3,133 research outputs found
Efficient light-emitting diodes from organic radicals with doublet emission
Organic light-emitting diodes (OLEDs) with doublet-spin radical emitters have emerged as a new route to efficient display technologies. In contrast to standard organic semiconductors, radical materials have unpaired electrons. This feature results in the most well-known examples of organic radicals being where they are reactive species in chemical reactions. Stabilized radicals can be used in optoelectronic applications, which exploit their optical and spin properties, allowing up to 100% internal quantum efficiency (IQE) for electroluminescence. Highly efficient OLEDs have been demonstrated, which operate in the doublet-spin electronic state manifold with doublet emission. The radical-based devices present a departure from the singlet- and triplet-level considerations that impose efficiency limits in OLEDs for typical organic semiconductors (25% IQE). This Perspective focuses on radical doublet emitters for optoelectronics, outlining how the photo- and spin-physics of unpaired electron systems present new avenues for research in light-emitting applications
MAGELLAN/M2FS SPECTROSCOPY of the RETICULUM 2 DWARF SPHEROIDAL GALAXY
Š 2015. The American Astronomical Society. All rights reserved.We present results from spectroscopic observations with the Michigan/Magellan Fiber System (M2FS) of 182 stellar targets along the line of sight (LOS) to the newly discovered "ultrafaint" object Reticulum 2 (Ret 2). For 37 of these targets, the spectra are sufficient to provide simultaneous estimates of LOS velocity (νlos, median random error δνlos= 1.4 km s-1), effective temperature (Teff, Î Teff K), surface gravity (loh g, δlog g = 0.63 dex), and iron abundance ([Fe/H], δ[Fe/H] = 0.47 dex). We use these results to confirm 17 stars as members of Ret 2. From the member sample we estimate a velocity dispersion of Ďνlos = 3.60.7+1.0km s-1 about a mean of ăνlosă = 64.3-1.2+1.2 km s-1 in the solar rest frame ( âź -90.9 km s-1 in the Galactic rest frame), and a metallicity dispersion of Ď [Fe/H] = 0.49-0.140.19 dex about a mean of ă [Fe/H]ă= -2.58-0.33+0.34. These estimates marginalize over possible velocity and metallicity gradients, which are consistent with zero. Our results place Ret 2 on chemodynamical scaling relations followed by the Milky Way's dwarf-galactic satellites. Under assumptions of dynamic equilibrium and negligible contamination from binary stars - both of which must be checked with deeper imaging and repeat spectroscopic observations - the estimated velocity dispersion suggests a dynamical mass of M(Rh)â5RhĎνlos;2/(2G) = 2.4-0.8+1.4 Ă 105 Mâenclosed within projected halflight radius Rh âź32 pc, with mass-to-light ratio â2M (Rh)/LV = 467-168+286in solar units
MAGELLAN/M2FS SPECTROSCOPY of the RETICULUM 2 DWARF SPHEROIDAL GALAXY
We present results from spectroscopic observations with the Michigan/Magellan
Fiber System (M2FS) of 182 stellar targets along the line of sight to the
newly-discovered `ultrafaint' object Reticulum 2 (Ret 2). For 38 of these
targets, the spectra are sufficient to provide simultaneous estimates of
line-of-sight velocity (, median random error km s), effective temperature (, K), surface gravity (, dex) and
iron abundance ([Fe/H], dex). We use these
results to confirm 18 stars as members of Ret 2. From the member sample we
estimate a velocity dispersion of km
s about a mean of km
s in the solar rest frame ( km s in the Galactic rest
frame), and a metallicity dispersion of dex about a mean of . These estimates marginalize over possible
velocity and metallicity gradients, which are consistent with zero. Our results
place Ret 2 on chemodynamical scaling relations followed by the Milky Way's
dwarf-galactic satellites. Under assumptions of dynamic equilibrium and
negligible contamination from binary stars---both of which must be checked with
deeper imaging and repeat spectroscopic observations---the estimated velocity
dispersion suggests a dynamical mass of
enclosed within projected halflight radius pc, with
mass-to-light ratio in
solar units
Direct measurement of antiferromagnetic domain fluctuations
Measurements of magnetic noise emanating from ferromagnets due to domain
motion were first carried out nearly 100 years ago and have underpinned much
science and technology. Antiferromagnets, which carry no net external magnetic
dipole moment, yet have a periodic arrangement of the electron spins extending
over macroscopic distances, should also display magnetic noise, but this must
be sampled at spatial wavelengths of order several interatomic spacings, rather
than the macroscopic scales characteristic of ferromagnets. Here we present the
first direct measurement of the fluctuations in the nanometre-scale spin-
(charge-) density wave superstructure associated with antiferromagnetism in
elemental Chromium. The technique used is X-ray Photon Correlation
Spectroscopy, where coherent x-ray diffraction produces a speckle pattern that
serves as a "fingerprint" of a particular magnetic domain configuration. The
temporal evolution of the patterns corresponds to domain walls advancing and
retreating over micron distances. While the domain wall motion is thermally
activated at temperatures above 100K, it is not so at lower temperatures, and
indeed has a rate which saturates at a finite value - consistent with quantum
fluctuations - on cooling below 40K. Our work is important because it provides
an important new measurement tool for antiferromagnetic domain engineering as
well as revealing a fundamental new fact about spin dynamics in the simplest
antiferromagnet.Comment: 19 pages, 4 figure
Hemorrhagic Shock Caused by Rupture of an Intra-Abdominal Leydig Cell Tumour: Case Report
The rupture of an intra-abdominal testicular neoplasm is a rare cause of acute abdomen and massive intra-abdominal haemorrhage. We report the case of a 70-year-old male presenting a massive intra-abdominal bleeding caused by a Leydig cell tumour in an undescended testis. The clinical details and pathology of this rare testicular tumour are discussed
Random Walks on Stochastic Temporal Networks
In the study of dynamical processes on networks, there has been intense focus
on network structure -- i.e., the arrangement of edges and their associated
weights -- but the effects of the temporal patterns of edges remains poorly
understood. In this chapter, we develop a mathematical framework for random
walks on temporal networks using an approach that provides a compromise between
abstract but unrealistic models and data-driven but non-mathematical
approaches. To do this, we introduce a stochastic model for temporal networks
in which we summarize the temporal and structural organization of a system
using a matrix of waiting-time distributions. We show that random walks on
stochastic temporal networks can be described exactly by an
integro-differential master equation and derive an analytical expression for
its asymptotic steady state. We also discuss how our work might be useful to
help build centrality measures for temporal networks.Comment: Chapter in Temporal Networks (Petter Holme and Jari Saramaki
editors). Springer. Berlin, Heidelberg 2013. The book chapter contains minor
corrections and modifications. This chapter is based on arXiv:1112.3324,
which contains additional calculations and numerical simulation
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Advice about diet and smoking for people with or at risk of age-related macular degeneration: a cross-sectional survey of eye care professionals in the UK.
BACKGROUND: In the absence of a cure, there has been considerable interest in attempts to prevent or reduce the progression of age-related macular degeneration (AMD) by targeting particular modifiable risk factors. The aim of this study was to conduct a cross-sectional survey of the current practice of UK eye care professionals in relation to advice given on diet and other lifestyle modifications for patients with or at risk of AMD. METHODS: Optometrists and ophthalmologists on the membership databases of professional organisations for the two professions were invited to participate in an online survey. The survey was open for 12 weeks between July and September 2012. RESULTS: A total of 1,468 responses were received (96.3% from optometrists and 3.7% from ophthalmologists). The response rate of those receiving the invitation was 16.2% (1,414/8735) for optometrists and 6% (54/1460) for ophthalmologists. A majority of respondents reported that they frequently provide dietary advice to patients with established AMD (67.9%) and those at risk of AMD (53.6%). Typical advice consisted of a recommendation to eat plenty of leafy green vegetables and eat more oily fish. The decision to recommend nutritional supplements was based on the risk of progression to advanced AMD, with approximately 93% of respondents recommending supplementation in a patient with advanced AMD in one eye. However for the majority, the type of supplement recommended did not comply with current best research evidence, based on the findings of the Age-related Eye Disease Study (AREDS). Only one in three optometrists regularly assessed smoking status and advised on smoking cessation. CONCLUSIONS: Within a large sample of eye care professionals, consisting predominantly of optometrists, who responded to a cross-sectional survey, there was active engagement in providing nutritional advice to patients with or at risk of AMD. However, the results demonstrate a need to raise awareness of the evidence underpinning the use of nutritional supplements together with an increased involvement in targeted smoking cessation
Structural analysis and corrosion studies on an ISO 5832-9 biomedical alloy with TiO2 solâgel layers
The aim of this study was to demonstrate the
relationship between the structural and corrosion properties
of an ISO 5832-9 biomedical alloy modified with titanium
dioxide (TiO2) layers. These layers were obtained via the
solâgel method by acid-catalyzed hydrolysis of titanium
isopropoxide in isopropanol solution. To obtain TiO2 layers
with different structural properties, the coated samples
were annealed at temperatures of 200, 300, 400, 450, 500,
600 and 800 C for 2 h. For all the prepared samples,
accelerated corrosion measurements were performed in
Tyrodeâs physiological solution using electrochemical
methods. The most important corrosion parameters were
determined: corrosion potential, polarization resistance,
corrosion rate, breakdown and repassivation potentials.
Corrosion damage was analyzed using scanning electron
microscopy. Structural analysis was carried out for selected
TiO2 coatings annealed at 200, 400, 600 and 800 C. In
addition, the morphology, chemical composition, crystallinity,
thickness and density of the deposited TiO2 layers
were determined using suitable electron and X-ray measurement
methods. It was shown that the structure and
character of interactions between substrate and deposited
TiO2 layers depended on annealing temperature. All the
obtained TiO2 coatings exhibit anticorrosion properties, but
these properties are related to the crystalline structure and
character of substrateâlayer interaction. From the point of
view of corrosion, the best TiO2 solâgel coatings for stainless steel intended for biomedical applications seem to
be those obtained at 400 C.This study was supported by Grant No. N N507
501339 of the National Science Centre. The authors wish to express
their thanks to J. Borowski (MEDGAL, Poland) for the Rex 734 alloy
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