3,170 research outputs found
Operation plan for the High Density Tape/LANDSAT Imagery Verification and Extraction System (HDT/LIVES) data processing support
There are no author-identified significant results in this report
Operation plan for the data 100/LARS terminal system
The Data 100/LARS terminal system provides an interface for processing on the IBM 3031 computer system at Purdue University's Laboratory for Applications of Remote Sensing. The environment in which the system is operated and supported is discussed. The general support responsibilities, procedural mechanisms, and training established for the benefit of the system users are defined
High Density Tape Reformatting System/LANDSAT Imagery Verification and Extraction System (HDTRS/LIVES) production test throughput analysis
There are no author-identified significant results in this report
Collisions of boosted black holes: perturbation theory prediction of gravitational radiation
We consider general relativistic Cauchy data representing two nonspinning,
equal-mass black holes boosted toward each other. When the black holes are
close enough to each other and their momentum is sufficiently high, an
encompassing apparent horizon is present so the system can be viewed as a
single, perturbed black hole. We employ gauge-invariant perturbation theory,
and integrate the Zerilli equation to analyze these time-asymmetric data sets
and compute gravitational wave forms and emitted energies. When coupled with a
simple Newtonian analysis of the infall trajectory, we find striking agreement
between the perturbation calculation of emitted energies and the results of
fully general relativistic numerical simulations of time-symmetric initial
data.Comment: 5 pages (RevTex 3.0 with 3 uuencoded figures), CRSR-107
Initial Data and Coordinates for Multiple Black Hole Systems
We present here an alternative approach to data setting for spacetimes with
multiple moving black holes generalizing the Kerr-Schild form for rotating or
non-rotating single black holes to multiple moving holes. Because this scheme
preserves the Kerr-Schild form near the holes, it selects out the behaviour of
null rays near the holes, may simplify horizon tracking, and may prove useful
in computational applications. For computational evolution, a discussion of
coordinates (lapse function and shift vector) is given which preserves some of
the properties of the single-hole Kerr-Schild form
Stuffed Black Holes
Initial data corresponding to spacetimes containing black holes are
considered in the time symmetric case. The solutions are obtained by matching
across the apparent horizon different, conformally flat, spatial metrics. The
exterior metric is the vacuum solution obtained by the well known conformal
imaging method. The interior metric for every black hole is regular everywhere
and corresponds to a positive energy density. The resulting matched solutions
cover then the whole initial (Cauchy) hypersurface, without any singularity,
and can be useful for numerical applications. The simpler cases of one black
hole (Schwarzschild data) or two identical black holes (Misner data) are
explicitly solved. A procedure for extending this construction to the multiple
black hole case is also given, and it is shown to work for all time symmetric
vacuum solutions obtained by the conformal imaging method. The numerical
evolution of one such 'stuffed' black hole is compared with that of a pure
vacuum or 'plain' black hole in the spherically symmetric case.Comment: 12 pages, Latex, 4 postscript figures, corrected some typos, new
section about physical interpretatio
The Innermost Stable Circular Orbit of Binary Black Holes
We introduce a new method to construct solutions to the constraint equations
of general relativity describing binary black holes in quasicircular orbit.
Black hole pairs with arbitrary momenta can be constructed with a simple method
recently suggested by Brandt and Bruegmann, and quasicircular orbits can then
be found by locating a minimum in the binding energy along sequences of
constant horizon area. This approach produces binary black holes in a
"three-sheeted" manifold structure, as opposed to the "two-sheeted" structure
in the conformal-imaging approach adopted earlier by Cook. We focus on locating
the innermost stable circular orbit and compare with earlier calculations. Our
results confirm those of Cook and imply that the underlying manifold structure
has a very small effect on the location of the innermost stable circular orbit.Comment: 8 pages, 3 figures, RevTex, submitted to PR
Understanding initial data for black hole collisions
Numerical relativity, applied to collisions of black holes, starts with
initial data for black holes already in each other's strong field. The initial
hypersurface data typically used for computation is based on mathematical
simplifying prescriptions, such as conformal flatness of the 3-geometry and
longitudinality of the extrinsic curvature. In the case of head on collisions
of equal mass holes, there is evidence that such prescriptions work reasonably
well, but it is not clear why, or whether this success is more generally valid.
Here we study these questions by considering the ``particle limit'' for head on
collisions of nonspinning holes. Einstein's equations are linearized in the
mass of the small hole, and described by a single gauge invariant spacetime
function psi, for each multipole. The resulting equations have been solved by
numerical evolution for collisions starting from various initial separations,
and the evolution is studied on a sequence of hypersurfaces. In particular, we
extract hypersurface data, that is psi and its time derivative, on surfaces of
constant background Schwarzschild time. These evolved data can then be compared
with ``prescribed'' data, evolved data can be replaced by prescribed data on
any hypersurface, and evolved further forward in time, a gauge invariant
measure of deviation from conformal flatness can be evaluated, etc. The main
findings of this study are: (i) For holes of unequal mass the use of prescribed
data on late hypersurfaces is not successful. (ii) The failure is likely due to
the inability of the prescribed data to represent the near field of the smaller
hole. (iii) The discrepancy in the extrinsic curvature is more important than
in the 3-geometry. (iv) The use of the more general conformally flat
longitudinal data does not notably improve this picture.Comment: 20 pages, REVTEX, 26 PS figures include
Extended Lifetime in Computational Evolution of Isolated Black Holes
Solving the 4-d Einstein equations as evolution in time requires solving
equations of two types: the four elliptic initial data (constraint) equations,
followed by the six second order evolution equations. Analytically the
constraint equations remain solved under the action of the evolution, and one
approach is to simply monitor them ({\it unconstrained} evolution).
The problem of the 3-d computational simulation of even a single isolated
vacuum black hole has proven to be remarkably difficult. Recently, we have
become aware of two publications that describe very long term evolution, at
least for single isolated black holes. An essential feature in each of these
results is {\it constraint subtraction}. Additionally, each of these approaches
is based on what we call "modern," hyperbolic formulations of the Einstein
equations. It is generally assumed, based on computational experience, that the
use of such modern formulations is essential for long-term black hole
stability. We report here on comparable lifetime results based on the much
simpler ("traditional") - formulation.
We have also carried out a series of {\it constrained} 3-d evolutions of
single isolated black holes. We find that constraint solution can produce
substantially stabilized long-term single hole evolutions. However, we have
found that for large domains, neither constraint-subtracted nor constrained
- evolutions carried out in Cartesian coordinates admit
arbitrarily long-lived simulations. The failure appears to arise from features
at the inner excision boundary; the behavior does generally improve with
resolution.Comment: 20 pages, 6 figure
Can a combination of the conformal thin-sandwich and puncture methods yield binary black hole solutions in quasi-equilibrium?
We consider combining two important methods for constructing
quasi-equilibrium initial data for binary black holes: the conformal
thin-sandwich formalism and the puncture method. The former seeks to enforce
stationarity in the conformal three-metric and the latter attempts to avoid
internal boundaries, like minimal surfaces or apparent horizons. We show that
these two methods make partially conflicting requirements on the boundary
conditions that determine the time slices. In particular, it does not seem
possible to construct slices that are quasi-stationary and avoid physical
singularities and simultaneously are connected by an everywhere positive lapse
function, a condition which must obtain if internal boundaries are to be
avoided. Some relaxation of these conflicting requirements may yield a soluble
system, but some of the advantages that were sought in combining these
approaches will be lost.Comment: 8 pages, LaTeX2e, 2 postscript figure
- …