13,411 research outputs found
Optical energies of AllnN epilayers
Optical energy gaps are measured for high-quality Al1−xInxN-on-GaN epilayers with a range of compositions around the lattice match point using photoluminescence and photoluminescence excitation spectroscopy. These data are combined with structural data to determine the compositional dependence of emission and absorption energies. The trend indicates a very large bowing parameter of 6 eV and differences with earlier reports are discussed. Very large Stokes' shifts of 0.4-0.8 eV are observed in the composition range 0.13<x<0.24, increasing approximately linearly with InN fraction despite the change of sign of the piezoelectric fiel
Domain Wall Fermions and the Eta Invariant
We extend work by Callan and Harvey and show how the phase of the chiral
fermion determinant in four dimensions is reproduced by zeromodes bound to a
domain wall in five dimensions. The analysis could shed light on the
applicability of zeromode fermions and the vacuum overlap formulation of
Narayanan and Neuberger for chiral gauge theories on the lattice.Comment: uuencoded file with 3 figures; uses macros harvmac, epsf. Revised
discussion of the Chern-Simons form and SU(2) anomaly in section 4, as well
as additional minor change
Integrating out the heaviest quark in N--flavour ChPT
We extend a known method to integrate out the strange quark in three flavour
chiral perturbation theory to the context of an arbitrary number of flavours.
As an application, we present the explicit formulae to one--loop accuracy for
the heavy quark mass dependency of the low energy constants after decreasing
the number of flavours by one while integrating out the heaviest quark in
N--flavour chiral perturbation theory.Comment: 18 pages, 1 figure. Text and references added. To appear in EPJ
Probing the Early Evolution of Young High-Mass Stars
Near-infrared imaging surveys of high-mass star-forming regions reveal an
amazingly complex interplay between star formation and the environment
(Churchwell et al. 2006; Alvarez et al. 2004). By means of near-IR spectroscopy
the embedded massive young stars can be characterized and placed in the context
of their birth site. However, so far spectroscopic surveys have been hopelessly
incomplete, hampering any systematic study of these very young massive stars.
New integral field instrumentation available at ESO has opened the possibility
to take a huge step forward by obtaining a full spectral inventory of the
youngest massive stellar populations in star-forming regions currently
accessible. Simultaneously, the analysis of the extended emission allows the
characterization of the environmental conditions. The Formation and Early
Evolution of Massive Stars (FEMS) collaboration aims at setting up a large
observing campaign to obtain a full census of the stellar content, ionized
material, outflows and PDR's over a sample of regions that covers a large
parameter space. Complementary radio, mm and infrared observations will be used
for the characterization of the deeply embedded population. For the first eight
regions we have obtained 40 hours of SINFONI observations. In this
contribution, we present the first results on three regions that illustrate the
potential of this strategy.Comment: To appear in ASP Conf. Proceedings of "Massive Star Formation:
Observations confront Theory", H. Beuther et al. (eds.), held in Heidelberg,
September 200
Mutations in SPG11, encoding spatacsin, are a major cause of spastic paraplegia with thin corpus callosum.
Autosomal recessive hereditary spastic paraplegia (ARHSP) with thin corpus
callosum (TCC) is a common and clinically distinct form of familial spastic
paraplegia that is linked to the SPG11 locus on chromosome 15 in most affected
families. We analyzed 12 ARHSP-TCC families, refined the SPG11 candidate interval
and identified ten mutations in a previously unidentified gene expressed
ubiquitously in the nervous system but most prominently in the cerebellum,
cerebral cortex, hippocampus and pineal gland. The mutations were either nonsense
or insertions and deletions leading to a frameshift, suggesting a
loss-of-function mechanism. The identification of the function of the gene will
provide insight into the mechanisms leading to the degeneration of the
corticospinal tract and other brain structures in this frequent form of ARHSP
Semiclassical strings in Sasaki-Einstein manifolds and long operators in N=1 gauge theories
We study the AdS/CFT relation between an infinite class of 5-d Ypq
Sasaki-Einstein metrics and the corresponding quiver theories. The long BPS
operators of the field theories are matched to massless geodesics in the
geometries, providing a test of AdS/CFT for these cases. Certain small
fluctuations (in the BMN sense) can also be successfully compared. We then go
further and find, using an appropriate limit, a reduced action, first order in
time derivatives, which describes strings with large R-charge. In the field
theory we consider holomorphic operators with large winding numbers around the
quiver and find, interestingly, that, after certain simplifying assumptions,
they can be described effectively as strings moving in a particular metric.
Although not equal, the metric is similar to the one in the bulk. We find it
encouraging that a string picture emerges directly from the field theory and
discuss possible ways to improve the agreement.Comment: 44 pages, LaTeX, 9 figures. v2: References adde
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High-K dielectric sulfur-selenium alloys.
Upcoming advancements in flexible technology require mechanically compliant dielectric materials. Current dielectrics have either high dielectric constant, K (e.g., metal oxides) or good flexibility (e.g., polymers). Here, we achieve a golden mean of these properties and obtain a lightweight, viscoelastic, high-K dielectric material by combining two nonpolar, brittle constituents, namely, sulfur (S) and selenium (Se). This S-Se alloy retains polymer-like mechanical flexibility along with a dielectric strength (40 kV/mm) and a high dielectric constant (K = 74 at 1 MHz) similar to those of established metal oxides. Our theoretical model suggests that the principal reason is the strong dipole moment generated due to the unique structural orientation between S and Se atoms. The S-Se alloys can bridge the chasm between mechanically soft and high-K dielectric materials toward several flexible device applications
Living with chronic migraine: a qualitative study on female patients' perspectives from a specialised headache clinic in Spain
OBJECTIVES: The aim of this study was to explore the views and experiences of a group of Spanish women suffering from chronic migraine (CM).
SETTING: Headache clinic at a university hospital in Madrid (Spain).
PARTICIPANTS: Purposeful sampling of patients that attended a specialised headache clinic for the first time between June 2016 and February 2017 was performed. The patients included were females aged 18–65 and with positive diagnoses of CM according to the International Classification of Headache disorders (third edition, beta version), with or without medication overuse. Accordingly, 20 patients participated in the study with a mean age of 38.65 years (SD 13.85).
DESIGN: Qualitative phenomenological study.
METHODS: Data were collected through in-depth interviews, researchers’ field notes and patients’ drawings. A thematic analysis was performed following appropriate guidelines for qualitative research.
RESULTS: Five main themes describing the significance of suffering emerged: (a) the shame of suffering from an invisible condition; (b) treatment: between need, scepticism and fear; (c) looking for physicians’ support and sincerity and fighting misconceptions; (d) limiting the impact on daily life through self-control; and (e) family and work: between understanding and disbelief. The disease is experienced as an invisible process, and the journey to diagnosis can be a long and tortuous one. Drug prescription by the physician is greeted with distrust and scepticism. Patients expect sincerity, support and the involvement of their doctors in relation to their disease. Pain becomes the main focus of the patient’s life, and it requires considerable self-control. The disease has a strong impact in the work and family environment, where the patient may feel misunderstood.
CONCLUSIONS: Qualitative research offers insight into the way patients with CM experience their disease and it may be helpful in establishing a more fruitful relationship with these patients
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