1,811 research outputs found
A covariant action principle for dissipative fluid dynamics: From formalism to fundamental physics
We present a new variational framework for dissipative general relativistic
fluid dynamics. The model extends the convective variational principle for
multi-fluid systems to account for a range of dissipation channels. The key
ingredients in the construction are i) the use of a lower dimensional matter
space for each fluid component, and ii) an extended functional dependence for
the associated volume forms. In an effort to make the concepts clear, the
formalism is developed in steps with the model example of matter coupled to
heat considered at each level. Thus we discuss a model for heat flow, derive
the relativistic Navier-Stokes equations and discuss why the individual
dissipative stress tensors need not be spacetime symmetric. We argue that the
new formalism, which notably does not involve an expansion away from an assumed
equilibrium state, provides a conceptual breakthrough in this area of research
and provide an ambitious list of directions in which one may want to extend it
in the future. This involves an exciting set of problems, relating to both
applications and foundational issues.Comment: 21 pages RevTex, 3 pdf figures, matches the published version. arXiv
admin note: text overlap with arXiv:1107.1005 by other author
The nonlinear development of the relativistic two-stream instability
The two-stream instability has been mooted as an explanation for a range of
astrophysical applications from GRBs and pulsar glitches to cosmology. Using
the first nonlinear numerical simulations of relativistic multi-species
hydrodynamics we show that the onset and initial growth of the instability is
very well described by linear perturbation theory. In the later stages the
linear and nonlinear description match only qualitatively, and the instability
does not saturate even in the nonlinear case by purely ideal hydrodynamic
effects.Comment: 15 pages, 9 figure
Stationary structure of relativistic superfluid neutron stars
We describe recent progress in the numerical study of the structure of
rapidly rotating superfluid neutron star models in full general relativity. The
superfluid neutron star is described by a model of two interpenetrating and
interacting fluids, one representing the superfluid neutrons and the second
consisting of the remaining charged particles (protons, electrons, muons). We
consider general stationary configurations where the two fluids can have
different rotation rates around a common rotation axis. The previously
discovered existence of configurations with one fluid in a prolate shape is
confirmed.Comment: 5 pages, 2 figures. Conference proceedings for the 26th Spanish
Relativity Meeting (ERE 2002), Menorca, Spain, 22-24 Sept. 200
The dynamics of neutron star crusts: Lagrangian perturbation theory for a relativistic superfluid-elastic system
The inner crust of a mature neutron star is composed of an elastic lattice of
neutron-rich nuclei penetrated by free neutrons. These neutrons can flow
relative to the crust once the star cools below the superfluid transition
temperature. In order to model the dynamics of this system, which is relevant
for a range of problems from pulsar glitches to magnetar seismology and
continuous gravitational-wave emission from rotating deformed neutron stars, we
need to understand general relativistic Lagrangian perturbation theory for
elastic matter coupled to a superfluid component. This paper develops the
relevant formalism to the level required for astrophysical applications.Comment: 31 pages, double spacing, minor typos fixe
Palimpsests: Salvage, Sacrifice, and the Subject of Truth in Photographs
A palimpsest is a new inscription on old materials, a form of media offering a hybrid yet hierarchical sense of time. Turning frequently to the writings of Alain Badiou, Roland Barthes, and Walter Benjamin, I examine two zines published in the wake of the death of a Chicago street artist and the confessional postcards of Frank Warren’s PostSecret mail art project to understand the formal traits and claims to truth photographs exhibit when they are transformed into palimpsests. The present intrudes on the past in these media, incompletely erasing or overwriting history to show the gaps in context and what slips from photographic memory
Reengineering of the national organization of the General Association of General Baptists
https://place.asburyseminary.edu/ecommonsatsdissertations/1106/thumbnail.jp
RAM-Efficient External Memory Sorting
In recent years a large number of problems have been considered in external
memory models of computation, where the complexity measure is the number of
blocks of data that are moved between slow external memory and fast internal
memory (also called I/Os). In practice, however, internal memory time often
dominates the total running time once I/O-efficiency has been obtained. In this
paper we study algorithms for fundamental problems that are simultaneously
I/O-efficient and internal memory efficient in the RAM model of computation.Comment: To appear in Proceedings of ISAAC 2013, getting the Best Paper Awar
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