• Journal of the Korean Society of Industry Convergence
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• 제20권2호
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• pp.115-124
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• 2017

This paper aims to develop an SMPS topology for handling a high range of input voltages based on a DC-DC flyback converter circuit. For this purpose, 2 capacitors of the same specifications were serially connected on the input terminal side, with a flyback converter of the same circuit configuration serially connected to each of them, so as to achieve high input voltage and an effect of dividing input voltage. The serially connected flyback converters have the transformer turn ratio of 1:1, so that each coil is used for the winding of a single transformer, which is a characteristic of doubly-fed configuration and enables the correction of input capacitor voltage imbalance. In addition, a pulse transformer was designed and fabricated in a way that can achieve the isolation and noise robustness of the PWM output signal of the PWM controller that applies gate voltage to individual flyback converter switches. PSIM simulation was carried out to verify such a structure and confirm its feasibility, and a 100W class stack was fabricated and used to verify the feasibility of the proposed high voltage SMPS topology.

• KOREAN JOURNAL OF CROP SCIENCE
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• 제24권2호
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• pp.9-16
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• 1979

528 Korean land races of barley were examined for IS agronomic traits to determine if any preferential trait associations with early heading and winter hardiness existed in this collection. Eight traits were non-randomly associated with the 1977～'78 cold damage levels, and seven traits were non-randomly associated with heading date. No early heading, least-cold-damaged land race lines were found. However the least-cold-damaged class preferentially associated with mid-early heading land race lines. Ten traits were preferentially associated with the mid-early heading, least-cold-damaged class. The utilization of these associations should increase the probability that genes for winter hardiness will be preserved in the mid-early heading selections from this collection.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2009년도 춘계학술대회 논문집
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• pp.731-734
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• 2009

KIER has been developed a compact and highly efficient fuel processor which is one of the key component of the residential PEM fuel cells system. The fuel processor uses methane steam reforming to convert natural gas to a mixture of water, hydrogen, carbon dioxide, carbon monoxide and unreacted methane. Then carbon monoxide is converted to carbon dioxide in water-gas-shift reactor and preferential oxidation reactor. A start-up time of the fuel processor is about 1h and CO concentration among the final product is maintained less than 5 vol. ppm. To achieve high thermal efficiency of 80% on a LHV basis, an optimal thermal network was designed. Internal heat exchange of the fuel processor is so efficient that the temperature of the reformed gas and the flue gas at the exit of the fuel processor remains less than $100^{\circ}C$. A compact design considering a mixing and distribution of the feed was applied to reduce the reactor volume. The current volume of the fuel processor is 17L with insulation.

• Journal of IKEEE
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• 제19권1호
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• pp.110-117
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• 2015

In this paper, a novel trench power MOSFET using a Separate-W-gated technique MOSFET (SWFET) is proposed. Because the SWFET has a very low $Q_{GD}$ compared to other forms of technology, it can be applied to high-speed power systems. The results found that the SWFET-applied $Q_{GD}$ was decreased by 40% when compared to simply using the more conventional trench gate MOSFET. $C_{ISS}$ (input capacitance : $C_{GS}+C_{GD}$), $C_{OSS}$ (output capacitance : $C_{GD}+C_{DS}$) and $C_{RSS}$ (reverse recovery capacitance : $C_{GD}$) were improved by 24%, 40%, and 50%, respectively. The switching characteristics of the inverter circuit shows a 24.9% enhancement of reverse recovery time, and the power efficiency of the DC-DC buck converter increased by 14.2%. In addition, the proposed SWFET does not require additional process steps and There was no degradation in the electrical performance of the current-voltage and on-resistance.

• Progress in Superconductivity and Cryogenics
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• 제2권2호
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• pp.6-10
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• 2000

1.5 kA class HTS current leads for a SMES magnet, which are connected to a conventional vapor cooled copper leads, were designed. The HTS leads are composed of Bi-2223/Ag-Au tapes and a stainless stell tube. The estimated critical current of the lead is about 1.6 kA at 77.3 K and in a self magnetic field, and the heat input to the liquid helium from the cold end of the 35 cm lead is 0.4 W/lead. It has been made clear that the heat input decreases with increase of the lead length and decrease of the warm end temperature and Ag-Au/SC ratio.

• Proceedings of the Korean Vacuum Society Conference
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.245.1-245.1
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• 2013

Polydiphenylacetylene (PDPA) derivatives are a class of conjugated polymer that contain intramolecular excimer emission originating the intramolecular stack structure. In contrast with conventional conjugated polymer, the fluorescence property of PDPA significantly depends on the intramolecular stack structure. In this regard, herein, we investigated new fluorescence switching mechanism of conjugated polyelectrolyte (CPE) based on PDPA. The developed CPE showed relatively weak fluorescence emission in water, while the polymer exhibited a great fluorescence amplification behavior by electrostatic complex with proteins. In addition, the CPE is highly sensitive to binding with a little protein despite of turn-on type fluorescence response. We found that the fluorescence switching of the CPE closely relate to a perturbation of the intramolecular stack structure. The new fluorescence switching mechanism of the CPE is very useful for protein assays and discrimination and it also would be provide new sensing approaches as basic sensing mechanism.

• Journal of Aerospace System Engineering
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• 제11권4호
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• pp.30-35
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• 2017

In this work, a manufacturing and structural test of 1kW class horizontal axis wind turbine blade using natural-fiber composite was performed. The aerodynamic design of blade was performed after investigation on design requirement. The structural design load was investigated after aerodynamic design of blade. And also, structural design of blade was carried out. The structural design of blade was carried out using the simplified methods such as the netting rule and the rule of mixture applied to composite. The structural safety of the designed blade structure is investigated through the various load cases, stress, deformation and buckling analyses using the FEM method. Finally, the blade manufacturing and structural test using natural composite was carried out.

• Journal of Nutrition and Health
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• 제43권1호
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• pp.86-96
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• 2010

This study was conducted to investigate the effects of residence types ((1) parent house, (2) dormitory or boarding home, (3) boarding home w/o food) on the dietary habits and health status of college women (20-23 y). Overall, 46.1% of college women reported that they were economically middle class and spent 200,000-390,000 won. Additionally, 17.4% of college women considered themselves healthy, while 33.8% reported that they were not healthy. Furthermore, 32.0% of college women had experience to control their weight and 39.8% reported that they exercised to control their weight. There were no significant differences in the height and weight of the subjects according to residential type, but the amount of skeletal muscles mass ($21.0\;{\pm}\;2.6\;kg$) of the subjects that lived in dormitory or boarding home was significantly higher (p < 0.05) than that of women who lived at home. Additionally, 30.8% of students that lived in private residences, 25.0% of students that dwelled in dormitory or boarding homes and 27.7% of students that boarding home w/o food had three regular meals every day (p < 0.05). It has been reported that 18.3% of college students eat processed and instant foods due to their convenience. In the present study, intakes of energy, protein, fat, vitamin A, vitamin $B_1$, vitamin $B_2$, vitamin $B_6$, niacin, vitamin C, vitamin E and folic acid for the subjects who lived in dormitory or boarding homes was significantly higher than those of students who lived in private residences (p < 0.05). Additionally, intakes of iron, calcium, and zinc were lower in the subjects that boarding home w/o food (p < 0.05). Finally, the blood glucose level was $84.7\;{\pm}\;13.0\;mg/dL$, and differed significantly by residential types (p < 0.05); however, the average glucose levels of all subjects were within the normal range (90-110 mg/dL).

• Journal of the Korean Institute of Gas
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• 제25권1호
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• pp.40-47
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• 2021

In this study, hazards of decomposition and explosion for tert-butylperoxymaleate(TBPM), an organic peroxide, were evaluated by using various equipment to determine the cause of a fire explosion accident. As a result of DSC analysis, the instantaneous power density of TBPM was 26,401 kW/ml, and the NFPA reactive index(Nr) was classified as 4. And the positive value of EP(explosive propagation) and SS(shock sensitivity) showed that the TBPM had a potential hazard of explosion. From the experimental results, the shock sensitivity and friction sensitivity was rated as class 4 and 5, respectively. In the pressure vessel test, TBPM was ranked USA-PVT No.4 and evaluated as a self-reactive substance. In the combustion rate test, TBPM had the combustion rate of 167 mm/sec and was evaluated as the flammable solid classification 2 in GHS.

• Proceedings of the KSME Conference
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2026-2031
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• 2007

Hydrogen is receiving much research attention as an alternative substitute for hydrocarbon fuels these days due to its cleanliness and renewability. However, hydrogen should be used with caution because of its high propensity for leak and wide flammable range. This study deals with a situation that hydrogen leaks and then forms a flammable mixture inside 1kW class residential fuel cell. The residential fuel cell was modeled as a box-shaped chamber with vent openings at the top and bottom, filled with various components such as reformer, desulfurizer, fuel cell stack and humidifier. Computational fluid dynamics (CFD) was used to simulate the diffusion, buoyant flow and accumulation of leaked hydrogen in the modeled chamber. From the simulation, the risk region vulnerable to flame was identified and the methods to minimize such hazardous region was discussed. When the vent openings are 1% of the total surface, as the quantity of hydrogen leakage increases the risk regions increases accordingly. As the vent openings of the total surface increased from 1% to 2.3%, averaged hydrogen mole fraction is under 1% in the system.