An empirical model of the global distribution of plasmaspheric hiss based on Van Allen Probes EMFISIS measurements

Using wave measurements from the EMFISIS instrument onboard Van Allen Probes,we investigate statistically the spatial distributions of the intensity of plasmaspheric hiss waves.To reproduce these empirical results,we establish a fitting model that is a thirdorder polynomial function of L-shell,magnetic local time(MLT),magnetic latitude(MLAT),and AE*.Quantitative comparisons indicate that the model’s fitting functions can reflect favorably the major empirical features of the global distribution of hiss wave intensity,including substorm dependence and the MLT asymmetry.Our results therefore provide a useful analytic model that can be readily employed in future simulations of global radiation belt electron dynamics under the impact of plasmaspheric hiss waves in geospace.

Ag doped urchin-like α-MnO2 toward efficient and bifunctional electrocatalysts for Li-02 batteries

Rechargeable Li-O2 batteries (LOBs) have been receiving intensive attention because of their ultra-high theoretical energy densityclose to the gasoline. Herein, Ag modified urchin-like α-MnO2 (Ag-MnO2) material with hierarchical porous structure is obtained bya facile one-step hydrothermal method. Ag-MnO2 possesses thick nanowires and presents hierarchical porous structure of mesoporesand macropores. The unique structure can expose more active sites, and provide continuous pathways for O2 and discharge productsas well. The doping of Ag leads to the change of electronic distribution in α-MnO2 (i.e., more oxygen vacancies), which playimportant roles in improving their intrinsic catalytic activity and conductivity. As a result, LOBs with Ag-MnO2 catalysts exhibit loweroverpotential, higher discharge specific capacity and much better cycle stability compared to pure a-MnO2. LOBs with Ag-MnO2catalysts exhibit a superior discharge specific capacity of 13,131 mA·h·g^-1 at a current density of 200 mA·h·g^-1, a good cycle stabilityof 500 cycles at the capacity of 500 mA·h·g^-1. When current density is increased to 400 mA·h·g^-1, LOBs still retain a long lifespan of170 cycles at a limited capacity of 1,000 mA·h·g^-1.