• Proceedings of the KSME Conference
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• 2008.11a
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• pp.132-137
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• 2008

A failure analysis of ammonia converter which suffered hydrogen attack in two years since its initial operating time was presented. It is constructed from 2.25 Cr.1 Mo steel. Analysis showed that the failure on closing seam weld joint was due to local improper post weld heat treatment (PWHT). Improper PWHT can introduce high residual stresses in thick-walled pressure vessel. High residual stress level in weld joint is very prone to hydrogen attack for any components which are operating in hydrogen gas environment. The repair procedures based on the principle to decrease the residual stress then proposed. The repair was controlled very carefully by applying several nondestructive tests in the each stage of repair. To assure the successful of the proposed repair, after one year since repair time, high temperature ultrasonic and TOFD methods were applied on-stream to this equipment in order to evaluate its post repair condition. The two methods showed good results on the repaired area.

• Macromolecular Research
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• v.14 no.4
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• pp.424-429
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• 2006

The synthesis of a series of poly(POSS-NBE-b-MTD) copolymers was successfully accomplished, taking advantage of sequential, ring-opening, metathesis block copolymerization using $RuCl_2(=CHPh)(PCy_3)_2$ catalyst. By using cyclopentyl-POSS-norbornene (POSS-NBE) monomer as the first block in the block copolymer, living poly(POSS-NBE) with controlled molecular weight and narrow molecular weight distribution was produced. Then, poly(POSS-NBE-b-MTD) copolymers were successfully prepared, in which sequential monomer addition of methyltetracyclododecene (MTD) to the living poly(POSS-NBE) chain ends was utilized to achieve quantitative crossover efficiency. Characterization by $^1H$ NMR spectroscopy and GPC confirmed the high definition and structural integrity of the poly(PO$S-NBE-b-MTD) copolymers. Thermal properties-and morphologies of the POSS-containing block copolymer nanocomposites were also investigated by using thermogravimetric analysis (TGA), transmission electron microscopy (TEM), and wide-angle X-ray scattering (WAXS).

• Proceedings of the Korean Society for Applied Microbiology Conference
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• 2001.06a
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• pp.165-168
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• 2001

Regulation of pyrimidine nucleotide synthesis has been studied extensively in enteric bacteria and Bacillus species. Varieties of control modes have been proposed for regulation of pyrimidine nucleotide biosynthetic (pyr) genes. In Bacillus caldolyticus and B. subtilis, it has been proved that pyrimidine de novo biosynthetic operon is controlled by a regulatory protein PyrR-mediated attenuation. Another Gram-positive bacteria including Enterococcus faecalis, Lactobacillus plantarum, and wctococcus lactis have been found to constitute a pyr gene cluster containing the pyrR gene. In addition, it has been proposed that the structure of the 5' leader region of the Gram-negative extreme thermophile Thermus strain Z05 pyr operon provides a novel mechanism of PyrR-dependent coupled transcription-translation attenuation. Bacterial genome sequencing projects have identified the PyrR homologues in Haemophilus influenzae, Synechocystis sp., Mycobacterium tuberculosis, Streptococcus pneumoniae, S. pyogenes, and Clostridium acetobutylicum, which are currently investigating for their physiological functions.

• Journal of Powder Materials
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• v.24 no.5
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• pp.351-356
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• 2017

Tin dioxide nanoparticles are prepared using a newly developed synthesis method of plasma-assisted electrolysis. A high voltage is applied to the tin metal plate to apply a high pressure and temperature to the synthesized oxide layer on the metal surface, producing nanoparticles in a low concentration of sulfuric acid. The particle size, morphology, and size distribution is controlled by the concentration of electrolytes and frequency of the power supply. The as-prepared powder of tin dioxide nanoparticles is used to fabricate a gas sensor to investigate the potential application. The particle-based gas sensor exhibits a short response and recovery time. There is sensitivity to the reduction gas for the gas flowing at rates of 50, 250, and 500 ppm of $H_2S$ gas.

• Advances in nano research
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• v.4 no.3
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• pp.157-165
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• 2016

The photocatalytic (PC) activity of anatase titania nanoparticles can be improved through codoping with transition metals and nitrogen. In addition, the PC activity can also be improved by creating monodisperse, mesoporous nanoparticles of titania. The question naturally arose as to whether combining these two characteristics would result in further improvement in the PC activity or not. Herein, we describe the synthesis and photocatalytic characteristics of codoped, monodisperse anatase titania. The transition metals tested in the polydisperse and the monodisperse forms were Mn, Co, Ni, and Cu. In each case, it was found that the monodisperse version had a higher PC activity compared to the corresponding polydisperse version.

• Journal of the Korean Institute of Telematics and Electronics
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• v.12 no.2
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• pp.24-27
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• 1975

A Synthesis method for multiple-input change transition-sensitive asynchronous sequential circuits is proposed. Both internal states and output states are synthesized from primitive flow tables. It is Btown that cur realization is faster than that of Chuang's. It is pointed out that Chuang's realization of output states contains malfunctions. In this paper, output stales are easily realized from primitive flaw table by the method of controlled excitation.

• Bulletin of the Korean Chemical Society
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• v.30 no.5
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• pp.1003-1008
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• 2009

The $O_sO_4$-catalyzed dihydroxylations of a monosubstituted allylic amine and $\gamma-amino-\alpha,\;\beta-unsaturated$ (E)-esters with bulky alkyl groups showed a high anti-selectivity. Since the acyclic conformation of N-acyloxy protected allylic amines was efficiently controlled by a bulky t-Bu or OBO ester group, the anti diastereoselectivity of >12.5:1 was obtained without applying a chiral reagent. The synthetic utility of the present method was demonstrated by a stereoselective and efficient synthesis of an $\alpha$-glucosidase inhibitor 15 from commercially available N-Cbz-L-serine 6 in 11 steps and 31% yield.

• Bulletin of the Korean Chemical Society
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• v.25 no.12
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• pp.1812-1816
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• 2004

The stereoselective synthesis 4′,6′-dually branched carbocyclic nucleosides was accomplished in this study. The introduction of a methyl group in the 6′$({\alpha})$-position was accomplished by Felkin-Anh controlled alkylation. The construction of the required 4′$({\alpha})$-quaternary carbon was carried out using a [3,3]-sigmatropic rearrangement. Bis-vinyl 6 was successfully cyclized using a Grubbs' catalyst II. The natural bases (adenine, cytosine) were efficiently coupled using a Pd(0) catalyst. When the synthesized compounds were examined for their activity against several viruses such as the HIV-1, HSV-1, HSV-2 and HCMV, the cytosine analogue 13 exhibited good antiviral activity against the HCMV.

• Bulletin of the Korean Chemical Society
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• v.34 no.2
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• pp.443-446
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• 2013

In this work, a novel strategy is provided to prepare silver nanoplates by a fibronectin (Fn) nanofibril template. First, Fn molecules were controlled to assemble into amyloid-like nanofibrils in highly concentrated ethanol aqueous solution. The resultant nanofibrils could serve as a soft template to direct the formation of silver nanoplates. It is worth noting that the silver nanoplates are excellent surface-enhanced Raman scattering (SERS) substrate with 4-aminothiophenol (4-ATP) molecule as a test probe. This high active SERS substrate can also be used to detect drug molecule, 2-thiouracil with high sensitivity.

• YAKHAK HOEJI
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• v.49 no.1
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• pp.20-24
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• 2005

The synthesis of 4',5'-doubly branched carbocyclic nucleosides was accomplished in this study. The selective methylation in the 5'-position was made by Felkin-Anh controlled Grignard addition. The construction of the required 4'-quaternary carbon was carried out by using a [3,3]-sigmatropic rearrangement. Bis-vinyl 6 was successfully cyclized using a Grubbs' catalyst II. The natural pyrimidine bases (cytosine, uracil, thymine) were efficiently coupled using a Pd(0) catalyst. When the synthesized compounds were examined for their activity against several viruses such as the HIV-1, HSV-1, HSV-2 and HCMV, the cytosine analogue 13 exhibited weak antiviral activity against the HCMV.