• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.189-189
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• 2012

Lead sulfide (PbS) nanocrystal quantum dots (NQDs) are promising materials for various optoelectronic devices, especially solar cells, because of their tunability of the optical band-gap controlled by adjusting the diameter of NQDs. PbS is a IV-VI semiconductor enabling infrared-absorption and it can be synthesized using solution process methods. A wide choice of the diameter of PbS NQDs is also a benefit to achieve the quantum confinement regime due to its large Bohr exciton radius (20 nm). To exploit these desirable properties, many research groups have intensively studied to apply for the photovoltaic devices. There are several essential requirements to fabricate the efficient NQDs-based solar cell. First of all, highly confined PbS QDs should be synthesized resulting in a narrow peak with a small full width-half maximum value at the first exciton transition observed in UV-Vis absorbance and photoluminescence spectra. In other words, the size-uniformity of NQDs ought to secure under 5%. Second, PbS NQDs should be assembled carefully in order to enhance the electronic coupling between adjacent NQDs by controlling the inter-QDs distance. Finally, appropriate structure for the photovoltaic device is the key issue to extract the photo-generated carriers from light-absorbing layer in solar cell. In this step, workfunction and Fermi energy difference could be precisely considered for Schottky and hetero junction device, respectively. In this presentation, we introduce the strategy to obtain high performance solar cell fabricated using PbS NQDs below the size of the Bohr radius. The PbS NQDs with various diameters were synthesized using methods established by Hines with a few modifications. PbS NQDs solids were assembled using layer-by-layer spin-coating method. Subsequent ligand-exchange was carried out using 1,2-ethanedithiol (EDT) to reduce inter-NQDs distance. Finally, Schottky junction solar cells were fabricated on ITO-coated glass and 150 nm-thick Al was deposited on the top of PbS NQDs solids as a top electrode using thermal evaporation technique. To evaluate the solar cell performance, current-voltage (I-V) measurement were performed under AM 1.5G solar spectrum at 1 sun intensity. As a result, we could achieve the power conversion efficiency of 3.33% at Schottky junction solar cell. This result indicates that high performance solar cell is successfully fabricated by optimizing the all steps as mentioned above in this work.

• Journal of dental hygiene science
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• v.12 no.2
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• pp.155-162
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• 2012

Somok, the heart wood of Caesalpinia sappan is used in traditional Chinese medicine. Adherence of S. mutans to the tooth surface can result in the formation of a dental plaque. This study was performed to investigate the antibacterial activity and bacterial adhesion of ethyl acetate extract from C. sappan against S. mutans ATCC 25175. The bacteria were cultured in brain heart infusion(BHI) broth, and then incubated under 5% $CO_2$ at $37^{\circ}C$ for 18~24 hours. The antimicrobial activity of the ethyl acetate extract of C. sappan was then examined using the paper disc methods and MIC. In addition, bacterial adherence to hydroxyapatite was also examined. The ethyl acetate extract was shown to produce inhibitory effects and had MIC values of 125 mg/ml against S. mutans ATCC 25175. The ethyl acetate extract inhibited adhesion of S. mutans to saliva coated-hydroxyapatite beads(S-HA). At 24 hr, the ethyl acetate extract significantly reduced the adherence of S. mutans to S-HA beads relative to the control. The isolated active substance was identified as brazilin($C_{16}H_{14}O_5$) by $^1H-NMR$ and $^{13}C-NMR$. Thus, the application of C. sappan can be considered a useful and practical method for the prevention of dental caries.

• Journal of Sensor Science and Technology
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• v.6 no.3
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• pp.214-220
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• 1997

A thin film optical waveguide sensor has been developed to measure and analyze quantitatively some inherent optical properties of biochemical substances. In this paper, two different kinds of thickness of thin film waveguide were prepared by RF sputtering of Corning-7059 glass(n = 1.588 at ${\lambda}=\;514nm$, Ar laser) on Pyrex glass substrates. We made a sensing membrane coated on the thin film waveguide with the poly(vinyl chloride-co-vinyl acetate-co-vinyl alcohol) (91 : 3 : 6) copolymer membrane based on $H^{+}$-selective chromoionophore and $K^{+}$-selective neutral ionophore and then proposed the thin film opptical waveguide ion sensor which can select a potassium ion. This sensor based ell the absorbance change by utilizing chromoionophore and neutral ionophore, which changes their absorption spectrum in the UV-vis region upon complexation of the corresponding ionic species, have been reported. The sensitivity dependence of the proposed sensor on interaction length, waveguide thickness, and content of a chromoionophore was investigated. This sensor has the measurement range of $10^{-6}M{\sim}1M$ for $K^{+}$ concentration and 90% response time of duration within 1 min. Also, our thin film optical waveguide sensor using the evanescent field was investigated as compared with conventional transmission sensor or optode sensor by the optical fiber. The sensitivity of thin-film waveguide $K^{+}$ sensor is higher than that of the conventional transmission sensor. The proposed sensor is expected to be useful to biochemical, medical, environmental inspection and so on.

• Journal of the Korean Society of Food Science and Nutrition
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• v.33 no.2
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• pp.381-385
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• 2004

This study was conducted to develop an HPLC method for determining pantothenic acid in fortified foods which has typically been determined by microbiological assay (MBA) according to AOAC and Korean Food Code approved methods. Pantothenic acid was determined by reversed-phase ion-pair HPLC using UV absorption (200 nm) after extraction with 20 mM potassium phosphate solution by sonication. The recovery of spiked samples and detection limit (LOD) by HPLC were 83.5∼109.6% and 0.5 ppm (mg/kg), respectively. The LOD of the microbiological assay (MBA) was much lower than that of HPLC. The concentrations of pantothenic acid analyzed in all tested samples (n=13) confirmed compliance with declared label claims. The range of recovery ratio by the HPLC method when compared to the microbiological assay was 91.9∼117.6%. There was not significant difference (p<0.01) between the HPLC and MBA methods and the equation of the regression curve was y=1.1428x-0.2269 (r=0.9842). This proposed HPLC method for determining pantothenic acid appears to be suitable for determining pantothenic acid concentrations above 0.25 mg/100 g in fortified foods.

• Journal of the Korean Chemical Society
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• v.45 no.6
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• pp.570-576
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• 2001

The europium doped yttrium oxybromide phosphors were synthesized by solid-state reaction method. The YOBr: $Eu^{3+}$ phosphor showed a strong and narrow red emission band at 621 nm and maximum emission intensity obtained when 0.05 mol Eu ions were doped. The red emission of $Eu^{3+}$ originated from $^5D_0$ ${\rightarrow}$ $^7F_2$electric dipole transition. In order to investigate on photoluminescence behavior, several experimental skills and numerical fittings are conducted to the YOBr: $Eu^{3+}$ phosphor. The emission spectrum was measured in the UV range and then decay curve of $^5D_0$ ${\rightarrow}$ $^7F_j$transitions was examined. The energy interaction type of YOBr: $Eu^{3+}$ phosphor was dipole-dipole interaction. In addition to the calculating by critical concentration, the critical distance ($R_0$) was calculated by decay curve fitting parameter from Inokuti-Hirayamas equation, and spectral overlap method. The critical distance was 17.03, 10.51 and 7.18$\AA$ for those methods, respectively. As considering systematic error of measurements, these values are within the same order, so that the above fitting methods are plausible and recommendable.

• The Korean Journal of Food And Nutrition
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• v.17 no.2
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• pp.156-162
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• 2004

This study was performed as a part of comparative biological studies of carotenoid pigment for the unutilized biological products. The content of total carotenoid in the integument of wild catfish were 0.27(${\pm}$0.7) mg％ and composed of 25.8％ zeaxanthin, 9.7％ diatoxanthin and 9.1 ％ cynthiaxanthin as major carotenoid. The content of total carotenoid in the integument of cultured catfish were 0.07(${\pm}$0.03) mg％ which is relatively lower compare to wild catfish and composed of 48.5％ lutein, 13.9％ zeaxanthin and 13.3％ isocryptoxanthin as major carotenoid. The total carotenoid contents of the slender catfish were 0.75(${\pm}$0.25) mg％ which is relatively higher compare to other species of catfishes. The carotenoids were composed of 24.5％ zeaxanthin, 24.1 ％ 7'8'-dihydro-${\beta}$-carotene-4-ol, 17.9％ 7'8'-dihydro-${\beta}$-carotene and 10.8％ 7'8'-dihydro-${\beta}$-carotene-3-01 as major carotenoid and 8.7％ diatoxanthin, 6.7％ cynthiaxanthin and 5.0％ lutein as minor carotenoid. Based on these data, as a comparative studies of carotenoid in integument of siluridae, parasiloxanthin and 7',8'-dihydroparasiloxanthin which are the characteristic carotenoid of catfish from biwa lake in Japan, Slender catfish contained more based on 7',8'-dihydro-${\beta}$-carotene while that of wild and cultured catfishes were not found, indicating that carotenoid pigment of slender catfish depend on their living conditions.

• Korean Journal of Remote Sensing
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• v.34 no.3
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• pp.481-494
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• 2018

The accurate radiative transfer model simulation is essential for an accurate ozone profile retrieval using optimal estimation from backscattered ultraviolet (BUV) measurement. The input parameters of the radiative transfer model are the main factors that determine the model accuracy. In particular, meteorological parameters such as temperature and surface pressure have a direct effect on simulating radiation spectrum as a component for calculating ozone absorption cross section and Rayleigh scattering. Hence, a sensitivity of UV ozone profile retrievals to these parameters has been investigated using radiative transfer model. The surface pressure shows an average error within 100 hPa in the daily / monthly climatological data based on the numerical weather prediction model, and the calculated ozone retrieval error is less than 0.2 DU for each layer. On the other hand, the temperature shows an error of 1-7K depending on the observation station and altitude for the same daily / monthly climatological data, and the calculated ozone retrieval error is about 4 DU for each layer. These results can help to understand the obtained vertical ozone information from satellite. In addition, they are expected to be used effectively in selecting the meteorological input data and establishing the system design direction in the process of applying the algorithm to satellite operation.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.345-346
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• 2013

InGaN material is being studied increasingly as a prospective material for solar cells. One of the merits for solar cell applications is that the band gap energy can be engineered from 0.7 eV for InN to 3.4 eV for GaN by varying of indium composition, which covers almost of solar spectrum from UV to IR. It is essential for better cell efficiency to improve not only the crystalline quality of the epitaxial layers but also fabrication of the solar cells. Fabrication includes transparent top electrodes and surface texturing which will improve the carrier extraction. Surface texturing is one of the most employed methods to enhance the extraction efficiency in LED fabrication and can be formed on a p-GaN surface, on an N-face of GaN, and even on an indium tin oxide (ITO) layer. Surface texturing method has also been adopted in InGaN-based solar cells and proved to enhance the efficiency. Since the texturing by direct etching of p-GaN, however, was known to induce the damage and result in degraded electrical properties, texturing has been studied widely on ITO layers. However, it is important to optimize the ITO thickness in Solar Cells applications since the reflectance is fluctuated by ITO thickness variation resulting in reduced light extraction at target wavelength. ITO texturing made by wet etching or dry etching was also revealed to increased series resistance in ITO film. In this work, we report a new way of texturing by deposition of thickness-optimized ITO films on ITO nano dots, which can further reduce the reflectance as well as electrical degradation originated from the ITO etching process.

• Applied Biological Chemistry
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• v.45 no.4
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• pp.212-217
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• 2002

We purified polyphenols from persimmon leaf and tested their biological activity. The 60% acetone extract was lyophilized and applied to test enzyme inhibition of glucosyltransferase and tyrosinase. GTase was 82.4% inhibited at $1.8{\times}10^{-1}$ mg/ml and tyrosinase 21.7% inhibited at 0.8 mg/ml. The acetone extract was fractionated into F-1, 2, 3, 4, 5 by Sephadex Q-50 gel filtration and the fraction-1 and 2 showed higher enzyme inhibition activity than the other fractions. To the Proteinase K treatment and autoclaving of the two fractions had no effect on the enzyme activity, but these results suggested that active fraction was not protein but phenol ring completed compounds. By Sephadex LH-20, MCI-gel and Bondapak $C_{18}$ column chromatographies, compouds 1, 2, 3 and 4 from F-1 fraction, compounds 5 and 6 from F-2 fraction and compounds 7 , 8 from F-3 fraction were purified and re-crystallized. The purified compounds was assumed to be condensed tannins of frame flavan-3-ol frame on the basis of color reagent reaction and to be a mixture of monomer, dimer and trimer according to TLC analysis.

• Microbiology and Biotechnology Letters
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• v.29 no.2
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• pp.84-89
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• 2001

Isolation and Characterization of Cathepsin B inhibitor Produced by Streptomyces luteogriseus KT-IO. Han, Kil~Hwan and Sang~Dal Kim*. Department of Applied Microbiology, Yeungnam Universit}/t Kyongsan 712749, Korea - The cathepsin B inhibitor produced by Streptomyces luteogriseus KT-IO was very stable in heat, acidic and alkaline conditions. The cathepsin B inhibitor was isolated from the extracted fraction of culture broth with butanol, methanol and chloroform subsequently, the inhibitor was purified with following several column chromatography sLlch as DEAE-Sephadex A-25, Sephadex G-15, silica gel 60, Sephadex LH-20, and preparative HPLC. The cathepsin B inhibitor showed positively to detective reaction of ninhydrine, 5% H2S04, iodine, but negatively to the reaction of Ehrlich's reagent, DNS, aniline. The molecular formular of cathepsin B inhibitor was elucidated by JR, lH and 13C-NMR, FAB mass and elemental analyzer. Consequently, it was identified as C4HlI04N6. The cathepsin B inhibitor had the mode of competitive inhibition with the reaction of cathepsin B.