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

SkewEngine: enhancing performance of intensive calculations on regular meshes

In various applications such as hyperspectral data manipulation, MRI data exploration, or visual basin identification in digital elevation models, performing arithmetic operations on each point of a data mesh that involve other points can lead to computationally intractable problems. This paper presents SkewEngine, a tool designed to improve the performance of intensive calculations on regular 2D or 3D data meshes, such as images, multispectral data volumes, or digital elevation models. SkewEngine addresses this problem by reorganizing the mesh in memory according to a preferred spatial direction, enabling more efficient execution of intensive calculations. It is demonstrated that SkewEngine offers significant speed improvements for a variety of test cases, suggesting its usefulness in a broader range of applications requiring intensive data processing on regular meshes.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

SkewEngine: enhancing performance of intensive calculations on regular meshes

In various applications such as hyperspectral data manipulation, MRI data exploration, or viewshed identification in digital elevation models, performing arithmetic operations on each point of a data mesh that involves other points can lead to computationally intractable problems. This paper presents SkewEngine, a tool designed to improve the performance of intensive calculations on regular 2-D data meshes, such as images, multispectral data volumes, or digital elevation models. SkewEngine addresses this problem by reorganizing the mesh in memory according to a preferred spatial direction, enabling more efficient execution of intensive calculations. It is demonstrated that SkewEngine offers significant speed improvements for various test cases, suggesting its usefulness in a broader range of applications requiring intensive data processing on regular meshes.Funding for open access charge: Universidad de Málaga/CBUA. This work has been fnanced by the Spanish Ministry of Science and Technology through the National Plan project PID2022-136575OB-I00, by the Andalusian Government and FEDER funds through the UMA20-FEDERJA-127 project, and by the University of Malaga (PIE22-099). We also thank the Supercomputing and Bioinformatics Service of the University of Malaga and the Spanish Supercomputing Network for facilitating access to the Picasso and Loginexa Supercomputers

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