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Sökning: WFRF:(Ebert Ute)

  • Resultat 1-3 av 3
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1.
  • Liu, Lipeng, 1990- (författare)
  • Physics of Electrical Discharge Transitions in Air
  • 2017
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Electrical discharges with a variety of different forms (streamers, glow corona, leaders, etc.) broadly exist in nature and in industrial applications. Under certain conditions, one electrical discharge can be transformed into another form. This thesis is aimed to develop and use numerical simulation models in order to provide a better physical understanding of two of such transitions, namely the glow-to-streamer and the streamer-to-leader transitions in air.In the first part, the thesis includes the two-dimensional simulation of the glow-to-streamer transition under a fast changing background electric field. The simulation is performed with a fluid model taking into account electrons. An efficient semi-Lagrangian algorithm is proposed to solve the convection-dominated continuity equations present in the model. The condition required for the glow-to-streamer transition is evaluated and discussed. In order to enable such simulations for configurations with large interelectrode gaps and long simulation times, an efficient simplified model for glow corona discharges and their transition into streamers is also proposed.The second part of the thesis is dedicated to investigate the dynamics of the streamer-to-leader transition in long air gaps at atmospheric pressure. The transition is studied with a one-dimensional thermo-hydrodynamic model and a detailed kinetic scheme for N2/O2/H2O mixtures. In order to evaluate the effect of humidity, the kinetic scheme includes the most important reactions with the H2O molecule and its derivatives. The analysis includes the simulation of the corresponding streamer bursts, dark periods and aborted leaders that may occur prior to the inception of a stable leader. The comparison between the proposed model and the widely-used model of Gallimberti is also presented.
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2.
  • Scholten, Olaf, et al. (författare)
  • Lightning Imaging with LOFAR
  • 2017
  • Ingår i: 7th International Conference on Acoustic and Radio EeV Neutrino Detection Activities (ARENA 2016). - : EDP Sciences.
  • Konferensbidrag (refereegranskat)abstract
    • We show that LOFAR can be used as a lightning mapping array with a resolution that is orders of magnitude better than existing arrays. In addition the polarization of the radiation can be used to track the direction of the stepping discharges. © 2017 The Authors, published by EDP Sciences.
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3.
  • Scholten, Olaf, et al. (författare)
  • Precision study of radio emission from air showers at LOFAR
  • 2017
  • Ingår i: RICAP16, 6TH ROMA INTERNATIONAL CONFERENCE ON ASTROPARTICLE PHYSICS. - : EDP Sciences.
  • Konferensbidrag (refereegranskat)abstract
    • Radio detection as well as modeling of cosmic rays has made enormous progress in the past years. We show this by using the subtle circular polarization of the radio pulse from air showers measured in fair weather conditions and the intensity of radio emission from an air shower under thunderstorm conditions.
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  • Resultat 1-3 av 3

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