• Journal of Photoscience
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• 제11권3호
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• pp.95-99
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• 2004

Optical absorption and emission studies have been carried out to understand the effect of deuterium on the solvent dependent photophysical properties of curcumin in deuterated solvents such as $CDCl_3,\;(CD_3)_2SO,\;(CD_3)_2CO,\;CD_3OD\;and\;CD_3CN$. Optical absorption spectral studies showed that there is no significant shift in absorption maxima compared to the non-deuterated solvent. The fluorescence maxima shows significant shift with polarity of solvent but not much affected by the deuteration. The fluorescence quantum yield of curcumin increased marginally in almost all the deuterated solvents, indicating reduction in the non-radiative pathways. The fluorescence decay was biexponential in all the solvents and the average fluorescence lifetime was not much affected with deuteration, but showed decrease with increasing solvent polarity. Based on these studies, it is concluded that intermolecular hydrogen transfer is only partially responsible for the excited state deactivation of curcumin.

• Bulletin of the Korean Chemical Society
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• 제24권8호
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• pp.1207-1210
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• 2003

The effect of solvent structure on the slope in the plot of ln K vs. solute carbon number was examined. It was found that the free energy of methylene group transfer from the gas phase into a solvent was always negative and that the absolute magnitude of interaction free energy between the methylene group and the solvent was always larger than the absolute magnitude of cavity formation free energy of the methylene group in the solvent. Thus, the slope in the plot of ln K vs. solute carbon number was always positive and its value decreases with increase of solvent polarity since the cavity formation energy of the CH₂ unit increases with increase of solvent polarity while the dispersive interaction energy of the CH₂ unit is virtually invariant. We also examined the effect of sequential addition of CH₂ unit to a solvent molecule upon ln K for three homologous series of solvents: n-alkanes, n-alcohols, and n-nitriles. Characteristic trends in the plots of ln K vs. solvent carbon number were observed for individual solvent groups. A decrease of ln K with solvent carbon number was observed for n-alkanes. An abrupt increase in ln K followed by levelling off was observed for n-alcohols while a final slight decrease in ln K after an abrupt increase followed by rapid levelling off was noted for n-nitriles. All of theses phenomena were found related to variation in cavity formation energy. It was clearly shown that a structural change of a polar solvent by sequential addition of CH₂ units causes an abrupt polarity decrease initially, then gradual levelling off, and finally, conversion to a virtually nonpolar solvent if enough CH₂ units are added.

• Korean Chemical Engineering Research
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• 제47권4호
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• pp.430-435
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• 2009

실란커플링제인 glycidoxypropyl trimethoxysilane과 vinyltriethoxysilane을 출발물질로 하여 sol-gel 법에 의해 유-무기 혼성 용액을 제조하였다. 이 용액에 spiropyran 계 광 변색 염료를 다양한 종류의 용매에 용해시킨 후 혼합하여 광변색 코팅 용액을 제조하였다. 그 후 기재인 polycarbonate 시트에 코팅시키고 열 경화시켜 광 변색성을 갖는 하드 코팅 막을 제조하였다. 이 과정 중 spiropyran을 용해시킨 용매의 극성이 코팅 막의 광변색 특성에 미치는 영향을 조사하였다. Spiropyran을 용해시킨 용매의 극성이 증가할수록 겔 매트릭스에서의 spiropyran의 열린 구조가 더욱 안정화되므로 코팅 막의 소색속도가 감소하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2011년도 제42회 하계학술대회
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• pp.1552-1553
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• 2011

The HVDC transformer which is one of the main equipments for HVDC(High Voltage Direct Current) electric power transmission systems is exposed to not only AC voltage but also the inflowing DC voltage which comes from the DC-AC converter systems. Therefore, the HVDC transformer insulation system is required to withstand the electric field stress under AC, DC and DC polarity reversal conditions. However the electric field distributions under those conditions are different because the AC electric field and DC electric field are governed by permittivity and conductivity, respectively. In this study, the changes of electric potential and electric field of conventional AC transformer insulation system under DC polarity reversal test condition were analyzed by FEM(Finite Element Method). The DC electric field stress was concentrated in the solid insulators while the AC electric field stress was concentrated in the mineral oil. In addition, the electric stress under that condition which is affected by the surface charge accumulation at the interfaces between insulators was evaluated. The stress in some parts could be higher than that of AC and DC condition, during polarity reversal test. The result of this study would be helpful for the HVDC transformer insulation system design.

• 인지과학
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• 제23권1호
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• pp.97-107
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• 2012

오피니언 마이닝과 정서 분석에 대한 기존 연구에서는 정서 단어에 부정어를 붙일 경우 긍정, 부정의 극성과 값이 뒤바뀐다고 가정하고 부정어를 처리하였다. 그러나 지금까지 정서 단어에 부정어가 발생했을 때 극성이 어느 정도 바뀌는지에 대한 정량적 연구는 없었다. 따라서 본 논문에서는 한국어 정서 단어와 그 부정형에 대해서 정서가와 각성 차원을 측정하였다. 결과, 정서 단어에 부정형이 올 경우 정서가와 각성 차원의 중간 수준을 기준으로 극성을 뒤바꾸고 값은 약 30~50% 약화되었다. 이 결과를 오피니언 마이닝과 정서 분석 연구에서 부정어를 처리하는 기준으로 제시하였다.

• Journal of Astronomy and Space Sciences
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• 제31권2호
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• pp.145-148
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• 2014

There was a research on the prolongation of solar cycle 23 by the solar cyclic variation of solar, interplanetary geomagnetic parameters by Oh & Kim (2013). They also suggested that the sunspot number cannot typically explain the variation of total solar irradiance any more. Instead of the sunspot number, a new index is introduced to explain the degree of solar activity. We have analyzed the frequency of sunspot appearance, the length of solar cycle, and the rise time to a solar maximum as the characteristics of solar cycle. Then, we have examined the predictability of solar activity by the characteristics of preceding solar cycle. We have also investigated the hemispheric variation of flare index for the periods that the leading sunspot has the same magnetic polarity. As a result, it was found that there was a good correlation between the length of preceding solar cycle and spotless days. When the length of preceding solar cycle gets longer, the spotless days increase. It is also shown that the shorter rise time to a solar maximum is highly correlated with the increase of sunspots at a solar maximum. Therefore, the appearance frequency of spotless days and the length of solar cycle are more significant than the general sunspot number as an index of declining solar activity. Additionally, the activity of flares leads in the northern hemisphere and is stronger in the hemisphere with leading sunspots in positive polarity than in the hemisphere with leading sunspots in negative polarity. This result suggests that it is necessary to analyze the magnetic polarity's effect on the flares and to interpret the period from the solar maximum to solar maximum as the definition of solar cycle.

• Journal of Radiation Protection and Research
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• 제34권2호
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• pp.43-48
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• 2009

When the PDD (percentage depth dose) in the megavoltage beams is measured in the water phantom, the polarity and ion recombination effects of ionization chambers with depth in water are not usually taken into consideration. We try to investigate if those variations with depth should be taken into consideration or could be ignored for the thimble type semiflex ionization chamber (PTW $31010^{TM}$, SN 1551). According to the recommendation of IAEA TRS-398, the 4 representative depths of $d_s$, $d_{max}$, $d_{90}$ and $d_{50}$ were used for the electron beams. For the photon beams, the 4 depths were arbitrarily chosen for the photon beams, which were $d_s$, $d_{max}$, $d_{10}$ and $d_{20}$. For the high energy photon beam both polarity and ion recombination factors of the chamber with depth in water gives the good agreements within the maximum $\pm$0.2%, while the $C_{polS}$ with depth came within the maximum $\pm$ 0.4% and the $C_{IRS}$ within the maximum $\pm$0.6% in every electron beam used. This study shows that PDI (percentage depth ionization) could be a good approximation to PDD for the chamber used.

• 한국전기전자재료학회논문지
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• 제33권3호
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• pp.245-248
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• 2020

The wettability of silicon carbide (SiC) crystal, which has 6H-SiC and 4H-SiC regions prepared using the physical vapor transport (PVT) method, is quantitatively analyzed using dispensed deionized (DI) water droplets. Regardless of the polytypes in SiC, the average of five contact angle measurements showed a difference of about 6° between the Si-face and C-face. The contact angle on the Si-face (C-face) is measured after the removal of the native oxide using BOE (6:1), and revealed a significant decrease of the contact angle from 74.9° (68.4°) to 47.7° (49.3°) and from 75.8° (70.2°) to 51.6° (49.5°) for the 4H-SiC and 6H-SiC regions, respectively. The contact angle of the Si-face recovered over time during room temperature oxidation in air; in contrast, that of the C-face did not recover to the initial value. This study shows that the contact angle is very sensitive to SiC surface polarity, specific surface conditions, and process time. Contact angle measurements are expected to be a rapid way of determining the surface polarity and wettability of SiC crystals.

• Journal of Korea Trade
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• 제24권7호
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• pp.1-28
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• 2020

Purpose - This paper empirically investigates the predictors and main determinants of consumers' ratings of mobile applications in the Google Play Store. Using a linear and nonlinear model comparison to identify the function of users' review, in determining application rating across countries, this study estimates the direct effects of users' reviews on the application rating. In addition, extending our modelling into a sentimental analysis, this paper also aims to explore the effects of review polarity and subjectivity on the application rating, followed by an examination of the moderating effect of user reviews on the polarity-rating and subjectivity-rating relationships. Design/methodology - Our empirical model considers nonlinear association as well as linear causality between features and targets. This study employs competing theoretical frameworks - multiple regression, decision-tree and neural network models - to identify the predictors and main determinants of app ratings, using data from the Google Play Store. Using a cross-validation method, our analysis investigates the direct and moderating effects of predictors and main determinants of application ratings in a global app market. Findings - The main findings of this study can be summarized as follows: the number of user's review is positively associated with the ratings of a given app and it positively moderates the polarity-rating relationship. Applying the review polarity measured by a sentimental analysis to the modelling, it was found that the polarity is not significantly associated with the rating. This result best applies to the function of both positive and negative reviews in playing a word-of-mouth role, as well as serving as a channel for communication, leading to product innovation. Originality/value - Applying a proxy measured by binomial figures, previous studies have predominantly focused on positive and negative sentiment in examining the determinants of app ratings, assuming that they are significantly associated. Given the constraints to measurement of sentiment in current research, this paper employs sentimental analysis to measure the real integer for users' polarity and subjectivity. This paper also seeks to compare the suitability of three distinct models - linear regression, decision-tree and neural network models. Although a comparison between methodologies has long been considered important to the empirical approach, it has hitherto been underexplored in studies on the app market.

• 한국진공학회지
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• 제19권5호
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• pp.347-352
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• 2010

SiOC 박막의 유전상수를 서로 다른 2가지 방법을 사용하여 계산하고 그 차이점에 대하여 비교분석하였다. SiOC 박막의 유전장수는 전형적인 유전상수 측정법으로써 MIS 구조를 이용하여 C-V 측정법에 의하여 얻을 수 있으며, 또한 엘립소미터를 이용한 굴절률로부터 $n^2$을 구하는 방법이 있다. SiOC 박막의 유전상수는 쌍극자, 이온, 전자의 성분으로 이루어지며, 댁개 쌍극자 성분은 무시된다. 박막을 증착하는 동안 플라즈마에 의한 프리커서의 해리로부터 이온결합이 생성되면서 증착된다. 증착한 박막의 유전상수는 주로 이온결합 효과가 주를 이루었다. 열처리를 하면서 OH 수산기의 기화에 의해 유전상수는 감소되는데 이때 이온의 효과도 더불어 감소하게 된다. 상대적으로 무시되었던 전자에 의한 분극의 효과가 나타나면서 유전상수는 더욱 감소하였다. 하지만 물리 화학적 그리고 전기적으로 안정된 SiOC 박막은 이온과 전자에 의한 분극의 효과가 없어지는 무 분극성의 박막으로서 유전상수는 열처리한 박막에서 2.0 정도인 것으로 측정되었다.