Synthetic properties of bright metal-poor variables. II. BL Her stars

We investigate the properties of the so-called BL Her stars, i.e., Population II Cepheids with periods shorter than 8 days, using updated pulsation models and evolutionary tracks computed adopting a metal abundance in the range of Z=0.0001 to Z=0.004. We derive the predicted Period-Magnitude (PM) and Period-Wesenheit (PW) relations at the various photometric bands and we show that the slopes of these relations are in good agreement with the slopes determined by observed variables in Galactic globular clusters, independently of the adopted M_V(RR)-[Fe/H] relation to get the cluster RR Lyrae-based distance. Moreover, we show that also the distances provided by the predicted PM and PW relations for BL Her stars agree within the errors with the RR Lyrae based values. The use of the predicted relations with W Vir stars, which are Population II Cepheids with periods longer than 8 days, provides no clear evidence for or against a change in the PM and PW slopes around P~10 days.Comment: 12 pages, 6 figures, 6 tables, accepted for publication in A&A on date 16/05/200

A methodology for the customization of hinged ankle-foot orthoses based on in vivo helical axis calculation with 3D printed rigid shells

This study aims to develop techniques for ankle joint kinematics analysis using motion capture based on stereophotogrammetry. The scope is to design marker attachments on the skin for a most reliable identification of the instantaneous helical axis, to be targeted for the fabrication of customized hinged ankle-foot orthoses. These attachments should limit the effects of the experimental artifacts, in particular the soft-tissue motion artifact, which affect largely the accuracy of any in vivo ankle kinematics analysis. Motion analyses were carried out on two healthy subjects wearing customized rigid shells that were designed through 3D scans of the subjects’ lower limbs and fabricated by additive manufacturing. Starting from stereophotogrammetry data collected during walking and dorsi-plantarflexion motor tasks, the instantaneous and mean helical axes of ankle joint were calculated. The customized shells matched accurately the anatomy of the subjects and allowed for the definition of rigid marker clusters that improved the accuracy of in vivo kinematic analyses. The proposed methodology was able to differentiate between subjects and between the motor tasks analyzed. The observed position and dispersion of the axes were consistent with those reported in the literature. This methodology represents an effective tool for supporting the customization of hinged ankle-foot orthoses or other devices interacting with human joints functionality

A pulsational distance to Omega Centauri based on Near-Infrared Period-Luminosity relations of RR Lyrae stars

We present new Near-Infrared (J,K) magnitudes for 114 RR Lyrae stars in the globular cluster Omega Cen (NGC 5139) which we combine with data from the literature to construct a sample of 180 RR Lyrae stars with J and K mean magnitudes on a common photometric system. This is presently the largest such sample in any stellar system. We also present updated predictions for J,K-band Period-Luminosity relations for both fundamental and first-overtone RR Lyrae stars, based on synthetic horizontal branch models with metal abundance ranging from Z=0.0001 to Z=0.004. By adopting for the Omega Cen variables with measured metal abundances an alpha-element enhancement of a factor of 3 (about 0.5 dex) with respect to iron we find a true distance modulus of 13.70 (with a random error of 0.06 and a systematic error of 0.06), corresponding to a distance d=5.5 Kpc (with both random and systematic errors equal to 0.03 Kpc). Our estimate is in excellent agreement with the distance inferred for the eclipsing binary OGLEGC-17, but differ significantly from the recent distance estimates based on cluster dynamics and on high amplitude Delta Scuti stars.Comment: 24 pages, 7 figures, accepted for publication on The Astrophysical Journa

Star Counts in the Globular Cluster Omega Centauri. I. Bright Stellar Components

We present an extensive photometry on HB, RGB, and MSTO stars in Omega Cen. The central regions of the cluster were covered with a mosaic of F435W, F625W, and F658N-band data collected with ACS/HST. The outer reaches were covered with a large set of U,B,V,I-band data collected with the [email protected] ESO/MPI telescope. The final catalogue includes ~1.7 million stars. We identified ~3,200 likely HB stars and ~12,500 stars brighter than the subgiant branch and fainter than the RGB bumps. The HB morphology changes with the radial distance. The relative number of extreme HB stars decreases from ~30% to ~21% when moving from the center toward the outer regions of the cluster, while the fraction of less hot HB stars increases from ~62% to ~72%. We performed a detailed comparison between observed ratios of different stellar tracers and predictions based on canonical evolutionary models with a primordial helium (Y=0.23) content and metal abundances (Z=0.0002,0.001) that bracket the observed spread in metallicity of Omega Cen stars. We found that the empirical star counts of HB stars are on average larger (30%-40%) than predicted. Moreover, the rate of HB stars is 43% larger than the MSTO rate. The discrepancy between the rate of HB compared with the rate of RG and MSTO stars supports the evidence that we are facing a true excess of HB stars. The same comparison was performed by assuming a mix of stellar populations made with 70% of canonical stars and 30% of He-enhanced stars. The discrepancy between theory and observations decreases by a factor of two when compared with rates predicted by canonical He content models, but still 15%-25% (Y=0.42) and 15%-20% (Y=0.33) higher than observed. Furthermore, the ratio between HB and MSTO star counts are ~24% (Y=0.42) and 30% (Y=0.33) larger than predicted lifetime ratios.Comment: 54 pages, 17 figures,to be published in ApJ, see link at http://stellari.wiki.zoho.co

On the distance and reddening of the starburst galaxy IC10

We present deep and accurate optical photometry of the Local Group starburst galaxy IC10. The photometry is based on two sets of images collected with the Advanced Camera for Surveys and with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. We provide new estimates of the Red Giant Branch tip (TRGB) magnitude, m_{F814W}^{TRGB}=21.90+-0.03, and of the reddening, E(B-V)=0.78+-0.06, using field stars in the Small Magellanic Cloud (SMC) as a reference. Adopting the SMC and two globulars, Omega Centauri and 47 Tucanae, as references we estimate the distance modulus to IC10: independent calibrations give weighted average distances of mu=24.51+-0.08 (TRGB) and mu=24.56+-0.08 (RR Lyrae). We also provide a new theoretical calibration for the TRGB luminosity, and using these predictions we find a very similar distance to IC10 (mu~24.60+-0.15). These results suggest that IC10 is a likely member of the M31 subgroup.Comment: 4 pages, 4 figures, ApJ Letters accepte

Fertility and economic instability: the role of unemployment and job displacement

In this paper, we study the separate effects of unemployment and job displacement on fertility in a sample of white collar women in Austria. Using an instrumental variable approach, we show that unemployment incidence as such has no negative effect on fertility decisions, but the very fact of being displaced from a career-oriented job has. Fertility rates for women affected by a firm closure are significantly below those of a control group, even after 6 years, and this is so irrespective of the incidence or the duration of the associated unemployment spell

Optimización de la logística de distribución utilizando técnicas de la inteligencia artificial

La logística en Argentina está influida por el decisivo peso de la producción primaria en la organización del sistema, por una orientación prevalente hacia las exportaciones globales y las dirigidas al mercado regional sudamericano, y por una matriz de transporte dominada por el transporte automotor de cargas y la concentración portuaria. La logística remite a flujos de materiales y de información; a lugares de manipulación, depósito y transformación de las mercancías; a redes y nodos de circulación; y a tiempos de movimiento y no movimiento que responden a aspectos materiales (las infraestructuras, los transportes y las cargas) y también a aspectos funcionales (los servicios, las normativas y regulaciones). En suma, la logística implica un uso del territorio en el tiempo, una convergencia espacio-temporal, una organización y sincronización de flujos a través de estrategias sobre los nodos y las redes. Esta aproximación resalta las limitaciones de miradas parciales y destaca la necesidad de considerar una perspectiva integral que incluya, además, los aspectos organizacionales y de coordinación. La consideración de infraestructuras de circulación; servicios de transporte; infraestructuras de comunicaciones; servicios de almacenamiento y agregado de valor; normativas y regulaciones y costos operativos, entre otros, da cuenta del desafío que involucra una coordinación amplia de políticas estatales de diferente tipo y a cargo de estructuras administrativas diversas. El despliegue de la logística como uno de los “usos del territorio”, abre la posibilidad de acentuar el enfoque territorial. En esta línea de investigación se aborda la optimización de la logística de distribución de cargas y paquetería. Para tal fin se propone el desarrollo de software logístico, que incorpore herramientas basadas en inteligencia artificial, como soporte para la toma de decisiones a nivel gerencial y asistido por herramientas que permitan evaluar la incidencia de la matriz de costos y buscar el equilibrio del sistema. Se considera que el abordaje de la optimización de la logística de distribución centrada en la provincia de La Pampa tendría impacto en la matriz productiva y de servicios de toda la región.Red de Universidades con Carreras en Informátic