830 research outputs found
Physical instrumental vetoes for gravitational-wave burst triggers
We present a robust strategy to \emph{veto} certain classes of instrumental
glitches that appear at the output of interferometric gravitational-wave (GW)
detectors.This veto method is `physical' in the sense that, in order to veto a
burst trigger, we make use of our knowledge of the coupling of different
detector subsystems to the main detector output. The main idea behind this
method is that the noise in an instrumental channel X can be \emph{transferred}
to the detector output (channel H) using the \emph{transfer function} from X to
H, provided the noise coupling is \emph{linear} and the transfer function is
\emph{unique}. If a non-stationarity in channel H is causally related to one in
channel X, the two have to be consistent with the transfer function. We
formulate two methods for testing the consistency between the burst triggers in
channel X and channel H. One method makes use of the \emph{null-stream}
constructed from channel H and the \emph{transferred} channel X, and the second
involves cross-correlating the two. We demonstrate the efficiency of the veto
by `injecting' instrumental glitches in the hardware of the GEO 600 detector.
The \emph{veto safety} is demonstrated by performing GW-like hardware
injections. We also show an example application of this method using 5 days of
data from the fifth science run of GEO 600. The method is found to have very
high veto efficiency with a very low accidental veto rate.Comment: Minor changes, To appear in Phys. Rev.
Bayesian parameter estimation in the second LISA Pathfinder Mock Data Challenge
A main scientific output of the LISA Pathfinder mission is to provide a noise
model that can be extended to the future gravitational wave observatory, LISA.
The success of the mission depends thus upon a deep understanding of the
instrument, especially the ability to correctly determine the parameters of the
underlying noise model. In this work we estimate the parameters of a simplified
model of the LISA Technology Package (LTP) instrument. We describe the LTP by
means of a closed-loop model that is used to generate the data, both injected
signals and noise. Then, parameters are estimated using a Bayesian framework
and it is shown that this method reaches the optimal attainable error, the
Cramer-Rao bound. We also address an important issue for the mission: how to
efficiently combine the results of different experiments to obtain a unique set
of parameters describing the instrument.Comment: 14 pages, 4 figures, submitted to PR
The burden of cardiovascular disease in sub-Saharan Africa
Correspondence: The burden of cardiovascular disease in sub-Saharan Africa by Anthony Mbewu
The Newcastle ENDOPREM™: a validated patient reported experience measure for gastrointestinal endoscopy
OBJECTIVES: Measuring patient experience of gastrointestinal (GI) procedures is a key component of evaluation of quality of care. Current measures of patient experience within GI endoscopy are largely clinician derived and measured; however, these do not fully represent the experiences of patients themselves. It is important to measure the entirety of experience and not just experience directly during the procedure. We aimed to develop a patient-reported experience measure (PREM) for GI procedures. DESIGN: Phase 1: semi-structured interviews were conducted in patients who had recently undergone GI endoscopy or CT colonography (CTC) (included as a comparator). Thematic analysis identified the aspects of experience important to patients. Phase 2: a question bank was developed from phase 1 findings, and iteratively refined through rounds of cognitive interviews with patients who had undergone GI procedures, resulting in a pilot PREM. Phase 3: patients who had attended for GI endoscopy or CTC were invited to complete the PREM. Psychometric properties were investigated. Phase 4 involved item reduction and refinement. RESULTS: Phase 1: interviews with 35 patients identified six overarching themes: anxiety, expectations, information & communication, embarrassment & dignity, choice & control and comfort. Phase 2: cognitive interviews refined questionnaire items and response options. Phase 3: the PREM was distributed to 1650 patients with 799 completing (48%). Psychometric properties were found to be robust. Phase 4: final questionnaire refined including 54 questions assessing patient experience across five temporal procedural stages. CONCLUSION: This manuscript gives an overview of the development and validation of the Newcastle ENDOPREM™, which assesses all aspects of the GI procedure experience from the patient perspective. It may be used to measure patient experience in clinical care and, in research, to compare patients' experiences of different endoscopic interventions
Fibrosis in the kidney: is a problem shared a problem halved?
Fibrotic disorders are commonplace, take many forms and can be life-threatening. No better example of this exists than the progressive fibrosis that accompanies all chronic renal disease. Renal fibrosis is a direct consequence of the kidney's limited capacity to regenerate after injury. Renal scarring results in a progressive loss of renal function, ultimately leading to end-stage renal failure and a requirement for dialysis or kidney transplantation
A comparison of methods for gravitational wave burst searches from LIGO and Virgo
The search procedure for burst gravitational waves has been studied using 24
hours of simulated data in a network of three interferometers (Hanford 4-km,
Livingston 4-km and Virgo 3-km are the example interferometers). Several
methods to detect burst events developed in the LIGO Scientific Collaboration
(LSC) and Virgo collaboration have been studied and compared. We have performed
coincidence analysis of the triggers obtained in the different interferometers
with and without simulated signals added to the data. The benefits of having
multiple interferometers of similar sensitivity are demonstrated by comparing
the detection performance of the joint coincidence analysis with LSC and Virgo
only burst searches. Adding Virgo to the LIGO detector network can increase by
50% the detection efficiency for this search. Another advantage of a joint
LIGO-Virgo network is the ability to reconstruct the source sky position. The
reconstruction accuracy depends on the timing measurement accuracy of the
events in each interferometer, and is displayed in this paper with a fixed
source position example.Comment: LIGO-Virgo working group submitted to PR
LISA and LISA PathFinder, the endeavour to detect low frequency GWs
This is a review about LISA and its technology demonstrator, LISA PathFinder.
We first describe the conceptual problems which need to be overcome in order to
set up a working interferometric detector of low frequency Gravitational Waves
(GW), then summarise the solutions to them as currently conceived by the LISA
mission team. This will show that some of these solutions require new
technological abilities which are still under development, and which need
proper test before being fully implemented. LISA PathFinder (LPF) is the the
testbed for such technologies. The final part of the paper will address the
ideas and concepts behind the PathFinder as well as their impact on LISA.Comment: 25 pages, 21 figures, presented at the Spanish Relativity Meeting,
Mallorca September 2006. Will be published in Journal of Physics: Conference
Series, IOP. To be published in Journal of Physics: Conference Series, IO
Triple Michelson Interferometer for a Third-Generation Gravitational Wave Detector
The upcoming European design study `Einstein gravitational-wave Telescope'
represents the first step towards a substantial, international effort for the
design of a third-generation interferometric gravitational wave detector. It is
generally believed that third-generation instruments might not be installed
into existing infrastructures but will provoke a new search for optimal
detector sites. Consequently, the detector design could be subject to fewer
constraints than the on-going design of the second generation instruments. In
particular, it will be prudent to investigate alternatives to the traditional
L-shaped Michelson interferometer. In this article, we review an old proposal
to use three Michelson interferometers in a triangular configuration. We use
this example of a triple Michelson interferometer to clarify the terminology
and will put this idea into the context of more recent research on
interferometer technologies. Furthermore the benefits of a triangular detector
will be used to motivate this design as a good starting point for a more
detailed research effort towards a third-generation gravitational wave
detector.Comment: Minor corrections to the main text and two additional appendices. 14
pages, 6 figure
The upgrade of GEO600
The German / British gravitational wave detector GEO 600 is in the process of
being upgraded. The upgrading process of GEO 600, called GEO-HF, will
concentrate on the improvement of the sensitivity for high frequency signals
and the demonstration of advanced technologies. In the years 2009 to 2011 the
detector will undergo a series of upgrade steps, which are described in this
paper.Comment: 9 pages, Amaldi 8 conference contributio
Bayesian inference on compact binary inspiral gravitational radiation signals in interferometric data
Presented is a description of a Markov chain Monte Carlo (MCMC) parameter
estimation routine for use with interferometric gravitational radiational data
in searches for binary neutron star inspiral signals. Five parameters
associated with the inspiral can be estimated, and summary statistics are
produced. Advanced MCMC methods were implemented, including importance
resampling and prior distributions based on detection probability, in order to
increase the efficiency of the code. An example is presented from an
application using realistic, albeit fictitious, data.Comment: submitted to Classical and Quantum Gravity. 14 pages, 5 figure
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