351 research outputs found
Gravitational Waves from Rotating Proto-Neutron Stars
We study the effects of rotation on the quasi normal modes (QNMs) of a newly
born proto neutron star (PNS) at different evolutionary stages, until it
becomes a cold neutron star (NS). We use the
Cowling approximation, neglecting spacetime perturbations, and consider
different models of evolving PNS. The frequencies of the modes of a PNS are
considerably lower than those of a cold NS, and are further lowered by
rotation; consequently, if QNMs were excited in a sufficiently energetic
process, they would radiate waves that could be more easily detectable by
resonant-mass and interferometric detectors than those emitted by a cold NS. We
find that for high rotation rates, some of the g-modes become unstable via the
CFS instability; however, this instability is likely to be suppressed by
competing mechanisms before emitting a significant amount of gravitational
waves.Comment: 5 pages, proceedings of the 5th Edoardo Amaldi Conference On
Gravitational Wave
Ex-nihilo: Obstacles Surrounding Teaching the Standard Model
The model of the Big Bang is an integral part of the national curriculum for
England. Previous work (e.g. Baxter 1989) has shown that pupils often come into
education with many and varied prior misconceptions emanating from both
internal and external sources. Whilst virtually all of these misconceptions can
be remedied, there will remain (by its very nature) the obstacle of ex-nihilo,
as characterised by the question `how do you get something from nothing?' There
are two origins of this obstacle: conceptual (i.e. knowledge-based) and
cultural (e.g. deeply held religious viewpoints). The article shows how the
citizenship section of the national curriculum, coming `online' in England from
September 2002, presents a new opportunity for exploiting these.Comment: 6 pages. Accepted for publication in Physics E
Predators reduce extinction risk in noisy metapopulations
Background
Spatial structure across fragmented landscapes can enhance regional population persistence by promoting local “rescue effects.” In small, vulnerable populations, where chance or random events between individuals may have disproportionately large effects on species interactions, such local processes are particularly important. However, existing theory often only describes the dynamics of metapopulations at regional scales, neglecting the role of multispecies population dynamics within habitat patches.
Findings
By coupling analysis across spatial scales we quantified the interaction between local scale population regulation, regional dispersal and noise processes in the dynamics of experimental host-parasitoid metapopulations. We find that increasing community complexity increases negative correlation between local population dynamics. A potential mechanism underpinning this finding was explored using a simple population dynamic model.
Conclusions
Our results suggest a paradox: parasitism, whilst clearly damaging to hosts at the individual level, reduces extinction risk at the population level
Superradiant instability of large radius doubly spinning black rings
We point out that 5D large radius doubly spinning black rings with rotation
along S^1 and S^2 are afflicted by a robust instability. It is triggered by
superradiant bound state modes. The Kaluza-Klein momentum of the mode along the
ring is responsible for the bound state. This kind of instability in black
strings and branes was first suggested by Marolf and Palmer and studied in
detail by Cardoso, Lemos and Yoshida. We find the frequency spectrum and
timescale of this instability in the black ring background, and show that it is
active for large radius rings with large rotation along S^2. We identify the
endpoint of the instability and argue that it provides a dynamical mechanism
that introduces an upper bound in the rotation of the black ring. To estimate
the upper bound, we use the recent black ring model of Hovdebo and Myers, with
a minor extension to accommodate an extra small angular momentum. This
dynamical bound can be smaller than the Kerr-like bound imposed by regularity
at the horizon. Recently, the existence of higher dimensional black rings is
being conjectured. They will be stable against this mechanism.Comment: 21 pages, 3 figures. Overall minor improvements in discussions added.
Matches published version in PR
Instability of non-supersymmetric smooth geometries
Recently certain non-supersymmetric solutions of type IIb supergravity were
constructed [hep-th/0504181], which are everywhere smooth, have no horizons and
are thought to describe certain non-BPS microstates of the D1-D5 system. We
demonstrate that these solutions are all classically unstable. The instability
is a generic feature of horizonless geometries with an ergoregion. We consider
the endpoint of this instability and argue that the solutions decay to
supersymmetric configurations. We also comment on the implications of the
ergoregion instability for Mathur's `fuzzball' proposal.Comment: v2: typos corrected, reference adde
Numerical evolution of secular bar-mode instability induced by the gravitational radiation reaction in rapidly rotating neutron stars
The evolution of a nonaxisymmetric bar-mode perturbation of rapidly rotating
stars due to a secular instability induced by gravitational wave emission is
studied in post-Newtonian simulations taking into account gravitational
radiation reaction. A polytropic equation of state with the polytropic index
is adopted. The ratio of the rotational kinetic energy to the
gravitational potential energy is chosen in the range between 0.2 and
0.26. Numerical simulations were performed until the perturbation grows to the
nonlinear regime, and illustrate that the outcome after the secular instability
sets in is an ellipsoidal star of a moderately large ellipticity \agt 0.7. A
rapidly rotating protoneutron star may form such an ellipsoid, which is a
candidate for strong emitter of gravitational waves for ground-based laser
interferometric detectors. A possibility that effects of magnetic fields
neglected in this work may modify the growth of the secular instability is also
mentioned.Comment: PRD, accepted for publicatio
Reverberation Mapping Measurements of Black Hole Masses in Six Local Seyfert Galaxies
We present the final results from a high sampling rate, multi-month,
spectrophotometric reverberation mapping campaign undertaken to obtain either
new or improved Hbeta reverberation lag measurements for several relatively
low-luminosity AGNs. We have reliably measured thetime delay between variations
in the continuum and Hbeta emission line in six local Seyfert 1 galaxies. These
measurements are used to calculate the mass of the supermassive black hole at
the center of each of these AGNs. We place our results in context to the most
current calibration of the broad-line region (BLR) R-L relationship, where our
results remove outliers and reduce the scatter at the low-luminosity end of
this relationship. We also present velocity-resolved Hbeta time delay
measurements for our complete sample, though the clearest velocity-resolved
kinematic signatures have already been published.Comment: 52 pages (AASTeX: 29 pages of text, 8 tables, 7 figures), accepted
for publication in the Astrophysical Journa
A Revised Broad-Line Region Radius and Black Hole Mass for the Narrow-Line Seyfert 1 NGC 4051
We present the first results from a high sampling rate, multi-month
reverberation mapping campaign undertaken primarily at MDM Observatory with
supporting observations from telescopes around the world. The primary goal of
this campaign was to obtain either new or improved Hbeta reverberation lag
measurements for several relatively low luminosity AGNs. We feature results for
NGC 4051 here because, until now, this object has been a significant outlier
from AGN scaling relationships, e.g., it was previously a ~2-3sigma outlier on
the relationship between the broad-line region (BLR) radius and the optical
continuum luminosity - the R_BLR-L relationship. Our new measurements of the
lag time between variations in the continuum and Hbeta emission line made from
spectroscopic monitoring of NGC 4051 lead to a measured BLR radius of R_BLR =
1.87 (+0.54 -0.50) light days and black hole mass of M_BH = 1.73 (+0.55 -0.52)
x 10^6 M_sun. This radius is consistent with that expected from the R_BLR-L
relationship, based on the present luminosity of NGC 4051 and the most current
calibration of the relation by Bentz et al. (2009a). We also present a
preliminary look at velocity-resolved Hbeta light curves and time delay
measurements, although we are unable to reconstruct an unambiguous
velocity-resolved reverberation signal.Comment: 38 pages, 7 figures, accepted for publication in ApJ, changes from v1
reflect suggestions from anonymous refere
Ecological Invasion, Roughened Fronts, and a Competitor's Extreme Advance: Integrating Stochastic Spatial-Growth Models
Both community ecology and conservation biology seek further understanding of
factors governing the advance of an invasive species. We model biological
invasion as an individual-based, stochastic process on a two-dimensional
landscape. An ecologically superior invader and a resident species compete for
space preemptively. Our general model includes the basic contact process and a
variant of the Eden model as special cases. We employ the concept of a
"roughened" front to quantify effects of discreteness and stochasticity on
invasion; we emphasize the probability distribution of the front-runner's
relative position. That is, we analyze the location of the most advanced
invader as the extreme deviation about the front's mean position. We find that
a class of models with different assumptions about neighborhood interactions
exhibit universal characteristics. That is, key features of the invasion
dynamics span a class of models, independently of locally detailed demographic
rules. Our results integrate theories of invasive spatial growth and generate
novel hypotheses linking habitat or landscape size (length of the invading
front) to invasion velocity, and to the relative position of the most advanced
invader.Comment: The original publication is available at
www.springerlink.com/content/8528v8563r7u2742
Protocol for a prospective observational cohort study collecting data on demographics, symptoms and biomarkers in people with mesothelioma (ASSESS-meso)
Introduction: Mesothelioma is a heterogeneous disease that can be challenging to monitor and prognosticate. ASSESS-meso is a multicentre, prospective, longitudinal observational cohort study of patients with mesothelioma. The primary aim is to describe different clinical phenotypes and investigate predictive and prognostic factors, including biomarkers from blood and pleural fluid. The secondary aim is to provide a resource for future trials and substudies.
Methods and analysis: We aim to recruit 700 patients with a histological, cytological or clinicopathological diagnosis of mesothelioma, at any anatomical site (pleural, peritoneal, pericardial, etc). Longitudinal data will be collected, including clinical information, radiological investigations, blood tests and patient-reported outcome measures for breathlessness, chest pain and sweats. Preplanned analyses will use Cox proportional hazards method to evaluate factors associated with survival, linear and logistic regression models to investigate associations with symptoms, and analysis of variance modelling to explore changes in symptoms over time.
Ethics and dissemination: Ethical approval has been granted by the Research Ethics Committee South West—Central Bristol (17-SW-0019) and Health Research Authority (IRAS ID 220360). A study steering committee has been established and results will be published OpenAccess in peer-reviewed journals.
Trial registration number ISRCTN: 61861764
- …