999 research outputs found
Where’s the risk? Landscape epidemiology of gastrointestinal parasitism in Alberta beef cattle
Sherpa Romeo green journal; open accessBackground: Gastrointenstinal nematodes (GIN) present a serious challenge to the health and productivity of
grazing stock around the globe. However, the epidemiology of GIN transmission remains poorly understood in
northern climates. Combining use of serological diagnostics, GIS mapping technology, and geospatial statistics, we
evaluated ecological covariates of spatial and temporal variability in GIN transmission among bovine calves
pastured in Alberta, Canada.
Methods: Sera were collected from 1000 beef calves across Alberta, Canada over three consecutive years (2008–2010)
and analyzed for presence of anti-GIN antibodies using the SVANOVIR Ostertagia osteragi-Ab ELISA kit. Using a GIS and
Bayesian multivariate spatial statistics, we evaluated the degree to which variation in specific environmental covariates
(e.g. moisture, humidity, temperature) was associated with variation in spatial and temporal heterogeneity in exposure
to GIN (Nematodirus and other trichostrongyles, primarily Ostertagia and Cooperia).
Results: Variation in growing degree days above a base temperature of 5 °C, humidity, air temperature, and
accumulated precipitation were found to be significant predictors of broad–scale spatial and temporal variation in
serum antibody concentrations. Risk model projections identified that while transmission in cattle from southeastern
and northwestern Alberta was relatively low in all years, rate of GIN transmission was generally higher in the central
region of Alberta.
Conclusions: The spatial variability in risk is attributed to higher average humidity, precipitation and moderate
temperatures in the central region of Alberta in comparison with the hot, dry southeastern corner of the province and
the cool, dry northwestern corner. Although more targeted sampling is needed to improve model accuracy, our
projections represent an important step towards tying treatment recommendations to actual risk of infection.Ye
Magnetic form factor of SrFeAs
Neutron diffraction measurements have been carried out to investigate the
magnetic form factor of the parent SrFe2As2 system of the iron-based
superconductors. The general feature is that the form factor is approximately
isotropic in wave vector, indicating that multiple d-orbitals of the iron atoms
are occupied as expected based on band theory. Inversion of the diffraction
data suggests that there is some elongation of the spin density toward the As
atoms. We have also extended the diffraction measurements to investigate a
possible jump in the c-axis lattice parameter at the structural phase
transition, but find no detectable change within the experimental
uncertainties
Generic Model Refactorings
Many modeling languages share some common concepts and principles. For example, Java, MOF, and UML share some aspects of the concepts\ud
of classes, methods, attributes, and inheritance. However, model\ud
transformations such as refactorings specified for a given language\ud
cannot be readily reused for another language because their related\ud
metamodels may be structurally different. Our aim is to enable a\ud
flexible reuse of model transformations across various metamodels.\ud
Thus, in this paper, we present an approach allowing the specification\ud
of generic model transformations, in particular refactorings, so\ud
that they can be applied to different metamodels. Our approach relies\ud
on two mechanisms: (1) an adaptation based mainly on the weaving\ud
of aspects; (2) the notion of model typing, an extension of object\ud
typing in the model-oriented context. We validated our approach by\ud
performing some experiments that consisted of specifying three well\ud
known refactorings (Encapsulate Field, Move Method, and Pull Up Method)\ud
and applying each of them onto three different metamodels (Java,\ud
MOF, and UML)
Magnetic coupling in ferromagnetic semiconductor (Ga,Mn)As/(Al,Ga,Mn)As bilayers
We report on a study of ferromagnetic semiconductor (Ga,Mn)As/(Al,Ga,Mn)As bilayers using magnetometry and polarized neutron reflectivity (PNR). From depth-resolved characterization of the magnetic structure obtained by PNR, we concluded that the (Ga,Mn)As and (Al,Ga,Mn)As layers have in-plane and perpendicular-to-plane magnetic easy axes, respectively, with weak interlayer coupling. Therefore, the layer magnetizations align perpendicular to each other under low magnetic fields and parallel at high fields
Hydrodynamical Survey of First Overtone Cepheids
A hydrodynamical survey of the pulsational properties of first overtone
Galactic Cepheids is presented. The goal of this study is to reproduce their
observed light- and radial velocity curves. The comparison between the models
and the observations is made in a quantitative manner on the level of the
Fourier coefficients. Purely radiative models fail to reproduce the observed
features, but convective models give good agreement.
It is found that the sharp features in the Fourier coefficients are indeed
caused by the P1/P4 = 2 resonance, despite the very large damping of the 4th
overtone. For the adopted mass-luminosity relation the resonance center lies
near a period of 4.2d +/- 0.2 as indicated by the observed radial velocity
data, rather than near 3.2d as the light-curves suggest.Comment: ApJ, 12 pages, (slightly) revise
Vertically Graded Anisotropy in Co/Pd Multilayers
Depth-grading of magnetic anisotropy in perpendicular magnetic media has been
predicted to reduce the field required to write data without sacrificing
thermal stability. To study this prediction, we have produced Co/Pd multilayers
with depth-dependent Co layer thickness. Polarized neutron reflectometry shows
that the thickness grading results in a corresponding magnetic anisotropy
gradient. Magnetometry reveals that the anisotropy gradient promotes domain
nucleation upon magnetization reversal - a clear experimental demonstration of
the effectiveness of graded anisotropy for reducing write-field
Heavy Quarkonium Physics
This report is the result of the collaboration and research effort of the
Quarkonium Working Group over the last three years. It provides a comprehensive
overview of the state of the art in heavy-quarkonium theory and experiment,
covering quarkonium spectroscopy, decay, and production, the determination of
QCD parameters from quarkonium observables, quarkonia in media, and the effects
on quarkonia of physics beyond the Standard Model. An introduction to common
theoretical and experimental tools is included. Future opportunities for
research in quarkonium physics are also discussed.Comment: xviii + 487 pages, 260 figures. The full text is also available at
the Quarkonium Working Group web page: http://www.qwg.to.infn.i
On the pulsation mode identification of short-period Galactic Cepheids
We present new theoretical Period-Radius (PR) relations for first overtone
Galactic Cepheids. Current predictions are based on several sequences of
nonlinear, convective pulsation models at solar chemical composition (Y=0.28,
Z=0.02) and stellar masses ranging from 3.0 to 5.5 Mo. The comparison between
predicted and empirical radii of four short-period Galactic Cepheids suggests
that QZ Nor and EV Sct are pulsating in the fundamental mode, whereas Polaris
and SZ Tau pulsate in the first overtone. This finding supports the mode
identifications that rely on the comparison between direct and
Period-Luminosity (PL) based distance determinations but it is somewhat at
variance with the mode identification based on Fourier parameters. In fact, we
find from our models that fundamental and first overtone pulsators attain, for
periods ranging from 2.7 to 4 d, quite similar phi_21 values, making mode
discrimination from this parameter difficult. The present mode identifications
for our sample of Cepheids are strengthened by the accuracy of their empirical
radius estimates, as well as by the evidence that predicted fundamental and
first overtone radii do not show, within the current uncertainty on the
Mass-Luminosity (ML) relation, any degeneracy in the same period range.
Accurate radius determinations are therefore an excellent tool to unambiguously
determine the pulsation modes of short-period Cepheids.Comment: 15 pages, 3 postscript figures, accepted for publication on ApJ
Letter
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