5,471 research outputs found
The Lives of Stars: Insights From the TGAS-RAVE-LAMOST Dataset
In this paper we investigate how the chemical and kinematic properties of
stars vary as a function of age. Using data from a variety of photometric,
astrometric and spectroscopic surveys, we calculate the ages, phase space
information and orbits for 125,000 stars covering a wide range of stellar
parameters.
We find indications that the inner regions of the disk reached high levels of
enrichment early, while the outer regions were more substantially enriched in
intermediate and recent epochs. We consider these enrichment histories through
comparison of the ages of stars, their metallicities, and kinematic properties,
such as their angular momentum in the solar neighborhood (which is a proxy for
orbital radius). We calculate rates at which the velocity dispersions evolve,
investigate the Oort constants for different aged populations (finding a
slightly negative and for all ages, being most negative for the oldest stars), as well as examine
the behavior of the velocity vertex deviation angle as a function of age (which
we find to fall from 15 degrees for the 2 Gyr aged population to 6
degrees at around 6.5 Gyr of age, after which it remains unchanged). We find
evidence for stellar churning, and find that the churned stars have a slightly
younger age distribution than the rest of the data.Comment: 18 Pages, 14 Figures, Accepted Ap
Red Runaways: Hypervelocity Stars, Hills Ejecta and Other Outliers in the F-M Star Regime
In this paper we analyze a sample of metal-rich (>-0.8 dex) main sequence
stars in the extended solar neighborhood, investigating kinematic outliers from
the background population. The data, which are taken from the Sloan Digital Sky
Survey, are kinematically profiled as a function of distance from the Galactic
plane using full six dimensional phase space information. Each star is examined
in the context of these kinematic profiles and likelihoods are assigned to
quantify whether a star matches the underlying profile. Since some of these
stars are likely to have been ejected from the disc, we trace back their orbits
in order to determine potential ejection radii. We find that objects with low
probability (i.e. `outliers') are typically more metal poor, faster and, most
importantly, have a tendency to originate from the inner Galaxy compared to the
underlying population.
We also compose a sample of stars with velocities exceeding the local escape
velocity. Although we do not discount that our sample could be contaminated by
objects with spurious proper motions, a number of stars appear to have been
ejected from the disc with exceptionally high velocities. Some of these are
consistent with being ejected from the spiral arms and hence are a rich
resource for further study. Finally we look at objects whose orbits are
consistent with them being ejected at high speeds from the Galactic center. Of
these objects we find that one, J135855.65+552538.19, is inconsistent with
halo, bulge and disk kinematics and could plausibly have been ejected from the
Galactic nucleus via a Hills mechanism.Comment: 17 Pages, 12 Figures, Accepted to A
Alien Registration- Vickers, Mary C. (Gardiner, Kennebec County)
https://digitalmaine.com/alien_docs/29159/thumbnail.jp
Flow modifying device
A swirler for a gas turbine engine combustor is disclosed for simultaneously controlling combustor flow rate, swirl angle, residence time and fuel-air ratio to provide three regimes of operation. A first regime is provided in which fuel-air ratio is less than stoichiometric, NOx is produced at one level, and combustor flow rate is high. In a second regime, fuel-air ratio is nearly stoichiometric, NOx production is less than that of the first regime, and combustor flow rate is low. In a third regime, used for example at highoff, fuel-air ratio is greater than stoichiometric and the combustor flow rate is less than in either of the other regimes
LAMOST 1: A Disrupted Satellite in the Constellation Draco
Using LAMOST spectroscopic data, we find a strong signal of a comoving group
of stars in the constellation of Draco. The group, observed near the apocenter
of its orbit, is 2.6 kpc from the Sun with a metallicity of -0.64 dex. The
system is observed as a streaming population of unknown provenance with mass of
about 2.1E4 solar masses and an absolute V band magnitude of about -3.6. Its
high metallicity, diffuse physical structure, and eccentric orbit may indicate
that the progenitor satellite was a globular cluster rather than a dwarf galaxy
or an open cluster.Comment: 6 pages, 4 Figures, 1 Table, Accepted to ApJ
Evaluating recommended audiometric changes to candidacy using the speech intelligibility index
INTRODUCTION: The National Institute of Health and Care Excellence (NICE) has derived candidacy guidelines for cochlear implants in the UK based on audiometric thresholds (90 dB HL or above at 2 and 4 kHz; hereafter referred to as the 90 dB HL criteria). Recent research has proposed that these criteria should be changed to 80 dB HL at 2 and 4 kHz (hereafter referred to as the 80 dB HL criteria) in the ear to be implanted. METHODS: In this study, we analysed aided SII scores derived for different hearing loss profiles falling within the current 90 dB HL criteria and equivalent profiles falling within the new 80 dB HL criteria. RESULTS: The aided SII scores demonstrated that the majority of potential hearing configurations falling within the new proposed 80 dB HL criteria have aided SII values of less than 0.65 (a recommended cut-off point below which there is not sufficient audibility to receive adequate benefit through hearing aids). CONCLUSIONS: This supports the proposed change to the 80 dB HL criterion level and also highlights the additional value of the SII score in supporting candidacy decisions for CI, especially for borderline candidates
Public service innovation and multiple institutional logics: the case of hybrid social enterprise providers of health and wellbeing
Public sector organisations are confronted with growing health and social care needs in combination with severe resource constraints, prompting interest in innovative responses to such challenges. Public service and social innovation is poorly understood, particularly where innovators must navigate between the norms, practices and logics of public, private and civil society sectors. We contribute to the understanding of how innovating hybrid organisations are able to creatively combine co-existing logics. Case study evidence from newly established social enterprise providers of health and wellbeing services in England is utilised to examine how innovations are shaped by (i) an incumbent state or public sector logic, and two ‘challenger’ logics relating to (ii) the market and increasing competition; and (iii) civil society, emphasising social value and democratic engagement with employees and service users. The analysis shows how a more fluid and creative interplay of logics can be observed in relation to specific strategies and practices. Within organisations, these strategies relate to the empowerment of staff to be creative, financial management, and knowledge sharing and protection. The interplay of logics shaping social innovation is also found in relationships with key stakeholders, notably public sector funders, service users and service delivery partners. Implications are drawn for innovation in public services and hybrid organisations more broadly
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