4,295 research outputs found
Mapping the gravitational wave background
The gravitational wave sky is expected to have isolated bright sources
superimposed on a diffuse gravitational wave background. The background
radiation has two components: a confusion limited background from unresolved
astrophysical sources; and a cosmological component formed during the birth of
the universe. A map of the gravitational wave background can be made by
sweeping a gravitational wave detector across the sky. The detector output is a
complicated convolution of the sky luminosity distribution, the detector
response function and the scan pattern. Here we study the general
de-convolution problem, and show how LIGO (Laser Interferometric Gravitational
Observatory) and LISA (Laser Interferometer Space Antenna) can be used to
detect anisotropies in the gravitational wave background.Comment: 16 pages, 6 figures. Submitted to CQ
Frontâline perspectives on âjoinedâupâ working relationships: a qualitative study of social prescribing in the west of Scotland
Cross-sector collaboration has been promoted by government policies in the United Kingdom and many western welfare states for decades. Literature on joint working has focused predominantly on the strategic level, neglecting the role of individual practitioners in putting âjoined-up workingâ into practice. This paper takes the case of âsocial prescribingâ in the West of Scotland as an instance of joined-up working, in which primary healthcare professionals are encouraged to refer patients to non-medical sources of support in the third sector. This study draws on social capital theory to analyse the quality of the relationships between primary healthcare professionals and third sector practitioners. Eighteen health professionals and 15 representatives of third sector organisations participated in a qualitative interview study. Significant barriers to collaborative working were evident. The two stakeholder groups expressed different understandings of health, with few primary healthcare professionals considering non-medical sources of support to be useful or relevant. Health professionals were mistrustful of unknown third sector organisations, and concerned about their accountability for referrals that were not successful or positive for the patient. Third sector practitioners sought to build trust through face-to-face interactions with health professionals. However, primary healthcare professionals and third sector practitioners were not connected in effective networks. We highlight the on-going imbalance of power between primary healthcare professionals and third sector organisations. Strategic collaborations should be complemented by efforts to build shared understandings, trust and connections between the diverse frontline workers whose mutual co-operation is necessary to achieve effective joined-up working
Comment on "Gravity Waves, Chaos, and Spinning Compact Binaries"
In this comment, I argue that chaotic effects in binary black hole inspiral
will not strongly impact the detection of gravitational waves from such
systems.Comment: 1 page, comment on gr-qc/991004
Applying coupon-collecting theory to computer-aided assessments
Computer-based tests with randomly generated questions allow a large number
of different tests to be generated. Given a fixed number of alternatives for
each question, the number of tests that need to be generated before all
possible questions have appeared is surprisingly low.Comment: 19 pages; bibliographic information added as follows. To appear in
Bingham, N. H., and Goldie, C. M. (eds), Probability and Mathematical
Genetics: Papers in Honour of Sir John Kingman. London Math. Soc. Lecture
Note Series. Cambridge: Cambridge Univ. Pres
Polytropic stars in three-dimensional spacetime
We investigate three-dimensional perfect fluid stars with polytropic equation
of state, matched to the exterior three-dimensional black hole geometry of
Banados, Teitelboim and Zanelli. A new class of exact solutions for a generic
polytropic index is found and analysed.Comment: 3 pages, revte
Detecting the Cosmic Gravitational Wave Background with the Big Bang Observer
The detection of the Cosmic Microwave Background Radiation (CMB) was one of
the most important cosmological discoveries of the last century. With the
development of interferometric gravitational wave detectors, we may be in a
position to detect the gravitational equivalent of the CMB in this century. The
Cosmic Gravitational Background (CGB) is likely to be isotropic and stochastic,
making it difficult to distinguish from instrument noise. The contribution from
the CGB can be isolated by cross-correlating the signals from two or more
independent detectors. Here we extend previous studies that considered the
cross-correlation of two Michelson channels by calculating the optimal signal
to noise ratio that can be achieved by combining the full set of interferometry
variables that are available with a six link triangular interferometer. In
contrast to the two channel case, we find that the relative orientation of a
pair of coplanar detectors does not affect the signal to noise ratio. We apply
our results to the detector design described in the Big Bang Observer (BBO)
mission concept study and find that BBO could detect a background with
.Comment: 15 pages, 12 Figure
Facing the LISA Data Analysis Challenge
By being the first observatory to survey the source rich low frequency region
of the gravitational wave spectrum, the Laser Interferometer Space Antenna
(LISA) will revolutionize our understanding of the Cosmos. For the first time
we will be able to detect the gravitational radiation from millions of galactic
binaries, the coalescence of two massive black holes, and the inspirals of
compact objects into massive black holes. The signals from multiple sources in
each class, and possibly others as well, will be simultaneously present in the
data. To achieve the enormous scientific return possible with LISA,
sophisticated data analysis techniques must be developed which can mine the
complex data in an effort to isolate and characterize individual signals. This
proceedings paper very briefly summarizes the challenges associated with
analyzing the LISA data, the current state of affairs, and the necessary next
steps to move forward in addressing the imminent challenges.Comment: 4 pages, no figures, Proceedings paper for the TeV Particle
Astrophysics II conference held Aug 28-31 at the Univ. of Wisconsi
LISA data analysis I: Doppler demodulation
The orbital motion of the Laser Interferometer Space Antenna (LISA) produces
amplitude, phase and frequency modulation of a gravitational wave signal. The
modulations have the effect of spreading a monochromatic gravitational wave
signal across a range of frequencies. The modulations encode useful information
about the source location and orientation, but they also have the deleterious
affect of spreading a signal across a wide bandwidth, thereby reducing the
strength of the signal relative to the instrument noise. We describe a simple
method for removing the dominant, Doppler, component of the signal modulation.
The demodulation reassembles the power from a monochromatic source into a
narrow spike, and provides a quick way to determine the sky locations and
frequencies of the brightest gravitational wave sources.Comment: 5 pages, 7 figures. References and new comments adde
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