[Commits] [svn:einsteintoolkit] www/ (Rev. 749)

[knarf at cct.lsu.edu]

User: knarf
Date: 2011/11/24 02:37 PM

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  index.php
 /seminars/2011_11_28/
  Zachariah_Etienne.jpg, index.php

Log:
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+<?php $title='Einstein Toolkit Seminars';
+include_once($_SERVER['DOCUMENT_ROOT'].'/global/header.php');?>
+
+<h2>Improved EM Gauge Condition for GRMHD Simulations with AMR</h2>
+
+<h3>Abstract</h3>
+<p>
+We recently developed a new GRMHD code with AMR that evolves the
+electromagnetic (EM) vector potential A<sub>i</sub> instead of the magnetic fields
+directly.  Evolving A<sub>i</sub> enables one to use any interpolation scheme on
+refinement level boundaries and still guarantee that the magnetic field remains
+divergenceless. As in classical EM, a gauge choice must be made when evolving
+A<sub>i</sub>, and we originally chose a straightforward ``algebraic'' gauge condition
+to simplify the A<sub>i</sub> evolution equation.  However, magnetized black
+hole-neutron star (BHNS) simulations in this gauge exhibit unphysical behavior,
+including the spurious appearance of strong magnetic fields on refinement level
+boundaries. This spurious behavior is exacerbated when matter crosses
+refinement boundaries during tidal disruption of the NS.  We demonstrate via an
+eigenvalue analysis and a numerical study that zero-speed modes in the
+algebraic gauge, coupled with the frequency filtering that occurs on refinement
+level boundaries, are responsible for the creation of spurious magnetic fields.
+We show that the EM Lorenz gauge exhibits no zero-speed modes, and as a
+consequence, spurious magnetic effects are quickly propagated away, allowing
+for long-term, stable magnetized BHNS evolutions.
+</p>
+
+<h3>Presenter: Zachariah Etienne</h3>
+<img href="Zachariah_Etienne.jpg" width="20%" alt="Zachariah Etienne">
+<p>
+NSF Astronomy <&amp> Astrophysics Postdoctoral Fellow, University of Illinois
+</p>
+<p>
+Numerical Relativity Group Research interests: My research interests span all
+of computational astrophysics. Much of my past work has focused on simulating
+the mergers of compact binary systems, including BHNS, BHBH, WDNS, and NSNS. My
+current work focuses on BHBH mergers, as well as studying MHD effects in BHNS
+mergers.
+</p>
+
+<?php include_once($_SERVER['DOCUMENT_ROOT'].'/global/footer.php');?>



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+<?php $title='Einstein Toolkit Seminars';
+include_once($_SERVER['DOCUMENT_ROOT'].'/global/header.php');?>
+
+<p>The Einstein Toolkit (irregularly at the moment) hosts seminars on topics of
+interest to the numerical relativity community. Date, time and (virtual)
+location are, besides here, announced on the Einstein Toolkit mailing list.
+</p>
+
+<?php include_once($_SERVER['DOCUMENT_ROOT'].'/global/footer.php');?>



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