One-dimensional Particle-In-Cell simulation of electron beam plasma interaction
The theory of the two-stream instability is used to validate the initial phase of a developing code which ultimately aims to simulate the generation of VLF chorus. A one dimensional Particle-in-Cell simulation shows that waves are generated when a warm electron beam is injected into a cold background plasma with components of the electric field being excited. After a few time steps the phase space reveals a distortion of the beam and the creation of potential holes, causing electrons to oscillate.
Wave‐particle interactions in the equatorial source region of whistler‐mode emissions
Wave-particle interactions can play a key role in the process of transfer of energy between different electron populations in the outer Van Allen radiation belt. We present a case study of wave-particle interactions in the equatorial source region of whistler-mode emissions. We select measurements of the Cluster spacecraft when these emissions are observed in the form of random hiss with only occasional discrete chorus wave packets, and where the wave propagation properties are very similar to previously analyzed cases of whistler-mode chorus. We observe a positive divergence of the Poynting flux at minima of the magnetic field modulus along the magnetic field lines, indicating the central position of the source. In this region we perform a linear stability analysis based on the locally measured electron phase space densities. We find two unstable electron populations. The first of them consists of energy-dispersed and highly anisotropic injected electrons at energies of a few hundreds eV to a few keV, with the perpendicular temperature more than 10 times higher than the parallel temperature with respect to the magnetic field line. Another unstable population is formed by trapped electrons at energies above 10 keV. We show that the injected electrons at lower energies can be responsible for a part of the waves that propagate obliquely at frequencies above one half of the electron cyclotron frequency. Our model of the trapped electrons at higher energies gives insufficient growth of the waves below one half of the electron cyclotron frequency and a nonlinear generation mechanism might be necessary to explain their presence even in this simple case.
Dawn or dusk of the 5th age of research in educational technology? A literature review on (e-)leadership for technology-enhanced learning in higher education (2013-2017)
The aim of this article is to establish the extent to which the concept of e-leadership has taken off as a lens through which to study leadership for technology-enhanced learning (TEL) in higher education. Building on a previous study conducted in 2013, this article thus covers an exploratory review of the literature for the period 2103-2017. It analyses 49 articles which explore both the specific concept of e-leadership as well as other work dealing more generally with leadership and organisational change for TEL in higher education. The findings show that while none of the empirical studies identified in the literature refer explicitly to e-leadership, there are a number of interesting insights to be found in the theoretical articles. The results also highlight the widely different interpretations and applications of the concept of e-leadership and the consequent need for the definition to be refined. The paper concludes with recommendations for further multidisciplinary research at the intersection of the fields of educational technology and educational management, focusing on values, strategy, organisation and leadership interactions at meso level, the economy and public policy at macro level, and teaching and learning at the micro level, as well as for research in Leadership Development for TEL.