755 research outputs found
Core-crust transition pressure for relativistic slowly rotating neutron stars
We study the influence of core-\textit{crust} transition pressure changes on
the general dynamical properties of neutron star configurations. First we study
the matching conditions in core-\textit{crust} transition pressure region,
where phase transitions in the equation of state causes energy density jumps.
Then using a surface \textit{crust} approximation, we can construct
configurations where the matter is described by the equation of state of the
core of the star and the core-\textit{crust} transition pressure. We will
consider neutron stars in the slow rotation limit, considering perturbation
theory up to second order in the angular velocity so that the deformation of
the star is also taken into account. The junction determines the parameters of
the star such as total mass, angular and quadrupolar momentum.Comment: 4 pages, 1 figur
New model of relativistic slowly rotating neutron stars with surface layer \textit{crust}: application to giant \textit{glitches} of Vela Pulsar
Introducing a surface layer of matter on the edge of a neutron star in slow
rigid rotation, we analyze, from an intrinsic point of view, the junction
conditions that must be satisfied between the interior and exterior solutions
of the Einstein equations. In our model the core-\textit{crust} transition
pressure arise as an essential parameter in the description of a configuration.
As an application of this formalism, we describe giant \textit{glitches} of the
Vela pulsar as a result of variations in the transition pressure, finding that
these small changes are compatible with the expected temperature variations of
the inner crust during \textit{glitch} time.Comment: 4 pages, 2 figures, to appear in Proceedings of Spanish Relativity
Meeting 2010 (ERE 2010) held in Granada, Spai
Blood–brain barrier and foetal-onset hydrocephalus, with a view on potential novel treatments beyond managing CSF flow
[EN] Despite decades of research, no compelling non-surgical therapies have been developed for foetal hydrocephalus. So
far, most efforts have pointed to repairing disturbances in the cerebrospinal fluid (CSF) flow and to avoid further brain
damage. There are no reports trying to prevent or diminish abnormalities in brain development which are inseparably
associated with hydrocephalus. A key problem in the treatment of hydrocephalus is the blood–brain barrier
that restricts the access to the brain for therapeutic compounds or systemically grafted cells. Recent investigations
have started to open an avenue for the development of a cell therapy for foetal-onset hydrocephalus. Potential cells
to be used for brain grafting include: (1) pluripotential neural stem cells; (2) mesenchymal stem cells; (3) geneticallyengineered
stem cells; (4) choroid plexus cells and (5) subcommissural organ cells. Expected outcomes are a proper
microenvironment for the embryonic neurogenic niche and, consequent normal brain development
Evidence of ongoing radial migration in NGC 6754: Azimuthal variations of the gas properties
Understanding the nature of spiral structure in disk galaxies is one of the
main, and still unsolved questions in galactic astronomy. However, theoretical
works are proposing new testable predictions whose detection is becoming
feasible with recent development in instrumentation. In particular, streaming
motions along spiral arms are expected to induce azimuthal variations in the
chemical composition of a galaxy at a given galactic radius. In this letter we
analyse the gas content in NGC 6754 with VLT/MUSE data to characterise its 2D
chemical composition and H line-of-sight velocity distribution. We find
that the trailing (leading) edge of the NGC 6754 spiral arms show signatures of
tangentially-slower, radially-outward (tangentially-faster, radially-inward)
streaming motions of metal-rich (poor) gas over a large range of radii. These
results show direct evidence of gas radial migration for the first time. We
compare our results with the gas behaviour in a -body disk simulation
showing spiral morphological features rotating with a similar speed as the gas
at every radius, in good agreement with the observed trend. This indicates that
the spiral arm features in NGC 6754 may be transient and rotate similarly as
the gas does at a large range of radii.Comment: 8 pages, 4 figures, accepted for publication in ApJL 2016 September
2
Universal relations for quasinormal modes of neutron stars in gravity
We construct quasinormal modes for neutron stars in gravity in the
Einstein frame, considering scalar masses in the sub-neV range. In particular,
we investigate the fundamental quadrupole fluid f-modes and the dipole fluid
F-modes. Employing six equations of state covering matter content with
nucleons, hyperons, and quarks, we then propose universal relations for the
quadrupole f-modes and dipole F-modes. The dipole F-modes are ultra-long lived
and, for the lower scalar masses, their frequencies are inversely proportional
to the corresponding Compton wavelength.Comment: 25 pages, 23 figures; Some figures update
Census of HII regions in NGC 6754 derived with MUSE: Constraints on the metal mixing scale
We present a study of the HII regions in the galaxy NGC 6754 from a two
pointing mosaic comprising 197,637 individual spectra, using Integral Field
Spectrocopy (IFS) recently acquired with the MUSE instrument during its Science
Verification program. The data cover the entire galaxy out to ~2 effective
radii (re ), sampling its morphological structures with unprecedented spatial
resolution for a wide-field IFU. A complete census of the H ii regions limited
by the atmospheric seeing conditions was derived, comprising 396 individual
ionized sources. This is one of the largest and most complete catalogue of H ii
regions with spectroscopic information in a single galaxy. We use this
catalogue to derive the radial abundance gradient in this SBb galaxy, finding a
negative gradient with a slope consistent with the characteristic value for
disk galaxies recently reported. The large number of H ii regions allow us to
estimate the typical mixing scale-length (rmix ~0.4 re ), which sets strong
constraints on the proposed mechanisms for metal mixing in disk galaxies, like
radial movements associated with bars and spiral arms, when comparing with
simulations. We found evidence for an azimuthal variation of the oxygen
abundance, that may be related with the radial migration. These results
illustrate the unique capabilities of MUSE for the study of the enrichment
mechanisms in Local Universe galaxies.Comment: 13 pages, 7 Figurs, accepted for publishing in A&
Tourist spaces and tourism policy in Spain and Portugal
Advances in Cultura, Tourism and Hospitality Research;10, 235-249This study analyses the relationship between the development of the tourism policy of Spain and Portugal and their effects on regional imbalances. Despite the proximity of the two countries and their specialisation in tourism, there are few comparative studies on tourism of the two Iberian countries. The study focuses on the two major phases of tourism policy: the period of mass tourism and post-Fordist stage. In the conclusions we refer the debate on the existence of a model of development based on tourism to the Latin countries of Southern Europe and we note the export process of the Spanish low-cost tourism model to other countries.Financiado por el Gobierno de España, Programa Fundamental de Investigación, Proyecto de I+D (CSO2012-30840) "Geografías de la crisis: análisis de los territorios urbanos y turísticos de las Islas Baleares, Costa del Sol y principales destinos del Caribe y América Central"
Magnetic permeability of ( Fe Co Ge ) 88 Zr 6 B 5 Cu 1 alloys: Thermal stability in a wide temperature range.
Temperature dependence, from room temperature up to 1000 K, of the initial permeability of
Fe83−xCoxGe5Zr6B5Cu1 x=5 and 20 alloys at different stages of devitrification is reported. As
nanocrystallization progresses, room temperature decreases but high temperature one increases,
leading to an improvement of its thermal stability extended from room temperature up to 915 K,
characterized by a temperature coefficient of permeability 0.1%/K 4000 and 0.04%/K
800 for 5 and 20 at. % Co containing alloys, respectively
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