103,263 research outputs found

    Root growth and signalling: the role of calcium channels

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    Roots acquire calcium not only as a macronutrient but also to serve as a second messenger in signalling and a component of exocytosis for growth. Plasma membrane channels are sufficient to deliver calcium from the apoplast to the cytosol to enable its participation in nutrition, adaptation and development. The identity and regulatory mechanisms of these channels are central to our understanding of how calcium manages to ā€œdo it allā€. By studying Arabidopsis roots, itā€™s been possible to discover plasma membrane channels involved in growth and signalling, allied to the finding that plants utilise the most damaging reactive oxygen species, the hydroxyl radical, constructively. As an overarching regulator, roots utilise extracellular purine nucleotides in a calcium-based signalling system that differs substantially from that of animals.Universidad de MĆ”laga. Campus Internacional AndalucĆ­a Tec

    The Binary Zoo: The Calculation of Production Rates of Binaries Through 2+1 Encounters in Globular Clusters

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    In studying encounters between binaries and single stars, one is interested in three classes of events: exchanges of stars, hardening of the original binary by a third star, and the production of merged objects. We present a means for computing cross sections for these three outcomes for an arbitrary binary and single star as might be found in the core of a globular cluster. The cross sections for a number of binaries in various stellar populations are then computed. We consider multiple encounters and the ultimate fate of a population of binaries fed into the cores of different globular cluster models. We see that the presence of only a relatively small number of binaries (containing 10\% of the stars) will boost the production rate of astrophysically-interesting objects by a factor of at least a few over the rates expected from encounters between single stars. In particular, the ratio of smothered neutron stars to low-mass X-ray binaries (LMXBs) may be greatly increased, possibly explaining, in part, the excess of millisecond pulsars compared to LMXBs.Comment: uuencoded compressed postscript. The preprint is also available at http://www.ast.cam.ac.uk/preprint/PrePrint.htm

    Women's birth experiences in Pakistan: the importance of the Dai

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    Aim: The aim of this paper is to present findings from a research study undertaken to explore women's life and birth experiences in Pakistan. Method: The design was ethnographic (Denzin, 1978) with an anthropological slant. Participant observation was undertaken in a maternity hospital in Pakistan and an over-50s luncheon club in the UK. Following two focus groups, in-depth interviews were undertaken with 16 women. Data were collected from observation, experience gained during nine field trips to Pakistan and the use of a reflective research diary. Findings/results: The main theme that emerged was the importance of the Dai (untrained traditional birth attendant) in women's accounts of their experiences. This theme included her influence on the women's birth experience and her work in the context of relatives and other health professionals. Other sub-themes not covered in this paper were boy preference, the omnipresent medical model, birth systems, the powerful symbolism of blood, purity shame and honour, and specifically from the women interviewed in the UK ā€“ coming to England and modernisation. Implications: The Dai was considered essential for the birth and currently 80% of all rural births are attended by Dai. However the medical professionals and policy-makers in Pakistan consider Dai practice to be dangerous and aim to establish systems for supervising and supporting skilled birth attendants, including the development of emergency referral services and a community midwife programme. Further research on women's experiences of birth in the home and hospital in Pakistan are necessary to inform government policy

    ā€˜Making the best of thingsā€™: relatives' experiences of decisions about care-home entry

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    Despite the growing awareness of the significance of helping a relative to relocate to a care home as a key phase in the care-giving career, relatively few British studies have explored this experience in depth. Informed by a constructivist perspective, this study sought a better understanding of nursing home placements from the viewpoint of relatives. Data were collected in 37 semi-structured interviews involving 48 people who had assisted a close relative to move into a nursing home. Analysis revealed three perceived phases to the transition: ā€˜making the best of itā€™, ā€˜making the moveā€™ and ā€˜making it betterā€™. The relatives' experiences through these phases had five perceived elements, all of which were continua, from absent to very strong, reflecting the extent to which they were felt. They were: operating ā€˜under pressureā€™ or not; ā€˜in the knowā€™ or ā€˜working in the darkā€™; ā€˜working togetherā€™ or ā€˜working aloneā€™; ā€˜in control of eventsā€™ or not, and ā€˜supportedā€™ or ā€˜unsupportedā€™ both practically and emotionally. This paper reports findings about the first phase of the transition, ā€˜making the best of itā€™, and documents the experiences of decision-making about nursing home placements. It is argued that health and social care practitioners have enormous potential to influence whether or not helping a relative to move into a nursing home is perceived as a positive choice

    ā€œDo one, teach oneā€ : the new paradigm in general surgery residency training

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    Moving Mirror Model of Hawking Evaporation

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    The moving mirror model is designed to extract essential features of the black hole formation and the subsequent Hawking radiation by neglecting complication due to a finite curvature. We extend this approach to dynamically treat back reaction against the mirror motion due to Hawking radiation. It is found that a unique model in two spacetime dimensions exists in which Hawking radiation completely stops and the end point of evaporation contains a disconnected remnant. When viewed from asymptotic observers at one side of the spacetime, quantum mechanical correlation is recovered in the end. Although the thermal stage accompanying short range correlation may last for an arbitrarily long period, at a much longer time scale a long tail of non-thermal correlation is clearly detected.Comment: 39 pages, TU-94-452 (Corrupted figure file has been replaced. No change of the text.

    Probing the Low Surface Brightness Dwarf Galaxy Population of the Virgo Cluster

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    We have used public data from the Next Generation Virgo Survey (NGVS) to investigate the dwarf galaxy population of the Virgo cluster beyond what has previously been discovered. We initially mask and smooth the data, and then use the object detection algorithm Sextractor to make our initial dwarf galaxy selection. All candidates are then visually inspected to remove artefacts and duplicates. We derive Sextractor parameters to best select low surface brightness galaxies using g band central surface brightness values of 22.5 to 26.0 mag sq arc sec and exponential scale lengths of 3.0 - 10.0 arc sec to identify 443 cluster dwarf galaxies - 303 of which are new detections. These new detections have a surface density that decreases with radius from the cluster centre. We also apply our selection algorithm to 'background', non-cluster, fields and find zero detections. In combination, this leads us to believe that we have isolated a cluster dwarf galaxy population. The range of objects we are able to detect is limited because smaller scale sized galaxies are confused with the background, while larger galaxies are split into numerous smaller objects by the detection algorithm. Using data from previous surveys combined with our data, we find a faint end slope to the luminosity function of -1.35+/-0.03, which does not significantly differ to what has previously been found for the Virgo cluster, but is a little steeper than the slope for field galaxies. There is no evidence for a faint end slope steep enough to correspond with galaxy formation models, unless those models invoke either strong feedback processes or use warm dark matter.Comment: Accepted for publication in MNRA
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