296 research outputs found
Adaptive thermal compensation of test masses in advanced LIGO
As the first generation of laser interferometric gravitational wave detectors
near operation, research and development has begun on increasing the
instrument's sensitivity while utilizing the existing infrastructure. In the
Laser Interferometer Gravitational Wave Observatory (LIGO), significant
improvements are being planned for installation in ~2007, increasing strain
sensitivity through improved suspensions and test mass substrates, active
seismic isolation, and higher input laser power. Even with the highest quality
optics available today, however, finite absorption of laser power within
transmissive optics, coupled with the tremendous amount of optical power
circulating in various parts of the interferometer, result in critical
wavefront deformations which would cripple the performance of the instrument.
Discussed is a method of active wavefront correction via direct thermal
actuation on optical elements of the interferometer. A simple nichrome heating
element suspended off the face of an affected optic will, through radiative
heating, remove the gross axisymmetric part of the original thermal distortion.
A scanning heating laser will then be used to remove any remaining
non-axisymmetric wavefront distortion, generated by inhomogeneities in the
substrate's absorption, thermal conductivity, etc. A proof-of-principle
experiment has been constructed at MIT, selected data of which are presented.Comment: 11 pages, 7 figures, submitted to Classical and Quantum Gravit
Clinical and Molecular Epidemiology of Crimean-Congo Hemorrhagic Fever in Humans in Uganda, 2013-2019
Crimean-Congo Hemorrhagic Fever (CCHF) is endemic in Uganda, yet its epidemiology remains largely uncharacterized. To better understand its occurrence within Uganda, case reports of patients hospitalized with CCHF between 2013 and 2019 were reviewed. Further, genome sequences of CCHF-positive RNA obtained during this period were determined for phylogenetic comparisons. We found that a total of 32 cases (75% males; CFR, 31.2%), aged between 9 to 68 years, were reported during the study period. Most cases were detected during July to December of each outbreak year (81.2%; P < 0.01) and were located along the "cattle corridor" (68.7%, P = 0.03). The most common presenting symptoms were fever (93.8%), hemorrhage (81.3%), headache (78.1 %), fatigue (68.8%), vomiting (68.8%), and myalgia (65.6%). In five patients for whom hematological data were available, varied abnormalities were observed including thrombocytopenia, leukopenia, anemia, lymphopenia, lymphocytosis, polycythemia, and microcytosis. About 56.3% (P = 0.47) of patients reported tick bites or exposure to livestock as their potential source of infection. Person-to-person transmission was suspected for two cases. Using unbiased metagenomics, we found that the viral S- and L- segments have remained conserved in Africa 2 Glade since the 1950s. In contrast, the M segment split into two geographically interspersed Glades; one that belongs to Africa 2 and another that is ancestral to Africa 1 and 2. Overall, this data summarizes information on the history and clinical presentation of human CCHF in Uganda. Importantly, it identifies vulnerable populations as well as temporal and geographic regions in Uganda where surveillance and control interventions could be focused
The Samurai Project: verifying the consistency of black-hole-binary waveforms for gravitational-wave detection
We quantify the consistency of numerical-relativity black-hole-binary
waveforms for use in gravitational-wave (GW) searches with current and planned
ground-based detectors. We compare previously published results for the
mode of the gravitational waves from an equal-mass
nonspinning binary, calculated by five numerical codes. We focus on the 1000M
(about six orbits, or 12 GW cycles) before the peak of the GW amplitude and the
subsequent ringdown. We find that the phase and amplitude agree within each
code's uncertainty estimates. The mismatch between the modes
is better than for binary masses above with respect to
the Enhanced LIGO detector noise curve, and for masses above
with respect to Advanced LIGO, Virgo and Advanced Virgo. Between the waveforms
with the best agreement, the mismatch is below . We find that
the waveforms would be indistinguishable in all ground-based detectors (and for
the masses we consider) if detected with a signal-to-noise ratio of less than
, or less than in the best cases.Comment: 17 pages, 9 figures. Version accepted by PR
Initial data for Einstein's equations with superposed gravitational waves
A method is presented to construct initial data for Einstein's equations as a
superposition of a gravitational wave perturbation on an arbitrary stationary
background spacetime. The method combines the conformal thin sandwich formalism
with linear gravitational waves, and allows detailed control over
characteristics of the superposed gravitational wave like shape, location and
propagation direction. It is furthermore fully covariant with respect to
spatial coordinate changes and allows for very large amplitude of the
gravitational wave.Comment: Version accepted by PRD; added convergence plots, expanded
discussion. 9 pages, 9 figure
The Structure of Episodic Memory: Ganeri's ‘Mental Time Travel and Attention’
We offer a framework for assessing what the structure of episodic memory might be, if one accepts the Buddhist denial of persisting selves. This paper is a response to Jonardon Ganeri's paper "Mental time travel and attention", which explores Buddhaghosa's ideas about memory. (It will eventually be published with a reply by Ganeri)
The ligo gravitational wave observatories: Recent results and future plans
The LIGO interferometers are operating as gravitational wave observatories, with a noise level near an order of magnitude of the goal and the first scientific data recently taken. This data has been analyzed for four different categories of gravitational wave sources; millisecond bursts, inspiralling binary neutron stars, periodic waves from a known pulsar, and stochastic background. Research and development is also underway for the next generation LIGO detector, Advanced LIGO
Setting upper limits on the strength of periodic gravitational waves from PSR J1939+2134 using the first science data from the GEO 600 and LIGO detectors
Data collected by the GEO 600 and LIGO interferometric gravitational wave detectors during their first observational science run were searched for continuous gravitational waves from the pulsar J1939+2134 at twice its rotation frequency. Two independent analysis methods were used and are demonstrated in this paper: a frequency domain method and a time domain method. Both achieve consistent null results, placing new upper limits on the strength of the pulsar's gravitational wave emission. A model emission mechanism is used to interpret the limits as a constraint on the pulsar's equatorial ellipticity
Searching for gravitational waves from known pulsars
We present upper limits on the amplitude of gravitational waves from 28
isolated pulsars using data from the second science run of LIGO. The results
are also expressed as a constraint on the pulsars' equatorial ellipticities. We
discuss a new way of presenting such ellipticity upper limits that takes
account of the uncertainties of the pulsar moment of inertia. We also extend
our previous method to search for known pulsars in binary systems, of which
there are about 80 in the sensitive frequency range of LIGO and GEO 600.Comment: Accepted by CQG for the proceeding of GWDAW9, 7 pages, 2 figure
Upper limits on the strength of periodic gravitational waves from PSR J1939+2134
The first science run of the LIGO and GEO gravitational wave detectors
presented the opportunity to test methods of searching for gravitational waves
from known pulsars. Here we present new direct upper limits on the strength of
waves from the pulsar PSR J1939+2134 using two independent analysis methods,
one in the frequency domain using frequentist statistics and one in the time
domain using Bayesian inference. Both methods show that the strain amplitude at
Earth from this pulsar is less than a few times .Comment: 7 pages, 1 figure, to appear in the Proceedings of the 5th Edoardo
Amaldi Conference on Gravitational Waves, Tirrenia, Pisa, Italy, 6-11 July
200
Improving the sensitivity to gravitational-wave sources by modifying the input-output optics of advanced interferometers
We study frequency dependent (FD) input-output schemes for signal-recycling
interferometers, the baseline design of Advanced LIGO and the current
configuration of GEO 600. Complementary to a recent proposal by Harms et al. to
use FD input squeezing and ordinary homodyne detection, we explore a scheme
which uses ordinary squeezed vacuum, but FD readout. Both schemes, which are
sub-optimal among all possible input-output schemes, provide a global noise
suppression by the power squeeze factor, while being realizable by using
detuned Fabry-Perot cavities as input/output filters. At high frequencies, the
two schemes are shown to be equivalent, while at low frequencies our scheme
gives better performance than that of Harms et al., and is nearly fully
optimal. We then study the sensitivity improvement achievable by these schemes
in Advanced LIGO era (with 30-m filter cavities and current estimates of
filter-mirror losses and thermal noise), for neutron star binary inspirals, and
for narrowband GW sources such as low-mass X-ray binaries and known radio
pulsars. Optical losses are shown to be a major obstacle for the actual
implementation of these techniques in Advanced LIGO. On time scales of
third-generation interferometers, like EURO/LIGO-III (~2012), with
kilometer-scale filter cavities, a signal-recycling interferometer with the FD
readout scheme explored in this paper can have performances comparable to
existing proposals. [abridged]Comment: Figs. 9 and 12 corrected; Appendix added for narrowband data analysi
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