1,181 research outputs found
Spin Echo Decay in a Stochastic Field Environment
We derive a general formalism with which it is possible to obtain the time
dependence of the echo size for a spin in a stochastic field environment. Our
model is based on ``strong collisions''. We examine in detail three cases
where: (I) the local field is Ising-like, (II) the field distribution is
continuous and has a finite second moment, and (III) the distribution is
Lorentzian. The first two cases show a T2 minimum effect and are exponential in
time cubed for short times. The last case can be approximated by a
phenomenological stretched exponential.Comment: 11 pages + 3 postscript figure
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Operationalising and measuring language dominance
The paper offers a new way to measure language ability in bilinguals, based on measures of lexical richness. The validity of proposed approach is tested in a variety of ways
Parents' postnatal depressive symptoms and their children's academic attainment at 16 years: Pathways of risk transmission
This is the author accepted manuscript. The final version is available from Wiley via the DOI in this record.The aim of the study was to examine whether parentsâ increased postnatal depressive symptoms predicted
childrenâs academic attainment over time, and whether the parent-child relationship, childrenâs prior
academic attainment and mental health mediated this association.
We conducted secondary analyses on the Avon Longitudinal Study of Parents and Children data (12,607
mothers, 9,456 fathers). Each parent completed the Edinburgh-Postnatal Depression Scale at 8 weeks after
the childâs birth (predictor) and a questionnaire about the mother-child and father-child relationship at 7
years and 1 month (mediator). The childrenâs mental health problems were assessed with the teacher version
of the Strengths and Difficulties Questionnaire at 10-11 years (mediator). We used data on the childrenâs
academic attainment on UK Key Stage 1 (5-7 years; mediator) and Key Stage 4 (General Certificate of
Secondary Education (GCSE)16 years) (outcome). We adjusted for the parentsâ education, and child gender
and cognitive ability.
The results revealed that parentsâ depressive symptoms at 8 weeks predicted lower academic performance in
children at 16 years. Mothersâ postnatal depressive symptoms had an indirect effect through childrenâs
mental health problems on academic outcomes at 16 years via negative mother-child relationship, and prior
academic attainment. There was a significant negative indirect effect of fathersâ postnatal depressive
symptoms on academic attainment at 16 years via negative father-child relationship on child mental health.
The findings suggest that the family environment (parental mental health and parent-child relationship) and
childrenâs mental health should be potential targets for support programmes for children of depressed
parents.Medical Research Council (MRC)Wellcome Trus
Subwavelength grating metamaterial waveguides and ring resonators on a silicon nitride platform
We propose and demonstrate subwavelength grating (SWG) metamaterial
waveguides and ring resonators on a silicon nitride platform for the first
time. The SWG waveguide is engineered such that a large overlap of 53% of the
Bloch mode with the top cladding material is achieved, demonstrating excellent
potential for applications in evanescent field sensing and light amplification.
The devices, which have critical dimensions greater than 100 nm, are fabricated
using a commercial rapid turn-around silicon nitride prototyping foundry
process using electron beam lithography. Experimental characterization of the
fabricated device reveals excellent ring resonator internal quality factor
(2.11x10^5) and low propagation loss (~1.5 dB/cm) in the C-band, a significant
improvement of both parameters compared to silicon based SWG ring resonators.
These results demonstrate the promising prospects of SWG metamaterial
structures for silicon nitride based photonic integrated circuits.Comment: 12 pages, 7 figures, submitted to Laser & Photonics Reviews for
publicatio
Vortex State of TlBaCuO via Tl NMR at 2 Tesla
We report a Tl NMR study of vortex state for an aligned
polycrystalline sample of an overdoped high- superconductor
TlBaCuO (85 K) with magnetic field 2 T along
the c axis. We observed an imperfect vortex lattice, so-called Bragg glass at
=5 K, coexistence of vortex solid with liquid between 10 and 60 K, and
vortex melting between 65 and 85 K. No evidence for local antiferromagnetic
ordering at vortex cores was found for our sample.Comment: 4 pages with 5 figure
Superconducting Fluctuations and the Pseudogap in the Slightly-overdoped High-Tc Superconductor TlSr2CaCu2O6.8: High Magnetic Field NMR Studies
From measurements of the ^{63}Cu Knight shift (K) and the nuclear
spin-lattice relaxation rate (1/T_{1}) under magnetic fields from zero up to 28
T in the slightly overdoped superconductor TlSr_{2}CaCu_{2}O_{6.8} (T_{c}=68
K), we find that the pseudogap behavior, {\em i.e.}, the reductions of 1/T_{1}T
and K above T_{c} from the values expected from the normal state at high T, is
strongly field dependent and follows a scaling relation. We show that this
scaling is consistent with the effects of the Cooper pair density fluctuations.
The present finding contrasts sharply with the pseudogap property reported
previously in the underdoped regime where no field effect was seen up to 23.2
T. The implications are discussed.Comment: 10 pages, 4 GIF figures, to be published in Phys. Rev. Let
Green Plants in the Red: A Baseline Global Assessment for the IUCN Sampled Red List Index for Plants
Plants provide fundamental support systems for life on Earth and are the basis for all terrestrial ecosystems; a decline in plant diversity will be detrimental to all other groups of organisms including humans. Decline in plant diversity has been hard to quantify, due to the huge numbers of known and yet to be discovered species and the lack of an adequate baseline assessment of extinction risk against which to track changes. The biodiversity of many remote parts of the world remains poorly known, and the rate of new assessments of extinction risk for individual plant species approximates the rate at which new plant species are described. Thus the question âHow threatened are plants?â is still very difficult to answer accurately. While completing assessments for each species of plant remains a distant prospect, by assessing a randomly selected sample of species the Sampled Red List Index for Plants gives, for the first time, an accurate view of how threatened plants are across the world. It represents the first key phase of ongoing efforts to monitor the status of the worldâs plants. More than 20% of plant species assessed are threatened with extinction, and the habitat with the most threatened species is overwhelmingly tropical rain forest, where the greatest threat to plants is anthropogenic habitat conversion, for arable and livestock agriculture, and harvesting of natural resources. Gymnosperms (e.g. conifers and cycads) are the most threatened group, while a third of plant species included in this study have yet to receive an assessment or are so poorly known that we cannot yet ascertain whether they are threatened or not. This study provides a baseline assessment from which trends in the status of plant biodiversity can be measured and periodically reassessed
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