• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.51-51
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• 2008

Carbon nanotubes (CNTs) have long been reported as an ideal material due to their excellent electrical conductivity and chemical and mechanical stability as well as their high aspect ratios for field emission devices. CNT emitters made by screen printing the organic binder-based CNT paste may act as a source to release gases inside a vacuum panel. These residual gases may cause a catastrophic damage by electrical arcing or ion bombardment to the vacuum microelectronic devices and may change their physical or electrical properties by adsorbing on the CNT emitter surface. In this study, we analyzed the composition of residual gases inside the vacuum-sealed panel by residual gas analyzer (RGA), investigating the effects of individual gases of different kinds at several pressures on the field emission characteristics of CNT emitters. The residual gases included $H_2$, CO, $CO_2$, $N_2$, $CH_4$, $H_2O$, $C_2H_6$, and Ar. Effect of residual gases on the field emission was studied by observing the variation of the pulse voltages with the duty ratio of3.3% to keep the constant emission current of $28{\mu}A$. Each gas species was introduced to a vacuum chamber up to three different pressures ($5\times10^{-7}$, $5\times10^{-6}$, and $5\times10^{-5}$ torr) each for 1 h while electron emission was continued. The three different pressure regions were separated by keeping a high vacuum of $\sim10^{-8}$ torr for a 1 h. The emission was terminated 6 h after the third gas exposure was completed. Field emission characteristics under residual gases will be discussed in terms of their adsorption and desorption on the surface of CNTs and the resultant change of work function.

• Journal of Environmental Science International
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• v.26 no.8
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• pp.903-911
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• 2017

The purpose of this study was to measure the bioactivity and antioxidant activity of peel from Gardenia jasminoides fructus Ellis (GJE) in Namhae, Korea, following some established methods. CM (Chloroform:Methanol, 2:1, v/v), 70% ethanol, and n-butanol extracts were collected. Flavonoid content and value as a functional food ingredient of GJE peel was investigated through assessing antioxidant [DPPH (1,1'-diphenyl-2-picrylhydrazyl), ABTS (2,2-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid)], and hydroxyl radical scavenging activities; superoxide dismutase like ability; ferrous ion-chelating capacity; and tannin content by solvent extraction. Solvent extract antioxidant activities significantly increased (p<0.05) at increasing concentrations (0.2, 0.4, 0.6 mg/mL). GJE peel extracts were less active than the positive control [ascorbic acid, BHA (butylated hydroxyanisole), and EDTA (ethylenediaminetetraacetic acid disodium salt dihydrate)]. Based on the results of this study, GJE peel could be used as a natural antioxidant source due to its high antioxidant activity and bioactive compound content.

• Fisheries and Aquatic Sciences
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• v.12 no.4
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• pp.249-257
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• 2009

This study is conducted to partially purify an antioxidative peptide in a two-step gelatin hydrolysate from Alaska pollock surimi refiner discharge, which was obtained by sequential treatment with Pronase E and Flavourzyme. The two-step gelatin hydrolysate was fractionated using chromatographic methods. Based on the same protein concentration of each fraction, the antioxidative activities (85.1-95.4%) of positive fractions fractionated by ion-exchange chromatography were higher than those (27.2-87.8%) from gel filtration. Then, further purification of the positive fractions was performed. Among them, the partially purified A1C1L2G1 and A1C1L2G2 fractions showed 96.2% and 85.1% inhibition, respectively, of linoleic acid peroxidation. The A1C1L2G1 fraction was composed of 15 kinds of amino acids and the predominant amino acids were proline, glycine and alanine. The results obtained in this study suggested that the fraction partially purified through chromatographic methods from the two-step gelatin hydrolysate of Alaska pollock surimi refiner discharge could be useful as a supplementary source for improving health functionality.

• Journal of Sensor Science and Technology
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• v.29 no.4
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• pp.255-260
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• 2020

In this study, we developed a method of improving the surface-enhanced Raman spectroscopy (SERS) response characteristics by depositing a nanoporous Ag metal thin film through cluster source sputtering after forming a pyramidal texture structure on the Si substrate surface. A reactive ion etching (RIE) system with a metal mesh inside the system was used to form a pyramidal texture structure on the Si surface without following a complicated photolithography process, unlike in case of the conventional RIE system. The size of the texture structure increased with the RIE process time. However, after a process time of 60 min, the size of the structure did not increase but tended to saturate. When the RF power increased from 200 to 250 W, the size of the pyramidal texture structure increased from 0.45 to 0.8 ㎛. The SERS response characteristics were measured by depositing approximately 1.5 ㎛ of nanoporous Ag metal thin film through cluster sputtering on the formed texture structure by varying the RIE process conditions. The Raman signal strength of the nanoporous Ag metal thin film deposited on the Si substrate with the texture structure was higher than that deposited on the general silicon substrate by up to 19%. The Raman response characteristics were influenced by the pyramid size and the number of pyramids per unit area but appeared to be influenced more by the number of pyramids per unit area. Therefore, further studies are required in this regard.

• Analytical Science and Technology
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• v.15 no.3
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• pp.229-235
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• 2002

Plasma source ion implantation (PSII) technique was utilized to improve the wettability of polystyrene surfaces. It is well known that treated surfaces undergo aging, leading to hydrophobic recovery with time. We investigated the aging effect of polystyrene thin film on the various molecular weights. Polystyrenes with several molecular weights ($M_w$ = 760, 2430, 31600, 115700, 280000, 903600) were treated in different experimental conditions including gas species and pulse energy, and their hydrophilicity was measured by contact angle goniometer. To study wettability decay as a function of the molecular weight, PSII-treated samples were aged at different temperatures. Hydrophobic recovery of high molecular weight polystyrene was much slower than that of low molecular weight, even at high temperatures. The methods used to characterize treated surfaces were water contact angle measurement, TOF-SIMS, XPS, SEM and AFM.

• The Korean Journal of Mycology
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• v.25 no.4 s.83
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• pp.297-304
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• 1997

Effects of cultural conditions on the production of xylanase by Tremella fuciformis, symbiotic fungi and mixed fungi were investigated. The optimum carbon source for high production of xylanase by T. fuciformis, symbiotic fungi and mixed fungi was xylose. The optimum nitrogen source for both T. fuciformis and symbiotic fungi was $KNO_3$, whereas mixed fungi was $(NH_4)_2SO_4$. The optimum culture period for high production of xylanase was 5 days for both T. fuciformis and mixed fungi, and 6 days for symbiotic fungi, respectively. The optimum temperature for T. fuciformis and symbiotic fungi was $40^{\circ}C$, and the corresponding value for mixed fungi was $45^{\circ}C$. Xylanase activity was high at pH 6 for T. fuciformis and symbiotic fungi, and pH 7 for mixed fungi. Except $Hg^{2+}$ and $Pb^{2+}$, metal ions in T. fuciformis inhibited the activity of xylanase, and, thermal stability of xylanase in T. fuciformis, symbiotic fungi and mixed fungi maintained 80% of activity until $50^{\circ}C$. The Michaelis constant (Km) of xylan was $6.25{\times}10^{-5}\;M$ in T. fuciformis, $5.6{\times}10^{-2}\;M$ in symbiotic fungi, $5.2{\times}10^{-2}\;M$ in mixed fungi.

• Journal of radiological science and technology
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• v.32 no.4
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• pp.393-399
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• 2009

In this study, we measured the dose distribution of scattered ray in X-ray radiography room using an ion chamber and examined the dependency of scattered ray content on the scattered ray source and exposure condition. To study the factors of scattered ray occurrence in the acryl phantom, we measured the change in the scatted ray content according to the X-ray tube voltage (40~140 kV) and the field size ($10{\times}10\;cm^2$, $20{\times}20\;cm^2$, $35{\times}35\;cm^2$). For the $35{\times}35\;cm^2$ field size, the side-scattering rate ranged from 3.1% to 14.5%. The scattered ray contributions of the phantom, collimator, X-ray tube and wall were also measured. The scattered ray contribution of the phantom was higher than 95.4% for the entire tube voltage, and those of the collimator, X-ray tube and wall were 2.6%, 1.3% and 0.7%, respectively.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.2
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• pp.140-147
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• 2017

This paper describes the design and implementation of previously developed PMU (Power Monitoring Unit) for LiPB (Lithium-ion Polymer Battery) that is electric propulsion used as unmanned aerial vehicle's power source. Improved PMU provides stable voltage and current to various sensors and elctric motors necessary during flight. Voltage and current monitoring function that is measured by improved PMU more precisely be enhanced and the monitoring channel and temperature sensor is added. To verify the improved performance of the equipment, it is integrated to electric propulsion system of unmanned aerial vehicle. PMU is calibrated through the ground test. And PMU's performance is checked through the flight test.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.76-77
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• 2005

Single crystal $CuAlSe_2$ layers were grown on thoroughly etched semi-insulating GaAs(100) substrate at 410$^{\circ}C$ with hot wall epitaxy (HWE) system by evaporating $CuAlSe_2$ source at $680^{\circ}C$. The crystalline structure of the single crystal thin films was investigated by the photoluminescence(PL) and double crystal X-ray diffraction (DCXO). The temperature dependence of the energy band gap of the $CuAlSe_2$ obtained from the absorpt ion spectra was wel1 described by the Varshni's relation, $E_g$(T) = 2.8382 eV - ($8.86\times10^{-4}$ eV/H)$T_2$/(T + 155K). After the as-grown single crystal $CuAlSe_2$ thin films were annealed in Cu-, Se-, and Al-atmospheres, the origin of point defects of single crystal $CuAlSe_2$ thin films has been investigated by PL at 10 K. The native defects of $V_{cd}$, $V_{se}$, $Cd_{int}$, and $Se_{int}$ obtained by PL measurements were classified as donors or acceptors. And we concluded that the heat-treatment in the Cu-atmosphere converted single crystal $CuAlSe_2$ thin films to an optical n-type. Also. we confirmed that hi in $CuAlSe_2$/GaAs did not form the native defects because Al in single crystal $CuAlSe_2$ thin films existed in the form of stable bonds.

• Journal of Environmental Science International
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• v.27 no.7
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• pp.543-554
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• 2018

From November 2013 to December 2016, ambient fine particulate matter ($PM_{2.5}$) was sampled in the downtown area of Jeju City, South Korea, which has seen rapid urbanization. The atmospheric concentrations of elements were measured in the $PM_{2.5}$ samples. This study focused on Cd, Cr, Cu, Mn, Ni, Pb, As, Sb, Sn, V, and Zn. The concentrations of Al, Na, K, Fe, Ca, Mg, Sr, and La were also obtained for reference. The objectives of this study were to examine the contributions of these elements to $PM_{2.5}$ concentrations in downtown Jeju City, and to investigate the inter-element relationships and the elemental sources by using enrichment factors and principal components analysis (PCA). A composition analysis showed that the 19 elements constituted 6.65 % of the $PM_{2.5}$ mass, and Na, K, Al, Fe, Ca, Mg, and Zn constituted 98 % of the total ion mass. Seasonal trend analysis for the sampling period indicated that the concentrations of the elements increased from November to April. However, no substantial seasonal variations were found in the concentrations of the elements. The composition ratios of some elements (Cu/Zn, Cu/Cd, Cu/Pb, V/Ni, and V/La) were found to be out of range when compared to the literature from other urban areas. The ratios between the elements and the PCA results showed that local contaminant sources in Jeju City rarely influence the composition of $PM_{2.5}$. This suggests that the major sources of $PM_{2.5}$ in Jeju City may include long-range transport of fine particulate matter produced in other areas.