1,828 research outputs found
Does nitrate deposition following astrophysical ionizing radiation events pose an additional threat to amphibians?
It is known that amphibians are especially susceptible to the combination of
heightened UVB radiation and increased nitrate concentrations. Various
astrophysical events have been suggested as sources of ionizing radiation that
could pose a threat to life on Earth, through destruction of the ozone layer
and subsequent increase in UVB, followed by deposition of nitrate. In this
study, we investigate whether the nitrate deposition following an ionizing
event is sufficiently large to cause an additional stress beyond that of the
heightened UVB previously considered. We have converted predicted nitrate
depositions to concentration values, utilizing data from the New York State
Department of Environmental Conservation Acid Rain Monitoring Network web site.
Our results show that the increase in nitrate concentration in bodies of water
following the most intense ionization event likely in the last billion years
would not be sufficient to cause a serious additional stress on amphibian
populations and may actually provide some benefit by acting as fertilizer.Comment: This version is a longer, more detailed draft of an article submitted
to the journal Astrobiolog
Gamma-Ray Bursts as a Threat to Life on Earth
Gamma-ray bursts (GRBs) are likely to have made a number of significant
impacts on the Earth during the last billion years. The gamma radiation from a
burst within a few kiloparsecs would quickly deplete much of the Earth's
protective ozone layer, allowing an increase in solar ultraviolet radiation
reaching the surface. This radiation is harmful to life, damaging DNA and
causing sunburn. In addition, NO2 produced in the atmosphere would cause a
decrease in visible sunlight reaching the surface and could cause global
cooling. Nitric acid rain could stress portions of the biosphere, but the
increased nitrate deposition could be helpful to land plants. We have used a
two-dimensional atmospheric model to investigate the effects on the Earth's
atmosphere of GRBs delivering a range of fluences, at various latitudes, at the
equinoxes and solstices, and at different times of day. We have estimated DNA
damage levels caused by increased solar UVB radiation, reduction in solar
visible light due to NO2 opacity, and deposition of nitrates through rainout of
HNO3. In this paper I give a concise review of this work and discuss current
and future work on extending and improving our estimates of the terrestrial
impact of a GRB.Comment: 8 pages; submitted as part of proceedings of the ESLAB Symposium on
'Cosmic Cataclysms and Life', November 2008; to be published in a special
issue of the International Journal of Astrobiolog
Cost-effectiveness of superficial femoral artery endovascular interventions in the UK and Germany: a modelling study
Objectives: To assess the lifetime costs and cost-effectiveness of 5 endovascular interventions to treat superficial femoral arterial disease.
Design: A model-based health economic evaluation. An existing decision analytical model was used, with updated effectiveness data taken from the literature, and updated costs based on purchasing prices.
Setting: UK and German healthcare perspectives were considered.
Participants: Patients with intermittent claudication of the femoropopliteal arteries eligible for endovascular treatment.
Methods: UK and German healthcare perspectives were considered, as were different strategies for re-intervention.
Interventions: Percutaneous transluminal angioplasty (PTA) with bail-out bare metal stenting (assumed to represent the existing standard of care, and 4 alternatives: primary bare metal stents, drug-eluting stents, drug-eluting balloons (DEBs) and biomimetic stents).
Primary outcome measures: The incremental cost-effectiveness ratio between 2 treatments, defined as the incremental costs divided by the incremental quality-adjusted life years (QALYs).
Results: Use of a biomimetic stent, BioMimics 3D, was always estimated to dominate the other interventions, having lower lifetime costs and greater effectiveness, as measured by QALYs. Of the remaining interventions, DEBs were always the most effective, and PTA the least effective. There was uncertainty in the cost-effectiveness results, with key drivers being the costs and effectiveness of the biomimetic stent along with the costs of DEBs.
Conclusions: All 4 of the alternatives to PTA were more effective, with the biomimetic stent being the most cost-effective. As there was uncertainty in the results, and all of the interventions have different mechanisms of action, all 4 may be considered to be alternatives to PTA
Lookup tables to compute high energy cosmic ray induced atmospheric ionization and changes in atmospheric chemistry
A variety of events such as gamma-ray bursts and supernovae may expose the
Earth to an increased flux of high-energy cosmic rays, with potentially
important effects on the biosphere. Existing atmospheric chemistry software
does not have the capability of incorporating the effects of substantial cosmic
ray flux above 10 GeV . An atmospheric code, the NASA-Goddard Space Flight
Center two-dimensional (latitude, altitude) time-dependent atmospheric model
(NGSFC), is used to study atmospheric chemistry changes. Using CORSIKA, we have
created tables that can be used to compute high energy cosmic ray (10 GeV - 1
PeV) induced atmospheric ionization and also, with the use of the NGSFC code,
can be used to simulate the resulting atmospheric chemistry changes. We discuss
the tables, their uses, weaknesses, and strengths.Comment: In press: Journal of Cosmology and Astroparticle Physics. 6 figures,
3 tables, two associated data files. Major revisions, including results of a
greatly expanded computation, clarification and updated references. In the
future we will expand the table to at least EeV levels
The extended epoch of galaxy formation: age dating of ~3600 galaxies with 2<z<6.5 in the VIMOS Ultra-Deep Survey
We aim at improving constraints on the epoch of galaxy formation by measuring
the ages of 3597 galaxies with spectroscopic redshifts 2<z<6.5 in the VIMOS
Ultra Deep Survey (VUDS). We derive ages and other physical parameters from the
simultaneous fitting with the GOSSIP+ software of observed UV rest-frame
spectra and photometric data from the u-band up to 4.5 microns using composite
stellar population models. We conclude from extensive simulations that at z>2
the joint analysis of spectroscopy and photometry combined with restricted age
possibilities when taking into account the age of the Universe substantially
reduces systematic uncertainties and degeneracies in the age derivation. We
find galaxy ages ranging from very young with a few tens of million years to
substantially evolved with ages up to ~1.5-2 Gyr. The formation redshifts z_f
derived from the measured ages indicate that galaxies may have started forming
stars as early as z_f~15. We produce the formation redshift function (FzF), the
number of galaxies per unit volume formed at a redshift z_f, and compare the
FzF in increasing redshift bins finding a remarkably constant 'universal' FzF.
The FzF is parametrized with (1+z)^\zeta, with \zeta~0.58+/-0.06, indicating a
smooth 2 dex increase from z~15 to z~2. Remarkably this observed increase is of
the same order as the observed rise in the star formation rate density (SFRD).
The ratio of the SFRD with the FzF gives an average SFR per galaxy of
~7-17Msun/yr at z~4-6, in agreement with the measured SFR for galaxies at these
redshifts. From the smooth rise in the FzF we infer that the period of galaxy
formation extends from the highest possible redshifts that we can probe at z~15
down to redshifts z~2. This indicates that galaxy formation is a continuous
process over cosmic time, with a higher number of galaxies forming at the peak
in SFRD at z~2 than at earlier epochs. (Abridged)Comment: Submitted to A&A, 24 page
Nonlinear force-free magnetic field extrapolations: comparison of the Grad-Rubin and Wheatland-Sturrock-Roumeliotis algorithm
We compare the performance of two alternative algorithms which aim to
construct a force-free magnetic field given suitable boundary conditions. For
this comparison, we have implemented both algorithms on the same finite element
grid which uses Whitney forms to describe the fields within the grid cells. The
additional use of conjugate gradient and multigrid iterations result in quite
effective codes. The Grad-Rubin and Wheatland-Sturrock-Roumeliotis algorithms
both perform well for the reconstruction of a known analytic force-free field.
For more arbitrary boundary conditions the Wheatland-Sturrock-Roumeliotis
approach has some difficulties because it requires overdetermined boundary
information which may include inconsistencies. The Grad-Rubin code on the other
hand loses convergence for strong current densities. For the example we have
investigated, however, the maximum possible current density seems to be not far
from the limit beyond which a force free field cannot exist anymore for a given
normal magnetic field intensity on the boundary.Comment: 21 pages, 13 figure
WMAP-Compliant Benchmark Surfaces for MSSM Higgs Bosons
We explore `benchmark surfaces' suitable for studying the phenomenology of
Higgs bosons in the minimal supersymmetric extension of the Standard Model
(MSSM), which are chosen so that the supersymmetric relic density is generally
compatible with the range of cold dark matter density preferred by WMAP and
other observations. These benchmark surfaces are specified assuming that
gaugino masses m_{1/2}, soft trilinear supersymmetry-breaking parameters A_0
and the soft supersymmetry-breaking contributions m_0 to the squark and slepton
masses are universal, but not those associated with the Higgs multiplets (the
NUHM framework). The benchmark surfaces may be presented as M_A-tan_beta planes
with fixed or systematically varying values of the other NUHM parameters, such
as m_0, m_{1/2}, A_0 and the Higgs mixing parameter mu. We discuss the
prospects for probing experimentally these benchmark surfaces at the Tevatron
collider, the LHC, the ILC, in B physics and in direct dark-matter detection
experiments. An Appendix documents developments in the FeynHiggs code that
enable the user to explore for her/himself the WMAP-compliant benchmark
surfaces.Comment: Minor corrections, references added. 43 pages, 10 figures. Version to
appear in JHE
Defining and characterizing team resilience in elite sport
Objectives: The objectives of this study were to develop a definition of team resilience and to identify the resilient characteristics of elite sport teams.
Design and Method: Focus groups consisting of a total of 31 participants were conducted with five elite teams from a range of sports. An interpretive thematic analysis using inductive and deductive reasoning was employed to analyze the data.
Results and Conclusions: Team resilience was defined as a dynamic, psychosocial process which protects a group of individuals from the potential negative effect of the stressors they collectively encounter. It comprises of processes whereby team members use their individual and combined resources to positively adapt when experiencing adversity. Findings revealed four main resilient characteristics of elite sport teams: group structure, mastery approaches, social capital, and collective efficacy. This study extends resilience research in sport psychology by providing greater conceptual clarity of resilience at a team level. The implications of the findings for those conducting research in this area and for those consulting with elite sport teams are discussed
Epistasis and the sensitivity of phenotypic screens for beta thalassaemia
Genetic disorders of haemoglobin, particularly the sickle cell diseases and the alpha and beta thalassaemias, are the commonest inherited disorders worldwide. The majority of affected births occur in low-income and lower-middle income countries. Screening programmes are a vital tool to counter these haemoglobinopathies by: (i) identifying individual carriers and allowing them to make informed reproductive choices, and (ii) generating population level gene-frequency estimates, to help ensure the optimal allocation of public health resources. For both of these functions it is vital that the screen performed is suitably sensitive. One popular first-stage screening option to detect carriers of beta thalassaemia in low-income countries is the One Tube Osmotic Fragility Test (OTOFT). Here we introduce a population genetic framework within which to quantify the likely sensitivity and specificity of the OTOFT in different epidemiological contexts. We demonstrate that interactions between the carrier states for beta thalassaemia and alpha thalassaemia, glucose-6-phosphate dehydrogenase deficiency and Southeast Asian Ovalocytosis have the potential to reduce the sensitivity of OTOFTs for beta thalassaemia heterozygosity to below 70%. Our results therefore caution against the widespread application of OTOFTs in regions where these erythrocyte variants co-occur
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