71 research outputs found
Inner mean-motion resonances with eccentric planets: A possible origin for exozodiacal dust clouds
High levels of dust have been detected in the immediate vicinity of many
stars, both young and old. A promising scenario to explain the presence of this
short-lived dust is that these analogues to the Zodiacal cloud (or exozodis)
are refilled in situ through cometary activity and sublimation. As the
reservoir of comets is not expected to be replenished, the presence of these
exozodis in old systems has yet to be adequately explained.
It was recently suggested that mean-motion resonances (MMR) with exterior
planets on moderately eccentric () orbits could
scatter planetesimals on to cometary orbits with delays of the order of several
100 Myr. Theoretically, this mechanism is also expected to sustain continuous
production of active comets once it has started, potentially over
Gyr-timescales.
We aim here to investigate the ability of this mechanism to generate
scattering on to cometary orbits compatible with the production of an exozodi
on long timescales. We combine analytical predictions and complementary
numerical N-body simulations to study its characteristics.
We show, using order of magnitude estimates, that via this mechanism, low
mass discs comparable to the Kuiper Belt could sustain comet scattering at
rates compatible with the presence of the exozodis which are detected around
Solar-type stars, and on Gyr timescales. We also find that the levels of dust
detected around Vega could be sustained via our proposed mechanism if an
eccentric Jupiter-like planet were present exterior to the system's cold debris
disc.Comment: 15 pages, 12 figures; Accepted for publication in MNRA
XZ: Deriving redshifts from X-ray spectra of obscured AGN
Context: Redshifts are fundamental for our understanding of extragalactic
X-ray sources. Ambiguous counterpart associations, expensive optical
spectroscopy and/or multimission multiwavelength coverage to resolve
degeneracies make estimation often difficult in practice.
Aims: We attempt to constrain redshifts of obscured Active Galactic Nuclei
(AGN) using only low-resolution X-ray spectra.
Methods: Our XZ method fits AGN X-ray spectra with a moderately complex
spectral model incorporating a corona, torus obscurer and warm mirror. Using
the Bayesian X-ray Astronomy (BXA) package, we constrain redshift, column
density, photon index and luminosity simultaneously. The redshift information
primarily comes from absorption edges in Compton-thin AGN, and from the Fe
K fluorescent line in heavily obscured AGN. A new generic background
fitting method allows us to extract more information from limited numbers of
source counts.
Results: We derive redshift constraints for 74/321 hard-band detected sources
in the Chandra deep field South. Comparing with spectroscopic redshifts, we
find an outlier fraction of 8%, indicating that our model assumptions are
valid. For three Chandra deep fields, we release our XZ redshift estimates.
Conclusions: The independent XZ estimate is easy to apply and effective for a
large fraction of obscured AGN in todays deep surveys without the need for any
additional data. Comparing to different redshift estimation methods, XZ can
resolve degeneracies in photometric redshifts, help to detect potential
association problems and confirm uncertain single-line spectroscopic redshifts.
With high spectral resolution and large collecting area, this technique will be
highly effective for Athena/WFI observations.Comment: 20 pages, 16 figures in paper, 14 in appendice
Impact of Population III homogeneous stellar evolution on early cosmic reionisation
Context: Population III (Pop III) stars may be fast rotating. An expected
consequence of fast rotation is strong internal mixing that deeply affects
their evolutionary tracks in the Hertzsprung-Russell diagram and hence their
ionising power. aims: We investigate the impact on the ionising power of Pop
III stars in an extreme case of internal mixing, the one leading to chemically
homogeneous evolution (CHE). In that situation, during the main sequence phase,
the star keeps the same chemical composition from its center to its surface.
Homogeneous stars have larger effective temperatures and luminosities than
stars evolving non-homogeneously and thus are stronger ionising sources.
Methods: The stellar evolution models are based on polytropes with a time
varying hydrogen mass fraction. The ionisation model employs the self-similar
champagne flow solution from Shu et al. (2002), as well as numerical
simulations for the stochastic treatment of star clusters over a grid of
redshifts and halo masses. Results: We find that haloes containing chemically
homogeneous stars have an escape fraction of ionising photons about twice that
of haloes containing classical Pop III stars. By extrapolating the high-
ionisation history powered by Pop III stars (at ) to the
post-reionisation epoch, we derive the Thomson scattering optical depth ,
which is compared with the value measured by . We find that
is overproduced by , when all Pop III stars evolve
homogeneously. This indicates that CHE is unlikely to be realised in the
majority of Pop III stars, although the present study cannot exclude that a
fraction of them undergoes CHE. Conclusions: Fast rotation might have a
significant impact on the ionising budget of Pop III stars, and thus on early
cosmic reionisation.Comment: Accepted for publication in A&A (12 August 2022); 13 pages, 9 figure
Modelling Identity Disturbance: A Network Analysis of the Personality Structure Questionnaire (PSQ)
Due to the relevance of identity disturbance to personality disorder this study sought to complete a network analysis of a well validated measure of identity disturbance; the personality structure questionnaire (PSQ). A multi-site and cross-national methodology created an overall sample of N = 1549. The global network structure of the PSQ was analysed and jointly estimated networks were compared across four subsamples (UK versus Italy, adults versus adolescents, clinical versus community and complex versus common presenting problems). Stability analyses assessed the robustness of identified networks. Results indicated that PSQ3 (unstable sense of self) and PSQ5 (mood variability) were the most central items in the global network structure. Network structures significantly differed between the UK and Italy. Centrality of items was largely consistent across subsamples. This study provides evidence of the potential network structure of identity disturbance and so guides clinicians in targeting interventions facilitating personality integration
Incidence and recognition of acute respiratory distress syndrome in a UK intensive care unit.
The reported incidence of ARDS is highly variable (2.5%-19% of intensive care unit (ICU) patients) and varies depending on study patient population used. We undertook a 6-month, prospective study to determine the incidence and outcome of ARDS in a UK adult University Hospital ICU. 344 patients were admitted during the study period, of these 43 (12.5%) were determined to have ARDS. Patients with ARDS had increased mortality at 28 days and 2 years post-diagnosis, and there was under-recognition of ARDS in both medical records and death certificattion. Our findings have implications for critical care resource planning.This is the final version of the article. It first appeared from BMJ Thorax via ://dx.doi.org/10.1136/thoraxjnl-2016-20840
Evaluating progestogens for prevention of preterm birth international collaborative (EPPPIC) individual participant data (IPD) meta-analysis : protocol
BACKGROUND: Preterm birth is the most common cause of death and harm to newborn babies. Babies that are born early may have difficulties at birth and experience health problems during early childhood. Despite extensive study, there is still uncertainty about the effectiveness of progestogen (medications that are similar to the natural hormone progesterone) in preventing or delaying preterm birth, and in improving birth outcomes. The Evaluating Progestogen for Prevention of Preterm birth International Collaborative (EPPPIC) project aims to reduce uncertainty about the specific conditions in which progestogen may (or may not) be effective in preventing or delaying preterm birth and improving birth outcomes. METHODS: The design of the study involves international collaborative individual participant data meta-analysis comprising systematic review, re-analysis, and synthesis of trial datasets. Inclusion criteria are as follows: randomized controlled trials comparing progestogen versus placebo or non-intervention, or comparing different types of progestogen, in asymptomatic women at risk of preterm birth. Main outcomes are as follows; fetal/infant death, preterm birth or fetal death (<=37 weeks, <=34 weeks, <= 28 weeks), serious neonatal complications or fetal/infant death, neurosensory disability (measured at 18 months or later) or infant/child death, important maternal morbidity, or maternal death. In statistical methods, IPD will be synthesized across trials using meta-analysis. Both 'two-stage' models (where effect estimates are calculated for each trial and subsequently pooled in a meta-analysis) and 'one-stage' models (where all IPD from all trials are analyzed in one step, while accounting for the clustering of participants within trials) will be used. If sufficient suitable data are available, a network meta-analysis will compare all types of progesterone and routes of administration extending the one-stage models to include multiple treatment arms. DISCUSSION: EPPPIC is an international collaborative project being conducted by the forming EPPPIC group, which includes trial investigators, an international secretariat, and the research project team. Results, which are intended to contribute to improvements in maternal and child health, are expected to be publicly available in mid 2018. SYSTEMATIC REVIEW REGISTRATION: PROSPERO CRD42017068299
First Light And Reionisation Epoch Simulations (FLARES) XIII: the Lyman-continuum emission of high-redshift galaxies
The history of reionisation is highly dependent on the ionising properties of
high-redshift galaxies. It is therefore important to have a solid understanding
of how the ionising properties of galaxies are linked to physical and
observable quantities. In this paper, we use the First Light and Reionisation
Epoch Simulations (FLARES) to study the Lyman-continuum (LyC, i.e.
hydrogen-ionising) emission of massive () galaxies
at redshifts . We find that the specific ionising emissivity (i.e.
intrinsic ionising emissivity per unit stellar mass) decreases as stellar mass
increases, due to the combined effects of increasing age and metallicity.
FLARES predicts a median ionising photon production efficiency (i.e. intrinsic
ionising emissivity per unit intrinsic far-UV luminosity) of
, with values
spanning the range . This is
within the range of many observational estimates, but below some of the
extremes observed. We compare the production efficiency with observable
properties, and find a weak negative correlation with the UV-continuum slope,
and a positive correlation with the OIII equivalent width. We also consider the
dust-attenuated production efficiency (i.e. intrinsic ionising emissivity per
unit dust-attenuated far-UV luminosity), and find a median of
. Within our sample of
galaxies, it is the stellar populations in low
mass galaxies that contribute the most to the total ionising emissivity. Active
galactic nuclei (AGN) emission accounts for % of the total emissivity
at a given redshift, and extends the LyC luminosity function by dex.Comment: 18 pages, 17 figures, submitted to MNRA
Detection of Low Frequency Multi-Drug Resistance and Novel Putative Maribavir Resistance in Immunocompromised Pediatric Patients with Cytomegalovirus.
Human cytomegalovirus (HCMV) is a significant pathogen in immunocompromised individuals, with the potential to cause fatal pneumonitis and colitis, as well as increasing the risk of organ rejection in transplant patients. With the advent of new anti-HCMV drugs there is therefore considerable interest in using virus sequence data to monitor emerging resistance to antiviral drugs in HCMV viraemia and disease, including the identification of putative new mutations. We used target-enrichment to deep sequence HCMV DNA from 11 immunosuppressed pediatric patients receiving single or combination anti-HCMV treatment, serially sampled over 1-27 weeks. Changes in consensus sequence and resistance mutations were analyzed for three ORFs targeted by anti-HCMV drugs and the frequencies of drug resistance mutations monitored. Targeted-enriched sequencing of clinical material detected mutations occurring at frequencies of 2%. Seven patients showed no evidence of drug resistance mutations. Four patients developed drug resistance mutations a mean of 16 weeks after starting treatment. In two patients, multiple resistance mutations accumulated at frequencies of 20% or less, including putative maribavir and ganciclovir resistance mutations P522Q (UL54) and C480F (UL97). In one patient, resistance was detected 14 days earlier than by PCR. Phylogenetic analysis suggested recombination or superinfection in one patient. Deep sequencing of HCMV enriched from clinical samples excluded resistance in 7 of 11 subjects and identified resistance mutations earlier than conventional PCR-based resistance testing in 2 patients. Detection of multiple low level resistance mutations was associated with poor outcome
In vivo imaging reveals increased eosinophil uptake in the lungs of obese asthmatic patients.
To The Editor:
Eosinophils play an important pathogenic role in pulmonary and systemic conditions including eosinophilic asthma and eosinophilic granulomatosis with polyangiitis.1,2 While progress has been made in understanding the mechanisms responsible for the activation of these cells, existing biomarkers of eosinophilic inflammation are indirect and/or invasive and do not always correlate with tissue eosinophilia. Hence, there is a need to develop non-invasive biomarkers of tissue eosinophilia. We have previously demonstrated the capacity of SPECT (single photon emission computed tomography) to quantify neutrophil uptake into the lungs of COPD patients.3 We sought to determine whether this methodology could be used to quantify eosinophil kinetics and pulmonary uptake, which may differ amongst diseases characterized by eosinophilic inflammation. In particular, the role of the eosinophil in asthma with obesity, a distinct asthma endotype associated with increased severity,4 is controversial. We hypothesized that injection of radiolabeled eosinophils, coupled with SPECT/CT, would reveal changes in eosinophil kinetics in patients compared to healthy volunteers.This work was supported by Asthma UK [08/11], the Medical Research Council [grant number MR/J00345X/1], the Wellcome Trust [grant number 098351/Z/12/Z], Cambridge NIHR Biomedical Research Centre, Wellcome Trust Senior Fellowship (to CEB) [grant number WT082265], AirPROM 7th EU Framework grant and Leicester NIHR Biomedical Research Centre
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