546 research outputs found
An ultrastructural investigation of the surface microbiota present on the leaves and reproductive structures of the resurrection plant Myrothamnus flabellifolia
The leaves, flower and stems of the southern African angiosperm resurrection plant Myrothamnus flabellifolia were investigated at the ultrastructural level to determine the source of previously reported fungal contamination. Fungal mycelia and hyphae of the genera Aspergillus and Penicillium were found localized to the hydathodes of the leaves and stigmatic surfaces of the female flowers in both desiccated and hydrated specimens. A waxy bacterium of the genus Bacillus was found to colonise the waxy epidermal surfaces of the leaves and flowers which was also where fungal cells were found to be absent. It is suggested that the wax like deposits within the leaves and stems as well as over the epidermal surface prevent the growth of the fungal organisms. These fungi opportunistically invade moist surfaces, such as the floral stigmas, during periods of moisture availability and may thus negatively impact plant development
Alluvial fan records from southeast Arabia reveal multiple windows for human dispersal
The dispersal of human populations out of Africa into Arabia was most likely linked to episodes of climatic amelioration, when increased monsoon rainfall led to the activation of drainage systems, improved freshwater availability, and the development of regional vegetation. Here we present the first dated terrestrial record from southeast Arabia that provides evidence for increased rainfall and the expansion of vegetation during both glacial and interglacial periods. Findings from extensive alluvial fan deposits indicate that drainage system activation occurred during Marine Isotope Stage (MIS) 6 (ca. 160–150 ka), MIS 5 (ca. 130–75 ka), and during early MIS 3 (ca. 55 ka). The development of active freshwater systems during these periods corresponds with monsoon intensity increases during insolation maxima, suggesting that humid periods in Arabia were not confined to eccentricity-paced deglaciations, and providing paleoenvironmental support for multiple windows of opportunity for dispersal out of Africa during the late Pleistocene
Developing a framework of Quaternary dune accumulation in the northern Rub' al-Khali, Arabia
Located at the crossroads between Africa and Eurasia, Arabia occupies a pivotal position for human migration and dispersal during the Late Pleistocene. Deducing the timing of humid and arid phases is critical to understanding when the Rub' al-Khali desert acted as a barrier to human movement and settlement. Recent geological mapping in the northern part of the Rub' al-Khali has enabled the Quaternary history of the region to be put into a regional stratigraphical framework. In addition to the active dunes, two significant palaeodune sequences have been identified. Dating of key sections has enabled a chronology of dune accretion and stabilisation to be determined. In addition, previously published optically stimulated luminescence (OSL) dates have been put in their proper stratigraphical context, from which a record of Late Pleistocene dune activity can be constructed. The results indicate the record of dune activity in the northern Rub' al-Khali is preservation limited and is synchronous with humid events driven by the incursion of the Indian Ocean monsoon
Flux Lattice Melting and Lowest Landau Level Fluctuations
We discuss the influence of lowest Landau level (LLL) fluctuations near
H_{c2}(T) on flux lattice melting in YBaCuO (YBCO). We
show that the specific heat step of the flux lattice melting transition in YBCO
single crystals can be attributed largely to the degrees of freedom associated
with LLL fluctuations. These degrees of freedom have already been shown to
account for most of the latent heat. We also show that these results are a
consequence of the correspondence between flux lattice melting and the onset of
LLL fluctuations.Comment: 4 pages, 2 embedded figure
Fluctuation Study of the Specific Heat of MgB2
The specific heat of polycrystalline MgB has been measured with
high resolution ac calorimetry from 5 to 45 K at constant magnetic fields. The
excess specific heat above T is discussed in terms of Gaussian
fluctuations and suggests that MgB is a bulk superconductor with
Ginzburg-Landau coherence length \AA . The transition-width
broadening in field is treated in terms of lowest-Landau-level (LLL)
fluctuations. That analysis requires that \AA . The underestimate
of the coherence length in field, along with deviations from 3D LLL
predictions, suggest that there is an influence from the anisotropy of B
between the c-axis and the a-b plane.Comment: Phys. Rev. B 66, 134515 (2002
Establishing and Prioritising Research Questions for the Treatment of Alopecia Areata: The Alopecia Areata Priority Setting Partnership
BACKGROUND: Alopecia areata is a common hair loss disorder that results in patchy to complete hair loss. Many uncertainties exist around the most effective treatments for this condition. OBJECTIVES: To identify uncertainties in alopecia areata management and treatment that are important to both service users (people with hair loss, carers and relatives) and healthcare professionals. METHODS: An alopecia areata priority setting partnership was established between patients, their carers and relatives, and healthcare professionals to identify the most important uncertainties in alopecia areata. The methodology of the James Lind Alliance was followed to ensure a balanced, inclusive and transparent process. RESULTS: In total 2747 treatment uncertainties were submitted by 912 participants, of which 1012 uncertainties relating to alopecia areata (and variants) were analyzed. Questions were combined into "indicative uncertainties" following a structured format. A series of ranking exercises further reduced this list to a top 25 that were taken to a final prioritization workshop where the top 10 priorities were agreed. CONCLUSIONS: We present the top 10 research priorities for alopecia areata to guide researchers and funding bodies to support studies important to both patients and clinicians. This article is protected by copyright. All rights reserved
Recognition memory, self-other source memory, and theory-of-mind in children with autism spectrum disorder.
This study investigated semantic and episodic memory in autism spectrum disorder (ASD), using a task which assessed recognition and self-other source memory. Children with ASD showed undiminished recognition memory but significantly diminished source memory, relative to age- and verbal ability-matched comparison children. Both children with and without ASD showed an “enactment effect”, demonstrating significantly better recognition and source memory for self-performed actions than other-person-performed actions. Within the comparison group, theory-of-mind (ToM) task performance was significantly correlated with source memory, specifically for other-person-performed actions (after statistically controlling for verbal ability). Within the ASD group, ToM task performance was not significantly correlated with source memory (after controlling for verbal ability). Possible explanations for these relations between source memory and ToM are considered
Numerical studies of the phase diagram of layered type II superconductors in a magnetic field
We report on simulations of layered superconductors using the
Lawrence-Doniach model in the framework of the lowest Landau level
approximation. We find a first order phase transition with a dependence
which agrees very well with the experimental ``melting'' line in YBaCuO. The
transition is not associated with vortex lattice melting, but separates two
vortex liquid states characterised by different degrees of short-range
crystalline order and different length scales of correlations between vortices
in different layers. The transition line ends at a critical end-point at low
fields. We find the magnetization discontinuity and the location of the lower
critical magnetic field to be in good agreement with experiments in YBaCuO.
Length scales of order parameter correlations parallel and perpendicular to the
magnetic field increase exponentially as 1/T at low temperatures. The dominant
relaxation time scales grow roughly exponentially with these correlation
lengths. We find that the first order phase transition persists in the presence
of weak random point disorder but can be suppressed entirely by strong
disorder. No vortex glass or Bragg glass state is found in the presence of
disorder. The consistency of our numerical results with various experimental
features in YBaCuO, including the dependence on anisotropy, and the temperature
dependence of the structure factor at the Bragg peaks in neutron scattering
experiments is demonstrated.Comment: 25 pages (revtex), 19 figures included, submitted to PR
Deposition and provenance of the Early Pleistocene Siliceous Member in Westbury Cave, Somerset, England
Semi-viviparous embryo development and dehydrin expression in the mangrove Rhizophora mucronata Lam.
Rhizophora mucronata Lam. is a tropical mangrove with semi-viviparous (cotyledon body protrusion before shedding), non-quiescent and non-desiccating (recalcitrant) seeds. As recalcitrance has been thought to relate to the absence of desiccation-related proteins such as dehydrins, we for the first time systematically described and classified embryogenesis in R. mucronata and assessed the presence of dehydrin-like proteins. Embryogenesis largely follows the classic pattern till stage eight, the torpedo stage, with the formation of a cotyledonary body. Ovule and embryo express radical adaptations to semi-vivipary in the saline environment: (1) A large, highly vacuolated and persistent endosperm without noticeable food reserves that envelopes the developing embryo. (2) Absence of vascular tissue connections between embryo and maternal tissue, but, instead, transfer layers in between endosperm and integument and endosperm and embryo. Dehydrin-like proteins (55–65 kDa) were detected by the Western analysis, in the ovules till stage 10 when the integuments are dehisced. An additional 50 kDa band was detected at stages 6–8. Together these results suggest a continuous flow of water with nutrients from the integument via the endosperm to the embryo, circumventing the vascular route and probably suppressing the initially induced dehydrin expression
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