Model waveform accuracy standards for gravitational wave data analysis

Model waveforms are used in gravitational wave data analysis to detect and then to measure the properties of a source by matching the model waveforms to the signal from a detector. This paper derives accuracy standards for model waveforms which are sufficient to ensure that these data analysis applications are capable of extracting the full scientific content of the data, but without demanding excessive accuracy that would place undue burdens on the model waveform simulation community. These accuracy standards are intended primarily for broadband model waveforms produced by numerical simulations, but the standards are quite general and apply equally to such waveforms produced by analytical or hybrid analytical-numerical methods

The vegetation of Tasman Peninsula

Although its area is less than 1% of Tasmania, Tasman Peninsula possesses more than one- third of the total native vascular plants of the State. The number of species present is close to that predicted by the theories of island biogeography. There are 70 Tasmanian endemic vascular plant species present, representing 13 % of the total. This figure is lower than that expected on a proportional basis due to the absence from the peninsula of the distinctively Tasmanian alpine, wet and oligotrophic western environments. There are two vascular plants known only from the peninsula. Nevertheless there is a distinctly local flavour to the flora due to those components held in common with other predominantly lowland dolerite parts of southeastern Tasmania. The vegetation types present on the peninsula include coastal heaths, dune vegetation and wetlands, dry and wet sc!erophyll forests and some small areas ofsubalpine scrub and rainforests. The structure and composition of the vegetation on the peninsula reflect climatic, topographic, firing and biotic influences. Thus dry sclerophyll forests grade into wet sclerophyll forests as moisture availability increases . The forests grade into heaths as sites become more exposed to the prevailing salt-laden onshore winds. Within a particular vegetation type, the composition is influenced by local climate and landform but is also attributable to local drainage conditions, geological substrate and fire history. The plant species and communities present are, some exceptions, moderately well- conserved, but sensitivity in future management will be required to retain the character conferred on the peninsula by its native vegetation

Variation of tow force with velocity during offshore ploughing in granular materials

Pipeline plough behaviour has been investigated by means of reduced scale physical model testing. A testing programme was devised to investigate the influence of permeability, relative density, and plough depth on the associated tow force measured during ploughing over a range of velocities in saturated granular material. An increase in tow force with velocity was found during all of the tests and the results have been compared to previously developed analytical models. A new empirical equation has been developed to describe the change in tow force with velocity for a variety of model siliceous sand conditions. Application of this new approach to full-scale ploughing requires consideration of scaling effects and the use of appropriate input parameters determined to replicate field conditions. </jats:p

Investigating the noise residuals around the gravitational wave event GW150914

We use the Pearson cross-correlation statistic proposed by Liu and Jackson, and employed by Creswell et al., to look for statistically significant correlations between the LIGO Hanford and Livingston detectors at the time of the binary black hole merger GW150914. We compute this statistic for the calibrated strain data released by LIGO, using both the residuals provided by LIGO and using our own subtraction of a maximum-likelihood waveform that is constructed to model binary black hole mergers in general relativity. To assign a significance to the values obtained, we calculate the cross-correlation of both simulated Gaussian noise and data from the LIGO detectors at times during which no detection of gravitational waves has been claimed. We find that after subtracting the maximum likelihood waveform there are no statistically significant correlations between the residuals of the two detectors at the time of GW150914.Comment: 14 pages, 7 figures. Minor text and figure changes in final v3. Notebooks for generating the results are available at https://github.com/gwastro/gw150914_investigatio

Template banks to search for low-mass binary black holes in advanced gravitational-wave detectors

Coalescing binary black holes (BBHs) are among the most likely sources for the Laser Interferometer Gravitational-wave Observatory (LIGO) and its international partners Virgo and KAGRA. Optimal searches for BBHs require accurate waveforms for the signal model and effectual template banks that cover the mass space of interest. We investigate the ability of the second-order post-Newtonian TaylorF2 hexagonal template placement metric to construct an effectual template bank, if the template waveforms used are effective one body waveforms tuned to numerical relativity (EOBNRv2). We find that by combining the existing TaylorF2 placement metric with EOBNRv2 waveforms, we can construct an effectual search for BBHs with component masses in the range 3 Msolar <= m_1, m_2 <= 25 Msolar. We also show that the (computationally less expensive) TaylorF2 post-Newtonian waveforms can be used in place of EOBNRv2 waveforms when M <~ 11.4 Msolar. Finally, we investigate the effect of modes other than the dominant l = m = 2 mode in BBH searches. We find that for systems with (m_1/m_2)= 2.68 radians, there is no significant loss in the total possible signal-to-noise ratio due to neglecting modes other than l = m = 2 in the template waveforms. For a source population uniformly distributed in spacial volume, over the entire sampled region of the component-mass space, the loss in detection rate (averaged over a uniform distribution of inclination angle and sky-location/polarization angles), remains below ~11%. For binaries with high mass-ratios \textit{and} 0.31 <= \iota <= 2.68, including higher order modes could increase the signal-to-noise ratio by as much as 8% in Advanced LIGO. Our results can be used to construct matched-filter searches in Advanced LIGO and Advanced Virgo.Comment: 12 pages, 10 figure