6,275 research outputs found
Perturbations in the Kerr-Newman Dilatonic Black Hole Background: I. Maxwell waves
In this paper we analyze the perturbations of the Kerr-Newman dilatonic black
hole background. For this purpose we perform a double expansion in both the
background electric charge and the wave parameters of the relevant quantities
in the Newman-Penrose formalism. We then display the gravitational, dilatonic
and electromagnetic equations, which reproduce the static solution (at zero
order in the wave parameter) and the corresponding wave equations in the Kerr
background (at first order in the wave parameter and zero order in the electric
charge). At higher orders in the electric charge one encounters corrections to
the propagations of waves induced by the presence of a non-vanishing dilaton.
An explicit computation is carried out for the electromagnetic waves up to the
asymptotic form of the Maxwell field perturbations produced by the interaction
with dilatonic waves. A simple physical model is proposed which could make
these perturbations relevant to the detection of radiation coming from the
region of space near a black hole.Comment: RevTeX, 36 pages in preprint style, 1 figure posted as a separate PS
file, submitted to Phys. Rev.
Subtraction of Newtonian Noise Using Optimized Sensor Arrays
Fluctuations in the local Newtonian gravitational field present a limit to
high precision measurements, including searches for gravitational waves using
laser interferometers. In this work, we present a model of this perturbing
gravitational field and evaluate schemes to mitigate the effect by estimating
and subtracting it from the interferometer data stream. Information about the
Newtonian noise is obtained from simulated seismic data. The method is tested
on causal as well as acausal implementations of noise subtraction. In both
cases it is demonstrated that broadband mitigation factors close to 10 can be
achieved removing Newtonian noise as a dominant noise contribution. The
resulting improvement in the detector sensitivity will substantially enhance
the detection rate of gravitational radiation from cosmological sources.Comment: 29 pages, 11 figure
Force measurement during spinal mobilisation
PhDSpinal mobilisation or manipulation techniques are frequently used by physiotherapists
in the treatment of musculoskeletal disorders. Despite the reliance on these techniques
in clinical practice, there is little scientific evidence to substantiate their use.
A standard mobilisation couch was instrumented to enable measurement of the forces
applied to the trunk during mobilisation of the lumbar spine. Six load cells were
incorporated into the couch frame and linked to a personal computer to facilitate data
collection. The couch allowed the assessment of the magnitude of the mobilisation
force, its direction and the variation in applied load over time. The system was found to
be reliable and sensitive over the range of forces applied during mobilisation.
The system was used to collect data from a sample of 30 experienced therapists to
evaluate repeatability and reproducibility during the application of four grades of a
posteroanterior mobilisation and an End Feel, on the third lumbar vertebra. Whilst some
therapists demonstrated considerable variation in the forces applied both within one
measurement session and over a two week period, others were found to be relatively
consistent. The range of forces used by different therapists when performing the same
technique was substantial ranging between 63 N and 347 N for a Grade IV mobilisation.
A study was carried out involving 26 young healthy subjects, to determine the
characteristics of a mobilisation force applied to an asymptomatic spine. A further study
was undertaken involving a clinical sample of 16 patients, aged between 47- 64 years, to
evaluate the effect of age related degenerative changes of the lumbar spine on the
application of these techniques. The magnitude of the mobilisation force was found to
be similar for the healthy and the patient groups with median forces of 175 N and 171 N
during a Grade IV procedure, respectively. However, the forces applied to the patient
group exhibited a statistically significantly smaller amplitude and higher frequency of
oscillation than the healthy group for the same procedure (p < 0.01). Such
measurements are essential for the assessment of the efficacy of these techniques in
clinical practice.Chartered Society of Physiotherap
BBO and the Neutron-Star-Binary Subtraction Problem
The Big Bang Observer (BBO) is a proposed space-based gravitational-wave (GW)
mission designed primarily to search for an inflation-generated GW background
in the frequency range 0.1-1 Hz. The major astrophysical foreground in this
range is gravitational radiation from inspiraling compact binaries. This
foreground is expected to be much larger than the inflation-generated
background, so to accomplish its main goal, BBO must be sensitive enough to
identify and subtract out practically all such binaries in the observable
universe. It is somewhat subtle to decide whether BBO's current baseline design
is sufficiently sensitive for this task, since, at least initially, the
dominant noise source impeding identification of any one binary is confusion
noise from all the others. Here we present a self-consistent scheme for
deciding whether BBO's baseline design is indeed adequate for subtracting out
the binary foreground. We conclude that the current baseline should be
sufficient. However if BBO's instrumental sensitivity were degraded by a factor
2-4, it could no longer perform its main mission. It is impossible to perfectly
subtract out each of the binary inspiral waveforms, so an important question is
how to deal with the "residual" errors in the post-subtraction data stream. We
sketch a strategy of "projecting out" these residual errors, at the cost of
some effective bandwidth. We also provide estimates of the sizes of various
post-Newtonian effects in the inspiral waveforms that must be accounted for in
the BBO analysis.Comment: corrects some errors in figure captions that are present in the
published versio
Gravitational Waves and Dark Energy
The idea that dark energy is gravitational waves may explain its strength and its time-evolution. A possible concept is that dark energy is the ensemble of coherent bursts (solitons) of gravitational waves originally produced when the first generation of super-massive black holes was formed. These solitons get their initial energy as well as keep up their energy density throughout the evolution of the universe by stimulating emission from a background, a process which we model by working out this energy transfer in a Boltzmann equation approach. New Planck data suggest that dark energy has increased in strength over cosmic time, supporting the concept here. The transit of these gravitational wave solitons may be detectable. Key tests include pulsar timing, clock jitter and the radio background
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