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Neural network determination of cloud attenuation to estimate insolation using MTSAT-1R data
Yeom, J. -M.,Han, K. -S.,Kim, Y. -S.,Jang, J. -D. TaylorFrancis 2008 International journal of remote sensing Vol.29 No.21
<P> Surface solar insolation (SSI) is an important parameter for interpreting ocean-atmosphere interactions, climate change, surface heat flux, and the Earth's radiation budget. The successful calculation of SSI from satellite data depends strongly on how cloud attenuation is described because most clouds have large spatial and temporal variability and complicated physical characteristics. Moreover, the accuracy of SSI estimation under cloudy conditions is substantially lower than under clear skies. We have generated a neural network (NN)-based cloud factor retrieval system that improves SSI estimation accuracy under cloudy conditions. We used a multilayer feedforward NN with Levenberg-Marquardt backpropagation and an early stopping method to avoid overfitting. The number of hidden nodes was determined by trial and error because a too complicated network is apt to overfit, whereas a too simple network makes training the network difficult. Validation of the estimated SSI using the NN-based cloud factor was performed with pyranometer data obtained from 22 meteorological stations over the Korean peninsula. This SSI estimation for cloudy conditions showed good agreement with ground-based measurements: root mean square error (RMSE) = 67.38 W m-2; standard error (SE) = 54.78 W m-2. This accuracy indicates that the use of an NN-based cloud factor improves SSI estimation over the previous cloud factor system (SSIT: RMSE = 78.03 W m-2, SE = 52.64 W m-2) and the multiple regression-based cloud factor (SSIMR: RMSE = 79.20 W m-2, SE = 67.55 W m-2).</P>
Negotiating a way in: Conducting narrative inquiry with young children
M.P.Pearce,Yeom, Ji-Sook 건국대학교 중원인문연구소 2001 동화와 번역 Vol.1 No.-
본 연구에서는 이제까지의 유아교육연구가 유아들의 지식이나 경험에 대한 체험이야기(stories of lived experiences)에 관심을 기울여오지 않았음을 지적하면서, 유아를 대상으로 하는 교육 연구를 위한 하나의 의미 있는 방법으로서 질적 연구의 한 갈래인 내러티브 탐구(Narrative Inquiry)를 적용하는 과정을 기술한다. Pearce(1995)와 Yeom(1996)의 연구를 예로 들어 내러티브 탐구의 자료수집과정, 연구자의 역할, 관계의 전개, 윤리적인 이슈 등을 구체적으로 다룬다. 유아들과의 연구에 몰입하는 일이 무엇을 의미하는가에 대한 저자들의 숙고 및 탐색을 통해, 유아들의 경험을 드러내주고 그들의 목소리를 듣는 일이 중요함을 강조한다. 이를 위해 본 연구에서는 유아들에게 자신들의 이야기를 할 시간과 공간을 제공해 줄 것을 제안한다. 본 연구에서는 또한 대답을 제시해 줄 수는 없지만, 유아들과의 내러티브 탐구에서 고려해야 할 몇 가지 관심사에 대해 질문을 제기하고 논한다.
고온 압축변형된 니켈기 초내열 718 합금 결정립 조직의 EBSD 분석
나영상,이만형,염종택,박노광 대한금속재료학회 2003 대한금속·재료학회지 Vol.41 No.3
In order to characterize the dynamic change of microstructures in commercially-available superalloy 718, a series of compression tests were conducted by varying test temperature and strain rate. Orientation relationship and the misorientations between recrystallized grains as well as unrecrystallized grains were thoroughly investigated with EBSD technique. The dynamically-recrystallized grain size was similar regardless of the compression test condition except for the sample tested at 1066℃-0.005/sec condition, where the dynamically-recrystallized grain size was as large as 20 μm in average diameter. In case of the sample tested at 1066℃, flow stress drops caused by the strain softening were almost same at the strain rates of 0.5/sec and 0.005/sec in spite of the different fraction of dynamic recrystallization. It was concluded from the observation of the misorientation angle distribution that it was due to the active dynamic recovery in the unrecrystallized large grains at high temperature. It was also suggested from the variations of CSL boundary distribution that the characteristic redistribution of the dynamically-recrystallized grain boundary might be taken place during the compression at high temperature and low strain rate.
Yeom, J.M.,Ko, J.,Kim, H.O. Elsevier 2015 Computers and electronics in agriculture Vol.118 No.-
In this paper, satellite remote sensing was used as the input parameter of the GRAMI rice model to evaluate its applicability for simulating paddy rice crop condition and yield assessment at the field scale. Especially, the world's first Geostationary Ocean Color Imager (GOCI), which provides better temporal resolution than does MODIS, was applied to evaluate the estimation of intuitive paddy rice growth and development and to examine the feasibility for vegetation index profiles of the GRAMI rice model. Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data at 500-m resolution were used as reference data to validate the quality of the crop growth and development data derived from GOCI. Field measurements of paddy rice at Chonnam National University, Gwangju, South Korea, were performed to determine initial parameters of the GRAMI rice model, which is used to optimize biophysical processes in the soil-crop-atmosphere system. For angular-dependent vegetation products, daily rolling time series of vegetation indices of GOCI and MODIS were estimated using semi-empirical BRDF modeling based on 16-day composite procedures. The observed temporal variation in GOCI vegetation indices (VIs) based on BAR (bidirectional reflectance distribution function adjusted reflectance) showed a similar growing pattern to the simulated VIs of the crop model, but MODIS showed a difference between measured and simulated VIs during the cloudy monsoon season. The rice yields predicted by integrating satellite data and the GRAMI rice model were compared with field measurements and showed reasonable agreement with reference to paddy rice productivity in the study area.
Yeom, Bongjun,Sain, Trisha,Lacevic, Naida,Bukharina, Daria,Cha, Sang-Ho,Waas, Anthony M.,Arruda, Ellen M.,Kotov, Nicholas A. Nature Publishing Group 2017 Nature Vol. No.
<P>Tooth enamel comprises parallel microscale and nanoscale ceramic columns or prisms interlaced with a soft protein matrix(1-3). This structural motif is unusually consistent across all species from all geological eras(4-6). Such invariability-especially when juxtaposed with the diversity of other tissues-suggests the existence of a functional basis. Here we performed ex vivo replication of enamel-inspired columnar nanocomposites by sequential growth of zinc oxide nanowire carpets followed by layer-by-layer deposition of a polymeric matrix around these. We show that the mechanical properties of these nanocomposites, including hardness, are comparable to those of enamel despite the nanocomposites having a smaller hard-phase content. Our abiotic enamels have viscoelastic figures of merit (VFOM) and weight-adjusted VFOM that are similar to, or higher than, those of natural tooth enamels-we achieve values that exceed the traditional materials limits of 0.6 and 0.8, respectively. VFOM values describe resistance to vibrational damage, and our columnar composites demonstrate that lightweight materials of unusually high resistance to structural damage from shocks, environmental vibrations and oscillatory stress can be made using biomimetic design. The previously inaccessible combinations of high stiffness, damping and light weight that we achieve in these layer-by-layer composites are attributed to efficient energy dissipation in the interfacial portion of the organic phase. The in vivo contribution of this interfacial portion to macroscale deformations along the tooth's normal is maximized when the architecture is columnar, suggesting an evolutionary advantage of the columnar motif in the enamel of living species. We expect our findings to apply to all columnar composites and to lead to the development of high-performance load-bearing materials.</P>
The Oxidation of Methane at HCCI Engine Combustions
C. M. Liao(류춘명),J. M. Jin(진종무),D. H. Ha(하동흔),J. K. Yeom(염정국) 한국동력기계공학회 2007 한국동력기계공학회 학술대회 논문집 Vol.- No.-
압축천연가스(CNG)의 주요성분인 메탄의 산화와 연소를 HCCI엔진조건하에서 컴퓨터 시뮬레이션으로 연구하였다. 먼저, 당량비를 0.2에서 0.45까지 변화시켜 얻은 압력과 온도효과를 CHEMKIN을 사용하여 계산하였다. 그리고, 메탄의 운동학적 특성을 당량비 Ф=0.3, GRI 3.0 방법을 사용하여 계산하였다. 반응물과 생성물의 반응과정과 매개물의 프로파일은 운동학적 모델을 사용하였다. 마지막으로, 메탄의 산화반응의 주요 반응경로를 확인하기 위해 완전반응유동해석을 사용하였다.