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방사선조사가 백서 협점막에 미치는 영향에 관한 전자현미경적 연구
최승규,이상래,Choi Syng Kyu,Lee Sang Rae 대한영상치의학회 1987 Imaging Science in Dentistry Vol.17 No.1
The author studied the acute reaction of cobalt-60 irradiation to buccal mucosa in rats and difference of the effects of single versus fractionated exposure. 195 Sprague Dowley strain rats, weighing about 120gm, were used in this experiment. 3 rats served as controls and the remaining 192 rats were divided into six groups of 32 rats each. Experimental group Ⅰ, Ⅱ, Ⅲ were received a single dose of 15Gy, 16.5Gy, 18Gy and group Ⅳ, Ⅴ, Ⅵ were received two equal sized fractionated dose of 9Gy, 9.75Gy, 10.5Gy at 4 hour intervals, respectively. The experimental groups were irradiated with cobalt-60 teletherapy unit, Picker model 4M 60 (Field size, 12x5 cm, SSD, 50㎝, Dose rate, 222cGy/min, Depth, 1㎝). The animals were sacrificed at 1, 2, 3, 6, 12 hours, 1, 3, 7 days after irradiation and the changes of the irradiated buccal mucosa were observed by electron and light microscopy. The results were as follows: 1. A single exposure was more damaging than fractionated exposure, and as the radiation dose increased, the changes of cell organelles became faster, but the healing of radiation-induced damage in fractionated exposure was faster than in single exposure. 2. The radiation-induced changes of the basal cells were the most prominent in 18Gy-single exposure group, and the least in 18Gy-fractionated exposure group. 3. Electron-microscopically, there appeared nuclear changes, swelling of mitochondria and rough endoplasmic reticulum, decrease of free ribosome, presence of vesicles, widening of intercellular space, and loss of basal lamina. The early remarkable changes were partly loss of nuclear membrane and swelling of mitochondria. 4. Light-microscopically, derangement and pyknosis of basal cells, hydropic changes of spinous cells, enlargement of granular cells, indistinctness of basement membrane, and proliferation of epithelium were observed.
T6 열처리에 의한 Al-Mg-Si 합금의 비등방성 석출물 형상을 고려한 확률 의존적 석출강화효과
최승규,김광훈,김진평,김세훈,손승배,이석재 대한금속·재료학회 2021 대한금속·재료학회지 Vol.59 No.8
This study proposed a constitutive equation to predict the change in yield strength according to the behavior of β″ metastable precipitates, which have a profound effect on strength among materials precipitated during the T6 heat treatment of Al-Mg-Si alloy. The β″ precipitate is a metastable phase before it becomes a β (Mg2Si) precipitate, and is distributed in the form of nano-scale rods in the aluminum alloy matrix. Existing precipitation strengthening models assume the shape of the precipitate to be spherical, and in that case the equation that depends on the Orowan mechanism with the average precipitate size and distribution should dominate. However, precipitates are formed in various shapes and sizes by anisotropic growth. In particular, rod-shaped precipitates are not suitable for the existing precipitation strengthening model. In this study, an Al-Mg-Si alloy was fabricated by gravity casting followed by T6 heat treatment. The new precipitation strengthening effect equation proposes that the β″ precipitate affects yield strength during plastic deformation of the Al-Mg-Si alloy. The proposed precipitation strengthening effect equation probabilistically considers the Critical Resolved Shear Stress (CRSS), which varies depending on the angle between the dislocation and the precipitate, when the dislocation passes through a rod-shaped precipitate.
최승규,이성학,장재민,김정아,정우광,Choi, Seung-Kyu,Yi, Sung-Hak,Jang, Jae-Min,Kim, Jung-A,Jung, Woo-Gwang 한국재료학회 2007 한국재료학회지 Vol.17 No.5
Vertically aligned Zinc Oxide rod arrays were grown by the self-assembly hydrothermal process on the GaN epitaxial layer which has a same lattice structure with ZnO. Zinc nitrate and DETA solutions are used in the hydrothermal process. The $(HfO_2)$ thin film was deposited on GaN and the patterning was made by the photolithography technique. The selective growth of ZnO rod was achieved with the patterned GaN substrate. The fabricated ZnO rods are single crystal, and have grown along hexagonal c-axis direction of (002) which is the same growth orientation of GaN epitaxial layer. The density and the size of ZnO rod can be controlled by the pattern. The optical property of ordered array of vertical ZnO rods will be discussed in the present work.