• Journal of the Microelectronics and Packaging Society
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• v.13 no.4
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• pp.77-84
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• 2006

Surface roughness and wafer-level thickness distribution of the non-cyanide Au bumps were characterized with variations of the electroplating current density and the bath temperature. The Au bumps, electroplated at $3mA/cm^{2}\;and\;5mA/cm^{2}$, exhibited the surface roughness of $80{\sim}100nm$ without depending on the bath temperature of $40^{\circ}C\;and\;60^{\circ}C$. The Au bumps, electroplated with $8mA/cm^{2}$ at $40^{\circ}C\;and60^{\circ}C$, exhibited the surface roughness of 800nm and $80{\sim}100nm$, respectively. Wafer-level thickness deviation of the Au bumps became larger with increasing the current density from $3mA/cm^{2}\;to\;8mA/cm^{2}$. More uniform thickness distribution of the Au bumps was obtained at a bath temperature of $60^{\circ}C$ than that of $40^{\circ}C$.

• Nuclear Engineering and Technology
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• v.50 no.6
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• pp.869-876
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• 2018

The force of a direct current (DC) electromagnetic pump used to transport liquid lithium was analyzed to optimize its geometrical and electrical parameters by numerical simulation. In a heavy-ion accelerator, which is being developed in Korea, a liquid lithium film is utilized for its high charge-stripping efficiency for heavy ions of uranium. A DC electromagnetic pump with a flow rate of $6cm^3/s$ and a developed pressure of 1.5 MPa at a temperature of $200^{\circ}C$ was required to circulate the liquid lithium to form liquid lithium films. The current and magnetic flux densities in the flow gap, where a $Sm_2Co_{17}$ permanent magnet was used to generate a magnetic field, were analyzed for the electromagnetic force distribution generated in the pump. The pressure developed by the Lorentz force on the electromagnetic force was calculated by considering the electromotive force and hydraulic pressure drop in the narrow flow channel. The opposite force at the end part due to the magnetic flux density in the opposite direction depended on the pump geometrical parameters such as the pump duct length and width that defines the rectangular channels in the nonhomogeneous distributions of the current and magnetic fields.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2000.02a
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• pp.22-25
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• 2000

To improve the performance of high temperature superconducting current leads, variable cross-sectional area is considered. The cross-sectional area is varied as a function of current density to fix the safety factor along lead length. New integration method is devised to find optimum cross-sectional area distribution. New design of current lead has low heat leak into cryostat and less material than constant cross-sectional area leads. Conduction cooled lead is considered. The developed method is applied to Bi2223 current leads sheathed Ag-Au alloy.

• Proceedings of the KIEE Conference
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• 1999.07e
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• pp.2170-2172
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• 1999

A low energy large aperture(LELA) pulsed electron beam generator of a cold cathode type has been developed for environmental applications, for example, waste water cleaning, flue gas cleaning, and pasteurization etc. The operational principle is based on the emission of secondary electrons from cold cathode when ions in the plasma hit the cathode, which are accelerated toward exit window by the gradient of an electric potential. We have fabricated the LELA electron beam generator with the peak energy of 200keV and beam diameter of 200mm and obtained the large aperture electron beam in air. The electron beam current density has been investigated as a function of glow discharge current, accelerating voltage and radial distribution in front of the exit window foil. The plasma density and electron temperature have been measured in order to confirm the relation with the electron beam current density. We are going to upgrade the LELA electron beam generator in the electron energy, electron beam current and stability of operation for various applications.

• Progress in Superconductivity and Cryogenics
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• v.17 no.2
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• pp.25-30
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• 2015

In order to realize economical applications, it is important to reduce the ac loss of 2G high-temperature superconductor coated conductors. It seems to be reasonable that a multi-filamentary wire can decrease the magnetization loss. In this study, we prepared two samples of YBCO coated conductors with striations. We measured local superconducting properties of both samples by using Low Temperature Scanning Laser and Hall Probe Microscopy (LTSLHPM). The distribution of the local critical temperature of samples was analyzed from experimental results of Low Temperature Scanning Laser Microscopy (LTSLM) near the superconducting transition temperature. According to LTSLM results, spatial distributions of the local critical temperature of both samples are homogeneous. The local current density and the local magnetization in samples were explored from measuring stray fields by using Scanning Hall Probe Microscopy (SHPM). From SHPM results, the remanent field pattern of the one bridge sample in an external magnetic field confirms the Bean's critical state model and the three bridge sample has similar remanent field pattern of the one bridge sample. The local magnetization curve in the three bridge sample was measured from external fields from -500 Oe to 500 Oe. We visualized that the distribution of local hysteresis loss are related in the distribution of the remanent field of the three bridge sample. Although the field dependence of the critical current density must be taken into account, the relation of the local hysteresis loss and the remanent field from Bean's model was useful.

• 한국해양학회지
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• v.12 no.2
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• pp.75-81
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• 1977

Distribution of drifting larvae of Anadara broughtnoii SCHRENCK was studied based on the planktonic sampling which has been collected in fifteen sampling areas of southern coast of Korea and Ulsan Bay during summer season from 1973 to 1977. Vertical and horizontal occurrence was analyzed related to the environmental factors such as surface water temperature, current velocity and depth of water column. High density of the larvae was observed in the Chinhae Bay which included the sampling areas Rampo, Sockcheon, Majeon, Changpo, Dangdong, Bedun, Changchoa, and Wonmun. Maximum occurrence of the farvae was accompanied with the highest water temperature of the summer season, and it was usually August when the water temperature was over 27$^{\circ}C$. In August, 1975, the highest density of the farvae was observed, when the mean surface water temperature was the highest compared to those of other years. The first appearence of the drifting larvae was also related to the surface water temperature. Each year the larae begin to appear from the late July and the ready-to-fall larvae appear in abundance from the mid-August. Vertical distribution patterns of the larvae are closely related to the depth of the water column as well as to the current velocity. In shallow water the larvae tend to aggregate in the bottom layer, while they are diffused to some extent in deep water. In shallow water column ( 8m) more or less 75% of the total larvae individuals was observed in the lower 4m layer and in deep water column ( 16m) only 45% of those was found in the lower 4m layer. In the water of lower velocity a large fraction of the larvae population is distributed in the lower depth layer.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.3
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• pp.398-402
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• 2008

Recently, the development of superconducting fault current limiters (SFCLs) has been required as power demands increase in the power system. A distribution-level prototype resistive SFCL using coated conductor (CC) has been developed by Hyundai Heavy Industries Co., Ltd. and Yonsei University for the first time in the world. The ratings of the SFCL are 13.2kV/630A at normal operating condition. A novel non-inductive winding method is used in fabricating coils so there is almost zero impedance during normal operation. The distribution SFCL is cooled by sub-cooled liquid nitrogen $(LN_2)$ of 65K and 3 bar to enhance cryo-dielectric performance, critical current density, and thermal conductivity. In order to make reliable operation of an SFCL in real power systems, we monitored and controled its operation conditions by using supervisory control and data acquisition (SCADA) method. Thus, a monitoring system for the SFCL employing information technology (IT) is proposed and developed to be on the lookout for the operation conditions such as inside temperature, inside pressure, $LN_2$ level, voltage and current. Since operation temperature should be kept constant, bang-bang control for temperature feedback with a heater attached to the cold head of cryo-cooler is applied to the system. Short-circuit tests with prospective fault current of 10kA and AC dielectric withstand voltage tests up to 143kV for 1 minute were successfully performed at Korea Electrotechnology Research Institute. This paper deals with the development of a distribution level SFCL and its monitoring system for reliable operation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.12 s.255
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• pp.1228-1235
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• 2006

PEMFC(Proton Exchange Membrane Fuel Cell) is a low temperature fuel cell and has many probabilities of commercial use. However, water management is one of the serious technical problems for commercialization. It is necessary to understand the relationship between operation conditions and water behavior in PEMFC channel because it affects fuel cell performance. In this paper, the distribution of current density according to inlet humidity condition is mainly observed and discussed. If the anode inlet is well humidified, electro-osmotic drag is very active. For this reason, current density is very high at inlet side and the distribution is non-uniform.

• Progress in Superconductivity
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• v.11 no.1
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• pp.72-77
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• 2009

Low temperature scanning laser microscopy (LTSLM) can be used for a two-dimensional display of bolometric response arising from the localized excitation of a sample by the focused laser beam. In this study, the distribution of critical temperature ($T_c$) and critical current density ($J_c$) in YBCO coated conductor were analyzed using LTSLM. For improving the temperature stability, we have modified the system into a double-shielding type. Through the modification, the temperature stability was successfully improved from ${\pm}10mK\;to\;{\pm}2mK$. The superconducting properties of YBCO coated conductors were measured for the sample of a narrow bridge type using wet etching process. The spatial non-uniformity of the ac voltage response, ${\delta}V(x)$, which is proportional to ${\partial}\rho(x,J_B)/{\partial}T$ in the transition temperature region could be observed and displayed in a two-dimensional image.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.5
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• pp.1338-1346
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• 1994

The objective of this study is to investigate the effect of various parameters, such as temperature, mean current density and voltage on the performance of phosphoric acid fuel cell (PAFC) by numerical analysis. Two types of flow passages, which are Z-parallel type and Z-counter type, are evaluated to obtain the best current density and temperature distribution. Parametric studies and sensitivity analysis of the PAFC system's operation in single cell are accomplished. A steady state simulation of the entire system is developed using nonlinear ordinary differential equations. The finite difference method and trial and error procedures are used to obtain a solution.