141 research outputs found
A Search for High-Excitation Redshift Systems in the Absorption Spectra of Five Quasars
We have searched the absorption spectra of five quasars for the presence of redshift system dominated by the highly ionized doublets C iv, N v, and O vi, which could be the strongest lines produced by absorbing clouds with collisional ionization temperatures between 10^5 ° and 10^6 °K. There is at most marginal evidence for one such system apiece in the spectra of PHL 957 and 4C 05.34, which are the two quasars with the largest known emission redshifts. Highly ionized redshift systems of this type are not widespread among the five quasars we investigated; the number of redshifts found in the observed spectra is not significantly larger than the number found in similar random-number spectra. Less than 5 percent of the observed absorption lines are identified in a statistically significant way by redshift systems of this type
A Search for High-Excitation Redshift Systems in the Absorption Spectra of Five Quasars
We have searched the absorption spectra of five quasars for the presence of redshift system dominated by the highly ionized doublets C iv, N v, and O vi, which could be the strongest lines produced by absorbing clouds with collisional ionization temperatures between 10^5 ° and 10^6 °K. There is at most marginal evidence for one such system apiece in the spectra of PHL 957 and 4C 05.34, which are the two quasars with the largest known emission redshifts. Highly ionized redshift systems of this type are not widespread among the five quasars we investigated; the number of redshifts found in the observed spectra is not significantly larger than the number found in similar random-number spectra. Less than 5 percent of the observed absorption lines are identified in a statistically significant way by redshift systems of this type
The Large-scale Bipolar Wind in the Galactic Center
During a 9-month campaign (1996--1997), the Midcourse Space Experiment (MSX)
satellite mapped the Galactic Plane at mid-infrared wavelengths (4.3--21.3um).
Here we report evidence for a spectacular limb- brightened, bipolar structure
at the Galactic Center extending more than a degree (170 pc at 8.0 kpc) on
either side of the plane. The 8.3um emission shows a tight correlation with the
3, 6 and 11 cm continuum structure over the same scales. Dense gas and dust are
being entrained in a large-scale bipolar wind powered by a central starburst.
The inferred energy injection at the source is ~10^54/kappa erg for which
\kappa is the covering fraction of the dusty shell (kappa <= 0.1).
There is observational evidence for a galactic wind on much larger scales,
presumably from the same central source which produced the bipolar shell seen
by MSX. Sofue has argued that the North Polar Spur -- a thermal x-ray/radio
loop which extends from the Galactic Plane to b = +80 deg -- was powered by a
nuclear explosion (1-30 x 10^55 erg) roughly 15 Myr ago. We demonstrate that an
open-ended bipolar wind (~10^55 erg), when viewed in near-field projection,
provides the most natural explanation for the observed loop structure. The
ROSAT 1.5 keV diffuse x-ray map over the inner 45 deg provides compelling
evidence for this interpretation. Since the faint bipolar emission would be
very difficult to detect beyond the Galaxy, the phenomenon of large-scale
galactic winds may be far more common than has been observed to date.Comment: 24 pages, 6 figures, aastex. High resolution figures are available at
ftp://www.aao.gov.au/pub/local/jbh/astro-ph/GC/. Astrophysical Journal,
accepte
The Pt isotopes: comparing the Interacting Boson Model with Configuration Mixing and the Extended Consistent-Q formalism
The role of intruder configurations in the description of energy spectra and
B(E2) values in the Pt region is analyzed. In particular, we study the
differences between Interacting Boson Model calculations with or without the
inclusion of intruder states in the even Pt nuclei Pt. As a result,
it shows that for the description of a subset of the existing experimental
data, i.e., energy spectra and absolute B(E2) values up to an excitation energy
of about 1.5 MeV, both approaches seem to be equally valid. We explain these
similarities between both model spaces through an appropriate mapping. We point
out the need for a more extensive comparison, encompassing a data set as broad
(and complete) as possible to confront with both theoretical approaches in
order to test the detailed structure of the nuclear wave functions.Comment: To be published in NP
Chemical signatures of the first star clusters
The chemical abundance patterns of the oldest stars in the Galaxy are
expected to contain residual signatures of the first stars in the early
universe. Numerous studies attempt to explain the intrinsic abundance scatter
observed in some metal-poor populations in terms of chemical inhomogeneities
dispersed throughout the early Galactic medium due to discrete enrichment
events. Just how the complex data and models are to be interpreted with respect
to "progenitor yields" remains an open question. Here we show that stochastic
chemical evolution models to date have overlooked a crucial fact. Essentially
all stars today are born in highly homogeneous star clusters and it is likely
that this was also true at early times. When this ingredient is included, the
overall scatter in the abundance plane [Fe/H] vs. [X/Fe] (C-space), where X is
a nucleosynthetic element, can be much less than derived from earlier models.
Moreover, for moderately flat cluster mass functions (gamma < 2), and/or for
mass functions with a high mass cut-off (M_max > 10^5 M_sun), stars exhibit a
high degree of clumping in C-space that can be identified even in relatively
small data samples. Since stellar abundances can be modified by mass transfer
in close binaries, clustered signatures are essential for deriving the yields
of the first supernovae. We present a statistical test to determine whether a
given set of observations exhibit such behaviour. Our initial work focusses on
two dimensions in C-space, but we show that the clustering signal can be
greatly enhanced by additional abundance axes. The proposed experiment will be
challenging on existing 8-10m telescopes, but relatively straightforward for a
multi-object echelle spectrograph mounted on a 25-40m telescope.Comment: 24 pages, 17 figs; Astrophysical Journal (Sept 20 issue); a full copy
is available at
http://sydney.edu.au/science/physics/~jbh/share/firststarclusters.pd
Instabilities in the Envelopes and Winds of Very Massive Stars
The high luminosity of Very Massive Stars (VMS) means that radiative forces
play an important, dynamical role both in the structure and stability of their
stellar envelope, and in driving strong stellar-wind mass loss. Focusing on the
interplay of radiative flux and opacity, with emphasis on key distinctions
between continuum vs. line opacity, this chapter reviews instabilities in the
envelopes and winds of VMS. Specifically, we discuss how: 1) the iron opacity
bump can induce an extensive inflation of the stellar envelope; 2) the density
dependence of mean opacity leads to strange mode instabilities in the outer
envelope; 3) desaturation of line-opacity by acceleration of near-surface
layers initiates and sustains a line-driven stellar wind outflow; 4) an
associated line-deshadowing instability leads to extensive small-scale
structure in the outer regions of such line-driven winds; 5) a star with
super-Eddington luminosity can develop extensive atmospheric structure from
photon bubble instabilities, or from stagnation of flow that exceeds the
"photon tiring" limit; 6) the associated porosity leads to a reduction in
opacity that can regulate the extreme mass loss of such continuum-driven winds.
Two overall themes are the potential links of such instabilities to Luminous
Blue Variable (LBV) stars, and the potential role of radiation forces in
establishing the upper mass limit of VMS.Comment: 44 pages, 13 figures. Chapter to appear in the book "Very Massive
Stars in the Local Universe", Springer, J.S. Vink, e
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"Older Adults with ASD: The Consequences of Aging." Insights from a series of special interest group meetings held at the International Society for Autism Research 2016-2017
A special interest group (SIG) entitled "Older Adults with ASD: The Consequences of Aging" was held at the International Society for Autism Research (INSAR) annual meetings in 2016 and 2017. The SIG and subsequent meetings brought together, for the first time, international delegates who were members of the autistic community, researchers, practitioners and service providers. Based on aging autism research that is already underway in UK, Europe, Australia and North America, discussions focussed on conceptualising the parameters of aging when referring to autism, and the measures that are appropriate to use with older adults when considering diagnostic assessment, cognitive factors and quality of life in older age. Thus, the aim of this SIG was to progress the research agenda on current and future directions for autism research in the context of aging. A global issue on how to define 'aging' when referring to ASD was at the forefront of discussions. The âagingâ concept can in principle refer to all developmental transitions. However, in this paper we focus on the cognitive and physical changes that take place from mid-life onwards. Accordingly, it was agreed that aging and ASD research should focus on adults over the age of 50 years, given the high rates of co-occurring physical and mental health concerns and increased risk of premature death in some individuals. Moreover, very little is known about the cognitive change, care needs and outcomes of autistic adults beyond this age. Discussions on the topics of diagnostic and cognitive assessments, and of quality of life and well-being were explored through shared knowledge about which measures are currently being used and which background questions should be asked to obtain comprehensive and informative developmental and medical histories. Accordingly, a survey was completed by SIG delegates who were representatives of international research groups across four continents, and who are currently conducting studies with older autistic adults. Considerable overlap was identified across different research groups in measures of both autism and quality of life, which pointed to combining data and shared learnings as the logical next step. Regarding the background questions that were asked, the different research groups covered similar topics but the groups differed in the way these questions were formulated when working with autistic adults across a range of cognitive abilities. It became clear that continued input from individuals on the autism spectrum is important to ensure that questionnaires used in ongoing and future are accessible and understandable for people across the whole autistic spectrum, including those with limited verbal abilities
Repairing political trust for practical sustainability
High levels of trust in government are important in addressing complex issues, including
the realization of the mainstream sustainability agenda. However, trust in government has been
declining for decades across the western world, undermining legitimacy and hampering policy
implementation and planning for long-term sustainability. We hypothesize that an important factor
in this decline is citizen disappointment with the current types of public participation in governance
and that this could be reversed through a change from informing/consulting to a relationship of
partnership. Using case studies from Western Australia, the paper investigates whether an
intervention targeted at establishing a partnership relationship through mini-public, deliberative,
participatory budgeting would improve trust and help the implementation of sustainability. These
results show evidence of improvements in trust and provide conceptual and practical tools for
government administrations wishing to close the detrimental trust gap that may hamper the
implementation of a sustainability agenda
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