A Bayesian method for detecting stellar flares

We present a Bayesian-odds-ratio-based algorithm for detecting stellar flares in light curve data. We assume flares are described by a model in which there is a rapid rise with a half-Gaussian profile, followed by an exponential decay. Our signal model also contains a polynomial background model. This is required to fit underlying light curve variations that are expected in the data, which could otherwise partially mimic a flare. We characterise the false alarm probability and efficiency of this method and compare it with a simpler thresholding method based on that used in Walkowicz et al (2011). We find our method has a significant increase in detection efficiency for low signal-to-noise ratio (S/N) flares. For a conservative false alarm probability our method can detect 95% of flares with S/N less than ~20, as compared to S/N of ~25 for the simpler method. As an example we have applied our method to a selection of stars in Kepler Quarter 1 data. The method finds 687 flaring stars with a total of 1873 flares after vetos have been applied. For these flares we have characterised their durations and and signal-to-noise ratios.Comment: Accepted for MNRAS. The code used for the analysis can be found at https://github.com/BayesFlare/bayesflare/releases/tag/v1.0.

An Evidence Based Time-Frequency Search Method for Gravitational Waves from Pulsar Glitches

We review and expand on a Bayesian model selection technique for the detection of gravitational waves from neutron star ring-downs associated with pulsar glitches. The algorithm works with power spectral densities constructed from overlapping time segments of gravitational wave data. Consequently, the original approach was at risk of falsely identifying multiple signals where only one signal was present in the data. We introduce an extension to the algorithm which uses posterior information on the frequency content of detected signals to cluster events together. The requirement that we have just one detection per signal is now met with the additional bonus that the belief in the presence of a signal is boosted by incorporating information from adjacent time segments.Comment: 6 pages, 4 figures, submitted to AMALDI 7 proceeding

Obstetrics and Gynecology at the University of Iowa: Three leaders and 51 years

In his history of the Department of Obstetrics and Gynecology of the University of Iowa College of Medicine, William C. Keettel traced the evolution of the department from its origin in 1870 until 1980. This article will focus on a particular segment of the department’s history, that from 1926 to 1977, in which the department grew and developed to a position of national stature. During this 51-year period, departmental leadership was provided by three individuals, E. D. Plass (1926-1951), John H. Randall (1952-1959), and William C. Keettel (1959-1977) and this paper will consider these three men and their contributions to the department’s growth and development. The 1980 department history provided most of the basis of the article, although a small amount of the Randall section and a substantial amount of the Keettel section reflect my personal perspective and recollections

A new code for parameter estimation in searches for gravitational waves from known pulsars

We describe the consistency testing of a new code for gravitational wave signal parameter estimation in known pulsar searches. The code uses an implementation of nested sampling to explore the likelihood volume. Using fake signals and simulated noise we compare this to a previous code that calculated the signal parameter posterior distributions on both a grid and using a crude Markov chain Monte Carlo (MCMC) method. We define a new parameterisation of two orientation angles of neutron stars used in the signal model (the initial phase and polarisation angle), which breaks a degeneracy between them and allows more efficient exploration of those parameters. Finally, we briefly describe potential areas for further study and the uses of this code in the future.Comment: Accepted for proceedings of Amaldi 9 meetin

Advanced technologies for future ground-based, laser-interferometric gravitational wave detectors

We present a review of modern optical techniques being used and developed for the field of gravitational wave detection. We describe the current state-of-the-art of gravitational waves detector technologies with regard to optical layouts, suspensions and test masses. We discuss the dominant sources and noise in each of these subsystems and the developments that will help mitigate them for future generations of detectors. We very briefly summarise some of the novel astrophysics that will be possible with these upgraded detectors

Population synthesis and parameter estimation of neutron stars with continuous gravitational waves and third-generation detectors

Precise measurement of stellar properties through the observation of continuous gravitational waves from spinning non-axisymmetric neutron stars can shed light onto new physics beyond terrestrial laboratories. Although hitherto undetected, prospects for detecting continuous gravitational waves improve with longer observation periods and more sensitive gravitational wave detectors. We study the capability of the Advanced Laser Interferometer Gravitational-Wave Observatory, and the Einstein Telescope to measure the physical properties of neutron stars through continuous gravitational wave observations. We simulate a population of Galactic neutron stars, assume continuous gravitational waves from the stars have been detected, and perform parameter estimation of the detected signals. Using the estimated parameters, we infer the stars' moments of inertia, ellipticities, and the components of the magnetic dipole moment perpendicular to the rotation axis. The estimation of the braking index proved challenging and is responsible for the majority of the uncertainties in the inferred parameters. Using the Einstein Telescope with an observation period of 5 yrs, point estimates using median can be made with errors of ~ 10 - 100% and ~ 5 - 50% respectively, subject to the inference of the braking index. The perpendicular magnetic dipole moment could not be accurately inferred for neutron stars that emit mainly gravitational waves.Comment: 11 pages, 7 figure

The declining representativeness of the British party system, and why it matters

In a recent article, Michael Laver has explained ‘Why Vote-Seeking Parties May Make Voters Miserable’. His model shows that, while ideological convergence may boost congruence between governments and the median voter, it can reduce congruence between the party system and the electorate as a whole. Specifically, convergence can increase the mean distance between voters and their nearest party. In this article we show that this captures the reality of today’s British party system. Policy scale placements in British Election Studies from 1987 to 2010 confirm that the pronounced convergence during the past decade has left the Conservatives and Labour closer together than would be optimal in terms of minimising the policy distance between the average voter and the nearest major party. We go on to demonstrate that this comes at a cost. Respondents who perceive themselves as further away from one of the major parties in the system tend to score lower on satisfaction with democracy. In short, vote-seeking parties have left the British party system less representative of the ideological diversity in the electorate, and thus made at least some British voters miserable

Dynamic input to determine hip joint moments, power and work on the prosthetic limb of transfemoral amputees: ground reactions vs knee reactions

Study Design: Comparative analysis\ud Background: Calculations of lower limbs kinetics are limited by floor-mounted force-plates.\ud Objectives: Comparison of hip joint moments, power and mechanical work on the prosthetic limb of a transfemoral amputee calculated by inverse dynamics using either the ground reactions (force-plates) or knee reactions (transducer).\ud Methods: Kinematics, ground reactions and knee reactions were collected using a motion analysis system, two force-plates and a multi-axial transducer mounted below the socket, respectively.\ud Results: The inverse dynamics using ground reactions under-estimated the peaks of hip energy generation and absorption occurring at 63 % and 76 % of the gait cycle (GC) by 28 % and 54 %, respectively. This method over-estimated a phase of negative work at the hip (from 37 %GC to 56 %GC) by 24%. It under-estimated the phases of positive (from 57 %GC to 72 %GC) and negative (from 73 %GC to 98 %GC) work at the hip by 11 % and 58%, respectively.\ud Conclusions: A transducer mounted within the prosthesis has the capacity to provide more realistic kinetics of the prosthetic limb because it enables assessment of multiple consecutive steps and a wide range of activities without issues of foot placement on force-plates

Astrophysical calibration of gravitational-wave detectors

We investigate a method to assess the validity of gravitational-wave detector calibration through the use of gamma-ray bursts as standard sirens. Such signals, as measured via gravitational-wave observations, provide an estimated luminosity distance that is subject to uncertainties in the calibration of the data. If a host galaxy is identified for a given source then its redshift can be combined with current knowledge of the cosmological parameters yielding the true luminosity distance. This will then allow a direct comparison with the estimated value and can validate the accuracy of the original calibration. We use simulations of individual detectable gravitational-wave signals from binary neutron star (BNS) or neutron star-black hole systems, which we assume to be found in coincidence with short gamma-ray bursts, to estimate any discrepancy in the overall scaling of the calibration for detectors in the Advanced LIGO and Advanced Virgo network. We find that the amplitude scaling of the calibration for the LIGO instruments could on average be confirmed to within ∼10% for a BNS source within 100 Mpc. This result is largely independent of the current detector calibration method and gives an uncertainty that is competitive with that expected in the current calibration procedure. Confirmation of the calibration accuracy to within ∼20% can be found with BNS sources out to ∼500 Mpc