Cosmic web alignments with the shape, angular momentum and peculiar velocities of dark matter haloes

We study the alignment of dark matter haloes with the cosmic web characterized by the tidal and velocity shear fields. We focus on the alignment of their shape, angular momentum and peculiar velocities. We use a cosmological N-body simulation that allows to study dark matter halos spanning almost five orders of magnitude in mass ($10^{9}$-$10^{14}$) $h^{-1}$$M_{\odot}$ and spatial scales of $(0.5$-$1.0)$ $h^{-1}$ Mpc to define the cosmic web. We find that the halo shape presents the strongest alignment along the smallest tidal eigenvector, e.g. along filaments and walls, with a signal that gets stronger as the halo mass increases. In the case of the velocity shear field only massive halos $>10^{12}$ $h^{-1}$$M_{\odot}$ tend to have their shapes aligned along the largest tidal eigenvector; that is, perpendicular to filaments and walls. For the angular momentum we find alignment signals only for halos more massive than $10^{12}$ $h^{-1}$$M_{\odot}$ both in the tidal and velocity shear webs where the preferences are for it to be parallel to the middle eigenvector; perpendicular to filaments and parallel to walls. Finally, the peculiar velocities show a strong alignment along the smallest tidal eigenvector for all halo masses; halos move along filaments and walls. In the velocity shear the same alignment is present but weaker and only for haloes less massive than $10^{12}$ $h^{-1}$$M_{\odot}$. Our results clearly show that the two different algorithms we used to define the cosmic web describe different physical aspects of non-linear collapse and should be used in a complementary way to understand the effect of the cosmic web on galaxy evolution.Comment: 14 pages, 5 figures, MNRAS accepte

Stochastic angular momentum slews and flips and their effect on discs in galaxy formation models

The angular momentum of galactic discs in semi-analytic models of galaxy formation is usually updated in time as material is accreted to the disc by adopting a constant dimensionless spin parameter and little attention is paid to the effects of accretion with misaligned angular momenta. These effects are the subject of this paper, where we adopt a Monte-Carlo simulation for the changes in the direction of the angular momentum of a galaxy disc as it accretes matter based on accurate measurements from dark-matter haloes in the Millennium II simulation. In our semi-analytic model implementation, the flips seen the dark matter haloes are assumed to be the same for the cold baryons; however, we also assume that in the latter the flip also entails a difficulty for the disc to increase its angular momentum which causes the disc to become smaller relative to a no-flip case. This makes star formation to occur faster, specially in low mass galaxies at all redshifts allowing galaxies to reach higher stellar masses faster. We adopt a new condition for the triggering of starbursts during mergers. As these produce the largest flips it is natural to adopt the disc instability criterion to evaluate the triggering of bursts in mergers instead of one based on mass ratios as in the original model. The new implementation reduces the average lifetimes of discs by a factor of 2, while still allowing old ages for the present-day discs of large spiral galaxies. It also provides a faster decline of star formation in massive galaxies and a better fit to the bright end of the luminosity function at z = 0.Comment: 15 pages, 12 figures, MNRAS in pres

Galactic conformity measured in semi-analytic models

We study the correlation between the specific star formation rate of central galaxies and neighbour galaxies, also known as 'galactic conformity', out to 20 Mpc/h using three semi-analytic models (SAMs, one from L-GALAXIES and other two from GALFORM). The aim is to establish whether SAMs are able to show galactic conformity using different models and selection criteria. In all the models, when the selection of primary galaxies is based on an isolation criterion in real space, the mean fraction of quenched galaxies around quenched primary galaxies is higher than that around star-forming primary galaxies of the same stellar mass. The overall signal of conformity decreases when we remove satellites selected as primary galaxies, but the effect is much stronger in GALFORM models compared with the L-GALAXIES model. We find this difference is partially explained by the fact that in GALFORM once a galaxy becomes a satellite remains as such, whereas satellites can become centrals at a later time in L-GALAXIES. The signal of conformity decreases down to 60% in the L-GALAXIES model after removing central galaxies that were ejected from their host halo in the past. Galactic conformity is also influenced by primary galaxies at fixed stellar mass that reside in dark matter haloes of different masses. Finally, we explore a proxy of conformity between distinct haloes. In this case the conformity is weak beyond ~ 3 Mpc/h (<3% in L-GALAXIES, <1-2% in GALFORM models). Therefore, it seems difficult that conformity is directly related with a long-range effect.Comment: 15 pages, 7 figures. Accepted for publication in MNRA

Rho GTPases: regulation of cell polarity and growth in yeasts

11 páginas, 4 figuras, 1 tabla.-- El pdf del artículo es la versión post-print.Eukaryotic cells display a wide range of morphologies important for cellular function and development. A particular cell shape is made via the generation of asymmetry in the organization of cytoskeletal elements, usually leading to actin localization at sites of growth. The Rho family of GTPases is present in all eukaryotic cells, from yeast to mammals, and their role as key regulators in the signalling pathways that control actin organization and morphogenetic processes is well known. In the present review we will discuss the role of Rho GTPases as regulators of yeasts' polarized growth, their mechanism of activation and signalling pathways in Saccharomyces cerevisiae and Schizosaccharomyces pombe. These two model yeasts have been very useful in the study of the molecular mechanisms responsible for cell polarity. As in other organisms with cell walls, yeast's polarized growth is closely related to cell-wall biosynthesis, and Rho GTPases are critical modulators of this process. They provide the co-ordinated regulation of cell-wall biosynthetic enzymes and actin organization required to maintain cell integrity during vegetative growth.Work in the authors’ laboratory is supported by the Direcci-on General de Investigación, MICINN, Spain [grant number BFU2007-60675]; and the Junta de Castilla y León [grant number GR231].Peer reviewe

La transformación urbana de Medellín : 2004-2007

1 archivo PDF (Tipo: Presentación) : principalmente ilustraciones en color ; 129 diapositivas.En Colombia un porcentaje muy importante de la población vive en condiciones de pobreza y han generado sus satisfactores básicos de espacio urbano y vivienda por sus propios medios. De esta forma, la urbanización informal y la autoconstrucción han representado la alternativa para miles de habitantes de Medellín. La política urbana implementada en la gestión municipal 2004-2007, ha logrado que Medellín se haya transformado en un lapso de tiempo muy corto en una ciudad integrada para todos sus habitantes. Estos cambios, de reforma urbana, han sido posibles a partir de un plan urbano orientado en dos ejes fundamentales: la solución de los graves problemas y carencias en las comunas y la jerarquización y dignificación del espacio público de la ciudad. SUIQUINQU

DC-Voltage-Ratio Control Strategy for Multilevel Cascaded Converters Fed With a Single DC Source

Recently, a multilevel cascaded converter fed with a single DC source has been presented. An analysis of the steady-state working limits of this type of converter is presented in this paper. Limits of the maximum output voltage and the minimum and maximum loading conditions for stable operation of the converter are addressed. In this paper, a way to achieve any DC voltage ratio (inside the stable operation area of the converter) between the H-bridges of the single-DC-source cascaded H-bridge converter is presented. The proposed DC-voltage-ratio control is based on a time-domain modulation strategy that avoids the use of inappropriate states to achieve the DC-voltage-ratio control. The proposed technique is a feedforward-modulation technique which takes into account the actual DC voltage of each H-bridge of the converter, leading to output waveforms with low distortion. In this way, the dc voltage of the floating H-bridge can be controlled while the output voltage has low distortion independently of the desired DC voltage ratio. Experimental results from a two-cell cascaded converter are presented in order to validate the proposed DC-voltage-ratio control strategy and the introduced concepts.Ministerio de Ciencia y Tecnología TEC2006-03863Junta de Andalucía EXC/2005/TIC-117

Gestión de datos de investigación en los Observatorios de Turismo Regional en Chile

The article presents the results of a study about Chile's experience in the creation of Tourism Observatories in regions of Chile, considering two dimensions of study: firstly, regarding the level of performance achieved according to its basal purposes: To monitor tourism activity and generate information to aid decision-making, and secondly, to the way in which they conducted the management of tourism research data, considering management and opening processes. The main problem evidenced in the Observatories of tourism was the constitution, management and diffusion of the data that they had to provide.En el artículo se exponen los resultados de un estudio sobre la experiencia que tuvo Chile en la creación de Observatorios de turismo en regiones de Chile, considerando dos dimensiones de estudio: en primer lugar, respecto al nivel de desempeño alcanzado atendiendo a sus propósitos basales: monitorear la actividad turística y generar información de ayuda a la toma de decisiones, y en segundo lugar, respecto a la manera en que realizaron la gestión de datos de investigación en turismo, considerando procesos de gestión y apertura. El principal problema evidenciado en los Observatorios de turismo fue la constitución, gestión y difusión de los datos que debían proveer

Pedro Casaldáliga, el obispo con la mitra de paja

Entre las voces más críticas y demandantes dentro de la Iglesia católica en el siglo XX, que constataban la necesidad de un cambio de criterios y valores en el modo de ejercer su misión en el mundo, estuvo la de Pedro Casaldáliga, un sacerdote claretiano de origen catalán, nacido el 16 de febrero de 1928, que se convertiría en uno de los profetas más auténticos dentro y fuera de la Iglesia, y uno de los forjadores de la llamada Teología de la Liberación. En este capítulo, se revisa la vida y obra de Casaldáliga y algunos de los cimientos más importantes de su vida, que fundamentan su inspiración poética, su praxis y opciones pastorales al servicio de los hombres y la Iglesia

Ciudades en expansión y transformación. Crecimiento y estructura urbana en ciudades mexicanas

El trabajo que se presenta es una síntesis de un proyecto de investigación cuyo objetivo principal fue el de indagar acerca de las formas de expansión y de las transformaciones en la estructura urbana, esto es, de la forma de organización de los elementos materiales de la ciudad, en un grupo de ciudades mexicanas de tamaño medio que presentaron un rápido crecimiento demográfico y una expansión significativa de su área urbana en el periodo 1970-1990, pero a la vez, diferentes y específicos procesos económicos, sociales e históricos en su desarrollo urbano

Hábitat sustentable: temas, estrategias y proyectos

El urbanismo sustentable se orienta al desarrollo de comunidades urbanas en ambientes armónicos y equilibrados; se instrumenta en políticas públicas y proyectos urbanos que generan efectos positivos y sostenibles en el ámbito social y medioambiental. El presente artículo aborda temas generales y proyectos específicos que marcan tendencias en el fenómeno urbano y en las prácticas del urbanismo y la arquitectura sustentable en diferentes ámbitos del mundo. Se trata de textos presentados en el primer Seminario de Hábitat Sustentable organizado por la UAM-Azcapotzalco. Las prácticas del hábitat sustentable, con sus enfoques y planteamientos, deben ser vistas como una nueva etapa o paradigma en la larga tradición disciplinar de arquitectos y urbanistas. Las experiencias internacionales que se presentan son una muestra limitada, pero representativa, de la multiplicidad de temas y casos que hoy están dando impulso a la arquitectura y el urbanismo sustentable en el ámbito mundial.The sustainable urbanism focus into the development of urban communities in an harmonic context. This new practices have been arranged through public policies and urban projects with positive impacts in social and environmental terms. The article identifies general topics and specific projects that establish trends in the urban phenomena and the new sustainability practices in the entire world. These topics were exposed in the last ten editions of the International Urbanism Seminary (SUI), organized by the Universidad Autónoma Metropolitana-Azcapozlaco (UAM-A). This selection of topic and projects is only a little showcase of the enormous possibilities of situations that nowadays are driving the architecture and sustainable urbanism in the word