Wake Geometry Effects on Rotor Blade-Vortex Interaction Noise Directivity

Acoustic measurements from a model rotor wind tunnel test are presented which show that the directionality of rotor blade vortex interaction (BVI) noise is strongly dependent on the rotor advance ratio and disk attitude. A rotor free wake analysis is used to show that the general locus of interactions on the rotor disk is also strongly dependent on advance ratio and disk attitude. A comparison of the changing directionality of the BVI noise with changes in the interaction locations shows that the strongest noise radiation occurs in the direction of motion normal to the blade span at the time of interaction, for both advancing and retreating side BVI. For advancing side interactions, the BVI radiation angle down from the tip-path plane appears relatively insensitive to rotor operating condition and is typically between 40 and 55 deg below the disk. However, the azimuthal radiation direction shows a clear trend with descent speed, moving towards the right of the flight path with increasing descent speed. The movement of the strongest radiation direction is attributed to the movement of the interaction locations on the rotor disk with increasing descent speed

Frequency response calibration of recess-mounted pressure transducers

A technique is described for measuring the frequency response of pressure transducers mounted inside a model, where a narrow pipette leads to an orifice at the surface. An acoustic driver is mounted to a small chamber which has an opening at the opposite end with an O-ring seal to place over the orifice. A 3.18 mm (1/8 inch) reference microphone is mounted to one side of the chamber. The acoustic driver receives an input of white noise, and the transducer and reference microphone outputs are compared to obtain the frequency response of the pressure transducer. Selected results are presented in the form of power spectra for both the transducer and the reference, as well as the amplitude variation and phase shift between the two signals as a function of frequency. The effect of pipette length and the use of this technique for identifying both blocked orifices and faulty transducers are described

“ULACAV - Red Latinoamericana de Cátedras de Vivienda Social”

El objetivo ha sido promover acciones específicas de docencia, investigación y extensión en materia decooperativismo de vivienda entre las Universidades que conforman la Red Universitaria Latinoamericana deCátedras de Vivienda, a través de dos ejes: i) el conocimiento de la situación en Argentina, relacionada a laenseñanza de la economía social y solidaria y en particular del cooperativismo, ii) el rescate de laexperiencia internacional de algunas redes universitarias de origen latinoamericano y europeo, en materiade cooperativismo, con las que aparece conveniente establecer estrategias de integración que permitanmejorar las respuestas interdisciplinarias para la producción social del hábitat.Se parte de un análisis de la situación de la enseñanza del cooperativismo en general y del cooperativismode vivienda en particular, que se da hoy en diferentes universidades de la República Argentina yconcatenado con ello, las acciones de investigación y extensión que se llevan adelante. En oportunidad delCongreso Argentino de la Cooperación realizado en la Ciudad de Rosario (6, 7 Setiembre 2012), sepresentaron relevantes trabajos de investigación sobre los tres ejes que la educación superior debegarantizar. De allí surgen fuentes bibliográficas de enorme valor que ponen de manifiesto una centralidad dedichas investigaciones en las universidades de carácter estatal sin relevamiento de lo que sucede en elámbito universitario de gestión privada. Destacados autores nacionales, identificados como referentes de laeconomía social, trabajan con este sesgo de acentuar solamente lo público-estatal. Entonces es importantecomplementar esa información valiosa con lo que sucede en docencia, investigación y extensión desde lasuniversidades no estatales en materia de economía social y solidaria y de cooperativismo en particular,poniendo énfasis en las respuestas solidarias para la construcción de un hábitat social adecuado.Al respecto la Facultad de Arquitectura, Urbanismo y Diseño de la Universidad de Mendoza (FAUD-UM),considera que la producción cooperativa del Hábitat Social es uno de los caminos para optimizar el uso delos recursos destinados a solucionar los problemas habitacionales que aquejan a nuestra sociedad.Por ello, a través de su Cátedra de Vivienda Social y su Instituto de Vivienda Social (IVS), pone el acento enla formación de sus futuros profesionales en los conocimientos filosóficos y procesos de conformación delHábitat Cooperativo siguiendo tres ejes de acciones: a) respecto del grado y como parte de esta formación,se imparten conocimientos teóricos sobre asociativismo habitacional y se realizan trabajos prácticos queresponden a necesidades concretas de cooperativas locales (Mendoza, Argentina); b) en la formación deposgrado, actualmente se ha lanzado la Diplomatura Universitaria en Producción Asociativa deViviendas, que será continuada con una ESPECIALIZACIÓN y una MAESTRÍA EN HABITATCOOPERATIVO, en proceso de acreditación; c) en materia de investigación se desarrollan diferentesproyectos con participación de docentes-investigadores y alumnos y el respaldo del Centro deInvestigaciones Científicas y Tecnológicas y Vinculación (DICyTyV).La extensión universitaria desde la Cátedra y el IVS se realiza a través de convenios firmados, por ejemplocon la Federación de Cooperativas de Viviendas de Mendoza (FECOVIM) para que los estudiantes dearquitectura realicen cada año, prácticas en entidades de urbanización y vivienda de Mendoza.El segundo eje de análisis toma el caso de: a) la Red Universitaria Latinoamericana y Europea de Centros eInstitutos Universitarios de Cooperativismo – RULESCOOP; b) la Red de Investigadores Latinoamericanosde Economía Social y Solidaria – RILESS; c) la European Research Network – EMES; y d) la Asociación deUniversidades Grupo Montevideo AUGM- con su Comité Académico PROCOAS – Procesos Cooperativos eIniciativas Económicas Asociativas.En el marco institucional de ULACAV, camino a sus veinte años de existencia y tras valiosas experienciasque atraviesan los temas específicos de trabajo de la red, se espera poder profundizar la formación derecursos humanos en el área específica del cooperativismo habitacional. LA FAUD-UM como miembrotitular de la Red ULACAV, propone: 1) Crear un Programa de Movilidad Docente y Estudiantil paraintercambio de cátedras de vivienda social. 2) Promover investigaciones conjuntas 3) Establecervinculaciones y posibles convenios integrales de cooperación con las redes RULESCOOP, RILESS, EMESy PROCOAS – AUGM

Formation and Evolution of Dwarf Elliptical Galaxies - II. Spatially resolved star-formation histories

We present optical VLT spectroscopy of 16 dwarf elliptical galaxies (or dEs) comparable in mass to NGC 205, and belonging to the Fornax cluster and to nearby groups of galaxies. Using ULySS and STECKMAP, we derive radial profiles of the SSP-equivalent ages, metallicities and star-formation histories. The old stellar population of the dEs, which dominates their mass, is likely coeval with that of massive ellipticals or bulges, but the star formation efficiency is lower. Important intermediate age (1-5 Gyr) populations, and frequently tails of star formation until recent times are detected. These histories are reminiscent of their lower mass dSph counterparts of the Local Group. Most galaxies (10/16) show significant metallicity gradients, with metallicity declining by 0.5 dex over one half-light radius on average. These gradients are already present in the old population. The flattened (or discy), rotating objects (6/16) have flat metallicity profiles. This may be consistent with a distinct origin for these galaxies or it may be due to their geometry. The central SSP-equivalent age varies between 1 and 6 Gyr, with the age slowly increasing with radius in the vast majority of objects. The group and cluster galaxies have similar radial gradients and star-formation histories. The strong and old metallicity gradients place important constraints on the possible formation scenarios of dEs. Numerical simulations of the formation of spherical low-mass galaxies reproduce these gradients, but they require a longer time for them to build up. A gentle depletion of the gas, by ram-pressure stripping or starvation, could drive the gas-rich, star-forming progenitors to the present dEs.Comment: 21 pages, 9 figures. Accepted in MNRA

On the isolated dwarf galaxies: from cuspy to flat dark matter density profiles and metallicity gradients

The chemodynamical evolution of spherical multi-component self-gravitating models for isolated dwarf galaxies is studied. We compare their evolution with and without feedback effects from star formation processes. We find that initially cuspy dark matter profiles flatten with time as a result of star formation, without any special tuning conditions. Thus the seemingly flattened profiles found in many dwarfs do not contradict the cuspy profiles predicted by cosmological models. We also calculate the chemical evolution of stars and gas, to permit comparisons with observational data.Comment: Accepted the 28/01/1

Abundance patterns of multiple populations in Globular Clusters: a chemical evolution model based on yields from AGB ejecta

A large number of spectroscopic studies have provided evidence of the presence of multiple populations in globular clusters by revealing patterns in the stellar chemical abundances. This paper is aimed at studying the origin of these abundance patterns. We explore a model in which second generation (SG) stars form out of a mix of pristine gas and ejecta of the first generation of asymptotic giant branch stars. We first study the constraints imposed by the spectroscopic data of SG stars in globular clusters on the chemical properties of the asymptotic and super asymptotic giant branch ejecta. With a simple one-zone chemical model, we then explore the formation of the SG population abundance patterns focussing our attention on the Na-O, Al-Mg anticorrelations and on the helium distribution function. We carry out a survey of models and explore the dependence of the final SG chemical properties on the key parameters affecting the gas dynamics and the SG formation process. Finally, we use our chemical evolution framework to build specific models for NGC 2808 and M4, two Galactic globular clusters which show different patterns in the Na-O and Mg-Al anticorrelation and have different helium distributions. We find that the amount of pristine gas involved in the formation of SG stars is a key parameter to fit the observed O-Na and Mg-Al patterns. The helium distribution function for these models is in general good agreement with the observed one. Our models, by shedding light on the role of different parameters and their interplay in determining the final SG chemical properties, illustrate the basic ingredients, constraints and problems encountered in this self-enrichment scenario which must be addressed by more sophisticated chemical and hydrodynamic simulations.Comment: 19 pages, 10 figures, MNRAS accepte

Nature vs. nurture in the low-density environment: structure and evolution of early-type dwarf galaxies in poor groups

We present the stellar population properties of 13 dwarf galaxies residing in poor groups (low-density environment, LDE) observed with VIMOS@VLT. Ages, metallicities, and [alpha/Fe] ratios were derived from the Lick indices Hbeta, Mgb, Fe5270 and Fe5335 through comparison with our simple stellar population (SSP) models accounting for variable [alpha/Fe] ratios. For a fiducial subsample of 10 early-type dwarfs we derive median values and scatters around the medians of 5.7 \pm 4.4 Gyr, -0.26 \pm 0.28, and -0.04 \pm 0.33 for age, log Z/Zsun, and [alpha/Fe], respectively. For a selection of bright early-type galaxies (ETGs) from the Annibali et al.2007 sample residing in comparable environment we derive median values of 9.8 \pm 4.1 Gyr, 0.06 \pm 0.16, and 0.18 \pm 0.13 for the same stellar population parameters. It follows that dwarfs are on average younger, less metal rich, and less enhanced in the alpha-elements than giants, in agreement with the extrapolation to the low mass regime of the scaling relations derived for giant ETGs. From the total (dwarf + giant) sample we derive that age \propto sigma^{0.39 \pm 0.22}, Z \propto sigma^{0.80 \pm 0.16}, and alpha/Fe \propto sigma^{0.42 \pm 0.22}. We also find correlations with morphology, in the sense that the metallicity and the [alpha/Fe] ratio increase with the Sersic index n or with the bulge-to-total light fraction B/T. The presence of a strong morphology-[alpha/Fe] relation appears to be in contradiction to the possible evolution along the Hubble sequence from low B/T (low n) to high B/T (high n) galaxies. We also investigate the role played by environment comparing the properties of our LDE dwarfs with those of Coma red passive dwarfs from the literature. We find possible evidence that LDE dwarfs experienced more prolonged star formations than Coma dwarfs, however larger data samples are needed to draw more firm conclusions.Comment: Accepted for publication on A&

The turbulent destruction of clouds - I. A k-epsilon treatment of turbulence in 2D models of adiabatic shock-cloud interactions

The interaction of a shock with a cloud has been extensively studied in the literature, where the effects of magnetic fields, radiative cooling and thermal conduction have been considered. However, the formation of fully developed turbulence has often been prevented by the artificial viscosity inherent in hydrodynamical simulations, and a uniform post-shock flow has been assumed in all previous single-cloud studies. In reality, the flow behind the shock is also likely to be turbulent, with non-uniform density, pressure and velocity structure created as the shock sweeps over inhomogenities upstream of the cloud. To address these twin issues we use a sub-grid compressible k-epsilon turbulence model to estimate the properties of the turbulence generated in shock-cloud interactions and the resulting increase in the transport coefficients that the turbulence brings. A detailed comparison with the output from an inviscid hydrodynamical code puts these new results into context. We find that cloud destruction in inviscid and k-epsilon models occurs at roughly the same speed when the post-shock flow is smooth and when the density contrast between the cloud and inter-cloud medium is less than 100. However, there are increasing and significant differences as this contrast increases. Clouds subjected to strong ``buffeting'' by a highly turbulent post-shock environment are destroyed significantly quicker. Additional calculations with an inviscid code where the post-shock flow is given random, grid-scale, motions confirms the more rapid destruction of the cloud. Our results clearly show that turbulence plays an important role in shock-cloud interactions, and that environmental turbulence adds a new dimension to the parameter space which has hitherto been studied (abridged).Comment: 31 pages, 22 figures, accepted for publication in MNRA

A Keck/DEIMOS spectroscopic survey of the faint M31 satellites And IX, And XI, And XII, and And XIII

We present the first spectroscopic analysis of the faint M31 satellite galaxies, AndXI and AndXIII, and a reanalysis of existing spectroscopic data for two further faint companions, And IX and AndXII. By combining data obtained using the DEIMOS spectrograph mounted on the Keck II telescope with deep photometry from the Suprime-Cam instrument on Subaru, we have calculated global properties for the dwarfs, such as systemic velocities, metallicites and half-light radii.We find each dwarf to be very metal poor ([Fe/H] -2 both photometrically and spectroscopically, from their stacked spectrum), and as such, they continue to follow the luminosity-metallicity relationship established with brighter dwarfs. We are unable to resolve a dispersion for And XI due to small sample size and low S/N, but we set a one sigma upper limit of sigma-v <5 km/s. For And IX, And XII and And XIII we resolve velocity dispersions of v=4.5 (+3.4,-3.2), 2.6(+5.1,-2.6) and 9.7(+8.9,-4.5) km/s, and derive masses within the half light radii of 6.2(+5.3,-5.1)x10^6 Msun, 2.4 (+6.5,-2.4)x10^6 Msun and 1.1(+1.4,-0.7)x10^7 Msun respectively. We discuss each satellite in the context of the Mateo relations for dwarf spheroidal galaxies, and the Universal halo profiles established for Milky Way dwarfs (Walker et al. 2009). For both galaxies, this sees them fall below the Universal halo profiles of Walker et al. (2009). When combined with the findings of McConnachie & Irwin (2006a), which reveal that the M31 satellites are twice as extended (in terms of both half-light and tidal radii) as their Milky Way counterparts, these results suggest that the satellite population of the Andromeda system could inhabit halos that are significantly different from those of the Milky Way in terms of their central densities (abridged).Comment: 26 pages, 18 figures, MNRAS submitte