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  • 1
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    Investigation of Early Planted Winter Canola as a Dual-Purpose Crop for Silage and Seed Production (2015)
    Wiley
    Details
    Publication Date: 2015-09-01
    Print ISSN: 0002-1962
    Electronic ISSN: 1435-0645
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Wiley
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  • 2
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    Resolving structure of the disc around HD100546 at 7 mm with ATCA (2015)
    Oxford University Press
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    Publication Date: 2015-08-15
    Description: There is much evidence that planet formation is occurring in the disc around the Herbig Be star HD100546. To learn more about the processes occurring in this disc, we conducted high-resolution imaging at 43/45 GHz with the Australia Telescope Compact Array. Multiple array configurations were used, providing a best spatial resolution of ~0.15 arcsec, or 15 au at HD100546's distance of ~100 pc. Significant structure is revealed, but its precise form is dependent on the u – v plane sampling used for the image reconstruction. At a resolution of ≤30 au, we detected an inner gap in the disc with a radius of ~25 au and a position angle approximately along the known disc major axis. With different weighting, and an achieved resolution of ~15 au, emission appears at the centre and the disc takes on the shape of an incomplete ring, much like a horseshoe, again with a gap radius of ~25 au. The position angle of the disc major axis and its inclination from face-on are determined to be 140° ± 5° and 40° ± 5°, respectively. The ~25 au gap radius is confirmed by a null in the real part of the binned visibilities at 320 ± 10 k, whilst the non-axisymmetric nature is also confirmed through significant structure in the imaginary component. The emission mechanism at the central peak is most likely to be free–free emission from a stellar or disc wind. Overall our data support the picture of at least one, but probably several, giant planets orbiting HD100546 within 25 au.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 3
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    Cometary ices in forming protoplanetary disc midplanes (2016)
    Oxford University Press
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    Publication Date: 2016-08-11
    Description: Low-mass protostars are the extrasolar analogues of the natal Solar system. Sophisticated physicochemical models are used to simulate the formation of two protoplanetary discs from the initial prestellar phase, one dominated by viscous spreading and the other by pure infall. The results show that the volatile prestellar fingerprint is modified by the chemistry en route into the disc. This holds relatively independent of initial abundances and chemical parameters: physical conditions are more important. The amount of CO 2 increases via the grain-surface reaction of OH with CO, which is enhanced by photodissociation of H 2 O ice. Complex organic molecules are produced during transport through the envelope at the expense of CH 3 OH ice. Their abundances can be comparable to that of methanol ice (few per cent of water ice) at large disc radii ( R 〉 30 au). Current Class II disc models may be underestimating the complex organic content. Planet population synthesis models may underestimate the amount of CO 2 and overestimate CH 3 OH ices in planetesimals by disregarding chemical processing between the cloud and disc phases. The overall C/O and C/N ratios differ between the gas and solid phases. The two ice ratios show little variation beyond the inner 10 au and both are nearly solar in the case of pure infall, but both are subsolar when viscous spreading dominates. Chemistry in the protostellar envelope en route to the protoplanetary disc sets the initial volatile and prebiotically significant content of icy planetesimals and cometary bodies. Comets are thus potentially reflecting the provenances of the midplane ices in the solar nebula.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    The complex chemistry of outflow cavity walls exposed: the case of low-mass protostars (2015)
    Oxford University Press
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    Publication Date: 2015-07-01
    Description: Complex organic molecules are ubiquitous companions of young low-mass protostars. Recent observations suggest that their emission stems, not only from the traditional hot corino, but also from offset positions. In this work, 2D physicochemical modelling of an envelope-cavity system is carried out. Wavelength-dependent radiative transfer calculations are performed and a comprehensive gas-grain chemical network is used to simulate the physical and chemical structure. The morphology of the system delineates three distinct regions: the cavity wall layer with time-dependent and species-variant enhancements; a torus rich in complex organic ices, but not reflected in gas-phase abundances and the remaining outer envelope abundant in simpler solid and gaseous molecules. Strongly irradiated regions, such as the cavity wall layer, are subject to frequent photodissociation in the solid phase. Subsequent recombination of the photoproducts leads to frequent reactive desorption, causing gas-phase enhancements of several orders of magnitude. This mechanism remains to be quantified with laboratory experiments. Direct photodesorption is found to be relatively inefficient. If radicals are not produced directly in the icy mantle, the formation of complex organics is impeded. For efficiency, a sufficient number of FUV photons needs to penetrate the envelope, and elevated cool dust temperatures need to enable grain-surface radical mobility. As a result, a high stellar luminosity and a sufficiently wide cavity favour chemical complexity. Furthermore within this paradigm, complex organics are demonstrated to have unique lifetimes and be grouped into early (formaldehyde, ketene, methanol, formic acid, methyl formate, acetic acid and glycolaldehyde) and late (acetaldehyde, dimethyl ether and ethanol) species.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    Temporal evolution and electric potential structure of the auroral acceleration region from multispacecraft measurements (2012)
    Wiley
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    Publication Date: 2012-12-06
    Description: Bright aurorae can be excited by the acceleration of electrons into the atmosphere in violation of ideal magnetohydrodynamics. Modeling studies predict that the accelerating electric potential consists of electric double layers at the boundaries of an acceleration region but observations suggest that particle acceleration occurs throughout this region. Using multispacecraft observations from Cluster, we have examined two upward current regions on 14 December 2009. Our observations show that the potential difference below C4 and C3 changed by up to 1.7 kV between their respective crossings, which were separated by 150 s. The field-aligned current density observed by C3 was also larger than that observed by C4. The potential drop above C3 and C4 was approximately the same in both crossings. Using a novel technique of quantitively comparing the electron spectra measured by Cluster 1 and 3, which were separated in altitude, we determine when these spacecraft made effectively magnetically conjugate observations, and we use these conjugate observations to determine the instantaneous distribution of the potential drop in the AAR. Our observations show that an average of 15% of the potential drop in the AAR was located between C1 at 6235 km and C3 at 4685 km altitude, with a maximum potential drop between the spacecraft of 500 V, and that the majority of the potential drop was below C3. Assuming a spatial invariance along the length of the upward current region, we discuss these observations in terms of temporal changes and the vertical structure of the electrostatic potential drop and in the context of existing models and previous single- and multispacecraft observations.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    Average magnetotail electron and proton pitch angle distributions from Cluster PEACE and CIS observations (2011)
    Wiley
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    Publication Date: 2011-03-24
    Description: We present results from the first systematic survey of proton and electron pitch angle distributions in the magnetotail, based on Cluster CIS and PEACE data binned by proton plasma β (βp). The proton distributions conform to the canonical picture of magnetotail ions - a boundary layer made up of Earthward streaming and bidirectional field-aligned particles, consistent with recent observations of time-varying beamlets, which gives way to a broadly isotropic central plasma sheet when βp ∼ 3. The electron distributions are significantly different from the canonical picture. A “boundary layer” made up of bidirectional field-aligned electrons is observed to values of βp as high as 17. This boundary quickly gives way to perpendicular-dominated electrons close to the neutral sheet. Hence, our results suggest that, on average, there is no extended, isotropic electron plasma sheet and that the proton plasma sheet is not routinely encountered until higher βp than commonly assumed.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    POMK mutations disrupt muscle development leading to a spectrum of neuromuscular presentations (2014)
    Oxford University Press
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    Publication Date: 2014-10-09
    Description: Dystroglycan is a transmembrane glycoprotein whose interactions with the extracellular matrix (ECM) are necessary for normal muscle and brain development, and disruptions of its function lead to dystroglycanopathies, a group of congenital muscular dystrophies showing extreme genetic and clinical heterogeneity. Specific glycans bound to the extracellular portion of dystroglycan, α-dystroglycan, mediate ECM interactions and most known dystroglycanopathy genes encode glycosyltransferases involved in glycan synthesis. POMK , which was found mutated in two dystroglycanopathy cases, is instead involved in a glycan phosphorylation reaction critical for ECM binding, but little is known about the clinical presentation of POMK mutations or of the function of this protein in the muscle. Here, we describe two families carrying different truncating alleles, both removing the kinase domain in POMK, with different clinical manifestations ranging from Walker–Warburg syndrome, the most severe form of dystroglycanopathy, to limb-girdle muscular dystrophy with cognitive defects. We explored POMK expression in fetal and adult human muscle and identified widespread expression primarily during fetal development in myocytes and interstitial cells suggesting a role for this protein during early muscle differentiation. Analysis of loss of function in the zebrafish embryo and larva showed that pomk function is necessary for normal muscle development, leading to locomotor dysfuction in the embryo and signs of muscular dystrophy in the larva. In summary, we defined diverse clinical presentations following POMK mutations and showed that this gene is necessary for early muscle development.
    Print ISSN: 0964-6906
    Electronic ISSN: 1460-2083
    Topics: Biology , Medicine
    Published by Oxford University Press
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  • 8
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    Methanol along the path from envelope to protoplanetary disc (2014)
    Oxford University Press
    Details
    Publication Date: 2014-10-10
    Description: Interstellar methanol is considered to be a parent species of larger, more complex organic molecules. A physicochemical simulation of infalling parcels of matter is performed for a low-mass star-forming system to trace the chemical evolution from cloud to disc. An axisymmetric 2D semi-analytic model generates the time-dependent density and velocity distributions, and full continuum radiative transfer is performed to calculate the dust temperature and the UV radiation field at each position as a function of time. A comprehensive gas–grain chemical network is employed to compute the chemical abundances along infall trajectories. Two physical scenarios are studied, one in which the dominant disc growth mechanism is viscous spreading, and another in which continuous infall of matter prevails. The results show that the infall path influences the abundance of methanol entering each type of disc, ranging from complete loss of methanol to an enhancement by a factor of 〉1 relative to the prestellar phase. Critical chemical processes and parameters for the methanol chemistry under different physical conditions are identified. The exact abundance and distribution of methanol is important for the budget of complex organic molecules in discs, which will be incorporated into forming planetary system objects such as protoplanets and comets. These simulations show that the comet-forming zone contains less methanol than in the precollapse phase, which is dominantly of prestellar origin, but also with additional layers built up in the envelope during infall. Such intriguing links will soon be tested by upcoming data from the Rosetta mission.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    Temporal patterns in allele frequencies of the gamete-recognition locus M7 lysin within a population of Mytilus galloprovincialis in southwestern England (2016)
    Oxford University Press
    Details
    Publication Date: 2016-11-04
    Description: Loci that encode proteins involved in gamete recognition often show patterns of rapid adaptive evolution and recent studies have shown that different alleles at gamete-recognition loci can be favoured under different sperm concentrations, leading to density-dependent selection during fertilization. While these density-dependent fertilization processes are likely to vary across time and space, it is possible that they are not typically observed at the larger scale of larval recruitment since most larval cohorts likely consist of multiple pools of larvae produced under a variety of sperm concentrations, which tends to homogenize the allele frequencies across time and space. We tested the hypothesis that allele frequency of the gamete-recognition locus M7 lysin in Mytilus galloprovincialis would show significant temporal variation among cohorts of spat and adult age classes. Adult and juvenile mussels and multiple cohorts of newly settled spat were collected from four locations within a predominantly pure population of M. galloprovincialis in southwestern England. Each mussel was then genotyped at the species-specific locus Glu-5' and the gamete-recognition locus M7 lysin. Allele frequencies at Glu-5' did not differ among any age classes or cohorts, suggesting that the samples did not contain migrants from adjacent hybrid populations with M. edulis . Similarly, there was little evidence of variation in allele frequencies at M7 lysin among cohorts of spat or among juvenile and adult age classes. The lack of significant temporal variation in allele frequency at M7 lysin suggests that the results of local and small-scale density-dependent selection may not typically be observed during recruitment of marine organisms with pelagic larval stages.
    Print ISSN: 0260-1230
    Electronic ISSN: 1464-3766
    Topics: Biology
    Published by Oxford University Press
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  • 10
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    A primordial origin for molecular oxygen in comets: a chemical kinetics study of the formation and survival of O2 ice from clouds to discs (2016)
    Oxford University Press
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    Publication Date: 2016-12-29
    Description: Molecular oxygen has been confirmed as the fourth most abundant molecule in cometary material (O 2 /H 2 O ~ 4 per cent) and is thought to have a primordial nature, i.e. coming from the interstellar cloud from which our Solar system was formed. However, interstellar O 2 gas is notoriously difficult to detect and has only been observed in one potential precursor of a solar-like system. Here, the chemical and physical origin of O 2 in comets is investigated using sophisticated astrochemical models. Three origins are considered: (i) in dark clouds; (ii) during forming protostellar discs; and (iii) during luminosity outbursts in discs. The dark cloud models show that reproduction of the observed abundance of O 2 and related species in comet 67P/C-G requires a low H/O ratio facilitated by a high total density (≥10 5  cm –3 ), and a moderate cosmic ray ionization rate (≤10 –16  s –1 ) while a temperature of 20 K, slightly higher than the typical temperatures found in dark clouds, also enhances the production of O 2 . Disc models show that O 2 can only be formed in the gas phase in intermediate disc layers, and cannot explain the strong correlation between O 2 and H 2 O in comet 67P/C-G together with the weak correlation between other volatiles and H 2 O. However, primordial O 2 ice can survive transport into the comet-forming regions of discs. Taken together, these models favour a dark cloud (or ‘primordial’) origin for O 2 in comets, albeit for dark clouds which are warmer and denser than those usually considered as Solar system progenitors.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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