2,723 research outputs found
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
Study of flight management requirements during SST low visibility approach and landing operations. Volume 1 - Definition of baseline SST landing system
Baseline instrument landing system for low visibility approach and landing of supersonic transport
Rat cerebral cortical synaptoneurosomal membranes. Structure and interactions with imidazobenzodiazepine and 1,4-dihydropyridine calcium channel drugs
Small angle x-ray scattering has been used to investigate the structure of synaptoneurosomal (SNM) membranes from rat cerebral cortex. Electron micrographs of the preparation showed SNM with classical synaptic appositions intact, other vesicles, occasional mitochondria, and some myelin. An immunoassay for myelin basic protein placed the myelin content of normal rat SNM at less than 2% by weight of the total membrane present. X-Ray diffraction patterns showed five diffraction orders with a unit cell repeat for the membrane of 71 to 78 A at higher hydration states. At lower hydration, 11 orders appeared; the unit cell repeat was 130 A, indicating that the unit cell contained two membranes. Electron density profiles for the 130-A unit cell were determined; they clearly showed the two opposed asymmetrical membranes of the SNM vesicles. SNM membrane/buffer partition coefficients (Kp) of imidazobenzodiazepine and 1,4-dihydropyridine (DHP) calcium channel drugs were measured; Kp's for DHP drugs were approximately five times higher in rabbit light sarcoplasmic reticulum than in SNM. Ro 15–1788 and the DHP BAY K 8644 bind primarily to the outer monolayer of vesicles of intact SNM membranes. Nonspecific equilibrium binding of Ro 15–1788 occurs mainly in the upper acyl chain of the bilayer in lipid extracts of SNM membrane
The age of Wolfe Creek meteorite crater (Kandimalal), Western Australia
Wolfe Creek crater lies in northwestern Australia at the edge of the Great Sandy Desert. Together with Meteor Crater, it is one of the two largest craters on Earth from which meteorite fragments have been recovered. The age of the impact is poorly constrained and unpublished data places the event at about 300,000 years ago. In comparison, Meteor Crater is well constrained by exposure dating. In this paper, we present new ages for Wolfe Creek Crater from exposure dating using the cosmogenic nuclides 10Be and 26Al, together with optically stimulated luminescence ages (OSL) on sand from a site created by the impact. We also present a new topographic survey of the crater using photogrammetry. The exposure ages range from ~86 to 128 ka. The OSL ages indicate that the age of the impact is most likely to be ~120 ka with a maximum age of 137 ka. Considering the geomorphic setting, the most likely age of the crater is 120 ± 9 ka. Last, we review the age of Meteor Crater in Arizona. Changes in production rates and scaling factors since the original dating work revise the impact age to 61.1 ± 4.8 ka, or ~20% older than previously reported
Long term study of the seismic environment at LIGO
The LIGO experiment aims to detect and study gravitational waves using ground
based laser interferometry. A critical factor to the performance of the
interferometers, and a major consideration in the design of possible future
upgrades, is isolation of the interferometer optics from seismic noise. We
present the results of a detailed program of measurements of the seismic
environment surrounding the LIGO interferometers. We describe the experimental
configuration used to collect the data, which was acquired over a 613 day
period. The measurements focused on the frequency range 0.1-10 Hz, in which the
secondary microseismic peak and noise due to human activity in the vicinity of
the detectors was found to be particularly critical to interferometer
performance. We compare the statistical distribution of the data sets from the
two interferometer sites, construct amplitude spectral densities of seismic
noise amplitude fluctuations with periods of up to 3 months, and analyze the
data for any long term trends in the amplitude of seismic noise in this
critical frequency range.Comment: To be published in Classical and Quantum Gravity. 24 pages, 15
figure
The local atomic quasicrystal structure of the icosahedral Mg25Y11Zn64 alloy
A local and medium range atomic structure model for the face centred
icosahedral (fci) Mg25Y11Zn64 alloy has been established in a sphere of r = 27
A. The model was refined by least squares techniques using the atomic pair
distribution (PDF) function obtained from synchrotron powder diffraction. Three
hierarchies of the atomic arrangement can be found: (i) five types of local
coordination polyhedra for the single atoms, four of which are of Frank-Kasper
type. In turn, they (ii) form a three-shell (Bergman) cluster containing 104
atoms, which is condensed sharing its outer shell with its neighbouring
clusters and (iii) a cluster connecting scheme corresponding to a
three-dimensional tiling leaving space for few glue atoms. Inside adjacent
clusters, Y8-cubes are tilted with respect to each other and thus allow for
overall icosahedral symmetry. It is shown that the title compound is
essentially isomorphic to its holmium analogue. Therefore fci-Mg-Y-Zn can be
seen as the representative structure type for the other rare earth analogues
fci-Mg-Zn-RE (RE = Dy, Er, Ho, Tb) reported in the literature.Comment: 12 pages, 8 figures, 2 table
Gravitational perturbations of Schwarzschild spacetime at null infinity and the hyperboloidal initial value problem
We study gravitational perturbations of Schwarzschild spacetime by solving a
hyperboloidal initial value problem for the Bardeen-Press equation.
Compactification along hyperboloidal surfaces in a scri-fixing gauge allows us
to have access to the gravitational waveform at null infinity in a general
setup. We argue that this hyperboloidal approach leads to a more accurate and
efficient calculation of the radiation signal than the common approach where a
timelike outer boundary is introduced. The method can be generalized to study
perturbations of Kerr spacetime using the Teukolsky equation.Comment: 14 pages, 9 figure
The impact of heavy-quark loops on LHC dark matter searches
If only tree-level processes are included in the analysis, LHC monojet
searches give weak constraints on the dark matter-proton scattering cross
section arising from the exchange of a new heavy scalar or pseudoscalar
mediator with Yukawa-like couplings to quarks. In this letter we calculate the
constraints on these interactions from the CMS 5.0/fb and ATLAS 4.7/fb searches
for jets with missing energy including the effects of heavy-quark loops. We
find that the inclusion of such contributions leads to a dramatic increase in
the predicted cross section and therefore a significant improvement of the
bounds from LHC searches.Comment: 12 pages, 1 table, 3 figures, v2: extended discussion and improved
relic density calculation - matches published versio
Hydro-without-Hydro Framework for Simulations of Black Hole-Neutron Star Binaries
We introduce a computational framework which avoids solving explicitly
hydrodynamic equations and is suitable to study the pre-merger evolution of
black hole-neutron star binary systems. The essence of the method consists of
constructing a neutron star model with a black hole companion and freezing the
internal degrees of freedom of the neutron star during the course of the
evolution of the space-time geometry. We present the main ingredients of the
framework, from the formulation of the problem to the appropriate computational
techniques to study these binary systems. In addition, we present numerical
results of the construction of initial data sets and evolutions that
demonstrate the feasibility of this approach.Comment: 16 pages, 7 figures. To appear in the Classical and Quantum Gravity
special issue on Numerical Relativit
NEOWISE Observations of Near-Earth Objects: Preliminary Results
With the NEOWISE portion of the \emph{Wide-field Infrared Survey Explorer}
(WISE) project, we have carried out a highly uniform survey of the near-Earth
object (NEO) population at thermal infrared wavelengths ranging from 3 to 22
m, allowing us to refine estimates of their numbers, sizes, and albedos.
The NEOWISE survey detected NEOs the same way whether they were previously
known or not, subject to the availability of ground-based follow-up
observations, resulting in the discovery of more than 130 new NEOs. The
survey's uniformity in sensitivity, observing cadence, and image quality have
permitted extrapolation of the 428 near-Earth asteroids (NEAs) detected by
NEOWISE during the fully cryogenic portion of the WISE mission to the larger
population. We find that there are 98119 NEAs larger than 1 km and
20,5003000 NEAs larger than 100 m. We show that the Spaceguard goal of
detecting 90% of all 1 km NEAs has been met, and that the cumulative size
distribution is best represented by a broken power law with a slope of
1.320.14 below 1.5 km. This power law slope produces 1,900
NEAs with 140 m. Although previous studies predict another break in the
cumulative size distribution below 50-100 m, resulting in an increase in
the number of NEOs in this size range and smaller, we did not detect enough
objects to comment on this increase. The overall number for the NEA population
between 100-1000 m are lower than previous estimates. The numbers of near-Earth
comets will be the subject of future work.Comment: Accepted to Ap
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