15,401 research outputs found
Evolving relativistic fluid spacetimes using pseudospectral methods and finite differencing
We present a new code for solving the coupled Einstein-hydrodynamics
equations to evolve relativistic, self-gravitating fluids. The Einstein field
equations are solved on one grid using pseudospectral methods, while the fluids
are evolved on another grid by finite differencing. We discuss implementation
details, such as the communication between the grids and the treatment of
stellar surfaces, and present code tests.Comment: To appear in the Proceedings of the Eleventh Marcel Grossmann Meetin
The Nonlinear Sigma Model With Distributed Adaptive Mesh Refinement
An adaptive mesh refinement (AMR) scheme is implemented in a distributed
environment using Message Passing Interface (MPI) to find solutions to the
nonlinear sigma model. Previous work studied behavior similar to black hole
critical phenomena at the threshold for singularity formation in this flat
space model. This work is a follow-up describing extensions to distribute the
grid hierarchy and presenting tests showing the correctness of the model.Comment: 6 pages, 5 figure
HARES: an efficient method for first-principles electronic structure calculations of complex systems
We discuss our new implementation of the Real-space Electronic Structure
method for studying the atomic and electronic structure of infinite periodic as
well as finite systems, based on density functional theory. This improved
version which we call HARES (for High-performance-fortran Adaptive grid
Real-space Electronic Structure) aims at making the method widely applicable
and efficient, using high performance Fortran on parallel architectures. The
scaling of various parts of a HARES calculation is analyzed and compared to
that of plane-wave based methods. The new developments that lead to enhanced
performance, and their parallel implementation, are presented in detail. We
illustrate the application of HARES to the study of elemental crystalline
solids, molecules and complex crystalline materials, such as blue bronze and
zeolites.Comment: 17 two-column pages, including 9 figures, 5 tables. To appear in
Computer Physics Communications. Several minor revisions based on feedbac
A new approach to high resolution, high contrast electron microscopy of macromolecular block copolymer assemblies
Determining the structure of macromolecular samples is vital for understanding and adapting their function. Transmission electron microscopy (TEM) is widely used to achieve this, but, owing to the weak electron scattering cross-section of carbon, TEM images of macromolecular samples are generally low contrast and low resolution. Here we implement a fast and practically simple routine to achieve high-contrast imaging of macromolecular samples using exit wave reconstruction (EWR), revealing a new level of structural detail. This is only possible using ultra-low contrast supports such as the graphene oxide (GO) used here and as such represents a novel application of these substrates. We apply EWR on GO membranes to study self-assembled block copolymer structures, distinguishing not only the general morphology or nanostructure, but also evidence for the substructure (i.e. the polymer chains) which gives insight into their formation mechanisms and functional properties
GiRaFFE: An Open-Source General Relativistic Force-Free Electrodynamics Code
We present GiRaFFE, the first open-source general relativistic force-free
electrodynamics (GRFFE) code for dynamical, numerical-relativity generated
spacetimes. GiRaFFE adopts the strategy pioneered by McKinney and modified by
Paschalidis and Shapiro to convert a GR magnetohydrodynamic (GRMHD) code into a
GRFFE code. In short, GiRaFFE exists as a modification of IllinoisGRMHD, a
user-friendly, open-source, dynamical-spacetime GRMHD code. Both GiRaFFE and
IllinoisGRMHD leverage the Einstein Toolkit's highly-scalable infrastructure to
make possible large-scale simulations of magnetized plasmas in strong,
dynamical spacetimes on adaptive-mesh refinement (AMR) grids. We demonstrate
that GiRaFFE passes a large suite of both flat and curved-spacetime code tests
passed by a number of other state-of-the-art GRFFE codes, and is thus ready for
production-scale simulations of GRFFE phenomena of key interest to relativistic
astrophysics.Comment: 23 pages, 4 figures. Consistent with published versio
A 3D radiative transfer framework: I. non-local operator splitting and continuum scattering problems
We describe a highly flexible framework to solve 3D radiation transfer
problems in scattering dominated environments based on a long characteristics
piece-wise parabolic formal solution and an operator splitting method. We find
that the linear systems are efficiently solved with iterative solvers such as
Gauss-Seidel and Jordan techniques. We use a sphere-in-a-box test model to
compare the 3D results to 1D solutions in order to assess the accuracy of the
method. We have implemented the method for static media, however, it can be
used to solve problems in the Eulerian-frame for media with low velocity
fields.Comment: A&A, in press. 14 pages, 19 figures. Full resolution figures
available at ftp://phoenix.hs.uni-hamburg.de/preprints/3DRT_paper1.pdf HTML
version (low res figures) at
http://hobbes.hs.uni-hamburg.de/~yeti/PAPERS/3drt_paper1/index.htm
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