• The Journal of the Korean dental association
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• v.49 no.1
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• pp.7-14
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• 2011

The purpose of this study is to discuss the economic outlook of dentistry in relation to pessimistic economic perspectives of Korea and to present subsequent solutions. The expectation of the future economic growth rate of Korea is gloom with not only a love rate of increase in population due to an aging society and a low birthrate, but also with a declined number of productive populations. Moreover, the future of dentistry in Korea is obscure. Even with a dwindling population growth, an average of 750 new dentists graduate from dental school every year. The 30-35% of the new graduates practice in public hospitals; and 65~70% of them open up their own private practices, However, unlike in the past, the occurrence of dental practice bankruptcy has been increasing with a competitive environment, excessive initial investment, knowledgeable patients, and etc. Therefore, it is essential to re-evaluate the number of new graduates. Also, it is necessary to supply a greater number of public hospitals with newly licensed dentists, who have various clinic experience, participate in research and development, and experience appropriate hospital management skills.

• Transactions on Electrical and Electronic Materials
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• v.6 no.1
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• pp.6-9
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• 2005

Aging characteristics of 0.2PMN-0.8PZT multilayer ceramic actuators (MCA) has been investigated by applying both triangular wave function for unpoled and unipolar wave for poling. P-E hysteresis loops of the MCA had been distorted after about 90 million cycles running in triangular wave function. Effective electromechanical coupling coefficient was calculated in resonant and anti resonant frequencies. And pseudo-piezoelectric constant $d_{33}$ was also estimated from the strain versus electric field characteristics. The crack growth of MCA was clearly observed along to the boundary between electrode and inactive area. That results were thought due to the internal tensile stress came from both actuation of $d_{33}$ mode and motion of Poisson ratio.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.05c
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• pp.203-207
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• 2002

In order to evaluate the aging of mineral oil immersed distribution transformers, it gathered some insulation oil in over loaded and long time(exceed their service life, 13yrs.) aged transformers in the field, we measured moisture content, acid number, dielectric strength of the oil as defined in KS C 2101 standard. And also, it had been measured dielectric constant, specific resistant, $tan{\delta}$ on aged transformer oil at from $10^{\circ}C$ to $130^{\circ}C$. These results are compared with a new mineral oil. From this study, it can be considered that the analysis of mineral oil may be suitable for evaluation of life expectancy in distribution transformers

• Proceedings of the KIEE Conference
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• 1999.07e
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• pp.2314-2316
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• 1999

This study describes the results of aging characteristics of polymer insulators through the tracking wheel test. In order to evaluate the reliability of polymer insulators, 4 polymer insulators which used in the field were selected. Electrical tests such as power frequency voltage test, steep-front impulse voltage test were performed after tracking wheel test. Chemical structure and contact angle were measured for investigating an aging characteristics. Although some changes have occurred on the surface of insulator, there are no critical changes between new and tracking wheel tested insulator.

• Proceedings of the KIEE Conference
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• 1997.07d
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• pp.1393-1395
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• 1997

In order to investigate the interfacial effects on the aging of power cables, we analyzed recently failed cables using characterization techniques. In this study, some cables showed a convolution which can cause the concentration of electric field and carbonized impurities at the surface of insulation. Also there is a relation between the degree of cross- linking and volume resistivity. From the hot oil test, the sites of water tree and void coincided with each other.

• Elastomers and Composites
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• v.53 no.2
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• pp.67-74
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• 2018

Magneto-rheological elastomers (MREs) are smart materials in which the inherent stiffness and damping properties can be changed by the influence of an external magnetic field. The magneto-rheological (MR) effect depends on the orientation characteristics of the dispersed magneto-responsible particles (MRPs) in the matrix. In this study, natural rubber (NR) and ethylene propylene diene rubber (EPDM) were blended and used as a matrix of an MRE. EPDM was pre-cured before blending with NR. The Mooney viscosity, curing characteristics, and mechanical properties were analyzed with various pre-curing conditions of EPDM and the NR/EPDM blend. The results show that excellent mechanical properties of the NR/EPDM blend-based MRE were obtained when the pre-curing time of EPDM was 60 min. The aging property of the NR-based MRE was improved by the introduction of pre-cured EPDM. Also, the anisotropic MRE showed a higher MR effect than that of the isotropic MRE.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.403-404
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• 2008

In this study, we prepared ITO thin film on glass, polycarbonate (PC) and polyethersulfone (PES) substrate in Facing Targets sputtering (FTS) system. Properties of as-deposited thin films's aging change were investigated as a function of time placed in the air. The electrical and optical properties of as-deposited thin films were employed by a four point probe and an UV/VIS spectrometer, an X-ray diffractometer (XRD), a Field Emission Scanning Electron Microscope(FESEM) and a Hall Effect measurement. As a result, as time went by, transmittance of all films did not change but resistivity of films was decreasing.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.149-150
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• 2005

Thyristor breakdown voltage variation acceleration aging test was investigated. The breakdown voltage was deceased after 1000 hours acceleration aging test. It temperature rising caused by electric field concentration at the edge beveling region of the thyristor was confirmed using Silvaco device simulation. The local temperature rising is driving force for the defect propagation. Consequently, propagated defects of the beveling region seems to decrease thyristor's breakdown voltage.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.9
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• pp.527-531
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• 2016

In this study, p-type thin film transistors consisting of CuO channels were fabricated by sol-gel process, with copper (II) acetate monohydrate precursors. At $500^{\circ}C$, the deposited films were fully converted into monoclinic phase CuO. The fabricated CuO thin film transistors deliver field effect mobility in saturation regime of $0.015cm^2/Vs$, and $I_{on}/I_{off}$ of ${\sim}10^3$. The degradation of the performance of the fabricated CuO thin film transistor caused by the exposure to air has been studied.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.3
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• pp.212-224
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• 2010

The usefulness of the magnetic camera for non-destructive testing of aging aircraft is discussed in this paper. The magnetic camera can be used f magnetic particle testing(MT), magnetic flux leakage testing(MFLT), eddy current testing(ECT) and penetration testing(PT). It measures the distribution of a magnetic field and visualizes the magnetic pattern. Near and far side cracks, fatigue, thickness degradation, and cracks under rivets have been detected. The possibility of quantitative evaluation was also examined. Using indirect experiments, we verified the detection ability of the sensor for cracks in titanium and advanced composite materials.