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Turbulent mixing in a T-junction causes thermal striping which is irregular and frequent fluctuation of thermal layer. Thermal striping is a significant thermal problem because it causes unpredicted high cycle thermal fatigue and fatigue cracking in piping systems. Since this phenomenon is hardly detected by common plant instruments due to high frequency and complex mechanism, numerical approaches are indispensable for a precise evaluation. This research was carried out to define a suitable and effective numerical method for evaluating thermal stress and fatigue induced by thermal striping. A three-dimensional hydro-thermo-mechanical analysis was performed based on one-way separate analysis method to find out the characteristics of stress components and its results were compared to the results of a one-dimensional simplified analysis. It was found that the detailed three-dimensional analysis is indispensable because one-dimensional simplified analysis can overestimate or underestimate according to the assumed heat transfer coefficient and cannot estimate the considerable mean stress effects.
포도당 20%와 효모엑기스가 함유된 배지에서 40oC에서 48시간에 걸친 에탄올발효 과정 중에 일어나는 고온성 알코올 발효 효모균주 Saccharomyces cerevisiae KNU5377의 세포 내에서 일어나는 생리적 변화를 살펴보고자 했다. 그 결과, 이 발효 효모균주는 40℃ 48시간의 발효로써 11.4% alcohol을 생성하여, 고온발효인데도 불구하고 우수한 발효능을 가진 것을 확인할 수 있었다. 또한 12시간 발효과정동안 배지의 pH가 시작단계의 pH 6.0이 4.1로 내려갔으며, 이후 에탄올발효가 완성될 때까지 거의 변화하지 않고 이 값으로 유지되었다. 발효 12시간이 지나면서 세포막의 지방산의 조성은 불포화지방산인 C<SUB>16:1</SUB> (palmitoleic acid)가 포화지방산인 C<SUB>16:0</SUB> (palmitic acid)보다 1.5배나 증가하였으며, C<SUB>18:1</SUB>보다는 2배 가까이 증가하여 구성되어 있었다. 48시간 배양한 세포의 2차 전기영동(2-D)을 통한 세포내 단백질의 발현정도를 proteomics분석법으로 살펴본 바, phosphoglycerate kinase가 가장 크게 발현했음을 Mass Spectrometry를 통해 알 수 있었다. 그 뒤를 이어 adenylate kinase, Cys3p, Tdh3p, translational elongation factor 등이 크게 발현된 것을 알게 되었다. 이들은 직간접적으로 해당과정에 관여하는 인자들 이어서, 고온 장시간에 걸친 에탄올발효를 하는 이 발효 효모균주의 세포에게는 생존과 에탄올발효를 위하여 해당과정 관여 인자가 중요한 역할을 하고 있다는 것을 강력히 시사하였다. In this study, physiological changes in a thermotolerant yeast Saccharomyces cerevisiae KNU5377 cell exposed to 48-hour alcohol fermentation at 40℃ were investigated. After 12 hours of alcohol fermentation at 40℃, the C16:1 unsaturated acid of plasma membrane increased to 1.5 times more than the C16:0 saturated fatty acid, and to about 2 times more for the C18:1 unsaturated fatty acid. Fermentation at both 30℃- and 37℃- fermentation showed the same pattern as that done at 40℃. The pH of the alcohol-fermentation medium was reduced to pH 4.1 from a starting pH of 6.0 through the 12-hr fermentation and then maintained this level during the continuing fermentation. With the process of fermentation, the remaining glucose was reduced, but its amount remaining during the 40℃-fermentation was less reduced than those fermented at 30℃ and 37oC. In the study investigating the changing pattern of cellular proteins in the alcohol-fermenting cells, the SDS-PAGE and 2-D data indicated the most expressed dot was phosphoglycerate kinase, which is one enzyme involved in glycolysis. Why this enzyme was most expressed in the cells exposed to unfavorable conditions such as high temperature, increasing concentration of produced alcohol and long time exposure to other stress factors remains unsolved.
Legionella is a pathogenic bacteria associated to aquatic habit of natural and artificial environments. Clinical cases of legionellosis have been reported in Korea but there is a lack of information about the incidence of this bacterium on environmental sources. Thus, we investigated the contamination of Legionella on water supply systems in Gwangju, Korea, including cooling towers, public baths, hospitals and fountains. Legionella spp. were detected from 81 samples (16.9%) out of 480 samples collected and the major species of Legionella isolates was identified to L. pneumophila serogroup (sg) 1 (n=33). The result of PFGE pattern analysis for L. pneumophila sg 1 isolates was discriminated into 11 pulsotypes. In dendrogram of PFGE, the clusters of isolates from cooling tower were quite different from those derived from hot water system of public bath. Surveillance for 4 sentinel public baths showed that their water supply systems had been contaminated with Legionella spp. and L. pneumophila sg 5 or sg 6 was the major isolate. The similarity of its PFGE patterns was 92.3%, 96.6%, respectively. Thus, PFGE may be a useful tool in molecular epidemiology studies, and the monitor and control for water supply systems of public utilizing facilities will be able to provide a resolution for the reduction of Legionella infection.
Freeze-dried kimchi fractions, water-soluble (WSK) versus water-insoluble (WISK), on their effects on plasma lipids and for their fibrinolytic activities were studied. Nineteen middle-aged healthy subjects were assigned to WSK, WISK, or placebo during 6 weeks of kimchi supplementation. Subjects in the WSK and WISK groups were supplemented with 3 grams of kimchi pills (equivalent to 60 grams of fresh kimchi), while the placebo group was on their normal diets. LDL/HDL and atherogenic index decreased in the subjects who received kimchi pills, but not in those in the placebo group. The levels of plasma triglyceride were significantly decreased in the WSK group compared with those in the WISK group (p<0.05). However, there was no difference in the levels of total cholesterol and HDL between the two groups. Fibrinolytic activity of WISK was significantly higher than that of WSK.