2,146 research outputs found
Mergers of Black Hole -- Neutron Star binaries. I. Methods and First Results
We use a 3-D relativistic SPH (Smoothed Particle Hydrodynamics) code to study
mergers of black hole -- neutron star (BH--NS) binary systems with low mass
ratios, adopting as a representative case. The
outcome of such mergers depends sensitively on both the magnitude of the BH
spin and its obliquity (i.e., the inclination of the binary orbit with respect
to the equatorial plane of the BH). In particular, only systems with
sufficiently high BH spin parameter and sufficiently low orbital
inclinations allow any NS matter to escape or to form a long-lived disk outside
the BH horizon after disruption. Mergers of binaries with orbital inclinations
above lead to complete prompt accretion of the entire NS by the BH,
even for the case of an extreme Kerr BH. We find that the formation of a
significant disk or torus of NS material around the BH always requires a
near-maximal BH spin and a low initial inclination of the NS orbit just prior
to merger.Comment: to appear in ApJ, 54 pages, 19 figure
Barotropic thin shells with linear EOS as models of stars and circumstellar shells in general relativity
The spherically symmetric thin shells of the barotropic fluids with the
linear equation of state are considered within the frameworks of general
relativity. We study several aspects of the shells as completely relativistic
models of stars, first of all the neutron stars and white dwarfs, and
circumstellar shells. The exact equations of motion of the shells are obtained.
Also we calculate the parameters of the equilibrium configurations, including
the radii of static shells. Finally, we study the stability of the equilibrium
shells against radial perturbations.Comment: final version; ps-version of figure is available by email request to
[email protected]
Tipificación de dos nombres en el género Asperula (Rubiaceae)
The typification of two names in the genus Asperula, A. cynanchica subsp. pyrenaica and A. paui subsp. dianensis (Rubiaceae), applicable to species endemic to the Iberian Peninsula and France, is discussed. Specimens from UPS (Herbarium Burser, Uppsala University) and BC (Institut Botànic of Barcelona) are indicated and designated as lectotypes of, respectively, A. pyrenaica and A. paui var. dianensisSe discute la tipificación de dos nombres en el género Asperula, A. cynanchica subsp. pyrenaica y A. paui subsp. dianensis (Rubiaceae) aplicables a especies endémicas de la Península Ibérica y Francia. Especímenes de UPS (Herbario Burser, Universidad de Uppsala) y BC (Institut Botànic de Barcelona) son indicados y designados como lectotipos de A. pyrenaica and A. paui var. dianensis, respectivamente
Mass of perfect fluid black shells
The spherically symmetric singular perfect fluid shells are considered for
the case of their radii being equal to the event horizon (the black shells). We
study their observable masses, depending at least on the three parameters,
viz., the square speed of sound in the shell, instantaneous radial velocity of
the shell at a moment when it reaches the horizon, and integration constant
related to surface mass density. We discuss the features of black shells
depending on an equation of state.Comment: 1 figure, LaTeX; final version + FA
Tipificació de dos noms Cavanillesians, Galium Fruticescens (Rubiaceae) i Scorzonera pumila (Compositae)
The Cavanillesian names Galium fruticescens and Scorzonera pumila, basionym of Launaea pumila, are lectotypified from original specimens preserved in the Cavanilles herbarium in the Royal Botanic Garden of Madrid (MA).Els noms cavanillesians Galium fruticescens i Scorzonera pumila, basiònim de Launaea pumila, són lectotipificats a partir d’espècimens que pertanyen al material original de l’autor conservat a l’herbari del Reial Jardí Botànic de Madrid (MA)
Why, when, and how fast innovations are adopted
When the full stock of a new product is quickly sold in a few days or weeks,
one has the impression that new technologies develop and conquer the market in
a very easy way. This may be true for some new technologies, for example the
cell phone, but not for others, like the blue-ray. Novelty, usefulness,
advertising, price, and fashion are the driving forces behind the adoption of a
new product. But, what are the key factors that lead to adopt a new technology?
In this paper we propose and investigate a simple model for the adoption of an
innovation which depends mainly on three elements: the appeal of the novelty,
the inertia or resistance to adopt it, and the interaction with other agents.
Social interactions are taken into account in two ways: by imitation and by
differentiation, i.e., some agents will be inclined to adopt an innovation if
many people do the same, but other will act in the opposite direction, trying
to differentiate from the "herd". We determine the conditions for a successful
implantation of the new technology, by considering the strength of advertising
and the effect of social interactions. We find a balance between the
advertising and the number of anti-herding agents that may block the adoption
of a new product. We also compare the effect of social interactions, when
agents take into account the behavior of the whole society or just a part of
it. In a nutshell, the present model reproduces qualitatively the available
data on adoption of innovation.Comment: 11 pages, 13 figures (with subfigures), full paper (EPJB 2012) on
innovation adoption mode
Investigation of Graded La2NiO4+ Cathodes to Improve SOFC Electrochemical Performance
Mixed ionic and electronic conducting MIEC oxides are promising materials for use as cathodes in solid oxide fuel cells SOFCs due to their enhanced electrocatalytic activity compared with electronic conducting oxides. In this paper, the MIEC oxide La2NiO4+ was prepared by the sol-gel route. Graded cathodes were deposited onto yttria-stabilized zirconia YSZ pellets by dip-coating, and electrochemical impedance spectroscopy studies were performed to characterize the symmetrical cell performance. By adapting the slurries, cathode layers with different porosities and thicknesses were obtained. A ceria gadolinium oxide CGO barrier layer was introduced, avoiding insulating La2Zr2O7 phase formation and thus reducing resistance polarization of the cathode. A systematic correlation between microstructure, composition, and electrochemical performance of these cathodes has been performed. An improvement of the electrochemical performance has been demonstrated, and a reduction in the area specific resistance ASR by a factor of 4.5 has been achieved with a compact interlayer of La2NiO4+ between the dense electrolyte and the porous La2NiO4+ cathode layer. The lowest observed ASR of 0.11 cm2 at 800°C was obtained from a symmetrical cell composed of a YSZ electrolyte, a CGO interlayer, an intermediate compact La2NiO4+ layer, a porous La2NiO4+ electrode layer, and a current collection layer of platinum paste
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