1,744 research outputs found
Sulphur-bearing molecules in AGB stars I: The occurrence of hydrogen sulfide
Through a survey of (sub-)millimetre emission lines of various
sulphur-bearing molecules, we aim to determine which molecules are the primary
carriers of sulphur in different types of AGB stars. In this paper, the first
in a series, we investigate the occurrence of HS in AGB circumstellar
envelopes and determine its abundance, where possible. We have surveyed 20 AGB
stars with a range of mass-loss rates and of different chemical types using the
APEX telescope to search for rotational transition lines of five key
sulphur-bearing molecules: CS, SiS, SO, SO and HS. Here we present our
results for HS, including detections, non-detections and detailed radiative
transfer modelling of the detected lines. We compare results based on different
descriptions of the molecular excitation of HS and different abundance
distributions, including those derived from chemical modelling results. We
detected HS towards five AGB stars, all of which have high mass-loss rates
of yr and are oxygen-rich. HS
was not detected towards the carbon or S-type stars that fall in a similar
mass-loss range. For the stars in our sample with detections, we find peak
o-HS abundances relative to H between and . Overall, we conclude that HS can play a significant role in
oxygen-rich AGB stars with higher mass-loss rates, but is unlikely to play a
key role in stars of other chemical types or the lower mass-loss rate
oxygen-rich stars. For two sources, V1300 Aql and GX Mon, HS is most likely
the dominant sulphur-bearing molecule in the circumstellar envelope.Comment: 14 pages, 7 figures, accepted in A&
Dawn of the red and dead : stellar kinematics of massive quiescent galaxies out to z = 2
The first massive elliptical galaxies were already in place when the Universe was only 3 billions years old. Surprisingly, they are more compact in comparison to their present-day counterparts. In this thesis these recent findings are assessed by measuring the stellar kinematics of massive z=2 galaxies from spectra obtained with X-Shooter on the Very Large Telescope. This thesis work shows that high-redshift galaxies are truly very massive and structurally very different from present-day galaxies, yet they follow the same scaling relations.Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO) en het Leids Kerkhoven Bosscha fonds (LKBF).UBL - phd migration 201
Disentangling physics and chemistry in AGB outflows: revealing degeneracies when adding complexity
Observations of the outflows of asymptotic giant branch (AGB) stars continue
to reveal their chemical and dynamical complexity. Spherical asymmetries, such
as spirals and disks, are prevalent and thought to be caused by binary
interaction with a (sub)stellar companion. Furthermore, high density outflows
show evidence of dust-gas interactions. The classical chemical model of these
outflows - a gas-phase only, spherically symmetric chemical kinetics model - is
hence not appropriate for a majority of observed outflows. We have included
several physical and chemical advancements step-by-step: a porous density
distribution, dust-gas chemistry, and internal UV photons originating from a
close-by stellar companion. Now, we combine these layers of complexity into the
most chemically and physically advanced chemical kinetics model of AGB outflows
to date. By varying over all model parameters, we obtain a holistic view of the
outflow's composition and how it (inter)depends on the different complexities.
A stellar companion has the largest influence, especially when combined with a
porous outflow. We compile sets of gas-phase molecules that trace the
importance of dust-gas chemistry and allow us to infer the presence of a
companion and porosity of the outflow. This shows that our new chemical model
can be used to infer physical and chemical properties of specific outflows, as
long as a suitable range of molecules is observed.Comment: Faraday Discussions 2023, accepted manuscript. 15 pages, 7 figures, 4
tables. Supplementary information can be found at
https://pubs.rsc.org/en/content/articlelanding/2023/fd/d3fd00039
Fast human activity recognition in lifelogging
This paper addresses the problem of fast Human Activity Recognition (HAR) in visual lifelogging. We identify the importance of visual features related to HAR and we specifically evaluate the HAR discrimination potential of Colour Histograms and Histogram of Oriented Gradients. In our evaluation we show that colour can be a low-cost and effective means of low-cost HAR when performing single-user classification. It is also noted that, while much more efficient, global image descriptors perform as well or better than local descriptors in our HAR experiments. We believe that both of these findings are due to the fact that a user’s lifelog is rich in reoccurring scenes and environments
Hydrophobic drug/toxin binding sites in voltage-dependent K+ and Na+ channels
In the Na(v)channel family the lipophilic drugs/toxins binding sites and the presence of fenestrations in the channel pore wall are well defined and categorized. No such classification exists in the much larger K(v)channel family, although certain lipophilic compounds seem to deviate from binding to well-known hydrophilic binding sites. By mapping different compound binding sites onto 3D structures of Kv channels, there appear to be three distinct lipid-exposed binding sites preserved in K(v)channels: the front and back side of the pore domain, and S2-S3/S3-S4 clefts. One or a combination of these sites is most likely the orthologous equivalent of neurotoxin site 5 in Na(v)channels. This review describes the different lipophilic binding sites and location of pore wall fenestrations within the K(v)channel family and compares it to the knowledge of Na(v)channels
The Relation between Dynamical Mass-to-light Ratio and Color for Massive Quiescent Galaxies out to z ~ 2 and Comparison with Stellar Population Synthesis Models
Article / Letter to editorSterrewach
Investigating Anomalous Photochemistry in the Inner Wind of IRC+10216 Through ALMA Observations of HCN
In recent years, many questions have arisen regarding the chemistry of
photochemical products in the carbon-rich winds of evolved stars. To address
them, it is imperative to constrain the distributions of such species through
high angular resolution interferometric observations covering multiple
rotational transitions. We used archival ALMA observations to map rotational
lines involving high energy levels of cyanoacetylene (HCN) toward the inner
envelope (radius <8"/1000 AU) of the carbon star IRC+10216. The observed lines
include the J=28-27, J=30-29, and J=38-37, transitions of HCN in its ground
vibrational state. In contrast to previous observations of linear carbon chains
toward this AGB star which show extended, hollow emission at 15"-20" radii
(e.g. CH, CH, HCN), the maps of the HCN lines here show compact
morphologies comprising various arcs and density enhancements, with significant
emission from gas clumps at an angular distance of ~3" (350 AU) from the
central AGB star. We compared visibility sampled non-LTE radiative transfer
models with the observed brightness distributions, and derive a fractional
abundance with respect to H of for HCN at the radii probed by
these lines. These results are consistent with enhanced photochemistry
occurring in warm (~200 K) regions of the circumstellar envelope. After
application of a specialized chemical model for IRC+10216, we find evidence
that the enhanced HCN abundances in the inner wind are most likely due to a
solar-type binary companion initiating photochemistry in this region.Comment: 17 pages, 9 figures, 2 tables. Accepted for publication in Ap
A <i>Falciformispora senegalensis</i> grain model in <i>Galleria mellonella</i> larvae
Eumycetoma is a subcutaneous implantation mycosis often found in the foot. One of the hallmarks of eumycetoma is the formation of grains. These grains are either black or white, and the consistency and morphology differs per causative agent. The two most common causative agents of black-grain eumycetoma are Madurella mycetomatis and Falciformispora senegalensis. Since grains cannot be formed in vitro, in vivo models are needed to study grain formation. Here, we used the invertebrate Galleria mellonella to establish an in vivo grain model for F. senegalensis. Three different F. senegalensis strains were selected, and four different inocula were used to infect G. mellonella larvae, ranging from 0.04 mg/larvae to 10 mg/larvae. Larval survival was monitored for 10 days. Grain formation was studied macroscopically and histologically. The efficacy of antifungal therapy was determined for itraconazole, amphotericin B, and terbinafine. A concentration of 10 mg F. senegalensis per larva was lethal for the majority of the larvae within 10 days. At this inoculum, grains were formed within 24 h after infection. The grains produced in the larvae resembled those formed in human patients. Amphotericin B given at 1 mg/kg 4 h, 28 h, and 52 h after infection prolonged larval survival. No enhanced survival was noted for itraconazole or terbinafine. In conclusion, we developed a F. senegalensis grain model in G. mellonella larvae in which grains were formed that were similar to those formed in patients. This model can be used to monitor grain formation over time and study antifungal efficacy.</p
Dutch patients, retail chicken meat and poultry share the same ESBL genes, plasmids and strains
Intestinal carriage of extended-spectrum beta-lactamase (ESBL) -producing bacteria in food-producing animals and contamination of retail meat may contribute to increased incidences of infections with ESBL-producing bacteria in humans. Therefore, distribution of ESBL genes, plasmids and strain genotypes in Escherichia coli obtained from poultry and retail chicken meat in the Netherlands was determined and defined as ‘poultry-associated’ (PA). Subsequently, the proportion of E. coli isolates with PA ESBL genes, plasmids and strains was quantified in a representative sample of clinical isolates. The E. coli were derived from 98 retail chicken meat samples, a prevalence survey among poultry, and 516 human clinical samples from 31 laboratories collected during a 3-month period in 2009. Isolates were analysed using an ESBL-specific microarray, sequencing of ESBL genes, PCR-based replicon typing of plasmids, plasmid multi-locus sequence typing (pMLST) and strain genotyping (MLST). Six ESBL genes were defined as PA (blaCTX-M-1, blaCTX-M-2, blaSHV-2, blaSHV-12, blaTEM-20, blaTEM-52): 35% of the human isolates contained PA ESBL genes and 19% contained PA ESBL genes located on IncI1 plasmids that were genetically indistinguishable from those obtained from poultry (meat). Of these ESBL genes, 86% were blaCTX-M-1 and blaTEM-52 genes, which were also the predominant genes in poultry (78%) and retail chicken meat (75%). Of the retail meat samples, 94% contained ESBL-producing isolates of which 39% belonged to E. coli genotypes also present in human samples. These findings are suggestive for transmission of ESBL genes, plasmids and E. coli isolates from poultry to humans, most likely through the food chain
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