• Journal of the Korean Ceramic Society
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• v.29 no.8
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• pp.667-673
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• 1992

The alumina-zirconia composite powders of core particle ZrO2 coated with Al2O3 were prepared by the hydrolysis-deposition of the mixed aluminum salt solution of Al2(SO4)3-Al(NO3)3-Urea. The effects of hydrolysis reaction and coating parameters on characteristics of coated powders and composites were also investigated. The degree of coating could be estimated from the ratio of tetra-/mono-ZrO2 present at the room temperature after heat-treating coated powders at 120$0^{\circ}C$ and the result of TEM observations. When the content of ZrO2 in the dispersed coating system, the coating time, and the volume ratio of water/solution were 50 mg/g, 180 min, and 5, respectively the coating efficiency was maximum (the ratio of tetra-/mono-ZrO2 was 87/13). The relative densities of coated Al2O3-ZrO2 composites sintered at 1$650^{\circ}C$ for 4 hrs were about 91~98% and the maximum ratio of tetra-/mono-ZrO2 in Al2O3-20wt% ZrO2 composites was 62/38.

• Restorative Dentistry and Endodontics
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• v.7 no.1
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• pp.65-69
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• 1981

This study was conducted to evaluate the cleansing effect of RC-Prep (10% Urea-peroxide, 15% EDTA) on apical third of root canal. Thirty single rooted human teeth were divided into three groups, and ten canals in each group were all enlarged three sizes greater than their original diameter with K-type files and irrigated with each of three irrigants. The three used irrigants were RC-prep (Premier Co.) in combination with 3.5% Sodium hypochlorite, Normal saline, 3.5% Na OCL. In each group, one of three irrigants were used in conjunction with instrumentation as they would be during clinical condition. After final irrigation, the canals were dried with paper points and the teeth were split longitudinally. The cleanness of canal walls iii the apical region were examined with Scanning Electron Microscope. The following results were drawn. 1. The use of Rc-Prep in combination with 3.5% NaOCl showed more clean canal surface than the use of other two irrigants. 2. The canals used RC-Prep in combination with 3.5% NaOCl revealed remnants of pulp tissue and smeared layer, but the openings of dentinal tubules were relatively clean and wide. 3. There was no significant difference in the debridement effect of 3.5% NaOCl and Saline solution. 4. The use of Saline solution showed great amount of remnants of pulp tissue which couldn't find in the use of 3.5% NaOCl.

• Korean Journal of Breeding Science
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• v.41 no.2
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• pp.84-91
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• 2009

Rice consumption per capta, in South Korea, has been decreased dramatically, owing to the changes of living patterns. Because of not only the major energy source of Korean people but also major income source of Korean farmers, diversifying end-use-quality of rice has been demanded. To the context, 'Suweon 472', a high yielding and early mature japonica line and released as 'Namilbyeo' to framers in 2002, was treated with a chemical mutagen, Sodium Azide to find endosperm mutant types. A total of nine endosperm mutat lines, including five waxy, one dull, two floury, and one white core type, were identified from the 3,542 mutatagen treated lines. Amylose contents, iodine reaction, disintegration in alkali solution, gelatinization in urea solution and amylogram properties of those nine endosperm mutant lines were evaluated to address the possibility as new genetic materials for diversifying rice quality of Korean japonica cultivars. All embryo mutants were clearly differentiated from their wild type, 'Suweon 472', in terms of physic-chemical properties evaluated. The endosperm mutant lines would be very useful in expanding untiliztation of rice through opening new rice markets of processed foods from Korean japonica rice.

• Korean Journal of Soil Science and Fertilizer
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• v.41 no.4
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• pp.260-266
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• 2008

Small lysimeter experiment under rain shelter plastic film house was conducted to investigate the effect of soil characteristics on the leaching and soil solution concentration of nitrate and phosphate. Three soils were obtained from different agricultural sites of Korea: Soil A (mesic family of Typic Dystrudepts), Soil B (mixed, mesic family of Typic Udifluvents), and Soil C (artificially disturbed soils under greenhouse). Organic-C contents were in the order of Soil C ($32.4g\;kg^{-1}$) > Soil B ($15.0g\;kg^{-1}$) > Soil A ($8.1g\;kg^{-1}$). Inorganic-N concentration also differed significantly among soils, decreasing in the order of Soil B > Soil C > Soil A. Degree of P saturation (DPS) of Soil C was 178%, about three and fifteen times of Soil B (38%) and Soil A (6%). Prior to treatment, soils in lysimeters (dia. 300 mm, soil length 450 mm) were tabilized by repeated drying and wetting procedures for two weeks. After urea at $150kg\;N\;ha^{-1}$ and $KH_2PO_4$ at $100kg\;P_2O_5\;ha^{-1}$ were applied on the surface of each soil, total volume of irrigation was 213 mm at seven occasions for 65 days. At 13, 25, 35, 37, and 65 days after treatment, soil solution was sampled using rhizosampler at 10, 20, and 30 cm depth and leachate was sampled by free drain out of lysimeter. The volume of leachate was the highest in Soil C, and followed by the order of Soils A and B, whereas the amount of leached nitrate had a reverse trend, i.e. Soil B > Soil A > Soil C. Soil A and B had a significant increase of the nitrate concentration of soil solution at depth of 10 cm after urea-N treatment, but Soil C did not. High nitrate mobility of Soil B, compared to other soils, is presumably due to relatively high clay content, which could induce high extraction of nitrate of soil matrix by anion exclusion effect and slow rate of water flow. Contrary to Soil B, high organic matter content of Soil C could be responsible for its low mobility of nitrate, inducing preferential flow by water-repellency and rapid immobilization of nitrate by a microbial community. Leached phosphate was detected in Soil C only, and continuously increased with increasing amount of leachate. The phosphate concentration of soil solution in Soil B was much lower than in Soil C, and Soil A was below detection limit ($0.01mg\;L^{-1}$), overall similar to the order of degree of P saturation of soils. Phosphate mobility, therefore, could be largely influenced by degree of P saturation of soils but connect with apparent leaching loss only more than any threshold of P accumulation.

• The Korean Journal of Ceramics
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• v.6 no.2
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• pp.159-163
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• 2000

Alumina fibre has been synthesized successfully by sol-gel technique. Boehmite sol was prepared by hydrolyzing aluminium iso-propoxide and peptizing it with nitric acid. The stable sol thus obtained was used for fibre drawing when their viscosity reached the required value as a result of progress of the hydrolyzation and polycondensation reaction. The fibres dried at 11$0^{\circ}C$ for 12 hours were sintered at 1$600^{\circ}C$ for 5 hours. A reasonable sintered density with better microstructure and strength have been attained using 2 wt% of urea, magnesia and silica as sinter additives. Thermal analysis with sintering additives of 2 wt% and phase determination of the heat treated fibres using XRD and FT IR spectra confirms the phase transitions. The observation of surface and cross-section of the fibres were made using SEM. Fibres of uniform circular cross-section is obtained by fixing the shape in a setting solution.

• Biotechnology and Bioprocess Engineering:BBE
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• v.1 no.1
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• pp.9-12
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• 1996

In order to produce the single chain precursor of a novel human insulin analogue, (B30-Homoserine) insulin, the fermentative behaviors of Escherichia coli JM103 were studied, which harbors pKBA plasmid carrying a hybrid gene in which the gene for a single chain precursor was fused with lacZ gene under tac promoter. The maximal induction of gene expression was achieved when more than 0.05 mM of isopropyl-$\beta$-D-thiogalactopyranoside(IPTG) was supplemented to fermentation medium after 4 h cultivation of E. coli, and followed by longer than 2-h fermentation. The hybrid protein of the single chain insulin precursor was isolated from cytoplasmic inclusion bodies by dissolving in 8M urea solution, and purified through DEAE-Sephacel and Sephadex G-200 column chromatographies with a recovery of 35%. The finally purified hybrid protein showed a single band on sodium dodecyl sulfate-polyacrylamide gel.

• Journal of the Korean Chemical Society
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• v.24 no.1
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• pp.73-79
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• 1980

N-Vinylurea(VU) was radically copolymerized with vinyl acetate (VAc). VU-vinyl alcohol (VA) copolymer, which is a water-soluble polymer with pendent urea and hydroxyl groups, was synthesized by the methanolysis of the VU-VAc copolymer.VU shows vinyl polymerization, and this result is in agreement with that of Nozakura, et al. Huggins constant for the aqueous solution of the VU-VA copolymer containing more than about 30 mole percent of VU was observed to be a high value.

• Parasites, Hosts and Diseases
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• v.50 no.2
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• pp.181-183
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• 2012

The author reported previously on separation of the outer tegument of the spargana (plerocercoids of Spirometra mansoni) using high concentration of urea solution. To determine which layer of the tegument is separated by this method, an electron microscopic analysis has been processed in this study. It was confirmed that the basement layer of the tegument is separated from the parenchyme of the sparganum. In addition, the antigenicity of the separated outer tegument against the human sparganosis patient sera was evaluated. Numerous antigenic proteins, including 16 and 55 kDa proteins, were noticed in the separated tegument; however, there were no diagnostic 31/36 kDa molecules in this tegument. The molecules reactive with the patient sera in the tegument are to be characterized in future studies.

• Membrane and Water Treatment
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• v.1 no.2
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• pp.159-169
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• 2010

The effect of external recycle on the performance of dialysis in countercurrent-flow rectangular membrane modules was investigated both theoretically and experimentally. Theoretical analysis of mass transfer in parallel-flow device with and without recycle is analogous to heat transfer in parallel-flow heat exchangers. Experiments were carried out with the use of a microporous membrane to dialyze urea aqueous solution by pure water. In contrast to a device with recycle, improvement in mass transfer is achievable if parallel-flow dialysis is operated in a device of same size with recycle which provides the increase of fluid velocity, resulting in reduction of mass-transfer resistance, especially for rather low feed volume rate.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2009.05a
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• pp.150-150
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• 2009

We prepared the Au-coated $TiO_2$ (Au/$TiO_2$) nanoparticles by deposition-precipitation (DP) method with and without bases (urea or NaOH) and investigated the effects of pH on the preparation of Au/$TiO_2$ nanoparticles for various kinds of bases. For the DP method without bases, the Au nanoparticles in the diameter of about 50 nm were generated in the solution by the reduction reaction with trisodium citrate and they did not deposit on the surface of $TiO_2$. For the DP method with bases, Au precursors deposited on the surface of $TiO_2$ and then reduced to the Au nanoparticles in the diameter of 4-5 nm on the surface of $TiO_2$ by the reaction with trisodium citrate.