5,703 research outputs found
Network sensitivity to geographical configuration
Gravitational wave astronomy will require the coordinated analysis of data
from the global network of gravitational wave observatories. Questions of how
to optimally configure the global network arise in this context. We have
elsewhere proposed a formalism which is employed here to compare different
configurations of the network, using both the coincident network analysis
method and the coherent network analysis method. We have constructed a network
model to compute a figure-of-merit based on the detection rate for a population
of standard-candle binary inspirals. We find that this measure of network
quality is very sensitive to the geographic location of component detectors
under a coincident network analysis, but comparatively insensitive under a
coherent network analysis.Comment: 7 pages, 4 figures, accepted for proceedings of the 4th Edoardo
Amaldi conference, incorporated referees' suggestions and corrected diagra
The ACIGA Data Analysis programme
The Data Analysis programme of the Australian Consortium for Interferometric
Gravitational Astronomy (ACIGA) was set up in 1998 by the first author to
complement the then existing ACIGA programmes working on suspension systems,
lasers and optics, and detector configurations. The ACIGA Data Analysis
programme continues to contribute significantly in the field; we present an
overview of our activities.Comment: 10 pages, 0 figures, accepted, Classical and Quantum Gravity,
(Proceedings of the 5th Edoardo Amaldi Conference on Gravitational Waves,
Tirrenia, Pisa, Italy, 6-11 July 2003
Numerical wave optics and the lensing of gravitational waves by globular clusters
We consider the possible effects of gravitational lensing by globular
clusters on gravitational waves from asymmetric neutron stars in our galaxy. In
the lensing of gravitational waves, the long wavelength, compared with the
usual case of optical lensing, can lead to the geometrical optics approximation
being invalid, in which case a wave optical solution is necessary. In general,
wave optical solutions can only be obtained numerically. We describe a
computational method that is particularly well suited to numerical wave optics.
This method enables us to compare the properties of several lens models for
globular clusters without ever calling upon the geometrical optics
approximation, though that approximation would sometimes have been valid.
Finally, we estimate the probability that lensing by a globular cluster will
significantly affect the detection, by ground-based laser interferometer
detectors such as LIGO, of gravitational waves from an asymmetric neutron star
in our galaxy, finding that the probability is insignificantly small.Comment: To appear in: Proceedings of the Eleventh Marcel Grossmann Meetin
Spectral Line Removal in the LIGO Data Analysis System (LDAS)
High power in narrow frequency bands, spectral lines, are a feature of an
interferometric gravitational wave detector's output. Some lines are coherent
between interferometers, in particular, the 2 km and 4 km LIGO Hanford
instruments. This is of concern to data analysis techniques, such as the
stochastic background search, that use correlations between instruments to
detect gravitational radiation. Several techniques of `line removal' have been
proposed. Where a line is attributable to a measurable environmental
disturbance, a simple linear model may be fitted to predict, and subsequently
subtract away, that line. This technique has been implemented (as the command
oelslr) in the LIGO Data Analysis System (LDAS). We demonstrate its application
to LIGO S1 data.Comment: 11 pages, 5 figures, to be published in CQG GWDAW02 proceeding
Binary Population and Spectral Synthesis Version 2.1: construction, observational verification and new results
The Binary Population and Spectral Synthesis (BPASS) suite of binary stellar
evolution models and synthetic stellar populations provides a framework for the
physically motivated analysis of both the integrated light from distant stellar
populations and the detailed properties of those nearby. We present a new
version 2.1 data release of these models, detailing the methodology by which
BPASS incorporates binary mass transfer and its effect on stellar evolution
pathways, as well as the construction of simple stellar populations. We
demonstrate key tests of the latest BPASS model suite demonstrating its ability
to reproduce the colours and derived properties of resolved stellar
populations, including well- constrained eclipsing binaries. We consider
observational constraints on the ratio of massive star types and the
distribution of stellar remnant masses. We describe the identification of
supernova progenitors in our models, and demonstrate a good agreement to the
properties of observed progenitors. We also test our models against photometric
and spectroscopic observations of unresolved stellar populations, both in the
local and distant Universe, finding that binary models provide a
self-consistent explanation for observed galaxy properties across a broad
redshift range. Finally, we carefully describe the limitations of our models,
and areas where we expect to see significant improvement in future versions.Comment: 69 pages, 45 figures. Accepted for publication in PASA. Accompanied
by a full, documented data release at http://bpass.auckland.ac.nz and
http://warwick.ac.uk/bpas
Atom lithography using MRI-type feature placement
We demonstrate the use of frequency-encoded light masks in neutral atom
lithography. We demonstrate that multiple features can be patterned across a
monotonic potential gradient. Features as narrow as 0.9 microns are fabricated
on silicon substrates with a metastable argon beam. Internal state manipulation
with such a mask enables continuously adjustable feature positions and feature
densities not limited by the optical wavelength, unlike previous light masks.Comment: 4 pages, 4 figure
Uncertainty in multitask learning: joint representations for probabilistic MR-only radiotherapy planning
Multi-task neural network architectures provide a mechanism that jointly
integrates information from distinct sources. It is ideal in the context of
MR-only radiotherapy planning as it can jointly regress a synthetic CT (synCT)
scan and segment organs-at-risk (OAR) from MRI. We propose a probabilistic
multi-task network that estimates: 1) intrinsic uncertainty through a
heteroscedastic noise model for spatially-adaptive task loss weighting and 2)
parameter uncertainty through approximate Bayesian inference. This allows
sampling of multiple segmentations and synCTs that share their network
representation. We test our model on prostate cancer scans and show that it
produces more accurate and consistent synCTs with a better estimation in the
variance of the errors, state of the art results in OAR segmentation and a
methodology for quality assurance in radiotherapy treatment planning.Comment: Early-accept at MICCAI 2018, 8 pages, 4 figure
- …