Guests Theoretical Physics I - Prof. Schlickeiser



Prof. Dr. Felix Spanier von der North-West University, Potchefstroom, Southafrica, ist zu Gast bei Prof. Dr. Reinhard Schlickeiser (TP IV) und hält im Rahmen des Seminars "Weltraum- und Astrophysik" am 09.12.2014 um 14:15 Uhr in NB 7/67 einen Vortrag über “Emission mechanisms in AGN - a non-linear puzzle”. Interessierte sind herzlich willkommen!

Abstract: Active Galactiv Nuclei are nowadays one of the most interesting objects of extragalactic astronomy. Their wideband spectrum and their extreme properties - in terms of energy as well as in terms of variability - can be studied with recent experiments like HESS and Fermi. Although the amount of observational data is increasing rapidly, we do not yet understand the intrinsic mechanics of these objects. While there is consensus that AGN host populations of nonthermal particles, it is neither clear whether these are only leptons or also protons nor is it clear, which emission mechanism plays a role.
In my talk I want to outline the problems in understanding the emission mechanisms. One of the major problems is the nonlinear coupling of different processes, which effectively prevents a simple linear analysis and a mapping of observational spectra and internal parameters. I will present different approaches of modeling AGN, their predictions and their pitfalls.

Prof. Dr. Felix Spanier



Dr. Ioannis Kourakis von der Queens University Belfast, Northern Ireland ist zu Gast bei Prof. Dr. Reinhard Schlickeiser und hält am Mittwoch, 26.11.2014 ab 10:15 Uhr in NB 7/67 im Rahmen des Seminars "Weltraum- und Astrophysik" einen Vortrag über “Rogue Waves in Electromagnetic Beam-Plasma Interactions: modeling and phenomenology”. Interessierte sind herzlich willkommen! 

Abstract: Extreme events in the form of rogue waves (freak waves) occur widely in the open sea. These are space‐and time‐localised excitations, which appear unexpectedly and are characterised by significant amplitude (exceeding 2.5 times the average turbulence level in their environment). Beyond ocean dynamics, the mechanisms underlying rogue wave formation are now being investigated in various physical contexts, including materials science, nonlinear optics and plasma physics , to mention but a few.
Inspired by the ubiquity of this challenging phenomenon, we have undertaken an investigation, from first principles, of the occurrence of rogue waves associated with the propagation of an electromagnetic pulse in a plasma. A multiscale technique is employed to solve the fluid‐Maxwell equations describing a weakly nonlinear circularly polarized electromagnetic pulses in collisional magnetized plasmas. A nonlinear Schrodinger (NLS) type equation is shown to govern the amplitude of the vector potential. A brief review of existing theories based on non‐stationary envelope solutions of the NLS equation is presented (Peregrine soliton, Akhmediev breather, Kuznetzov‐Ma breather), and the variation of their structural properties with the magnetic field is investigated. Recent advances on numerical investigations of the occurrence of rogue waves in plasmas are presented and discussed. 

Dr. Ioannis Kourakis



Prof. Dr. Yuri Litvinenko von der University of Waikato, New Zealand ist zu Gast bei Prof. Dr. Reinhard Schlickeiser (TP IV). Er hält im Rahmen des Seminars "Weltraum- und Astrophysik" am Mittwoch, 12.11.2014, 10:15 Uhr in NB 7/67 einen Vortrag über “Regular and diffusive photospheric flux cancellation”. Interessierte sind herzlich eingeladen!

Abstract: Photospheric flux cancellation on the Sun is considered. Observations imply that cancellation can be a diffusive rather than regular process. A criterion is derived, which quantifies the parameter range in which diffusive photospheric cancellation should occur. Regular cancellation models are shown to give a quantitatively accurate description of photospheric cancellation. Application of the results to large-scale dispersal of the photospheric magnetic flux is discussed. 

Yuri Litvinenko



Prof. Dr. Stefaan Poedts von der Katholieke Universiteit Leuven in Belgien hält am 23.01.2014 im Physikalischen Kolloquium (12:15, H-NB) einen Vortrag über "A New Plasma Kinetic Paradigm for the Solar Coronal Heating Problem". Die Einführung hält Prof. Dr. Reinhard Schlickeiser.
Interessierte sind herzlich willkommen!



Vom 9.7.-31.12.2013 ist Herr Mohemedreza Taghadosi, ein Doktorand aus dem Iran, Gast am Lehrstuhl für Weltraum- und Astrophysik (TP4). Herr Taghadosi ist ein Experte zur Berechnung der nichtlinearen Entwicklung der Filamentierungs-Instabilität in stromgetriebenen Plasmen. In einem Vortrag im TP4-Lehrstuhlseminar hat er ein sehr interessantes Verfahren vorgestellt, das sich auch für unsere Arbeiten zur kosmischen Magnetfelderzeugung durch Filamentierungsinstabiltäten nutzen lässt. 

Lehrstuhl für Weltraum- und Astrophysik