982 research outputs found

    Suppression of carrier induced ferromagnetism by composition and spin fluctuations in diluted magnetic semiconductors

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    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 nin_i. Our approach permits to derive the equation for a critical temperature TcT_c of ferromagnetic phase transition with respect to the above fluctuations. We apply our theory to the analysis of influence of composition fluctuations on TcT_c in diluted magnetic semiconductors (DMS) with RKKY indirect spin-spin interaction.Comment: 6 pages, 2 figure

    Dementia in rural settings: A scoping review exploring the personal experiences of people with dementia and their carers

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    Rural areas tend to be inhabited by more older people and thus have a higher prevalence of dementia. Combined with lower population densities and more sparse geography, rural areas pose numerous barriers and costs relating to support and resource provision. This may leave people with dementia in rural places at a significant disadvantage, leading to a heavy reliance on informal support networks. The present study explores the personal experiences of people living with dementia and carers living in rural areas, seeking to discover both benefits and challenges, as well as recommendations within the literature for improving the lives of those affected by dementia in rural areas. A scoping review following the framework of Arksey and O'Malley identified 60 studies that describe or discuss the personal experience of dementia (either by the person with dementia or carer), in relation to living in rural or remote geographical areas. Four overarching themes were derived, namely the possible benefits of living in a rural community (supportive rural communities), sources of strength described by people affected by dementia in rural areas (managing and coping), detrimental aspects of living in a rural community (rural community challenges) and difficulties with dementia care services. Three further themes yielded recommendations for improving the experience of dementia in rural areas. This review highlights some potential opportunities related to living in rural areas for people living with dementia. These often come with parallel challenges, reflecting a delicate balance between being well-supported and being in crisis for those living in rural areas. Given the limited access to formal services, supporting people with dementia in rural areas requires input and innovation from the people, organisations and services local to those communities

    Nonintegrability of the two-body problem in constant curvature spaces

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    We consider the reduced two-body problem with the Newton and the oscillator potentials on the sphere S2{\bf S}^{2} and the hyperbolic plane H2{\bf H}^{2}. For both types of interaction we prove the nonexistence of an additional meromorphic integral for the complexified dynamic systems.Comment: 20 pages, typos correcte

    Spectral dependence of magnetooptical Kerr effect in EuS-based ferromagnetic semiconductor multilayers

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    The magnetooptical Kerr effect (MOKE) magnetometry was used to study the magnetic hysteresis loops of EuS-PbS and EuS-SrS semiconductor epitaxial multilayers composed of ferromagnetic layers of EuS and nonmagnetic ultrathin spacer layers of PbS or SrS. The spectral dependence of the MOKE in EuS-based semiconductor multilayers was studied in the photon energy range covering the fundamental interband electronic transitions in EuS. The measurements of the longitudinal MOKE established two maxima on the spectral dependence of the Kerr rotation for the photon energy hν of 1.65 eV and 2.1 eV. This experimental finding has been explained based on the model of the electronic band structure of EuS. The observed maxima of the Kerr rotation correspond to the electronic transitions from the localized 4f levels of Eu 2+ ions and from 3p valence band to the 5d6s conduction band of EuS

    Summer effects on body mass index (BMI) gain and growth patterns of American Indian children from kindergarten to first grade: a prospective study

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    <p>Abstract</p> <p>Background</p> <p>Overweight and obesity are highly prevalent among American Indian children, especially those living on reservations. There is little scientific evidence about the effects of summer vacation on obesity development in children. The purpose of this study was to investigate the effects of summer vacation between kindergarten and first grade on growth in height, weight, and body mass index (BMI) for a sample of American Indian children.</p> <p>Methods</p> <p>Children had their height and weight measured in four rounds of data collection (yielded three intervals: kindergarten, summer vacation, and first grade) as part of a school-based obesity prevention trial (Bright Start) in a Northern Plains Indian Reservation. Demographic variables were collected at baseline from parent surveys. Growth velocities (Z-score units/year) for BMI, weight, and height were estimated and compared for each interval using generalized linear mixed models.</p> <p>Results</p> <p>The children were taller and heavier than median of same age counterparts. Height Z-scores were positively associated with increasing weight status category. The mean weight velocity during summer was significantly less than during the school year. More rapid growth velocity in height during summer than during school year was observed. Obese children gained less adjusted-BMI in the first grade after gaining more than their counterparts during the previous two intervals. No statistically significant interval effects were found for height and BMI velocities.</p> <p>Conclusions</p> <p>There was no indication of a significant summer effect on children's BMI. Rather than seasonal or school-related patterns, the predominant pattern indicated by weight-Z and BMI-Z velocities might be related to age or maturation.</p> <p>Trial registration</p> <p>Bright Start: Obesity Prevention in American Indian Children Clinical Trial Govt ID# <a href="http://www.clinicaltrials.gov/ct2/show/NCT00123032">NCT00123032</a></p

    Observations and asteroseismic analysis of the rapidly pulsating hot B subdwarf PG 0911+456

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    The principal aim of this project is to determine the structural parameters of the rapidly pulsating subdwarf B star PG 0911+456 from asteroseismology. Our work forms part of an ongoing programme to constrain the internal characteristics of hot B subdwarfs with the long-term goal of differentiating between the various formation scenarios proposed for these objects. First comparisons of asteroseismic values with evolutionary theory look promising, however it is clear that more targets are needed for meaningful statistics to be derived. The observational pulsation periods of PG 0911+456 were extracted from rapid time-series photometry using standard Fourier analysis techniques. Supplemented by spectroscopic estimates of the star's mean atmospheric parameters, they were used as a basis for the "forward modelling" approach in asteroseismology. The latter culminates in the identification of one or more "optimal" models that can accurately reproduce the observed period spectrum. This naturally leads to an identification of the oscillations detected in terms of degree l and radial order k, and infers the structural parameters of the target. From the photometry it was possible to extract 7 independent pulsation periods in the 150-200 s range with amplitudes between 0.05 and 0.8 % of the star's mean brightness. An asteroseismic search of parameter space identified several models that matched the observed properties of PG 0911+456 well, one of which was isolated as the "optimal" model on the basis of spectroscopic and mode identification considerations. All the observed pulsations are identified with low-order acoustic modes with degree indices l=0,1,2 and 4, and match the computed periods with a dispersion of only ~0.26 %.Comment: accepted for publication in A&A, 14 pages, 13 figure
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