• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.8
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• pp.461-465
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• 2016

n-type silicon shows the better tolerance towards metal impurities with a higher minority carrier lifetime compared to p-type silicon substrate. Due to better lifetime stability as compared to p-type during illumination made the photovoltaic community to switch toward n-type wafers for high efficiency silicon solar cells. We fabricated the front electrode of the n-type solar cell with AgAl paste. The electrodes characteristics of the AgAl paste depend on the contact junction depth that is closely related to the firing temperature. Metal contact depth with p+ emitter, with optimized depth is important as it influence the resistance. In this study, we optimize the firing condition for the effective formation of the metal depth by varying the firing condition. The firing was carried out at temperatures below $670^{\circ}C$ with low contact depth and high contact resistance. It was noted that the contact resistance was reduced with the increase of firing temperature. The contact resistance of $5.99m{\Omega}cm^2$ was shown for the optimum firing temperature of $865^{\circ}C$. Over $900^{\circ}C$, contact junction is bonded to the Si through the emitter, resulting the contact resistance to shunt. we obtained photovoltaic parameter such as fill factor of 76.68%, short-circuit current of $40.2mA/cm^2$, open-circuit voltage of 620 mV and convert efficiency of 19.11%.

• Corrosion Science and Technology
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• v.9 no.4
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• pp.147-152
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• 2010

Conventional paints for conversion coating applications in steel production derived mainly from water-based polymer dispersions containing several additives actually show good general performance, but suffer from poor scratch and abrasion resistance during use. The reason for this is because the relatively soft organic binder matrix dominates the mechanical surface properties. In order to maintain the high quality and decorative function of coated steel sheets, the mechanical performance of the surface needs to be improved significantly. In fact the wear resistance should be enhanced without affecting the optical appearance of the coatings by using appropriate nanoparticulate additives. In this direction, nanocomposite coating compositions (Nanomer$^{(R)}$) have been derived from water-based polymer dispersions with an increasing amount of surface-modified nanoparticles in aqueous dispersion in order to monitor the effect of degree of filling with rigid nanoparticles. The surface of nanoparticles has been modified for optimum compatibility with the polymer matrix in order to achieve homogeneous nanoparticle dispersion over the matrix. This approach has been extended in such a way that a more expanded hybrid network has been condensed on the nanoparticle surface by a hydrolytic condensation reaction in addition to the quasi-monolayer type small molecular surface modification. It was expected that this additional modification will lead to more intensive cross-linking in coating systems resulting in further improved scratch-resistance compared to simple addition of nanoparticles with quasi-monolayer surface modification. The resulting compositions have been coated on zinc-galvanized steel and cured. The wear resistance and the corrosion protection of the modified coating systems have been tested in dependence on the compositional change, the type of surface modification as well as the mixing conditions with different shear forces. It has been found out that for loading levels up to 50 wt.-% nanoparticles, the mechanical wear resistance remains almost unaffected compared to the unmodified resin. In addition, the corrosion resistance remained unaffected even after $180^{\circ}$ bending test showing that the flexibility of coating was not decreased by nanoparticle addition. Electron microscopy showed that the inorganic nanoparticles do not penetrate into the organic resin droplets during the mixing process but rather formed agglomerates outside the polymer droplet phase resulting in quite moderate cross linking while curing, because of viscosity. The proposed mechanisms of composite formation and cross linking could explain the poor effect regarding improvement of mechanical wear resistance and help to set up new synthesis strategies for improved nanocomposite morphologies, which should provide increased wear resistance.

• Journal of the Korean Chemical Society
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• v.27 no.4
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• pp.244-254
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• 1983

Single crystals of sodium thiosulfate $(Na_2S_2O_3) have been grown from the saturated solution by the evaporation method at the optimum condition. Radiation damages in the crystal by ${\gamma}$-irradiation of $20{\times}10^6$ Rontgen have given rise to paramagnetic centers. The anisotropic spectra of each paramagnetic species have been obtained with the X-band EPR spectrometer at room temperature. When an isotropic D.P.P.H. at g value of 2.0036 is based on. ESR Spectra of the single crystal are recorded for each rotation about the perpendicular a, b and c axis with intervals of $10^{\circ}$ from $0^{\circ}$to $180^{\circ}$ in order to find out the properties of the crystal for anglar variation of the anisotropic peaks. The g values are calculated from the line position between the anisotropic peaks and the isotropic peaks of D.P.P.H. and then principal g values and their direction cosines of the species is obtained by the diagonalization of 9 matrix elements of the corresponding g values. From the analysis of the characteristic principal g values and direction cosines for ${\gamma}$-irradiated $Na_2S_2O_3$ crystal, anisotropic peaks corresponding to $SO_2^+, SO_2^- $are identified and the existences of unidentified and unstable paramagnetic defects are verified.

• Journal of the Korean Chemical Society
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• v.46 no.4
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• pp.336-345
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• 2002

In this study, we have screened $Eu^{3+}$- and $Tb^{3+}$-activated candidate phosphors for PDP in the sys-tems of CaO-Gd$_2$O$_3$-Al$_2$O$_3$ by combinatorial chemistry and investigated the synthetic temperature, optimum com-position and luminescent properties about the candidate phosphors. To construct the emission intensity library by VUV PL, we have synthesized 210 different compositional samples using a polymerized-complex method. Good luminescent samples were identified by X-ray diffraction method. $Ca_$\alpha$$G$d_{0.95-$\alpha$-$\beta$}Al_$\beta$O_$\delta$$ : Eu(0.02< $\alpha$+$\beta$ <0.04) phos-phors screened as a red phosphor have good color purity than commercial phosphor. In the candidate phosphors of CaGdAl$_3O_7$ : Tb, Ca$Al_{12}O_{19}$ : Tb, Gd$_4$Al$_2O_9$ : Tb, and Gd$_3Al_5O_{12}$ : Tb CaGdAl$_3O_7$ : Tb, and Ca$Al_{12}O_{19}$ : Tb have shorter decay time than commercial phosphor.

• Clean Technology
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• v.18 no.2
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• pp.170-176
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• 2012

A series of acrylic copolymers containing perfluoroalkyl acrylate were synthesized by 2-step emulsion polymerization of variety of acrylate monomers (ethyl acrylate, butyl acrylate or methyl methacrylate) with perfluoroalkyl ethyl acrylate (PFA) and glycidyl methacrylate (GMA) monomers. This study focused on effects of monomer compositions (the kind of acrylate monomer, contents of PFA and GMA) and composition of surfactants [(sodium dodecyl sulphate/nonylphenol 10mole ethoxylate (NP-10)] and initiator content on the contact angles and surface free energy. It was found that the copolymer having an optimum composition (BA : 87 wt%, GMA : 8.7 wt% and PFA : 4.3 wt%) was shown to be quite surface active [surface free energy : 19.89 mN/m and contact angles : $103.5^{\circ}$ (water) and $78.7^{\circ}$ (methylene iodide)] in the solid state. This result suggests that the optimal copolymer containing fluorinated monomer synthesized in this study have high potential as a low surface energy material, which may have high oil- and water-repellent surface and have been proposed as acrylic syntan for leather and also as soil-resistant/oil and water repellent coating for textiles and wood etc.

• Food Science of Animal Resources
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• v.32 no.2
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• pp.220-227
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• 2012

The objective of this study was to investigate the influence of emulsion processing with various homogenization treatments on the physical properties of nanoparticles. For the manufacturing of nanoparticles, by taking the emulsion-diffusion method, various coating materials, such as gum arabic, hydroxyethyl starch, polycarprolactone, paraffin wax, ${\kappa}$-carrageenan and emulsifiers like Tween$^{(R)}$60, Tween$^{(R)}$80, monoglyceride and Pluronic$^{(R)}$F68, were added into the emulsion system. Furthermore, the various speeds (7,000 rpm to 10,000 rpm), and times (15 s to 60 s) of homogenization were treated during the emulsion- diffusion process. NEO II homomixer was the most effective homogenizer for making nanoparticles as 51 nm ($D_{10}$) and 26 nm ($D_{50}$). To manufacture smaller nanoparticles, by using NEO II homomixer, 10,000 rpm of agitation speed, polycaprolactone as coating material, and Pluronic$^{(R)}$F68 as an emulsifier were the optimum operating conditions and components. For the stability of nanoparticles for 7 days, $20^{\circ}C$ of storage temperature was appropriate to maintain the particle size. From these results, the type of homogenizer, homogenization speed, homogenization time and storage temperature could affect the particle size. Moreover, type of coating materials and emulsifier also influenced the size and stability of the nanoparticles.

• Applied Biological Chemistry
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• v.50 no.2
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• pp.87-94
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• 2007

A bacterium which has high enzymatic activities such as amylase, cellulase and protease was isolated from Korean traditional soybean food, doenjang. The isolated bacterium was identified to Bacillus subtilis HS25 by the test of morphological and biochemical properties according to Bergey's Manual of Systematic Bacteriology and API 50 CHL kit, and by the 16S rDNA sequence. The isolated B. subtilis HS25 had a potent antibacterial activity against food born causative or pathogenic bacteria. B. subtilis HS25 is endospore forming cell and contained flagella and abundant viscous material at the out layer of cell wall. It was rod type bacterium $(0.5{\sim}0.8{\times}3{\sim}5{\mu}m)$ having biochemical characteristics such as gram staining(+), catalase(+), oxidase(-) and hydrolysis of esculin(+). The optimal medium compositions for production of antibacterial substance in the B. subtilis HS25 were 1% of soluble starch, 0.5% of yeast extract, 0.5% of peptone and 0.05% of MgCl$_2{\cdot}6H_{2}O$. The optimum temperature and pH of the growth of the B. subtilis HS25 was 35$^{\circ}C$ and pH 7.5, respectively. The antibacterial activity was more high in neutral to a little alkaline pH (6.5-10.5) than in acidic pH. The optimal shaking speed to grow and to produce antibacterial substance of the B. subtilis HS25 was 160${\sim}$200 rpm. The optimal culture time for antibacterial activities of the bacterium were shown to be in the range of 12-36 hr.

• Microbiology and Biotechnology Letters
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• v.16 no.2
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• pp.92-97
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• 1988

Cysteinylglycinase was partially purified from Proteus mirabilis by consecutive procedure. The specific activity was increased about 16-fold to that of cell-free extract. The enzyme was found rather unstable on ammonium sulfate precipitation ann the precipitated enzyme protein became partially insoluble during dialysis. The precipitated enzyme was found to be solubilized by treatment of 4% Triton X-100 effectiviely, The optimum temperature and pH of the enzyme activity were 35$^{\circ}C$ and 7.3, respectively. After heat treatment of the enzyme at 5$0^{\circ}C$ for 30 min, it lost the activity to 70%. The enzyme was stable at pH 7.0-8.0. The molecular weight of the cysteinylglycinase was found to be about 190,000 by Sephadex G-150 gel filtration. The enzyme was activated by the addition of Mn$^{2+}$ and $Mg^{2+}$ ions. The maximal activation was obtained in preincubation with $Mg^{2+}$ ion for 30 min. The enzyme catalyzed the hydrolysis of various dipeptides and tripeptides. The Km and Vmax values for cysteinylglycine were 1.60 mM and 0.24 m unit/ mg, respectively.

• Microbiology and Biotechnology Letters
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• v.16 no.2
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• pp.119-125
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• 1988

$\beta$-Glucosidase of Cellulomonas sp. CS1-1 in cellular compartment was localized with cell-bound form while Avicelase and carboxymethylcellulase (CMCase) were appeared with extracellular enzyme. Cell growth on cellulose or CMC minimal broth was increased by glucose addition. $\beta$-Glucosidase production on cellobiose or CMC minimal broth was repressed by the addition of glucose. However, on CMC minimal broth, the enzyme production was specially stimulated by cellobiose addition. $\beta$-Glucosidase production was also induced by CMC, starcth and maltose compared with glycerol, arabinose, xylose and trehalose. From the above results, it was concluded that glucose effect on $\beta$-glucosidase biosynthesis showed catabolite repression, but enzyme production was induced by cellobiose, CMC, and starch, indicating that $\beta$-glucosidase is inducible enzyme. Yeast extract stimulated $\beta$-glucosidase production more than peptone and ammonium sulfate. $\beta$-Glucosidase activity was increased with 50mM MgCl$_2$in 10mM potassium phosphate buffer (pH 7.0). Optimum conditions for enzyme activities were pH 6.0 and 42$^{\circ}C$, Km value of $\beta$-glucosidase for p-nitrophenyl-$\beta$-D-glucosidase was 0.256mM and Ki for $\beta$-D(+)-glucose was 9.0mM.

• Journal of Microbiology and Biotechnology
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• v.23 no.4
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• pp.499-510
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• 2013

Among 25 isolates, Aspergillus fumigatus ASH (JX006238) was identified as a potent producer of homocysteine ${\gamma}$-lyase. The nutritional requirements to maximize the enzyme yield were optimized under submerged (SF) and solid-state fermentation (SSF) conditions, resulting in a 5.2- and 2.3-fold increase, respectively, after the last purification step. The enzyme exhibited a single homogenous band of 50 kDa on SDS-PAGE, along with an optimum pH of 7.8 and pH stability range of 6.5 to 7.8. It also showed a pI of 5.0, as detected by pH precipitation with no glycosyl residues. The highest enzyme activity was obtained at $37-40^{\circ}C$, with a $T_m$ value of $70.1^{\circ}C$. The enzyme showed clear catalytic and thermal stability below $40^{\circ}C$, with $T_{1/2}$ values of 18.1, 9.9, 5.9, 3.3, and 1.9 h at $30^{\circ}C$, $35^{\circ}C$, $40^{\circ}C$, $50^{\circ}C$, and $60^{\circ}C$, respectively. Additionally, the enzyme $K_r$ values were 0.002, 0.054, 0.097, 0.184, and 0.341 $S^{-1}$ at $30^{\circ}C$, $35^{\circ}C$, $40^{\circ}C$, $50^{\circ}C$, and $60^{\circ}C$, respectively. The enzyme displayed a strong affinity to homocysteine, followed by methionine and cysteine when compared with non-S amino acids, confirming its potency against homocysteinuria-related diseases, and as an anti-cardiovascular agent and a specific biosensor for homocysteinuria. The enzyme showed its maximum affinity for homocysteine ($K_m$ 2.46 mM, $K_{cat}\;1.39{\times}10^{-3}\;s^{-1}$), methionine ($K_m$ 4.1 mM, $K_{cat}\;0.97{\times}10^{-3}\;s^{-1}$), and cysteine ($K_m$ 4.9 m M, $K_{cat}\;0.77{\times}10^{-3}\;s^{-1}$). The enzyme was also strongly inhibited by hydroxylamine and DDT, confirming its pyridoxal 5'-phosphate (PLP) identity, yet not inhibited by EDTA. In vivo, using Swiss Albino mice, the enzyme showed no detectable negative effects on platelet aggregation, the RBC number, aspartate aminotransferase, alanine aminotransferase, or creatinine titer when compared with negative controls.