3,596 research outputs found
Interstellar Ti II in the Milky Way and Magellanic Clouds
We discuss several sets of Ti II absorption-line data, which probe a variety
of interstellar environments in our Galaxy and in the Magellanic Clouds.
Comparisons of high-resolution (FWHM ~ 1.3-1.5 km/s) Ti II spectra of Galactic
targets with corresponding high-resolution spectra of Na I, K I, and Ca II
reveal both similarities and differences in the detailed structure of the
absorption-line profiles -- reflecting component-to-component differences in
the ionization and depletion behaviour of those species. Moderate-resolution
(FWHM ~ 3.4-4.5 km/s) spectra of more heavily reddened Galactic stars provide
more extensive information on the titanium depletion in colder, denser clouds
-- where more than 99.9 per cent of the Ti may be in the dust phase.
Moderate-resolution (FWHM ~ 4.5-8.7 km/s) spectra of stars in the Magellanic
Clouds suggest that the titanium depletion is generally much less severe in the
LMC and SMC than in our Galaxy [for a given N(H_tot), E(B-V), or molecular
fraction f(H_2)] -- providing additional evidence for differences in depletion
patterns in those two lower-metallicity galaxies. We briefly discuss possible
implications of these results for the interpretation of gas-phase abundances in
QSO absorption-line systems and of variations in the D/H ratio in the local
Galactic ISM.Comment: 56 pages, 26 figures, accepted to MNRA
The restoration of intertidal habitats for non-breeding waterbirds through breached managed realignment
Conservation of intertidal habitats in the UK is vital in order to continue to support
nationally and internationally important populations of non-breeding waterbirds.
Historic reclamation for agriculture and industry has resulted in the loss and degradation
of large areas of these intertidal habitats in estuaries and they continue to be threatened
by sea-level rise. Managed realignment is one method which is increasingly being used
to restore intertidal habitats. As managed realignment is a relatively new restoration
technique, the extent to which knowledge of the biology of estuaries is applicable to
managed realignment sites is unclear. Habitat restoration is often unsuccessful or
incomplete, so a detailed knowledge of both the natural system and the characteristics
of restored systems will usually be necessary to recreate fully-functional estuarine
habitats.
This thesis focuses on Nigg Bay Managed Realignment Site (Nigg Bay MRS),
the first managed realignment site in Scotland, and follows the first four years of
ecological development to gain an understanding of how breached realignment can be
used to restore intertidal habitats to support non-breeding waterbirds. This thesis has
six major aims: (i) to describe the development of saltmarsh, (ii) to describe the
development of intertidal flat, (iii) to describe the colonisation by non-breeding
waterbirds (iv) to determine how tidal cycle and weather affect patterns of waterbird
use, (v) to determine which factors affect the spatial distribution of waders and finally
(vi) to determine the patterns of use by individual birds.
Four summers after the re-establishment of tidal conditions, almost all of the
saltmarsh species recorded on the nearby saltmarsh had colonised Nigg Bay MRS, although recognisable communities had yet to establish. Three winters after the re-
establishment of tidal conditions in Nigg Bay MRS, the sediments had a significantly
smaller particle size and higher organic matter content compared to the fine sands of the
adjacent intertidal flats. The intertidal invertebrate community also differed from the
adjacent intertidal flats. Nigg Bay MRS attracted large numbers of non-breeding
waterbirds and supported each of the most common wader and wildfowl species present
in the wider estuary. Nigg Bay MRS performs a number of important functions for
non-breeding waterbirds by: (i) providing a foraging and resting habitat when the tide is
absent and intertidal sediments in Nigg Bay are exposed; (ii) providing a foraging
resource as the tide passes over the intertidal sediments within the site once the
intertidal flats in Nigg Bay are inundated; and (iii) providing a high tide roosting site.
On days with low temperatures and high wind speeds, more waterbirds use Nigg Bay
MRS, suggesting that it is likely to be providing sheltering benefits. Nigg Bay MRS
also provides top-up feeding habitat. The factors that often influence the spatial
distributions of waders in estuaries appear to be operating within Nigg Bay MRS.
Wader densities are greater on the intertidal flats when they are accessible than on the
saltmarsh. Wader densities are also greatest close to creeks and drainage channels,
possibly due to higher invertebrate densities, more accessible prey or sheltering
benefits. Colour-ringing and radio-tracking of Common Redshank established that
Nigg Bay MRS has a subset of regular users, including both adults and juveniles, and
the wader assemblage at night may differ from the assemblage during the day.
These findings are discussed in terms of the implications for locating, designing
and managing future managed realignment projects
The influence of early questions on learning from text
In this research we explored the use of short-answer questions to improve learning from chapter-like texts (3395 words). Experiment 1 investigated the influence of pre-questions on recall from a text passage when tested a week later; two question sets were counterbalanced within the experimental group. Participants with pre-questions scored higher both overall (d = 3.6, 95%CI [2.4, 4.8]) and on novel questions (d = 2.0 [1.6, 2.4]). In Experiment 2, questions were made available immediately after studying the text either alongside the text, open-book, or closed-book with the opportunity to check answers, or not at all with additional study time. Learning was tested after a week. Although the immediate test scores were substantially higher for open- than closed-book tests, week-delayed performance on the same items was much worse for open-book tests and was moderately improved for closed-book tests. For seen questions, closed-book tests led to better delayed recall than did open-book tests, d = 0.7 [0.02, 1.5]. For novel questions, observed differences were small; ds = .2 [-0.6, 0.9] for both comparisons
HII Shells Surrounding Wolf-Rayet stars in M31
We present the results of an ongoing investigation to provide a detailed view
of the processes by which massive stars shape the surrounding interstellar
medium (ISM), from pc to kpc scales. In this paper we have focused on studying
the environments of Wolf-Rayet (WR) stars in M31 to find evidence for WR
wind-ISM interactions, through imaging ionized hydrogen nebulae surrounding
these stars.
We have conducted a systematic survey for HII shells surrounding 48 of the 49
known WR stars in M31. There are 17 WR stars surrounded by single shells, or
shell fragments, 7 stars surrounded by concentric limb brightened shells, 20
stars where there is no clear physical association of the star with nearby
H-alpha emission, and 4 stars which lack nearby H-alpha emission. For the 17+7
shells above, there are 12 which contain one or two massive stars (including a
WR star) and that are <=40 pc in radius. These 12 shells may be classical WR
ejecta or wind-blown shells. Further, there may be excess H-alpha point source
emission associated with one of the 12 WR stars surrounded by putative ejecta
or wind-blown shells. There is also evidence for excess point source emission
associated with 11 other WR stars. The excess emission may arise from
unresolved circumstellar shells, or within the extended outer envelopes of the
stars themselves.
In a few cases we find clear morphological evidence for WR shells interacting
with each other. In several H-alpha images we see WR winds disrupting, or
punching through, the walls of limb-brightened HII shells.Comment: 20 pages, 4 figures (in several parts: some .jpg and others .ps),
accepted to AJ (appearing Oct, 1999
Report of the soil reaction committee on the investigation of the glass electrode method
RESP-
The Arches cluster revisited: II. A massive eclipsing spectroscopic binary in the Arches cluster
We have carried out a spectroscopic variability survey of some of the most massive stars in the Arches cluster, using K-band observations obtained with SINFONI on the VLT. One target, F2, exhibits substantial changes in radial velocity; in combination with new KMOS and archival SINFONI spectra, its primary component is found to undergo radial velocity variation with a period of 10.483+/-0.002 d and an amplitude of ~350 km/s-1. A secondary radial velocity curve is also marginally detectable. We reanalyse archival NAOS-CONICA photometric survey data in combination with our radial velocity results to confirm this object as an eclipsing SB2 system, and the first binary identified in the Arches. We model it as consisting of an 82+/-12 Mâ WN8-9h primary and a 60+/-8 Mâ O5-6 Ia+ secondary, and as having a slightly eccentric orbit, implying an evolutionary stage prior to strong binary interaction. As one of four X-ray bright Arches sources previously proposed as colliding-wind massive binaries, it may be only the first of several binaries to be discovered in this cluster, presenting potential challenges to recent models for the Arches' age and composition. It also appears to be one of the most massive binaries detected to date; the primary's calculated initial mass of >~120 Mâ would arguably make this the most massive binary known in the Galaxy
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