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Evaluating three models of schoolâuniversity partnership at the University of York : learning lessons and planning for the future
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This Article Corrects: âEffectiveness of a Pediatric Emergency Medicine Curriculum in a Public Tanzanian Referral Hospitalâ
Physical weathering intensity controls bioavailable primary iron(II) silicate content in major global dust sources
The speciation of iron (Fe) reaching the ocean, for instance in windâblown dust and coastal sediments, impacts its bioavailability to phytoplankton and its impact on atmospheric carbon dioxide (CO2) and climate. For dust reaching the Southern Ocean, primary Fe(II) silicates that are physically weathered from bedrock are highly bioavailable compared to more chemically weathered, Fe(III)ârich species, suggesting that weathering in dust source regions impacts the bioavailable Fe supply. However, this phenomenon has not been studied in other important terrestrial Fe sources, where weathering regimes and source geology vary. Here, we use Fe Xâray absorption spectroscopy on marine sediment cores to show that major global dust and sediment sources impacted by high physical weathering contain abundant primary minerals and thus are overlooked as a source of highly bioavailable Fe globally. Thus, it is important to consider the role of physical versus chemical weathering in Fe fertilization and biotic CO2 cycling
Determination of Cepheid parameters by light-curve template-fitting
We describe techniques to characterise the light-curves of regular variable
stars by applying principal component analysis (PCA) to a training set of high
quality data, and to fit the resulting light-curve templates to sparse and
noisy photometry to obtain parameters such as periods, mean magnitudes etc. The
PCA approach allows us to efficiently represent the multi-band light-curve
shapes of each variable, and hence quantitatively describe the average
behaviour of the sample as a smoothly varying function of period, and also the
range of variation around this average.
In this paper we focus particularly on the utility of such methods for
analysing HST Cepheid photometry, and present simulations which illustrate the
advantages of our PCA template-fitting approach. These are: accurate parameter
determination, including light-curve shape information; simultaneous fitting to
multiple passbands; quantitative error analysis; objective rejection of
variables with non Cepheid-like light-curves or those with potential period
aliases.
We also use PCA to confirm that Cepheid light-curve shapes are systematically
different (at the same period) between the Milky Way (MW) and the Large and
Small Magellanic Clouds (LMC, SMC), and consider whether light-curve shape
might therefore be used to estimate the mean metallicities of Cepheid samples,
thus allowing metallicity corrections to be applied to derived distance
estimates.Comment: MNRAS in press: revised in light of referees comment
Zurek-Kibble domain structures: The Dynamics of Spontaneous Vortex formation in Annular Josephson Tunnel Junctions
Phase transitions executed in a finite time show a domain structure with
defects, that has been argued by Zurek and Kibble to depend in a characteristic
way on the quench rate. In this letter we present an experiment to measure the
Zurek-Kibble scaling exponent sigma. Using symmetric and long Josephson Tunnel
Junctions, for which the predicted index is sigma = 0.25, we find sigma = 0.27
+/- 0.05. Further, there is agreement with the ZK prediction for the overall
normalisation.Comment: To be published in Phys. Rev. Lett
The Hubble Diagram of Type Ia Supernovae in Non-Uniform Pressure Universes
We use the redshift-magnitude relation, as derived by D\c{a}browski (1995),
for the two exact non-uniform pressure spherically symmetric Stephani universes
with the observer positioned at the center of symmetry, to test the agreement
of these models with recent observations of high redshift type Ia supernovae
(SNIa), as reported in Perlmutter et al. (1997). By a particular choice of
model parameters, we show that these models give an excellent fit to the
observed redshifts and (corrected) B band apparent magnitudes of the SNIa data,
but for an age of the Universe which is typically about two Gyr greater than in
the corresponding Friedmann model.
Based on a value of and assuming , the P97 data
implies a Friedmann age of at most 13 Gyr and in fact a best-fit (for ) age of only 10 Gyr. Our Stephani models, on the other hand, can give a
good fit to the P97 data with an age of up to 15 Gyr and could, therefore,
significantly alleviate the conflict between recent cosmological and
astrophysical age predictions. The choice of model parameters is quite robust:
one requires only that the non-uniform pressure parameter, , in one of the
models is negative and satisfies |a| \lte 3 km s Mpc. By
allowing slightly larger, negative, values of one may `fine tune' the model
to give an even better fit to the P97 data.Comment: 36 pages, 2 tables, 6 figures, AAS Latex 4.0, vastly revised version,
new title and abstract, to appear in Ap
Domestication of the Annual Legume \u3cem\u3eTrigonella balansae\u3c/em\u3e for Mixed Farming Systems in Southern Australia
An accession of the annual legume Trigonella balansae Boiss. and Reuter. has been selected for commercial release in Australia. The annual legume has significant potential as a self-regenerating pasture within mixed farming systems. As part of a duty-of-care assessment, we tested the hypothesis that sheep grazing the trigonella cultivar will have similar liveweight, condition scores, health and wool production to sheep grazing two widely adopted annual legumes, subterranean clover (Trifolium subterraneum L. cv Dalkeith) and French serradella (Ornithopus sativus Brot. cv. Erica). Forage dry matter digestibility (DMD), crude protein (CP), fibre, mineral content and isoflavones were measured across the plantâs lifecycle. The data supported the hypotheses and there were no significant differences in liveweight, wool growth, wool yield or condition score that were associated with pasture species. The mineral content of trigonella requires further investigation
Density of Bloch Waves after a Quench
Production of Bloch waves during a rapid quench is studied by analytical and
numerical methods. The density of Bloch waves decays exponentially with the
quench time. It also strongly depends on temperature. Very few textures are
produced for temperatures lower than a characteristic temperature proportional
to the square of the magnetic field.Comment: 4 pages in RevTex + 3 .ps files; improved presentation; version to
appear in PR
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