127 research outputs found
Molecular Genetic Typing of Staphylococcus aureus from Cows, Goats, Sheep, Rabbits and Chickens
End of project reportsS. aureus can also cause a number of infections in animals such as tick-associated pyaemia in lambs, staphylococcosis in rabbits, septicaemia, abscesses and chondronecrosis in chickens and pneumonia and osteomyelitis complex in turkeys. S. aureus is the most frequent cause of bovine mastitis, a disease that is of economic importance worldwide (Beck et al., 1992). Typically staphylococcal mastitis is chronic in nature, with subclinical mastitis being the most common form
Magnetic Fields in Stellar Jets
Although several lines of evidence suggest that jets from young stars are
driven magnetically from accretion disks, existing observations of field
strengths in the bow shocks of these flows imply that magnetic fields play only
a minor role in the dynamics at these locations. To investigate this apparent
discrepancy we performed numerical simulations of expanding magnetized jets
with stochastically variable input velocities with the AstroBEAR MHD code.
Because the magnetic field B is proportional to the density n within
compression and rarefaction regions, the magnetic signal speed drops in
rarefactions and increases in the compressed areas of velocity-variable flows.
In contrast, B ~ n^0.5 for a steady-state conical flow with a toroidal field,
so the Alfven speed in that case is constant along the entire jet. The
simulations show that the combined effects of shocks, rarefactions, and
divergent flow cause magnetic fields to scale with density as an intermediate
power 1 > p > 0.5. Because p > 0.5, the Alfven speed in rarefactions decreases
on average as the jet propagates away from the star. This behavior is extremely
important to the flow dynamics because it means that a typical Alfven velocity
in the jet close to the star is significantly larger than it is in the
rarefactions ahead of bow shocks at larger distances, the one place where the
field is a measurable quantity. We find that the observed values of weak fields
at large distances are consistent with strong fields required to drive the
observed mass loss close to the star. For a typical stellar jet the crossover
point inside which velocity perturbations of 30 - 40 km/s no longer produce
shocks is ~ 300 AU from the source
A New Look at T Tauri Star Forbidden Lines: MHD Driven Winds from the Inner Disk
Magnetohydrodynamic (MHD) and photoevaporative winds are thought to play an
important role in the evolution and dispersal of planet-forming disks. We
report the first high-resolution (6\kms) analysis of [S II]
4068, [O I] 5577, and [O I] 6300 lines from a sample
of 48 T Tauri stars. Following Simon et al. (2016), we decompose them into
three kinematic components: a high-velocity component (HVC) associated with
jets, and a low-velocity narrow (LVC-NC) and broad (LVC-BC) components. We
confirm previous findings that many LVCs are blueshifted by more than 1.5
kms thus most likely trace a slow disk wind. We further show that the
profiles of individual components are similar in the three lines. We find that
most LVC-BC and NC line ratios are explained by thermally excited gas with
temperatures between 5,00010,000 K and electron densities
cm. The HVC ratios are better reproduced by shock
models with a pre-shock H number density of cm.
Using these physical properties, we estimate for the LVC and for the HVC. In
agreement with previous work, the mass carried out in jets is modest compared
to the accretion rate. With the likely assumption that the NC wind height is
larger than the BC, the LVC-BC is found
to be higher than the LVC-NC. These results suggest that most of the mass loss
occurs close to the central star, within a few au, through an MHD driven wind.
Depending on the wind height, MHD winds might play a major role in the
evolution of the disk mass.Comment: 45 pages, 23 figures, and 7 tables, accepted by Ap
Population and Virulence Factor Analysis of Staphylococcus aureus from Bovine Mastitis.
End of Project ReportsStaphylococcus aureus is a major cause of bovine mastitis and the disease
is responsible for substantial economic losses in the dairy industry
world-wide. A large number of commonly accepted virulence factors are
associated with S. aureus but it is yet to be elucidated which of these are
important for infection of the bovine udder.
A rational and effective strategy for the control of intramammary
infections may need to be directed against clones of S. aureus that
commonly cause disease. The objective of this study was to characterise
the genetic variance of S. aureus isolate populations from infected
udders in Ireland using RAPD-PCR, ribotyping and multilocus enzyme
electrophoresis (MLEE). Similar S. aureus isolates collected in the USA
were also typed in order to compare strain differences in staphylococcal
populations in a different environment. Phenotypic diversity based on
a number of presumed virulence factors together with antibiotic
sensitivity was examined and correlations between phenotype and
genotype were identified, if present. In addition, a pathogenicity island
encoding multiple superantigens was completely sequenced and
characterised. Knockout mutants of these superantigens were also
constructed and in vitro functional analysis performed.
Laboratory animal experiments (mice and rabbits) were used to study
the relative pathogenicity of individual staphylococcal strains (mice) and
also to measure the immunological responses after prolonged exposure
to the predominant strains (rabbits)
A Spectroscopic Survey of Subarcsecond Binaries in the Taurus-Auriga Dark Cloud with the Hubble Space Telescope
We report the results of a spectroscopic survey of 20 close T Tauri binaries
in the Taurus-Auriga dark cloud where the separations between primaries and
their secondaries are less than the typical size of a circumstellar disk around
a young star. Analysis of low-resolution and medium-resolution STIS spectra
yields the stellar luminosities, reddenings, ages, masses, mass accretion
rates, IR excesses, and emission line luminosities for each star in each pair.
We examine the ability of IR color excesses, H-alpha equivalent widths, [O I]
emission, and veiling to distinguish between weak emission and classical T
Tauri stars. Four pairs have one cTTs and one wTTs; the cTTs is the primary in
three of these systems. This frequency of mixed pairs among the close T Tauri
binaries is similar to the frequency of mixed pairs in wider young binaries.
Extinctions within pairs are usually similar; however, the secondary is more
heavily reddened than the primary in some systems, where it may be viewed
through the primary's disk. Mass accretion rates of primaries and secondaries
are strongly correlated, and H-alpha luminosities, IR excesses, and ages also
correlate within pairs. Primaries tend to have somewhat larger accretion rates
than their secondaries do, and are typically slightly older than their
secondaries according to three different sets of modern pre-main-sequence
evolutionary tracks. Age differences for XZ Tau and FS Tau, systems embedded in
reflection nebulae, are striking; the secondary in each pair is less massive
but more luminous than the primary. The stellar masses of the UY Aur and GG Tau
binaries measured from their rotating molecular disks are about 30% larger than
the masses inferred from the spectra and evolutionary tracks
SpinSpotter: An Automated Algorithm for Identifying Stellar Rotation Periods With Autocorrelation Analysis
Spinspotter is a robust and automated algorithm designed to extract stellar
rotation periods from large photometric datasets with minimal supervision. Our
approach uses the autocorrelation function (ACF) to identify stellar rotation
periods up to one-third the observational baseline of the data. Our algorithm
also provides a suite of diagnostics that describe the features in the ACF,
which allows the user to fine-tune the tolerance with which to accept a period
detection. We apply it to approximately 130,000 main-sequence stars observed by
the Transiting Exoplanet Survey Satellite (TESS) at 2-minute cadence during
Sectors 1-26, and identify rotation periods for 13,504 stars ranging from 0.4
to 14 days. We demonstrate good agreement between our sample and known values
from the literature and note key differences between our population of rotators
and those previously identified in the Kepler field, most notably a large
population of fast-rotating M dwarfs. Our sample of rotating stars provides a
data set with coverage of nearly the entire sky that can be used as a basis for
future gyrochronological studies, and, when combined with proper motions and
distances from Gaia, to search for regions with high densities of young stars,
thus identifying areas of recent star formation and undiscovered moving group
members. Our algorithm is publicly available for download and use on GitHub.Comment: 14 pages, 5 figures, Accepted for publication in The Astrophysical
Journa
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