10 research outputs found
Integration and Performance of the Newtonian Calibrator and IWAVE for Exploring the Laser Interferometer Gravitational Wave Observatory Data.
No full textUpgrades to IWAVE, a frequency tracking tool invented by Edward J. Daw
at the University of Sheffield, has expanded the utility of the tool. Resonant
characteristics observed in the Laser Interferometer Gravitational Wave Observa-
tories - such as violin modes, test mass body modes and calibration signals - can
be resolved accurately, even in tightly packed regions of frequency space using a
multi-line tracker in real-time on the LIGO front end.
Furthermore, using IWAVE to develop test mass thermometers, real-time esti-
mates of the test mass temperature is available, useful for thermal tuning of LIGO.
This is achieved by tracking and calibrating test mass body modes, a coupling be-
tween the laser TEM modes and the mechanical response of the optics. The test
mass thermometers can be extrapolated into a larger thermal monitoring pipeline
useful for current and future gravitation wave observatory thermal modelling.
The LIGO calibration is a complicated folding of the many control systems
noise sources that affect the interferometer. Presented here is the installation,
commissioning and successful operation of the LIGO Hanford Newtonian Calibra-
tor - a new R&D effort with the University of Washington that uses a spinning
constellation of masses - to induce length changes in the interferometer arms by
applying a small force to the test mass. These forces are modelled with three real-
isations of Newton Law of Gravity and all show good agreement to one another
Quality of Life Following Repair of Large Hiatal Hernia is Improved but not Influenced by Use of Mesh: Results From a Randomized Controlled Trial
No full textAuthor version made available following 12 month embargo from date of publication (5 Feb 2015) in accordance with Publisher copyright policy.Introduction
Laparoscopic surgery is the treatment of choice for repair of large hiatus hernia, but can be
followed by recurrence. Repair with prosthetic mesh has been recommended to prevent
recurrence, although complications following mesh repair have generated disagreement about
whether or not mesh should be used. The early objective and clinical results of a randomized
trial of repair with mesh vs. sutures have been reported, and revealed few differences. In the
current study we evaluated quality of life outcomes within this trial at follow-up to 2 years.
Methods
In a multicenter prospective double-blind randomized trial three methods for repair of large
hiatus hernia were compared: sutures vs. repair with absorbable mesh (Surgisis) vs. nonabsorbable
(Timesh). Quality of life assessment using the Short-Form 36 (SF-36)
questionnaire was undertaken at 3, 6, 12 and 24 months after surgery. SF-36 outcomes (8
individual scales and 2 composite scales) were determined for each group, and compared
between groups, and across different follow-up points.
Results
126 patients were enrolled - 43 sutures, 41 absorbable mesh and 42 non-absorbable mesh. 115
(91.3%) completed a preoperative questionnaire, and 113 (89.7%) completed the postoperative
questionnaire at 3 months, 116 (92.1%) at 6 months, 114 (90.5%) at 12 months, and
91 (72.2%) at 24 months. The SF-36 Physical and Mental Component scores (PCS & MCS)
improved significantly following surgery, and this improvement was sustained across 24
months follow-up (p<0.001 for PCS and MCS at each follow-up point). There were no
significant differences between the groups for the component scores or the eight SF-36
subscale scores at each follow-up time. 29 individuals had a recurrence at 6 months follow-up,
of which 9 were symptomatic. The PCS were higher in patients with recurrence vs. without
(p<0.01), and in patients with a symptomatic recurrence vs. asymptomatic recurrence vs. no
recurrence (p=0.001).
Conclusion
SF-36 measured quality of life improved significantly after repair of large hiatal hernia at up
to 2 years follow-up, and there were no differences in outcome for the different repair techniques. The use of mesh vs. no mesh in repair of large hiatal hernia did not influence
quality of life
IWAVE -- An Adaptive Filter Approach to Phase Lock and the Dynamic Characterisation of Pseudo-Harmonic Waves
No full textWe present a novel adaptive filtering approach to the dynamic characterisation of waves of varying frequency and amplitude embedded in arbitrary noise backgrounds. This method, known as IWAVE, possesses critical advantages over conventional techniques making it a useful new tool in the dynamic characterisation of a wide range of data containing embedded oscillating signals. After a review of existing techniques, we present the IWAVE algorithm, derive its key characteristics, and provide tests of its performance using simulated and real world data
Initial results from the LIGO Newtonian calibrator
No full textThe precise calibration of the strain readout of the LIGO gravitational wave observatories is paramount to the accurate interpretation of gravitational wave events. This calibration is traditionally done by imparting a known force on the test masses of the observatory via radiation pressure. Here, we describe the implementation of an alternative calibration scheme: the Newtonian calibrator. This system uses a rotor consisting of both quadrupole and hexapole mass distributions to apply a time-varying gravitational force on one of the observatory’s test masses. The force produced by this rotor can be predicted to
<
1
%
relative uncertainty and is well resolved in the readout of the observatory. This system currently acts as a cross-check of the existing absolute calibration system
Characterization of systematic error in Advanced LIGO calibration
No full textThe raw outputs of the detectors within the Advanced Laser Interferometer Gravitational-Wave Observatory need to be calibrated in order to produce the estimate of the dimensionless strain used for astrophysical analyses. The two detectors have been upgraded since the second observing run and finished the year-long third observing run. Understanding, accounting, and/or compensating for the complex-valued response of each part of the upgraded detectors improves the overall accuracy of the estimated detector response to gravitational waves. We describe improved understanding and methods used to quantify the response of each detector, with a dedicated effort to define all places where systematic error plays a role. We use the detectors as they stand in the first half (six months) of the third observing run to demonstrate how each identified systematic error impacts the estimated strain and constrain the statistical uncertainty therein. For this time period, we estimate the upper limit on systematic error and associated uncertainty to be <7% in magnitude and <4 deg in phase (68% confidence interval) in the most sensitive frequency band 20–2000 Hz. The systematic error alone is estimated at levels of <2% in magnitude and <2 deg in phase
Point absorbers in Advanced LIGO
No full textSmall, highly absorbing points are randomly present on the surfaces of the main interferometer optics in Advanced LIGO. The resulting nanometer scale thermo-elastic deformations and substrate lenses from these micron-scale absorbers significantly reduce the sensitivity of the interferometer directly though a reduction in the power-recycling gain and indirect interactions with the feedback control system. We review the expected surface deformation from point absorbers and provide a pedagogical description of the impact on power buildup in second generation gravitational wave detectors (dual-recycled Fabry–Perot Michelson interferometers). This analysis predicts that the power-dependent reduction in interferometer performance will significantly degrade maximum stored power by up to 50% and, hence, limit GW sensitivity, but it suggests system wide corrections that can be implemented in current and future GW detectors. This is particularly pressing given that future GW detectors call for an order of magnitude more stored power than currently used in Advanced LIGO in Observing Run 3. We briefly review strategies to mitigate the effects of point absorbers in current and future GW wave detectors to maximize the success of these enterprises
Open data from the first and second observing runs of Advanced LIGO and Advanced Virgo
No full textAdvanced LIGO and Advanced Virgo are actively monitoring the sky and collecting gravitational-wave strain data with sufficient sensitivity to detect signals routinely. In this paper we describe the data recorded by these instruments during their first and second observing runs. The main data products are the gravitational-wave strain arrays, released as time series sampled at 16384 Hz. The datasets that include this strain measurement can be freely accessed through the Gravitational Wave Open Science Center at http://gw-openscience.org, together with data-quality information essential for the analysis of LIGO and Virgo data, documentation, tutorials, and supporting software
Model comparison from LIGO-Virgo data on GW170817's binary components and consequences for the merger remnant
No full textGW170817 is the very first observation of gravitational waves originating from the coalescence of two compact objects in the mass range of neutron stars, accompanied by electromagnetic counterparts, and offers an opportunity to directly probe the internal structure of neutron stars. We perform Bayesian model selection on a wide range of theoretical predictions for the neutron star equation of state. For the binary neutron star hypothesis, we find that we cannot rule out the majority of theoretical models considered. In addition, the gravitational-wave data alone does not rule out the possibility that one or both objects were low-mass black holes. We discuss the possible outcomes in the case of a binary neutron star merger, finding that all scenarios from prompt collapse to long-lived or even stable remnants are possible. For long-lived remnants, we place an upper limit of 1.9 kHz on the rotation rate. If a black hole was formed any time after merger and the coalescing stars were slowly rotating, then the maximum baryonic mass of non-rotating neutron stars is at most 3.05 , and three equations of state considered here can be ruled out. We obtain a tighter limit of 2.67 for the case that the merger results in a hypermassive neutron star
A guide to LIGO-Virgo detector noise and extraction of transient gravitational-wave signals
No full textThe LIGO Scientific Collaboration and the Virgo Collaboration have cataloged eleven confidently detected gravitational-wave events during the first two observing runs of the advanced detector era. All eleven events were consistent with being from well-modeled mergers between compact stellar-mass objects: black holes or neutron stars. The data around the time of each of these events have been made publicly available through the Gravitational-Wave Open Science Center. The entirety of the gravitational-wave strain data from the first and second observing runs have also now been made publicly available. There is considerable interest among the broad scientific community in understanding the data and methods used in the analyses. In this paper, we provide an overview of the detector noise properties and the data analysis techniques used to detect gravitational-wave signals and infer the source properties. We describe some of the checks that are performed to validate the analyses and results from the observations of gravitational-wave events. We also address concerns that have been raised about various properties of LIGO-Virgo detector noise and the correctness of our analyses as applied to the resulting data
LIGO detector characterization in the second and third observing runs
No full textInternational audienceThe characterization of the Advanced LIGO detectors in the second and third observing runs has increased the sensitivity of the instruments, allowing for a higher number of detectable gravitational-wave signals, and provided confirmation of all observed gravitational-wave events. In this work, we present the methods used to characterize the LIGO detectors and curate the publicly available datasets, including the LIGO strain data and data quality products. We describe the essential role of these datasets in LIGO–Virgo Collaboration analyses of gravitational-waves from both transient and persistent sources and include details on the provenance of these datasets in order to support analyses of LIGO data by the broader community. Finally, we explain anticipated changes in the role of detector characterization and current efforts to prepare for the high rate of gravitational-wave alerts and events in future observing runs
