Byung-Woo Lee

Microstructure and mechanical properties of silicon nitride with tape cast tri-layer structures

Four kinds of silicon nitride samples with tri-laminate structures were prepared by stacking tapes with aligned β-Si3N4 whisker seeds. Three-point flexural strengths of the samples were measured at both room temperature and 1673 K. As the total thickness of the layers with the whisker seeds aligned parallel to tension was increased, the flexural strength was increased at both room temperature and at 1673 K. The flexural strength at 1673 K was more sensitive to orientations of the grains in the surface layer than that at room temperature. Observation of the fracture surface revealed that the grains growing from the neighboring whisker seeds were often broken such that they formed a single one grain. Extensive brittle fracture of the grains without much grain pull-out occurred even at 1673 K for the samples.

Biological Activity of Extracts of the Starfish Asterias amurensis

Nowadays, starfish is one of problems about interruption of marine ecosystem, so many researchers are focusing on application of the starfish (Asterias amurensis). In this study, we investigated the contractile and relaxant activity of the smooth muscles and the antimicrobial and antioxidant activity of six different tissues (muscle, gut, liver, tube feet, gonads, and body) of A. amurensis. Frozen samples were extracted with distilled water containing 1% acetic acid. Extracts from all the tissues, except the body tissue, showed potent antimicrobial activity against Escherichia coli D31. The dorsal retractor muscles (DRM) of muscle and gut extracts showed strong contraction responses. On the other hand, contractile activity on esophagus of squid Todarodes pacificus could be detected in all tissues tested. The contractile activity of the liver extract was higher than that of the other tissues. The body, tube feet, and liver extracts showed the contractile activity on the intestine of the panther puffer fish (Takifugu pardalis). Relaxation response on the DRM of starfish (A. pectinifera) was observed in all tissues tested. Increased antioxidant activity was observed in the gut, liver, and body extracts. The results suggest that the starfish (A. amurensis) is a potential source of novel bioactive compounds.

Effect of 18 F Irradiation on Neurotransmitters in the Brains of Goldfish Carassius auratus

In order to investigate the changes in bioactive materials induced in goldfish brains by 18 F irradiation, the variations in the neurotransmitter levels in the whole brain were studied. The distance between the goldfish and 580 mCi of 18 F was about 4 cm, and the exposure lasted for 4 hrs. The absorption level calculated based on the distance, exposure time, and half-life of 18 F was approximately 2 Gy. After sacrifice by 18 F irradiation or untreated conditions, ten brains were dissected or immediately frozen, respectively. The tissues were extracted in acetic acid. After lyophilization, the samples were dissolved in distilled water and were further purified on a reverse-phase HPLC column. There were no differences in the intensities of the bioactive materials between 18 F-exposed goldfish and control goldfish, while the only peak corresponded to 13 min, which indicated a significant increase in the irradiated brains. Our analysis has found that this compound is tryptophan. This result suggests that 18 F leads to changes in a classical neurotransmitter, tryptophan, in both the brains of control goldfish and goldfish contaminated by irradiation.