• Bulletin of the Korean Chemical Society
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• v.29 no.3
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• pp.551-554
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• 2008

An improved HPLC method for the separation of madecassoside isomers (madecassoside and asiaticoside-B) has been developed. The isomers can be separated with high resolution from extracts of Centella asiatica by HPLC using $\beta$-cyclodextrin as a mobile phase added on a $C_{18}$ column. The result shows that the isomers can be separated with a mobile phase consisting of methanol:water (50:50, v/v) with 4 mmol/L $\beta$-CD. To elucidate the mechanism of the separation of madecassoside and asiaticoside-B, this paper studied the separation of their aglycon parts (madecassic acid and terminolic acid), another pair of isomers. The isomers can also be separated with high resolution with a mobile phase consisting of methanol:water (65:35, v/v) with 4 mmol/L $\beta$-CD and the pH of the mobile phase was adjusted to 4. The paper also studied the separation of the two isomers by HPLC using $\alpha$-CD and Glucosyl-$\beta$-CD as a mobile phase additive in order to elucidate the mechanism of the separation process.

• Bulletin of the Korean Chemical Society
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• v.34 no.10
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• pp.2978-2982
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• 2013

A doubly tethered $N-CH_3$ amide chiral stationary phase (CSP 4) based on (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid was applied to the resolution of an antiarrythmic agent, tocainide, and its analogues and the chromatographic resolution results were compared with those on a singly tethered N-H amide CSP (CSP 1), a singly tethered $N-CH_3$ amide CSP (CSP 2) and a doubly tethered N-H amide CSP (CSP 3) under an identical aqueous mobile phase condition. CSP 4 was found to be generally better than other CSPs in terms of the separation factors (${\alpha}$) and resolutions (RS). The retention times of analytes denoted by the retention factors ($k_1$) on CSP 4 were quite long compared to those on other CSPs because of the improved lipophilicity of CSP 4. The long retention times of analytes on CSP 4 were successfully controlled by the addition of a small amount of ammonium acetate to aqueous mobile phase without hurting the chiral recognition efficiency. The variation of the content and type of organic and acidic modifier in aqueous mobile phase was found not to change the chiral recognition efficiency significantly.

• Nutritional Sciences
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• v.1 no.1
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• pp.61-69
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• 1998

Five hundred and seventy-eight healthy subjects (351 men and 227 women) with a mean age of 44.8 years (45.2 for men, 44.3 for women) participated in this study. The serum concentrations of $\alpha$-tocopherol, \beta$-carotene, $\alpha$-carotene, zeaxanthin + lutein, cryptoxanthin, lycopene and retinol of normal Koreans were measured, and their relation to gender, age, BMI, alcohol consumption, cigarette smoking, and menopausal status were evaluated. The concentrations of $\alpha$-tocopherol, carotenoids and retinol in serum were measured simultaneously by reverse phase HPLC (multi-wavelength, gradient and computerized automatic system). Average serum levels of $\alpha$-tocopherol, \beta$-carotene and retinol were 10.1$\pm$0.41\mu$g/dl, 33.1$\pm$1.24\mu$g/dl, and 82.0$\pm$1.63\mu$g/dl for men and 11.1$\pm$0.74\mu$g/ml, 48.1$\pm$1.60\mu$g/dl and 64.5$\pm$1.96\mu$g/dl for women, respectively, Serum concentrations of $\alpha$-tocopheol \beta$-carotene, $\alpha$-carotene, cryptoxanthin and lycopene appeared to be higher in women than in men. The serum concentrations of zeaxanthin + lutein increased with the increase in age of men and those of $\alpha$-carotene and \beta$-carotene increased with the increase in age of women. For men, current smokers showed significantly lower serum concentrations of \beta$-carotene and $\alpha$-carotene than ex-smokers (p <0.05) . Current drinkers also showed significantly lower serum \beta$-carotene and zeaxanthin + lutein concentrations than ex-drinkers. For women, current smokers showed significantly love. serum concentrations of zeaxanthin+lutein and cryptoxanthin than ex-smokes (p<0.05). Men with BMI$\geq$24 showed significantly lower serum concentrations of \beta$-carotene, $\alpha$-carotene, lycopene and cryptoxanthin than men with BMI < 20. The mean concentrations of $\alpha$-tocopherol, \beta$-carotene, $\alpha$-carotene and lycopene far postmenopausal women were higher than those for premenopausal women (p<0.05). In conclusion, there were obvious differences in serum $\alpha$-tocopherol and carotenoids levels depending on gender, age, cigarette-smoking habits, alcohol consumption, BMI and menopausal status. further studies are required to establish the normal levels of these vitamins for children and the elderly and to elucidate their roles in different disease states.

• Nuclear Engineering and Technology
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• v.24 no.1
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• pp.75-85
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• 1992

The texture changes and their effect on the 0.2% yield strength of Zircaloy-4 sheet were examined after quenched from the ($\alpha$+$\beta$) phase temperature. When the prior ($\alpha$+$\beta$) gram size was slightly larger than that of the $\alpha$-annealed, the observed texture was similar to the $\alpha$-annealed texture having an ideal orientation of the (0001) basal pole at 30$^{\circ}$away from the normal direction toward the transverse direction. When the prior ($\alpha$+$\beta$) grain size was twice as large as that of the $\alpha$-annealed, the location of maximum basal pole intensity was distributed between the transverse and the rolling direction making an angle 15$^{\circ}$from the normal direction, and the observed texture became isotropic. It was found that the Kearns texture parameter, fr, in the rolling direction increased steadily, and fr in the transverse direction increased slightly, while fr in the the normal direction decreased with increasing heat treatment time. With a small increase in fr, the 0.2% yield strength increased drastically. The influence of texture was analyzed by deriving the Schmid orientation factors and the resolved shear stresses for the deformation systems. It was found that the large increase in the 0.2% yield strength was attributed mainly to the microstructural changes and partly to the texture changes by the ($\alpha$+$\beta$) heat treatment.

• Korean Journal of Microbiology
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• v.40 no.4
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• pp.328-333
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• 2004

The maximum productivity of ${\alpha}-galactosidase,$ capable of hydrolyzing completely ${\alpha}-D-l,6-galactopyranosyl$ linkages within oligomeric substrates such as melibiose, raffinose and stachyose to liberate galactose residue, was reached to 718 mU/ml in the culture filtrate of Bacillus licheniformis at death phase. The ${\alpha}-galactosidase$ was identified to show different efficiencies for hydrolyzing the ${\alpha}-galactooligosaccharides$ according to analysis of reaction products by both TLC and quantification of the liberated reducing sugars. The enzyme was active on ${\alpha}-galactooligosaccharides$ in the order of melibiose, raffinose, and stachyose. Though the hydrolyzing activity of enzyme was faintly inhibited by reaction products such as galactose, glucose and sucrose with amounts of five folds more than the added substrates (20 mM), the largest inhibition of enzyme activity was caused by galactose among the end products. Unknown compound, which migrated slower than melibiose on TLC, was detected during hydrolysis reaction of melibiose, suggesting that the ${\alpha}-galactosidase$ has a glycosyl transferase activity. In addition, the enzyme was able to hydrolyze efficiently raffinose and stachyose existed in the soluble extract of soybean meal.

• Proceedings of the Korean Vacuum Society Conference
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• 2009.08a
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• pp.214-214
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• 2009

• Bulletin of the Korean Chemical Society
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• v.26 no.6
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• pp.998-1000
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• 2005

• Proceedings of the PSK Conference
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• 2002.04a
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• pp.186.2-186.2
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• 2002

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.12
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• pp.277-284
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• 2013

The analysis of phase synchronization characteristics from EEG signals is important for the understanding of information processing functionality in the brain network. In this paper, wavelet transformation(WT), Hilbert tansformation (HT), complex demodulation (CD) methods having time localization characteristics were applied to real evoked potential data and noise added simulation data with center frequencies corresponding to EEG bands for the estimation performance analysis of phase offset, phase changing point, and interband crosstalk. The WT is the best both in ${\delta}$, ${\theta}$, and ${\alpha}$ band signal decomposition, and in analyzing phase synchronization performance. The CD can be efficiently used in changing point detection under tolerant noise condition because of its abrupt performance degradation over noise endurance level. From experimental observations, the WT is the most suitable in phase synchronization application of EEG signal, and the CD can be affordable in restricted application such as changing point detection for higher bands than ${\delta}$. Particularly, WT and CD can be used to detect the changing instant of brain function by indirectly estimating the phase changing point.

• Korean Journal of Materials Research
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• v.3 no.6
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• pp.661-667
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• 1993

Effects of $SiH_4//WF_6$(=R) ratio on the electrical properties of W films such as resistvity, contact resistance, junction leakage current in the selective W CVD technology for contact barrier metal were investigated with the emphasis on the role of $\alpha$-W Resistivity of W increases with increasing R, which is primarily due to the phase transformation from $\alpha$-W to , $\alpha$-W. $\alpha$-W found in the SiH4 reduced CVD W film is stabilized by Si incorporated into the W film rather than by oxygen. $\alpha$-W is found in the W film deposited on the Si substrate for high R, while $\alpha$-W is not found in the W film deposited on the TiN substrate even for high R. Also junction leakages increase with increasing R, which is caused not only by the vertical Si consumption but also the lateral Si consumption.