5,666 research outputs found
Constraining Lorentz-violating, Modified Dispersion Relations with Gravitational Waves
Modified gravity theories generically predict a violation of Lorentz
invariance, which may lead to a modified dispersion relation for propagating
modes of gravitational waves. We construct a parametrized dispersion relation
that can reproduce a range of known Lorentz-violating predictions and
investigate their impact on the propagation of gravitational waves. A modified
dispersion relation forces different wavelengths of the gravitational wave
train to travel at slightly different velocities, leading to a modified phase
evolution observed at a gravitational-wave detector. We show how such
corrections map to the waveform observable and to the parametrized
post-Einsteinian framework, proposed to model a range of deviations from
General Relativity. Given a gravitational-wave detection, the lack of evidence
for such corrections could then be used to place a constraint on Lorentz
violation. The constraints we obtain are tightest for dispersion relations that
scale with small power of the graviton's momentum and deteriorate for a steeper
scaling.Comment: 11 pages, 3 figures, 2 tables: title changed slightly, published
versio
A post-Newtonian diagnosis of quasiequilibrium configurations of neutron star-neutron star and neutron star-black hole binaries
We use a post-Newtonian diagnostic tool to examine numerically generated
quasiequilibrium initial data sets for non-spinning double neutron star and
neutron star-black hole binary systems. The PN equations include the effects of
tidal interactions, parametrized by the compactness of the neutron stars and by
suitable values of ``apsidal'' constants, which measure the degree of
distortion of stars subjected to tidal forces. We find that the post-Newtonian
diagnostic agrees well with the double neutron star initial data, typically to
better than half a percent except where tidal distortions are becoming extreme.
We show that the differences could be interpreted as representing small
residual eccentricity in the initial orbits. In comparing the diagnostic with
preliminary numerical data on neutron star-black hole binaries, we find less
agreement.Comment: 17 pages, 6 tables, 8 figure
Neutrino Oscillations, Fluctuations and Solar Magneto-gravity Waves
This review has two parts. The first part summarizes the current
observational constraints on fluctuations in the solar medium deep within the
solar Radiative Zone, and shows how the KamLAND and SNO-salt data combine to
make the experimental determination of the neutrino oscillation parameters
largely insensitive to prior assumptions about the nature of these
oscillations. As part of a search for plausible sources of solar fluctuations
to which neutrinos could be sensitive, the second part of the talk summarizes a
preliminary analysis of the influence of magnetic fields on helioseismic waves.
Using simplifying assumptions which should apply to modes in the solar
radiative zone, we find a resonance between Alfven waves and helioseismic
g-modes which potentially modifies the solar density profile fairly
significantly over comparatively short distance scales, too narrow to be ruled
out by present-day analyses of p-wave helioseismic spectra.Comment: Plenary talk presented at AHEP 2003, Valencia, Spain, October 200
What disability? I am a leader! Understanding leadership in HE from a disability perspective
This article is based on the findings of an externally funded, mixed-methods research project conducted at one English university. This small-scale project aimed to examine leadership, barriers to becoming a leader and the support needed to overcome them, from the perspectives of disabled staff. An online questionnaire was sent to all 66 members of staff who had disclosed their disabled status to the university and 22 responses were received. Twelve participants were then interviewed as two focus groups to discuss their views on leadership and its relation to their role. Six more respondents opted for individual face-to-face/telephone interviews. The findings indicated that over half of the respondents were already engaged in ‘formal’ leadership and even more exercised ‘informal’ leadership. This key finding seems to contradict the under-representation of disabled academics in leadership reported in the literature. Despite their engagement in leadership, disabled staff faced several institutional and personal barriers. The findings suggest that having an impairment per se might not necessarily deter disabled staff from exercising leadership. A number of support strategies are recommended to facilitate their participation in (formal) leadership
Stochastic oscillations of adaptive networks: application to epidemic modelling
Adaptive-network models are typically studied using deterministic
differential equations which approximately describe their dynamics. In
simulations, however, the discrete nature of the network gives rise to
intrinsic noise which can radically alter the system's behaviour. In this
article we develop a method to predict the effects of stochasticity in adaptive
networks by making use of a pair-based proxy model. The technique is developed
in the context of an epidemiological model of a disease spreading over an
adaptive network of infectious contact. Our analysis reveals that in this model
the structure of the network exhibits stochastic oscillations in response to
fluctuations in the disease dynamic.Comment: 11 pages, 4 figure
Alternative TEL-JAK2 fusions associated with T-cell acute lymphoblastic leukemia and atypical chronic myelogenous leukemia dissected in zebrafish
Background Chromosomal translocations resulting in alternative fusions of the human TEL (ETV6) and JAK2 genes have been observed in cases of acute lymphoblastic leukemia and chronic myelogenous leukemia, but a full understanding of their role in disease etiology has remained elusive. In this study potential differences between these alternative TEL-JAK2 fusions, including their lineage specificity, were investigated.Design and Methods TEL-JAK2 fusion types derived from both T-cell acute lymphoblastic leukemia and atypical chronic myelogenous leukemia were generated using the corresponding zebrafish tel and jak2a genes and placed under the control of either the white blood cell-specific spi1 promoter or the ubiquitously-expressed cytomegalovirus promoter. These constructs were injected into zebrafish embryos and their effects on hematopoiesis examined using a range of molecular approaches. In addition, the functional properties of the alternative fusions were investigated in vitro.Results Injection of the T-cell acute lymphoblastic leukemia-derived tel-jak2a significantly perturbed lymphopoiesis with a lesser effect on myelopoiesis in zebrafish embryos. In contrast, injection of the atypical chronic myelogenous leukemia-derived tel-jak2a resulted in significant perturbation of the myeloid compartment. These phenotypes were observed regardless of whether expressed in a white blood cell-specific or ubiquitous manner, with no overt cellular proliferation outside of the hematopoietic cells. Functional studies revealed subtle differences between the alternative forms, with the acute lymphoblastic leukemia variant showing higher activity, but reduced downstream signal transducer and activator of transcription activation and decreased sensitivity to JAK2 inhibition. JAK2 activity was required to mediate the effects of both variants on zebrafish hematopoiesis.Conclusions This study indicates that the molecular structure of alternative TEL-JAK2 fusions likely contributes to the etiology of disease. The data further suggest that this class of oncogene exerts its effects in a cell lineage-specific manner, which may be due to differences in downstream signaling.<br /
Anticoagulant rodenticides on our public and community lands: spatial distribution of exposure and poisoning of a rare forest carnivore.
Anticoagulant rodenticide (AR) poisoning has emerged as a significant concern for conservation and management of non-target wildlife. The purpose for these toxicants is to suppress pest populations in agricultural or urban settings. The potential of direct and indirect exposures and illicit use of ARs on public and community forest lands have recently raised concern for fishers (Martes pennanti), a candidate for listing under the federal Endangered Species Act in the Pacific states. In an investigation of threats to fisher population persistence in the two isolated California populations, we investigate the magnitude of this previously undocumented threat to fishers, we tested 58 carcasses for the presence and quantification of ARs, conducted spatial analysis of exposed fishers in an effort to identify potential point sources of AR, and identified fishers that died directly due to AR poisoning. We found 46 of 58 (79%) fishers exposed to an AR with 96% of those individuals having been exposed to one or more second-generation AR compounds. No spatial clustering of AR exposure was detected and the spatial distribution of exposure suggests that AR contamination is widespread within the fisher's range in California, which encompasses mostly public forest and park lands Additionally, we diagnosed four fisher deaths, including a lactating female, that were directly attributed to AR toxicosis and documented the first neonatal or milk transfer of an AR to an altricial fisher kit. These ARs, which some are acutely toxic, pose both a direct mortality or fitness risk to fishers, and a significant indirect risk to these isolated populations. Future research should be directed towards investigating risks to prey populations fishers are dependent on, exposure in other rare forest carnivores, and potential AR point sources such as illegal marijuana cultivation in the range of fishers on California public lands
Patterns of Natural and Human-Caused Mortality Factors of a Rare Forest Carnivore, the Fisher (Pekania pennanti) in California.
Wildlife populations of conservation concern are limited in distribution, population size and persistence by various factors, including mortality. The fisher (Pekania pennanti), a North American mid-sized carnivore whose range in the western Pacific United States has retracted considerably in the past century, was proposed for threatened status protection in late 2014 under the United States Endangered Species Act by the United States Fish and Wildlife Service in its West Coast Distinct Population Segment. We investigated mortality in 167 fishers from two genetically and geographically distinct sub-populations in California within this West Coast Distinct Population Segment using a combination of gross necropsy, histology, toxicology and molecular methods. Overall, predation (70%), natural disease (16%), toxicant poisoning (10%) and, less commonly, vehicular strike (2%) and other anthropogenic causes (2%) were causes of mortality observed. We documented both an increase in mortality to (57% increase) and exposure (6%) from pesticides in fishers in just the past three years, highlighting further that toxicants from marijuana cultivation still pose a threat. Additionally, exposure to multiple rodenticides significantly increased the likelihood of mortality from rodenticide poisoning. Poisoning was significantly more common in male than female fishers and was 7 times more likely than disease to kill males. Based on necropsy findings, suspected causes of mortality based on field evidence alone tended to underestimate the frequency of disease-related mortalities. This study is the first comprehensive investigation of mortality causes of fishers and provides essential information to assist in the conservation of this species
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