The paper forms the first part of an introduction to possible impacts of climate change on daily streamflow and extremes in the Province of Ontario, Canada. In this study, both conceptual and statistical streamflow si...The paper forms the first part of an introduction to possible impacts of climate change on daily streamflow and extremes in the Province of Ontario, Canada. In this study, both conceptual and statistical streamflow simulation modeling theories were collectively applied to simulate daily streamflow volumes. Based on conceptual rainfall-runoff modeling principle, the predictors were selected to take into account several physical factors that affect streamflow, such as (1) current and previous quantities of rainfall over the watershed, (2) an index of pre-storm moisture conditions, (3) an index of pre-storm evapotranspiration capacities, and (4) a seasonal factor representing seasonal variation of streamflow volume. These rainfall-runoff conceptual factors were applied to an autocorrelation correction regression procedure to develop a daily streamflow simulation model for each of the four selected river basins. The streamflow simulation models were validated using a leave-one-year-out cross-validation scheme. The simulation models identified that the explanatory predictors are consistent with the physical processes typically associated with high-streamflow events. Daily streamflow simulation models show that there are significant correlations between daily streamflow observations and model validations, with model R2s of 0.68-0.71, 0.61-0.62, 0.71-0.74, and 0.95 for Grand, Humber, Upper Thames, and Rideau River Basins, respectively. The major reason for the model performance varying across the basins might be that rainfall-runoff response time and physical characteristics differ significantly among the selected river basins. The results suggest that streamflow simulation models can be used to assess possible impacts of climate change on daily streamflow and extremes at a local scale, which is major objective of a companion paper (Part II).展开更多
We demonstrate the feasibility of using a carbon nanotube to nanopump molecules.Molecular dynamics simulations show that the transport and ejection of a C20 molecule via a single-walled carbon nanotube(SWNT)can be ach...We demonstrate the feasibility of using a carbon nanotube to nanopump molecules.Molecular dynamics simulations show that the transport and ejection of a C20 molecule via a single-walled carbon nanotube(SWNT)can be achieved by a sustained mechanical actuation driven by two oscillating tips.The optimal condition for nanopumping is found when the tip oscillation frequency and magnitude correlate to form quasi steady-state mechanical wave propagation in the SWNT,so that the energy transfer process is optimal leading to maximal molecular translational motion and minimal rotational motion.Our finding provides a potentially useful mechanism for using an SWNT as a vehicle to deliver large drug molecules.展开更多
文摘The paper forms the first part of an introduction to possible impacts of climate change on daily streamflow and extremes in the Province of Ontario, Canada. In this study, both conceptual and statistical streamflow simulation modeling theories were collectively applied to simulate daily streamflow volumes. Based on conceptual rainfall-runoff modeling principle, the predictors were selected to take into account several physical factors that affect streamflow, such as (1) current and previous quantities of rainfall over the watershed, (2) an index of pre-storm moisture conditions, (3) an index of pre-storm evapotranspiration capacities, and (4) a seasonal factor representing seasonal variation of streamflow volume. These rainfall-runoff conceptual factors were applied to an autocorrelation correction regression procedure to develop a daily streamflow simulation model for each of the four selected river basins. The streamflow simulation models were validated using a leave-one-year-out cross-validation scheme. The simulation models identified that the explanatory predictors are consistent with the physical processes typically associated with high-streamflow events. Daily streamflow simulation models show that there are significant correlations between daily streamflow observations and model validations, with model R2s of 0.68-0.71, 0.61-0.62, 0.71-0.74, and 0.95 for Grand, Humber, Upper Thames, and Rideau River Basins, respectively. The major reason for the model performance varying across the basins might be that rainfall-runoff response time and physical characteristics differ significantly among the selected river basins. The results suggest that streamflow simulation models can be used to assess possible impacts of climate change on daily streamflow and extremes at a local scale, which is major objective of a companion paper (Part II).
基金Department of Energy-Basic Energy Science program.In addition,M.C.thanks the China Scholarship Council and D.X.thanks the Natural Science Foundation of China(Nos.50410179 and 50772068)for their support.
文摘We demonstrate the feasibility of using a carbon nanotube to nanopump molecules.Molecular dynamics simulations show that the transport and ejection of a C20 molecule via a single-walled carbon nanotube(SWNT)can be achieved by a sustained mechanical actuation driven by two oscillating tips.The optimal condition for nanopumping is found when the tip oscillation frequency and magnitude correlate to form quasi steady-state mechanical wave propagation in the SWNT,so that the energy transfer process is optimal leading to maximal molecular translational motion and minimal rotational motion.Our finding provides a potentially useful mechanism for using an SWNT as a vehicle to deliver large drug molecules.
