• Transactions of the Korean hydrogen and new energy society
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• v.26 no.2
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• pp.136-147
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• 2015

Dead-ended operation of Proton Exchange Membrane Fuel Cell(PEMFC) provides the simplification of fuel cell systems to reduce fuel consumption and weight of fuel cell. However, the water accumulation within the channel prohibits a uniform supply of fuel. Optimization of the purge strategy is required to increase the fuel cell efficiency since fuel and water are removed during the purge process. In this study, we investigated the average voltage output which depends on two interrelated conditions, namely, the supply gas pressure, purging valve open time. In addition, flow visualization was performed to better understand the water build-up on the anode side and cathode side of PEMFC in terms of a variety of the current density. We analyzed the correlation between the purge condition and water flooding.

• BMB Reports
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• v.30 no.4
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• pp.274-279
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• 1997

Acetolactate synthase (ALS) catalyzes the first common step in the biosynthesis of branchedchain amino acids, valine, leucine, and isoleucine. ALS is the target site for several structually diverse classes of herbicides including sulfonylureas, imidazolinones. and triazolopyrimidines. We have purified ALS from etiolated barley shoots to homogeneity. The five major purification steps are ammonium sulfate fractionation, DEAE anion exchange, hydroxylapatite, Bio-Gel A gel filtration, and low pressure Mono-Q chrornatoqraphy. Approximately 170-fold purification was achieved and the yield was 0.45% of initial activity in the crude extract. Both SDS-PAGE and Western blot analysis showed a single polypeptide of ALS with an apparent molecular mass of 64 kDa. The result of nondenaturing gel electrophoresis with activity staining indicated that the molecular mass of its native form is approximately 225 to 250 kDa. The values of $K_m$ for pyruvate. pl. and optimum pH of ALS were determined to be 2.0 mM, 5.2. and 7.0. respectively Feedback inhibition studies showed that ALS is more susceptible to leucine than valine. And $IC_{50}$ value of Cadre, a class of irnidazolinones, is about $1.5\mu{M}$ for ALS.

• Biomolecules & Therapeutics
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• v.4 no.1
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• pp.46-50
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• 1996

Inhibition of the growth of human cancer cells by proteins secreted from 373-L1 cells was investigated in the present study. The growth of human cancer cells was inhibited by co-culture with 373-L1 cells under 10% FBS and DME, DME, GIT and serumless medium, respectively. The conditioned medium of cultured 373-L1 cells under serumless medium was concentrated 100-fold through an ultrafiltration cell with a 10,000 molecular weight cutoff at 4$^{\circ}C$ under positive pressure using nitrogen(373-L1 EM). 373-L1 EM inhibited the growth of HeLa, Hep G 2, KHOS-Np, A43l and MCF-7 cells. 3T3-L1 EM was purified with FPLC, DEAE-ion exchange chromatography and phenyl-sepharose chromatography. The major protein of 373-L1 EM has a molecular weight of 66,000-68,000 in SDS-PAGE analysis. The results suggest that the inhibitory activity of 373-L1 EM appears to be due to some protein(m.w.66,000-68,000) secreted by 373-L1 cells.

• Transactions of the Korean hydrogen and new energy society
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• v.1 no.1
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• pp.1-8
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• 1989

The hydriding kinetic mechanism and the change of the hydriding reaction rate of $MmNi_{4.5}Al_{0.5}$ during the thermally induced hydrogen absorption-desorption cycling are investigated. Comparison of the reaction rate data which are obtained by the pressure sweep method with the theoretical rate equations suggests that the hydriding rate controlling step has changed from the dissociative chemisorption of hydrogen molecules at the surface to the hydrogen diffusion through the hydride phase with the increase of the hydriding fraction. These hydriding kinetic mechanism is not changed during the cycling. However, the intrinsic hydriding reaction rate of $MmNi_{4.5}Al_{0.5}$ after 5500 cycles increases significantly comparing with the activated one. It is suggested that the change of the hydriding kinetic behavior due to intrinsic degradation of $MmNi_{4.5}Al_{0.5}$ can be interpreted as follows ; the formation of nickel cluster at the surface of the sample and the host metal atom exchange in bulk by thermal cycling.

• Membrane and Water Treatment
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• v.4 no.2
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• pp.109-126
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• 2013

Surface modification by low-pressure ammonia ($NH_3$) plasma on commercial thin-film composite (TFC) membranes was investigated in this study. Surface hydrophilicity, total surface free energy, ion exchange capacity (IEC) and zeta (${\zeta}$)-potentials were determined for the TFC membranes. Qualitative and quantitative analyses of the membrane surface chemistry were conducted by attenuated total reflectance Fourier transform infrared (ATR FT-IR) spectroscopy. Results showed that the $NH_3$ plasma treatment increased the surface hydrophilicity, in particular at a plasma treatment time longer than 5 min at 50 W of plasma power. Total surface free energy was influenced by the basic polar components introduced by the $NH_3$ plasma, and isoelectric point (IEP) was shifted to higher pH region after the modification. A ten (10) min $NH_3$ plasma treatment at 90 W was found to be adequate for the TFC membrane modification, resulting in a membrane with better characteristics than the TFC membranes without the modification for water treatment. The thin-film chemistry (i.e., fully-aromatic and semi-aromatic nature in the interfacial polymerization) influenced the initial stage of plasma modification.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.06a
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• pp.1083-1090
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• 2005

Repeated ribs are used on heat exchange surfaces to promote turbulence and enhance convective heat transfer. Applications include fuel rods of gas-cooled nuclear reactors, inside cavities of turbine blades, and internal surfaces pipes used in heat exchangers. Despite the great number of literature papers, only few experimental data concern detailed distributions of friction factors and heat transfer coefficients in square channels varying the number of rough walls. This issue is tackled by investigating effects of different number of ribbed walls on heat transfer and friction characteristics in square channel. The rough wall have a 45$^{\circ}$ inclined square rib. Uniform heat flux is maintained on whole inner heat transfer channel area. The heat transfer coefficient and friction factor values increase with increasing the number of rough walls.

• Journal of Power System Engineering
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• v.9 no.1
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• pp.5-13
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• 2005

Acoustic emission(AE) is defined as the transient elastic waves thar are generated by the rapid release of energy. The advantage of AE is that very early crack growth can be detected well before a highly stressed component may fail. At present, an exact diagnosis is the most reliable means for determining the soundness of structures during power plant operations. AE monitoring has been applied successfully in power plants to determine mechanical problems, pressure vessel integrity and external valves leaks, vacuum leaks, the onset of cavitation in pumps and valves, the presence of flow(or no flow) in piping and heat exchange equipment, etc. Acoustic emission(AE) technology has recently strengthened its application base, and practitioners' understanding of the technique's fundamentals. This paper introduces the methods of a survey and assessment on AE monitoring applications in nuclear, fossil and hydraulic power plant. The main objective of this paper was to obtain information on various applications of AE technology in power plant.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.7 no.1
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• pp.110-115
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• 2004

This experiment was conducted to investigate the effect of light intensities on the growth responses, carbohydrate contents and the characteristics of leaf gas exchange in Miscanthus sinensis and Pennisetum purpurascens. The plant height and leaf length were increased to about 30% in the sun. However, those were reduced severely in the shade, and leaf necrosis was also observed. The representative growth index and the dry weight of 2 species were 50% higher than shade and the rate was reduced according to the decrease of light intensities. Total carbohydrate contents showed very similar changes to that of dry weight. However, any notable influences were observed at above the light intensities of 250~500${\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$ in the half shade. The size of spikes and the earliest spiking appeared in the sun and the spike color was decolorized as decreased in light intensities, irrespective of species. Photosynthetic rate of 2 species was 2 times higher in the sun than those in the shade, and it showed the typical photoresponses of sun plant. Stomatal conductances and intercelluar $CO_2$ concetration showed similar changes to that of photosynthetic rate. On the contrary, vapor pressure deficit was increased more in the shade than in the sun.

• Journal of the Korean Wood Science and Technology
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• v.24 no.2
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• pp.20-25
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• 1996

Wood chips of oak(Quercus mongolica) and larch(Larix leptolepis) were exploded with the optimum condition. Main components of exploded wood were separated with hot hot water and methanol. The hemicelluloses were purified from hot water extracts and alditol complexs were prepared from purified hemicellulose. And also, cellulose nitrate was prepared from extractive residue and characterized. The results can be summarized as follows. 1. Amounts of carbohydrate(72~79%) in the crude hemicellulose of larch wood was more than those of oak wood(55~66%). 2. The crude hemicelluloses were mainly composed of oligosaccharides in oak wood but those in larch wood contained about 50% monosaccharides. 3. Decolorization of hemicellulose was successful with activated charcoal and ion-exchange resin treatment. The alditol yields were 56.3~82.9%. 4. The degree of substitution(D.S.) of cellulose nitrate was 1.95~2.87 and it showed a good acetone solubility.

• Economic and Environmental Geology
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• v.32 no.1
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• pp.101-111
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• 1999

Sedimentary organic matter, exposed to continental surficial environment, reacts with oxygen supplied from the atmosphee and forms carbon-containing oxidation products. Knowledge of the rate and mechanisms of sedimentary organic matter weathering is important because it is one of the major controls on atmospheric oxygen level through geologic time. Under the abiological conditions, the oxidation rate of coal organic matter by molecular oxygen is enhanced by the increase of oxygen concentration and temperature. At ambient temperature and pressure, aqueous coal oxidation results in the formation of dissolved $CO_2$ dissolved organic carbon and solid oxidation products which are all quantitatively significant reaction products. The effects of pH, ultraviolet light, and microbial activity on the weathering of sedimentary organic matter are poorly contrained. Based on the results of geochmical and environmental studies, it is believed that the photochemical reaction should play an important role in the decomposition and oxidation of sedimentary organic matter removed from the weathering profile. At higher pH conditions, the production rate of DOC can be accelerated due to base catalysis. These high molecular weight oranic matter can react with man-made pollutants such as heavy metal ions via adsorption/desorption or ion exchange reactions. The effect of microbial activity on the oxidative weathering of sedimentary organic matter is poorly understood and remains to be studied.