• Journal of the Korean Ceramic Society
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• v.43 no.2 s.285
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• pp.106-113
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• 2006

PMN-PZT films with thickness of $5\;{\mu}m$ were deposited on $Pt/Ti/SiO_2/Si$ substrate at room temperature using aerosol deposition process. The films showed fairly dense microstructure without any crack. XRD and TEM analysis revealed that the films consisted of randomly oriented nanocrystalline and amorphous phases. Post-annealing process was employed to induce crystallization and grain growth of the as-deposited films and to improve the electrical properties. The annealed film showed markedly improved electrical properties in comparison with as-deposited film. The film after annealing at $700^{\circ}C$ for 1h exhibited the best electrical properties. Dielectric constant $(\varepsilon_r)$, remanent polarization $(P_r)$ and piezoelectric constant $(d_{33})$ were 1050, $13\;{\mu}C/cm^2$ and 120 pC/N, respectively.

• The korean journal of orthodontics
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• v.47 no.5
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• pp.306-312
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• 2017

Objective: The purpose of this study was to examine the effect of commercially available fluoride-containing oral rinses on the corrosion behavior of titanium alloys, which are the main components of orthodontic miniscrews. Methods: Four commercially available oral rinses (solution A, pH 4.46/260 ppm fluoride; solution B, pH 4.41/178 ppm fluoride; solution C, pH 6.30/117 ppm fluoride; and solution D, pH 4.17/3.92 ppm fluoride) were tested on titanium alloy (Ti-6Al-4V) circular plates, and saline was used as the control. The open-circuit potential and potentiodynamic polarization of these materials were measured. Thereafter, all samples were evaluated under a field-emission scanning electron microscope. Results: Among the tested oral rinses, except solution D, the more the fluoride content was, the greater was the corrosion potential downtrend; the corrosion resistance of the titanium alloy sample was also lowered significantly (p < 0.05). Field-emission scanning electron microscopic analysis of the surface morphology of the titanium alloy samples revealed that all samples had some defects, crevices, or pitting after exposure to the oral rinses than before treatment. In particular, the samples in solution A showed the most changes. Conclusions: Commercially available oral rinses having a high fluoride concentration and a low pH may reduce the corrosion resistance of titanium alloys used in dental appliances such as orthodontic titanium miniscrews and brackets.

• Korean Journal of Social Welfare
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• v.64 no.2
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• pp.55-83
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• 2012

Self-employment rate is high in Korean labor market, while the income gap within self-employed is also high. Although, there are very few studies that addressed on the income inequality of self-employed. Thus, this study has measured the earnings inequality of self-employed by generalized entropy indices and decomposed inequality factor and trend. The empirical study is based on Korea Welfare Panel Study wave 1~4. The main result from this analysis is summarized in three points. Firstly, earnings inequality of self-employed is severely high and the earnings polarization within self-employed has become more serious in Korea. Secondly, this study provides the evidence that the main factor of earnings inequality of self-employed is the status of self-employment, education level, age group, workplace scale and industry. Thirdly, the contribution of relative changes in the incomes of the status of self-employment is the largest to the inequality trend. In terms of education level, age group and industry, the increase of inequality within group(pure effect) mainly attributes to the rise of earnings inequality of self-employed and the change effect of group composition contributes to deterioration of inequality.

• Composites Research
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• v.33 no.5
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• pp.251-255
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• 2020

In this study, TiC ceramic particulate reinforced steel composites was fabricated using a liquid pressing infiltration process. Studies were conducted on microstructure analysis and basic physical properties such as hardness and corrosion characteristics in salt water environment for comparison with commercial nodular cast iron. As a result of comparison of corrosion characteristics in a salt water environment, both corrosion potential and corrosion current density were lower than that of ductile graphite cast iron. The lower calculated corrosion rate confirms that the TiC-Fe metal composite has superior corrosion resistance than the cast iron.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.21 no.10
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• pp.141-149
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• 2007

This paper introduce to improve the reliability of the expected service life and the insulation condition evaluation of the high voltage induction motors by assessing, comparing and analyzing the correlation between the dielectric properties of the off-line insulation diagnostic test and dielectric strength on the insulation breakdown test. The insulation diagnostic tests include insulation resistance, polarization index(P.I.), dissipation factor($tan{\delta}$), maximum partial discharges($Q_{max}$) and AC breakdown test. This study evaluated the correlation between insulation diagnostic test and AC breakdown test for stator winding of high voltage induction motor. On the basis of these test results, we expect that this study can be used for effectively assessing the results of insulation diagnostic tests for similar class induction motors in service at industrial field.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.7
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• pp.584-587
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• 2017

In this paper, the radar cross section of the integrated mast module for battleship is analyzed. The computation program based on physical optics and physical theory of diffraction is developed and the computed results are compared with those of commercial simulator to check the accuracy of computations. The radar cross section is calculated in terms of the mast shape, incident angle, and polarization. The radar cross section can be reduced through the change of the mast slope and the chamfered mast, which can be applied to a mast with a low radar cross section.

• Journal of Applied Reliability
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• v.18 no.3
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• pp.271-279
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• 2018

Purpose: Probabilistic safety analysis was performed to enhance the safety and reliability of nuclear power plants because traditional deterministic approach has limitations in predicting the risk of failure by crack growth. The study introduces a probabilistic approach to establish a basis for probabilistic safety assessment of passive components. Methods: For probabilistic modeling of fatigue crack growth rate (FCGR), various FCGR tests were performed either under constant load amplitude or constant ${\Delta}K$ conditions by using heat treated X-750 at low temperature with adequate cathodic polarization. Bayesian inference was employed to update uncertainties of the FCGR model using additional information obtained from constant ${\Delta}K$ tests. Results: Four steps of Bayesian parameter updating were performed using constant ${\Delta}K$ test results. The standard deviation of the final posterior distribution was decreased by a factor of 10 comparing with that of the prior distribution. Conclusion: The method for developing a probabilistic crack growth model has been designed and demonstrated, in the paper. Alloy X-750 has been used for corrosion fatigue crack growth experiments and modeling. The uncertainties of parameters in the FCGR model were successfully reduced using the Bayesian inference whenever the updating was performed.

• 한국지구물리탐사학회:학술대회논문집
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• 2005.05a
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• pp.197-202
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• 2005

The electromagnetic signals associated with the seismic activity in the south-east offshore of Kii peninsula, Japan, were clearly recorded at the MT sites in Jeju island, Korea. In this research, we have identified the co-seismic electromagnetic signals associated with the seismic activity and have analyzed the characteristics of significant electromagnetic variations. The analysis of phase velocity, power spectral density, MT impedance and polarization direction shows that the significant earthquake signals have the frequency band of about 0.05 to 0.5 Hz and that the sources of electromagnetic field are local effects of passing seismic waves. The simple approximation using electrokinetic effect successfully explains the co-seismic EM signals coincides with measured data but cannot explain the localities of electromagnetic variations.

• The Korean Journal of Applied Statistics
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• v.27 no.7
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• pp.1125-1137
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• 2014

This paper studies what affects the private education cost for the elementary, middle, and high school students. It is a big issue now because there can be a problem in the equal opportunity for education if the portion of private education cost is very high in the total education cost. If we spend more time and money on the private education than the school education, it can cause the polarization among the classes and regions. The excessive private education also can deteriorate the school system. we use various regression and classification methods to analyze the cost of private education and find the important variables in the models. we found that large cities spend more money on the private education than small cities. We also found that high school students spend more than middle school students and the elementary students and the household with more income spend more money on the private education.

• Journal of the Korea Fashion and Costume Design Association
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• v.10 no.1
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• pp.145-159
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• 2008

This study has examined the shift in fashion styles in Korea by analyzing trends in fashion environment and fashion image by seasons in Korea to understand the domestic fashion flow from 2000 to 2006. Since 2000, with the well-being trend, polarization of consumption, preference in luxury orientation, and digital revolution, consumers became individualized and detail oriented. They also became smart consumers equipped with information and knowledge in making choice and purchasing products suiting their taste. To satisfy the consumer trend, fashion market also saw changes such as expansion of advanced distribution, totalization of brands, growing of on-line shopping mall, expansion of outdoor-wear market, and formation of masstage(mass+prestage) market. Fashion images in domestic women's wear since 2000 are analyzed as classic, elegant, minimalism, romantic, bohemian & vintage, ethnic, glam, girlish, kidult, sportive, femiculine, military, and lingerie image. Classic, romantic, and bohemian & vintage are the images that were popular throughout 2000 to 2006. Fashion images of domestic women's wear showed changes in three periods: Sportive image was popular in FW 2002; military image in SS 2003 to SS 2005; and femiculine, glam, and minimalism images in FW 2005 to FW 2006. Through information and detail-oriented emotion, the wide-ranging acceptance of global trends, the consumer tendency towards purchasing products quickly and conveniently, the speedy supply of trendy products both on-line and in-store, and the evolution of the fashion market towards providing one-stop shopping and a cultural space, different fashion images have all emerged at the same time in Korea. It looks like this phenomenon is set to continue for a while.