1,209 research outputs found
Synthesis of 19F in Wolf-Rayet stars
Meynet and Arnould (1993) have suggested that Wolf-Rayet (WR) stars could
significantly contaminate the Galaxy with 19F. In their scenario, 19F is
synthesized at the beginning of the He-burning phase from the 14N left over by
the previous CNO-burning core, and is ejected in the interstellar medium when
the star enters its WC phase. Recourse to CNO seeds makes the 19F yields
metallicity-dependent. These yields are calculated on grounds of detailed
stellar evolutionary sequences for an extended range of initial masses (from 25
to 120 Msol) and metallicities (Z = 0.008, 0.02 and 0.04). The adopted mass
loss rate prescription enables to account for the observed variations of WR
populations in different environments. The 19F abundance in the WR winds of 60
Msol model stars is found to be about 10 to 70 times higher than its initial
value, depending on the metallicity. This prediction is used in conjunction
with a very simple model for the chemical evolution of the Galaxy to predict
that WR stars could be significant (dominant?) contributors to the solar system
fluorine content. We also briefly discuss the implications of our model on the
possible detection of fluorine at high redshift.Comment: 2 figures; requires LaTeX A&A class file; accepted for publication in
Astron. Astrophy
The production of short-lived radionuclides by new non-rotating and rotating Wolf-Rayet model stars
It has been speculated that WR winds may have contaminated the forming solar
system, in particular with short-lived radionuclides (half-lives in the
approximate 10^5 - 10^8 y range) that are responsible for a class of isotopic
anomalies found in some meteoritic materials. We revisit the capability of the
WR winds to eject these radionuclides using new models of single non-exploding
WR stars with metallicity Z = 0.02. The earlier predictions for non-rotating WR
stars are updated, and models for rotating such stars are used for the first
time in this context. We find that (1) rotation has no significant influence on
the short-lived radionuclide production by neutron capture during the core
He-burning phase, and (2) 26Al, 36Cl, 41Ca, and 107Pd can be wind-ejected by a
variety of WR stars at relative levels that are compatible with the meteoritic
analyses for a period of free decay of around 10^5 y between production and
incorporation into the forming solar system solid bodies. We confirm the
previously published conclusions that the winds of WR stars have a radionuclide
composition that can meet the necessary condition for them to be a possible
contaminating agent of the forming solar system. Still, it remains to be
demonstrated from detailed models that this is a sufficient condition for these
winds to have provided a level of pollution that is compatible with the
observations.Comment: 8 pages, 8 figure
Spectroscopy of the heaviest nuclei (theory)
Recent progress in the applications of covariant density functional theory
(CDFT) to the description of the spectroscopy of the heaviest nuclei is
reviewed. The analysis of quasiparticle spectra in actinides and the heaviest A
~ 250 nuclei provides a measure of the accuracy of the description of
single-particle energies in CDFT and an additional constraint for the choice of
effective interactions for the description of superheavy nuclei. The response
of these nuclei to the rotation is rather well described by cranked
relativistic Hartree+Bogoliubov theory and it serves as a supplementary tool in
configuration assignment in odd-mass nuclei. A systematic analysis of the
fission barriers with allowance for triaxial deformation shows that covariant
density functional theory is able to describe fission barriers on a level of
accuracy comparable with the best phenomenological macroscopic+microscopic
approaches.Comment: 10 pages, 7 figures, invited talk of A.V. Afanasjev at the
International Nuclear Physics Conference (INPC 2010), Vancouver, Canada, July
4-9, 2010, to be published in Journal of Physics G: Conference Series (JPCS
Bifidobacterium mongoliense genome seems particularly adapted to milk oligosaccharide digestion leading to production of antivirulent metabolites
Background: Human milk oligosaccharides (HMO) could promote the growth of bifidobacteria, improving young children's health. In addition, fermentation of carbohydrates by bifidobacteria can result in the production of metabolites presenting an antivirulent activity against intestinal pathogens. Bovine milk oligosaccharides (BMO), structurally similar to HMO, are found at high concentration in cow whey. This is particularly observed for 3′-sialyllactose (3′SL). This study focused on enzymes and transport systems involved in HMO/BMO metabolism contained in B. crudilactis and B. mongoliense genomes, two species from bovine milk origin. The ability of B. mongoliense to grow in media supplemented with whey or 3′SL was assessed. Next, the effects of cell-free spent media (CFSM) were tested against the virulence expression of Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium. Results: Due to the presence of genes encoding β-galactosidases, β-hexosaminidases, α-sialidases and α-fucosidases, B. mongoliense presents a genome more sophisticated and more adapted to the digestion of BMO/HMO than B. crudilactis (which contains only β-galactosidases). In addition, HMO/BMO digestion involves genes encoding oligosaccharide transport systems found in B. mongoliense but not in B. crudilactis. B. mongoliense seemed able to grow on media supplemented with whey or 3′SL as main source of carbon (8.3 ± 1.0 and 6.7 ± 0.3 log cfu/mL, respectively). CFSM obtained from whey resulted in a significant under-expression of ler, fliC, luxS, stx1 and qseA genes (- 2.2, - 5.3, - 2.4, - 2.5 and - 4.8, respectively; P < 0.05) of E. coli O157:H7. CFSM from 3′SL resulted in a significant up-regulation of luxS (2.0; P < 0.05) gene and a down-regulation of fliC (- 5.0; P < 0.05) gene. CFSM obtained from whey resulted in significant up-regulations of sopD and hil genes (2.9 and 3.5, respectively; P < 0.05) of S. Typhimurium, while CFSM obtained from 3′SL fermentation down-regulated hil and sopD genes (- 2.7 and - 4.2, respectively; P < 0.05). Conclusion: From enzymes and transporters highlighted in the genome of B. mongoliense and its potential ability to metabolise 3′SL and whey, B. mongoliense seems well able to digest HMO/BMO. The exact nature of the metabolites contained in CFSM has to be identified still. These results suggest that BMO associated with B. mongoliense could be an interesting synbiotic formulation to maintain or restore intestinal health of young children
Validating accelerometry-derived proxies of energy expenditure using the doubly-labelled water method in the smallest penguin species
Acknowledgements We are grateful to Dr Catherine Hambly and Peter Thompson for technical assistance with the isotope analysis for the doubly labelled water measurements. We thank Parks Victoria (in particular, the rangers at Gabo Island and Port Campbell Offices) and Kevin Lotte for logistical support. Funding This project was funded by the Holsworth Wildlife Research Endowment – Equity Trustees Charitable Foundation and the Ecological Society of Australia and Deakin University internal funds.Peer reviewedPublisher PD
Machine learning to detect marine animals in UAV imagery: effect of morphology, spacing, behaviour and habitat
Machine learning algorithms are being increasingly used to process large volumes of wildlife imagery data from unmanned aerial vehicles (UAVs); however, suitable algorithms to monitor multiple species are required to enhance efficiency. Here, we developed a machine learning algorithm using a low-cost computer. We trained a convolutional neural network and tested its performance in: (1) distinguishing focal organisms of three marine taxa (Australian fur seals, loggerhead sea turtles and Australasian gannets; body size ranges: 0.8–2.5 m, 0.6–1.0 m, and 0.8–0.9 m, respectively); and (2) simultaneously delineating the fine-scale movement trajectories of multiple sea turtles at a fish cleaning station. For all species, the algorithm performed best at detecting individuals of similar body length, displaying consistent behaviour or occupying uniform habitat (proportion of individuals detected, or recall of 0.94, 0.79 and 0.75 for gannets, seals and turtles, respectively). For gannets, performance was impacted by spacing (huddling pairs with offspring) and behaviour (resting vs. flying shapes, overall precision: 0.74). For seals, accuracy was impacted by morphology (sexual dimorphism and pups), spacing (huddling and creches) and habitat complexity (seal sized boulders) (overall precision: 0.27). For sea turtles, performance was impacted by habitat complexity, position in water column, spacing, behaviour (interacting individuals) and turbidity (overall precision: 0.24); body size variation had no impact. For sea turtle trajectories, locations were estimated with a relative positioning error of <50 cm. In conclusion, we demonstrate that, while the same machine learning algorithm can be used to survey multiple species, no single algorithm captures all components optimally within a given site. We recommend that, rather than attempting to fully automate detection of UAV imagery data, semi-automation is implemented (i.e. part automated and part manual, as commonly practised for photo-identification). Approaches to enhance the efficiency of manual detection are required in parallel to the development of effective implementation of machine learning algorithms
Nucleosynthesis in Massive Stars With Improved Nuclear and Stellar Physics
We present the first calculations to follow the evolution of all stable
nuclei and their radioactive progenitors in stellar models computed from the
onset of central hydrogen burning through explosion as Type II supernovae.
Calculations are performed for Pop I stars of 15, 19, 20, 21, and 25 M_sun
using the most recently available experimental and theoretical nuclear data,
revised opacity tables, neutrino losses, and weak interaction rates, and taking
into account mass loss due to stellar winds. A novel ``adaptive'' reaction
network is employed with a variable number of nuclei (adjusted each time step)
ranging from about 700 on the main sequence to more than 2200 during the
explosion. The network includes, at any given time, all relevant isotopes from
hydrogen through polonium (Z=84). Even the limited grid of stellar masses
studied suggests that overall good agreement can be achieved with the solar
abundances of nuclei between 16O and 90Zr. Interesting discrepancies are seen
in the 20 M_sun model and, so far, only in that model, that are a consequence
of the merging of the oxygen, neon, and carbon shells about a day prior to core
collapse. We find that, in some stars, most of the ``p-process'' nuclei can be
produced in the convective oxygen burning shell moments prior to collapse; in
others, they are made only in the explosion. Serious deficiencies still exist
in all cases for the p-process isotopes of Ru and Mo.Comment: 53 pages, 17 color figures (3 as separate GIF images), slightly
extended discussion and references, accepted by Ap
A sex-influenced flexible foraging strategy in a tropical seabird, the magnificent frigatebird
© The authors and the University of Liverpool 2019. To successfully exploit resources, animals must be adapted to operate under phenotypic and environmental constraints. The strategies that predators use to locate prey are therefore diverse, particularly for breeding central-place foragers that must balance investment in reproduction and self-maintenance. Magnificent frigatebirds Fregata magnificens are tropical seabirds with intriguing morphology and feeding ecology, which display strikingly unequal levels of parental care (males deserting offspring months before females). These unusual traits can better help us understand the links between movement behaviour and breeding strategies in this poorly studied species. Using archival GPS, GPS-GSM loggers, bird-borne cameras and dietary data, we investigated the foraging ecology of chick-rearing magnificent frigatebirds from a breeding population in the Cayman Islands. This population engages in 2 main foraging strategies: (1) coastal trips over the continental shelf, where individuals target reef species and engage in kleptoparasitism, and (2) offshore trips during which birds feed on schooling pelagic prey. Differences in strategy use were partially linked to sex, with males (which invest less in offspring) roaming further from nests, and showing a higher propensity to forage offshore. Video data further indicated differences in social information use between strategies: foraging with conspecifics was more prevalent in coastal environments than pelagic. We suggest that observed variation in at-sea behaviour may partially be mediated by sex-based differences in parental roles, and/or size differences leading to intraspecific competition. Our study provides evidence of bimodal foraging and sheds new light on the importance of both pelagic and coastal feeding in this enigmatic species
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