9,667 research outputs found

    The planetary nebula Abell 48 and its [WN] nucleus

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    We have conducted a detailed multi-wavelength study of the peculiar nebula Abell 48 and its central star. We classify the nucleus as a helium-rich, hydrogen-deficient star of type [WN4-5]. The evidence for either a massive WN or a low-mass [WN] interpretation is critically examined, and we firmly conclude that Abell 48 is a planetary nebula (PN) around an evolved low-mass star, rather than a Population I ejecta nebula. Importantly, the surrounding nebula has a morphology typical of PNe, and is not enriched in nitrogen, and thus not the `peeled atmosphere' of a massive star. We estimate a distance of 1.6 kpc and a reddening, E(B-V) = 1.90 mag, the latter value clearly showing the nebula lies on the near side of the Galactic bar, and cannot be a massive WN star. The ionized mass (~0.3 M_Sun) and electron density (700 cm^-3) are typical of middle-aged PNe. The observed stellar spectrum was compared to a grid of models from the Potsdam Wolf-Rayet (PoWR) grid. The best fit temperature is 71 kK, and the atmospheric composition is dominated by helium with an upper limit on the hydrogen abundance of 10 per cent. Our results are in very good agreement with the recent study of Todt et al., who determined a hydrogen fraction of 10 per cent and an unusually large nitrogen fraction of ~5 per cent. This fraction is higher than any other low-mass H-deficient star, and is not readily explained by current post-AGB models. We give a discussion of the implications of this discovery for the late-stage evolution of intermediate-mass stars. There is now tentative evidence for two distinct helium-dominated post-AGB lineages, separate to the helium and carbon dominated surface compositions produced by a late thermal pulse. Further theoretical work is needed to explain these recent discoveries.Comment: 19 pages, 10 figures, to appear in MNRAS. Version 3 incorporates proof correction

    High resolution characterisation of microstructural evolution in Rbx_{x}Fe2y_{2-y}Se2_{2} crystals on annealing

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    The superconducting and magnetic properties of phase-separated Ax_xFe2y_{2-y}Se2_2 compounds are known to depend on post-growth heat treatments and cooling profiles. This paper focusses on the evolution of microstructure on annealing, and how this influences the superconducting properties of Rbx_xFe2y_2-ySe2_2 crystals. We find that the minority phase in the as-grown crystal has increased unit cell anisotropy (c/a ratio), reduced Rb content and increased Fe content compared to the matrix. The microstructure is rather complex, with two-phase mesoscopic plate-shaped features aligned along {113} habit planes. The minority phase are strongly facetted on the {113} planes, which we have shown to be driven by minimising the volume strain energy introduced as a result of the phase transformation. Annealing at 488K results in coarsening of the mesoscopic plate-shaped features and the formation of a third distinct phase. The subtle differences in structure and chemistry of the minority phase(s) in the crystals are thought to be responsible for changes in the superconducting transition temperature. In addition, scanning photoemission microscopy has clearly shown that the electronic structure of the minority phase has a higher occupied density of states of the low binding energy Fe3d orbitals, characteristic of crystals that exhibit superconductivity. This demonstrates a clear correlation between the Fe-vacancy-free phase with high c/a ratio and the electronic structure characteristics of the superconducting phase.Comment: 6 figures v2 is exactly the same as v1. The typesetting errors in the abstract have been correcte

    Beam lead technology

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    Beam lead technology for microcircuit interconnections with applications to metallization, passivation, and bondin

    Business Value Is not only Dollars - Results from Case Study Research on Agile Software Projects

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    Business value is a key concept in agile software development. This paper presents results of a case study on how business value and its creation is perceived in the context of agile projects. Our overall conclusion is that the project participants almost never use an explicit and structured approach to guide the value creation throughout the project. Still, the application of agile methods in the studied cases leads to satisfied clients. An interesting result of the study represents the fact that the agile process of many projects differs significantly from what is described in the agile practitioners’ books as best practices. The key implication for research and practice is that we have an incentive to pursue the study of value creation in agile projects and to complement it by providing guidelines for better client’s involvement, as well as by developing structured methods that will enhance the value-creation in a project

    Life satisfaction and musculoskeletal complaints in a population seeking osteopathy care: consecutive sample of 611 patients.

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    BackgroundLife satisfaction is a component of the subjective well-being construct. Research consistently suggests that life satisfaction is associated with enhanced social benefits and improved health outcomes. However, its relationship to musculoskeletal health outcomes is underexplored. This study evaluates the life satisfaction of a patient population presenting with musculoskeletal complaints, and the relationship of life satisfaction with other health demographics and behaviours.MethodThe study used a consecutive sampling design. Patients attending the Victoria University Osteopathy Clinic (Melbourne, Australia) were invited to complete the PROMIS® General Life Satisfaction scale (GLSS) along with questions related to health demographics and behaviours.ResultsThe GLSS T-score was not significantly different for gender, being born outside of Australia, speaking English at home, or complaint chronicity.ConclusionsLife satisfaction did not appear to be related to a range of health and demographic variables in the current musculoskeletal pain cohort. The PROMIS® General Life Satisfaction scale could prove useful to explore the relationship between life satisfaction and treatment outcomes for musculoskeletal complaints

    Defective pro-IL-1beta responses in macrophages from aged mice

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    BACKGROUND: Cytokines regulated by the inflammasome pathway have been extensively implicated in various age-related immune pathologies. We set out to elucidate the contribution of the nod-like receptor protein 3 (NLRP3) inflammasome pathway to the previously described deficiencies in IL-1beta production by macrophages from aged mice. We examined the production of pro-IL-1beta and its conversion into IL-1beta as two separate steps and compared these cytokine responses in bone marrow derived macrophages from young (6-8 weeks) and aged (18-24 months) C57BL/6 mice. FINDINGS: Relative to macrophages from young mice, macrophages from aged mice produced less pro-IL-1beta after TLR4 stimulation with LPS. However upon activation of the NLRP3 inflammasome with ATP, macrophages from young and aged mice were able to efficiently convert and secrete intracellular pro-cytokines as functional cytokines. CONCLUSIONS: Lower levels of IL-1beta production are a result of slower and lower overall production of pro-IL-1beta in macrophages from aged mice

    Major outcomes of an authentic astronomy research experience professional development program: An analysis of 8 years of data from a teacher research program

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    The NASA/IPAC Teacher Archive Research Program (NITARP) provides a year-long authentic astronomy research project by partnering a research astronomer with small groups of educators. NITARP has worked with a total of 103 educators since 2005. In this paper, surveys are explored that were obtained from 74 different educators, at up to four waypoints during the course of 13 months, from the class of 2010 through the class of 2017; those surveys reveal how educator participants describe the major changes and outcomes in themselves fostered by NITARP. Three-quarters of the educators self-report some or major changes in their understanding of the nature of science. The program provides educators with experience collaborating with astronomers and other educators, and forges a strong link to the astronomical research community; the NITARP community of practice encourages and reinforces these linkages. During the experience, educators get comfortable with learning complex new concepts, with ∼40% noting in their surveys that their approach to learning has changed. Educators are provided opportunities for professional growth; at least 12% have changed career paths substantially in part due to the program, and 14% report that the experience was “life changing.” At least 60% express a desire to include richer, more authentic science activities in their classrooms. This work illuminates what benefits the program brings to its participants; the NITARP approach could be mirrored in similar professional development programs in other STEM subjects
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