833 research outputs found
Probing the Fermi surface by positron annihilation and Compton scattering
Positron annihilation and Compton scattering are important probes of the Fermi surface. Relying on conservation
of energy and momentum, being bulk sensitive and not limited by short electronic mean-free-paths, they can
provide unique information in circumstances when other methods fail. Using a variety of examples, their contribution
to knowledge about the electronic structure of a wide range of materials is demonstrated
Fermi surface of the colossal magnetoresistance perovskite La_{0.7}Sr_{0.3}MnO_{3}
Materials that exhibit colossal magnetoresistance (CMR) are currently the
focus of an intense research effort, driven by the technological applications
that their sensitivity lends them to. Using the angular correlation of photons
from electron-positron annihilation, we present a first glimpse of the Fermi
surface of a material that exhibits CMR, supported by ``virtual crystal''
electronic structure calculations. The Fermi surface is shown to be
sufficiently cubic in nature that it is likely to support nesting.Comment: 5 pages, 5 PS figure
Three-dimensional in situ observations of compressive damage mechanisms in syntactic foam using X-ray microcomputed tomography
Royal Society Grant number RG140680 Lloyd's Register Foundation (GB) Oil and Gas Academy of Scotland Open access via Springer Compact AgreementPeer reviewedPublisher PD
Female teat size is a reliable indicator of annual breeding success in European badgers: Genetic validation
Assessing which females have bred successfully is a central requirement in many ecological field studies,
providing an estimate of the effective female population size. Researchers have applied teat measurements
previously to assess whether females, in a variety of mammalian species, have bred; however, this
technique has not been validated genetically. Furthermore, several analytical techniques are available to
classify individuals, but their misclassification rates have not been compared. We used 22 microsatellite
loci to assign maternity, with 95% confidence, within a high-density population of European badgers Meles
meles, as plural and subterranean breeding means that maternity cannot be inferred from behavioural
observations. The teat lengths and diameters of 136 females, measured May–July 1994–2005, from social
groups in which all offspring were assigned a mother, were reliable indicators of recent breeding success.
A Generalised Linear Mixed Model (GLMM) classified both breeding and non-breeding females with
lower error rates than discriminant analyses and crude teat-size criteria. The GLMM model logit probability
=
−20 + 1.8 month + 1.6 mean teat length + 1.0 mean teat diameter can be applied quickly in the field
to assess the probability with which a female badger should be assigned maternity. This is a low-cost
measure which, after validation, could be used in other badger or mammalian populations to assess the
breeding success of females. This may be a particularly useful welfare tool for veterinary practitioners,
especially during badger culls
An investigation of the sensitivity of the Fermi surface to the treatment of exchange and correlation
The Group V and VI transition metals share a common Fermi surface feature of
hole ellipsoids at the N point in the Brillouin zone. In clear contrast to the
other Fermi surface sheets, which are purely of d character, these arise from a
band that has a significant proportion of p character. By performing local
density approximation (LDA), generalized gradient approximation (GGA), strongly
constrained and appropriately normed (SCAN) meta-GGA, and GW approximation
calculations, we find that the p character part of this band (and therefore the
Fermi surface) is particularly sensitive to the exchange-correlation
approximation. LDA and GGA calculations inadequately describe this feature,
predicting N hole ellipsoid sizes that are consistently too large in comparison
to various experimental measurements, whereas quasiparticle self-consistent GW
calculations predict a size that is slightly too small (and non-self-consistent
GW calculations that use an LDA starting point predict a size that is much too
small). Overall, for the metals tested here, SCAN provides the most accurate
Fermi surface predictions, mostly correcting the discrepancies between
measurements and calculations that were observed when LDA calculations were
used. However, none of the tested exchange-correlation approximations succeeds
in simultaneously bringing all of the measurable properties of these metals
into good experimental agreement, particularly where magnetism is concerned.
The SCAN calculations predict antiferromagnetic moments for Cr that are 3 times
larger than the experimental value (1.90 compared to 0.62 )
Vacancies, disorder-induced smearing of the electronic structure, and its implications for the superconductivity of anti-perovskite MgCNi
The anti-perovskite superconductor MgCNi was studied using
high-resolution x-ray Compton scattering combined with electronic structure
calculations. Compton scattering measurements were used to determine
experimentally a Fermi surface that showed good agreement with that of our
supercell calculations, establishing the presence of the predicted hole and
electron Fermi surface sheets. Our calculations indicate that the Fermi surface
is smeared by the disorder due to the presence of vacancies on the C and Ni
sites, but does not drastically change shape. The 20\% reduction in the Fermi
level density-of-states would lead to a significant () suppression
of the superconducting for pair-forming electron-phonon coupling.
However, we ascribe the observed much smaller reduction at our
composition (compared to the stoichiometric compound) to the suppression of
pair-breaking spin fluctuations.Comment: 11 pages, 3 figure
Maximum entropy deconvolution of resonant inelastic x-ray scattering spectra
Resonant inelastic x-ray scattering (RIXS) has become a powerful tool in the
study of the electronic structure of condensed matter. Although the linewidths
of many RIXS features are narrow, the experimental broadening can often hamper
the identification of spectral features. Here, we show that the Maximum Entropy
technique can successfully be applied in the deconvolution of RIXS spectra,
improving the interpretation of the loss features without a severe increase in
the noise ratio
Caution is required in the implementation of 90-day mortality indicators for radiotherapy in a curative setting: A retrospective population-based analysis of over 16,000 episodes
Background: 90-day mortality (90DM) has been proposed as a clinical indicator in radiotherapy delivered in a curative setting. No large scale assessment has been made. Its value in allowing robust comparisons between centres and facilitating service improvement is unknown. Methods: All radiotherapy treatments delivered in a curative setting over seven years were extracted from the local electronic health record and linked to cancer registry data. 90DM rates were assessed and factors associated with this outcome were investigated using logistic regression. Cause of death was identified retrospectively further characterising the cause of 90DM. Results: Overall 90DM was 1.25%. Levels varied widely with diagnosis (0.20%-5.45%). Age (OR 1.066, 1.043-1.073), year of treatment (OR 0.900, 0.841-0.969) and diagnosis were significantly associated with 90DM on multi-variable logistic regression. Cause of death varied with diagnosis; 50.0% post-operative in rectal cancer, 40.4% treatment-related in head and neck cancer, 59.4% disease progression in lung cancer. Conclusion: Despite the drive to report centre level comparative outcomes, this study demonstrates that 90DM cannot be adopted routinely as a clinical indicator due to significant population heterogeneity and low event rates. Further national investigation is needed to develop a meaningful robust indicator that delivers appropriate comparisons and drive improvements in care
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