15,736 research outputs found
Disrupted asteroid P/2016 G1. II. Follow-up observations from the Hubble Space Telescope
After the early observations of the disrupted asteroid P/2016 G1 with the
10.4m Gran Telescopio Canarias (GTC), and the modeling of the dust ejecta, we
have performed a follow-up observational campaign of this object using the
Hubble Space Telescope (HST) during two epochs (June 28 and July 11, 2016). The
analysis of these HST images with the same model inputs obtained from the GTC
images revealed a good consistency with the predicted evolution from the GTC
images, so that the model is applicable to the whole observational period from
late April to early July 2016. This result confirms that the resulting dust
ejecta was caused by a relatively short-duration event with onset about 350
days before perihelion, and spanning about 30 days (HWHM). For a size
distribution of particles with a geometric albedo of 0.15, having radii limits
of 1 m and 1 cm, and following a power-law with index --3.0, the total
dust mass ejected is 210 kg. As was the case with the GTC
observations, no condensations in the images that could be attributed to a
nucleus or fragments released after the disruption event were found. However,
the higher limiting magnitude reachable with the HST images in comparison with
those from GTC allowed us to impose a more stringent upper limit to the
observed fragments of 30 m.Comment: 10 pages, 2 figures Accepted by Astronomical Journal, Nov. 2, 201
Rotating Superconductors and the London Moment: Thermodynamics versus Microscopics
Comparing various microscopic theories of rotating superconductors to the
conclusions of thermodynamic considerations, we traced their marked difference
to the question of how some thermodynamic quantities (the electrostatic and
chemical potentials) are related to more microscopic ones: The electron's the
work function, mean-field potential and Fermi energy -- certainly a question of
general import.
After the correct identification is established, the relativistic correction
for the London Moment is shown to vanish, with the obvious contribution from
the Fermi velocity being compensated by other contributions such as
electrostatics and interactions.Comment: 23 pages 4 fi
Trion dynamics in coupled double quantum wells. Electron density effects
We have studied the coherent dynamics of injected electrons when they are
either free or bounded both in excitons and in trions (charged excitons). We
have considered a remotely doped asymmetric double quantum well where an excess
of free electrons and the direct created excitons generate trions. We have used
the matrix density formalism to analyze the electron dynamics for different
concentration of the three species. Calculations show a significant
modification of the free electron inter-sublevel oscillations cWe have studied
the coherent dynamics of injected electrons when they are aused by electrons
bound in excitons and trions. Based on the present calculations we propose a
method to detect trions through the emitted electromagnetic radiation or the
current density.Comment: 14 pages, 13 figure
Snake orbits and related magnetic edge states
We study the electron motion near magnetic field steps at which the strength
and/or sign of the magnetic field changes. The energy spectrum for such systems
is found and the electron states (bound and scattered) are compared with their
corresponding classical paths. Several classical properties as the velocity
parallel to the edge, the oscillation frequency perpendicular to the edge and
the extent of the states are compared with their quantum mechanical
counterpart. A class of magnetic edge states is found which do not have a
classical counterpart.Comment: 8 pages, 10 figure
Human resource management in Spain : are cultural barriers preventing the adoption of global practices?
This paper addresses the extent to which culture is affecting the adoption of global human resource management (HRM) practices by Spanish organizations. One of our main objectives was to offer a thorough review of the recent empirical evidence regarding HRM practices in Spanish organizations. Another goal was to discuss these findings in light of the Spanish culture in order to identify possible cultural barriers to the adoption of global HRM practices. Our results suggest that Spanish organizations are slowly adopting global practices; however, many traditional practices remain. We suggest that the cultural variables of low future orientation, high power distance, and low institutional collectivism may exert continuing pressures that will hinder the adoption of certain global HRM practices.En este artículo estudiamos hasta qué punto la cultura está afectando a la implementación de prácticas globales de GRH por parte de organizaciones españolas. Uno de nustros objetivos principales es ofrecer una revisión profunda de la evidencia empírica reciente sobre las prácticas de GRH en organizaciones españolas. Nuestro segundo objetivo consiste en discutir dicha evidencia desde el punto de vista de la cultura española con el objeto de identificar posibles barreras culturales a la adopción de las prácticas globales de GRH. Nuestras conclusiones sugieren que las organizaciones españolas están adoptando lentamente prácticas globales, sin embargo, aún persisten muchas prácticas tradicionales. Sugerimos que variables culturales como baja orientación al futuro, alta distancia de poder y bajo colectivismo institucional pueden seguir ejerciendo presiones continuas que dificultarán la adopción de ciertas prácticas globales de GRH.Publicad
A New Fast Motion Estimation and Mode Decision algorithm for H.264 Depth Maps encoding in Free Viewpoint TV
In this paper, we consider a scenario where 3D scenes are modeled through a View+Depth representation. This representation is to be used at the rendering side to generate synthetic views for free viewpoint video. The encoding of both type of data (view and depth) is carried out using two H.264/AVC encoders. In this scenario we address the reduction of the encoding complexity of depth data. Firstly, an analysis of the Mode Decision and Motion Estimation processes has been conducted for both view and depth sequences, in order to capture the correlation between them. Taking advantage of this correlation, we propose a fast mode decision and motion estimation algorithm for the depth encoding. Results show that the proposed algorithm reduces the computational burden with a negligible loss in terms of quality of the rendered synthetic views. Quality measurements have been conducted using the Video Quality Metric
Appearance of room temperature ferromagnetism in Cu-doped TiO films
In recent years there has been an intense search for room temperature
ferromagnetism in doped dilute semiconductors, which have many potentially
applications in spintronics and optoelectronics. We report here the unexpected
observation of significant room temperature ferromagnetism in a semiconductor
doped with nonmagnetic impurities, Cu-doped TiO thin films grown by Pulsed
Laser Deposition. The magnetic moment, calculated from the magnetization
curves, resulted surprisingly large, about 1.5 per Cu atom. A large
magnetic moment was also obtained from ab initio calculations using the
supercell method for TiO with Cu impurities, but only if an oxygen vacancy
in the nearest-neighbour shell of Cu was present. This result suggests that the
role of oxygen vacancies is crucial for the appearance of ferromagnetism. The
calculations also predict that Cu doping favours the formation of oxygen
vacancies.Comment: 4 pages, 3 figures, published in Phys. Rev. B (Rapid Comm.
Collapse of the ESR fine structure throughout the coherent temperature of the Gd-doped Kondo Semiconductor
Experiments on the Electron Spin Resonance (ESR) in the filled
skutterudite (), at temperatures
where the host resistivity manifests a smooth insulator-metal crossover,
provides evidence of the underlying Kondo physics associated with this system.
At low temperatures (below ), behaves
as a Kondo-insulator with a relatively large hybridization gap, and the
ESR spectra displays a fine structure with lorentzian line shape,
typical of insulating media. The electronic gap is attributed to the large
hybridization present in the coherent regime of a Kondo lattice, when Ce
4f-electrons cooperate with band properties at half-filling. Mean-field
calculations suggest that the electron-phonon interaction is fundamental at
explaining the strong 4f-electron hybridization in this filled skutterudite.
The resulting electronic structure is strongly temperature dependent, and at
about the system undergoes an insulator-to-metal
transition induced by the withdrawal of 4f-electrons from the Fermi volume, the
system becoming metallic and non-magnetic. The ESR fine structure
coalesces into a single dysonian resonance, as in metals. Still, our
simulations suggest that exchange-narrowing via the usual Korringa mechanism,
alone, is not capable of describing the thermal behavior of the ESR spectra in
the entire temperature region ( - K). We propose that temperature
activated fluctuating-valence of the Ce ions is the missing ingredient that,
added to the usual exchange-narrowing mechanism, fully describes this unique
temperature dependence of the ESR fine structure observed in
.Comment: 19 pages, 6 figure
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