8,249 research outputs found
Precession during merger 1: Strong polarization changes are observationally accessible features of strong-field gravity during binary black hole merger
The short gravitational wave signal from the merger of compact binaries
encodes a surprising amount of information about the strong-field dynamics of
merger into frequencies accessible to ground-based interferometers. In this
paper we describe a previously-unknown "precession" of the peak emission
direction with time, both before and after the merger, about the total angular
momentum direction. We demonstrate the gravitational wave polarization encodes
the orientation of this direction to the line of sight. We argue the effects of
polarization can be estimated nonparametrically, directly from the
gravitational wave signal as seen along one line of sight, as a slowly-varying
feature on top of a rapidly-varying carrier. After merger, our results can be
interpreted as a coherent excitation of quasinormal modes of different angular
orders, a superposition which naturally "precesses" and modulates the
line-of-sight amplitude. Recent analytic calculations have arrived at a similar
geometric interpretation. We suspect the line-of-sight polarization content
will be a convenient observable with which to define new high-precision tests
of general relativity using gravitational waves. Additionally, as the nonlinear
merger process seeds the initial coherent perturbation, we speculate the
amplitude of this effect provides a new probe of the strong-field dynamics
during merger. To demonstrate the ubiquity of the effects we describe, we
summarize the post-merger evolution of 104 generic precessing binary mergers.
Finally, we provide estimates for the detectable impacts of precession on the
waveforms from high-mass sources. These expressions may identify new precessing
binary parameters whose waveforms are dissimilar from the existing sample.Comment: 11 figures; v2 includes response to referee suggestion
Intrinsic selection biases of ground-based gravitational wave searches for high-mass BH-BH mergers
The next generation of ground-based gravitational wave detectors may detect a
few mergers of comparable-mass M\simeq 100-1000 Msun ("intermediate-mass'', or
IMBH) spinning black holes. Black hole spin is known to have a significant
impact on the orbit, merger signal, and post-merger ringdown of any binary with
non-negligible spin. In particular, the detection volume for spinning binaries
depends significantly on the component black hole spins. We provide a fit to
the single-detector and isotropic-network detection volume versus (total) mass
and arbitrary spin for equal-mass binaries. Our analysis assumes matched
filtering to all significant available waveform power (up to l=6 available for
fitting, but only l<= 4 significant) estimated by an array of 64 numerical
simulations with component spins as large as S_{1,2}/M^2 <= 0.8. We provide a
spin-dependent estimate of our uncertainty, up to S_{1,2}/M^2 <= 1. For the
initial (advanced) LIGO detector, our fits are reliable for
(). In the online version of this
article, we also provide fits assuming incomplete information, such as the
neglect of higher-order harmonics. We briefly discuss how a strong selection
bias towards aligned spins influences the interpretation of future
gravitational wave detections of IMBH-IMBH mergers.Comment: 18 pages, 15 figures, accepted by PRD. v2 is version accepted for
publication, including minor changes in response to referee feedback and
updated citation
Pore geometry as a control on rock strength
This study was funded via RJW's University of Leicester start-up fund, as part of AAB's PhD project. We thank Don Swanson and Mike Poland at HVO, Hawai'i, for their help and advice during fieldwork planning and sample collection in the Koa'e fault system, and the National Park Service for granting a research permit to collect rock samples. Sergio Vinciguerra is thanked for access to the Rock Mechanics and Physics lab at the British Geological Survey and Audrey Ougier-Simonin is thanked for her help preparing samples and advice during testing. We thank Mike Heap (EOST Strasbourg) and an anonymous reviewer for their detailed and careful comments that greatly improved the manuscript.Peer reviewedPostprin
Distance-generalized Core Decomposition
The -core of a graph is defined as the maximal subgraph in which every
vertex is connected to at least other vertices within that subgraph. In
this work we introduce a distance-based generalization of the notion of
-core, which we refer to as the -core, i.e., the maximal subgraph in
which every vertex has at least other vertices at distance within
that subgraph. We study the properties of the -core showing that it
preserves many of the nice features of the classic core decomposition (e.g.,
its connection with the notion of distance-generalized chromatic number) and it
preserves its usefulness to speed-up or approximate distance-generalized
notions of dense structures, such as -club.
Computing the distance-generalized core decomposition over large networks is
intrinsically complex. However, by exploiting clever upper and lower bounds we
can partition the computation in a set of totally independent subcomputations,
opening the door to top-down exploration and to multithreading, and thus
achieving an efficient algorithm
Test of recent advances in extracting information from option prices
© 2017 Elsevier Inc. A large literature exists on techniques for extracting probability distributions for future asset prices from option prices. No definitive method has been developed however. The parametric 'mixture of normals', and non-parametric 'smoothed implied volatility' methods remain the most widespread approaches. These though are subject to estimation errors due to discretization, truncation, and noise. Recently, several authors have derived 'model free' formulae for computing the moments of the risk neutral density (RND) directly from option prices, without first estimating the full density. The accuracy of these formulae is studied here for the first time. The Black-Scholes formula is used to generate option prices, and error curves for the first 4 moments of the RND are computed using the 'model-free' formulae. It is found that, in practice, the formulae are prone to large and economically significant errors, because they contain definite integrals that can only be solved numerically. We show that without mathematically equivalent expressions with analytical solutions the formulae are difficult to deploy effectively in practice
Teenage drinking and interethnic friendships.
This report explores the links between young people’s interethnic friendships and their drinking patterns and behaviours.
Britain is a multicultural society, but little is currently known about if, and how, young people mix with friends from different ethnic backgrounds and the potential impact of this on drinking attitudes and behaviours. Research was undertaken to examine these links using quantitative and qualitative methods among a sample of 14-and 15-year-olds in diverse locations in London and Berkshire.
The report:
• explores the intra- and interethnic mix of young people’s
friendship groups as described by young people in
questionnaires and interviews;
• analyses how drinking patterns vary by ethnicity, religion and gender;
• investigates the links between young people’s background
characteristics, their friendship groups (including the ethnicity of friends) and their reported drinking rates; and
• looks at the implications of the findings, including
recommendations for harm reduction based on education and
peer support programmes
Topological relaxation of entangled flux lattices: Single vs collective line dynamics
A symbolic language allowing to solve statistical problems for the systems
with nonabelian braid-like topology in 2+1 dimensions is developed. The
approach is based on the similarity between growing braid and "heap of colored
pieces". As an application, the problem of a vortex glass transition in
high-T_c superconductors is re-examined on microscopic levelComment: 4 pages (revtex), 4 figure
Source apportionment of PM<sub>2.5</sub> in Cork Harbour, Ireland using a combination of single particle mass spectrometry and quantitative semi-continuous measurements
An aerosol time-of-flight mass spectrometer (ATOFMS) was deployed for the measurement of the size resolved chemical composition of single particles at a site in Cork Harbour, Ireland for three weeks in August 2008. The ATOFMS was co-located with a suite of semi-continuous instrumentation for the measurement of particle number, elemental carbon (EC), organic carbon (OC), sulfate and particulate matter smaller than 2.5 μm in diameter (PM<sub>2.5</sub>). The temporality of the ambient ATOFMS particle classes was subsequently used in conjunction with the semi-continuous measurements to apportion PM<sub>2.5</sub> mass using positive matrix factorisation. The synergy of the single particle classification procedure and positive matrix factorisation allowed for the identification of six factors, corresponding to vehicular traffic, marine, long-range transport, various combustion, domestic solid fuel combustion and shipping traffic with estimated contributions to the measured PM<sub>2.5</sub> mass of 23%, 14%, 13%, 11%, 5% and 1.5% respectively. Shipping traffic was found to contribute 18% of the measured particle number (20–600 nm mobility diameter), and thus may have important implications for human health considering the size and composition of ship exhaust particles. The positive matrix factorisation procedure enabled a more refined interpretation of the single particle results by providing source contributions to PM<sub>2.5</sub> mass, while the single particle data enabled the identification of additional factors not possible with typical semi-continuous measurements, including local shipping traffic
Out of the Frying Pan and into the Fire: The Emergence of Depublication in the Wake of Vacatur
Out of the Frying Pan and into the Fire: The Emergence of Depublication in the Wake of Vacatur
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