1,797 research outputs found
Suppression of carrier induced ferromagnetism by composition and spin fluctuations in diluted magnetic semiconductors
We suggest an approach to account for spatial (composition) and thermal
fluctuations in "disordered" magnetic models (e.g. Heisenberg, Ising) with
given spatial dependence of magnetic spin-spin interaction. Our approach is
based on introduction of fluctuating molecular field (rather than mean field)
acting between the spins. The distribution function of the above field is
derived self-consistently. In general case this function is not Gaussian,
latter asymptotics occurs only at sufficiently large spins (magnetic ions)
concentrations . Our approach permits to derive the equation for a
critical temperature of ferromagnetic phase transition with respect to
the above fluctuations. We apply our theory to the analysis of influence of
composition fluctuations on in diluted magnetic semiconductors (DMS) with
RKKY indirect spin-spin interaction.Comment: 6 pages, 2 figure
Reconstruction, rumpling, and Dirac states at the (001) surface of a topological crystalline insulator Pb1-xSnxSe
Equilibrium atomic configuration and electronic structure of the (001)
surface of IV-VI semiconductors PbTe, PbSe, SnTe and SnSe, is studied using the
density functional theory (DFT) methods. At surfaces of all those compounds,
the displacements of ions from their perfect lattice sites reveal two features
characteristic of the rock salt crystals. First, the ionic displacements occur
only along the direction perpendicular to the surface, and they exhibit the
rumpling effect, i.e., the vertical shifts of cations and anions differ.
Second, the interlayer spacing of the first few monolayers at the surface
oscillates. Our results are in good agreement with the previous X-ray
experimental data and theoretical results where available. They also are
consistent with the presence of two {110} mirror planes at the (001) surface of
the rock salt. One the other hand, experiments preformed for the topological
PbSn Se alloy indicate breaking of the mirror symmetry due to a
large 0.3 {\AA} relative displacement of the cation and anion sublattices at
the surface, which induces the opening of the gap of the Dirac cones. Our
results for PbSnSe including the simulated STM images, are in
contradiction with these findings, since surface reconstructions with broken
symmetry are never the ground state configurations. The impact of the
theoretically determined surface configurations and of the chemical disorder on
the surface states is analyzed.Comment: 9 pages, 11 figure
Influenza vaccination, inverse care and homelessness: cross-sectional survey of eligibility and uptake during the 2011/12 season in London
Background:
Influenza vaccination eligibility and uptake among homeless adults has not been previously assessed in the UK. This cross-sectional survey aimed to measure the proportion of homeless people visited by an NHS outreach service (Find and Treat) who were eligible for and had received vaccination during 2011/12.
Methods:
A cross-sectional survey was carried out in 27 separate homeless hostels, day centres and drug services in London between July and August in 2012. Eligibility for the survey was by virtue of being in attendance at one of 27 venues visited by Find and Treat. No specific exclusion criteria were used.
Results:
455 clients took part in the survey out of 592 approached (76.9%). A total of 190 homeless people (41.8%; 95% CI: 34.5,50.5) were eligible for influenza vaccination. In those aged 16–64, eligibility due to clinical risk factors was 38.9% (95% CI: 31.5,48.2). Uptake of vaccination in homeless 16–64 year olds with a clinical risk factor during the 2011/12 influenza season was 23.7% (95% CI: 19.8,28.3) compared to national levels of 53.2% (excluding pregnant women). In those aged over 65, uptake was 42.9% (95% CI: 16.7,100.0) compared with 74.0% nationally.
Conclusions:
This study demonstrates that the homeless population have high levels of chronic health problems predisposing them to severe complications of influenza, but vaccine uptake levels that are less than half those seen among eligible GP patient groups in England. It provides a clear example of the health inequalities and inverse care law that impact this population. The results of this study provide strong justification for intensifying efforts to ensure homeless people have access to influenza vaccination
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