131 research outputs found
Evaluation of Satellite-Based Rainfall Estimates in the Lower Mekong River Basin (Southeast Asia)
Satellite-based precipitation is an essential tool for regional water resource applications that requires frequent observations of meteorological forcing, particularly in areas that have sparse rain gauge networks. To fully realize the utility of remotely sensed precipitation products in watershed modeling and decision-making, a thorough evaluation of the accuracy of satellite-based rainfall and regional gauge network estimates is needed. In this study, Tropical Rainfall Measuring Mission (TRMM) Multi-Satellite Precipitation Analysis (TMPA) 3B42 v.7 and Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS) daily rainfall estimates were compared with daily rain gauge observations from 2000 to 2014 in the Lower Mekong River Basin (LMRB) in Southeast Asia. Monthly, seasonal, and annual comparisons were performed, which included the calculations of correlation coefficient, coefficient of determination, bias, root mean square error (RMSE), and mean absolute error (MAE). Our validation test showed TMPA to correctly detect precipitation or no-precipitation 64.9% of all days and CHIRPS 66.8% of all days, compared to daily in-situ rainfall measurements. The accuracy of the satellite-based products varied greatly between the wet and dry seasons. Both TMPA and CHIRPS showed higher correlation with in-situ data during the wet season (JuneSeptember) as compared to the dry season (NovemberJanuary). Additionally, both performed better on a monthly than an annual time-scale when compared to in-situ data. The satellite-based products showed wet biases during months that received higher cumulative precipitation. Based on a spatial correlation analysis, the average r-value of CHIRPS was much higher than TMPA across the basin. CHIRPS correlated better than TMPA at lower elevations and for monthly rainfall accumulation less than 500 mm. While both satellite-based products performed well, as compared to rain gauge measurements, the present research shows that CHIRPS might be better at representing precipitation over the LMRB than TMPA
Surface Structural Disordering in Graphite upon Lithium Intercalation/Deintercalation
We report on the origin of the surface structural disordering in graphite
anodes induced by lithium intercalation and deintercalation processes. Average
Raman spectra of graphitic anodes reveal that cycling at potentials that
correspond to low lithium concentrations in LixC (0 \leq x < 0.16) is
responsible for most of the structural damage observed at the graphite surface.
The extent of surface structural disorder in graphite is significantly reduced
for the anodes that were cycled at potentials where stage-1 and stage-2
compounds (x > 0.33) are present. Electrochemical impedance spectra show larger
interfacial impedance for the electrodes that were fully delithiated during
cycling as compared to electrodes that were cycled at lower potentials (U <
0.15 V vs. Li/Li+). Steep Li+ surface-bulk concentration gradients at the
surface of graphite during early stages of intercalation processes, and the
inherent increase of the LixC d-spacing tend to induce local stresses at the
edges of graphene layers, and lead to the breakage of C-C bonds. The exposed
graphite edge sites react with the electrolyte to (re)form the SEI layer, which
leads to gradual degradation of the graphite anode, and causes reversible
capacity loss in a lithium-ion battery.Comment: 12 pages, 5 figure
An Electrochemical Route for Making Porous Nickel Oxide Electrochemical Capacitors
Porous nickel oxide films were prepared by electrochemically precipitating nickel hydroxide and heating the hydroxide in air at 300°C. The resulting nickel oxide films behave as an electrochemical capacitor with a specific capacitance of 59 F/g electrode material. These nickel oxide films maintain high utilization at high rates of discharge (i.e., high power density) and have excellent cycle life. Porous cobalt oxide films were also synthesized. Although the specific capacitances of these films are approximately one-fifth that of the nickel oxide films, the results demonstrate the versatility of fabricating a wide range of porous metal oxide films using this electrochemical route for use in capacitor applications
Studies on the Capacitance of Nickel Oxide Films: Effect of Heating Temperature and Electrolyte Concentration
Nickel oxide films were prepared by electrochemically precipitating the hydroxide and heating it in air to form the oxide. The resulting oxide films behave as a capacitor. The capacitance of the oxide depends on the heating temperature, showing a maximum at 300°C. The mechanism of charge storage was studied by measuring the capacitance and surface area as a function of heating temperature, and the capacitance in different electrolytes and potential windows. The charge-storage mechanism is believed to be a surface redox reaction involving adsorbed hydroxyl ions
- …