9,718 research outputs found
Two-band superconductivity in doped SrTiO films and interfaces
We investigate the possibility of multi-band superconductivity in SrTiO
films and interfaces using a two-dimensional two-band model. In the undoped
compound, one of the bands is occupied whereas the other is empty. As the
chemical potential shifts due to doping by negative charge carriers or
application of an electric field, the second band becomes occupied, giving rise
to a strong enhancement of the transition temperature and a sharp feature in
the gap functions, which is manifested in the local density of states spectrum.
By comparing our results with tunneling experiments in Nb-doped SrTiO, we
find that intra-band pairing dominates over inter-band pairing, unlike other
known multi-band superconductors. Given the similarities with the value of the
transition temperature and with the band structure of LaAlO/SrTiO
heterostructures, we speculate that the superconductivity observed in
SrTiO interfaces may be similar in nature to that of bulk SrTiO,
involving multiple bands with distinct electronic occupations.Comment: revised expanded versio
Competing order and nature of the pairing state in the iron pnictides
We show that the competition between magnetism and superconductivity can be
used to determine the pairing state in the iron arsenides. To this end we
demonstrate that the itinerant antiferromagnetic phase (AFM) and the
unconventional sign-changing superconducting state (SC) are near the
borderline of microscopic coexistence and macroscopic phase separation,
explaining the experimentally observed competition of both ordered states. In
contrast, conventional pairing is not able to coexist with magnetism.
Expanding the microscopic free energy of the system with competing orders
around the multicritical point, we find that static magnetism plays the role of
an intrinsic interband Josephson coupling, making the phase diagram sensitive
to the symmetry of the Cooper pair wavefunction. We relate this result to the
quasiparticle excitation spectrum and to the emergent SO symmetry of
systems with particle-hole symmetry. Our results rely on the assumption that
the same electrons that form the ordered moment contribute to the
superconducting condensate and that the system is close to particle-hole
symmetry. We also compare the suppression of SC in different regions of the
FeAs phase diagram, showing that while in the underdoped side it is due to the
competition with AFM, in the overdoped side it is related to the disappearance
of pockets from the Fermi surface.Comment: 24 pages, 13 figures; revised versio
FM 047-02: a collisional pair of galaxies with a ring
Aims. We investigate the nature of the galaxy pair FM 047-02, which has been
proposed as an archetype of the Solitaire types of peculiar (collisional) ring
galaxies. Methods. The study is based on long-slit spectrophotometric data in
the range of 3500-9500 angstrons obtained with the Gemini Multi-ObjectComment: 07 pages, 06 figures, 02 tables. arXiv admin note: text overlap with
arXiv:1206.071
Perspectivas de contribuição das práticas educomunicativas socioambientais para o objetivo do desenvolvimento sustentável, ODS-15 Vida na terra.
Edição especial dos resumos do IUFRO World Congress, 25., 2019, Curitiba
Perspectivas de contribuição das práticas educomunicativas socioambientais para o objetivo do desenvolvimento sustentável, ODS-15 Vida na terra.
Edição especial dos resumos do IUFRO World Congress, 25., 2019, Curitiba
The individuals' discretionary behaviors at work. An overview and analysis of its growing interest
Nearly forty years have passed since the term Organizational Citizenship Behavior appeared. Despite a current consensus among scholars about the citizenship gestures as prosocial acts of employees that benefit the organization, it does not apply commonly to the exponential growth of all OCB-related concepts. The concept's expansion has confused the researchers and practitioners, mainly when choosing the most appropriate instruments (constructs) and dimensions to use in their area of interest and context. A systematic literature review was conducted and 420 articles were analyzed. Results point that the trends on OCB-like behaviors goes higher, with an average annual growth rate of new studies of 3.13%. United States (39%) and China (25%) lead but some "under-studied" contexts like Africa, Latin America, the Caribbean, and Oceania start being studied towards OCB. New trends appear in the spectrum of the many different domains and disciplines related to OCB, while leadership and task performance remain the most studied domains and disciplines. In future studies, researchers must freely choose the OCB dimensions and constructs they want to use or adapt to meet their needs and research needs since there is no written rule about their use, only the care to be taken with the context and discipline studying.info:eu-repo/semantics/publishedVersio
Conhecimento dos serviços da FCCN junto da comunidade cientÃfica e tecnológica nacional: um inquérito por questionário
O relatório aqui apresentado resulta de uma prestação de serviços, por parte de uma equipa do ISCTE-IUL,
à FCCN (Fundação para a Computação CientÃfica Nacional). Esta visou apoiar o lançamento de um inquérito
por questionário aos membros da comunidade cientÃfica e tecnológica nacional, com o fim de aferir a
perceção acerca dos serviços da FCCN, designadamente em termos de Conectividade, Computação,
Colaboração, Conhecimento e Segurança.info:eu-repo/semantics/publishedVersio
Population expansion in the North African Late Pleistocene signalled by mitochondrial DNA haplogroup U6
Background
<br/>
The archaeology of North Africa remains enigmatic, with questions of population continuity versus discontinuity taking centre-stage. Debates have focused on population transitions between the bearers of the Middle Palaeolithic Aterian industry and the later Upper Palaeolithic populations of the Maghreb, as well as between the late Pleistocene and Holocene.
<br/>
Results
Improved resolution of the mitochondrial DNA (mtDNA) haplogroup U6 phylogeny, by the screening of 39 new complete sequences, has enabled us to infer a signal of moderate population expansion using Bayesian coalescent methods. To ascertain the time for this expansion, we applied both a mutation rate accounting for purifying selection and one with an internal calibration based on four approximate archaeological dates: the settlement of the Canary Islands, the settlement of Sardinia and its internal population re-expansion, and the split between haplogroups U5 and U6 around the time of the first modern human settlement of the Near East.
<br/>
Conclusions
<br/>
A Bayesian skyline plot placed the main expansion in the time frame of the Late Pleistocene, around 20 ka, and spatial smoothing techniques suggested that the most probable geographic region for this demographic event was to the west of North Africa. A comparison with U6's European sister clade, U5, revealed a stronger population expansion at around this time in Europe. Also in contrast with U5, a weak signal of a recent population expansion in the last 5,000 years was observed in North Africa, pointing to a moderate impact of the late Neolithic on the local population size of the southern Mediterranean coast
On the nature of the near-UV extended light in Seyfert galaxies
We study the nature of the extended near-UV emission in the inner kiloparsec
of a sample of 15 Seyfert galaxies which have both near-UV (F330W) and narrow
band [OIII] high resolution Hubble images. For the majority of the objects we
find a very similar morphology in both bands. From the [OIII] images we
construct synthetic images of the nebular continuum plus the emission line
contribution expected through the F330W filter, which can be subtracted from
the F330W images. We find that the emission of the ionised gas dominates the
near-UV extended emission in half of the objects. A further broad band
photometric study, in the bands F330W (U), F547M (V) and F160W (H), shows that
the remaining emission is dominated by the underlying galactic bulge
contribution. We also find a blue component whose nature is not clear in 4 out
of 15 objects. This component may be attributed to scattered light from the
AGN, to a young stellar population in unresolved star clusters, or to
early-disrupted clusters. Star forming regions and/or bright off-nuclear star
clusters are observed in 4/15 galaxies of the sample.Comment: 23 pages, 6 figures, 3 tables; accepted for publication in MNRA
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