6,670 research outputs found

    Assessing the contribution of Centaur impacts to ice giant luminosities

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    Voyager 2 observations revealed that the internal luminosity of Neptune is an order of magnitude higher than that of Uranus. If the two planets have similar interior structures and cooling histories, the luminosity of Neptune can only be explained by invoking some energy source beyond gravitational contraction. This paper investigates whether Centaur impacts could provide the energy necessary to produce the luminosity of Neptune. The major findings are (1) that impacts on both Uranus and Neptune are too infrequent to provide luminosities of order the observed value for Neptune, even for optimistic impact-rate estimates, and (2) that Uranus and Neptune rarely have significantly different impact-generated luminosities at any given time. Uranus and Neptune most likely have structural differences that force them to cool and contract at different rates.Comment: 19 pages, including 4 figures. Accepted for publication in Icaru

    Nursing education and regulation: international profiles and perspectives

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    This review of nurse education and regulation in selected OECD countries forms part of ongoing work on contemporary nursing careers and working lives, based at the National Nursing Research Unit, King’s College London. The review was commissioned by the Department of Health to inform their work in considering the UK’s position in relation to the Bologna declaration and changes that may emanate from the implementation of Modernising Nursing Careers (DH 2006). While much of the information in the review was obtained from publications and websites, we also contacted key personnel in most of the countries included for an up-to-date review of developments in their country and would like to thank them all for providing this information

    In search of an international experience: Towards a 'Bildung' understanding of MBA learning

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    Detection of Low Mass-ratio Stellar Binary Systems

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    O- and B-type stars are often found in binary systems, but the low binary mass-ratio regime is relatively unexplored due to observational difficulties. Binary systems with low mass-ratios may have formed through fragmentation of the circumstellar disk rather than molecular cloud core fragmen- tation. We describe a new technique sensitive to G- and K-type companions to early B stars, a mass-ratio of roughly 0.1, using high-resolution, high signal-to-noise spectra. We apply this technique to a sample of archived VLT/CRIRES observations of nearby B-stars in the CO bandhead near 2300 nm. While there are no unambiguous binary detections in our sample, we identify HIP 92855 and HIP 26713 as binary candidates warranting follow-up observations. We use our non-detections to determine upper limits to the frequency of FGK stars orbiting early B-type primaries.Comment: 13 pages, 7 figures Accepted to the Astrophysical Journa

    A Correlation Between the Eclipse Depths of Kepler Gas Giant Candidates and the Metallicities of their Parent Stars

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    Previous studies of the interior structure of transiting exoplanets have shown that the heavy element content of gas giants increases with host star metallicity. Since metal-poor planets are less dense and have larger radii than metal-rich planets of the same mass, one might expect that metal-poor stars host a higher proportion of gas giants with large radii than metal-rich stars. Here I present evidence for a negative correlation at the 2.3-sigma level between eclipse depth and stellar metallicity in the Kepler gas giant candidates. Based on Kendall's tau statistics, the probability that eclipse depth depends on star metallicity is 0.981. The correlation is consistent with planets orbiting low-metallicity stars being, on average, larger in comparison with their host stars than planets orbiting metal-rich stars. Furthermore, since metal-rich stars have smaller radii than metal-poor stars of the same mass and age, a uniform population of planets should show a rise in median eclipse depth with [M/H]. The fact that I find the opposite trend indicates that substantial changes in gas giant interior structure must accompany increasing [M/H]. I investigate whether the known scarcity of giant planets orbiting low-mass stars could masquerade as an eclipse depth-metallicity correlation, given the degeneracy between metallicity and temperature for cool stars in the Kepler Input Catalog. While the eclise depth-metallicity correlation is not yet on firm statistical footing and will require spectroscopic [Fe/H] measurements for validation, it is an intriguing window into how the interior structure of planets and even the planet formation mechanism may be changing with Galactic chemical evolution.Comment: Accepted for publication in the Astrophysical Journal. 13 pages total, including 6 text pages, 5 figures and 2 table

    Photophoresis boosts giant planet formation

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    In the core accretion model of giant planet formation, a solid protoplanetary core begins to accrete gas directly from the nebula when its mass reaches about 5 earth masses. The protoplanet has at most a few million years to reach runaway gas accretion, as young stars lose their gas disks after 10 million years at the latest. Yet gas accretion also brings small dust grains entrained in the gas into the planetary atmosphere. Dust accretion creates an optically thick protoplanetary atmosphere that cannot efficiently radiate away the kinetic energy deposited by incoming planetesimals. A dust-rich atmosphere severely slows down atmospheric cooling, contraction, and inflow of new gas, in contradiction to the observed timescales of planet formation. Here we show that photophoresis is a strong mechanism for pushing dust out of the planetary atmosphere due to the momentum exchange between gas and dust grains. The thermal radiation from the heated inner atmosphere and core is sufficient to levitate dust grains and to push them outward. Photophoresis can significantly accelerate the formation of giant planets.Comment: accepted in Astronomy and Astrophysics, 201

    Fulfilling Lives: Supporting people with multiple needs, Evaluation Report, Year 1

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    This report is prepared for the Big Lottery Fund (the Fund) by the national evaluationteam and provides emerging findings and lessons learned from the first year of thenational evaluation of the Fulfilling Lives: Supporting people with multiple needsinitiative hereafter referred to as Fulfilling Lives (multiple needs).The national evaluation has been designed to determine the degree to which the initiativeis successfully achieving its aims and how they are being achieved. The evaluation will beboth formative and summative in nature, in that, it will inform the ongoing design and delivery of Fulfilling Lives (multiple needs) and its component projects as well as assessoverall achievements and value for money to inform future decision and policy making.Within this context, the evaluation has a number of objectives:— To track and assess the achievements of the initiative and to estimate the extent to whichthese are attributable to the projects and interventions delivered.— To calculate the costs of the projects and the corresponding value of benefits to theexchequer and wider society. This will enable an assessment of value for money of theprogramme and for individual interventions.— To identify what interventions and approaches work well, for which people, families andcommunities and in which circumstances and contexts.— To assess the extent to which the Big Lottery Fund's principles are incorporated into projectdesign and delivery and to determine the degree to which these principles affect successfuldelivery and outcomes.— To explore project implementation, understand problems faced and to facilitate theidentification of solutions and lessons learned
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