Evaluation of Constant Potential Method in Simulating Electric Double-Layer Capacitors

A major challenge in the molecular simulation of electric double layer capacitors (EDLCs) is the choice of an appropriate model for the electrode. Typically, in such simulations the electrode surface is modeled using a uniform fixed charge on each of the electrode atoms, which ignores the electrode response to local charge fluctuations induced by charge fluctuations in the electrolyte. In this work, we evaluate and compare this Fixed Charge Method (FCM) with the more realistic Constant Potential Method (CPM), [Reed, et al., J. Chem. Phys., 126, 084704 (2007)], in which the electrode charges fluctuate in order to maintain constant electric potential in each electrode. For this comparison, we utilize a simplified LiClO$_4$-acetonitrile/graphite EDLC. At low potential difference ($\Delta\Psi\le 2V$), the two methods yield essentially identical results for ion and solvent density profiles; however, significant differences appear at higher $\Delta\Psi$. At $\Delta\Psi\ge 4V$, the CPM ion density profiles show significant enhancement (over FCM) of "partially electrode solvated" Li$^+$ ions very close to the electrode surface. The ability of the CPM electrode to respond to local charge fluctuations in the electrolyte is seen to significantly lower the energy (and barrier) for the approach of Li$^+$ ions to the electrode surface.Comment: Corrected typo

Topographic Mapping Through Measurement of Vehicle Attitude

A self-propelled agricultural sprayer was equipped with four RTK DGPS receivers, and an Inertial Measurement Unit (IMU) to measure vehicle attitude and field elevation as the vehicle was driven across a field. Data was collected in a stop-and-go fashion at 3.05 m (10 ft) intervals, as well as in a continuous fashion at three different speed levels. Using ordinary kriging, surface grids were interpolated using only elevation measurement, as well as combinations of elevation and vehicle attitude measurements. The resulting surfaces were compared to each other to evaluate the effect of including attitude measurement on DEM (Digital Elevation Model) accuracy. At the widest row spacing, the DEMs generated with attitude measurements had lower RMSE than those DEMs generated without attitude measurements. Vehicle speed also affected DEM accuracy. Vehicle attitude measurements have the potential to improve DEM accuracy for larger swath widths in ordinary field operations