating solutions, sulfate, chloride and pyrophosphate.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1322-1327
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• 2004

In the present work, a series of experiments have been performed on electro-hydrodynamic atomization of non-conducting liquid using a charge injection type nozzle. Effects of liquid flow rate, input voltage, and distance between the needle and the ground electrode (nozzle-embedded metal plate) have been examined. For fixed electrode distances, total and spray currents increase with increase of liquid flow rate and input voltage. When the distance between the needle and the ground electrode becomes closer, total, leakage and spray current increase, but the onset voltage for dielectric breakdown decreases. When the electric field strength of the liquid jet exceeds that for the air breakdown, a portion of the electric charges in the liquid jet is dissipated into the ambient air, and the charge density shows a limiting value. Atomization quality can be improved by increasing the flow rate because the higher charge density is achieved with the larger liquid velocity in addition to the enhanced aerodynamic effect.

• ETRI Journal
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• v.27 no.1
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• pp.118-121
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• 2005

Silicon dioxide ($SiO_2$) films prepared by plasma-enhanced atomic-layer deposition were successfully grown at temperatures of $100\;to\;250^{\circ}C$, showing self-limiting characteristics. The growth rate decreases with an increasing deposition temperature. The relative dielectric constants of $SiO_2$ films are ranged from 4.5 to 7.7 with the decrease of growth temperature. A $SiO_2$ film grown at $250^{\circ}C$ exhibits a much lower leakage current than that grown at $100^{\circ}C$ due to its high film density and the fact that it contains deeper electron traps.

• Journal of the Korean institute of surface engineering
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• v.36 no.2
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• pp.194-199
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• 2003

Polarization measurements were peformed to investigate the electrochemical behavior of copper ions and limiting current density in waste rinse water from copper electroplating processes. A newly designed cyclone type electrolyzer was tested to recover the copper powder. Synthetic solutions were prepared using analytical grade $CuSO_4$ to the desired waste water concentration and pH was adjusted with $H_2$$SO_4$. Electrowinning was peformed at room temperature and the solution was cycled with a pump. Results showed that more than 99 percent of Cu was recovered and the size of the recovered Cu powder ranges from 0.1 - $0.5\mu\textrm{m}$. The chemical composition of the Cu powder mainly consists of $Cu_2$O and Cu and can be easily reduced to pure Cu powder.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.1
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• pp.78-84
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• 2004

Low voltage circuit breakers which interrupt rapidly and raise the reliability of power supply are widely used in power distribution systems. In the paper, it has been investigated how much interrupting capability is improved by correcting the shape of the contact system in molded case circuit breaker(below MCCB), especially contacts and arc runner. Prior to the interrupting testing, it is necessary for the optimum design tc analyze electromagnetic forces on the contact system generated by current and flux density. This paper presents both our computational analysis and test results on contact system in MCCB

• The Korean Journal of Physiology and Pharmacology
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• v.5 no.1
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• pp.33-40
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• 2001

The aim of present study was to define the cellular mechanisms underlying changes in delayed rectifier $K^+\;(K_{DR})$ channel function in isoproterenol-induced hypertrophy. It has been proposed that $K_{DR}$ channels play a role in regulation of vascular tone by limiting membrane depolarization in arterial smooth muscle cells. The alterations of the properties of coronary $K_{DR}$ channels have not been studied as a possible mechanism for impaired coronary reserve in cardiac hypertrophy. The present study was carried out to compare the properties of coronary $K_{DR}$ channels in normal and hypertrophied hearts. These channels were measured from rabbit coronary smooth muscle cells using a patch clamp technique. The main findings of the study are as follows: (1) the $K_{DR}$ current density was decreased without changes of the channel kinetics in isoproterenol-induced hypertrophy; (2) the sensitivity of coronary $K_{DR}$ channels to 4-AP was increased in isoproterenol-induced hypertrophy. From the above results, we suggest for the first time that the alteration of $K_{DR}$ channels may limit vasodilating responses to several stimuli and may be involved in impaired coronary reserve in isoproterenol-induced hypertrophy.

• Journal of the Korean Electrochemical Society
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• v.3 no.3
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• pp.152-156
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• 2000

The effect of cupric ion concentration on the throwing power has been studied in the electrodeposition of Cu on the porous reticular electrodes with the electrolytes of $CuSO_4\;and\;H_2SO_4$. Sulfuric acid electrolytes with lower concentration of $CuSO_4$ improved throwing power in electrodeposition of copper not only due to higher cathodic polarizability but also due to higher conductivity of the electrolytes. The increase in conductivity of the electrolytes at low concentration of $CuSO_4$ could be also illustrated by the decrease in viscosity of the electrolytes. It was found that both the throwing power and the limiting current density should be taken into account in the electrodeposition of Cu on the reticular electrodes. According to the experimental results, the electrolyte of 0.2M $CuSO_4$ and 0.5M $H_2SO_4$ was found to be the most appropriate condition at the current density of $10mA/cm^2$.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.11
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• pp.29-34
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• 2004

This paper reports the RF dispersion and linearity characteristics of unpassivated AlGaN/InGaN/GaN high electron-mobility transistors (HEMTs) grown by molecular beam epitaxy (MBE). The devices with a 0.5 ${\mu}{\textrm}{m}$ gate-length exhibited relatively good DC characteristics with a maximum drain current of 730 mA/mm and a peak g$_{m}$ of 156 mS/mm. Highly linear characteristic was observed by relatively flat DC transconductance (g$_{m}$) and good inter-modulation distortion characteristics, which indicates tight channel carrier confinement of the InGaN channel. Little current collapse in pulse I-V and load-pull measurements was observed at elevated temperatures and a relatively high power density of 1.8 W/mm was obtained at 2 GHz. These results indicate that current collapse related with surface states will not be a power limiting factor for the AlGaN/InGaN HEMTs.

• Journal of Microbiology and Biotechnology
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• v.23 no.12
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• pp.1765-1773
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• 2013

The cathode reaction is one of the most seriously limiting factors in a microbial fuel cell (MFC). The critical dissolved oxygen (DO) concentration of a platinum-loaded graphite electrode was reported as 2.2 mg/l, about 10-fold higher than an aerobic bacterium. A series of MFCs were run with the cathode compartment inoculated with activated sludge (biotic) or not (abiotic) on platinum-loaded or bare graphite electrodes. At the beginning of the operation, the current values from MFCs with a biocathode and abiotic cathode were $2.3{\pm}0.1$ and $2.6{\pm}0.2mA$, respectively, at the air-saturated water supply in the cathode. The current from MFCs with an abiotic cathode did not change, but that of MFCs with a biotic cathode increased to 3.0 mA after 8 weeks. The coulomb efficiency was 59.6% in the MFCs with a biotic cathode, much higher than the value of 15.6% of the abiotic cathode. When the DO supply was reduced, the current from MFCs with an abiotic cathode decreased more sharply than in those with a biotic cathode. When the respiratory inhibitor azide was added to the catholyte, the current decreased in MFCs with a biotic cathode but did not change in MFCs with an abiotic cathode. The power density was higher in MFCs with a biotic cathode ($430W/m^3$ cathode compartment) than the abiotic cathode MFC ($257W/m^3$ cathode compartment). Electron microscopic observation revealed nanowire structures in biofilms that developed on both the anode and on the biocathode. These results show that an electron-consuming bacterial consortium can be used as a cathode catalyst to improve the cathode reaction.