38,746 research outputs found
Refinement and growth enhancement of Al2Cu phase during magnetic field assisting directional solidification of hypereutectic Al-Cu alloy.
International audienceUnderstanding how the magnetic fields affect the formation of reinforced phase during solidification is crucial to tailor the structure and therefor the performance of metal matrix in situ composites. In this study, a hypereutectic Al-40 wt.% Cu alloy has been directionally solidified under various axial magnetic fields and the morphology of Al2Cu phase was quantified in 3D by means of high resolution synchrotron X-ray tomography. With rising magnetic fields, both increase of Al2Cu phase's total volume and decrease of each column's transverse section area were found. These results respectively indicate the growth enhancement and refinement of the primary Al2Cu phase in the magnetic field assisting directional solidification. The thermoelectric magnetic forces (TEMF) causing torque and dislocation multiplication in the faceted primary phases were thought dedicate to respectively the refinement and growth enhancement. To verify this, a real structure based 3D simulation of TEMF in Al2Cu column was carried out, and the dislocations in the Al2Cu phase obtained without and with a 10T high magnetic field were analysed by the transmission electron microscope
Incidence of symptomatic toxoplasma eye disease: aetiology and public health implications.
Ocular disease is the commonest disabling consequence of toxoplasma infection. Incidence and lifetime risk of ocular symptoms were determined by ascertaining affected patients in a population-based, active reporting study involving ophthalmologists serving a population of 7.4 million. Eighty-seven symptomatic episodes were attributed to toxoplasma infection. Bilateral visual acuity of 6/12 or less was found in seven episodes (8%) and was likely to have been transient in most cases. Black people born in West Africa had a 100-fold higher incidence of symptoms than white people born in Britain. Only two patients reported symptoms before 10 years of age. The estimated lifetime risk of symptoms in British born individuals (52% of all episodes) was 18/100000 (95% confidence interval: 10.8-25.2). The low risk and mild symptoms in an unscreened British population indicate limited potential benefits of prenatal or postnatal screening. The late age at presentation suggests a mixed aetiology of postnatally acquired and congenital infection for which primary prevention may be appropriate, particularly among West Africans
Change and Aging Senescence as an adaptation
Understanding why we age is a long-lived open problem in evolutionary
biology. Aging is prejudicial to the individual and evolutionary forces should
prevent it, but many species show signs of senescence as individuals age. Here,
I will propose a model for aging based on assumptions that are compatible with
evolutionary theory: i) competition is between individuals; ii) there is some
degree of locality, so quite often competition will between parents and their
progeny; iii) optimal conditions are not stationary, mutation helps each
species to keep competitive. When conditions change, a senescent species can
drive immortal competitors to extinction. This counter-intuitive result arises
from the pruning caused by the death of elder individuals. When there is change
and mutation, each generation is slightly better adapted to the new conditions,
but some older individuals survive by random chance. Senescence can eliminate
those from the genetic pool. Even though individual selection forces always win
over group selection ones, it is not exactly the individual that is selected,
but its lineage. While senescence damages the individuals and has an
evolutionary cost, it has a benefit of its own. It allows each lineage to adapt
faster to changing conditions. We age because the world changes.Comment: 19 pages, 4 figure
Spectral analysis of the biharmonic operator subject to Neumann boundary conditions on dumbbell domains
We consider the biharmonic operator subject to homogeneous boundary
conditions of Neumann type on a planar dumbbell domain which consists of two
disjoint domains connected by a thin channel. We analyse the spectral behaviour
of the operator, characterizing the limit of the eigenvalues and of the
eigenprojections as the thickness of the channel goes to zero. In applications
to linear elasticity, the fourth order operator under consideration is related
to the deformation of a free elastic plate, a part of which shrinks to a
segment. In contrast to what happens with the classical second order case, it
turns out that the limiting equation is here distorted by a strange factor
depending on a parameter which plays the role of the Poisson coefficient of the
represented plate.Comment: To appear in "Integral Equations and Operator Theory
Gap modification of atomically thin boron nitride by phonon mediated interactions
A theory is presented for the modification of bandgaps in atomically thin
boron nitride (BN) by attractive interactions mediated through phonons in a
polarizable substrate, or in the BN plane. Gap equations are solved, and gap
enhancements are found to range up to 70% for dimensionless electron-phonon
coupling \lambda=1, indicating that a proportion of the measured BN bandgap may
have a phonon origin
In Defense of the Epistemic Imperative
Sample (2015) argues that scientists ought not to believe that their theories are true because they cannot fulfill the epistemic obligation to take the diachronic perspective on their theories. I reply that Sample’s argument imposes an inordinately heavy epistemic obligation on scientists, and that it spells doom not only for scientific theories but also for observational beliefs and philosophical ideas that Samples endorses. I also delineate what I take to be a reasonable epistemic obligation for scientists. In sum, philosophers ought to impose on scientists only an epistemic standard that they are willing to impose on themselves
Quantitative genetics of gastrointestinal strongyle burden and associated body condition in feral horses
This is the author accepted manuscript. The final version is available on open access from Elsevier via the DOI in this recordVariability in host resistance or tolerance to parasites is nearly ubiquitous, and is of key significance
in understanding the evolutionary processes shaping host-parasite interactions. While ample
research has been conducted on the genetics of parasite burden in livestock, relatively little has been
done in free-living populations. Here, we investigate the sources of (co)variation in strongyle
nematode faecal egg count (FEC) and body condition in Sable Island horses, a feral population in
which parasite burden has previously been shown to negatively correlate with body condition. We
used the quantitative genetic “animal model” to understand the sources of (co)variation in these
traits, and tested for impacts of an important spatial gradient in habitat quality on the parameter
estimates. Although FEC is significantly heritable (h
2 = 0.43 ± 0.11), there was no evidence for
significant additive genetic variation in body condition (h
2 = 0.04 ± 0.07), and therefore there was
also no significant genetic covariance between the two traits. The negative phenotypic covariance
between these traits therefore does not derive principally from additive genetic effects. We also
found that both FEC and body condition increase from east to west across the island, which
indicates that the longitudinal environmental gradient is not responsible for the negative phenotypic
association observed between these traits. There was also little evidence to suggest that quantitative
genetic parameters were biased when an individual’s location along the island’s environmental
gradient was not incorporated into the analysis. This research provides new and important insights
into the genetic basis and adaptive potential of parasite resistance in free-living animals, and
highlights the importance of environmental heterogeneity in modulating host-parasite interactions
in wild vertebrate systems.Natural Sciences and Engineering Research Council of CanadaCanada Foundation for InnovationRoyal Society International ExchangeRyan Dubé and Heather Ryan Veterinary and Research FundNSERC-CREATE Host-Parasite Interactions Training ProgramLeverhulme Trus
Distinguishing Dirac vs Majorana Neutrinos at CEνNS experiments
A transition magnetic moment between active and sterile neutrinos can induce the Primakoff upscattering process at the coherent elastic neutrino nucleus scattering experiments, leading to very stringent limits on the transition dipole coupling as a function of the sterile neutrino mass. Here we discuss how a novel radiative upscattering mode with an additional photon emitted in the final state can lead to exploration of new parameter space in the transition dipole coupling vs. sterile neutrino mass plane and provide distinguishable differential distributions for a Dirac vs Majorana sterile state mediating such a mode
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