1,905 research outputs found
Gravitino fields in Schwarzschild black hole spacetimes
The analysis of gravitino fields in curved spacetimes is usually carried out
using the Newman-Penrose formalism. In this paper we consider a more direct
approach with eigenspinor-vectors on spheres, to separate out the angular parts
of the fields in a Schwarzschild background. The radial equations of the
corresponding gauge invariant variable obtained are shown to be the same as in
the Newman-Penrose formalism. These equations are then applied to the
evaluation of the quasinormal mode frequencies, as well as the absorption
probabilities of the gravitino field scattering in this background.Comment: 21 pages, 2 figures. arXiv admin note: text overlap with
arXiv:1006.3327 by other author
Strong Modification of the Nonlinear Optical Response of Metallic Subwavelength Hole Arrays
The influence of hole shape on the nonlinear optical properties of metallic subwavelength hole arrays is investigated. It is found that the amount of second harmonics generated can be enhanced by changing the hole shape. In part this increase is a direct result of the effect of hole shape on the linear transmission properties. Remarkably, in addition to enhancements that follow directly from the linear properties of the array, we find a hot hole shape. For rectangular holes the effective nonlinear response is enhanced by more than 1 order of magnitude for one particular aspect ratio. This enhancement can be attributed to slow propagation of the fundamental wavelength through the holes which occurs close to the hole cutoff
Characterizing dw1335-29, a recently discovered dwarf satellite of M83
The number, distribution, and properties of dwarf satellites are crucial
probes of the physics of galaxy formation at low masses and the response of
satellite galaxies to the tidal and gas dynamical effects of their more massive
parent.To make progress, it is necessary to augment and solidify the census of
dwarf satellites of galaxies outside the Local Group. M\"uller et al. (2015)
presented 16 dwarf galaxy candidates near M83, but lacking reliable distances,
it is unclear which candidates are M83 satellites. Using red giant branch stars
from the HST/GHOSTS survey in conjunction with ground-based images from
VLT/VIMOS, we confirm that one of the candidates, dw1335-29-- with a projected
distance of 26 kpc from M83 and a distance modulus of -- is a satellite of M83. We estimate an absolute magnitude
, an ellipticity of , a half light
radius of pc, and [Fe/H] = . Owing to
dw1335-29's somewhat irregular shape and possible young stars, we classify this
galaxy as a dwarf irregular or transition dwarf. This is curious, as with a
projected distance of 26 kpc from M83, dw1335-29 is expected to lack recent
star formation. Further study of M83's dwarf population will reveal if star
formation in its satellites is commonplace (suggesting a lack of a hot gas
envelope for M83 that would quench star formation) or rare (suggesting that
dw1335-29 has a larger M83-centric distance, and is fortuitously projected to
small radii).Comment: 7 pages, 5 figures, accepted for publication in MNRA
Notes on Succession in Old Fields in Southeastern Ontario: the Herbs
Vegetation in abandoned hayfields was monitored during 1976-1998. An earlier successional stage followed ploughing. Changes in tree, shrub and vine populations have been reported earlier and showed expected increases in species richness and cover. Highest species richness of herbs occurred three years after ploughing. Non-woody species richness trended irregularly downward, while non-woody cover was variable, peaking in 1987. Within the herbaceous community, year-to-year changes in cover and frequency of species in the following selected groups are reported here: 18 grasses including sown and adventive species; 13 legumes including two sown species; 14 macroforbs of the Compositae, including a goldenrod, Solidago canadensis, which dominated parts of the fields; a rosette weed, Taraxacum officinalis; sedges, horsetails and some other minor components. Grasses and goldenrods were grazed, sometimes intensively and repeatedly, by insects; grasses were impacted by skipper larvae (Thymelicus lineola), and goldenrods by beetle larvae (Trirhabda spp.). Effects of repeated outbreaks on host plant cover are shown for two plots (100 m2) matching the scale of outbreaks
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Case Study Shows Disconnect on Civic Journalism's Role
This in-depth case study examines attempts to transform a traditional newsroom to one oriented around civic journalism principles, offering a unique look at the resistance toward those principles even in a digital environment that facilitates new audience relationships. Civic journalism emphasizes understanding and addressing community concerns from a citizen perspective. This study finds that journalists still struggle to integrate citizens’ contributions into newsroom practice in meaningful ways
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Newswork within a Culture of Job Insecurity: Producing News amidst Organizational and Industry Uncertainty
Rapid change in the news industry and the prevalence of layoffs, buyouts, and closings have led many newsworkers to experience job insecurity and worry about their long-term futures in journalism. Our research uses a case study of employees at an independently owned media company in the United States to explore the various ways newsworkers respond to this culture of job insecurity and how their responses affect efforts to change news practices. Findings demonstrate that those who believe their jobs are at risk are unlikely to change their practices and even some who perceive job security are reticent to initiate change. As a result, the culture of job insecurity in the news industry has a limiting effect on changes to journalism practice
Diverse Stellar Haloes in Nearby Milky Way-Mass Disc Galaxies
We have examined the resolved stellar populations at large galactocentric
distances along the minor axis (from 10 kpc up to between 40 and 75 kpc), with
limited major axis coverage, of six nearby highly-inclined Milky Way-mass disc
galaxies using HST data from the GHOSTS survey. We select red giant branch
stars to derive stellar halo density profiles. The projected minor axis density
profiles can be approximated by power laws with projected slopes of between
and and a diversity of stellar halo masses of , or of the total galaxy stellar masses. The typical
intrinsic scatter around a smooth power law fit is dex owing to
substructure. By comparing the minor and major axis profiles, we infer
projected axis ratios at kpc between . The GHOSTS
stellar haloes are diverse, lying between the extremes charted out by the
(rather atypical) haloes of the Milky Way and M31. We find a strong correlation
between the stellar halo metallicities and the stellar halo masses. We compare
our results with cosmological models, finding good agreement between our
observations and accretion-only models where the stellar haloes are formed by
the disruption of dwarf satellites. In particular, the strong observed
correlation between stellar halo metallicity and mass is naturally reproduced.
Low-resolution hydrodynamical models have unrealistically high stellar halo
masses. Current high-resolution hydrodynamical models appear to predict stellar
halo masses somewhat higher than observed but with reasonable metallicities,
metallicity gradients and density profiles.Comment: 26 pages, 17 figures. Accepted for publication in MNRA
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