203 research outputs found
Lithium abundances in globular cluster giants: NGC 1904, NGC 2808, and NGC 362
The presence of multiple populations in globular clusters has been well
established thanks to high-resolution spectroscopy. It is widely accepted that
distinct populations are a consequence of different stellar generations:
intra-cluster pollution episodes are required to produce the peculiar chemistry
observed in almost all clusters. Unfortunately, the progenitors responsible
have left an ambiguous signature and their nature remains unresolved. To
constrain the candidate polluters, we have measured lithium and aluminium
abundances in more than 180 giants across three systems: NGC~1904, NGC~2808,
and NGC~362. The present investigation along with our previous analysis of M12
and M5 affords us the largest database of simultaneous determinations of Li and
Al abundances. Our results indicate that Li production has occurred in each of
the three clusters. In NGC~362 we detected an M12-like behaviour, with first
and second-generation stars sharing very similar Li abundances favouring a
progenitor that is able to produce Li, such as AGB stars. Multiple progenitor
types are possible in NGC~1904 and NGC~2808, as they possess both an
intermediate population comparable in lithium to the first generation stars and
also an extreme population, that is enriched in Al but depleted in Li. A simple
dilution model fails in reproducing this complex pattern. Finally, the internal
Li variation seems to suggest that the production efficiency of this element is
a function of the cluster's mass and metallicity - low-mass or relatively
metal-rich clusters are more adept at producing Li.Comment: Accepted for publication in MNRAS. 10 pages, 8 figure
Asteroseismic sensitivity to internal rotation along the red-giant branch
Transport of angular momentum in stellar interiors is currently not well
understood. Asteroseismology can provide us with estimates of internal rotation
of stars and thereby advances our understanding of angular momentum transport.
We can measure core-rotation rates in red-giant stars and we can place upper
bounds on surface-rotation rates using measurements of dipole () modes.
Here, we aim to determine the theoretical sensitivity of modes of different
spherical degree towards the surface rotation. Additionally, we aim to identify
modes that can potentially add sensitivity at intermediate radii. We used
asteroseismic rotational inversions to probe the internal stellar rotation
profiles in red-giant models from the base of the red-giant branch up to the
luminosity bump. We used the inversion method of multiplicative optimally
localised averages (MOLA) to assess how well internal and surface rotation
rates can be recovered from different mode sets and different synthetic
rotation profiles. We confirm that dipole mixed modes are sufficient to set
constraints on the average core-rotation rates in red giants. However,
surface-rotation rates estimated with only dipole mixed modes are contaminated
by the core rotation. We show that the sensitivity to the surface rotation
decreases from the base of the red-giant branch until it reaches a minimum at
0.6-0.8 due to a glitch in the buoyancy frequency. Thereafter a
narrow range of increased surface sensitivity just below the bump luminosity
exists. Quadrupole and octopole modes have more sensitivity in the outer parts
of the star. If observed, quadrupole and octopole modes enable us to
distinguish between differential and solid body rotation in the convection
zone. To obtain accurate estimates of rotation rates at intermediate radii,
acoustic oscillation modes with a spherical degree of are needed.Comment: accepted for publication in Astronomy and Astrophysics, revised
manuscript after language editin
The Asymptotic Giant Branches of GCs: Selective Entry Only
The handful of available observations of AGB stars in Galactic Globular
Clusters suggest that the GC AGB populations are dominated by cyanogen-weak
stars. This contrasts strongly with the distributions in the RGB (and other)
populations, which generally show a 50:50 bimodality in CN band strength. If it
is true that the AGB populations show very different distributions then it
presents a serious problem for low mass stellar evolution theory, since such a
surface abundance change going from the RGB to AGB is not predicted by stellar
models. However this is only a tentative conclusion, since it is based on very
small AGB sample sizes. To test whether this problem really exists we have
carried out an observational campaign specifically targeting AGB stars in GCs.
We have obtained medium resolution spectra for about 250 AGB stars across 9
Galactic GCs using the multi-object spectrograph on the AAT (2df/AAOmega). We
present some of the preliminary findings of the study for the second parameter
trio of GCs: NGC 288, NGC 362 and NGC 1851. The results indeed show that there
is a deficiency of stars with strong CN bands on the AGB. To confirm that this
phenomenon is robust and not just confined to CN band strengths and their
vagaries, we have made observations using FLAMES/VLT to measure elemental
abundances for NGC 6752.We present some initial results from this study also.
Our sodium abundance results show conclusively that only a subset of stars in
GCs experience the AGB phase of evolution. This is the first direct, concrete
confirmation of the phenomenon.Comment: 4 pages, to appear in conference proceedings of "Reading the book of
globular clusters with the lens of stellar evolution", Rome, 26-28 November
201
Phylogenetic inference using cytochrome c oxidase subunit I (COI) in the poultry red mite, Dermanyssus gallinae in the United Kingdom relative to a European framework
The poultry red mite (Dermanyssus gallinae), an obligatory blood feeding ectoparasite, is primarily associated with laying hens where it is estimated to cause losses of ~€231 million per annum to European farmers. Moderate to high infestation levels result in negative impacts on hen welfare, including increased cannibalism, irritation, feather pecking, restlessness, anaemia and mortality. Acaricides are currently the prevailing method of population control for D. gallinae, although resistance against some classes of acaricide has been widely reported. The development of resistance highlights a growing need for research into alternative control methods, including the development of a suitable and effective vaccine. Understanding the genetic structure of D. gallinae populations can support improved management of acaricide resistance and sustainability of future vaccines, but limited data are currently available. The aim of this study was to characterise D. gallinae isolates from Europe, targeting the cytochrome c oxidase subunit 1 (COI) gene to gain an insight into population structure and genetic diversity of currently circulating mites. Dermanyssus gallinae isolates were collected from Albania, Belgium, Croatia, Czech Republic, Denmark, France, Greece, Italy, the Netherlands, Portugal, Romania, Slovenia, Turkey and the United Kingdom. Genomic DNA was extracted from individual adult D. gallinae mites and a 681bp fragment of the COI gene was amplified and sequenced. Phylogenetic analyses of 195 COI sequences confirmed the presence of multiple lineages across Europe with 76 distinct haplotypes split across three main haplogroups and six sub-haplogroups. Importantly there is considerable inter- and intra-country variation across Europe, which could result from the movement of poultry or transfer of contaminated equipment and/or materials and husbandry practices
Spatial-spectral flexible optical networking:enabling switching solutions for a simplified and efficient SDM network platform
The traffic carried by core optical networks grows at a steady but remarkable pace of 30-40% year-over-year. Optical transmissions and networking advancements continue to satisfy the traffic requirements by delivering the content over the network infrastructure in a cost and energy efficient manner. Such core optical networks serve the information traffic demands in a dynamic way, in response to requirements for shifting of traffics demands, both temporally (day/night) and spatially (business district/residential). However as we are approaching fundamental spectral efficiency limits of singlemode fibers, the scientific community is pursuing recently the development of an innovative, all-optical network architecture introducing the spatial degree of freedom when designing/operating future transport networks. Spacedivision- multiplexing through the use of bundled single mode fibers, and/or multi-core fibers and/or few-mode fibers can offer up to 100-fold capacity increase in future optical networks. The EU INSPACE project is working on the development of a complete spatial-spectral flexible optical networking solution, offering the network ultra-high capacity, flexibility and energy efficiency required to meet the challenges of delivering exponentially growing traffic demands in the internet over the next twenty years. In this paper we will present the motivation and main research activities of the INSPACE consortium towards the realization of the overall project solution
Quality of life returns from basic research
<p>Abstract</p> <p>Background</p> <p>Assessing the consequences of research is an increasingly important task in research and innovation policy. This paper takes a broader view of those consequences than the conventional economic approach, placing researchers and their activities in the centre of the assessment process and examining results for professional practice and general education as well as contributions to knowledge.</p> <p>Methods</p> <p>The paper uses historical and documentary analysis to illustrate the approach, focusing on U.S. biomedicine over the past century. At aggregate level, the analysis attributes portions of the change in aggregate health indicators to research and research-based institutions, through several available types of logic: either through correlations between timing of institutional changes and changes in the indicators or through direct or indirect causal connections.</p> <p>Results</p> <p>The analysis shows that while biomedical research has certainly contributed to improved health in the United States, other factors have also contributed. In some ways the institutional structure of science-based medicine has worked against creating benefits for some groups in U.S. society.</p> <p>Conclusions</p> <p>The paper concludes with a call for more strategic attention to dimensions of impact other than knowledge outcomes and for participatory planning for research.</p
Enabling transparent technologies for the development of highly granular flexible optical cross-connects
Flexible optical networking is identified today as the solution that offers smooth system upgradability towards Tb/s capacities and optimized use of network resources. However, in order to fully exploit the potentials of flexible spectrum allocation and networking, the development of a flexible switching node is required capable to adaptively add, drop and switch tributaries with variable bandwidth characteristics from/to ultra-high capacity wavelength channels at the lowest switching granularity. This paper presents the main concept and technology solutions envisioned by the EU funded project FOX-C, which targets the design, development and evaluation of the first functional system prototype of flexible add-drop and switching cross-connects. The key developments enable ultra-fine switching granularity at the optical subcarrier level, providing end-to-end routing of any tributary channel with flexible bandwidth down to 10Gb/s (or even lower) carried over wavelength superchannels, each with an aggregated capacity beyond 1Tb/s. © 2014 IEEE
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