1,656 research outputs found

    Systematic challenges for future gravitational wave measurements of precessing binary black holes

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    The properties of precessing, coalescing binary black holes are presently inferred through comparison with two approximate models of compact binary coalescence. In this work we show these two models often disagree substantially when binaries have modestly large spins (a≳0.4a\gtrsim 0.4) and modest mass ratios (q≳2q\gtrsim 2). We demonstrate these disagreements using standard figures of merit and the parameters inferred for recent detections of binary black holes. By comparing to numerical relativity, we confirm these disagreements reflect systematic errors. We provide concrete examples to demonstrate that these systematic errors can significantly impact inferences about astrophysically significant binary parameters. For the immediate future, parameter inference for binary black holes should be performed with multiple models (including numerical relativity), and carefully validated by performing inference under controlled circumstances with similar synthetic events.Comment: 12 pages, 9 figure

    The dependence of test-mass thermal noises on beam shape in gravitational-wave interferometers

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    In second-generation, ground-based interferometric gravitational-wave detectors such as Advanced LIGO, the dominant noise at frequencies f∌40f \sim 40 Hz to ∌200\sim 200 Hz is expected to be due to thermal fluctuations in the mirrors' substrates and coatings which induce random fluctuations in the shape of the mirror face. The laser-light beam averages over these fluctuations; the larger the beam and the flatter its light-power distribution, the better the averaging and the lower the resulting thermal noise. In semi-infinite mirrors, scaling laws for the influence of beam shape on the four dominant types of thermal noise (coating Brownian, coating thermoelastic, substrate Brownian, and substrate thermoelastic) have been suggested by various researchers and derived with varying degrees of rigour. Because these scaling laws are important tools for current research on optimizing the beam shape, it is important to firm up our understanding of them. This paper (1) gives a summary of the prior work and of gaps in the prior analyses, (2) gives a unified and rigorous derivation of all four scaling laws, and (3) explores, relying on work by J. Agresti, deviations from the scaling laws due to finite mirror size.Comment: 25 pages, 10 figures, submitted to Class. Quantum Gra

    The Slowly Formed Guiselin Brush

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    We study polymer layers formed by irreversible adsorption from a polymer melt. Our theory describes an experiment which is a ``slow'' version of that proposed by Guiselin [Europhys. Lett., v. 17 (1992) p. 225] who considered instantaneously irreversibly adsorbing chains and predicted a universal density profile of the layer after swelling with solvent to produce the ``Guiselin brush.'' Here we ask what happens when adsorption is not instantaneous. The classic example is chemisorption. In this case the brush is formed slowly and the final structure depends on the experiment's duration, tfinalt_{final}. We find the swollen layer consists of an inner region of thickness z∗∌tfinal−5/3z^* \sim t_{final}^{-5/3} with approximately constant density and an outer region extending up to height h∌N5/6h \sim N^{5/6} which has the same density decay ∌z−2/5\sim z^{-2/5} as for the Guiselin case.Comment: 7 pages, submitted to Europhysics Letter

    Post-1995 French cinema: return of the social, return of the political?

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    A key trend in post-1995 French cinema has been the return of the social. Analysing this trend, this article seeks to evaluate its politic impact. Using HervĂ© Le Roux’s Reprise (1997) and AgnĂšs Varda’s Les Glaneurs et la glaneuse (2000) as key meta-texts, it suggests that the current wave of politically engaged cinema needs to be approached in new ways that recognise how films trace the impact of a politically unmediated, ‘raw’ real on groups or individuals. It further suggests that the withdrawal of political mediation gives the films an essential ambiguity and a melodramatic quality that, rather than mere clichĂ©, may be a privileged way to engage with the violence of the real. Film is now not so much in the van but dans le bain of a diverse socio-political stirring
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