• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.2
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• pp.134-139
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• 2000

Ternary system of 40PMN-30PT-30PMW was prepared by using different reaction process. The PMN-PT was synthesized firstly, then it reacted to $PbWO_4$ as PbO and $WO_3$ sources. The dielectric constants were dependent on the density of sintered body and decreased with sintering temperature above $950^{\circ}C$. The highest dielectric constant was 24,000 in a sample sintered at $950^{\circ}C$ with the dielectric loss of 3 %. The temperature dependence of the dielectric constant were decreased with the increase of sintering temperature due to the appearance of double peak maxima. The lowest change in dielectric constant was -37-0 % from -55 to $125^{\circ}C$in a sample sintered at $1150^{\circ}C$ with dielectric constant of 9,900 at room temperature.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.5
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• pp.2524-2528
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• 2013

Cell opening characteristics dependent on the cell openers for the conventional formulation of a closed-cell polyurethane foam (PUF) was studied using 1-butanol and lithium salt of 12-hydroxystearic acid (Li-12HSA) as the reactive cell opening agents. While cell openining content of only 10.5 % was obtained for the sample with 4 phr of 1-butanol as the single reactive cell opener, that of 98.0% could be obtained for the sample with 2 phr of Li-12HSA as the reactive co-cell opener. As the results, it showed that a fully open-cell rigid PUF could be obtained by introducing a novel reactive cell opener, having a functional group able to form a bulky side-chain on the urethane networks, without severe loss of mechanical properties of the closed-cell PUF like cell size, bulk density, and thermal conductivity.

• Progress in Superconductivity
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• v.13 no.2
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• pp.105-110
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• 2011

SQUID sensor-based ultra low-field magnetic resonance apparatus with ${\mu}T$-level measurement field requires a strong prepolarization magnetic field ($B_p$) to magnetize its sample and obtain magnetic resonance signal with a high signal-to-noise ratio. This $B_p$ needs to be ramped down very quickly so that it does not interfere with signal acquisition which must take place before the sample magnetization relaxes off. A MOSFET switch-based $B_p$ coil driver has current ramp-down time ($t_{rd}$) that increases with $B_p$ current, which makes it unsuitable for driving high-field $B_p$ coil made of superconducting material. An energy cycling-type current driver has been developed for such a coil. This driver contains a storage capacitor inside a switch in IGBT-diode bridge configuration, which can manipulate how the capacitor is connected between the $B_p$ coil and its current source. The implemented circuit with 1.2 kV-tolerant devices was capable of driving 32 A current into a thick copper-wire solenoid $B_p$ coil with a 182 mm inner diameter, 0.23 H inductance, and 5.4 mT/A magnetic field-to-current ratio. The measured trd was 7.6 ms with a 160 ${\mu}F$ storage capacitor. trd was dependent only on the inductance of the coil and the capacitance of the driver capacitor. This driver is scalable to significantly higher current of superconducting $B_p$ coils without the $t_{rd}$ becoming unacceptably long with higher $B_p$ current.

• The Journal of the Korea Contents Association
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• v.17 no.2
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• pp.384-393
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• 2017

The purpose of this study was to find out the subjective cognition-patterns of school aged children with borderline intelligence function to the School using Q Methodology. Q-sample was included 21 statements obtained from literatures and in-depth interviews with 4 specialist & 4 children with borderline intelligence function. P-sample was consisted through the consent of 18 children with borderline intelligence function and their parents. The 21 selected Q-statements were classified into a normal distribution using a 5 point scale. The collected data analyzed using a Quanl PC program. This study found out two subjective cognition-patterns of school aged children with borderline intelligence function to the school. Two types were 'participatory & dependent type', and 'onlooking & atrophic type'. This research finding can be used to make clear understanding on diverse voices of school aged children with borderline intelligence function to the School. And this result will attribute to mediations of educational welfare practice for maintaining a safe & healthy learning environment.

• Advances in environmental research
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• v.6 no.2
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• pp.95-111
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• 2017

The valorization of swine manure samples, i.e., de-watered cake (SMc) and solid digestate (SMd), in products with beneficial value, i.e., low cost activated carbons (ACs), is studied. For this purpose slow pyrolysis and steam activation at three different duration times are applied. Additionally, the obtained ACs are characterized and tested towards removal of Cr(VI) from aqueous solutions. It is revealed that BET surface area varies in the range of $236-267m^2/g$ for ACs prepared from SMc sample and in the range of $411-432m^2/g$ for ACs prepared from SMd sample. Despite the low determined surface area of prepared ACs, a high total Cr removal capacity is observed occurring through a "coupled adsorption-reduction" mechanism. Higher Cr(VI) removal capacity is demonstrated for ACs having higher surface area ($q_m$ is 140.9 mg/g according Langmuir modelling). Cr(VI) removal is found to be pH dependent with a maximum at pH 1. However at that pH significant amounts of Cr remain in the solution as Cr(III). At pH 2 lower amount of Cr(VI) is removed compensated by a higher removal of Cr(III) resulting in a higher amount of adsorbed $Cr_{tot}$. Therefore adsorption at pH 2 is found to be appropriate. The removal capacity of the studied ACs towards Cr(VI) is almost independent of activation time.

• Journal of the Korea Safety Management & Science
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• v.16 no.1
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• pp.169-176
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• 2014

This research discusses the characteristics and the implementation strategies for two types of quality metrics to analyze innovation effects in six sigma projects: fixed specification type and moving specification type. $Z_{st}$, $P_{pk}$ are quality metrics of fixed specification type that are influenced by predetermined specification. In contrast, the quality metrics of moving specification type such as Strictly Standardized Mean Difference(SSMD), Z-Score, F-Statistic and t-Statistic are independent from predetermined specification. $Z_{st}$ sigma level obtains defective rates of Parts Per Million(PPM) and Defects Per Million Opportunities(DPMO). However, the defective rates between different industrial sectors are incomparable due to their own technological inherence. In order to explore relative method to compare defective rates between different industrial sectors, the ratio of specification and natural tolerance called, $P_{pk}$, is used. The drawback of this $P_{pk}$ metric is that it is highly dependent on the specification. The metrics of F-Statistic and t-Statistic identify innovation effect by comparing before-and-after of accuracy and precision. These statistics are not affected by specification, but affected by type of statistical distribution models and sample size. Hence, statistical significance determined by above two statistics cannot give a same conclusion as practical significance. In conclusion, SSMD and Z-Score are the best quality metrics that are uninfluenced by fixed specification, theoretical distribution model and arbitrary sample size. Those metrics also identify the innovation effects for before-and-after of accuracy and precision. It is beneficial to use SSMD and Z-Score methods along with popular methods of $Z_{st}$ sigma level and $P_{pk}$ that are commonly employed in six sigma projects. The case studies from national six sigma contest from 2011 to 2012 are proposed and analyzed to provide the guidelines for the usage of quality metrics for quality practitioners.

• Korean Journal of Environmental Agriculture
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• v.33 no.2
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• pp.134-137
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• 2014

BACKGROUND: Dissipation of herbicides in paddy water varies significantly, being dependent on environmental conditions such as sunlight. The photodegradation under natural sunlight may be one of natural degradation routes of herbicides dissipation. Therefore, the aim of this study was to monitor the degradation of butachlor and pyrazosulfuron-ethyl in paddy water under natural sunlight. METHODS AND RESULTS: The 12 water sample bottles of treatment were covered by quart glass plates, which allow about 90% of UV radiation (280-2000 nm) to pass through, to minimize the UV attenuation. The other 12 water sample bottles of the control were covered by glass lids and wrapped with aluminum foils to prevent the sunlight. The concentration of butachlor and pyrazosulfuron-ethyl in paddy water samples bottles was monitored under ambient conditions with and without natural sunlight. The concentration of butachlor and pyrazosulfuron-ethyl for treatment decreased from $355.3{\mu}g/L$ to $37.8{\mu}g/L$ and from $10.5{\mu}g/L$ to $3.9{\mu}g/L$, respectively, during consecutive 21 days after herbicide application under natural sunlight. CONCLUSION: The concentration of butachlor in paddy water decreased quickly under ambient conditions with natural sunlight. The degradation of butachlor in paddy water was enhanced by the natural sunlight. However, the degradation of pyrazosulfuron-ethyl was insignificant under natural sunlight.

• Journal of Family Resource Management and Policy Review
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• v.15 no.3
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• pp.131-151
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• 2011

This study attempted to estimate the level of perceived lack of time in Korean society, to link it to time management and to identify the possible association that accounts for time shortage. I employed the gender perspective in order to reveal the dynamics and complexity of the perception of a lack of time in the population. The sample for the study was drawn from the 1999 and 2009 Korean time diary data collected by the Korean National Statistical Office. From the original data, I selected a sample of second shift families(men and women who are presently working and raising children) living in metropolitan areas(including Seoul and six major urban areas in Korea). The dependent variable was time pressure measured by a single-item question on a four-point likert scale. The results of the study showed that working mothers perceived a greater time shortage as compared to working fathers. The time use pattern showed change during the periods, indicating that people worked fewer hours in paid labor and enjoyed more leisure hours and personal care hours. However, on average, people seemed to have experienced a greater time lack in 2009 as compared to 1999. The results from the ordered logistic regression model revealed that even though there were similarities in the impact of relevant factors, men's perception of a lack of time was more closely linked with their work role and social status, while for women, this perception was influenced by work and family duties. This indicates that Korean working mothers and fathers are facing a double jeopardy of time shortage in terms of combining their work and family roles. As a result, the level of time pressure by gender is converging toward a "never enough" phase. These findings generated policy implications and detailed suggestions.

• The Journal of Industrial Distribution & Business
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• v.9 no.6
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• pp.49-55
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• 2018

Purpose - This paper examines the effect of related party transactions on crash firm-specific stock price crash risk. Ownership of a typical Korean conglomerate is concentrated in a single family. In those entities, management and board positions are often filled by family members. Therefore, a dominant shareholder can benefit from related party transactions. In Korea, firms have to report related party transactions in financial statement footnotes. However, those are not disclosed in detail. The more related party transactions are the greater information risk. Thus, companies with related party transactions are likely to experience stock price crashes. Research design, data, and methodology - 2,598 firm-year observations are used for the main analysis. Those samples are from TS2000 database from 2009 to 2013, and the database covers KOSPI-listed firms in Korea. The proxy for related party transactions (RTP) is calculated by dividing total transactions to the related-party by total sales. A dummy variable is used as a dependent variable (CRASH) in the regression model. Logistic regression is used to explain the relationship between related party transactions and crash risk. Then, the sample was separated into two groups; tunneling firms and propping firms. The relation between related party transactions and crash risk variances with features of the transaction were investigated. Results - Using a sample of KOSPI-listed firms in TS2000 database for the period of 2009-2013, I find that stock price crash risk increases as the trade volume of related-party transactions increases. Specifically, I find that the coefficient of RPT is significantly positive, supporting the prediction. In addition, this relationship is strong and robust in tunneling firms. Conclusions - The results report that firms with related party transactions are more likely to experience stock price crashes. The results mean that related party transactions increase the possibility of future stock price crashes by enlarging information asymmetry between controlling shareholders and minority shareholders. In case of tunneling, it could be seen that related party transactions are positively associated with stock crash risk. The result implies that the characteristic of the transaction influences crash risk. This study is related to a literature that investigates the effect of related party transactions on the stock market.

• Korean Management Science Review
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• v.32 no.2
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• pp.91-109
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• 2015

The M&A of firms has been emerged as the effective means of fast diversification and growth in dynamic environment. However, the empirical research about M&A in Korea has not been implemented rich due to the difficulty of obtaining M&A data. In this research, we empirically investigate the relationships among M&A, environment and firms' performance focused on Korean manufacturing firms, understanding the current practice of M&A in Korea. We use the Manufacturing Productivity Panel Survey Data, which are collected by Korea Productivity Center in 2013. The sample size is 575 and the sample is divided into M&A group and non-M&A group. We conduct logit analysis with the independent variables of environment factors (munificence, dynamic, uncertainty), and firms' performance (sales growth, ROS, labor productivity and Inventory turnover), and dependent variable of M&A group or non M&A group. The results show that M&A is closely related to environment feature and firm performance: M&A firms are likely to be the higher munificence and dynamic and the lower sales growth and higher profitability than non-M&A group. In addition, we also examine the characteristics of firms by M&A types (competitors, customer/supplier and firms from unrelated industry). These results imply that if firms confront the pressure of uncertainty (dynamic) and the lower growth, they tend to choose M&A. Futhermore, to profoundly understand the behavior of firms about M&A, it is required to classify the M&A firms by merge types.