72 research outputs found
Ptychographic reconstruction of attosecond pulses
We demonstrate a new attosecond pulse reconstruction modality which uses an
algorithm that is derived from ptychography. In contrast to other methods,
energy and delay sampling are not correlated, and as a result, the number of
electron spectra to record is considerably smaller. Together with the robust
algorithm, this leads to a more precise and fast convergence of the
reconstruction.Comment: 12 pages, 7 figures, the MATLAB code for the method described in this
paper is freely available at
http://figshare.com/articles/attosecond_Extended_Ptychographyc_Iterative_Engine_ePIE_/160187
Beyond the Bowen-York extrinsic curvature for spinning black holes
It is well-known that Bowen-York initial data contain spurious radiation.
Although this ``junk'' radiation has been seen to be small for non-spinning
black-hole binaries in circular orbit, its magnitude increases when the black
holes are given spin. It is possible to reduce the spurious radiation by
applying the puncture approach to multiple Kerr black holes, as we demonstrate
for examples of head-on collisions of equal-mass black-hole binaries.Comment: 10 pages, 2 figures, submitted to special "New Frontiers in Numerical
Relativity" issue of Classical and Quantum Gravit
Binary black holes on a budget: Simulations using workstations
Binary black hole simulations have traditionally been computationally very
expensive: current simulations are performed in supercomputers involving dozens
if not hundreds of processors, thus systematic studies of the parameter space
of binary black hole encounters still seem prohibitive with current technology.
Here we show how the multi-layered refinement level code BAM can be used on
dual processor workstations to simulate certain binary black hole systems. BAM,
based on the moving punctures method, provides grid structures composed of
boxes of increasing resolution near the center of the grid. In the case of
binaries, the highest resolution boxes are placed around each black hole and
they track them in their orbits until the final merger when a single set of
levels surrounds the black hole remnant. This is particularly useful when
simulating spinning black holes since the gravitational fields gradients are
larger. We present simulations of binaries with equal mass black holes with
spins parallel to the binary axis and intrinsic magnitude of S/m^2= 0.75. Our
results compare favorably to those of previous simulations of this particular
system. We show that the moving punctures method produces stable simulations at
maximum spatial resolutions up to M/160 and for durations of up to the
equivalent of 20 orbital periods.Comment: 20 pages, 8 figures. Final version, to appear in a special issue of
Class. Quantum Grav. based on the New Frontiers in Numerical Relativity
Conference, Golm, July 200
Spatial and temporal variability of selected trace metals in Kiel Bight and Mecklenburg Bight : data report from 1990/92 = Räumliche und zeitliche Variabilität ausgewählter Spurenmetalle in der Kieler und Mecklenburger Bucht
Merger of black hole-neutron star binaries in full general relativity
We present our latest results for simulation for merger of black hole
(BH)-neutron star (NS) binaries in full general relativity which is performed
preparing a quasicircular state as initial condition. The BH is modeled by a
moving puncture with no spin and the NS by the -law equation of state
with and corotating velocity field as a first step. The mass of the
BH is chosen to be or , and the rest-mass
of the NS with relatively large radius of the NS
--14 km. The NS is tidally disrupted near the innermost stable
orbit but --90% of the material is swallowed into the BH and resulting
disk mass is not very large as even for small BH mass . The result indicates that the system of a BH and a massive disk
of is not formed from nonspinning BH-NS binaries irrespective
of BH mass, although a disk of mass is a possible outcome
for this relatively small BH mass range as --4. Our results
indicate that the merger of low-mass BH and NS may form a central engine of
short-gamma-ray bursts.Comment: 14 pages. To appear in a special issue of Classical and Quantum
Gravity: New Frontiers in Numerical Relativit
Multipolar analysis of spinning binaries
We present a preliminary study of the multipolar structure of gravitational
radiation from spinning black hole binary mergers. We consider three different
spinning binary configurations: (1) one "hang-up" run, where the black holes
have equal masses and large spins initially aligned with the orbital angular
momentum; (2) seven "spin-flip" runs, where the holes have a mass ratio q=4,
the spins are anti-aligned with the orbital angular momentum, and the initial
Kerr parameters of the holes j_1=j_2=j_i are fine-tuned to produce a
Schwarzschild remnant after merger; (3) three "super-kick" runs where the mass
ratio q=M_1/M_2=1, 2, 4 and the spins of the two holes are initially located on
the orbital plane, pointing in opposite directions. For all of these
simulations we compute the multipolar energy distribution and the Kerr
parameter of the final hole. For the hang-up run, we show that including
leading-order spin-orbit and spin-spin terms in a multipolar decomposition of
the post-Newtonian waveforms improves the agreement with the numerical
simulation.Comment: corrected minor typos in Eqs.(2),(3); final version accepted by CQ
Phenomenological template family for black-hole coalescence waveforms
Recent progress in numerical relativity has enabled us to model the
non-perturbative merger phase of the binary black-hole coalescence problem.
Based on these results, we propose a phenomenological family of waveforms which
can model the inspiral, merger, and ring-down stages of black hole coalescence.
We also construct a template bank using this family of waveforms and discuss
its implementation in the search for signatures of gravitational waves produced
by black-hole coalescences in the data of ground-based interferometers. This
template bank might enable us to extend the present inspiral searches to
higher-mass binary black-hole systems, i.e., systems with total mass greater
than about 80 solar masses, thereby increasing the reach of the current
generation of ground-based detectors.Comment: Minor changes, Submitted to Class. Quantum Grav. (Proc. GWDAW11
Energy and directional signatures for plane quantized gravity waves
Solutions are constructed to the quantum constraints for planar gravity
(fields dependent on z and t only) in the Ashtekar complex connection
formalism. A number of operators are constructed and applied to the solutions.
These include the familiar ADM energy and area operators, as well as new
operators sensitive to directionality (z+ct vs. z-ct dependence). The
directionality operators are quantum analogs of the classical constraints
proposed for unidirectional plane waves by Bondi, Pirani, and Robinson (BPR).
It is argued that the quantum BPR constraints will predict unidirectionality
reliably only for solutions which are semiclassical in a certain sense. The ADM
energy and area operators are likely to have imaginary eigenvalues, unless one
either shifts to a real connection, or allows the connection to occur other
than in a holonomy. In classical theory, the area can evolve to zero. A quantum
mechanical mechanism is proposed which would prevent this collapse.Comment: 54 pages; LaTe
Are moving punctures equivalent to moving black holes?
When simulating the inspiral and coalescence of a binary black-hole system,
special care needs to be taken in handling the singularities. Two main
techniques are used in numerical-relativity simulations: A first and more
traditional one ``excises'' a spatial neighbourhood of the singularity from the
numerical grid on each spacelike hypersurface. A second and more recent one,
instead, begins with a ``puncture'' solution and then evolves the full
3-metric, including the singular point. In the continuum limit, excision is
justified by the light-cone structure of the Einstein equations and, in
practice, can give accurate numerical solutions when suitable discretizations
are used. However, because the field variables are non-differentiable at the
puncture, there is no proof that the moving-punctures technique is correct,
particularly in the discrete case. To investigate this question we use both
techniques to evolve a binary system of equal-mass non-spinning black holes. We
compare the evolution of two curvature 4-scalars with proper time along the
invariantly-defined worldline midway between the two black holes, using
Richardson extrapolation to reduce the influence of finite-difference
truncation errors. We find that the excision and moving-punctures evolutions
produce the same invariants along that worldline, and thus the same spacetimes
throughout that worldline's causal past. This provides convincing evidence that
moving-punctures are indeed equivalent to moving black holes.Comment: 4 pages, 3 eps color figures; v2 = major revisions to introduction &
conclusions based on referee comments, but no change in analysis or result
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