6,541 research outputs found
Quantitative Risk Assessment of Developing Salmonellosis through Consumption of Beef in Lusaka Province, Zambia
Based on the Codex Alimentarious framework, this study quantitatively assessed the risk of developing salmonellosis through consumption of beef in Lusaka Province of Zambia. Data used to achieve this objective were obtained from reviews of scientific literature, Government reports, and survey results from a questionnaire that was administered to consumers to address information gaps from secondary data. The Swift Quantitative Microbiological Risk Assessment (sQMRA) model was used to analyse the data. The study was driven by a lack of empircally-based risk estimation despite a number of reported cases of salmonellosis in humans.
A typology of consumers including all age groups was developed based on their beef consumption habits, distinguishing between those with low home consumption, those with medium levels of home consumption, and those with high levels through restaurant consumption. This study shows that the risk of developing salmonellosis in this population, from consuming beef, was generally low. At ID50 of 9.61 × 103 cfu/g and a retail contamination concentration of 12 cfu/g, the risk of developing salmonellosis through the consumption of beef prepared by consumers with low and medium levels of beef consumption was estimated at 0.06% and 0.08%, respectively, while the risk associated with restaurant consumption was estimated at 0.16% per year.
The study concludes that the risk of developing salmonellosis among residents in Lusaka province, as a result of beef consumption, was generally low, mainly due to the methods used for food preparation. Further work is required to broaden the scope of the study and also undertake microbiological evaluation of ready-to-eat beef from both the household and restaurant risk exposure pathways
The Terzan 5 puzzle: discovery of a third, metal-poor component
We report on the discovery of 3 metal-poor giant stars in Terzan 5, a complex
stellar system in the the Galactic bulge, known to have two populations at
[Fe/H]=-0.25 and +0.3. For these 3 stars we present new echelle spectra
obtained with NIRSPEC at Keck II, which confirm their radial velocity
membership and provide average [Fe/H]=-0.79 dex iron abundance and
[alpha/Fe]=+0.36 dex enhancement. This new population extends the metallicity
range of Terzan~5 0.5 dex more metal poor, and it has properties consistent
with having formed from a gas polluted by core collapse supernovae.Comment: Accepted for publication on ApJ Lette
Coherence of neutrino flavor mixing in quantum field theory
In the simplistic quantum mechanical picture of flavor mixing, conditions on
the maximum size and minimum coherence time of the source and detector regions
for the observation of interference---as well as the very viability of the
approach---can only be argued in an ad hoc way from principles external to the
formalism itself. To examine these conditions in a more fundamental way, the
quantum field theoretical -matrix approach is employed in this paper,
without the unrealistic assumption of microscopic stationarity. The fully
normalized, time-dependent neutrino flavor mixing event rates presented here
automatically reveal the coherence conditions in a natural, self-contained, and
physically unambiguous way, while quantitatively describing the transition to
their failure.Comment: 12 pages, submitted to Phys. Rev.
Proper motions in Terzan 5: membership of the multi-iron sub-populations and first constrain to the orbit
By exploiting two sets of high-resolution images obtained with HST ACS/WFC
over a baseline of ~10 years we have measured relative proper motions of
~70,000 stars in the stellar system Terzan 5. The results confirm the
membership of the three sub-populations with different iron abudances
discovered in the system. The orbit of the system has been derived from a first
estimate of its absolute proper motion, obtained by using bulge stars as
reference. The results of the integration of this orbit within an axisymmetric
Galactic model exclude any external accretion origin for this cluster. Terzan 5
is known to have chemistry similar to the Galactic bulge; our findings support
a kinematic link between the cluster and the bulge, further strengthening the
possibility that Terzan 5 is the fossil remnant of one of the pristine clumps
that originated the bulge.Comment: 25 pages, 14 figures, accepted for publication by Ap
Halos of Spiral Galaxies. III. Metallicity Distributions
(Abriged) We report results of a campaign to image the stellar populations in
the halos of highly inclined spiral galaxies, with the fields roughly 10 kpc
(projected) from the nuclei. We use the F814W (I) and F606W (V) filters in the
Wide Field Planetary Camera 2, on board the Hubble Space telescope. Extended
halo populations are detected in all galaxies. The color-magnitude diagrams
appear to be completely dominated by giant-branch stars, with no evidence for
the presence of young stellar populations in any of the fields. We find that
the metallicity distribution functions are dominated by metal-rich populations,
with a tail extending toward the metal poor end. To first order, the overall
shapes of the metallicity distribution functions are similar to what is
predicted by simple, single-component model of chemical evolution with the
effective yields increasing with galaxy luminosity. However, metallicity
distributions significantly narrower than the simple model are observed for a
few of the most luminous galaxies in the sample. It appears clear that more
luminous spiral galaxies also have more metal-rich stellar halos. The
increasingly significant departures from the closed-box model for the more
luminous galaxies indicate that a parameter in addition to a single yield is
required to describe chemical evolution. This parameter, which could be related
to gas infall or outflow either in situ or in progenitor dwarf galaxies that
later merge to form the stellar halo, tends to act to make the metallicity
distributions narrower at high metallicity.Comment: 20 pages, 8 figures (ApJ, in press
Ceci n'est pas a globular cluster: the metallicity distribution of the stellar system Terzan 5
We present new determinations of the iron abundance for 220 stars belonging
to the stellar system Terzan 5 in the Galactic bulge. The spectra have been
acquired with FLAMES at the Very Large Telescope of the European Southern
Observatory and DEIMOS at the Keck II Telescope. This is by far the largest
spectroscopic sample of stars ever observed in this stellar system. From this
dataset, a subsample of targets with spectra unaffected by TiO bands was
extracted and statistically decontaminated from field stars. Once combined with
34 additional stars previously published by our group, a total sample of 135
member stars covering the entire radial extent of the system has been used to
determine the metallicity distribution function of Terzan 5. The iron
distribution clearly shows three peaks: a super-solar component at
[Fe/H] dex, accounting for 29% of the sample, a dominant sub-solar
population at [Fe/H] dex, corresponding to 62% of the total, and a
minor (6%) metal-poor component at [Fe/H] dex. Such a broad,
multi-modal metallicity distribution demonstrates that Terzan 5 is not a
genuine globular cluster but the remnant of a much more complex stellar system.Comment: 29 pages, 10 figures. Accepted for publication by Ap
Nonsingular, big-bounce cosmology from spinor-torsion coupling
The Einstein-Cartan-Sciama-Kibble theory of gravity removes the constraint of
general relativity that the affine connection be symmetric by regarding its
antisymmetric part, the torsion tensor, as a dynamical variable. The minimal
coupling between the torsion tensor and Dirac spinors generates a spin-spin
interaction which is significant in fermionic matter at extremely high
densities. We show that such an interaction averts the unphysical big-bang
singularity, replacing it with a cusp-like bounce at a finite minimum scale
factor, before which the Universe was contracting. This scenario also explains
why the present Universe at largest scales appears spatially flat, homogeneous
and isotropic.Comment: 7 pages; published versio
Stellar Companions and the Age of HD 141569 and its Circumstellar Disk
We investigate the stellar environment of the Beta Pictoris-like star HD
141569 with optical spectroscopy and near infrared imaging. The B9.5Ve primary,
and an M2 and an M4 type star both located in projection less than nine
arseconds away have the same radial velocity and proper motion and therefore
almost certainly form a triple star system. From their x-ray flux, lithium
absorption and location on pre-main-sequence evolutionary tracks, the
companions appear to be 5 Myr old. HD 141569 A is now one of the few stars with
a circumstellar disk that has a well-determined age. The circumstellar disk is
composed of secondary debris material (Fisher et al. 2000), thus placing an
upper limit on the time needed for disk processing. These three stars may be
part of an association of young stars.Comment: 18 pages incl. 7 ps figures, aastex v5.0, accepted for publication in
Ap
An Empirical Measure of the Rate of White Dwarf Cooling in 47 Tucanae
We present an empirical determination of the white dwarf cooling sequence in
the globular cluster 47 Tucanae. Using spectral models, we determine
temperatures for 887 objects from Wide Field Camera 3 data, as well as 292
objects from data taken with the Advanced Camera for Surveys. We make the
assumption that the rate of white dwarf formation in the cluster is constant.
Stellar evolution models are then used to determine the rate at which objects
are leaving the main sequence, which must be the same as the rate at which
objects are arriving on the white dwarf sequence in our field. The result is an
empirically derived relation between temperature () and time () on
the white dwarf cooling sequence. Comparing this result to theoretical cooling
models, we find general agreement with the expected slopes between 20,000K and
30,000K and between 6,000K and 20,000K, but the transition to the Mestel
cooling rate of is found to occur at hotter
temperatures, and more abruptly than is predicted by any of these models.Comment: 10 pages, 16 figures, accepted for publication in Ap
Variable stars in Terzan 5: additional evidence of multi-age and multi-iron stellar populations
Terzan 5 is a complex stellar system in the Galactic bulge, harboring stellar
populations with very different iron content ({\Delta}[Fe/H] ~1 dex) and with
ages differing by several Gyrs. Here we present an investigation of its
variable stars. We report on the discovery and characterization of three RR
Lyrae stars. For these newly discovered RR Lyrae and for six Miras of known
periods we provide radial velocity and chemical abundances from spectra
acquired with X-SHOOTER at the VLT. We find that the three RR Lyrae and the
three short period Miras (P<300 d) have radial velocity consistent with being
Terzan 5 members. They have sub-solar iron abundances and enhanced
[{\alpha}/Fe], well matching the age and abundance patterns of the 12 Gyr
metal-poor stellar populations of Terzan 5. Only one, out of the three long
period (P>300 d) Miras analyzed in this study, has a radial velocity consistent
with being Terzan 5 member. Its super-solar iron abundance and solar-scaled
[{\alpha}/Fe] nicely match the chemical properties of the metal rich stellar
population of Terzan 5 and its derived mass nicely agrees with being several
Gyrs younger than the short period Miras. This young variable is an additional
proof of the surprising young sub-population discovered in Terzan 5.Comment: 20 pages, 4 figures, in press on the Ap
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