Electron scale coherent structure as micro accelerator in the Earth's magnetosheath.

Turbulent energy dissipation is a fundamental process in plasma physics that has not been settled. It is generally believed that the turbulent energy is dissipated at electron scales leading to electron energization in magnetized plasmas. Here, we propose a micro accelerator which could transform electrons from isotropic distribution to trapped, and then to stream (Strahl) distribution. From the MMS observations of an electron-scale coherent structure in the dayside magnetosheath, we identify an electron flux enhancement region in this structure collocated with an increase of magnetic field strength, which is also closely associated with a non-zero parallel electric field. We propose a trapping model considering a field-aligned electric potential together with the mirror force. The results are consistent with the observed electron fluxes from ~50 eV to ~200 eV. It further demonstrates that bidirectional electron jets can be formed by the hourglass-like magnetic configuration of the structure.

Self-consistent kinetic model of nested electron- and ion-scale magnetic cavities in space plasmas.

NASA's Magnetospheric Multi-Scale (MMS) mission is designed to explore the proton- and electron-gyroscale kinetics of plasma turbulence where the bulk of particle acceleration and heating takes place. Understanding the nature of cross-scale structures ubiquitous as magnetic cavities is important to assess the energy partition, cascade and conversion in the plasma universe. Here, we present theoretical insight into magnetic cavities by deriving a self-consistent, kinetic theory of these coherent structures. By taking advantage of the multipoint measurements from the MMS constellation, we demonstrate that our kinetic model can utilize magnetic cavity observations by one MMS spacecraft to predict measurements from a second/third spacecraft. The methodology of "observe and predict" validates the theory we have derived, and confirms that nested magnetic cavities are self-organized plasma structures supported by trapped proton and electron populations in analogous to the classical theta-pinches in laboratory plasmas.

[Effect of composite flocculants made of polyaluminium chloride and polydimethyldiallyammonium chloride on ultra-filtration membrane characteristics].

The composite flocculants made of polyaluminium chloride and polydimethyldiallyammonium chloride (PAC-JY01) were used to treat the humic acid-kaolin simulation of water simples by enhanced coagulation. The effluent from coagulation continued to be treated by ultrafiltration. The objective of this research is to identify the mechanism of coagulation affecting UF due to different treated water quality and operational status of UF. The research shows that, in the coagulation-ultrafiltration (UF) hybrid process, the optimum coagulant dosage and pH value are 3 mg/L and pH = 6, respectively. At the optimum condition, the removal efficiency of UV254 and turbidity are 79.30%, 99.70%, respectively. In test conditions, the larger flocs are easy to deposit on the membrane surface causing membrane fouling.

Tail reconnection triggering substorm onset.

Magnetospheric substorms explosively release solar wind energy previously stored in Earth's magnetotail, encompassing the entire magnetosphere and producing spectacular auroral displays. It has been unclear whether a substorm is triggered by a disruption of the electrical current flowing across the near-Earth magnetotail, at approximately 10 R(E) (R(E): Earth radius, or 6374 kilometers), or by the process of magnetic reconnection typically seen farther out in the magnetotail, at approximately 20 to 30 R(E). We report on simultaneous measurements in the magnetotail at multiple distances, at the time of substorm onset. Reconnection was observed at 20 R(E), at least 1.5 minutes before auroral intensification, at least 2 minutes before substorm expansion, and about 3 minutes before near-Earth current disruption. These results demonstrate that substorms are likely initiated by tail reconnection.