614 research outputs found
SAtlas: Spherical Versions of the Atlas Stellar Atmosphere Program
Context: The current stellar atmosphere programs still cannot match some
fundamental observations of the brightest stars, and with new techniques, such
as optical interferometry, providing new data for these stars, additional
development of stellar atmosphere codes is required. Aims: To modify the
open-source model atmosphere program Atlas to treat spherical geometry,
creating a test-bed stellar atmosphere code for stars with extended
atmospheres. Methods: The plane-parallel Atlas has been changed by introducing
the necessary spherical modifications in the pressure structure, in the
radiative transfer and in the temperature correction. Results: Several test
models show that the spherical program matches the plane-parallel models in the
high surface gravity regime, and matches spherical models computed by Phoenix
and by MARCS in the low gravity case.Comment: 10 pages, 10 figures, Accepted for publication in A&
Temperature dependent transport in suspended graphene
The resistivity of ultra-clean suspended graphene is strongly temperature
dependent for 5K<T<240K. At T~5K transport is near-ballistic in a device of
~2um dimension and a mobility ~170,000 cm^2/Vs. At large carrier density,
n>0.5*10^11 cm^-2, the resistivity increases with increasing T and is linear
above 50K, suggesting carrier scattering from acoustic phonons. At T=240K the
mobility is ~120,000 cm^2/Vs, higher than in any known semiconductor. At the
charge neutral point we observe a non-universal conductivity that decreases
with decreasing T, consistent with a density inhomogeneity <10^8 cm^-2
Conductivity of graphene: How to distinguish between samples with short and long range scatterers
Applying a quasiclassical equation to carriers in graphene we found a way how
to distinguish between samples with the domination of short and long range
scatterers from the conductivity measurements. The model proposed explains
recent transport experiments with chemically doped as well as suspended
graphene.Comment: 6 pages, 3 figures, some references have been corrected and revise
Vibrational Enhancement of the Effective Donor - Acceptor Coupling
The paper deals with a simple three sites model for charge transfer phenomena
in an one-dimensional donor (D) - bridge (B) - acceptor (A) system coupled with
vibrational dynamics of the B site. It is found that in a certain range of
parameters the vibrational coupling leads to an enhancement of the effective
donor - acceptor electronic coupling as a result of the formation of the
polaron on the B site. This enhancement of the charge transfer efficiency is
maximum at the resonance, where the effective energy of the fluctuating B site
coincides with the donor (acceptor) energy.Comment: 5 pages, 3 figure
Superconductivity coexisting with phase-separated static magnetic order in (Ba,K)FeAs, (Sr,Na)FeAs and CaFeAs
The recent discovery and subsequent developments of FeAs-based
superconductors have presented novel challenges and opportunities in the quest
for superconducting mechanisms in correlated-electron systems. Central issues
of ongoing studies include interplay between superconductivity and magnetism as
well as the nature of the pairing symmetry reflected in the superconducting
energy gap. In the cuprate and RE(O,F)FeAs (RE = rare earth) systems, the
superconducting phase appears without being accompanied by static magnetic
order, except for narrow phase-separated regions at the border of phase
boundaries. By muon spin relaxation measurements on single crystal specimens,
here we show that superconductivity in the AFeAs (A = Ca,Ba,Sr)
systems, in both the cases of composition and pressure tunings, coexists with a
strong static magnetic order in a partial volume fraction. The superfluid
response from the remaining paramagnetic volume fraction of
(BaK)FeAs exhibits a nearly linear variation in T
at low temperatures, suggesting an anisotropic energy gap with line nodes
and/or multi-gap effects.Comment: 14 pages 7 figures (4 for main text and 3 for on-line supplementary
documents
Methodological approaches to determining the marine radiocarbon reservoir effect
The marine radiocarbon reservoir effect is an offset in 14C age between contemporaneous organisms from the terrestrial environment and organisms that derive their carbon from the marine environment. Quantification of this effect is of crucial importance for correct calibration of the <sup>14</sup>C ages of marine-influenced samples to the calendrical timescale. This is fundamental to the construction of archaeological and palaeoenvironmental chronologies when such samples are employed in <sup>14</sup>C analysis. Quantitative measurements of temporal variations in regional marine reservoir ages also have the potential to be used as a measure of process changes within Earth surface systems, due to their link with climatic and oceanic changes. The various approaches to quantification of the marine radiocarbon reservoir effect are assessed, focusing particularly on the North Atlantic Ocean. Currently, the global average marine reservoir age of surface waters, R(t), is c. 400 radiocarbon years; however, regional values deviate from this as a function of climate and oceanic circulation systems. These local deviations from R(t) are expressed as +R values. Hence, polar waters exhibit greater reservoir ages (δR = c. +400 to +800 <sup>14</sup>C y) than equatorial waters (δR = c. 0 <sup>14</sup>C y). Observed temporal variations in δR appear to reflect climatic and oceanographic changes. We assess three approaches to quantification of marine reservoir effects using known age samples (from museum collections), tephra isochrones (present onshore/offshore) and paired marine/terrestrial samples (from the same context in, for example, archaeological sites). The strengths and limitations of these approaches are evaluated using examples from the North Atlantic region. It is proposed that, with a suitable protocol, accelerator mass spectrometry (AMS) measurements on paired, short-lived, single entity marine and terrestrial samples from archaeological deposits is the most promising approach to constraining changes over at least the last 5 ky BP
'It would be easier if sheâd diedâ: young people with parents with dementia articulating inadmissible stories
In the U.K. context where the emphasis is (quite rightly) on living well with dementia, on positivity and enabling
approaches, it can be difficult for researchers to investigate and report negative experiences. Failing to re-present
perceptions and experiences as they are lived, however, does a serious disservice to the research endeavor and can
prevent policy and service development and positive change. In this article, we present some stories told by participants
in an Alzheimerâs Society (United Kingdom) Funded project uniquely investigating the perceptions and experiences of
children and young people who have a parent with dementia. Sometimes the stories were not easy to hear, especially
when they challenged dominant master narratives around dementia. We discuss our view that when the young people
we spoke with told us how things were for them, we were ethically bound to respect and disseminate their accounts
Am I just not good enough? The creation, development and questioning of a high performance coaching identity
While the career experiences and trajectories of various sports workers have received increased scholarly attention, those of professional coaches have, in comparison, received scant consideration. This paper focuses on the career experiences of Maeve (a pseudonym), a high performance coach, and the critical incidents related to the creation, development, and, ultimately, questioning of her professional identity. Data were collected through a series of narrative-biographical interviews and were subject to a process of iterative data analysis. The results indicated that her significant investment into her coaching self, combined with the vagaries and uncertain nature of work in high performance coaching, led her to experience a biographical disruption that interrupted the narrative coherence of her coaching life. The findings add further credence to recent critiques of only understanding and representing coaching careers in a linear and chronically staged fashion
"From âWhat the hell is going on?â to the âMushy middle groundâ to âgetting used to a new normalâ: Young peopleâs biographical narratives around navigating parental dementia"
The number of young people who have a parent with dementia is rising as a result of improvements in diagnosis of young onset variants and demographic shifts. There has, however, been very little research focusing on this group. Accounts elicited as part of the Perceptions and Experiences of Young People With a Parent With Dementia described the period, usually some years, leading up to a diagnosis of a dementia and then the progress of the condition post diagnosis. These narratives were characterised by confusion, uncertainty, trauma and distress as the young people struggled to make sense of the significant and often extreme, behavioural and attitudinal changes that were symptoms of the illness. This paper describes and discusses how the young people experienced and navigated the temporal messiness and consequent biographical disruption arising from parental dementia
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