969 research outputs found
Bayesian estimation of pulsar parameters from gravitational wave data
We present a method of searching for, and parameterizing, signals from known
radio pulsars in data from interferometric gravitational wave detectors. This
method has been applied to data from the LIGO and GEO 600 detectors to set
upper limits on the gravitational wave emission from several radio pulsars.
Here we discuss the nature of the signal and the performance of the technique
on simulated data. We show how to perform a coherent multiple detector analysis
and give some insight in the covariance between the signal parameters.Comment: 9 pages, 6 figures. Accepted to Phys. Rev. D. A few small changes
from previous versio
Propeller Study. Part 2: the Design of Propellers for Minimum Noise
The design of propellers which are efficient and yet produce minimum noise requires accurate determinations of both the flow over the propeller. Topics discussed in relating aerodynamic propeller design and propeller acoustics include the necessary approximations and assumptions involved, the coordinate systems and their transformations, the geometry of the propeller blade, and the problem formulations including the induced velocity, required in the determination of mean lines of blade sections, and the optimization of propeller noise. The numerical formulation for the lifting-line model are given. Some applications and numerical results are included
A Metropolis-Hastings algorithm for extracting periodic gravitational wave signals from laser interferometric detector data
The Markov chain Monte Carlo methods offer practical procedures for detecting
signals characterized by a large number of parameters and under conditions of
low signal-to-noise ratio. We present a Metropolis-Hastings algorithm capable
of inferring the spin and orientation parameters of a neutron star from its
periodic gravitational wave signature seen by laser interferometric detector
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
Figuring Out the Doha Round
The global economic and financial crisis has awakened protectionist sentiments around the world, and policymakers have failed to actively seek trade liberalization. In light of this, some have proposed abandoning the Doha Round and starting over with a new agenda. Figuring Out the Doha Round argues that this is far from the time to drop the Doha Round and that it is now more important than ever to sustain political support for the rules-based multilateral trade system. This important new study recommends modest increments in market access commitments by G-20 countries beyond tariff and subsidy cuts in agriculture and nonagricultural market access (NAMA), and policy reforms in customs procedures and related areas that slash red tape and cut transactions costs for exporting and importing goods and services. With additional effort by the G-20 countries, WTO countries can put together a Doha package that is both ambitious and balanced between the interests of developed and developing countries. The study finds that following these recommendations can lead to a world GDP gain of almost $300 billion a year.
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
Detecting gravitational radiation from neutron stars using a six-parameter adaptive MCMC method
We present a Markov chain Monte Carlo technique for detecting gravitational
radiation from a neutron star in laser interferometer data. The algorithm can
estimate up to six unknown parameters of the target, including the rotation
frequency and frequency derivative, using reparametrization, delayed rejection
and simulated annealing. We highlight how a simple extension of the method,
distributed over multiple computer processors, will allow for a search over a
narrow frequency band. The ultimate goal of this research is to search for
sources at a known locations, but uncertain spin parameters, such as may be
found in SN1987A.Comment: Submitted to Classical and Quantum Gravity for GWDAW-8 proceeding
Robust Bayesian detection of unmodelled bursts
A Bayesian treatment of the problem of detecting an unmodelled gravitational
wave burst with a global network of gravitational wave observatories reveals
that several previously proposed statistics have implicit biases that render
them sub-optimal for realistic signal populations.Comment: 9 pages, 1 figure, submitted to CQG Amaldi proceedings special issu
An Evidence Based Search Method For Gravitational Waves From Neutron Star Ring-downs
The excitation of quadrupolar quasi-normal modes in a neutron star leads to
the emission of a short, distinctive, burst of gravitational radiation in the
form of a decaying sinusoid or `ring-down'. We present a Bayesian analysis
method which incorporates relevant prior information about the source and known
instrumental artifacts to conduct a robust search for the gravitational wave
emission associated with pulsar glitches and soft -ray repeater flares.
Instrumental transients are modelled as sine-Gaussian and their evidence, or
marginal likelihood, is compared with that of Gaussian white noise and
ring-downs via the `odds-ratio'. Tests using simulated data with a noise
spectral density similar to the LIGO interferometer around 1 kHz yield 50%
detection efficiency and 1% false alarm probability for ring-down signals with
signal-to-noise ratio . For a source at 15 kpc this requires an
energy of 1.3\times 10^{-5}M_{\astrosun}c^2 to be emitted as gravitational
waves.Comment: 14 pages, 12 figure
Optimal time-domain combination of the two calibrated output quadratures of GEO 600
GEO 600 is an interferometric gravitational wave detector with a 600 m arm-length and which uses a dual-recycled optical configuration to give enhanced sensitivity over certain frequencies in the detection band. Due to the dual-recycling, GEO 600 has two main output signals, both of which potentially contain gravitational wave signals. These two outputs are calibrated to strain using a time-domain method. In order to simplify the analysis of the GEO 600 data set, it is desirable to combine these two calibrated outputs to form a single strain signal that has optimal signal-to-noise ratio across the detection band. This paper describes a time-domain method for doing this combination. The method presented is similar to one developed for optimally combining the outputs of two colocated gravitational wave detectors. In the scheme presented in this paper, some simplifications are made to allow its implementation using time-domain methods
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