320 research outputs found
Advances in Using MRI to Estimate the Risk of Future Outcomes in Mental Health - Are We Getting There?
[No abstract available
Teucrium campanulatum L. (Lamiaceae), una nova espècie per a Catalunya
Es dóna a conèixer una nova localitat de Teucrium campanulatum al Segrià, que representa una novetat per a la flora de Catalunya. S'ha elaborat un mapa de la distribució de l'espècie, a partir de material d'herbari i bibliografia, i se'n comenta també l'ecologia. Es discuteix sobre les figures de protecció de l'espècie en l'àmbit espanyol, així com la seva inclusió al «Catàleg de la flora amenaçada de Catalunya».Tecucrium campanulatum has been found in Catalonia (Spain) for first time. The distribution map of the species is presented in all its area and comments about its ecology are done. We discussed about the protection of this species in other Spanish regions and the need to include it in the Red List for Catalonia
Forming first-ranked early-type galaxies through hierarchical dissipationless merging
We have developed a computationally competitive N-body model of a
previrialized aggregation of galaxies in a flat LambdaCDM universe to assess
the role of the multiple mergers that take place during the formation stage of
such systems in the configuration of the remnants assembled at their centres.
An analysis of a suite of 48 simulations of low-mass forming groups (of about
1E13 solar masses) demonstrates that the gravitational dynamics involved in
their hierarchical collapse is capable of creating realistic first-ranked
galaxies without the aid of dissipative processes. Our simulations indicate
that the brightest group galaxies (BGGs) constitute a distinct population from
other group members, sketching a scenario in which the assembly path of these
objects is dictated largely by the formation of their host system. We detect
significant differences in the distribution of Sersic indices and total
magnitudes, as well as a luminosity gap between BGGs and the next brightest
galaxy that is positively correlated with the total luminosity of the parent
group. Such gaps arise from both the grow of BGGs at the expense of lesser
companions and the decrease in the relevance of second-ranked objects in equal
measure. This results in a dearth of intermediate-mass galaxies which explains
the characteristic central dip detected in their luminosity functions in
dynamically young galaxy aggregations. The fact that the basic global
properties of our BGGs define a thin mass fundamental plane strikingly similar
to that followed giant early-type galaxies in the local universe reinforces
confidence in the results obtained.Comment: 25 pages, 14 figures, 3 tables. Accepted to MNRA
Scale Radii and Aggregation Histories of Dark Haloes
Relaxed dark-matter haloes are found to exhibit the same universal density
profiles regardless of whether they form in hierarchical cosmologies or via
spherical collapse. Likewise, the shape parameters of haloes formed
hierarchically do not seem to depend on the epoch in which the last major
merger took place. Both findings suggest that the density profile of haloes
does not depend on their aggregation history. Yet, this possibility is
apparently at odds with some correlations involving the scale radius r_s found
in numerical simulations. Here we prove that the scale radius of relaxed,
non-rotating, spherically symmetric haloes endowed with the universal density
profile is determined exclusively by the current values of four independent,
though correlated, quantities: mass, energy and their respective instantaneous
accretion rates. Under this premise and taking into account the inside-out
growth of haloes during the accretion phase between major mergers, we build a
simple physical model for the evolution of r_s along the main branch of halo
merger trees that reproduces all the empirical trends shown by this parameter
in N-body simulations. This confirms the conclusion that the empirical
correlations involving r_s do not actually imply the dependence of this
parameter on the halo aggregation history. The present results give strong
support to the explanation put forward in a recent paper by Manrique et al.
(2003) for the origin of the halo universal density profile.Comment: 13 pages, 8 figures, accepted for publication in MNRA
Implications of Halo Inside-out Growth on the X-Ray Properties of Nearby Galaxy Systems within the Preheating Scenario
We present an entirely analytic model for a preheated, polytropic
intergalactic medium in hydrostatic equilibrium within a NFW dark halo
potential in which the evolution of the halo structure between major merger
events proceeds inside-out by accretion. This model is used to explain, within
a standard CDM cosmogony, the observed X-ray properties of nearby
relaxed, non-cooling flow groups and clusters of galaxies. We find that our
preferred solution to the equilibrium equations produces scaling relations in
excellent agreement with observations, while simultaneously accounting for the
typical structural characteristics of the distribution of the diffuse baryons.
In the class of preheating models, ours stands out because it offers a unified
description of the intrahalo medium for galaxy systems with total masses above
\sm 2\times 10^{13}\msun, does not produce baryonic configurations with large
isentropic cores, and reproduces faithfully the observed behavior of the gas
entropy at large radii. All this is achieved with a moderate level of energy
injection of about half a keV, which can be easily accommodated within the
limits of the total energy released by the most commonly invoked feedback
mechanisms, as well as with a polytropic index of 1.2, consistent with both
many observational determinations and predictions from high-resolution
gas-dynamical simulations of non-cooling flow clusters. More interestingly, our
scheme offers a physical motivation for the adoption of this specific value of
the polytropic index, as it is the one that best ensures the conservation after
halo virialization of the balance between the total specific energies of the
gas and dark matter components for the full range of masses investigated.Comment: 18 pages, 11 figures, accepted for publication in the Astrophysical
Journa
Two-Temperature Intracluster Medium in Merging Clusters of Galaxies
We investigate the evolution of intracluster medium during a cluster merger,
explicitly considering the relaxation process between the ions and electrons by
N-body and hydrodynamical simulations. When two subclusters collide each other,
a bow shock is formed between the centers of two substructures and propagate in
both directions along the collision axis. The shock primarily heats the ions
because the kinetic energy of an ion entering the shock is larger than that of
an electron by the ratio of masses. In the post-shock region the energy is
transported from the ions to electrons via Coulomb coupling. However, since the
energy exchange timescale depends both on the gas density and temperature,
distribution of electron temperature becomes more complex than that of the
plasma mean temperature, especially in the expanding phase. After the collision
of two subclusters, gas outflow occurs not only along the collision axis but
also in its perpendicular direction. The gas which is originally located in the
central part of the subclusters moves both in the parallel and perpendicular
directions. Since the equilibrium timescale of the gas along these directions
is relatively short, temperature difference between ions and electrons is
larger in the directions tilted by the angles of with respect to
the collision axis. The electron temperature could be significantly lower that
the plasma mean temperature by at most. The significance of our
results in the interpretation of X-ray observations is briefly discussed.Comment: 20 pages, 11 figures, Accepted for publication in Ap
The origin of HI-deficiency in galaxies on the outskirts of the Virgo cluster. I. How far can galaxies bounce out of clusters?
Spiral galaxies that are deficient in neutral Hydrogen are observed on the
outskirts of the Virgo cluster. If their orbits have crossed the inner parts of
the cluster, their interstellar gas may have been lost through ram pressure
stripping by the hot X-ray emitting gas of the cluster. We estimate the maximum
radius out to which galaxies can bounce out of a virialized system using
analytical arguments and cosmological N-body simulations. In particular, we
derive an expression for the turnaround radius in a flat cosmology with a
cosmological constant that is simpler than previously derived expressions. We
find that the maximum radius reached by infalling galaxies as they bounce out
of their cluster is roughly between 1 and 2.5 virial radii. Comparing to the
virial radius of the Virgo cluster, which we estimate from X-ray observations,
these HI-deficient galaxies appear to lie significantly further away from the
cluster center. Therefore, if their distances to the cluster core are correct,
the HI-deficient spiral galaxies found outside of the Virgo cluster cannot have
lost their gas by ram pressure from the hot intracluster gas.Comment: A&A, in press. 8 pages LaTeX2e with 1 figur
Curso de Redes Interactivo
El artículo presenta una plataforma de desarrollo de cursos interactivos de autoaprendizaje en soporte informático para alumnos no presenciales y de repaso para los presenciales. Está basado en un programa modular que presenta al alumno la información de los cursos, accesible por unidades temáticas. Cada unidad consta de
una introducción, diversos apartados y un breve resumen. El programa es fácilmente ampliable por su arquitectura modular. Dentro de las unidades de cada curso se puede encontrar texto, esquemas, dibujos ilustrativos, gráficos, secuencias animadas y, también, una serie de preguntas intercaladas. Los dibujos, gráficos y demás elementos explicativos que no sean texto escrito contribuyen a captar la atención del alumno y las
preguntas ayudan a asimilar conceptos reflexionando sobre lo expuesto. El programa lee información previamente introducida por el profesor en bases de datos. Existe una base de datos principal a partir de la cual se puede acceder a los contenidos de todos los cursos disponibles.Boronat Segui, F.; Solanes, A.; Lloret, J. (2003). Curso de Redes Interactivo. Jornadas Sobre Enseñanza en las Escuelas de Telecomunicación. http://hdl.handle.net/10251/671
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