9,233 research outputs found
Photon trapping and energy transfer in multiple-dye plastic matrices: an efficient solar-energy concentrator
Experiments are described illustrating enhanced photon trapping and efficient energy transfer in mixed-dye planar solar concentrators containing, for example, Rhodamine 6G and Coumarin 6. These concentrators intercept more of the solar spectrum to give an enhanced photon-flux gain that exceeds the single-dye concentrator. It is also shown that the energy absorbed by the donor dye is transferred efficiently into the emitting acceptor by two competing processes
Behavior of bulk high-temperature superconductors of finite thickness subjected to crossed magnetic fields
Crossed magnetic field effects on bulk high-temperature superconductors have
been studied both experimentally and numerically. The sample geometry
investigated involves finite-size effects along both (crossed) magnetic field
directions. The experiments were carried out on bulk melt-processed Y-Ba-Cu-O
(YBCO) single domains that had been pre-magnetized with the applied field
parallel to their shortest direction (i.e. the c-axis) and then subjected to
several cycles of the application of a transverse magnetic field parallel to
the sample ab plane. The magnetic properties were measured using orthogonal
pick-up coils, a Hall probe placed against the sample surface and
Magneto-Optical Imaging (MOI). We show that all principal features of the
experimental data can be reproduced qualitatively using a two-dimensional
finite-element numerical model based on an E-J power law and in which the
current density flows perpendicularly to the plane within which the two
components of magnetic field are varied. The results of this study suggest that
the suppression of the magnetic moment under the action of a transverse field
can be predicted successfully by ignoring the existence of flux-free
configurations or flux-cutting effects. These investigations show that the
observed decay in magnetization results from the intricate modification of
current distribution within the sample cross-section. It is also shown that the
model does not predict any saturation of the magnetic induction, even after a
large number (~ 100) of transverse field cycles. These features are shown to be
consistent with the experimental data.Comment: 41 pages, 9 figures, accepted in Phys. Rev. B Changes : 8 references
added, a few precisions added, some typos correcte
Pharmacokinetics of Quinapril and its Active Metabolite Quinaprilat During Continuous Ambulatory Peritoneal Dialysis
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97278/1/j.1552-4604.1990.tb01857.x.pd
Astrophysical Observations with the HEROES Balloon-borne Payload
The High Energy Replicated Optics to Explore the Sun (HEROES) payload flew on a balloon from Ft. Sumner, NM, September 21-22, 2013. HEROES is sensitive from about 20-75 keV and comprises 8 optics modules, each consisting of 13-14 nickel replicated optics shells and 8 Xenon-filled positionsensitive proportional counter detectors. HEROES is unique in that it is the first hard X-ray telescope that will observe the Sun and astrophysical targets in the same balloon flight. Our astrophysics targets include the Crab nebula and pulsar and the black hole binary GRS 1915+105. In this presentation, I will describe the HEROES mission, the data analysis pipeline and calibrations, and preliminary astrophysics results
Anomalous Thermal Transport in Quantum Wires
We study thermal transport in a one-dimensional quantum wire, connected to
reservoirs. Despite of the absence of electron backscattering, interactions in
the wire strongly influence thermal transport. Electrons propagate with unitary
transmission through the wire and electric conductance is not affected. Energy,
however, is carried by bosonic excitations (plasmons) which suffer from
scattering even on scales much larger than the Fermi wavelength. If the
electron density varies randomly, plasmons are localized and {\em charge-energy
separation} occurs. We also discuss the effect of plasmon-plasmon interaction
using Levinson's theory of nonlocal heat transport.Comment: replaced with published versio
Properties of the Chandra Sources in M81
The Chandra X-ray Observatory obtained a 50-ks observation of the central
region of M81 using the ACIS-S in imaging mode. The global properties of the 97
x-ray sources detected in the inner 8.3x8.3 arcmin field of M81 are examined.
Roughly half the sources are concentrated within the central bulge. The
remainder are distributed throughout the disk with the brightest disk sources
lying preferentially along spiral arms. The average hardness ratios of both
bulge and disk sources are consistent with power law spectra of index Gamma~1.6
indicative of a population of x-ray binaries. A group of much softer sources
are also present. The background source-subtracted logN-logS distribution of
the disk follows a power law of index ~ -0.5 with no change in slope over three
decades in flux. The logN-logS distribution of the bulge follows a similar
shape but with a steeper slope above ~4.0e+37 ergs/s. There is unresolved x-ray
flux from the bulge with a radial profile similar to that of the bulge sources.
This unresolved flux is softer than the average of the bulge sources and
extrapolating the bulge logN-logS distribution towards weaker sources can only
account for 20% of the unresolved flux. No strong time variability was observed
for any source with the exception of one bright, soft source.Comment: 5 pages, 3 color PS figures, to appear in ApJ
A level playing âfieldâ? A Bourdieusian analysis of the career aspirations of further education students on sports courses
There is currently a distinct dearth of research into how sports studentsâ career aspirations are formed during their post-compulsory education. This article, based on an ethnographic study of sport students in tertiary education, draws on data collected from two first-year cohorts (n = 34) on two different courses at a further education college in England. The study draws on ethnographic observations, and semi-structured group interviews, to examine in-depth the contrasting occupational perspectives emergent within these two groups of mainly working-class students, and how specific cultural practices affect studentsâ career aspirations. Utilising a Bourdieusian framework, the paper analyses the internalised, often latent cultural practices that impact upon these studentsâ diverse career aspirations. The hitherto under-researched dimension of inter-habitus interaction and also the application of doxa are outlined. The article reveals how the two student cohorts are situated within a complex field of relations, where struggles for legitimisation, academic accomplishment and numerous forms of lucrative capital become habituated. The study offers salient Bourdieusian-inspired insights into the career aspirations of these predominantly working-class students and the ways in which certain educational practices contribute to the production and reproduction of class inequalities
Developing mathematical thinking in the primary classroom: liberating students and teachers as learners of mathematics
This paper reports on a research study conducted with a group of practising primary school teachers (n = 24) in North East Scotland during 2011â2012. The teachers were all participants in a newly developed Masters course that had been designed with the aim of promoting the development of mathematical thinking in the primary classroom as part of project supported by the Scottish Government. The paper presents the background for this initiative within the context of the Scottish Curriculum for Excellence reform. Particular attention is given to the epistemological positioning of the researchers as this influenced both the curriculum design process and also the theoretical framing of the research study which are both described. The project was set up within a design research framework, which aimed to promote classroom-based action research on the part of participants through the course and also research by the university researchers into the process of curriculum development. The research questions focused on the teachersâ confidence, competence, attitudes and beliefs in relation to mathematics and their expectations and experiences of the impact on pupil learning arising from this course. Empirical data were drawn from pre- and post-course surveys, interviews and observations of the discussion forums in the online environment. Findings from this study highlight the way the course had a transformational and emancipatory impact on these teachers. They also highlight ways in which the âframingâ of particular aspects of the curriculum had an oppressive impact on learners in the ways that suppressed creativity and limited the exercise of learner autonomy. Furthermore, they highlight the ways in which a number of these teachers had experienced mathematics as a school subject in very negative ways, involving high levels of âsymbolic violenceâ and of being âlabelledâ
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