16,391 research outputs found
Using simulation to estimate the power of a badger vaccine trial
The aim of this study was to estimate the power of a badger vaccine field trial using simulation techniques. The effects of sample size, sensitivity and specificity of the diagnostic test, transmission rate between unvaccinated badgers, Vaccine Efficacy for Susceptibility (VES) and Vaccine Efficacy for Infectiousness (VEI) on study power were determined. The most striking result was the large effect of the specificity of the diagnostic test on study power. Sample size had a small effect on power. Study power increased with increasing transmission rate between non-vaccinated badgers. Changes in VES had a higher impact on power than changes in VEI. In summary, study power in group randomized trials depends not only on sample size but on many other parameters. In the current vaccine trial, power was highly dependent on the specificity of the diagnostic test. Therefore, it is critical that the diagnostic test used in the badger vaccine trial is optimized to maximise test specificity
The Central Region in M100: Observations and Modeling
We present new high-resolution observations of the center of the late-type
spiral M100 (NGC 4321) supplemented by 3D numerical modeling of stellar and gas
dynamics, including star formation (SF). NIR imaging has revealed a stellar
bar, previously inferred from optical and 21 cm observations, and an
ovally-shaped ring-like structure in the plane of the disk. The K isophotes
become progressively elongated and skewed to the position angle of the bar
(outside and inside the `ring') forming an inner bar-like region. The galaxy
exhibits a circumnuclear starburst in the inner part of the K `ring'. Two
maxima of the K emission have been observed to lie symmetrically with respect
to the nucleus and equidistant from it slightly leading the stellar bar. We
interpret the twists in the K isophotes as being indicative of the presence of
a double inner Lindblad resonance (ILR) and test this hypothesis by modeling
the gas flow in a self-consistent gas + stars disk embedded in a halo, with an
overall NGC4321-like mass distribution. We have reproduced the basic morphology
of the region (the bar, the large scale trailing shocks, two symmetric K peaks
corresponding to gas compression maxima which lie at the caustic formed by the
interaction of a pair of trailing and leading shocks in the vicinity of the
inner ILR, both peaks being sites of SF, and two additional zones of SF
corresponding to the gas compression maxima, referred usually as `twin peaks').Comment: 31 pages, postscript, compressed, uuencoded. 21 figures available in
postscript, compressed form by anonymous ftp from
ftp://asta.pa.uky.edu/shlosman/main100 , mget *.ps.Z. To appear in Ap.
Gravitino Dark Matter and Neutrino Masses in Partial Split Supersymmetry
Partial Split Supersymmetry with bilinear R-parity violation allows to
reproduce all neutrino mass and mixing parameters. The viable dark matter
candidate in this model is the gravitino. We study the hypothesis that both
possibilities are true: Partial Split Supersymmetry explains neutrino physics
and that dark matter is actually composed of gravitinos. Since the gravitino
has a small but non-zero decay probability, its decay products could be
observed in astrophysical experiments. Combining bounds from astrophysical
photon spectra with the bounds coming from the mass matrix in the neutrino
sector we derive a stringent upper limit for the allowed gravitino mass. This
mass limit is in good agreement with the results of direct dark matter
searches.Comment: 22 pages, 3 figure
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