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Space Charge Effect on Grain Growth Kinetics of Tetragonal Zirconia Polycrystal
Chon, Uong The Korean Ceramic Society 1999 The Korean journal of ceramics Vol.5 No.1
The effect of aliovalent dopents, $Nb_3O_5$ and MnO, on the grain growth kinetics of 12 mol% ceria stabilized tetragonal zirconia polycrystals (Ce-TZP) was studied. All specimens were sintered at $1550^{\circ}C$ for 20 minutes prior to annealing at different temperatures to study grain growth kinetics. Grain growth kinetics of Ce-TZP and 1 mol% $Nb_2O_5$ doped Ce-TZP (Ce-TZP/$Nb_3O_5$) during annealing at 1475, 1550, and $1600^{\circ}C$ adequately matched with square law $(D^2-D_\;o^2=k_at)$. However, grain growth in 1 mol% MnO suppressed grain growth in Ce-TZP by drag force exerted by $Mn^{+2}$ ions which segregated strongly to the positively-charged grain boundaries of Ce-TZP, $Nb_2O_5$ enhanced grain growth by increasing the concentration of vacancies of $Zr^{+4}$ ion and $Ce^{+4}$ ions. Surface analysis with X-ray photoelectron spectroscopy (XPS) showed the segregation of Mn+2 ions to grain boundaries. The kinetics of grain growth obtained in the base Ce-TZP and the Ce-TZPs with the aliovalent dopants were examined in the context of impurity drag effect and space charge effect.
Dependence of Phase Stability of Tetragonal Zirconia Polycrystal on Dopants
Chon, Uong The Korean Ceramic Society 1998 The Korean journal of ceramics Vol.4 No.4
The effect of aliovalent dopants, $ Nb_2O_5$ and MnO, on the phase stability of 12 mol% ceria partially-stabilized zirconia (Ce-TZP) polycrystals was studied. Both dopants (MnO and $ Nb_2O_5$) significantly increased the stability of the tetragonal zirconia phase (Mb temperature lower than liquid nitrogen temperature). The enhancement of the stability of the tetragonal phase in Ce-TZP doped with 1 mol% of Mno(Ce-TZP/MnO) andCe-TZP doped with 1 mol% of $ Nb_2O_5$(Ce-TZP/$ Nb_2O_5$) were explained by the significant reduction of the driving force, -${\Delta}$Gchem, for the tetragonal-to-mono-clinic phase transformation caused by the addition of MnO and $ Nb_2O_5$. The enhanced stability of the tetragonal phase in the Ce-TZP and Al2O3 composite (Ce-TZP/$Al_2O_3$) is believed to be caused by smaller grain size, moderate reduction in the chemical driving force and increase in the strain energy barrier to the transformation. Mechanical properties of the Ce-TZP and the Ce-TZP/$Al_2O_3$ with (i) the same grain size and (ii) the same Mb temperature were examined by measuring stress-strain behavior in 3 point bending. The Ce-TZP/$Al_2O_3$ composite doped with 1.3w% MnO (Ce-TZP/$Al_2O_3$/MnO), which had the same grain size as the Ce-TZP and De-TZP/$Al_2O_3$ showed more transformation plasticity than either the Ce-TZP or the Ce-TZP/$Al_2O_3$ composite. The Ce-TZP wihch had the same Mb temperature as that of the Ce-TZP/$Al_2O_3$/MnO did not show any transformation plasticity.
The change of Coastal line during 50 years(Haundae and kwananri beach)
Choi, Chul Uong,Kim, Young Seup,Yoon, Hong Joo,Park, Kyung Won 대한원격탐사학회 2001 International Symposium on Remote Sensing Vol.17 No.1
MODIS (Moderate Resolution Imaging Spectroradiometer) is the key instrument aboard the Terra That Pusan Gwanganri and haundae beach are sea sand reduced and coastline is many controversy about decrease. Analyze aerial photo of past 50 years and national oceanographic research institute's Pusan port water level observation data in this research and studied about coastline change of Gwanganri swimming beach. Also, whether draw authentic history cast shadow and DEM that use aerial photo every 3 years and Gwanganri and coastline change of sea transport swimming beach happened, some part changed, and analyzed how much area that change is.
최철웅 ( Chul Uong Choi ),김호용 ( Ho Young Kim ),전성우 ( Sung Woo Jun ) 大韓遠隔探査學會 2003 大韓遠隔探査學會誌 Vol.19 No.4
원격탐사는 각종 상업용 위성과 항공사진을 바탕으로 연구된다. 그러나 이러한 자료는 연구자들이 원하는 시기와 장소에서 촬영하는데 기상조건 및 경제적 이유로 많은 어려움을 겪고 있다. 이러한 문제점을 해결하는 작은 방안의 하나로 본 연구에서는 소형비행기 및 초경량 비행기에 탈 부착이 가능한 소형 다중분광 자동 항공촬영시스템을 개발하였다. 본 항공촬영시스템은 연구실 자체에서 보유한 고해상도 다중분광카메라(가시대역, 적외선대역)와 열 적외선 카메라, 자체 제작한 자동카메라 정밀자세조정장치, 촬영관제 소형컴퓨터, gimbal, GPS수신기, 기상센서 등으로 구성되어 있다. 이에 대한 성능평가 및 분석을 경북 칠포지역에서 2회, 낙동강지역에서 3회, 경안천 지역에서 2회 실시하였다. 그 결과, 다양한 항공사진, 기상자료 및 GPS자료를 획득할 수 있었고, 환경감시 등에 유용성이 매우 높음을 알 수 있었다. The cost of deploying Geological and Environmental information gathering systems, especially when such systems obtain remote sensing and photographic data through the use of commercial satellites and aircraft. Besides the high cost equipment required, adverse weather conditions can further restrict a researcher`s ability to collect data anywhere and anytime. To mitigate this problem, we have developed a compact, multi-spectral automatic Aerial photographic system. This system`s Multi-spectral camera is capable of the visible (RGB) and infrared (NIR) bands (3032*2008 pixel). It consists of a thermal infrared camera and automatic balance control, and can be managed by a palm-top computer. Other features includes a camera gimbal system, GPS receiver, weather sensor among others. We have evaluated the efficiency of this system in several field tests at the following locations: Kyongsang-bukdo beach, Nakdong river (at each site of mulkeum-namji and koryung-gumi), and Kyungahn River. Its tested ability in aerial photography, weather data, as well as GPS data acquisition demonstrates its flexibility as a tool for environmental data monitoring.
The study of Arirang EOC and Landsat TM synergism for land use classification
Choi, Chul Uong,Jung, Hui Cheul 대한원격탐사학회 2000 International Symposium on Remote Sensing Vol.16 No.1
This study presents the integration of Arirang EOC and Landsat Thematic Mapper(TM) data for land use classification. The study area of 1000 Kmz is located in the City of Pusan, Korea, has several classes of land use, including urban, agriculture, water(sea/river) and forests. EOC images were ortho-rectified arid filtered using an average filter. The TM and EOC images were registered and transformed using the principal components transformation (PCA). The principle components derived from Landsat TM, co-registered TM/EOC filtered, and TM/EOC images were classified using the maximum likelihood approach. The statistic tests of $quot;Goodness of fit$quot; were also made to assess the statistical properties of the image. The results, confirmed by Kappa statistics, show a significant improvement when classifying the principal components of EOC and TM images for urban, rice field and forest classes.
Environmental Change Detection Using NDVI and Census data
Choi, Chuli Uong,Kim, Young Seup 대한원격탐사학회 2000 International Symposium on Remote Sensing Vol.16 No.1
In the past decades, the city of Pusan, the metropolis and international harbor of more than 3.5 trillion population, has been experiencing vast land-use and environmental changes. Construction of a new harbor and associated transport networks, development of new town and inner city renewal programs all are major force shaping and expanding the urban environment. These developing activities produced concerns over the environmental quality, in particular green space and sound land use planning strategies towards a better living environment. Normalized difference vegetation index(NDVI) was developed from four different dates of Landsat TM data and was used to study the changing quality of Pusan from 1984 to 1997. Conventional change detection techniques helped to highlight the amount and quality of green space. NDVI values with urban census and land-cover data revealed the area changing pattern and relationship to the level of crowding as depicted from a factor analysis of census data. This study showed the integration of NDVI and social data provided the meaningful information of management of the environmental quality for urban planning and management.