Applications of Markov Chain Monte Carlo methods to continuous gravitational wave data analysis

A new algorithm for the analysis of gravitational wave data from rapidly rotating neutron stars has been developed. The work is based on the Markov Chain Monte Carlo algorithm and features enhancements specifically targeted to this problem. The algorithm is tested on both synthetic data and hardware injections in the LIGO Hanford interferometer during its third science run ("S3''). By utilising the features of this probabilistic algorithm a search is performed for a rotating neutron star in the remnant of SN1987A within in frequency window of 4 Hz and a spindown window of 2E-10 Hz/s. A method for setting upper limits is described and used on this data in the absence of a detection setting an upper limit on strain of 7.3E-23. A further application of MCMC methods is made in the area of data analysis for the proposed LISA mission. An algorithm is developed to simultaneously estimate the number of sources and their parameters in a noisy data stream using reversible jump MCMC. An extension is made to estimate the position in the sky of a source and this is further improved by the implementation of a fast approximate calculation of the covariance matrix to enhance acceptance rates. This new algorithm is also tested upon synthetic data and the results are presented here. Conclusions are drawn from the results of this work, and comments are made on the development of MCMC algorithms within the field of gravitational wave data analysis, with a view to their increasing usage

Network timing and the 2015 leap second

© Springer International Publishing Switzerland 2016. Using a testbed with reference timestamping, we collected timing data from public Stratum-1 NTP servers during the leap second event of end-June 2015. We found a wide variety of anomalous serverside behaviors, both at the NTP protocol level and in the server clocks themselves, which can last days or even weeks after the event. Out of 176 servers, only 61% had no erroneous behavior related to the leap second event that we could detect

Rot at the roots? Examining public timing infrastructure

© 2016 IEEE. Timekeeping is central to network measurement. In typical systems, its accuracy is ultimately dependent on the forest of timeservers accessible over the network, whose roots are the stratum-1 timeservers, which benefit from reference hardware. It is essential that these servers are accurate and reliable, and it is commonly assumed that this is the case. We put this belief to the test through an examination of around 100 publicly accessible stratum-1 servers, using datasets spanning over 3 years, collected in a testbed with reference timestamping. We develop a methodology capable of disambiguating the effects of routing changes, congestion related variability, and server anomalies on timestamps. We use it to make a first assessment of the health of (public) network timing, by reporting on the type, severity, and frequency of anomalies we encounter

Finding the Right Tree: Topology Inference Despite Spatial Dependences

© 1963-2012 IEEE. Network tomographic techniques have almost exclusively been built on a strong assumption of mutual independence of link processes. We introduce model classes for link loss processes with non-Trivial spatial dependencies, for which the tree topology is nonetheless identifiable from leaf measurements using multicast probing. We show that these classes are large in a well-defined sense, and we provide an algorithm, SLTD, capable of returning the correct topology with certainty in the limit of infinite data

The varying role of the GP in the pathway between colonoscopy and surgery for colorectal cancer: a retrospective cohort study

Extent: 11p.Objectives: To describe general practitioner (GP) involvement in the treatment referral pathway for colorectal cancer (CRC) patients. Design: A retrospective cohort analysis of linked data. Setting: A population-based sample of CRC patients diagnosed from August 2004 to December 2007 in New South Wales, Australia, using the 45 and Up Study, cancer registry diagnosis records, inpatient hospital records and Medicare claims records. Participants: 407 CRC patients who had a colonoscopy followed by surgery. Primary outcome measures: Patterns of GP consultations between colonoscopy and surgery (ie, between diagnosis and treatment). We investigated whether consulting a GP presurgery was associated with time to surgery, postsurgical GP consultations or rectal cancer cases having surgery in a centre with radiotherapy facilities. Results: Of the 407 patients, 43% (n=175) had at least one GP consultation between colonoscopy and surgery. The median time from colonoscopy to surgery was 27 days for those with an intervening GP consultation and 15 days for those without the consultation. 55% (n=223) had a GP consultation up to 30 days postsurgery; it was more common in cases of patients who consulted a GP presurgery than for those who did not (65% and 47%, respectively, adjusted OR 2.71, 95% CI 1.50 to 4.89, p=0.001). Of the 142 rectal cancer cases, 23% (n=33) had their surgery in a centre with radiotherapy facilities, with no difference between those who did and did not consult a GP presurgery (21% and 25% respectively, adjusted OR 0.84, 95% CI 0.27 to 2.63, p=0.76). Conclusions: Consulting a GP between colonoscopy and surgery was associated with a longer interval between diagnosis and treatment, and with further GP consultations postsurgery, but for rectal cancer cases it was not associated with treatment in a centre with radiotherapy facilities. GPs might require a more defined and systematic approach to CRC management.David Goldsbury, Mark Harris, Shane Pascoe, Michael Barton, Ian Olver, Allan Spigelman, Justin Beilby, Craig Veitch, David Weller, Dianne L O'Connel

A Bayesian approach to the follow-up of candidate gravitational wave signals

Ground-based gravitational wave laser interferometers (LIGO, GEO-600, Virgo and Tama-300) have now reached high sensitivity and duty cycle. We present a Bayesian evidence-based approach to the search for gravitational waves, in particular aimed at the followup of candidate events generated by the analysis pipeline. We introduce and demonstrate an efficient method to compute the evidence and odds ratio between different models, and illustrate this approach using the specific case of the gravitational wave signal generated during the inspiral phase of binary systems, modelled at the leading quadrupole Newtonian order, in synthetic noise. We show that the method is effective in detecting signals at the detection threshold and it is robust against (some types of) instrumental artefacts. The computational efficiency of this method makes it scalable to the analysis of all the triggers generated by the analysis pipelines to search for coalescing binaries in surveys with ground-based interferometers, and to a whole variety of signal waveforms, characterised by a larger number of parameters.Comment: 9 page

Self-similar traffic and network dynamics

Copyright © 2002 IEEEOne of the most significant findings of traffic measurement studies over the last decade has been the observed self-similarity in packet network traffic. Subsequent research has focused on the origins of this self-similarity, and the network engineering significance of this phenomenon. This paper reviews what is currently known about network traffic self-similarity and its significance. We then consider a matter of current research, namely, the manner in which network dynamics (specifically, the dynamics of transmission control protocol (TCP), the predominant transport protocol used in today's Internet) can affect the observed self-similarity. To this end, we first discuss some of the pitfalls associated with applying traditional performance evaluation techniques to highly-interacting, large-scale networks such as the Internet. We then present one promising approach based on chaotic maps to capture and model the dynamics of TCP-type feedback control in such networks. Not only can appropriately chosen chaotic map models capture a range of realistic source characteristics, but by coupling these to network state equations, one can study the effects of network dynamics on the observed scaling behavior. We consider several aspects of TCP feedback, and illustrate by examples that while TCP-type feedback can modify the self-similar scaling behavior of network traffic, it neither generates it nor eliminates it.Ashok Erramilli, Matthew Roughan, Darryl Veitch and Walter Willinge

Compact cavity-dumped Q-switched Er: YAG laser

Published 13 September 2016Abstract not availableLachlan Harris, Myles Clark, Peter Veitch, and David Ottawa

Acoustics of Roman Ostia: Aural Architecture, Noise and Urban Space in the Second Century CE

This thesis introduces a methodology for the acoustic analysis of Roman urban space, through an in-depth study of Ostia Antica. The archaeological site of Ostia offers the opportunity to analyse the acoustic effects of second century CE building techniques in a variety of spaces. The acoustic analyses introduced are the first application of a quantitative and qualitative sensory study approach to Roman urban space. The original approach draws on digital humanities tools in combination with traditional archaeological site analyses in the interpretation of noise and acoustics. The thesis is developed in three main parts. First, an exploration of the Roman literary sources through a digital humanities approach, which contextualises the literary urban image of noise in Rome. Noise was a key element in the social perception of urban space. The Latin literary sources display an urban image of noise, especially noise relating to movement. This concern did not manifest itself in legal control of noise, but instead relied on social stigma and moral judgements. Second, an acoustic model was developed and analysed some of the primary building types and streets in second century CE Ostia. Sound isolation was only possible in certain places, a product of other construction techniques and design choices. Third, a social historical investigation of the everyday rhythms of work, which were the background noise of Ostia, was undertaken to develop an approach to urban divisions of space not visible in architecture. These three parts are grounded in spatial and social theory, drawing on work from urban geography and sensory studies. This thesis shows the importance of acoustic analysis in understanding Roman architecture and urbanism in the second century CE. It develops an original approach to modelling and analysing architecture through acoustics. The application of such a model to the urban arrangement and layout of a Roman site has not been undertaken before. This thesis, therefore, forms an original contribution to the field of classical archaeology through the implementation and interpretation of acoustic modelling of partially preserved buildings, as well as the models application to the urban arrangement of second century CE Ostia