3,441 research outputs found
The self-care for people initiative: the outcome evaluation.
To determine the effects of a community-based training programme in self-care on the lay population
Ultra-luminous X-ray sources and neutron-star-black-hole mergers from very massive close binaries at low metallicity
Gravitational waves from the binary black hole (BH) merger GW150914 may
enlighten our understanding of ultra-luminous X-ray sources (ULXs), as
BHs>30Msun can reach luminosities>4x10^39 erg s^-1 without exceeding their
Eddington limit. It is then important to study variations of evolutionary
channels for merging BHs, which might instead form accreting BHs and become
ULXs. It was recently shown that massive binaries with mass ratios close to
unity and tight orbits can undergo efficient rotational mixing and evolve
chemically homogeneously, resulting in a compact BH binary. We study similar
systems by computing ~120000 detailed binary models with the MESA code covering
a wide range of initial parameters. For initial mass ratios M2/M1~0.1-0.4,
primaries >40Msun can evolve chemically homogeneously, remaining compact and
forming a BH without undergoing Roche-lobe overflow. The secondary then expands
and transfers mass to the BH, initiating a ULX phase. We predict that ~1 out of
10^4 massive stars evolves this way, and that in the local universe 0.13 ULXs
per Msun yr^-1 of star-formation rate are observable, with a strong preference
for low-metallicities. At metallicities log Z>-3, BH masses in ULXs are limited
to 60Msun due to the occurrence of pair-instability supernovae which leave no
remnant, resulting in an X-ray luminosity cut-off. At lower metallicities, very
massive stars can avoid exploding as pair-instability supernovae and instead
form BHs with masses above 130Msun, producing a gap in the ULX luminosity
distribution. After the ULX phase, neutron-star-BH binaries that merge in less
than a Hubble time are produced with a formation rate <0.2 Gpc^-3 yr^-1. We
expect that upcoming X-ray observatories will test these predictions, which
together with additional gravitational wave detections will provide strict
constraints on the origin of the most massive BHs that can be produced by
stars.Comment: Accepted for publication in A&A. 19 Pages plus 16 pages of
appendices. Abstract abridge
Observational properties of massive black hole binary progenitors
The first directly detected gravitational waves (GW 150914) were emitted by
two coalescing black holes (BHs) with masses of ~36Msun and ~29Msun. Several
scenarios have been proposed to put this detection into an astrophysical
context. The evolution of an isolated massive binary system is among commonly
considered models. Various groups have performed detailed binary-evolution
calculations that lead to BH merger events. However, the question remains open
as to whether binary systems with the predicted properties really exist. The
aim of this paper is to help observers to close this gap by providing spectral
characteristics of massive binary BH progenitors during a phase where at least
one of the companions is still non-degenerate. Stellar evolution models predict
fundamental stellar parameters. Using these as input for our stellar atmosphere
code (PoWR), we compute a set of models for selected evolutionary stages of
massive merging BH progenitors at different metallicities. The synthetic
spectra obtained from our atmosphere calculations reveal that progenitors of
massive BH merger events start their lives as O2-3V stars that evolve to
early-type blue supergiants before they undergo core-collapse during the
Wolf-Rayet phase. When the primary has collapsed, the remaining system will
appear as a wind-fed high-mass X-ray binary. We provide feedback parameters,
broad band magnitudes, and spectral templates that should help to identify such
binaries in the future. Comparisons of empirically determined mass-loss rates
with those assumed by evolution calculations reveal significant differences.
The consideration of the empirical mass-loss rates in evolution calculations
will possibly entail a shift of the maximum in the predicted binary-BH merger
rate to higher metallicities, that is, more candidates should be expected in
our cosmic neighborhood than previously assumed.Comment: 64 pages, 30 figures, accepted for publication in Astronomy &
Astrophysics, v2: typos correcte
Codeine versus placebo for chronic cough in children (Review)
Background: Cough in children is a commonly experienced symptom that is associated with increased health service utilisation and burden to parents. The presence of chronic (equal to or more than four weeks) cough in children may indicate a serious underlying condition such as inhaled foreign body or bronchiectasis. Codeine (and derivative)-based medications are sometimes used to treat cough due to their antitussive properties. However, there are inherent risks associated with the use of these medications such as respiratory drive suppression, anaesthetic-induced anaphylaxis, and addiction. Metabolic response and dosage variability place children at increased risk of experiencing such side effects. A systematic review evaluating the quality of the available literature would be useful to inform management practices. Objectives: To evaluate the safety and efficacy of codeine (and derivatives) in the treatment of chronic cough in children. Search methods: We searched the Cochrane Airways Group Register of Trials, Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (1946 to 8 June 2016), EMBASE (1974 to 8 June 2016), the online trials registries of the World Health Organization and ClinicalTrials.gov, and the bibliographic references of publications. We imposed no language restrictions. Selection criteria: We considered studies eligible for analysis when: the participant population included children aged less than 18 years with chronic cough (duration equal to or more than four weeks at the time of intervention); and the study design evaluated codeine or codeine-based derivatives against placebo through a randomised controlled trial. Data collection and analysis: Two review authors independently screened the search results to determine eligibility against a standardised criteria, and we had a pre-planned method for analysis. Main results: We identified a total of 556 records, of which 486 records were excluded on the basis of title and abstract. We retrieved the remaining 70 references in full to determine eligibility. No studies fulfilled the inclusion criteria of this review, and thus we found no evidence to support or oppose the use of codeine or derivatives as antitussive agents for chronic cough in children. While chronic cough is not the same as acute cough, systematic reviews on the use of codeine efficacy for acute cough in children conclude an overall lack of evidence to support or oppose the use of over-the-counter cough and cold medications containing codeine (or derivatives) for treatment of acute cough in children. The lack of sufficient evidence to support the use of these medications has been consistently reaffirmed by medical experts in international chronic cough guidelines and by governing medical and pharmaceutical authorities in the USA, Europe, Canada, New Zealand, and Australia. Due to the lack of sufficient evidence to support efficacy, and the known risks associated with use - in particular the increased risks for children - these medications are now not recommended for children less than 12 years of age and children between 12 to 18 years with respiratory conditions. Authors' conclusions: This review has highlighted the absence of any randomised controlled trials evaluating codeine-based medications in the treatment of childhood chronic cough. Given the potential adverse events of respiratory suppression and opioid toxicity, national therapeutic regulatory authorities recommend the contraindication of access to codeine in children less than 12 years of age. We suggest that clinical practice adhere to clinical practice guidelines and thus refrain from using codeine or its derivatives to treat cough in children. Aetiological-based management practices continue to be advocated for children with chronic cough
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