Le jeudi 19 novembre 2015 à 14:00, en salle de conf de l'OSUR (RDC bât.
Le jeudi 19 novembre 2015 à 14:00
, en salle de conf de l'OSUR (RDC bât. 14B, Beaulieu), J. Brian A. Mitchell propose un séminaire intituléBall Lightning : Scientific Observation and Laboratory SurrogatesRésumé :
Ball lightning has been an enigma for centuries. A floating fireball that can pass through closed windows, can float in the air for seconds and whose mode of formation has defied scientific explanation. Indeed there have been factions who have attributed it to an optical illusion or a figment of an imagination, shocked at being too close to a lightning strike. Last year a Chinese research team succeeded (by chance) to film the phenomenon using a video camera equipped with a spectrograph . This observation was able to confirm that ball lightning is indeed a dusty plasma whose energy and longevity come from the chemical reaction of nanoparticles oxidizing in air. This is the so?called "Abrahamson Model" [2,3]. There is also the implication that microwaves created by the lightning play a role in the formation of this plasma and this can perhaps explain the fact that it is seen to pass through solid walls and windows. Experiments that reproduce microwave generated surrogates of ball lightning [4?6] will be presented along with results obtained with these objects in experiments at the European Synchrotron Radiation Facility.
The implications for effects on aircraft will be discussed along with the possibilities for laboratory experimentation in this regard.
1. Cen, J., Yuan, P. and Xue, S. "Observation of the Optical and Spectral Characteristics of Ball Lightning" Physical Review Letters 2014, 112, 035001?4.
2. Abrahamson, J. and Dinniss, J. "Ball lightning caused by oxidation of nanoparticle networks from normal lightning strikes on soil," Nature, 2000, 403, pp. 519?521.
3. Abrahamson, J., "Ball lightning from atmospheric discharges via metal nanosphere oxidation: from soils, wood or metals," Phil. Trans. R. Soc. Lond. A, 2002, 360, pp. 61?88.
4. Dikhtyar, V. and Jerby, E. "Fireball ejection from a molten hot?spot to air by localized microwaves," Physical Review Letters, 2006, 96, 04500?4.
5. Mitchell, J. B. A., LeGarrec, J.L., Sztucki, M., Narayanan, T. , Dikhtyar, V. and Jerby, E. "Evidence for nanoparticles in microwave?generated fireballs observed by synchrotron X?ray scattering," Physical Review Letters, 2008, 100, 065001?4
6. Meir, Y., Jerby , E. , Barkay, Z. , Ashkenazi, D., Mitchell, J.B.A. , Narayanan, T. , Eliaz, N. , Le Garrec , J.L. , Sztucki, M. and Meshcheryakov, O. " Observations of Ball?Lightning?Like Plasmoids Ejected from Silicon by Localized Microwaves" Materials 2013, 6, 4011?4030.Contact :J. Brian A. Mitchell (IPR)