3,635 research outputs found
Unravelling the Mysteries of the Leo Ring: An Absorption Line Study of an Unusual Gas Cloud
Since the 1980's discovery of the large (2x10^9 Msun) intergalactic cloud
known as the Leo Ring, this object has been the center of a lively debate about
its origin. Determining the origin of this object is still important as we
develop a deeper understanding of the accretion and feedback processes that
shape galaxy evolution. We present HST/COS observations of three sightlines
near the Ring, two of which penetrate the high column density neutral hydrogen
gas visible in 21 cm observations of the object. These observations provide the
first direct measurement of the metallicity of the gas in the Ring, an
important clue to its origins. Our best estimate of the metallicity of the ring
is ~10% Zsun, higher than expected for primordial gas but lower than expected
from an interaction. We discuss possible modifications to the interaction and
primordial gas scenarios that would be consistent with this metallicity
measurement.Comment: 11 pages, 7 figures, accepted Ap
Antonio Gramsci’s impact on critical pedagogy
This paper provides an account of Antonio Gramsci’s impact on the area of critical pedagogy. It indicates the Gramscian influence on the thinking of major exponents of the field. It foregrounds Gramsci's ideas and then indicates how they have been taken up by a selection of critical pedagogy exponents who were chosen on the strength of their identification and engagement with Gramsci's ideas, some of them even having written entire essays on Gramsci. The essay concludes with a discussion concerning an aspect of Gramsci's concerns, the question of powerful knowledge, which, in the present author's view, provides a formidable challenge to critical pedagogues.peer-reviewe
Metallicity and Ionization in High Velocity Cloud Complex C
We analyze HST and FUSE ultraviolet spectroscopic data for eleven sight lines
passing through the infalling high velocity cloud (HVC) Complex C. These sight
lines pass through regions with HI column densities ranging from N(HI) =
10^(18.1) to 10^(20.1). From [OI/HI] abundances, we find that Complex C
metallicities range from 0.09 to 0.29 Z_solar, with a column density weighted
mean of 0.13 Z_solar. Nitrogen (NI) is underabundant by factors of (0.01-0.07)
(N/H)_solar, significantly less than oxygen relative to solar abundances. This
pattern suggests nucleosynthetic enrichment by Type II SNe, consistent with an
origin in the Galactic fountain or infalling gas produced in winds from Local
Group galaxies. The range of metallicity and its possible (2 sigma) dependence
on N(HI) could indicate some mixing of primordial material with enriched gas
from the Milky Way, but the mixing mechanism is unclear. We also investigate
the significant highly ionized component of Complex C, detected in CIV, SiIV,
and OVI, but not in NV. High-ion column density ratios show little variance and
are consistent with shock ionization or ionization at interfaces between
Complex C and a hotter surrounding medium. Evidence for the former mechanism is
seen in the Mrk 876 line profiles, where the offset in line centroids between
low and high ions suggests a decelerating bowshock.Comment: Submitted to Ap
Correction to: Genetic characterization and expression analysis of wheat (\u3ci\u3eTriticum aestivum\u3c/i\u3e) line 07OR1074 exhibiting very low polyphenol oxidase (PPO) activity
The above mentioned article was published in 2015 with an error in the naming of one of the allele sequences for the PPO gene on the D genome. The PPO-D1f allele was incorrectly named as it is identical to the PPO-D1c allele previously published in GenBank by the authors on March 11th, 2014. An alignment between the previously published PPOD1c allele and a resequencing of the parental line 07OR1074 shows that the PPO-D1f allele is identical to the PPO-D1c allele. The allele in the paper referred to as PPO-D1f should be treated as PPO-D1c and can be accessed at NCBI with the following GenBank ID
Discovery of a Dwarf Post-Starburst Galaxy Near a High Column Density Ly-alpha Absorber
We report the discovery of a dwarf (M_B = -13.9) post-starburst galaxy
coincident in recession velocity (within uncertainties) with the highest column
density absorber (N_HI = 10^15.85 cm^{-2} at cz = 1586 km/s) in the 3C~273
sightline. This galaxy is by far the closest galaxy to this absorber, projected
just 71 kpc on the sky from the sightline. The mean properties of the stellar
populations in this galaxy are consistent with a massive starburst ~3.5 Gyrs
ago, whose attendant supernovae, we argue, could have driven sufficient gas
from this galaxy to explain the nearby absorber. Beyond the proximity on the
sky and in recession velocity, the further evidence in favor of this conclusion
includes both a match in the metallicities of absorber and galaxy, and the fact
that the absorber has an overabundance of Si/C, suggesting recent type II
supernova enrichment. Thus, this galaxy and its ejecta are the expected
intermediate stage in the fading dwarf evolutionary sequence envisioned by
Babul & Rees to explain the abundance of faint blue galaxies at intermediate
redshifts.Comment: 33 pages, 4 figures, ApJ in pres
Towards a framework for critical citizenship education
Increasingly countries around the world are promoting forms of "critical" citizenship in the planned curricula of schools. However, the intended meaning behind this term varies markedly and can range from a set of creative and technical skills under the label "critical thinking" to a desire to encourage engagement, action and political emancipation, often labelled "critical pedagogy". This paper distinguishes these manifestations of the "critical" and, based on an analysis of the prevailing models of critical pedagogy and citizenship education, develops a conceptual framework for analysing and comparing the nature of critical citizenship
A Study of the Reionization History of Intergalactic Helium with FUSE and VLT
We obtained high-resolution VLT and FUSE spectra of the quasar HE2347-4342 to
study the properties of the intergalactic medium between redshifts z=2.0-2.9.
The high-quality optical spectrum allows us to identify approximately 850 HeII
absorption components with column densities between N~5X10^11 and $ 10^18
cm^-2. The reprocessed FUSE spectrum extends the wavelength coverage of the
HeII absorption down to an observed wavelength of 920 A. Approximately 1400
HeII absorption components are identified, including 917 HeII Ly-alpha systems
and some of their HeII Ly-beta, Ly-gamma, and Ly-delta counterparts. The
ionization structure of HeII is complex, with approximately 90 components that
are not detected in the hydrogen spectrum. These components may represent the
effect of soft ionizing sources. The ratio Eta=N(HeII)/N(HI) varies
approximately from unity to more than a thousand, with a median value of 62 and
a distribution consistent with the intrinsic spectral indices of quasars. This
suggests that the dominant ionizing field is from the accumulated quasar
radiation, with contributions from other soft sources such as star-forming
regions and obscured AGN, which do not ionize helium. We find an evolution in
Eta toward smaller values at lower redshift, with the gradual disappearance of
soft components. At redshifts z>2.7, the large but finite increase in the HeII
opacity, Tau=5+/-1, suggests that we are viewing the end stages of a
reionization process that began at an earlier epoch. Fits of the absorption
profiles of unblended lines indicate comparable velocities between hydrogen and
He^+ ions. At hydrogen column densities N<3X10^12 cm^-2 the number of forest
lines shows a significant deficit relative to a power law, and becomes
negligible below N=10^11 cm^-2.Comment: 40 pages, 10 Postscript figures, uses Aastex.sty The Astrophysical
Journal, in pres
Reinventing College Physics for Biologists: Explicating an epistemological curriculum
The University of Maryland Physics Education Research Group (UMd-PERG)
carried out a five-year research project to rethink, observe, and reform
introductory algebra-based (college) physics. This class is one of the Maryland
Physics Department's large service courses, serving primarily life-science
majors. After consultation with biologists, we re-focused the class on helping
the students learn to think scientifically -- to build coherence, think in
terms of mechanism, and to follow the implications of assumptions. We designed
the course to tap into students' productive conceptual and epistemological
resources, based on a theoretical framework from research on learning. The
reformed class retains its traditional structure in terms of time and
instructional personnel, but we modified existing best-practices curricular
materials, including Peer Instruction, Interactive Lecture Demonstrations, and
Tutorials. We provided class-controlled spaces for student collaboration, which
allowed us to observe and record students learning directly. We also scanned
all written homework and examinations, and we administered pre-post conceptual
and epistemological surveys. The reformed class enhanced the strong gains on
pre-post conceptual tests produced by the best-practices materials while
obtaining unprecedented pre-post gains on epistemological surveys instead of
the traditional losses.Comment: 35 pages including a 15 page appendix of supplementary material
Contact orderability up to conjugation
We study in this paper the remnants of the contact partial order on the
orbits of the adjoint action of contactomorphism groups on their Lie algebras.
Our main interest is a class of non-compact contact manifolds, called convex at
infinity.Comment: 28 pages, 1 figur
Complementary network-based approaches for exploring genetic structure and functional connectivity in two vulnerable, endemic ground squirrels
The persistence of small populations is influenced by genetic structure and functional connectivity. We used two network-based approaches to understand the persistence of the northern Idaho ground squirrel (Urocitellus brunneus) and the southern Idaho ground squirrel (U. endemicus), two congeners of conservation concern. These graph theoretic approaches are conventionally applied to social or transportation networks, but here are used to study population persistence and connectivity. Population graph analyses revealed that local extinction rapidly reduced connectivity for the southern species, while connectivity for the northern species could be maintained following local extinction. Results from gravity models complemented those of population graph analyses, and indicated that potential vegetation productivity and topography drove connectivity in the northern species. For the southern species, development (roads) and small-scale topography reduced connectivity, while greater potential vegetation productivity increased connectivity. Taken together, the results of the two network-based methods (population graph analyses and gravity models) suggest the need for increased conservation action for the southern species, and that management efforts have been effective at maintaining habitat quality throughout the current range of the northern species. To prevent further declines, we encourage the continuation of management efforts for the northern species, whereas conservation of the southern species requires active management and additional measures to curtail habitat fragmentation. Our combination of population graph analyses and gravity models can inform conservation strategies of other species exhibiting patchy distributions
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