2,050 research outputs found
Ultrathin epitaxial Fe films in vicinal GaAs(001): A study by spin-resolved photoelectron spectroscopy
Thin epitaxial Fe films have been grown on vicinal GaAs(001) substrates and their remanent magnetic properties and the degree of substrate atom diffusion investigated using synchrotron-based photoelectron spectroscopy. The vicinal Fe films, though exhibiting greater As diffusion than their singular homologues, displayed better film quality both from the structural and the magnetic points of view. The spin-resolved valence spectra of the vicinal films resemble those for crystalline bulk Fe at lower film thicknesses than for singular films
Development and characterization of microsatellite loci for the haploidâdiploid red seaweed Gracilaria vermiculophylla
Microsatellite loci are popular molecular markers due to their resolution in distinguishing individual genotypes. However, they have rarely been used to explore the population dynamics in species with biphasic life cycles in which both haploid and diploid stages develop into independent, functional organisms. We developed microsatellite loci for the haploidâdiploid red seaweed Gracilaria vermiculophylla, a widespread non-native species in coastal estuaries of the Northern hemisphere. Forty-two loci were screened for amplification and polymorphism. Nine of these loci were polymorphic across four populations of the extant range with two to eleven alleles observed. Mean observed and expected heterozygosities ranged from 0.265 to 0.527 and 0.317 to 0.387, respectively. Overall, these markers will aid in the study of the invasive history of this seaweed and further studies on the population dynamics of this important haploidâdiploid primary producer
Large Magellanic Cloud Planetary Nebula Morphology: Probing Stellar Populations and Evolution
Planetary Nebulae (PNe) in the Large Magellanic Cloud (LMC) offer the unique
opportunity to study both the Population and evolution of low- and
intermediate-mass stars, by means of the morphological type of the nebula.
Using observations from our LMC PN morphological survey, and including images
available in the HST Data Archive, and published chemical abundances, we find
that asymmetry in PNe is strongly correlated with a younger stellar Population,
as indicated by the abundance of elements that are unaltered by stellar
evolution (Ne, Ar, S). While similar results have been obtained for Galactic
PNe, this is the first demonstration of the relationship for extra-galactic
PNe. We also examine the relation between morphology and abundance of the
products of stellar evolution. We found that asymmetric PNe have higher
nitrogen and lower carbon abundances than symmetric PNe. Our two main results
are broadly consistent with the predictions of stellar evolution if the
progenitors of asymmetric PNe have on average larger masses than the
progenitors of symmetric PNe. The results bear on the question of formation
mechanisms for asymmetric PNe, specifically, that the genesis of PNe structure
should relate strongly to the Population type, and by inference the mass, of
the progenitor star, and less strongly on whether the central star is a member
of a close binary system.Comment: The Astrophysical Journal Letters, in press 4 figure
Predicting the public health benefit of vaccinating cattle against Escherichia coli O157
Identifying the major sources of risk in disease transmission is key to designing effective controls. However, understanding of transmission dynamics across species boundaries is typically poor, making the design and evaluation of controls particularly challenging for zoonotic pathogens. One such global pathogen is Escherichia coli O157, which causes a serious and sometimes fatal gastrointestinal illness. Cattle are the main reservoir for E. coli O157, and vaccines for cattle now exist. However, adoption of vaccines is being delayed by conflicting responsibilities of veterinary and public health agencies, economic drivers, and because clinical trials cannot easily test interventions across species boundaries, lack of information on the public health benefits. Here, we examine transmission risk across the cattleâhuman species boundary and show three key results. First, supershedding of the pathogen by cattle is associated with the genetic marker stx2. Second, by quantifying the link between shedding density in cattle and human risk, we show that only the relatively rare supershedding events contribute significantly to human risk. Third, we show that this finding has profound consequences for the public health benefits of the cattle vaccine. A naĂŻve evaluation based on efficacy in cattle would suggest a 50% reduction in risk; however, because the vaccine targets the major source of human risk, we predict a reduction in human cases of nearly 85%. By accounting for nonlinearities in transmission across the humanâanimal interface, we show that adoption of these vaccines by the livestock industry could prevent substantial numbers of human E. coli O157 cases
Spitzer IRAC observations of newly-discovered planetary nebulae from the Macquarie-AAO-Strasbourg H-alpha Planetary Nebula Project
We compare H-alpha, radio continuum, and Spitzer Space Telescope (SST) images
of 58 planetary nebulae (PNe) recently discovered by the Macquarie-AAO-Strasbo-
urg H-alpha PN Project (MASH) of the SuperCOSMOS H-alpha Survey. Using InfraRed
Array Camera (IRAC) data we define the IR colors of PNe and demonstrate good
isolation between these colors and those of many other types of astronomical
object. The only substantive contamination of PNe in the color-color plane we
illustrate is due to YSOs. However, this ambiguity is readily resolved by the
unique optical characteristics of PNe and their environs. We also examine the
relationships between optical and MIR morphologies from 3.6 to 8.0um and
explore the ratio of mid-infrared (MIR) to radio nebular fluxes, which is a
valuable discriminant between thermal and nonthermal emission. MASH emphasizes
late evolutionary stages of PNe compared with previous catalogs, enabling study
of the changes in MIR and radio flux that attend the aging process. Spatially
integrated MIR energy distributions were constructed for all MASH PNe observed
by the GLIMPSE Legacy Project, using the H-alpha morphologies to establish the
dimensions for the calculations of the Midcourse Space Experiment (MSX), IRAC,
and radio continuum (from the Molonglo Observatory Synthesis Telescope and the
Very Large Array) flux densities. The ratio of IRAC 8.0-um to MSX 8.3-um flux
densities provides a measure of the absolute diffuse calibration of IRAC at 8.0
um. We independently confirm the aperture correction factor to be applied to
IRAC at 8.0um to align it with the diffuse calibration of MSX. The result
agrees with the recommendations of the Spitzer Science Center and with results
from a parallel study of HII regions. These PNe probe the diffuse calibration
of IRAC on a spatial scale of 9-77 arcsec.Comment: 48 pages, LaTeX (aastex), incl. 18 PostScript (eps) figures and 3
tables. Accepted by Astrophysical Journa
Quantitative data analysis of perceived barriers and motivators to physical activity in stroke survivors
Peer reviewedPublisher PD
Genetic Incompatibility Dampens Hybrid Fertility More Than Hybrid Viability: Yeast as a Case Study
Genetic incompatibility is believed to be the major cause of postzygotic
reproductive isolation. Despite huge efforts seeking for speciation-related
incompatibilities in the past several decades, a general understanding of how
genetic incompatibility evolves in affecting hybrid fitness is not available,
primarily due to the fact that the number of known incompatibilities is small.
Instead of further mapping specific incompatible genes, in this paper we aimed
to know the overall effects of incompatibility on fertility and viability, the
two aspects of fitness, by examining 89 gametes produced by yeast S.
cerevisiae - S. paradoxus F1 hybrids. Homozygous
F2 hybrids formed by autodiploidization of F1 gametes were subject to tests for
growth rate and sporulation efficiency. We observed much stronger defects in
sporulation than in clonal growth for every single F2 hybrid strain, indicating
that genetic incompatibility affects hybrid fertility more than hybrid viability
in yeast. We related this finding in part to the fast-evolving nature of
meiosis-related genes, and proposed that the generally low expression levels of
these genes might be a cause of the observation
Regulating Clothing Outwork: A Sceptic's View
By applying the strategies of international anti-sweatshop campaigns to the Australian context, recent regulations governing home-based clothing production hold retailers
responsible for policing the wages and employment conditions of clothing outworkers who manufacture clothing on their behalf. This paper argues that the new approach
oversimplifies the regulatory challenge by assuming (1) that Australian clothing production is organised in a hierarchical âbuyer-ledâ linear structure in which core
retail firms have the capacity to control their suppliersâ behaviour; (2) that firms act as unitary moral agents; and (3) that interventions imported from other times and places
are applicable to the contemporary Australian context. After considering some alternative regulatory approaches, the paper concludes that the new regulatory strategy effectively privatises responsibility for labour market conditions â a development that cries out for further debate
- âŠ