• Journal of the Korean Institute of Gas
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• v.12 no.4
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• pp.52-57
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• 2008

This paper studies on the wear corrosion behavior of induction hardening high strength cast iron in the acidic environments. In a variety of pH solutions, wear corrosion behavior of GC 300 with a variety of contact pressures was investigated, and corrosion wear behavior after immersion test was considered. Also, electrochemical polarization test for GC 300 was carried out in various pH solutions. The main results are as following: In the strong acidic environment, wear corrosion rate of GC 300 appears highly and in the neutral environment is stable. Also, graphitic corrosion in the strong acidic environment occurs. The corrosion current density of GC 300 becomes high in a order of pH 1 > pH 2 > pH 4 > pH 6.5.

• Journal of Radiation Protection and Research
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• v.14 no.2
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• pp.37-44
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• 1989

An improved water chemistry technique was studied to reduce radioactivity build-up in reactor coolant system. The technique is convering the current coordinated lithium-boron chemistry regime to the elevated lithium chemistry regime in order to maintain high pH. Correlations between reactor coolant pH and radioactivity build-up were analized by using pH data from domestic PWRs. Consequently, it was founded that high pH chemistry was moer effective for radioactivity build-up reduction than current chemistry regime. This fact had revealed that much portion of reactor coolant corrosion products were nickel ferrite rather than magnetite, and that pH value ranging 7.0-7.4 was appropriate for high-pH chemistry operation.

• Journal of Microbiology and Biotechnology
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• v.12 no.1
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• pp.1-7
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• 2002

The effects of DO and pH on the mass production of pullulan with high molecular weight and the morphology of A. pullulans ATCC 42023 were evaluated. A. pullulans showed a maximum production of pullulan (11.98 g/l) when the initial pH of the culture broth was 6.5 in a shake-flask culture. In a batch culture, the mixture of a yeast-like and mycelial cell forms was found at a pH of 4.5, and the maximum production of pullulan (13.31 g/l) was obtained. However, a high proportion of high molecular weight pullulan (M.W.>2,000,000) was produced at a pH of 6.5, with a yeast-like morphology. The maximum pullulan production yield ($51\%$) was obtained at a pH noncontrol (initial pH 6.5) and DO control (above $50\%$) condition. Pullulan degrading enzyme was activated when the pH of the broth was lower than 5.0 and the portion of low molecular weight pullulan was increased. The formation of a black pigment was observed at an initial stationary phase, at 40 h of fermentation. Therefore, the fermentation should be carried out in a pH noncontrol (initial pH of 6.5) and DO control (above $50\%$) condition, and should be harvested before reaching the stationary phase (around 40 h) for the production of high molecular weight pullulan.

• Journal of Animal Science and Technology
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• v.52 no.2
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• pp.111-116
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• 2010

This study was conducted to determine the effects of different feeding levels on the number of fecal lactic acid-producing bacteria and fecal pH in horses. In Exp. 1, 6 female cross-bred horses ($332.4{\pm}50.4\;kg$, 5 year old) were fed 2% hay or 2% concentrates of BW for 30 d, and the number of fecal Lactobacilli and Streptococci was measured. For Exp. 2, 5 castrated Thoroughbred ($474.5{\pm}64.6kg$, 4 year old) and 5 female cross-bred horses ($343.6{\pm}56.3\;kg$, 5 year old) were allotted to high- or low-concentrates diets (5 levels) for 30 d in a $5{\times}5$ Latin square design, and the fecal pH was assessed. In Exp. 3, 3 castrated Thoroughbred ($482.6{\pm}53.3\;kg$, 4 year old) were fed high- or low-alfalfa hay diets (3 levels) for 30 d in a $3{\times}3$ Latin square design, and the fecal pH was measured. Feeding high-concentrates diets increased (P<0.05) the number of fecal lactic acid-producing bacteria (Lactobacilli and Streptococci) and decreased (P<0.01) the fecal pH. Feeding alfalfa hay with high-concentrates diet (2% alfalfa hay + 1% concentrates of BW) decreased (P<0.01) the fecal pH. These results showed that feeding high-concentrates diets increased lactic acid-producing bacteria in the large intestine and decreased the intestinal or fecal pH causing colic or laminitis, indicating that the proper fiber/concentrates (1:1) should be maintained in horses.

• Macromolecular Research
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• v.11 no.3
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• pp.189-193
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• 2003

pH- and temperature-sensitive bifunctional hydrogels composed of N-isopropylacrylamide (NiPAAm) and a sulfadimethoxine monomer (SDM) derived from sulfadimethoxine were prepared. These hydrogels exhibit simultaneous pH- and temperature-induced volume-phase transitions. The pH-induced volume-phase transition behavior is produced by the ionization/deionization of SDM and is very sharp. In the high pH region, the ionization of SDM induces swelling of the hydrogels. In the low pH region, the deionization of SDM induces deswelling of the hydrogels. The temperature-induced volume-phase transition behavior of the bifunctional hydrogels exhibits negative thermosensitivity because of the NiPAAm component. The hydrogels swell even at low pH as the temperature decreases. The hydrogels swell at low temperature and high pH, and deswell at high temperature and low pH. The volume of the hydrogels dependl on the balance of the swelling and deswelling produced by the two competing stimuli, pH and temperature.

• Bulletin of the Korean Chemical Society
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• v.9 no.1
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• pp.40-44
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• 1988

The pH dependence studies of Raman spectra are reported for water-soluble free-base, Zn, Co and Cu tetrakis (4-sulfonatophenyl) porphine in pH 4, pH 7 and pH 13.9 aqueous solution. For free base porphine, the substantial differences are found in absorption and Raman spectra between pH 4 and pH 7 or pH 10 aqueous solutions due to the protonation at low pH. For Zn and Co porphyrins, the hydrolysis equilibrium constants are obtained by spectrophotometric titration experiments. The consistent shifts in Raman frequencies are found at high pH due to the hydrolysis. For Cu porphyrins, instead of hydrolysis the aggregation effect is detected at high pH through the absorption and Raman studies.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.447-447
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• 2012

최근 생물전자공학에서 의료 산업 환경 등 많은 분야에 응용 가능한 바이오센서의 연구가 활발해지고 있다. 그 중 의료 분야에서, 수소이온 ($H^+$)의 농도 감지는 인간의 질병을 예측하는데 중요한 지표가 되며 이러한 수소이온 ($H^+$) 농도의 변화를 실시간으로 감지하기 위해 반도체를 기반으로 한 다양한 pH 센서가 제안되었다. Ion sensitive field effect transistor (ISFET), electrolyte-insulator-semiconductor (EIS)는 대표적인 반도체 pH센서로, 작은 소자 크기, 견고한 구조, 빠른 응답속도와 CMOS 공정과의 호환성이 좋다는 장점이 있다. 특히, EIS는 제조공정이 간단하고 감지막의 감지 특성 평가가 용이하기 때문에 지속적으로 연구되고 있는 pH 센서이다. 센서의 감지 특성을 평가함에 있어 감지막의 감지감도와 안정성이 우수해야 하며 이를 위해 high-k 물질이 감지막으로 사용되고 있다. 추가적으로 high-k 물질은 기존의 $SiO_2$와 $Si_3N_4$를 대신하여 높은 유전상수로 인한 고성능, 고감도 센서제작을 가능케 한다. 본 연구에서는, high-k 물질인 $HfO_2$, $Ta_2O_5$, $ZrO_2$, $Al_2O_3$를 각각 $SiO_2$ 완충막에 적층한 이단 감지막을 제작하였고, 그 특성을 기존의 $SiO_2$, $Si_3N_4$ 감지막의 감지특성과 비교하였다. pH 감지 특성을 평가해 본 결과, 기존의 $SiO_2$, $Si_3N_4$ 감지막과 비교했을 때 high-k 물질의 감지막을 갖는 EIS pH 센서에서 감지감도와 안정성 모두 우수하게 나타났다. 특히, high-k 물질 중 $HfO_2$에서 감지감도가 다소 크게 평가되었으나, 화학적 용액에 대한 안정성은 떨어졌다. 반면에 $Al_2O_3$과 $Ta_2O_5$은 화학용액에 대한 안정성 측면에서 최적의 특성을 보임을 확인하였다. 결론적으로, high-k 물질에 대한 전반적인 평가를 통하여 높은 pH 감지감도뿐만 아니라 우수한 안정성의 EIS pH 센서를 제작 할 수 있었다.

• 한국생물공학회:학술대회논문집
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• 2001.11a
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• pp.731-734
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• 2001

An efficient fermentation strategy for the high level production of ultra-high-molecular weight poly(3-hdyroxybutyrate) (PHB) was developed. Although the cell and PHA concentrations obtained by flask cultures at different initial pH (6.0 or 6.9) were almost same level, the molecular mass of PHB produced were quite different along with the initial pH. When a recombinant Escherichia coli XL1-Blue harboring pJC2 containing the Alcaligenes latus PHB biosynthesis genes was cultivated in flask culture (pH 6.0), the PHB having a very high molecular weight of 22 MDa could be produced while only below 1 MDa at initial pH 6.9. The ultra-high-molecular weight PHB could be synthesized to high concentration of 89.8 g/L resulting in the PHB productivity of 2.07 g/L-h by simple fed-batch culture. In this study, we report that PHB having various molecular mass can be produced by employing metabolically engineered E. coli strains harboring the plasmids of different copy numbers containing the A. latus phbCAB genes.

• Bulletin of the Korean Chemical Society
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• v.29 no.8
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• pp.1510-1518
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• 2008

Results of intrinsic and extrinsic fluorescence studies on choline oxidase revealed that the enzyme at high alkaline pH values has more accessible hydrophobic patches relative to acidic pH. Fluorescence quenching studies with acrylamide confirm these changes. The quenching constants were also determined at different pH(s) by using the Stern-Volmer equation. CD studies showed that at higher pH a transition from $\alpha$-helix to $\beta$- structure was appeared while at lower pH the content of $\alpha$-helix structure was increased. Furthermore, analysis of the spectral data using chemometric method gave evidence for existence of intermediate components at very high pH(s). Results of thermal denaturation evaluated that the enzyme has the most instability at higher pH(s). Altogether low and high pH values caused significant alteration on secondary and tertiary structures of choline oxidase via inducing of an intermediate.

• Bulletin of the Korean Chemical Society
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• v.31 no.10
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• pp.2939-2942
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• 2010

A new high-temperature pH sensor has been successfully developed by reforming the internal reference systems of the pH sensors based on oxygen-ion conducting ceramic membrane. The conventional internal reference system, a mixture of Ni and NiO, has been replaced with partially oxidized Ni powders, where Ni and NiO coexist on the surface of particles, in order to avoid the cumbersome mixing step of Ni and NiO particles. The partially oxidized Ni particles were made by oxidizing Ni under air atmosphere at $600^{\circ}C$ and characterized by X-ray diffraction (XRD) and FTIR spectroscopy. The viability of the pH sensor developed was assessed in boric acid (1000 ppm-B)/ lithium hydroxide (1 to 3 ppm-Li) buffer solutions at $280^{\circ}C$. The pH sensor showed excellent accuracy with a small error less than ${\pm}0.2$ pH units.