Perpendicular Ion Heating by Low-frequency Alfven-wave Turbulence

Determining the mechanisms that heat the solar corona is a fundamental problem in heliospheric physics. One of the proposed models is based on low-frequency Alfven waves (o \u3c\u3c O i) launched from the coronal base. Theoretical studies and numerical simulations have shown that Alfven-wave low-beta turbulence primarily cascades to smaller scales perpendicular to the mean magnetic field rather than smaller parallel scales, where beta = 8pip/B 2 is the ratio of the plasma pressure to the magnetic pressure. Because of this, the wave frequencies at small scales remain small compared to the proton cyclotron frequency. In this work, we study the possibility of ion heating by this low-frequency Alfven-wave turbulence in a reduced magnetohydrodynamic (RMHD) simulation. In a low-beta plasma, when an ion\u27s gyroradius is comparable to the wave length in the perpendicular direction, the ion undergoes a random walk in the time-varying electrostatic potential. When the fluctuation amplitude exceeds a certain threshold, this stochastic mechanism provides ion heating in the plane perpendicular to the magnetic field lines. We evaluate the stochastic heating rate as a function of the amplitude of the turbulence and compare our findings to previous theoretical results

Innovative Practice of Foreign Language Teaching in the Post- pandemic Era: Case of a University in China

COVID-19 has posed a severe challenge to the foreign language teaching as well as the international education management in China This paper analyzes the key issues exposed in online learning the unprepared assessment of online course and crisis management of international students taking Shanghai University of International Business and Economics as an example Both the students and teachers showed a considerable dissatisfaction and their worries about the poor quality and efficiency of online instruction Other issues raised include teachers operation mistakes ineffective communication and connectivity issues Students are more likely to cheat in online exams due to the lack of supervision Different cultural backgrounds strict prevention and control have increased the difficulty of crisis management of the international student in China To make better use of online education in the post-epidemic era suggestions and recommendations are given in online classes and examinations Also an efficient crisis management model can be set up for the international students during the post-pandemic er

Particle acceleration in coalescent and squashed magnetic islands: II. Particle-in-cell approach

Aims. Particles are known to have effcient acceleration in reconnecting current sheets with multiple magnetic islands that are formed during a reconnection process. Using the test-particle approach, the recent investigation of particle dynamics in 3D magnetic islands, or current sheets with multiple X- and O-null points revealed that the particle energy gains are higher in squashed magnetic islands than in coalescent ones. However, this approach did not factor in the ambient plasma feedback to the presence of accelerated particles, which affects their distributions within the acceleration region.Methods. In the current paper, we use the particle-in-cell (PIC) approach to investigate further particle acceleration in 3 D Harris-type reconnecting current sheets with coalescent (merging) and squashed (contracting) magnetic islandswith different magnetic field topologies, ambient densities ranging between 1e8 − 1e12/m³ , proton-to-electron mass ratios, and island aspect ratios.Results. In current sheets with single or multiple X-nullpoints, accelerated particles of opposite charges are separated and ejected into the opposite semiplanes from the current sheet midplane, generating a strong polarisation electric field across a current sheet. Particles of the same charge form two populations: transit and bounced particles, each with very different energy and asymmetric pitch-angle distributions, which can be distinguished from observations. In some cases, the difference in energy gains by transit and bounced particles leads to turbulence generated by Buneman instability. Inmagnetic island topology, the different reconnection electric fields in squashed and coalescent islands impose different particle drift motions. This makes particle acceleration more efficient in squashed magnetic islands than in coalescent ones. The spectral indices of electron energy spectra are ∼ −4.2 for coalescent and ∼ −4.0 for squashed islands, which are lower than reported from the test-particle approach. The particles accelerated in magnetic islands are found trapped in the midplane of squashed islands, and shifted as clouds towards the X-nullpoints in coalescent ones.Conclusions. In reconnecting current sheets with multiple X- and O-nullpoints, particles are found accelerated on a much shorter spatial scale and gaining higher energies than near a single X-nullpoint. The distinct density and pitch-angle distributions of particles with high and low energy detected with the PIC approach can help to distinguish the observational features of accelerated particles

Design and Implementation of a Wireless Sensor Network for Smart Homes

Wireless sensor networks (WSNs) have become indispensable to the realization of smart homes. The objective of this paper is to develop such a WSN that can be used to construct smart home systems. The focus is on the design and implementation of the wireless sensor node and the coordinator based on ZigBee technology. A monitoring system is built by taking advantage of the GPRS network. To support multi-hop communications, an improved routing algorithm based on the Dijkstra algorithm is presented. Preliminary simulations have been conducted to evaluate the performance of the algorithm.Comment: International Workshop on Mobile Cyber-Physical Systems (MobiCPS 2010), in conjunction with UIC2010, IEEE, Xi'an, China, 26 - 29 October, 201