Electrostatic and electromagnetic waves excited by electron beam around the separatrix region are analyzed in detail during the collisionless magnetic reconnection with a weak guide field by using 2‐D particle‐in‐cell simulation with the adaptive mesh refinement. Broadband electrostatic waves are excited both in the inflow and outflow regions around the separatrices due to the electron bump‐on‐tail, two‐stream, and Buneman instabilities. In contrast, the quasi‐monochromatic electromagnetic waves are excited only in the inflow side of the separatrices due to a beam‐driven whistler instability. The localization of the whistler waves is attributed to the nonuniformity of the out‐of‐plane magnetic field By. The whistler instability is suppressed in the outflow side where By is too small for the oblique propagation. The electrostatic waves with distinct speeds can explain the in situ spacecraft observations. From the causality point of view, the waves are generated as the consequence of the electron bulk acceleration to thermalize the particles through wave‐particle interactions. These simulation results provide guidance to analyze high‐resolution wave observations during reconnection in the ongoing and upcoming satellite missions, as well as in dedicated laboratory experiments.
[1] Magnetic reconnection driven by an out-of-plane shear flow is carried out based on the three-dimensional Hall magnetohydrodynamics (MHD) code. The simulation results indicate that an out-of-plane shear flow can drive a secondary tearing instability to quickly form a magnetic island without a guide field or a flux rope with a guide field. It is found that the size of the flux rope within~240 Alfven time reaches about 20a (a is the initial current sheet thickness) that is roughly one Earth radius, the typical scale of Flux Transfer Event (FTE) observed at the dayside magnetopause. From a special simulation case based on the THEMIS data, it is found that an observed FTE is well reproduced by the Hall MHD simulation, which may give some clues on the generation mechanism of FTE.
To untangle the arching effect of a crowd as much as possible in emergency evacuations, we employ a theoretical model of equilibrium partition of crowd batch. Based on the shortest time arrangement of evacuation, the crowd is divided into appropriate batches according to the occupied time of evacuation channel in order to determine the occupant number of every evacuation passageway. The number of each batch crowd is calculated under the condition that the time of entering the evacuation passageway is equal to the time of crossing over the evacuation passageway. Subsequently, the shortest processing time (SPT) rule establishes the evacuation order of each batch. Taking a canteen of China Three Gorges University as a background, we obtain the waiting time from the first person to the last one entering the evacuation channel in every batch by simulation. This research utilizes data from simulations to observe an untangling process against the arching effect based on the SPT rule. More specifically, evacuation time only lasts for 180.1 s in order and is 1.6 s longer than that in disorder, but the arching effect disappears. Policy recommendations are offered to improve the evacuation scheme in disaster operations.
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