# 2016

25. October 2016

**Talks at ZARM**

Where: | ZARM, University of Bremen, Room 1280 |

When: | 16:00 hrs |

Speaker: | Jens Mahlmann (Valencia) |

Title: | "Magnetospheric electrodynamics" |

Abstract: | From an ongoing examination of magnetic field topologies around rotating black holes an overview of force-free, axisymmetric magnetospheric electrodynamics in Kerr spacetime is presented. Numerical strategies to solve the relativistic Grad-Shafranov equation motivate a closer look on the so called light cylinders from a General Relativity point of view. An outlook on a stability analysis for electromagnetic field configurations employing relativistic magnetohydrodynamics codes (e.g., CoCoNut, Einstein Toolkit) concludes the talk. |

09 August 2016

**Talks at ZARM**

Where: | ZARM, University of Bremen, Room 1280 |

When: | 14:30 hrs |

Speaker: | Torben Frost |

Title: | "Gravitational lensing by an accelerated black hole" |

01 August 2016

**Talks at ZARM**

Where: | ZARM, University of Bremen, Room 1730 |

When: | 14:00 hrs |

Speaker: | Prof. Dr. Gustaaf Jacobs, Department of Aerospace Engineering and Engineering Mechanics, San Diego State University |

Title: | "Lagrangian Coherent Structures and DNS with Discontinuous Galerkin methods" |

Abstract: | High-fidelity numerical tools based on high-order Discontinuous-Galerkin (DG) methods and Lagrangian Coherent Structure (LCS) theory for the study of separated, vortex-dominated flows are discussed. A numerical framework is presented that couples a higher-order DG-DNS solver with time-dependent analysis of the flow through LCS . At heart of this framework lies an algorithm that computes Finite-Time Lyapunov Exponent (FTLE) fields simultaneously with DNS and with spectral accuracy. The algorithm is applied to investigate the role of LCS in fluid mixing in the unstable bottom boundary layer under a solitary surface wave mimicked by a soliton-like pressure gradient driven flow in an oscillating water tunnel. The development of two and three-dimensional LCS fields for the unsteady separated flow over a NACA 65-(1)412 airfoil at a free-stream Reynolds number of Re=20,000 is also discussed. |

07 June 2016

**Talks at ZARM**

Where: | ZARM, University of Bremen |

Speaker: | by Dr. Steffen Aksteiner |

Title: | "Symbolic computer algebra and applications in linearized gravity" |

Abstract: | The symbolic computer algebra package xAct for Mathematica is an efficient tool for abstract differential geometric calculations. The speaker will review basic features of xAct and some of its applications in General Relativity. In the second part of the talk I will present more advances xAct tools based on spinors to elaborate the special geometry of the Kerr spacetime. Important consequences of the special geometry are symmetries and conservation laws for fields on the Kerr spacetime, including Maxwell and linearized gravity. |

25 February 2016

**Talks at ZARM**

Where: | ZARM, University of Bremen, Room 1280 |

When: | 11:00 am |

Speaker: | by Karen Schulze-Koops |

Abstract: | Karen Schulze-Koops is giving a seminar talk on the results of her Diploma Thesis. The Thesis deals with general-relativistic ray optics in a plasma. In particular, the Sachs equations for light bundles in a plasma are derived and a brief outlook on possible applications to cosmology is given. The talk will be in Englisch. Everybody is welcome. |

# 2015

6 October 2015

**Talks at ZARM**

Where: | ZARM, University of Bremen, Room 1280 |

When: | 14:30 hrs |

Speaker: | by Dr. Martin Scholtz (Charles University of Prague, Prague, Czech Republic |

Topic: | "Expanding impulsive weaves" |

Abstract: | As a byproduct of developing the twistor theory, Penrose has discovered an interesting method for generating exact solutions of Einstein's equations which describe impulsive waves. The method is known as the "scissors and paste" method and it is based on cutting a spacetime along the null hypersurface and then re-attaching both parts in a non-trivial way. In the talk, we review mathematical details of this procedure and give an interpretation of the resulting solution in terms of a snapping cosmic string. Then we report some recent results of the ongoing research. |