27,065 research outputs found
Measuring the Hidden Aspects of Solar Magnetism
2008 marks the 100th anniversary of the discovery of astrophysical magnetic
fields, when George Ellery Hale recorded the Zeeman splitting of spectral lines
in sunspots. With the introduction of Babcock's photoelectric magnetograph it
soon became clear that the Sun's magnetic field outside sunspots is extremely
structured. The field strengths that were measured were found to get larger
when the spatial resolution was improved. It was therefore necessary to come up
with methods to go beyond the spatial resolution limit and diagnose the
intrinsic magnetic-field properties without dependence on the quality of the
telescope used. The line-ratio technique that was developed in the early 1970s
revealed a picture where most flux that we see in magnetograms originates in
highly bundled, kG fields with a tiny volume filling factor. This led to
interpretations in terms of discrete, strong-field magnetic flux tubes embedded
in a rather field-free medium, and a whole industry of flux tube models at
increasing levels of sophistication. This magnetic-field paradigm has now been
shattered with the advent of high-precision imaging polarimeters that allow us
to apply the so-called "Second Solar Spectrum" to diagnose aspects of solar
magnetism that have been hidden to Zeeman diagnostics. It is found that the
bulk of the photospheric volume is seething with intermediately strong, tangled
fields. In the new paradigm the field behaves like a fractal with a high degree
of self-similarity, spanning about 8 orders of magnitude in scale size, down to
scales of order 10 m.Comment: To appear in "Magnetic Coupling between the Interior and the
Atmosphere of the Sun", eds. S.S. Hasan and R.J. Rutten, Astrophysics and
Space Science Proceedings, Springer-Verlag, Heidelberg, Berlin, 200
Developing modern multifunctional agroforestry systems for sustainable intensification
Agroforestry is a land-use system that integrates trees and shrubs with crops and/or livestock production. It has been identified by the International Assessment of Agricultural Knowledge, Science and Technology for Development (IAASTD, 2008) as a âwin-winâ approach that balances the production of commodities (food, feed, fuel, fibre, etc.) with non-commodity outputs such as environmental protection and cultural and landscape amenities. This paper will review the potential of agroforestry as part of a multifunctional working landscape in temperate regions, and will consider management and policy implications of widespread adoption of this form of land-use
Scanning photocurrent microscopy reveals electron-hole asymmetry in ionic liquid-gated WS2 transistors
We perform scanning photocurrent microscopy on WS2 ionic liquid-gated field
effect transistors exhibiting high-quality ambipolar transport. By properly
biasing the gate electrode we can invert the sign of the photocurrent showing
that the minority photocarriers are either electrons or holes. Both in the
electron- and the hole-doping regimes the photocurrent decays exponentially as
a function of the distance between the illumination spot and the nearest
contact, in agreement with a two-terminal Schottky-barrier device model. This
allows us to compare the value and the doping dependence of the diffusion
length of the minority electrons and holes on a same sample. Interestingly, the
diffusion length of the minority carriers is several times larger in the hole
accumulation regime than in the electron accumulation regime, pointing out an
electron-hole asymmetry in WS2
Mono- and Bilayer WS2 Light-Emitting Transistors
We have realized ambipolar ionic liquid gated field-effect transistors based
on WS2 mono- and bilayers, and investigated their opto-electronic response. A
thorough characterization of the transport properties demonstrates the high
quality of these devices for both electron and hole accumulation, which enables
the quantitative determination of the band gap ({\Delta}1L = 2.14 eV for
monolayers and {\Delta}2L = 1.82 eV for bilayers). It also enables the
operation of the transistors in the ambipolar injection regime with electrons
and holes injected simultaneously at the two opposite contacts of the devices
in which we observe light emission from the FET channel. A quantitative
analysis of the spectral properties of the emitted light, together with a
comparison with the band gap values obtained from transport, show the internal
consistency of our results and allow a quantitative estimate of the excitonic
binding energies to be made. Our results demonstrate the power of ionic liquid
gating in combination with nanoelectronic systems, as well as the compatibility
of this technique with optical measurements on semiconducting transition metal
dichalcogenides. These findings further open the way to the investigation of
the optical properties of these systems in a carrier density range much broader
than that explored until now.Comment: 22 pages, 6 figures, Nano Letters (2014
Local moment, itinerancy and deviation from Fermi liquid behavior in NaCoO for
Here we report the observation of Fermi surface (FS) pockets via the
Shubnikov de Haas effect in NaCoO for and 0.84,
respectively. Our observations indicate that the FS expected for each compound
intersects their corresponding Brillouin zones, as defined by the previously
reported superlattice structures, leading to small reconstructed FS pockets,
but only if a precise number of holes per unit cell is \emph{localized}. For
the coexistence of itinerant carriers and localized spins on a paramagnetic triangular superlattice leads at low temperatures
to the observation of a deviation from standard Fermi-liquid behavior in the
electrical transport and heat capacity properties, suggesting the formation of
some kind of quantum spin-liquid ground state.Comment: 4 pages, 4 figure
Digital library access for illiterate users
The problems that illiteracy poses in accessing information are gaining attention from the research community. Issues currently being explored include developing an understanding of the barriers to information acquisition experienced by different groups of illiterate information seekers; creating technology, such as software interfaces, that support illiterate users effectively; and tailoring content to increase its accessibility. We have taken a formative evaluation approach to developing and evaluating a digital library interface for illiterate users. We discuss modifications to the Greenstone platform, describe user studies and outline resulting design implications
On Galactic density modeling in the presence of dust extinction
Inferences about the spatial density or phase-space structure of stellar
populations in the Milky Way require a precise determination of the effective
survey volume. The volume observed by surveys such as Gaia or near-infrared
spectroscopic surveys, which have good coverage of the Galactic mid-plane
region, is highly complex because of the abundant small-scale structure in the
three-dimensional interstellar dust extinction. We introduce a novel framework
for analyzing the importance of small-scale structure in the extinction. This
formalism demonstrates that the spatially-complex effect of extinction on the
selection function of a pencil-beam or contiguous sky survey is equivalent to a
low-pass filtering of the extinction-affected selection function with the
smooth density field. We find that the angular resolution of current 3D
extinction maps is sufficient for analyzing Gaia sub-samples of millions of
stars. However, the current distance resolution is inadequate and needs to be
improved by an order of magnitude, especially in the inner Galaxy. We also
present a practical and efficient method for properly taking the effect of
extinction into account in analyses of Galactic structure through an effective
selection function. We illustrate its use with the selection function of
red-clump stars in APOGEE using and comparing a variety of current 3D
extinction maps.Comment: Code available at https://github.com/jobovy/mwdust and at
https://github.com/jobovy/apogee-map
Design, validation and dissemination of an undergraduate assessment tool using SimManÂź in simulated medical emergencies
Background: Increasingly, medical students are being taught acute medicine using whole-body simulator manikins.
Aim: We aimed to design, validate and make widely available two simple assessment tools to be used with Laerdal SimMan (R) for final year students.
Methods: We designed two scenarios with criterion-based checklists focused on assessment and management of two medical emergencies. Members of faculty critiqued the assessments for face validity and checklists revised. We assessed three groups of different experience levels: Foundation Year 2 doctors, third and final year medical students. Differences between groups were analysed, and internal consistency and interrater reliability calculated. A generalisability analysis was conducted using scenario and rater as facets in design.
Results: A maximum of two items were removed from either checklist following the initial survey. Significantly different scores for three groups of experience for both scenarios were reported (p0.90). Internal consistency was poor (alpha<50.5). Generalizability study results suggest that four cases would provide reliable discrimination between final year students.
Conclusions: These assessments proved easy to administer and we have gone some way to demonstrating construct validity and reliability. We have made the material available on a simulator website to enable others to reproduce these assessments
Polarization Switching Dynamics Governed by Thermodynamic Nucleation Process in Ultrathin Ferroelectric Films
A long standing problem of domain switching process - how domains nucleate -
is examined in ultrathin ferroelectric films. We demonstrate that the large
depolarization fields in ultrathin films could significantly lower the
nucleation energy barrier (U*) to a level comparable to thermal energy (kBT),
resulting in power-law like polarization decay behaviors. The "Landauer's
paradox": U* is thermally insurmountable is not a critical issue in the
polarization switching of ultrathin ferroelectric films. We empirically find a
universal relation between the polarization decay behavior and U*/kBT.Comment: 5 pages, 4 figure
Three-loop HTL gluon thermodynamics at intermediate coupling
We calculate the thermodynamic functions of pure-glue QCD to three-loop order
using the hard-thermal-loop perturbation theory (HTLpt) reorganization of
finite temperature quantum field theory. We show that at three-loop order
hard-thermal-loop perturbation theory is compatible with lattice results for
the pressure, energy density, and entropy down to temperatures .
Our results suggest that HTLpt provides a systematic framework that can used to
calculate static and dynamic quantities for temperatures relevant at LHC.Comment: 24 pages, 13 figs. 2nd version: improved discussion and fixing typos.
Published in JHE
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