765 research outputs found
Gravitational waveforms from the evaporating ACO cosmic string loop
The linearly polarized gravitational waveforms from a certain type of
rotating, evaporating cosmic string - the Allen-Casper-Ottewill loop - are
constructed and plotted over the lifetime of the loop. The formulas for the
waveforms are simple and exact, and describe waves which attenuate
self-similarly, with the amplitude and period of the waves falling off linearly
with time.Comment: 30 pages, 16 figure
Continuous self-similar evaporation of a rotating cosmic string loop
A solution of the linearized Einstein and Nambu-Goto equations is constructed
which describes the evaporation of a certain type of rotating cosmic string -
the Allen-Casper-Ottewill loop - under the action of its own self-gravity. The
solution evaporates self-similarly, and radiates away all its mass-energy and
momentum in a finite time. Furthermore, the corresponding weak-field metric can
be matched to a remnant Minkowski spacetime at all points on the future light
cone of the final evaporation point of the loop.Comment: 80 pages, 13 figures. Accepted for publication in Classical and
Quantum Gravit
Self-Similar Evaporation of a Rigidly-Rotating Cosmic String Loop
The gravitational back-reaction on a certain type of rigidly-rotating cosmic
string loop, first discovered by Allen, Casper and Ottewill, is studied at the
level of the weak-field approximation. The near-field metric perturbations are
calculated and used to construct the self-acceleration vector of the loop.
Although the acceleration vector is divergent at the two kink points on the
loop, its net effect on the trajectory over a single oscillation period turns
out to be finite. The net back-reaction on the loop over a single period is
calculated using a method due to Quashnock and Spergel, and is shown to induce
a uniform shrinkage of the loop while preserving its original shape. The loop
therefore evolves by self-similar evaporation.Comment: 41 pages, 5 figures. Accepted for publication in Classical and
Quantum Gravit
Report on an all-sky LIGO search for periodic gravitational waves in the S4 data
We report on an all-sky search with the LIGO detectors for periodic
gravitational waves in the frequency range 50-1000 Hz and having a negative
frequency time derivative with magnitude between zero and Hz/s. Data
from the fourth LIGO science run have been used in this search. Three different
semi-coherent methods of summing strain power were applied. Observing no
evidence for periodic gravitational radiation, we report upper limits on strain
amplitude and interpret these limits to constrain radiation from rotating
neutron stars.Comment: 5 pages, 1 figure, presented at Amaldi7, Sydney (July 2007
Field validation of habitat suitability models for vulnerable marine ecosystems in the South Pacific Ocean:Implications for the use of broad-scale models in fisheries management
AbstractManagement of human activities which impact the seafloor in the deep ocean is becoming increasingly important as bottom trawling and exploration for minerals, oil, and gas continue to extend into regions where fragile ecosystems containing habitat-forming deep-sea corals and sponges may be found. Spatial management of these vulnerable marine ecosystems requires accurate knowledge of their distribution. Predictive habitat suitability modelling, using species presence data and a suite of environmental predictor variables, has emerged as a useful tool for inferring distributions outside of known areas. However, validation of model predictions is typically performed with non-independent data. In this study, we describe the results of habitat suitability models constructed for four deep-sea reef-forming coral species across a large region of the South Pacific Ocean using MaxEnt and Boosted Regression Tree modelling approaches. In order to validate model predictions we conducted a photographic survey on a set of seamounts in an un-sampled area east of New Zealand. The likelihood of habitat suitable for reef-forming corals on these seamounts was predicted to be variable, but very high in some regions, particularly where levels of aragonite saturation, dissolved oxygen, and particulate organic carbon were optimal. However, the observed frequency of coral occurrence in analyses of survey photographic data was much lower than expected, and patterns of observed versus predicted coral distribution were not highly correlated. The poor performance of these broad-scale models is attributed to lack of recorded species absences to inform the models, low precision of global bathymetry models, and lack of data on the geomorphology and substrate of the seamounts at scales appropriate to the modelled taxa. This demonstrates the need to use caution when interpreting and applying broad-scale, presence-only model results for fisheries management and conservation planning in data poor areas of the deep sea. Future improvements in the predictive performance of broad-scale models will rely on the continued advancement in modelling of environmental predictor variables, refinements in modelling approaches to deal with missing or biased inputs, and incorporation of true absence data
Searching for stochastic gravitational-wave background with the co-located LIGO interferometers
This paper presents techniques developed by the LIGO Scientific Collaboration
to search for the stochastic gravitational-wave background using the co-located
pair of LIGO interferometers at Hanford, WA. We use correlations between
interferometers and environment monitoring instruments, as well as time-shifts
between two interferometers (described here for the first time) to identify
correlated noise from non-gravitational sources. We veto particularly noisy
frequency bands and assess the level of residual non-gravitational coupling
that exists in the surviving data.Comment: Proceedings paper from the 7th Edoardo Amaldi Conference on
Gravitational Waves, held in Sydney, Australia from 8-14 July 2007. Accepted
to J. Phys.: Conf. Se
- …