2,939 research outputs found
On the Existence of Radiation Gauges in Petrov type II spacetimes
The radiation gauges used by Chrzanowski (his IRG/ORG) for metric
reconstruction in the Kerr spacetime seem to be over-specified. Their
specification consists of five conditions: four, which we treat here as valid
gauge conditions, plus an additional condition on the trace of the metric
perturbation. In this work, we utilize a newly developed form of the perturbed
Einstein equations to establish a condition -- on a particular tetrad component
of the stress-energy tensor -- under which the full IRG/ORG can be imposed.
Using gauge freedom, we are able to impose the full IRG for Petrov type II and
type D backgrounds, using a different tetrad for each case. As a specific
example, we work through the process of imposing the IRG in a Schwarzschild
background, using a more traditional approach. Implications for metric
reconstruction using the Teukolsky curvature perturbations in type D spacetimes
are briefly discussed.Comment: 21 pages, uses iop style files. v2: proved a stronger result for type
II backgrounds, added a subsection on remaining gauge freedom in the full IRG
and improved calrity and readability throughout due to insightful referee
comments; published as Class. Quantum Grav. 24 (2007) 2367-238
Reconstruction of Black Hole Metric Perturbations from Weyl Curvature II: The Regge-Wheeler gauge
Perturbation theory of rotating black holes is described in terms of the Weyl
scalars and ; each satisfying the Teukolsky's complex master
wave equation with spin , and respectively representing outgoing and
ingoing radiation. We explicitly construct the metric perturbations out of
these Weyl scalars in the Regge-Wheeler gauge in the nonrotating limit. We
propose a generalization of the Regge-Wheeler gauge for Kerr background in the
Newman-Penrose language, and discuss the approach for building up the perturbed
spacetime of a rotating black hole. We also provide both-way relationships
between waveforms defined in the metric and curvature approaches in the time
domain, also known as the (inverse-) Chandrasekhar transformations, generalized
to include matter.Comment: 22 pages, no figure
Lectures on Linear Stability of Rotating Black Holes
These lecture notes are concerned with linear stability of the non-extreme
Kerr geometry under perturbations of general spin. After a brief review of the
Kerr black hole and its symmetries, we describe these symmetries by Killing
fields and work out the connection to conservation laws. The Penrose process
and superradiance effects are discussed. Decay results on the long-time
behavior of Dirac waves are outlined. It is explained schematically how the
Maxwell equations and the equations for linearized gravitational waves can be
decoupled to obtain the Teukolsky equation. It is shown how the Teukolsky
equation can be fully separated to a system of coupled ordinary differential
equations. Linear stability of the non-extreme Kerr black hole is stated as a
pointwise decay result for solutions of the Cauchy problem for the Teukolsky
equation. The stability proof is outlined, with an emphasis on the underlying
ideas and methods.Comment: 25 pages, LaTeX, 3 figures, lectures given at first DOMOSCHOOL in
July 2018, minor improvements (published version
Recommended from our members
Has the publics knowledge of anatomy been hamstrung? A questionnaire-based exploration of basic anatomical awareness within the general population
Despite a recent resurgence in public interest for anatomical sciences,1 little research exists to determine the extent of their knowledge. We aimed to assess this through a questionnaire-based localisation of anatomical structures.
Our findings suggest a significant gender discrepancy, as well as the presence of prevalent anatomical misconceptions which, to our best knowledge, have not been documented in the literature. These results have implications for the content and targeting of future public and clinical teaching
Distribution of Submerged Aquatic Vegetation In The Chesapeake Bay and Tributaries and Chincoteague Bay - 1992
The Near-Miss Effect in Blackjack: Group Play and Lone Play
Previous research in blackjack has demonstrated that gamblers report outcomes that are closer to wins when the player\u27s total approximates the dealer\u27s total. However, additional comparisons, such as to another player\u27s total or to 21, may affect the prevalence of a near-miss. The current study investigated the presence of a near-miss in blackjack while playing alone and with other players, and examined ratings in relation to the difference of the player\u27s, dealer´s and another player´s total from 21. College students played 25 hands of blackjack with only the dealer and another 25 hands with another player and the dealer and rated how close the outcome was to a win. The results demonstrated the presence of a near-miss effect as a function of the numerical distance from the player\u27s and another player´s total to 21, and the absence of a near-miss when the player busts
Black hole puncture initial data with realistic gravitational wave content
We present improved post-Newtonian-inspired initial data for non-spinning
black-hole binaries, suitable for numerical evolution with punctures. We
revisit the work of Tichy et al. [W. Tichy, B. Bruegmann, M. Campanelli, and P.
Diener, Phys. Rev. D 67, 064008 (2003)], explicitly calculating the remaining
integral terms. These terms improve accuracy in the far zone and, for the first
time, include realistic gravitational waves in the initial data. We investigate
the behavior of these data both at the center of mass and in the far zone,
demonstrating agreement of the transverse-traceless parts of the new metric
with quadrupole-approximation waveforms. These data can be used for numerical
evolutions, enabling a direct connection between the merger waveforms and the
post-Newtonian inspiral waveforms.Comment: 13 pages, 7 figures; replaced with published versio
Unravelling Active Galactic Nuclei
A complete flat-spectrum radio-loud sample of AGN includes a significant
fraction of Seyfert-like AGN including a NLS1. Analysis of their optical
spectra suggests that the reddest continuum colours are either associated with
AGN in nearby resolved galaxies, or distant quasars showing relatively narrow
permitted emission lines.Comment: Poster contribution presented at the Joint MPE,AIP,ESO workshop on
NLS1s, Bad Honnef, Dec. 1999, to appear in New Astronomy Reviews; also
available at http://wave.xray.mpe.mpg.de/conferences/nls1-worksho
A new grapevine yellows phytoplasma from the Buckland Valley of Victoria, Australia
A new phytoplasma detected in grapevines with grapevine yellows disease from the Buckland Valley of Victoria, Australia was characterized. Buckland Valley grapevine yellows phytoplasma (BVGYp) could not be amplified by PCR using primers specific for the stolbur (STOL, 16SrXII) group of phytoplasmas indicating that it was unlikely to be a STOL group phytoplasma. BVGYp was amplified by PCR using primers specific for both the aster yellows (AV, 16Sr I) and STOL phytoplasma groups, indicating that it may be more closely related to the AY group phytoplasmas. Sequence analysis of 16SrRNA gene sequences showed that BVGYp clustered with AY and STOL groups of phytoplasmas. Sequence similarities were determined by pairwise comparisons of the 16S rDNA sequence of BVGYp WAY and STOL group phytoplasmas and BVGYp was more closely related to the AY group phytoplasmas. Although the data indicate BVGYp may form a newAY subgroup, the similarity coefficients between BVGYp and phytoplasmas from the AY, STOL and Mexican periwinkle virescence groups, derived from putative RFLP patterns, were less than 90%, so BVGYp may actually form a new phytoplasma group.
Near-field radiative heat transfer between macroscopic planar surfaces
Near-field radiative heat transfer allows heat to propagate across a small
vacuum gap in quantities that are several orders of magnitude greater then the
heat transfer by far-field, blackbody radiation. Although heat transfer via
near-field effects has been discussed for many years, experimental verification
of this theory has been very limited. We have measured the heat transfer
between two macroscopic sapphire plates, finding an increase in agreement with
expectations from theory. These experiments, conducted near 300 K, have
measured the heat transfer as a function of separation over mm to m and as
a function of temperature differences between 2.5 and 30 K. The experiments
demonstrate that evanescence can be put to work to transfer heat from an object
without actually touching it
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