Within the usual Einstein Toolkit weekly meeting time, WebEx will be used for audio, video, and slides. The slides are available here (pdf, 11 MByte); unfortunately, the presentation itself was not recorded. The talk is based on this paper.

I discuss the implementation and performance of multipatch grids in the general relativistic hydrodynamics code "GRHydro" (see http://arxiv.org/abs/1212.1191). Multipatch methods allow one to cover the computational domain with multiple curvi-linear grid patches that can be adapted to the problem symmetry. For instance, rectangular Cartesian grids are useful for the region directly covering the central source (such as a binary neutron star system), but spherical grids are more efficient in the far-away region, e.g. the gravitational wave zone. Combining the different grid shapes can offer significant performance/accuracy benefits. The multipatch implementation in GRHydro is based on overlapping grids where ghost data between patches is exchanged via high-order Lagrange interpolation polynomials for spacetime variables, and second-order essentially non-oscillatory (ENO) interpolation for fluid variables that may contain shocks and other discontinuities. I describe the changes that were introduced to make GRHydro compatible with multipatch grids. In addition, I also briefly describe the implementation of cell-centered adaptive mesh-refinement and refluxing, a technique of ensuring numerical flux conservation at mesh refinement boundaries (corresponding to conservation of mass, energy, and momentum in the absence of gravity). I finally show the performance of the new updates to GRHydro by a number of test problems: (perturbed) TOV star, stellar collapse, and binary neutron star coalescence.

NASA Einstein Postdoctoral Fellow in Theoretical Astrophysics at the Theoretical Astrophysics (TAPIR) group at the California Institute of Technology

Research interests: I am interested in the modeling of gravitationally radiating sources such as coalescing compact binaries and collapsing stellar cores using numerical relativity. This work involves extending our understanding of the physics of these sources, their dynamics, and their emitted gravitational wave signature. A prime goal is the construction of template banks to be used in gravitational wave observatories such as LIGO, Virgo and GEO600. I develop and extend simulations based on Einstein's theory of general relativity that run on massively parallel computers. A particular focus of my research has been on gravitational-wave extraction techniques and binary black hole merger physics.