6,193 research outputs found
Every One Was Meant For Some One : By the writers of You\u27re an Indian
https://digitalcommons.library.umaine.edu/mmb-vp/5496/thumbnail.jp
Keplerian discs around post-AGB stars: a common phenomenon?
Aims: We aim at showing that the broad-band SED characteristics of our sample
of post-AGB stars are best interpreted, assuming the circumstellar dust is
stored in Keplerian rotating passive discs.
Methods: We present a homogeneous and systematic study of the Spectral Energy
Distributions (SEDs) of a sample of 51 post-AGB objects. The selection criteria
to define the whole sample were tuned to cover the broad-band characteristics
of known binary post-AGB stars. The whole sample includes 20 dusty RV Tauri
stars from the General Catalogue of Variable Stars (GCVS). We supplemented our
own Geneva optical photometry with literature data to cover a broad range of
fluxes from the UV to the far-IR.
Results: All the SEDs display very similar characteristics: a large IR excess
with a dust excess starting near the sublimation temperature, irrespective of
the effective temperature of the central star. Moreover, when available, the
long wavelength fluxes show a black-body slope indicative of the presence of a
component of large mm sized grains.
Conclusions: We argue that in all systems, gravitationally bound dusty discs
are present. The discs must be puffed-up to cover a large opening angle for the
central star and we argue that the discs have some similarity with the passive
discs detected around young stellar objects. We interpret the presence of a
disc to be a signature for binarity of the central object, but this will need
confirmation by long-term monitoring of the radial velocities. We argue that
dusty RV Tauri stars are those binaries which happen to be in the Population II
instability strip.Comment: 29 pages, 5 figures, accepted for publication in A&
The Chemical Compositions of the Type II Cepheids -- The BL Her and W Vir Variables
Abundance analyses from high-resolution optical spectra are presented for 19
Type II Cepheids in the Galactic field. The sample includes both short-period
(BL Her) and long-period (W Vir) stars. This is the first extensive abundance
analysis of these variables. The C, N, and O abundances with similar spreads
for the BL Her and W Vir show evidence for an atmosphere contaminated with
-process and CN-cycling products. A notable anomaly of the BL Her
stars is an overabundance of Na by a factor of about five relative to their
presumed initial abundances. This overabundance is not seen in the W Vir stars.
The abundance anomalies running from mild to extreme in W Vir stars but not
seen in the BL Her stars are attributed to dust-gas separation that provides an
atmosphere deficient in elements of high condensation temperature, notably Al,
Ca, Sc, Ti, and -process elements. Such anomalies have previously been seen
among RV Tau stars which represent a long-period extension of the variability
enjoyed by the Type II Cepheids. Comments are offered on how the contrasting
abundance anomalies of BL Her and W Vir stars may be explained in terms of the
stars' evolution from the blue horizontal branch.Comment: 41 pages including 11 figures and 4 tables; Accepted for publication
in Ap
Loneliness in early psychosis: a qualitative study exploring the views of mental health practitioners in early intervention services
BACKGROUND: Loneliness is an important public health problem with established adverse effects on physical and mental health. Although people with psychosis often experience high levels of loneliness, relatively little is known about the relationship between loneliness and early psychosis. Potential interventions to address loneliness might be easier to implement early in the illness when social networks and social skills may be more intact than at a later stage. We investigated the views of mental health practitioners about the context and causes of loneliness in people with early psychosis, and about potential interventions. METHODS: Semi-structured face-to-face interviews were conducted with mental health practitioners (n = 20). Participants were purposively recruited from four early intervention services for first-episode psychosis in the UK. Interviews were transcribed verbatim and thematic analysis was conducted. RESULTS: Participants believed that the majority of service users with early psychosis experience feelings of loneliness. They often saw socially isolated and disconnected clients and believed them to be lonely, but rarely discussed loneliness explicitly in clinical interactions. A combination of symptoms, stigma and negative sense of self were believed to underpin loneliness. Participants could not identify any specific current interventions delivered by their services for tackling loneliness, but thought some routinely provided interventions, including social groups and psychological treatments, could be helpful. They favoured making a wider range of loneliness interventions available and believed that community agencies beyond mental health services should be involved to make these effective and feasible to deliver. They suggested social participation interventions without an explicit mental health focus as potentially promising and valued a co-produced approach to intervention development. CONCLUSIONS: This study suggests that loneliness is not routinely discussed in early intervention services, and a targeted strategy for tackling it is lacking. Co-produced, individualised community approaches, and interventions that target symptoms, stigma and negative self-schemas might be beneficial in alleviating loneliness for people with early psychosis. Empirical research is needed to develop and test such interventions
Self-control tames the coupling of reactive radicals
Highly reactive or unstable chemical reagents are challenging to prepare, store, and safely handle, so chemists frequently generate them in situ from convenient precursors. In an ideal case, the rate of release of the reagent would be matched to the rate of its “capture” in the desired chemical reaction, thereby preventing the reagent from accumulating and minimizing any opportunity for decomposition. However, this synchronization is rarely achieved or even attempted: The rate of release is usually dictated by the conditions of the reaction (1), rather than being regulated by capture of the reagent. In this issue, Tellis et al. (2) on page 433 and Zuo et al. (3) on page 437 independently report the use of iridium photocatalysis (4, 5) to supply highly reactive radical coupling partners (R⋅) to a nickel-catalyzed carbon-carbon bond-forming process (see the figure). Intriguingly, the two points of contact between the iridium and nickel cycles enforce autoregulated release of the radical, ensuring its efficient capture by nickel rather than its decomposition via other pathways
A Sr-Rich Star on the Main Sequence of Omega Centauri
Abundance ratios relative to iron for carbon, nitrogen, strontium and barium
are presented for a metal-rich main sequence star ([Fe/H]=--0.74) in the
globular cluster omega Centauri. This star, designated 2015448, shows depleted
carbon and solar nitrogen, but more interestingly, shows an enhanced abundance
ratio of strontium [Sr/Fe] ~ 1.6 dex, while the barium abundance ratio is
[Ba/Fe]<0.6 dex. At this metallicity one usually sees strontium and barium
abundance ratios that are roughly equal. Possible formation scenarios of this
peculiar object are considered.Comment: 13 pages, 3 figures. Accepted to ApJ
Selective deactivation of gibberellins below the shoot apex is critical to flowering but not to stem elongation of Lolium
Gibberellins (GAs) cause dramatic increases in plant height and a genetic block in the synthesis of GA1 explains the dwarfing of Mendel's pea. For flowering, it is GA5 which is important in the long-day (LD) responsive grass, Lolium. As we show here, GA
Swift observations of the 2006 outburst of the recurrent nova RS Ophiuchi: II. 1D hydrodynamical models of wind driven shocks
Following the early Swift X-ray observations of the latest outburst of the
recurrent nova RS Ophiuchi in February 2006 (Paper I), we present new 1D
hydrodynamical models of the system which take into account all three phases of
the remnant evolution. The models suggest a novel way of modelling the system
by treating the outburst as a sudden increase then decrease in wind mass-loss
rate and velocity. The differences between this wind model and previous
Primakoff-type simulations are described. A more complex structure, even in 1D,
is revealed through the presence of both forward and reverse shocks, with a
separating contact discontinuity. The effects of radiative cooling are
investigated and key outburst parameters such as mass-loss rate, ejecta
velocity and mass are varied. The shock velocities as a function of time are
compared to the ones derived in Paper I. We show how the manner in which the
matter is ejected controls the evolution of the shock and that for a
well-cooled remnant, the shock deceleration rate depends on the amount of
energy that is radiated away.Comment: 9 pages, 5 figure
Mammalian sphingoid bases: Biophysical, physiological and pathological properties
Sphingoid bases encompass a group of long chain amino alcohols which form the essential structure of sphingolipids. Over the last years, these amphiphilic molecules were moving more and more into the focus of biomedical research due to their role as bioactive molecules. In fact, free sphingoid bases interact with specific receptors and target molecules, and have been associated with numerous biological and physiological processes. In addition, they can modulate the biophysical properties of biological membranes. Several human diseases are related to pathological changes in the structure and metabolism of sphingoid bases. Yet, the mechanisms underlying their biological and pathophysiological actions remain elusive. Within this review, we aimed to summarize the current knowledge on the biochemical and biophysical properties of the most common sphingoid bases and to discuss their importance in health and disease
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