27,474 research outputs found
The inverse problem for pulsating neutron stars: A ``fingerprint analysis'' for the supranuclear equation of state
We study the problem of detecting, and infering astrophysical information
from, gravitational waves from a pulsating neutron star. We show that the fluid
f and p-modes, as well as the gravitational-wave w-modes may be detectable from
sources in our own galaxy, and investigate how accurately the frequencies and
damping rates of these modes can be infered from a noisy gravitational-wave
data stream. Based on the conclusions of this discussion we propose a strategy
for revealing the supranuclear equation of state using the neutron star
fingerprints: the observed frequencies of an f and a p-mode. We also discuss
how well the source can be located in the sky using observations with several
detectors.Comment: 9 pages, 3 figure
Magnetic neutron star equilibria with stratification and type-II superconductivity
We construct two-fluid equilibrium configurations for neutron stars with
magnetic fields, using a self-consistent and nonlinear numerical approach. The
two-fluid approach - likely to be valid for large regions of all but the
youngest NSs - provides us with a straightforward way to introduce
stratification and allows for more realistic models than the ubiquitous
barotropic assumption. In all our models the neutrons are modelled as a
superfluid, whilst for the protons we consider two cases: one where they are a
normal fluid and another where they form a type-II superconductor. We consider
a variety of field configurations in the normal-proton case and purely toroidal
fields in the superconducting case. We find that stratification allows for a
stronger toroidal component in mixed-field configurations, though the poloidal
component remains the largest in all our models. We provide quantitative
results for magnetic ellipticities of NSs, both in the normal- and
superconducting-proton cases.Comment: 21 pages, 14 figures; some minor changes to match published versio
X-Ray Properties of the First Sunyaev-Zel'dovich Effect Selected Galaxy Cluster Sample from the South Pole Telescope
We present results of X-ray observations of a sample of 15 clusters selected via their imprint on the cosmic microwave background from the thermal Sunyaev-Zel'dovich (SZ) effect. These clusters are a subset of the first SZ-selected cluster catalog, obtained from observations of 178 deg^2
of sky surveyed by the South Pole Telescope (SPT). Using X-ray observations with Chandra and XMM-Newton, we estimate the temperature, T_X, and mass, M_g, of the intracluster medium within r_500 for each cluster. From these, we calculate Y_X = M_(g)T_X and estimate the total cluster mass using an M_(500)-Y_X scaling relation measured from previous X-ray studies. The integrated Comptonization, Y SZ, is derived from the SZ measurements, using additional information from the X-ray-measured gas density profiles and a universal temperature profile. We calculate scaling relations between the X-ray and SZ observables and find results generally consistent with other measurements and the expectations from simple self-similar behavior. Specifically, we fit a Y_(SZ)-Y_X relation and find a normalization of 0.82 Âą 0.07, marginally consistent with the predicted ratio of Y_(SZ)/Y_X = 0.91 Âą 0.01 that would be expected from the density and temperature models used in this work. Using the Y_X-derived mass estimates, we fit a
Y_(SZ)-M_500 relation and find a slope consistent with the self-similar expectation of Y_(SZ) â M^(5/3) with a normalization consistent with predictions from other X-ray studies. We find that the SZ mass estimates, derived from cosmological simulations of the SPT survey, are lower by a factor of 0.78 Âą 0.06 relative to the X-ray mass estimates. This offset is at a level of 1.3Ď when considering the
~15% systematic uncertainty for the simulation-based SZ masses. Overall, the X-ray measurements confirm that the scaling relations of the SZ-selected clusters are consistent with the properties of other X-ray-selected samples of massive clusters, even allowing for the broad redshift range (0.29 < z < 1.08) of the sample
Finite dimensional approximations to Wiener measure and path integral formulas on manifolds
Certain natural geometric approximation schemes are developed for Wiener
measure on a compact Riemannian manifold. These approximations closely mimic
the informal path integral formulas used in the physics literature for
representing the heat semi-group on Riemannian manifolds. The path space is
approximated by finite dimensional manifolds consisting of piecewise geodesic
paths adapted to partitions of . The finite dimensional manifolds of
piecewise geodesics carry both an and a type Riemannian
structures . It is proved that as the mesh of the partition tends to
,
where is the energy of the piecewise geodesic path , and
for and , is a ``normalization'' constant, is
the Riemannian volume form relative , and is Wiener measure on
paths on . Here and
where is the scalar curvature of . These results are also shown to
imply the well know integration by parts formula for the Wiener measure.Comment: 48 pages, latex2e using amsart and amssym
Superfluid instability of r-modes in "differentially rotating" neutron stars
Superfluid hydrodynamics affects the spin-evolution of mature neutron stars,
and may be key to explaining timing irregularities such as pulsar glitches.
However, most models for this phenomenon exclude the global instability
required to trigger the event. In this paper we discuss a mechanism that may
fill this gap. We establish that small scale inertial r-modes become unstable
in a superfluid neutron star that exhibits a rotational lag, expected to build
up due to vortex pinning as the star spins down. Somewhat counterintuitively,
this instability arises due to the (under normal circumstances dissipative)
vortex-mediated mutual friction. We explore the nature of the superfluid
instability for a simple incompressible model, allowing for entrainment
coupling between the two fluid components. Our results recover a previously
discussed dynamical instability in systems where the two components are
strongly coupled. In addition, we demonstrate for the first time that the
system is secularly unstable (with a growth time that scales with the mutual
friction) throughout much of parameter space. Interestingly, large scale
r-modes are also affected by this new aspect of the instability. We analyse the
damping effect of shear viscosity, which should be particularly efficient at
small scales, arguing that it will not be sufficient to completely suppress the
instability in astrophysical systems.Comment: RevTex, 11 figure
Inclusion of mussel meal in diets to growing/finishing pigs
This study showed that inclusion of mussel meal in diets to growing/finishing pigs yielded growth rate similar to those obtained with a conventional diet, whereas feed conversion ratio was higher. This implies that mussel meal is a potential alternative protein source that can replace fish and soybean meal in organic diets. By using mussels it would be possible to compose diets with 100% organic feed ingredients. However, mussel meal is currently expensive to produce and in addition more research regarding optimal inclusion level and possible off-flavor of the meat is needed
Bayesian Forecast Combination for VAR Models
We consider forecast combination and, indirectly, model selection for VAR models when there is uncertainty about which variables to include in the model in addition to the forecast variables. The key dierence from traditional Bayesian variable selection is that we also allow for uncertainty regarding which endogenous variables to include in the model. That is, all models include the forecast variables, but may otherwise have diering sets of endogenous variables. This is a dicult problem to tackle with a traditional Bayesian approach. Our solution is to focus on the forecasting performance for the variables of interest and we construct model weights from the predictive likelihood of the forecast variables. The procedure is evaluated in a small simulation study and found to perform competitively in applications to real world data.Bayesian model averaging; Predictive likelihood; GDP forecasts
Dynamical excitation of space-time modes of compact objects
We discuss, in the perturbative regime, the scattering of Gaussian pulses of
odd-parity gravitational radiation off a non-rotating relativistic star and a
Schwarzschild Black Hole. We focus on the excitation of the -modes of the
star as a function of the width of the pulse and we contrast it with the
outcome of a Schwarzschild Black Hole of the same mass. For sufficiently narrow
values of , the waveforms are dominated by characteristic space-time modes.
On the other hand, for sufficiently large values of the backscattered
signal is dominated by the tail of the Regge-Wheeler potential, the
quasi-normal modes are not excited and the nature of the central object cannot
be established. We view this work as a useful contribution to the comparison
between perturbative results and forthcoming -mode 3D-nonlinear numerical
simulation.Comment: RevTeX, 9 pages, 7 figures, Published in Phys. Rev.
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