5,030 research outputs found
Rings and spirals in barred galaxies. I Building blocks
In this paper we present building blocks which can explain the formation and
properties both of spirals and of inner and outer rings in barred galaxies. We
first briefly summarise the main results of the full theoretical description we
have given elsewhere, presenting them in a more physical way, aimed to an
understanding without the requirement of extended knowledge of dynamical
systems or of orbital structure. We introduce in this manner the notion of
manifolds, which can be thought of as tubes guiding the orbits. The dynamics of
these manifolds can govern the properties of spirals and of inner and outer
rings in barred galaxies. We find that the bar strength affects how unstable
the L1 and L2 Lagrangian points are, the motion within the 5A5A5Amanifold tubes
and the time necessary for particles in a manifold to make a complete turn
around the galactic centre. We also show that the strength of the bar, or, to
be more precise, of the non-axisymmetric forcing at and somewhat beyond the
corotation region, determines the resulting morphology. Thus, less strong bars
give rise to R1 rings or pseudorings, while stronger bars drive R2, R1R2 and
spiral morphologies. We examine the morphology as a function of the main
parameters of the bar and present descriptive two dimensional plots to that
avail. We also derive how the manifold morphologies and properties are modified
if the L1 and L2 Lagrangian points become stable. Finally, we discuss how
dissipation affects the manifold properties and compare the manifolds in
gas-like and in stellar cases. Comparison with observations, as well as clear
predictions to be tested by observations will be given in an accompanying
paper.Comment: Typos corrected to match the version in press in MNRA
Generation of H₂ on Board Lng Vessels for Consumption in the Propulsion System
[Abstract] At present, LNG vessels without reliquefaction plants consume the BOG (boil-off gas) in their engines and the excess is burned in the gas combustion unit without recovering any of its energy content. Excess BOG energy could be captured to produce H₂, a fuel with high energy density and zero emissions, through the installation of a reforming plant. Such
H₂ production would, in turn, require on-board storage for its subsequent consumption in the propulsion plant when navigating in areas with stringent anti-pollution regulations, thus reducing CO₂ and SOₓ emissions. This paper presents a review of the different H₂ storage systems and the methods of burning it in propulsion engines, to demonstrate the energetic viability thereof on board LNG vessels. Following the analysis, it is identified that a pressurised and cooled
H₂ storage system is the best suited to an LNG vessel due to its simplicity and the fact that it does not pose a safety hazard. There are a number of methods for consuming the H₂ generated in the DF engines that comprise the propulsión plant, but the use of a mixture of 70% CH₄-30% H₂ is the most suitable as it does not require any modifications to the
injection system. Installation of an on-board reforming plant and H₂ storage system generates sufficient H₂ to allow for almost 3 days’ autonomy with a mixture of 70%CH₄-30%H₂. This reduces the engine consumption of CH₄ by 11.38%,thus demonstrating that the system is not only energy-efficient, but lends greater versatility to the vessel
Kinematic groups across the MW disc: insights from models and from the RAVE catalogue
With the advent of the Gaia data, the unprecedented kinematic census of great
part of the Milky Way disc will allow us to characterise the local kinematic
groups and new groups in different disc neighbourhoods. First, we show here
that the models predict a stellar kinematic response to the spiral arms and bar
strongly dependent on disc position. For example, we find that the kinematic
groups induced by the spiral arm models change significantly if one moves only
~ 0.6 kpc in galactocentric radius, but ~ 2 kpc in azimuth. There are more and
stronger groups as one approaches the spiral arms. Depending on the spiral
pattern speed, the kinematic imprints are more intense in nearby vicinities or
far from the Sun. Secondly, we present a preliminary study of the kinematic
groups observed by RAVE. This sample will allow us, for the first time, to
study the dependence on Galactic position of the (thin and thick) disc moving
groups. In the solar neighbourhood, we find the same kinematics groups as
detected in previous surveys, but now with better statistics and over a larger
spatial volume around the Sun. This indicates that these structures are indeed
large scale kinematic features.Comment: 4 pages, 3 figures, to appear in the proceedings of "Assembling the
Puzzle of the Milky Way", Le Grand Bornand (April 17-22, 2011), C. Reyle, A.
Robin, M. Schultheis (eds.
Understanding the spiral structure of the Milky Way using the local kinematic groups
We study the spiral arm influence on the solar neighbourhood stellar
kinematics. As the nature of the Milky Way (MW) spiral arms is not completely
determined, we study two models: the Tight-Winding Approximation (TWA) model,
which represents a local approximation, and a model with self-consistent
material arms named PERLAS. This is a mass distribution with more abrupt
gravitational forces. We perform test particle simulations after tuning the two
models to the observational range for the MW spiral arm properties. We explore
the effects of the arm properties and find that a significant region of the
allowed parameter space favours the appearance of kinematic groups. The
velocity distribution is mostly sensitive to the relative spiral arm phase and
pattern speed. In all cases the arms induce strong kinematic imprints for
pattern speeds around 17 km/s/kpc (close to the 4:1 inner resonance) but no
substructure is induced close to corotation. The groups change significantly if
one moves only ~0.6 kpc in galactocentric radius, but ~2 kpc in azimuth. The
appearance time of each group is different, ranging from 0 to more than 1 Gyr.
Recent spiral arms can produce strong kinematic structures. The stellar
response to the two potential models is significantly different near the Sun,
both in density and kinematics. The PERLAS model triggers more substructure for
a larger range of pattern speed values. The kinematic groups can be used to
reduce the current uncertainty about the MW spiral structure and to test
whether this follows the TWA. However, groups such as the observed ones in the
solar vicinity can be reproduced by different parameter combinations. Data from
velocity distributions at larger distances are needed for a definitive
constraint.Comment: 18 pages, 21 figures, 4 tables; acccepted for publication in MNRA
Modelos de representación de imprecisión e incertidumbre en fusión de alto nivel
Actas de: XVII Congreso Español sobre Tecnologías y Lógica Fuzzy (ESTYLF 2014). Zaragoza, 5-7 de febrero de 2014.Las técnicas de fusión de datos e información procedente de redes de sensores necesitan manejar información incierta e imprecisa, puesto que es habitual enfrentarse a problemas en los que el conocimiento disponible es vago o insuficiente y/o los aparatos de medición están sujetos a fallos. Con el reciente auge de la denominada "fusión de alto nivel", que tiene como objetivo reconocer la situación observada e identificar posibles riesgos, este problema se ha acentuado, ya que los formalismos que se utilizan habitualmente para construir un modelo simbólico del escenario, como la lógica de primer orden y las ontologías, no proporcionan soporte para este tipo de conocimiento. En este trabajo repasamos varias propuestas recientes para representación y razonamiento con información incierta e imprecisa en fusión de alto nivel. Nos centramos en dos tipos: (a) las que incorporan estos mecanismos en los propios modelos de representación, como las ontologías probabilísticas y difusas y las redes lógicas de Markov; (b) las que extienden el proceso de fusión con una capa de gestión de incertidumbre adicional, como las basadas en argumentación probabilística.Este trabajo ha sido financiado por la Junta de Andalucía (P11-TIC-7460), la Comunidad de Madrid (S2009/TIC- 1485) y el Ministerio de Economía y Competitividad de España (TEC2012-37832-C02-01, TEC2011-28626-C02- 02, TIN2012-30939).Publicad
Formation of asymmetric arms in barred galaxies
ABSTRACTWe establish a dynamical mechanism to explain the origin of the asymmetry between the arms observed in some barred disc galaxies, where one of the two arms emanating from the bar ends is very well defined, while the second one displays a ragged structure, extending between its ridge and the bar. To this purpose, we study the invariant manifolds associated with the Lyapunov periodic orbits around the unstable equilibrium points at the ends of the bar. Matter from the galaxy centre is transported along these manifolds to the periphery, forming this way the spiral arms that emanate from the bar ends. If the mass distribution in the galaxy centre is not homogeneous, because of an asymmetric bar with one side stronger than the other, or because of a non-centred bulge, the dynamics about the two unstable Lagrange points at the ends of the bar will not be symmetric as well. One of their invariant manifolds becomes more extended than the other, enclosing a smaller section and the escaping orbits on it are fewer and dispersed in a wider region. The result is a weaker arm and more ragged than the one at the other end of the bar
Addicions a la flora algològica del Principat de Catalunya
In a sandy-bed near Arenys de Mar (Barcelona, Spain) some algal species were collected, using scuba-diving techniques, at 25-32 m depth. Three of them were for the first time found in the catalan coast: Halymenia latifolia Crouan & Crouan, Halymenia floresia (Clemente) C. Agardh var. pinnata Codomier and Carpomitra costata (Stackhouse) Batters var. mediterranea Feldmann
Generalized Berreman's model of the elastic surface free energy of a nematic liquid crystal on a sawtoothed substrate
In this paper we present a generalization of Berreman's model for the elastic
contribution to the surface free-energy density of a nematic liquid crystal in
presence of a sawtooth substrate which favours homeotropic anchoring, as a
function of the wavenumber of the surface structure , the tilt angle
and the surface anchoring strength . In addition to the previously
reported non-analytic contribution proportional to , due to the
nucleation of disclination lines at the wedge bottoms and apexes of the
substrate, the next-to-leading contribution is proportional to for a given
substrate roughness, in agreement with Berreman's predictions. We characterise
this term, finding that it has two contributions: the deviations of the nematic
director field with respect to the corresponding to the isolated disclination
lines, and their associated core free energies. Comparison with the results
obtained from the Landau-de Gennes model shows that our model is quite accurate
in the limit , when strong anchoring conditions are effectively achieved.Comment: 13 pages, 9 figures; revised version submitted to Phys. Rev.
Violencia en el puesto de trabajo sanitario, análisis situacional y experiencias de las víctimes
Les agressions sofrides pels treballadors del sector sanitari públic en raó de la seva activitat i materialitzades pels usuaris ( violència tipus II ) , han d'emmarcar com a situacions de risc laboral .
L'objectiu és comprendre a través de les vivències relatades pels treballadors , la seva freqüència , les característiques , antecedents i conseqüències dins el context d'un Departament de Salut , a través de la combinació de dos tipus de metodologia ( la qualitativa i la quantitativa ) que es complementen per ajudar-nos a comprendre el fenomen a estudi , i poder donar pas a dirigir accions preventives en el lloc de treball que evitin agressions dels clients externs cap als professionals sanitaris gràcies al descobriment dels factors de risc precipitadors que ens ajudaran a dibuixar línies mestres d'un programa d'intervenció psicosocial .Las agresiones sufridas por los trabajadores del sector sanitario público en razón de su actividad y materializadas por los usuarios (violencia tipo II), deben enmarcarse como situaciones de riesgo laboral.
El objetivo es comprender a través de las vivencias relatadas por los trabajadores, su frecuencia, las características, antecedentes y consecuencias dentro del contexto de un Departamento de Salud, a través de la combinación de dos tipos de metodología (la cualitativa y la cuantitativa) que se complementan para ayudarnos a comprender el fenómeno a estudio, y poder dar paso a dirigir acciones preventivas en el lugar de trabajo que eviten agresiones de los clientes externos hacia los profesionales sanitarios gracias al descubrimiento de los factores de riesgo precipitadores que nos ayudarán a dibujar líneas maestras de un programa de intervención psicosocial.The violence in the public health sector because of their activity and materialized by users (type II violence ) should be framed as situations of occupational hazard.
The goal is to understand through the experiences reported by workers , their frequency , characteristics , background and consequences in the context of a Department of Health, through the combination of two types of methodology ( qualitative and quantitative ) that They complement to help us understand the phenomenon to study, and to give way to direct preventive measures in the workplace to prevent attacks from external clients to health professionals through the discovery of precipitators risk factors that will help us draw lines master of a psychosocial intervention program
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