Control of the photodetachment of H^-near a metallic sphere surface by an elastic interface

According to the closed-orbit theory, we study the influence of elastic interface on the photodetachment of H- near a metallic sphere surface. First, we give a clear physical description of the detached electron movement between the elastic interface and the metallic sphere surface. Then we put forward an analytical formula for calculating the photodetachment cross section of this system. Our study suggests that the photodetachment cross section of H is changed with the distance between the elastic interface and H^-. Compared with the photodetachment cross section of H^- near a metallic sphere surface without the elastic interface, the cross section of our system oscillates and its oscillation is strengthened with the decrease of the distance from the elastic interface to H^-. In additon, our calcuation results suggest that the influence of the elastic interface becomes much more significant when it is located in the lower half space rather than in the upper half space. Therefore, we can control the photodetachment of H^- near a metallic sphere surface by changing the position of the elastic interface. We hope that our work is conducive to the understanding of the photodetachment process of negative ions near interfaces, cavities and ion traps.

Dynamics of a Rotating Sphere on Free Surface of Vibrated Granular Materials

We investigate the rotational dynamics of a low-density sphere on the free surface of a vertically vibrated granular material（VGM）. The dynamical behavior of the sphere is influenced by the external energy input from an electromagnetic shaker which is proportional to ε,where ε is equal to the ratio between the square of the dimensionless acceleration Γ and the square of the vibration frequency f of the container. Empirical results reveal that as the VGM transits from local-to-global convection,an increase in ε generally corresponds to an increase in the magnitudes of the rotational ω（RS） and translational v（CM） velocities of the sphere, an increase in the observed tilting angle θ（bed） of the VGM bed, and a decrease in the time t（wall） it takes the sphere to roll down the tilted VGM bed and hit the container wall. During unstable convection, an increase in ε results in a sharp decrease in the sphere＇s peak and mean ω（RS）,and a slight increase in t（wall）.For the range of ε values covered in this study, the sphere may execute persistent rotation, wobbling or jamming, depending on the vibration parameters and the resulting convective flow in the system.