17,773 research outputs found
Gap nodes induced by coexistence with antiferromagnetism in iron-based superconductors
We investigate the pairing in iron pnictides in the coexistence phase, which
displays both superconducting and antiferromagnetic orders. By solving the
pairing problem on the Fermi surface reconstructed by long-range magnetic
order, we find that the pairing interaction necessarily becomes
angle-dependent, even if it was isotropic in the paramagnetic phase, which
results in an angular variation of the superconducting gap along the Fermi
surfaces. We find that the gap has no nodes for a small antiferromagnetic order
parameter M, but may develop accidental nodes for intermediate values of M,
when one pair of the reconstructed Fermi surface pockets disappear. For even
larger M, when the other pair of reconstructed Fermi pockets is gapped by
long-range magnetic order, superconductivity still exists, but the
quasiparticle spectrum becomes nodeless again. We also show that the
application of an external magnetic field facilitates the formation of nodes.
We argue that this mechanism for a nodeless-nodal-nodeless transition explains
recent thermal conductivity measurements of hole-doped Ba_{1-x}K_xFe_2As_2.
[J-Ph. Read et.al. arXiv:1105.2232].Comment: 13 pages, 10 figures, submitted to PR
Clinical, histological and prognostic features of a novel nail-bed lesion of cats: 41 cases
There is a distinct subset of lesions arising on the digits of cats, located at or close to the nail-bed epithelium, which are typically composed of proliferative fibroblast-like cells, multinucleate giant cells and areas of osseous metaplasia, but currently there is no published literature detailing the clinical or histological features of these lesions. This study identified 41 such cases from two large commercial diagnostic laboratories and assessed various histological and clinical features; 22 cases had additional follow-up data available
Long Term Variability of SDSS Quasars
We use a sample of 3791 quasars from the Sloan Digital Sky Survey (SDSS)
Early Data Release (EDR), and compare their photometry to historic plate
material for the same set of quasars in order to study their variability
properties. The time base-line we attain this way ranges from a few months to
up to 50 years. In contrast to monitoring programs, where relatively few
quasars are photometrically measured over shorter time periods, we utilize
existing databases to extend this base-line as much as possible, at the cost of
sampling per quasar. Our method, however, can easily be extended to much larger
samples. We construct variability Structure Functions and compare these to the
literature and model functions. From our modeling we conclude that 1) quasars
are more variable toward shorter wavelengths, 2) their variability is
consistent with an exponentially decaying light-curve with a typical time-scale
of ~2 years, 3) these outbursts occur on typical time-scales of ~200 years.
With the upcoming first data release of the SDSS, a much larger quasar sample
can be used to put these conclusions on a more secure footing.Comment: 16 pages, accepted for publication in AJ, Sept issu
The optical-ultraviolet continuum of Seyfert 2 galaxies
This paper aims to understand the continuum of Seyfert 2 galaxies. By fitting
the single galaxies in the sample of Heckman et al. (1995) with composite
models (shock+ photoionization from the active center), we show that five main
components characterize the SED of the continuum. Shocks play an important role
since they produce a high temperature zone where soft X-rays are emitted.
We show that in the optical-UV range, the slope of the NLR emission
reproduces the observed values, and may be the main component of the
featureless continuum. The presence of star forming regions cannot be excluded
in the circumnuclear region of various Seyfert galaxies. An attempt is made to
find their fingerprints in the observed AGN spectra. Finally, it is
demonstrated that multi-cloud models are necessary to interpret the spectra of
single objects, even in the global investigation of a sample of galaxies.Comment: 26 pages, LaTeX (including 5 Tables) + 17 PostScript figures. To
appear in "The Astrophysical Journal
Observation of an orbital interaction-induced Feshbach resonance in 173-Yb
We report on the experimental observation of a novel inter-orbital Feshbach
resonance in ultracold 173-Yb atoms, which opens the possibility of tuning the
interactions between the 1S0 and 3P0 metastable state, both possessing
vanishing total electronic angular momentum. The resonance is observed at
experimentally accessible magnetic field strengths and occurs universally for
all hyperfine state combinations. We characterize the resonance in the bulk via
inter-orbital cross-thermalization as well as in a three-dimensional lattice
using high-resolution clock-line spectroscopy.Comment: 5 pages, 4 figure
Resistivity near a nematic quantum critical point: impact of acoustic phonons
FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOWe revisit the issue of the resistivity of a two-dimensional electronic system tuned to a nematic quantum critical point (QCP), focusing on the nontrivial impact of the coupling to the acoustic phonons. Due to the unavoidable linear coupling between the electronic nematic order parameter and the lattice strain fields, long-range nematic interactions mediated by the phonons emerge in the problem. By solving the semiclassical Boltzmann equation in the presence of scattering by impurities and nematic fluctuations, we determine the temperature dependence of the resistivity as the nematic QCP is approached. One of the main effects of the nematoelastic coupling is to smooth the electronic nonequilibrium distribution function, making it approach the simple cosine angular dependence even when the impurity scattering is not too strong. We find that at temperatures lower than a temperature scale set by the nematoelastic coupling, the resistivity shows the T-2 behavior characteristic of a Fermi liquid. This is in contrast to the T-4/3 low-temperature behavior expected for a lattice-free nematic quantum critical point. More importantly, we show that the effective resistivity exponent alpha(eff)(T) in rho(T) - rho(0) similar to T-alpha eff(T) displays a pronounced temperature dependence, implying that a nematic QCP cannot generally be characterized by a simple resistivity exponent. We discuss the implications of our results to the interpretation of experimental data, particularly in the nematic superconductor FeSe1-xSx.10011110FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO2017/16911-3We would like to thank A. Chubukov, A. Coldea, A. Klein, E. Miranda, H. Freire, I. Paul, and A. Schofield for stimulating discussions. V.S.d.C. is grateful for the financial support from FAPESP under Grant No. 2017/16911-3. R.M.F. is supported by the US Department of Energy, Office of Science, Basic Energy Sciences, under Award No. DE-SC0012336
THE IMPACT OF VOLUNTEERING AND THE ACQUISITION OF SKILLS THROUGH PRACTICE
This study intended to assess the impact of volunteering on society and understand how its practice
allows the acquisition of skills. In addition, it would make the population aware of the value and
importance of the different ways of volunteering. One of the central points of this investigation was to
understand how institutions should recruit and attract volunteers and ultimately how to retain them, by
understanding whether or not the volunteers’ initial motivations (i.e. which attract them) remain
unchanged along time. This study was carried out within the scope of the ENtRANCE Erasmus+
project, by students of the Research Methods and Techniques course integrated in the
Communication Sciences degree at Maia University Institute and had the collaboration of the
Volunteer School, Pista Mágica by contacting its volunteers and clarifying relevant information.
Several scientific articles were analysed, such as [1]; [2]; [3]; [4]; [5] which allowed a first approach to
such topic but with no answers found.info:eu-repo/semantics/publishedVersio
Possible unconventional superconductivity in substituted BaFeAs revealed by magnetic pair-breaking studies
The possible existence of a sign-changing gap symmetry in
BaFeAs-derived superconductors (SC) has been an exciting topic of
research in the last few years. To further investigate this subject we combine
Electron Spin Resonance (ESR) and pressure-dependent transport measurements to
investigate magnetic pair-breaking effects on BaFeAs (
Mn, Co, Cu, and Ni) single crystals. An ESR signal, indicative of the presence
of localized magnetic moments, is observed only for Cu and Mn compounds,
which display very low SC transition temperature () and no SC,
respectively. From the ESR analysis assuming the absence of bottleneck effects,
the microscopic parameters are extracted to show that this reduction of
cannot be accounted by the Abrikosov-Gorkov pair-breaking expression for a
sign-preserving gap function. Our results reveal an unconventional spin- and
pressure-dependent pair-breaking effect and impose strong constraints on the
pairing symmetry of these materials
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