259 research outputs found
A review of spatio-temporal modelling of quadrat count data with application to striga occurrent in al pearl millet field
Routine prenatal screening for congenital heart disease: what can be expected? A decision-analytic approach
OBJECTIVES: This study assessed the potential impact of fetal ultrasound
screening on the number of newborns affected by cardiac anomalies.
METHODS: A decision model was developed that included the prevalence and
history of congenital heart disease, characteristics of ultrasound, risk
of abortion, and attitude toward pregnancy termination. Probabilities were
obtained with a literature survey; sensitivity analysis showed their
influence on expected outcomes. RESULTS: Presently, screening programs may
prevent the birth of approximately 1300 severely affected newborns per
million second-trimester pregnancies. However, over 2000 terminations of
pregnancy would be required, 750 of which would have ended in intrauterine
death or spontaneous abortion. Further, 9900 false-positive screening
results would occur, requiring referral. Only the sensitivity of routine
screening and attitude toward termination of pregnancy appeared to
influence the yield substantially. CONCLUSIONS: The impact of routine
screening for congenital heart disease appeared relatively small. Further
data may be required to fully assess the utility of prenatal screening
Very Low Temperature Tunnelling Spectroscopy in the heavy fermion superconductor PrOsSb
We present scanning tunnelling spectroscopy measurements on the heavy fermion
superconductor PrOsSb. Our results show that the superconducting gap
opens over a large part of the Fermi surface. The deviations from isotropic BCS
s-wave behavior are discussed in terms of a finite distribution of values of
the superconducting gap.Comment: 4 pages, 4 figure
Particle Acceleration in Cosmic Sites - Astrophysics Issues in our Understanding of Cosmic Rays
Laboratory experiments to explore plasma conditions and stimulated particle
acceleration can illuminate aspects of the cosmic particle acceleration
process. Here we discuss the cosmic-ray candidate source object variety, and
what has been learned about their particle-acceleration characteristics. We
identify open issues as discussed among astrophysicists. -- The cosmic ray
differential intensity spectrum is a rather smooth power-law spectrum, with two
kinks at the "knee" (~10^15 eV) and at the "ankle" (~3 10^18 eV). It is unclear
if these kinks are related to boundaries between different dominating sources,
or rather related to characteristics of cosmic-ray propagation. We believe that
Galactic sources dominate up to 10^17 eV or even above, and the extragalactic
origin of cosmic rays at highest energies merges rather smoothly with Galactic
contributions throughout the 10^15--10^18 eV range. Pulsars and supernova
remnants are among the prime candidates for Galactic cosmic-ray production,
while nuclei of active galaxies are considered best candidates to produce
ultrahigh-energy cosmic rays of extragalactic origin. Acceleration processes
are related to shocks from violent ejections of matter from energetic sources
such as supernova explosions or matter accretion onto black holes. Details of
such acceleration are difficult, as relativistic particles modify the structure
of the shock, and simple approximations or perturbation calculations are
unsatisfactory. This is where laboratory plasma experiments are expected to
contribute, to enlighten the non-linear processes which occur under such
conditions.Comment: accepted for publication in EPJD, topical issue on Fundamental
physics and ultra-high laser fields. From review talk at "Extreme Light
Infrastructure" workshop, Sep 2008. Version-2 May 2009: adjust some wordings
and references at EPJD proofs stag
Dimensional Crossover of Localisation and Delocalisation in a Quantum Hall Bar
The 2-- to 1--dimensional crossover of the localisation length of electrons
confined to a disordered quantum wire of finite width is studied in a
model of electrons moving in the potential of uncorrelated impurities. An
analytical formula for the localisation length is derived, describing the
dimensional crossover as function of width , conductance and
perpendicular magnetic field . On the basis of these results, the scaling
analysis of the quantum Hall effect in high Landau levels, and the
delocalisation transition in a quantum Hall wire are reconsidered.Comment: 12 pages, 7 figure
Field Measurements of Terrestrial and Martian Dust Devils
Surface-based measurements of terrestrial and martian dust devils/convective vortices provided from mobile and stationary platforms are discussed. Imaging of terrestrial dust devils has quantified their rotational and vertical wind speeds, translation speeds, dimensions, dust load, and frequency of occurrence. Imaging of martian dust devils has provided translation speeds and constraints on dimensions, but only limited constraints on vertical motion within a vortex. The longer mission durations on Mars afforded by long operating robotic landers and rovers have provided statistical quantification of vortex occurrence (time-of-sol, and recently seasonal) that has until recently not been a primary outcome of more temporally limited terrestrial dust devil measurement campaigns. Terrestrial measurement campaigns have included a more extensive range of measured vortex parameters (pressure, wind, morphology, etc.) than have martian opportunities, with electric field and direct measure of dust abundance not yet obtained on Mars. No martian robotic mission has yet provided contemporaneous high frequency wind and pressure measurements. Comparison of measured terrestrial and martian dust devil characteristics suggests that martian dust devils are larger and possess faster maximum rotational wind speeds, that the absolute magnitude of the pressure deficit within a terrestrial dust devil is an order of magnitude greater than a martian dust devil, and that the time-of-day variation in vortex frequency is similar. Recent terrestrial investigations have demonstrated the presence of diagnostic dust devil signals within seismic and infrasound measurements; an upcoming Mars robotic mission will obtain similar measurement types
CAM - chem: description and evaluation of interactive atmospheric chemistry in the Community Earth System Model
We discuss and evaluate the representation of atmospheric chemistry in the global Community Atmosphere Model (CAM) version 4, the atmospheric component of the Community Earth System Model (CESM). We present a variety of configurations for the representation of tropospheric and stratospheric chemistry, wet removal, and online and offline meteorology. Results from simulations illustrating these configurations are compared with surface, aircraft and satellite observations. Major biases include a negative bias in the high-latitude CO distribution, a positive bias in upper-tropospheric/lower-stratospheric ozone, and a positive bias in summertime surface ozone (over the United States and Europe). The tropospheric net chemical ozone production varies significantly between configurations, partly related to variations in stratosphere-troposphere exchange. Aerosol optical depth tends to be underestimated over most regions, while comparison with aerosol surface measurements over the United States indicate reasonable results for sulfate , especially in the online simulation. Other aerosol species exhibit significant biases. Overall, the model-data comparison indicates that the offline simulation driven by GEOS5 meteorological analyses provides the best simulation, possibly due in part to the increased vertical resolution (52 levels instead of 26 for online dynamics). The CAM-chem code as described in this paper, along with all the necessary datasets needed to perform the simulations described here, are available for download at www.cesm.ucar.edu
Dark Matter And With Minimal Soft SUSY Breaking II
We update and extend to larger masses our previous analysis of the MSSM with
minimal [MSOSM] soft SUSY breaking boundary conditions. We
find a well--defined, narrow region of parameter space which provides the
observed relic density of dark matter, in a domain selected to fit precision
electroweak data, including top, bottom and tau masses. The model is highly
constrained which allows us to make several predictions. We find the light
Higgs mass GeV and also upper bounds on the mass of the
gluino \mgluino\lsim3.1 TeV and lightest neutralino \mchi\lsim450 GeV. As
the CP odd Higgs mass increases, the region of parameter space consistent
with WMAP data is forced to larger values of and smaller values of
. Hence, we find an upper bound m_A \lsim 1.3 TeV. This in turn leads to
lower bounds on (assuming minimal
flavor violation) and on the dark matter spin independent detection cross
section \sigsip > 10^{-9} pb. Finally, we extend our previous analysis to
include WIMP signals in indirect detection and find prospects for WIMP
detection generally much less promising than in direct WIMP searches.Comment: 24 page
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