2,689 research outputs found

    New method for the deposition of nickel oxide in porous scaffolds for electrodes in solid oxide fuel cells and electrolyzers

    Get PDF
    A simple chemical bath deposition is used to coat a complex porous ceramic scaffold with a conformal nickel layer. The resulting composite is used as a Solid Oxide Fuel Cell electrode and its electrochemical response is measured in humidified hydrogen. X-Ray tomography is used to determine microstructural parameters of the uncoated and Ni-coated porous structure, among other, the surface area to total volume, the radial pore size and size of the necks between pores

    Rapid grain growth in post-AGB disc systems from far-infrared and sub-millimetre photometry

    Full text link
    The timescales on which astronomical dust grows remain poorly understood, with important consequences for our understanding of processes like circumstellar disk evolution and planet formation.A number of post-asymptotic giant branch stars are found to host optically thick, dust- and gas-rich circumstellar discs in Keplerian orbits. These discs exhibit evidence of dust evolution, similar to protoplanetary discs; however since post-AGB discs have substantially shorter lifetimes than protoplanetary discs they may provide new insights on the grain-growth process. We examine a sample of post-AGB stars with discs to determine the FIR and sub-mm spectral index by homogeneously fitting a sample of data from \textit{Herschel}, the SMA and the literature. We find that grain growth to at least hundreds of micrometres is ubiquitous in these systems, and that the distribution of spectral indices is more similar to that of protoplanetary discs than debris discs. No correlation is found with the mid-infrared colours of the discs, implying that grain growth occurs independently of the disc structure in post-AGB discs. We infer that grain growth to \simmm sizes must occur on timescales <<105<<10^{5} yr, perhaps by orders of magnitude, as the lifetimes of these discs are expected to be 105\lesssim10^{5}~yr and all objects have converged to the same state. This growth timescale is short compared to the results of models for protoplanetary discs including fragmentation, and may provide new constraints on the physics of grain growth.Comment: 13 pages, 7 figures. Accepted for publication in MNRA

    The Non-thermal Radio Jet Toward the NGC 2264 Star Formation Region

    Full text link
    We report sensitive VLA 3.6 cm radio observations toward the head of the Cone nebula in NGC 2264, made in 2006. The purpose of these observations was to study a non-thermal radio jet recently discovered, that appears to emanate from the head of the Cone nebula. The jet is highly polarized, with well-defined knots, and one-sided. The comparison of our images with 1995 archive data indicates no evidence of proper motions nor polarization changes. We find reliable flux density variations in only one knot, which we tentatively identify as the core of a quasar or radio galaxy. An extragalactic location seems to be the best explanation for this jet.Comment: 12 pages, 5 figure

    Validación de un nuevo método de preconcentración y medición de mercurio en sedimentos utilizando materiales sol-gel dopados con extractantes sulfurados

    Get PDF
    El mercurio es un metal pesado altamente tóxico presente en el ambiente por causas naturales o antropogénicas. El mercurio contenido en los cuerpos receptores de agua tiende a precipitarse y acumularse en los sedimentos. Por lo tanto, las mediciones de mercurio en sedimentos representan un buen indicativo de la calidad del ecosistema. En este trabajo se presentan las diferentes etapas involucradas en el desarrollo de un nuevo método de separación, preconcentración y medición de mercurio en sedimentos con contenidos naturales de este elemento. La separación y preconcentración se realizó mediante el uso de nuevos materiales sorbentes preparados a través del proceso sol-gel utilizando CYANEX 471X (sulfuro de triisobutilfosfina) y CYANEX 301 (ácido bis (2,4,4-trimetilpentil) ditiofosfínico) como extractantes de mercurio. Se describe la optimización de la etapa de acoplamiento de los materiales empacados en columna, utilizando un sistema automatizado de inyección de flujo, para conectarla en línea con un espectrómetro de absorción atómica donde se realizó la medición de mercurio por generación de vapor frío. Como parte importante en el desarrollo de un nuevo método analítico, se encuentra su validación, la cual es materia de este trabajo. Por lo tanto, una vez optimizado, el método fue validado evaluando los siguientes parámetros: robustez, intervalo lineal y de trabajo, límite de detección y de cuantificación, selectividad, exactitud (repetibilidad y veracidad) e incertidumbre. El método fue aplicado para la medición de mercurio en un sedimento de presa con contenidos naturales de este analito. Los resultados se compararon con los obtenidos mediante espectrometría de masas con plasma inductivamente acoplado (ICP-MS) y espectrometría de fluorescencia atómica con generación de vapor frío (CV-AFS

    Hispanic Immigration to the United States

    Get PDF
    This chapter presents some of the exceptional characteristics of recent Hispanic immigration to the United States. In 2005, there were nearly 40 million Hispanic immigrants and descendants of Hispanic immigrants living in the U.S. The assimilation experience of this large cultural group does not seem to be following the path past immigrants to the U.S. followed. Most third generation Hispanics in the U.S. still find themselves with income and education levels below the U.S. averages. Most forecasts predict that about 60 million Hispanics and Hispanic-Americans will be living in the U.S. by 2030

    A massive cluster of Red Supergiants at the base of the Scutum-Crux arm

    Full text link
    We report on the unprecedented Red Supergiant (RSG) population of a massive young cluster, located at the base of the Scutum-Crux Galactic arm. We identify candidate cluster RSGs based on {\it 2MASS} photometry and medium resolution spectroscopy. With follow-up high-resolution spectroscopy, we use CO-bandhead equivalent width and high-precision radial velocity measurements to identify a core grouping of 26 physically-associated RSGs -- the largest such cluster known to-date. Using the stars' velocity dispersion, and their inferred luminosities in conjuction with evolutionary models, we argue that the cluster has an initial mass of \sim40,000\msun, and is therefore among the most massive in the galaxy. Further, the cluster is only a few hundred parsecs away from the cluster of 14 RSGs recently reported by Figer et al (2006). These two RSG clusters represent 20% of all known RSGs in the Galaxy, and now offer the unique opportunity to study the pre-supernova evolution of massive stars, and the Blue- to Red-Supergiant ratio at uniform metallicity. We use GLIMPSE, MIPSGAL and MAGPIS survey data to identify several objects in the field of the larger cluster which seem to be indicative of recent region-wide starburst activity at the point where the Scutum-Crux arm intercepts the Galactic bulge. Future abundance studies of these clusters will therefore permit the study of the chemical evolution and metallicity gradient of the Galaxy in the region where the disk meets the bulge.Comment: 49 pages, 22 figures. Accepted for publication in ApJ. Version with hi-res figures can be found at http://www.cis.rit.edu/~bxdpci/RSGC2.pd
    corecore