334 research outputs found
Stochastic Gravitational Wave Measurements with Bar Detectors: Dependence of Response on Detector Orientation
The response of a cross-correlation measurement to an isotropic stochastic
gravitational-wave background depends on the observing geometry via the overlap
reduction function. If one of the detectors being correlated is a resonant bar
whose orientation can be changed, the response to stochastic gravitational
waves can be modulated. I derive the general form of this modulation as a
function of azimuth, both in the zero-frequency limit and at arbitrary
frequencies. Comparisons are made between pairs of nearby detectors, such as
LIGO Livingston-ALLEGRO, Virgo-AURIGA, Virgo-NAUTILUS, and EXPLORER-AURIGA,
with which stochastic cross-correlation measurements are currently being
performed, planned, or considered.Comment: 17 pages, REVTeX (uses rcs, amsmath, hyperref, and graphicx style
files), 4 figures (8 eps image files
Site percolation and random walks on d-dimensional Kagome lattices
The site percolation problem is studied on d-dimensional generalisations of
the Kagome' lattice. These lattices are isotropic and have the same
coordination number q as the hyper-cubic lattices in d dimensions, namely q=2d.
The site percolation thresholds are calculated numerically for d= 3, 4, 5, and
6. The scaling of these thresholds as a function of dimension d, or
alternatively q, is different than for hypercubic lattices: p_c ~ 2/q instead
of p_c ~ 1/(q-1). The latter is the Bethe approximation, which is usually
assumed to hold for all lattices in high dimensions. A series expansion is
calculated, in order to understand the different behaviour of the Kagome'
lattice. The return probability of a random walker on these lattices is also
shown to scale as 2/q. For bond percolation on d-dimensional diamond lattices
these results imply p_c ~ 1/(q-1).Comment: 11 pages, LaTeX, 8 figures (EPS format), submitted to J. Phys.
Burst dynamics during drainage displacements in porous media: Simulations and experiments
We investigate the burst dynamics during drainage going from low to high
injection rate at various fluid viscosities. The bursts are identified as
pressure drops in the pressure signal across the system. We find that the
statistical distribution of pressure drops scales according to other systems
exhibiting self-organized criticality. The pressure signal was calculated by a
network model that properly simulates drainage displacements. We compare our
results with corresponding experiments.Comment: 7 pages, 4 figures. Submitted to Europhys. Let
An approximate binary-black-hole metric
An approximate solution to Einstein's equations representing two
widely-separated non-rotating black holes in a circular orbit is constructed by
matching a post-Newtonian metric to two perturbed Schwarzschild metrics. The
spacetime metric is presented in a single coordinate system valid up to the
apparent horizons of the black holes. This metric could be useful in numerical
simulations of binary black holes. Initial data extracted from this metric have
the advantages of being linked to the early inspiral phase of the binary
system, and of not containing spurious gravitational waves.Comment: 20 pages, 1 figure; some changes in Sec. IV B,C and Sec.
Prognostic value of nonangiogenic and angiogenic growth patterns in non-small-cell lung cancer
An essential prerequisite of nonangiogenic growth appears to be the ability of the tumour to preserve the parenchymal structures of the host tissue. This morphological feature is visible on a routine tissue section. Based on this feature, we classified haematoxylin and eosin-stained tissue sections from 279 patients with non-small-cell lung cancer into three growth patterns: destructive (angiogenic; n=196), papillary (intermediate; n=38) and alveolar (nonangiogenic; n=45). A Cox multiple regression model was used to test the prognostic value of growth patterns together with other relevant clinicopathological factors. For overall survival, growth pattern (P=0.007), N-status (P=0.001), age (P=0.020) and type of operation (P=0.056) were independent prognostic factors. For disease-free survival, only growth pattern (P=0.007) and N-status (P<0.001) had an independent prognostic value. Alveolar (hazard ratio=1.825, 95% confidence interval=1.117-2.980, P=0.016) and papillary (hazard ratio=1.977, 95% confidence interval=1.169-3.345, P=0.011) growth patterns were independent predictors of poor prognosis. The proposed classification has an independent prognostic value for overall survival as well as for disease-free survival, providing a possible explanation for survival differences of patients in the same disease stage
Precise determination of the bond percolation thresholds and finite-size scaling corrections for the s.c., f.c.c., and b.c.c. lattices
Extensive Monte-Carlo simulations were performed to study bond percolation on
the simple cubic (s.c.), face-centered cubic (f.c.c.), and body-centered cubic
(b.c.c.) lattices, using an epidemic kind of approach. These simulations
provide very precise values of the critical thresholds for each of the
lattices: pc(s.c.) = 0.248 812 6(5), pc(f.c.c.) = 0.120 163 5(10), and
pc(b.c.c.) = 0.180 287 5(10). For p close to pc, the results follow the
expected finite-size and scaling behavior, with values for the Fisher exponent
(2.189(2)), the finite-size correction exponent (0.64(2)), and
the scaling function exponent (0.445(1)) confirmed to be universal.Comment: 16 pgs, 7 figures, LaTeX, to be published in Phys. Rev.
Gravitational Wave and X-ray Signals from Stellar Disruption by a Massive Black Hole
Gravitational waves and X-ray flares are expected from tidal disruption of
stars by a massive black hole. Using a relativistic smoothed particle
hydrodynamics code, we investigate the fate of main sequence and Helium stars
in plunge orbits passing near Schwarzschild or a Kerr black holes of 10^5-6
Msun. We show that quadrupole gravitational waves emitted during the tidal
disruption process are described reasonable well by a point particle
approximation even in the strong encounter case. An additional hydrodynamic
calculation based on the Godunov method indicates that shocks develop for
sufficiently high tidal compressions. The shock-heating results in an X-ray
flare, which for solar-type stars disrupted by 10^6Msun black holes is in the
keV range, associated with the gravitational wave signal. The hardness and
duration of the X-ray flare may serve as a diagnostic of the mass of the
central black hole.Comment: 27 pages, 10 figures, accepted for publication in ApJ, additional
hydrodynamic calculation on shock development for high tidal compressio
First upper limit analysis and results from LIGO science data: stochastic background
I describe analysis of correlations in the outputs of the three LIGO
interferometers from LIGO's first science run, held over 17 days in August and
September of 2002, and the resulting upper limit set on a stochastic background
of gravitational waves. By searching for cross-correlations between the LIGO
detectors in Livingston, LA and Hanford, WA, we are able to set a 90%
confidence level upper limit of h_{100}^2 Omega_0 < 23 +/- 4.6.Comment: 7 pages; 1 eps figures; proceeding from 2003 Edoardo Amaldi Meeting
on Gravitational Wave
Percolation on two- and three-dimensional lattices
In this work we apply a highly efficient Monte Carlo algorithm recently
proposed by Newman and Ziff to treat percolation problems. The site and bond
percolation are studied on a number of lattices in two and three dimensions.
Quite good results for the wrapping probabilities, correlation length critical
exponent and critical concentration are obtained for the square, simple cubic,
HCP and hexagonal lattices by using relatively small systems. We also confirm
the universal aspect of the wrapping probabilities regarding site and bond
dilution.Comment: 15 pages, 6 figures, 3 table
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