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[1] This article presents a measurement of electrification generated by wind-blown sands in a field wind tunnel and a numerical methodology to simulate the effect of electrification on the sand saltation movement after the mutual couple interaction between the sand movement and the wind flow is taken into account. The measured data of electric charge on the ''uniform'' sands in the wind-tunnel tests show that the sign of electric charge, either negative or positive, is mainly dependent on the diameter size of sand particles, i.e., negative charge is gained when the diameter is smaller than 250 mm and positive charge is obtained if the diameter is larger than 500 mm, and that for both ''uniform'' and mixed sands, the average charge-to-mass ratio decreases with increasing the wind velocity, and increases with height from sand bed. Meanwhile, the measurement of electric field in wind-sand cloud related to the electric charge displays that the magnitude of electric field increases generally as the wind velocity and the height increase, and the direction of the field is always upwardly vertical to the Earth's surface, which is opposite to that of the fair-weather field. In order to exhibit the effect of electrification on sand saltation movement, a theoretical model by considering the mutual coupling interaction between wind flow and sand movement is proposed after the electric force exerted on the moving sands is considered. Through solving the nonlinear coupling dynamic equations by a proposed program, the effect of electrification on sand saltation motion, e.g., trajectory, is discussed quantitatively. After that, its effect on wind-sand transport flux, sand ejecta flux, and wind profile is also displayed. The results show that the prediction for the Bagnold's kink is good agreement with the measurement in literature.

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Vortices play a crucial role in determining the properties of superconductors as well as their applications. Therefore, characterization and manipulation of vortices, especially at the single-vortex level, is of great importance. Among many techniques to study single vortices, scanning tunnelling microscopy (STM) stands out as a powerful tool, due to its ability to detect the local electronic states and high spatial resolution. However, local control of superconductivity as well as the manipulation of individual vortices with the STM tip is still lacking. Here we report a new function of the STM, namely to control the local pinning in a superconductor through the heating effect. Such effect allows us to quench the superconducting state at nanoscale, and leads to the growth of vortex clusters whose size can be controlled by the bias voltage. We also demonstrate the use of an STM tip to assemble single-quantum vortices into desired nanoscale configurations.

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