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Sangdan Kim,Su Hyung Jang KOREAN SOCIETY OF CIVIL ENGINEERS 2007 KSCE JOURNAL OF CIVIL ENGINEERING Vol.11 No.4
<P>A new stochastic model for the propagation analysis of fluctuations in rainfall to soil water dynamics is proposed with major focus on its probabilistic structure. This model is derived by using cumulant expansion theory from a stochastic differential equation with stochastic rainfall forcing, and has the advantage of providing the probabilistic solution in the form of a probability distribution function, from which one can obtain the ensemble average behavior of the system. Steady state probability distribution function for soil water is obtained analytically and analyzed for different climate and soil conditions.</P>
Probabilistic Solution to Soil Water Evaporated Flow Equation
Sangdan Kim 대한토목학회 2006 KSCE journal of civil engineering Vol.10 No.1
A new stochastic model for one-dimensional evaporated soil water flow is proposed with major focus on its probabilistic structure. The newly developed model has the form of the Fokker-Planck equation, and its validity as a model for the probabilistic evolution of the nonlinear stochastic unsaturated flow process is investigated under a stochastic soil-related parameter (i.e., saturated hydraulic conductivity). This model is based on a parabolic type of stochastic partial differential equation, and has the advantage of providing the probabilistic solution in the form of a probability distribution function, from which one can obtain the ensemble average behavior of the flow system. The comparison results with Monte Carlo simulations show that the proposed model can reproduce well the vertically varying soil water wetting front depth. Overall, the ensemble averaging approach using the cumulant expansion method shows good promise for the stochastic modeling of nonlinear hydrologic processes.
Threshold Voltage Control for SnO2 Nanowire Transistors by Gas Treatment
Sangdan Kim,주상현 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.8
In order to apply nanowire transistors to next-generation electronic devices, it is crucial to control their characteristics. In particular, threshold voltage (V<sub>th</sub>) must be controlled, since it determines the driving voltage of the transistors. In this research, we were able to control threshold voltage (Vth) characteristics in both the negative and positive directions by performing H<sub>2</sub> and O<sub>2</sub> gas treatments at room temperature; this control was achieved since oxygen vacancies on the surface of oxide nanowire channel regions could be controlled with the treatments. The H<sub>2</sub> treatment changed Vth in the negative direction with the processing time (-0.6 V at 10 min; -0.9 V at 30 min; and -1.4 V at 60 min), whereas the O<sub>2</sub> treatment changed V<sub>th</sub> in the positive direction regardless of the processing time (+0.73 V at 10 min; +0.85 V at 30 min; +0.84 V at 60 min). This method can be applied to display-pixel and digital-logic circuits, especially those that employ nanowire transistors and require V<sub>th</sub> control.
Spatio-temporal characterization of Korean drought using severity-area-duration curve analysis
Kim, Sangdan,Kim, Bokyung,Ahn, Tae Jin,Kim, Hung Soo BLACKWELL PUBLISHING LTD. 2011 Water and environment journal Vol.25 No.1
<P>In this study, the depth-area-duration (DAD) analysis for characterizing an extreme precipitation event provides a basis for analysing drought events when storm depth is replaced by an appropriate measure of drought severity. Monthly precipitation is probabilistically transformed into standardized precipitation index (SPI) and SPI time series are decomposed into a mutually independent data set by the empirical orthogonal function (EOF) analysis. All EOFs are spatially expanded to a 6×6 km resolution by kriging, for which a commercial package, SuRFER™, is used. Twenty main drought events from the grid-based SPI time series are identified to construct the drought severity-effective area-drought duration (SAD) curves. The shape of SAD curves is similar to that of the rainfall DAD curves in the sense that drought severity and effective area are out of phase and that drought severity and duration are also out of phase. However, the severity reduction rate in SAD curves is much smaller than the corresponding rate in DAD analysis.</P>
Kim, Sangdan,Han, Suhee Wiley (John WileySons) 2010 Water environment research Vol.82 No.1
<P>Most related literature regarding designing urban non-point-source management systems assumes that precipitation event-depths follow the 1-parameter exponential probability density function to reduce the mathematical complexity of the derivation process. However, the method of expressing the rainfall is the most important factor for analyzing stormwater; thus, a better mathematical expression, which represents the probability distribution of rainfall depths, is suggested in this study. Also, the rainfall-runoff calculation procedure required for deriving a stormwater-capture curve is altered by the U.S. Natural Resources Conservation Service (Washington, D.C.) (NRCS) runoff curve number method to consider the nonlinearity of the rainfall-runoff relation and, at the same time, obtain a more verifiable and representative curve for design when applying it to urban drainage areas with complicated land-use characteristics, such as occurs in Korea. The result of developing the stormwater-capture curve from the rainfall data in Busan, Korea, confirms that the methodology suggested in this study provides a better solution than the pre-existing one.</P>