Probing the Binary Black Hole Merger Regime with Scalar Perturbations

We present results obtained by scattering a scalar field off the curved background of a coalescing binary black hole system. A massless scalar field is evolved on a set of fixed backgrounds, each provided by a spatial hypersurface generated numerically during a binary black hole merger. We show that the scalar field scattered from the merger region exhibits quasinormal ringing once a common apparent horizon surrounds the two black holes. This occurs earlier than the onset of the perturbative regime as measured by the start of the quasinormal ringing in the gravitational waveforms. We also use the scalar quasinormal frequencies to associate a mass and a spin with each hypersurface, and observe the compatibility of this measure with the horizon mass and spin computed from the dynamical horizon framework.Comment: 10 Pages and 6 figure

Frequency noise and intensity noise of next-generation gravitational-wave detectors with RF/DC readout schemes

The sensitivity of next-generation gravitational-wave detectors such as Advanced LIGO and LCGT should be limited mostly by quantum noise with an expected technical progress to reduce seismic noise and thermal noise. Those detectors will employ the optical configuration of resonant-sideband-extraction that can be realized with a signal-recycling mirror added to the Fabry-Perot Michelson interferometer. While this configuration can reduce quantum noise of the detector, it can possibly increase laser frequency noise and intensity noise. The analysis of laser noise in the interferometer with the conventional configuration has been done in several papers, and we shall extend the analysis to the resonant-sideband-extraction configuration with the radiation pressure effect included. We shall also refer to laser noise in the case we employ the so-called DC readout scheme.Comment: An error in Fig. 10 in the published version in PRD has been corrected in this version; an erratum has been submitted to PRD. After correction, this figure reflects a significant difference in the ways RF and DC readout schemes are susceptible to laser noise. In addition, the levels of mirror loss imbalances and input laser amplitude noise have also been updated to be more realistic for Advanced LIG

Against the complex versus simple distinction

This paper examines three proposals on the difference between complex and simple views about personal identity: Parfit’s original introduction of the distinction, Gasser and Stefan’s definition and Noonan’s recent proposal. I argue that the first two classify the paradigm cases of simplicity as complex, while Noonan’s proposal makes simplicity and complexity turn on features whose relevance for the distinction is questionable. Given these difficulties, I examine why we should be interested in whether a position is complex or simple. I describe two purposes of having a distinction, and show that extant accounts of the complex vs. simple distinction fail to serve these. I argue that unless we find a satisfying account of the difference between complex and simple positions, we should not frame discourses on personal identity in these terms.Publisher PDFPeer reviewe

Radiation from low-momentum zoom-whirl orbits

We study zoom-whirl behaviour of equal mass, non-spinning black hole binaries in full general relativity. The magnitude of the linear momentum of the initial data is fixed to that of a quasi-circular orbit, and its direction is varied. We find a global maximum in radiated energy for a configuration which completes roughly one orbit. The radiated energy in this case exceeds the value of a quasi-circular binary with the same momentum by 15%. The direction parameter only requires minor tuning for the localization of the maximum. There is non-trivial dependence of the energy radiated on eccentricity (several local maxima and minima). Correlations with orbital dynamics shortly before merger are discussed. While being strongly gauge dependent, these findings are intuitive from a physical point of view and support basic ideas about the efficiency of gravitational radiation from a binary system.Comment: 9 pages, 6 figures, Amaldi8 conference proceedings as publishe

Exchange biasing of single-domain Ni nanoparticles spontaneously grown in an antiferromagnetic MnO matrix

Exchange biased composites of ferromagnetic single-domain Ni nanoparticles embedded within large grains of MnO have been prepared by reduction of Ni$_x$Mn$_{1-x}$O$_4$ phases in flowing hydrogen. The Ni precipitates are 15-30 nm in extent, and the majority are completely encased within the MnO matrix. The manner in which the Ni nanoparticles are spontaneously formed imparts a high ferromagnetic- antiferromagnetic interface/volume ratio, which results in substantial exchange bias effects. Exchange bias fields of up to 100 Oe are observed, in cases where the starting Ni content $x$ in the precursor Ni$_x$Mn$_{1-x}$O$_4$ phase is small. For particles of approximately the same size, the exchange bias leads to significant hardening of the magnetization, with the coercive field scaling nearly linearly with the exchange bias field.Comment: 6 pages PDFLaTeX with 9 figure

Species Delimitation: A Case Study in a Problematic Ant Taxon

Species delimitation has been invigorated as a discipline in systematics by an influx of new character sets, analytical methods, and conceptual advances. We use genetic data from 68 markers, combined with distributional, bioclimatic, and coloration information, to hypothesize boundaries of evolutionarily independent lineages (species) within the widespread and highly variable nominal fire ant species Solenopsis saevissima, a member of a species group containing invasive pests as well as species that are models for ecological and evolutionary research. Our integrated approach uses diverse methods of analysis to sequentially test whether populations meet specific operational criteria (contingent properties) for candidacy as morphologically cryptic species, including genetic clustering, monophyly, reproductive isolation, and occupation of distinctive niche space. We hypothesize that nominal S. saevissima comprises at least 4-6 previously unrecognized species, including several pairs whose parapatric distributions implicate the development of intrinsic premating or postmating barriers to gene flow. Our genetic data further suggest that regional genetic differentiation in S. saevissima has been influenced by hybridization with other nominal species occurring in sympatry or parapatry, including the quite distantly related Solenopsis geminata. The results of this study illustrate the importance of employing different classes of genetic data (coding and noncoding regions and nuclear and mitochondrial DNA [mtDNA] markers), different methods of genetic data analysis (tree-based and non-tree based methods), and different sources of data (genetic, morphological, and ecological data) to explicitly test various operational criteria for species boundaries in clades of recently diverged lineages, while warning against over reliance on any single data type (e.g., mtDNA sequence variation) when drawing inference

Transplant Thought-Experiments: Two costly mistakes in discounting them

‘Transplant’ thought-experiments, in which the cerebrum is moved from one body to another, have featured in a number of recent discussions in the personal identity literature. Once taken as offering confirmation of some form of psychological continuity theory of identity, arguments from Marya Schechtman and Kathleen Wilkes have contended that this is not the case. Any such apparent support is due to a lack of detail in their description or a reliance on predictions that we are in no position to make. I argue that the case against them rests on two serious misunderstandings of the operation of thought-experiments, and that even if they do not ultimately support a psychological continuity theory, they do major damage to that theory’s opponents

Cardiovascular response to postural perturbations of different intensities in healthy young adults

The ability to regain control of balance is vital in limiting falls and injuries. Little is known regarding how the autonomic nervous system responds during recovery from balance perturbations of different intensities. The purpose of this study was to examine the cardiovascular response following a standing balance perturbation of varying intensities, quantify cardiac baroreflex sensitivity (cBRS) during standing perturbations, and to establish the stability of the cardiac baroreflex during quiet standing before and after balance disturbances. Twenty healthy participants experienced three different perturbation intensity conditions that each included 25 brief posteriorly-directed perturbations, 8–10 s apart. Three perturbation intensity conditions (low, medium, high) were given in random order. Physiological data were collected in quiet stance for 5 min before testing (Baseline) and again after the perturbation conditions (Recovery) to examine baroreflex stability. Beat-to-beat heart rate (HR) and systolic blood pressure (SBP) analysis post-perturbation indicated an immediate acceleration of the HR for 1–2 s, with elevated SBP 4–5 s post-perturbation. Heart rate changes were greatest in the medium (p = 0.035) and high (p = 0.012) intensities compared to low, while there were no intensity-dependent changes in SBP. The cBRS was not intensity-dependent (p = 0.402) but when perturbation conditions were combined, cBRS was elevated compared to Baseline (p = 0.046). The stability of baseline cBRS was excellent (ICC = 0.896) between quiet standing conditions. In summary, HR, but not SBP or cBRS were intensity-specific during postural perturbations. This was the first study to examine cardiovascular response and cBRS to postural perturbations