904 research outputs found

    Is 6-Li in metal-poor halo stars produced in situ by solar-like flares ?

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    The high 6-Li abundances recently measured in metal-poor halo stars are far above the value predicted by Big Bang nucleosynthesis. They cannot be explained by galactic cosmic-ray interactions in the interstellar medium either. Various pre-galactic sources of 6-Li have been proposed in the literature. We study the possibility that the observed 6-Li was produced by repeated solar-like flares on the main sequence of these low-metallicity stars. The time-dependent flaring activity of these objects is estimated from the observed evolution of rotation-induced activity in Pop I dwarf stars. As in solar flares, 6-Li could be mainly created in interactions of flare-accelerated 3-He with stellar atmospheric 4-He, via the reaction 4-He(3-He,p)6-Li. Stellar dilution and destruction of flare-produced 6-Li are evaluated from the evolutionary models of metal-poor stars developed by Richard and co-workers. Stellar depletion should be less important for 6-Li atoms synthesized in flares than for those of protostellar origin. Theoretical frequency distributions of 6-Li/7-Li ratios are calculated using a Monte-Carlo method and compared with the observations. Excellent agreement is found with the measured 6-Li/7-Li distribution, when taking into account the contribution of protostellar 6-Li originating from galactic cosmic-ray nucleosynthesis. We propose as an observational test of the model to seek for a positive correlation between 6-Li/7-Li and stellar rotation velocity. We also show that the amounts of 7-Li, Be and B produced in flares of metal-poor halo stars are negligible as compared with the measured abundances of these species. 6-Li in low-metallicity stars may be a unique evidence of the nuclear processes occuring in stellar flares

    Being seen in your pyjamas : the relationship between fashion, class, gender and space

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    Over the last decade class has re-emerged as a significant concept within British sociology, with prominent academics calling for a more Bourdieuian approach which focuses on class distinctions in cultural practices and tastes. Within this discussion, several note the important role fashion plays as a means of class distinction, though few have fully explore just how the fashion-class relationship operates. Based on empirical research, carried out as part of qualitative study into fashion practices and fashion discourse, this article examines the fashion-class relationship, by considering its links to both gender and space. It argues that the way in which women judge visibility and public space differs with class status and that this in turn has significant implications for women's fashion choices, and more specifically, dressing up. Indeed, whilst middle class participants tend to view almost any space as public and one in which they are visible, for working class participants neighbourhood and local spaces are seen to constitute semi-private spaces, whose audiences' opinions and judgements do not matter. As a result, being dressed in your pyjamas is not deeply problematic for these working class women in the context of their everyday lives, while for their middle class counterparts being seen in your pyjamas is something which should be avoided, at all cost. Moreover, as the article demonstrate, the wearing of pyjamas is often considered by middle class respondents as indicative of working classness. And thus, being seen in your pyjamas is undesirable on two counts

    ÉTUDE THÉORIQUE DU SPECTRE D'UN RAYONNEMENT GAMMA ÉMIS LORS D'UNE RÉACTION NUCLÉAIRE MESURES DE VIES MOYENNES

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    A l'aide des détecteurs à semi-conducteur, il s'est avéré possible de mesurer le spectre continu d'un rayonnement gamma émis lors d'une réaction nucléaire. Ce spectre, dû à l'effet Doppler, est fonction de la vie moyenne de l'état initial de la transition électromagnétique. Les résultats expérimentaux obtenus permettent d'envisager la mesure de vies moyennes

    Lithium-6 from Solar Flares

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    By introducing a hitherto ignored Li-6 producing process, due to accelerated He-3 reactions with He-4, we show that accelerated particle interactions in solar flares produce much more Li-6 than Li-7. By normalizing our calculations to gamma-ray data we demonstrate that the Li-6 produced in solar flares, combined with photospheric Li-7, can account for the recently determined solar wind lithium isotopic ratio, obtained from measurements in lunar soil, provided that the bulk of the flare produced lithium is evacuated by the solar wind. Further research in this area could provide unique information on a variety of problems, including solar atmospheric transport and mixing, solar convection and the lithium depletion issue, and solar wind and solar particle acceleration.Comment: latex 9 pages, 2 figures, ApJ Letters in pres

    Earthworm management in tropical agroecosystems

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    Data of 145 and 69 earthworm communities from managed and natural ecosystems, respectively, of four continents and 15 tropical countries were analysed. The aim of the study was to separate the influence of phylogenetic, environmental and agricultural factors on the structure of earthworm communities in agroecosystems, and to evaluate their relative importance in the whole soil macrofauna community. Earthworms comprise 40-90% of macrofaunal biomass in most ecosystems except for annually cropped systems. Three major conclusions were drawn from the analysis of community structure (regional analysis) : (i) crops were, independently of region, characterized by a loss of native species and by the dominance of exotic endogeics ; (ii) pastures were highly heterogenous in terms of native or exotic species dominance ; (iii) native species survived better in management ecosystems of India and Africa than in Mexico-Central America. Local analysis in selected countries indicated that, as a general rule, the intensity of agricultural practices is negatively correlated with the amount of native species and the total abundance and biomass of earthworms ; the only exception was found in the conversion of savannas to pastures, in Colombian llanos. (Résumé d'auteur

    Comparison of low--energy resonances in 15N(alpha,gamma)19F and 15O(alpha,gamma)19Ne and related uncertainties

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    A disagreement between two determinations of Gamma_alpha of the astro- physically relevant level at E_x=4.378 MeV in 19F has been stated in two recent papers by Wilmes et al. and de Oliveira et al. In this work the uncertainties of both papers are discussed in detail, and we adopt the value Gamma_alpha=(1.5^{+1.5}_{-0.8})10^-9eV for the 4.378 MeV state. In addition, the validity and the uncertainties of the usual approximations for mirror nuclei Gamma_gamma(19F) approx Gamma_gamma(19Ne), theta^2_alpha(19F) approx theta^2_alpha(19Ne) are discussed, together with the resulting uncertainties on the resonance strengths in 19Ne and on the 15O(alpha,gamma)19Ne rate.Comment: 9 pages, Latex, To appear in Phys. Rev.

    In vivo stem cell tracking using scintigraphy in a canine model of DMD

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    One of the main challenges in cell therapy for muscle diseases is to efficiently target the muscle. To address this issue and achieve better understanding of in vivo cell fate, we evaluated the relevance of a non-invasive cell tracking method in the Golden Retriever Muscular Dystrophy (GRMD) model, a well-recognised model of Duchenne Muscular Dystrophy (DMD). Mesoangioblasts were directly labelled with 111In-oxine, and injected through one of the femoral arteries. The scintigraphy images obtained provided the first quantitative mapping of the immediate biodistribution of mesoangioblasts in a large animal model of DMD. The results revealed that cells were trapped by the first capillary filters: the injected limb and the lung. During the days following injection, radioactivity was redistributed to the liver. In vitro studies, performed with the same cells prepared for injecting the animal, revealed prominent cell death and 111In release. In vivo, cell death resulted in 111In release into the vasculature that was taken up by the liver, resulting in a non-specific and non-cell-bound radioactive signal. Indirect labelling methods would be an attractive alternative to track cells on the mid- and long-term
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