• Analytical Science and Technology
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• v.8 no.3
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• pp.293-298
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• 1995

The stability of brass coated on steel cords with pH and applied constant potential changes in aqueous solution has been investigated by AC impedance measurements. In solutions of the constant pH, as a applied constant potential is shifted to positive potential, the coating pore resistance is reduced. The fact indicates that as a applied constant potential is shifted to positive potential, the brass coated is dissolved more in solution. The stability of brass coated on steel cords decrease in the order pH=7.1 > pH=4.0 > pH=10.0. The above results are demonstrated by the data of scanning of electronic microscopy(SEM)/energy dispersive spectrometer(EDS).

• Smart Structures and Systems
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• v.16 no.5
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• pp.891-918
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• 2015

In many of microdevices a part of a microbeam is covered by a piezoelectric layer. Depend on the application a DC or AC voltage is applied between upper and lower side of the piezoelectric layer. A common method in many of previous works for evaluating the response of these structures is discretizing by Galerkin method. In these works often single mode shape of a uniform microbeam i.e. the microbeam without piezoelectric layer has been used as comparison function, and so the convergence of the solution has not been verified. In this paper the Galerkin method is used for discretization, and a comprehensive analysis on the convergence of solution of equation that is discretized using this comparison function is studied for both clamped-clamped and clamped-free microbeams. The static and dynamic solution resulted from Galerkin method is compared to the modal expansion solution. In addition the static solution is compared to an exact solution. It is denoted that the required numbers of uniform microbeam mode shapes for convergence of static solution due to DC voltage depends on the position and thickness of deposited piezoelectric layer. It is shown that when the clamped-clamped microbeam is coated symmetrically by piezoelectric layer, then the convergence for static solution may be obtained using only first mode. This result is valid for clamped-free case when it is covered by piezoelectric layer from left clamped side to the right. It is shown that when voltage is AC then the number of required uniform microbeam shape mode for convergence is much more than the number of required mode in modal expansion due to the dynamic effect of piezoelectric layer. This difference increases by increasing the piezoelectric thickness, the closeness of the excitation frequency to natural frequency and decreasing the damping coefficient. This condition is often indefeasible in microresonator system. It is concluded that discreitizing the equation of motion using one mode shape of uniform microbeam as comparison function in many of previous works causes considerable errors.

• Journal of Power Electronics
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• v.7 no.3
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• pp.233-237
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• 2007

This paper deals with the new HVDC interaction which was observed in the Jeju-Haenam HVDC system. The interaction is not from a system malfunction or controller loop problem but from the change of AC network scheme and the network operating condition. We have found that the interaction is caused by the voltage oscillation between synchronous compensator and HVDC shunt reactor. We analyzed the cause of the interaction and suggested a solution.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.47 no.6
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• pp.28-39
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• 2010

The study aims at offering a solution to the problems of transmission delay and data throughput decrease as the number of contending On-Board Units (OBU) increases by applying CSMA medium access control protocol based upon IEEE 802.11p. In a competition-based medium, contention probability becomes high as OBU increases. In order to improve the performance of this medium access layer, the author proposes EDCA which a adaptive adjustment of the Contention Windows (CW) considering traffic density and data type. EDCA applies fixed values of Minimum Contention Window (CWmin) and Maximum Contention Window (CWmax) for each of four kinds of Access Categories (AC) for channel-specific service differentiation. EDCA does not guarantee the channel-specific features and network state whereas it guarantees inter-AC differentiation by classifying into traffic features. Thus it is not possible to actively respond to a contention caused by network congestion occurring in a short moment in channel. As a solution, CWminAS(CWmin Adaptation Scheme) and ACATICT(Adaptive Contention window Adjustment Technique based on Individual Class Traffic) are proposed as active CW control techniques. In previous researches, the contention probabilities for each value of AC were not examined or a single channel based AC value was considered. And the channel-specific demands of IEEE 802.11p and the corresponding contention probabilities were not reflected in the studies. The study considers the collision number of a previous service section and the current network congestion proposes a dynamic control technique ACCW(Adaptive Control of Contention windows in considering the WAVE situation) for CW of the next channel.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1997.10a
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• pp.161-164
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• 1997

Thin films of CdS were prepared from an aqueous solution containing Cd(Ac)$_2$, NH$_4$OH, NH$_4$Ac and (NH$_2$)$_2$CS for photovoltaic application. Growth rate of CdS films was increased with increasing temperature of reactive solution and with decreasing concentration of NH$_4$OH. Optical transmittances were more than 60%, independent with temperature and concentrations, and were changed with thickness of CdS films. Growth films mostly showed the presence of polycrystallines with mixed cubic and condition. The resistivities of CdS were decreased by doping boron and criticial amount of dopant was determined.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.205-206
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• 2002

In this paper we examined the contribution of mechanical and electrochemical factors in corrosive wear for Zr-alloy against $Al_2O_3$ ball in $Na_2SO_4$ solution. Normal load and the area of metallic specimen was varied to change the corrosion behavior. At the commence of sliding, the potential drop took place, which increased with load due to the great exposure of fresh surface. Wear volume was linearly proportional to load. The corrosion factor was about 15%. By increasing the Aa/Ac ratio, corrosion factor to total wear decreases and saturates above Aa/Ac=0.15.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.387-390
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• 2006

The protective layer of AC-PDP was fabricated by laminating an MgO green sheet. The MgO green sheet was made by coating MgO solution composed of solvent, dispersant, binder, and MgO nano-powder. The MgO solution was coated by the die casting method on the base film. We fabricated three kinds of MgO green sheets of which thicknesses were 20, 28, and $40\;{\mu}m$, respectively. The MgO nano-powder showed lower CL intensity and ${\gamma}i$ than the e-beam MgO. The MgO green sheet applied panels showed low luminance and current density. The efficiency was almost same as the conventional e-beam MgO panel.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.665-666
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• 2008

Inserted HTS (high temperature superconducting) coil is promisingly expected as a solution for achievement of higher fields such as GHz scale NMR magnet. However, HTS magnet causes persistent current decay in the persistent current mode and this decay should be compensated in order to keep stable magnetic field. As a solution for the decay in the HTS magnets, we proposed a new type superconducting power supply, i.e., linear type magnetic flux pump (LTMFP). The LTMFP mainly consists of DC bias coil, 3-phase AC coil and superconducting Nb foil. The compensating current in closed superconductive circuit can be easily controlled by the intensity of 3-phase AC current and its frequency. In this study, it has been investigated that the flux pump can effectively charge the current for various frequencies according to the different load magnets.

• Journal of Korea Foundry Society
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• v.34 no.4
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• pp.136-142
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• 2014

Numerical solution of thermal stress by CAE analysis could be an effective method in product development stage of castings to predict and treat the problem of solidification cracking of castings. Quantitative stress-strain data are necessary, in this case. Tension type apparatus of a solidification crack test which can measure stress-strain relationship quantitatively was developed and the test procedure was established by this research. Solidification crack strength obtained from the following test procedure could be utilized to evaluate it in terms of effect factors on thermo-plastic characteristic of solidifying alloy such as grain size of solid, grain morphology, distribution of solid grain, etc. Proposed test procedure is as follow: Prediction of temperature at the failure site of solidification cracked specimen by computer simulation of solidification, Calculation of solid fraction of the failure site from thermodynamic solution of solidification under Scheil condition.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.12
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• pp.48-54
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• 2003

Alumium alloys casting are gaining increased acceptance in the automotive and electronic industeries and squeeze casting is the most efficient method of manufacturing such mass produced parts. This study has been investigated the microstructures and mechanical properties of Al-7.0Si-0.4Mg (AC4C) alloy fabricated by squeeze casting process for development of Fuel system Parts (Fuel rail). The microstructure of squeeze casted specimen were composed of eutectic structure Alumimim solid solution and $Mg_2$Si precipitates. The tensile strength of as-solid solution treatment Al-7.0Si-0.4Mg ahoy revealed 298.5MPa. It was found that Al-7.0Si-0.4Mg alloy have good corrosion resistance in electrochemical polarization test.