36,524 research outputs found
Discovery of secular variations in the atmospheric abundances of magnetic Ap stars
The stars of the middle main sequence have relatively quiescent outer layers,
and unusual chemical abundance patterns may develop in their atmospheres. The
presence of chemical peculiarities reveal the action of such subsurface
phenomena as gravitational settling and radiatively driven levitation of trace
elements, and their competition with mixing processes such as turbulent
diffusion.
We want to establish whether abundance peculiarities change as stars evolve
on the main sequence, and provide observational constraints to diffusion
theory.
We have performed spectral analysis of 15 magnetic Bp stars that are members
of open clusters (and thus have well-known ages), with masses between about 3
and 4 M_sun. For each star, we measured the abundances of He, O, Mg, Si, Ti,
Cr, Fe, Pr and Nd.
We have discovered the systematic time evolution of trace elements through
the main-sequence lifetime of magnetic chemically peculiar stars as their
atmospheres cool and evolve toward lower gravity. During the main sequence
lifetime, we observe clear and systematic variations in the atmospheric
abundances of He, Ti, Cr, Fe, Pr and Nd. For all these elements, except He, the
atmospheric abundances decrease with age. The abundances of Fe-peak elements
converge toward solar values, while the rare-earth elements converge toward
values at least 100 times more abundant than in the Sun. Helium is always
underabundant compared to the Sun, evolving from about 1% up to 10% of the
solar He abundance. We have attempted to interpret the observed abundance
variations in the context of radiatively driven diffusion theory, which appears
to provide a framework to understand some, but not all, of the observed
anomalous abundance levels and variations.Comment: 13 pages, 5 figures, 5 tables, accepted for publication in A&
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Participatory action research in the development and delivery of self-harm awareness sessions in prison: involving service users in staff development
Radio frequency coaxial high pass filter Patent
Radio frequency coaxial filter to provide dc isolation and low frequency signal rejection in audio rang
Advancing image quantification methods and tools for analysis of nanoparticle electrokinetics
Image processing methods and techniques for high-throughput quantification of dielectrophoretic (DEP) collections onto planar castellated electrode arrays are developed and evaluated. Fluorescence-based dielectrophoretic spectroscopy is an important tool for laboratory investigations of AC electrokinetic properties of nanoparticles. This paper details new, first principle, theoretical and experimental developments of geometric feature recognition techniques that enable quantification of positive dielectrophoretic (pDEP) nanoparticle collections onto castellated arrays. As an alternative to the geometric-based method, novel statistical methods that do not require any information about array features, are also developed using the quantile and standard deviation functions. Data from pDEP collection and release experiments using 200 nm diameter latex nanospheres demonstrates that pDEP quantification using the statistic-based methods yields quantitatively similar results to the geometric-based method. The development of geometric- and statistic-based quantification methods enables high-throughput, supervisor-free image processing tools critical for dielectrophoretic spectroscopy and automated DEP technology development
Monitoring Winter Flow Conditions on the Ivishak River, Alaska
The Sagavanirktok River, a braided river on the Alaska North Slope, flows adjacent to the trans-Alaska pipeline for approximately 100 miles south of Prudhoe Bay. During an unprecedented flooding event in mid-May 2015, the pipeline was exposed in an area located approximately 20 miles south of Prudhoe Bay. The Ivishak River is a main tributary of the Sagavanirktok River, but little is known about its water flow characteristics and contribution to the Sagavanirktok River, especially in winter and during spring breakup. To gather this information, we installed water level sensors on two main tributaries of the Ivishak River (Upper Ivishak and Saviukviayak rivers), early in winter season 2016–2017, in open-water channels that showed promise as locations for long-term gauging stations. Our ultimate goal was to find a location for permanent deployment of water level sensors. By February, the first sites chosen were ice covered, so two additional sensors, one on each river, were deployed in different locations. Some of the sensors were lost (i.e., carried away by the current or buried under a thick layer of sediments). Water level data gathered from the sensors showed a maximum change of 1.07 m. Winter discharge measurements indicate a 44% reduction between February and April 2017. A summer discharge measurement shows a 430% increase from winter to summer
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Service user involvement in the evaluation of psycho-social intervention for self-harm: a systematic literature review
Background: The efficacy of interventions and treatments for self-harm is well researched. Previous reviews of the literature have highlighted the lack of definitively effective interventions for self-harm and have highlighted the need for future research. These recommendations are also reflected in clinical guidelines published by the National Institute for Health and Clinical Excellence (NICE, 2004) which also call for service user involvement in studies of treatment efficacy. Aims: A systematic review was undertaken to determine i) what contributions service users have made to the evaluation of psychosocial interventions ii) by what methods have service users been involved iii) in what ways could service user involvement supplement empirical evidence for interventions
Oscillating chiral currents in nanotubes: a route to nanoscale magnetic test tubes
With a view to optimising the design of carbon-nanotube (CNT) windmills and
to maximising the internal magnetic field generated by chiral currents, we
present analytical results for the group velocity components of an electron
flux through chiral carbon nanotubes. Chiral currents are shown to exhibit a
rich behaviour and can even change sign and oscillate as the energy of the
electrons is increased. We find that the transverse velocity and associated
angular momentum of electrons is a maximum for non-metallic CNTs with a chiral
angle of 18. Such CNTs are therefore the optimal choice for CNT windmills
and also generate the largest internal magnetic field for a given longitudinal
current. For a longitudinal current of order amps, this field can be
of order Teslas, which is sufficient to produce interesting spintronic
effects and a significant contribution to the self inductance.Comment: 4 pages, 1 figur
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