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Large Columns (large + column)

Distribution by Scientific Domains
Physics and Astronomy50%

Selected Abstracts

On the anomalous silicate absorption feature of the prototypical Seyfert 2 galaxy NGC 1068

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2010
M. Köhler
ABSTRACT The first detection of the silicate absorption feature in Active Galactic Nuclei (AGNs) was made at 9.7 ,m for the prototypical Seyfert 2 galaxy NGC 1068 35 yr ago, indicating the presence of a large column of silicate dust in the line of sight to the nucleus. It is now well recognized that type 2 AGNs exhibit prominent silicate absorption bands, while the silicate bands of type 1 AGNs appear in emission. More recently, using the Mid-Infrared Interferometric Instrument on the Very Large Telescope Interferometer, Jaffe et al. for the first time spatially resolved the parsec-sized dust torus around NGC 1068 and found that the 10 ,m silicate absorption feature of the innermost hot component exhibits an anomalous profile differing from that of the interstellar medium and that of common olivine-type silicate dust. While they ascribed the anomalous absorption profile to gehlenite (Ca2Al2SiO7, a calcium aluminium silicate species), we propose a physical dust model and argue that, although the presence of gehlenite is not ruled out, the anomalous absorption feature mainly arises from silicon carbide. [source]

Exploring a non-dimensional varying exponent equation relating minimum spouting velocity to maximum spoutable bed depth

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2009
Wei Du
Abstract The equation was critically examined for spouting both in small conical-cylindrical columns (Dc,<,0.5 m) and large cone-base or flat-bottom cylindrical columns (Dc,,,0.5 m). For small columns, a data base of 36 points with experimental measurements of both Hm and Um(=Ums at H,=,Hm) afforded some insights into the components of this equation and to the merits of the equation itself. For large columns, in the absence of verifiable methods of predicting Hm, correlation of Ums/Umf as a function of H/Hm, using the available experimental data on Ums, has not been achieved. L'équation a été examinée de manière critique pour le jaillissement dans de petites colonnes coniques et cylindriques, (Dc,<,0.5 m) et de larges colonnes cylindriques à base conique ou à fond plat, (Dc,,,0.5 m). Pour les petites colonnes, une base de données de 36 points composée des mesures expérimentales de Hm et Um (,=,Ums at H,=,Hm) a permis de mieux comprendre les composantes de cette équation et la qualité de l'équation elle-même. Pour les colonnes plus larges, en l'absence de méthodes vérifiables pour prédire Hm, la corrélation de Ums/Umf en fonction de H/Hm, à l'aide des données expérimentales disponibles sur Um, n'a pu être établie. [source]

Liquid Dispersion in Large Diameter Bubble Columns, with and without Internals

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2003
Ann Forret
Abstract Liquid mixing has been studied in a 1 m diameter bubble column, with and without internals (vertical cooling tubes). The presence of internals significantly affects both large scale recirculation and local dispersion. The most common approach to model liquid mixing is the one-dimensional axial dispersion model, validated many times in small bubble columns without internals. This paper shows that this model is still appropriate to large columns, but without internals. A two-dimensional model, taking into account a radially dependent axial velocity profile, and both axial and radial dispersion, is required to account for the internals on liquid mixing. Le mélange du liquide dans une colonne à bulles de 1 m de diamètre a été étudié, avec et sans internes (tubes verticaux simulant des échangeurs de chaleur). La présence d'internes affecte de manière significative à la fois la recirculation globale du liquide ainsi que la dispersion locale. L'approche la plus couramment employée pour modéliser le mélange du liquide est le modèle de dispersion axiale mono dimensionnel, validé maintes fois pour les petites colonnes à bulles sans internes. Cet article montre que ce modèle reste valable pour les colonnes de grande taille, sans internes. Par contre, la prise en compte des effets des internes sur le mélange liquide passe par l'utilisation d'un modèle bidimensionnel, prenant en compte le profile radiale de la vitesse axiale ainsi que les dispersions axiale et radiale. [source]

Optical and near-infrared observations of hard serendipitous Chandra sources

ASTRONOMISCHE NACHRICHTEN, Issue 1-2 2003
C.S. Crawford
Abstract We have been carrying out a successful observational programme targeted at finding the highly obscured quasars that are thought to be the main contributors to the hard X-ray background. Out of 56 sources so far studied with optical and near-infrared imaging and spectroscopy, we have found three definite and a further twelve possible Type II quasars. Few sources show significant line emission, suggesting that the line photons are depleted by the large columns of obscuring matter. The redshift distribution of our sources shows a distinct peak at z , 1. The broad-band colours and magnitudes of the optical/near-infrared counterparts indicate that the light in these bands is dominated by the continuum of a massive bright galaxy. [source]