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수도 도열병에 저항성인 통일품종에 대한 침입생리에 관한 연구
김광석,정봉구 한국균학회 1977 韓國菌學會誌 Vol.5 No.1
In order to investigate histopathologically the nature of varietal resistance and infection process of the rice bast fungus, Pyricularia oryzae. this experiment was undertaken by using the resistant cultivar Tongil and susceptible cultivars Norin No.6 and Jinheung in 1973 to 1974. 1) It was found that appressorium of the fungus forms not only at 4 hours after incubation under the favor able conditions butalso peak of appressorial formation is at 48 hours treatment. Physical stimulus known to be a definite factor for appressorial formation. The optimum temperature range for appressorial infection was at 24℃ to 28℃, and pH was between 4.8 to 8.0 with 6.8 as the optimum. 2) Although percent of appressorial formation on the leaves of resistant Tongil and susceptiible Norin No.6 were only slightly different, there was a remarkable difference between resistant and susceptible cultivars with regard to percent of hyphal infection and index for hyphal extension. Index of hyphal extension was 1.6-2.7 in Tonyil. while in susceptible cultivar was 3.4-6.6. The rate of discoloration of infected cells, a indication of hypersensitivity, was greater in the resistant than in susceptible cultivar. 3) Therefore, it could be concluded that resistance of Tongil cultivar may be attributable to a higher degree of mechanical barriers as well as a higher level of antifungal substance accumulation.
GaN 내 유도방출과 엑시톤-못(exciton-Mott) 전이에 관한 연구
김광석 한국물리학회 2004 새물리 Vol.48 No.6
GaN is strongly excitonic with a binding energy Ex ˘ 26 meV, and the band-edge optical properties are dominated by pronounced excitonic resonances. As the carrier density increases, the exciton shows optical nonlinearities due to a reduction in the oscillator strength, and this phenomenon is explained by screening effects and phase-space lling. Comparing the time-resolved reectance spectrum taken at early times after pump beam excitation with the unperturbed one, we measured the saturation of the exciton absorption with increasing carrier density. The exciton bleaching density (the so-called Mott density) was estimated for both resonant and non-resonant excitation. In particular, we found that the Mott density in the case of resonant excitation is much higher than that found in the case of non-resonant excitation. This results suggests that resonant excitons are screened more weakly than non-resonant excions, when free excitons and free carriers coexist. We measured the onset of stimulated emission in the photoluminescence spectrum. The band-filling effect was also considered by using a free-carrier model with quasi-chemical potentials for electrons and holes, and the gain threshold density was calculated. Both onset densities coincided with the Mott transition in the case of non-resonant excitation, and the results conrm the lasing in GaN arises from an electron-hole plasma.