2,905 research outputs found
Evidence for Correlated Titanium and Deuterium Depletion in the Galactic ISM
Current measurements indicate that the deuterium abundance in diffuse
interstellar gas varies spatially by a factor of ~4 among sightlines extending
beyond the Local Bubble. One plausible explanation for the scatter is the
variable depletion of D onto dust grains. To test this scenario, we have
obtained high signal-to-noise, high resolution profiles of the refractory ion
TiII along seven Galactic sightlines with D/H ranging from 0.65 to 2.1x10^-5.
These measurements, acquired with the recently upgraded Keck/HIRES
spectrometer, indicate a correlation between Ti/H and D/H at the >95% c.l.
Therefore, our observations support the interpretation that D/H scatter is
associated with differential depletion. We note, however, that Ti/H values
taken from the literature do not uniformly show the correlation. Finally, we
identify significant component-to-component variations in the depletion levels
among individual sightlines and discuss complications arising from this
behavior.Comment: 4 pages; Accepted to Astrophysical Journal Letter
The Large, Oxygen-Rich Halos of Star-Forming Galaxies Are A Major Reservoir of Galactic Metals
The circumgalactic medium (CGM) is fed by galaxy outflows and accretion of
intergalactic gas, but its mass, heavy element enrichment, and relation to
galaxy properties are poorly constrained by observations. In a survey of the
outskirts of 42 galaxies with the Cosmic Origins Spectrograph onboard the
Hubble Space Telescope, we detected ubiquitous, large (150 kiloparsec) halos of
ionized oxygen surrounding star-forming galaxies, but we find much less ionized
oxygen around galaxies with little or no star formation. This ionized CGM
contains a substantial mass of heavy elements and gas, perhaps far exceeding
the reservoirs of gas in the galaxies themselves. It is a basic component of
nearly all star-forming galaxies that is removed or transformed during the
quenching of star formation and the transition to passive evolution.Comment: This paper is part of a set of three papers on circumgalactic gas
observed with the Cosmic Origins Spectrograph on HST, to be published in
Science, together with related papers by Tripp et al. and Lehner & Howk, in
the November 18, 2011 edition. This version has not undergone final
copyediting. Please see Science online for the final printed versio
Handbook for Learning-centred evaluation of Computer-facilitated learning projects in higher education
This handbook supports a project funded by the Australian Government Committee for University Teaching and Staff Development (CUTSD). The amended project title is âStaff Development in Evaluation of Technology-based Teaching Development Projects: An Action Inquiry Approachâ.
The project is hosted by Murdoch University on behalf of the Australasian Society for Computers in Learning in Tertiary Education (ASCILITE), as a consortium of 11 universities.
The rationale of the project is to guide a group of university staff through the evaluation of a Computer-facilitated Learning (CFL1) project by a process of action inquiry and mentoring, supported by the practical and theoretical material contained in this handbook
Multiphase Gas In Galaxy Halos: The OVI Lyman-limit System toward J1009+0713
We have serendipitously detected a strong O VI-bearing Lyman limit system at
z_abs = 0.3558 toward the QSO J1009+0713 (z_em = 0.456) in our survey of
low-redshift galaxy halos with the Hubble Space Telescope's Cosmic Origins
Spectrograph. Its rest-frame equivalent width of W_r = 835 +/- 49 mA is the
highest for an intervening absorber yet detected in any low-redshift QSO
sightline, with absorption spanning 400 km s^-1 in its rest frame. HST/WFC3
images of the galaxy field show that the absorber is associated with two
galaxies lying at 14 and 46 kpc from the QSO line of sight. The bulk of the
absorbing gas traced by H I resides in two strong, blended component groups
that possess a total logN(HI) = 18 - 18.8. The ion ratios and column densities
of C, N, O, Mg, Si, S, and Fe, except the O VI, can be accommodated into a
simple photoionization model in which diffuse, low-metallicity halo gas is
exposed to a photoionizing field from stars in the nearby galaxies that
propagates into the halo at 10% efficiency. We constrain the metallicity firmly
within the range 0.1 - 1 Zsun, and photoionization modeling indirectly
indicates a subsolar metallicity of 0.05 - 0.5 Zsun. The appearance of strong O
VI and nine Mg II components and our review of similar systems in the
literature support the "interface" picture of high-velocity O VI: the total
strength of the O VI shows a positive correlation with the number of detected
components in the low-ionization gas, however the total O VI column densities
still far exceed the values expected from interface models for the number of
detected clouds.Comment: 20 pages, 11 figures, accepted for publication in Ap
Comparison of fibre optical measurements and discrete element simulations for the study of granulation in a spout fluidized bed
Spout fluidized beds are frequently used for the production of granules or particles through granulation. The products find application in a large variety of applications, for example detergents, fertilizers, pharmaceuticals and food. Spout fluidized beds have a number of advantageous properties, such as a high mobility of the particles, which prevents undesired agglomeration and yields excellent heat transfer properties. The particle growth mechanism in a spout fluidized bed as function of particle-droplet interaction has a profound influence on the particle morphology and thus on the product quality. Nevertheless, little is known about the details of the granulation process. This is mainly due to the fact that the granulation process is not visually accessible. In this work we use fundamental, deterministic models to enable the detailed investigation of granulation behaviour in a spout fluidized bed. A discrete element model is used describing the dynamics of the continuous gas-phase and the discrete droplets and particles. For each element momentum balances are solved. The momentum transfer among each of the three phases is described in detail at the level of individual elements. The results from the discrete element model simulations are compared with local measurements of particle volume fractions as well as particle velocities by using a novel fibre optical probe in a fluidized bed of 400 mm I.D. Simulations and experiments were carried out for three different cases using Geldart B type aluminium oxide particles: a freely bubbling fluidized bed; a spout fluidized bed without the presence of droplets and a spout fluidized bed with the presence of droplets. It is demonstrated how the discrete element model can be used to obtain information about the interaction of the discrete phases, i.e. the growth zone in a spout fluidized bed. Eventually this kind of information can be used to obtain closure information required in more coarse grained models
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