117,398 research outputs found
Using the INSPIRAL program to search for gravitational waves from low-mass binary inspiral
The INSPIRAL program is the LIGO Scientific Collaboration's computational
engine for the search for gravitational waves from binary neutron stars and
sub-solar mass black holes. We describe how this program, which makes use of
the FINDCHIRP algorithm (discussed in a companion paper), is integrated into a
sophisticated data analysis pipeline that was used in the search for low-mass
binary inspirals in data taken during the second LIGO science run.Comment: 11 pages, 3 figures, submitted to Classical and Quantum Gravity for
the special issue of the GWDAW9 Proceeding
Possible Signatures Of Dissipation From Time-Series Analysis Techniques Using A Turbulent Laboratory Magnetohydrodynamic Plasma
The frequency spectrum of magnetic fluctuations as measured on the Swarthmore Spheromak Experiment is broadband and exhibits a nearly Kolmogorov 5/3 scaling. It features a steepening region which is indicative of dissipation of magnetic fluctuation energy similar to that observed in fluid and magnetohydrodynamic turbulence systems. Two non-spectrum based time-series analysis techniques are implemented on this data set in order to seek other possible signatures of turbulent dissipation beyond just the steepening of fluctuation spectra. Presented here are results for the flatness, permutation entropy, and statistical complexity, each of which exhibits a particular character at spectral steepening scales which can then be compared to the behavior of the frequency spectrum
Penrose Diagram for a Transient Black Hole
A Penrose diagram is constructed for a spatially coherent black hole that
smoothly begins an accretion, then excretes symmetrically as measured by a
distant observer, with the initial and final states described by a metric of
Minkowski form. Coordinate curves on the diagram are computationally derived.
Causal relationships between space-time regions are briefly discussed. The life
cycle of the black hole demonstrably leaves asymptotic observers in an
unaltered Minkowski space-time of uniform conformal scale.Comment: 14 pages, 9 figures, spelling correction
Tensor interaction contributions to single-particle energies
We calculate the contribution of the nucleon-nucleon tensor interaction to
single-particle energies with finite-range matrix potentials and with
zero-range Skyrme potentials. The Skx Skyrme parameters including the
zero-range tensor terms with strengths calibrated to the finite-range results
are refitted to nuclear properties. The fit allows the zero-range
proton-neutron tensor interaction as calibrated to the finite-range potential
results and that gives the observed change in the single-particle gap
(h)-(g) going from Sn to
Sn. However, the experimental dependence of the spin-orbit
splittings in Sn and Pb is not well described when the tensor
is added, due to a change in the radial dependence of the total spin-orbit
potential. The gap shift and a good fit to the -dependence can be
recovered when the like-particle tensor interaction is opposite in sign to that
required for the matrix.Comment: 5 pages, 4 figures, accepted for publication as Rapid Communication
in Physical Review
Low-loss flake-graphene saturable absorber mirror for laser mode-locking at sub-200-fs pulse duration
Saturable absorbers are a key component for mode-locking femtosecond lasers.
Polymer films containing graphene flakes have recently been used in
transmission as laser mode-lockers, but suffer from high nonsaturable loss,
limiting their application in low-gain lasers. Here we present a saturable
absorber mirror based on a film of pure graphene flakes. The device is used to
mode lock an erbium-doped fiber laser, generating pulses with state-of-the-art,
sub-200-fs duration. The laser characteristic indicate that the film exhibits
low nonsaturable loss (13% per pass) and large absorption modulation depth (45%
of low-power absorption)
Black Hole Entropy from Conformal Field Theory in Any Dimension
Restricted to a black hole horizon, the ``gauge'' algebra of surface
deformations in general relativity contains a Virasoro subalgebra with a
calculable central charge. The fields in any quantum theory of gravity must
transform accordingly, i.e., they must admit a conformal field theory
description. Applying Cardy's formula for the asymptotic density of states, I
use this result to derive the Bekenstein-Hawking entropy. This method is
universal---it holds for any black hole, and requires no details of quantum
gravity---but it is also explicitly statistical mechanical, based on counting
microscopic states.Comment: 9 pages, LaTeX, no figures. Slightly shortened and polished for
journal; no significant changes in substanc
Spatio-Temporal Low Count Processes with Application to Violent Crime Events
There is significant interest in being able to predict where crimes will
happen, for example to aid in the efficient tasking of police and other
protective measures. We aim to model both the temporal and spatial dependencies
often exhibited by violent crimes in order to make such predictions. The
temporal variation of crimes typically follows patterns familiar in time series
analysis, but the spatial patterns are irregular and do not vary smoothly
across the area. Instead we find that spatially disjoint regions exhibit
correlated crime patterns. It is this indeterminate inter-region correlation
structure along with the low-count, discrete nature of counts of serious crimes
that motivates our proposed forecasting tool. In particular, we propose to
model the crime counts in each region using an integer-valued first order
autoregressive process. We take a Bayesian nonparametric approach to flexibly
discover a clustering of these region-specific time series. We then describe
how to account for covariates within this framework. Both approaches adjust for
seasonality. We demonstrate our approach through an analysis of weekly reported
violent crimes in Washington, D.C. between 2001-2008. Our forecasts outperform
standard methods while additionally providing useful tools such as prediction
intervals
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