1,178 research outputs found

    On the Persistent Shape and Coherence of Pulsating Auroral Patches

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    The pulsating aurora covers a broad range of fluctuating shapes that are poorly characterized. The purpose of this paper is therefore to provide objective and quantitative measures of the extent to which pulsating auroral patches maintain their shape, drift and fluctuate in a coherent fashion. We present results from a careful analysis of pulsating auroral patches using all-sky cameras. We have identified four well-defined individual patches that we follow in the patch frame of reference. In this way we avoid the space-time ambiguity which complicates rocket and satellite measurements. We find that the shape of the patches is remarkably persistent with 85-100% of the patch being repeated for 4.5-8.5 min. Each of the three largest patches has a temporal correlation with a negative dependence on distance, and thus does not fluctuate in a coherent fashion. A time-delayed response within the patches indicates that the so-called streaming mode might explain the incoherency. The patches appear to drift differently from the SuperDARN-determined E\stackrel{\rightarrow}{E} X B\stackrel{\rightarrow}{B} convection velocity. However, in a nonrotating reference frame the patches drift with 230-287 m/s in a north eastward direction, which is what typically could be expected for the convection return flow

    Inositol 1,3,4,5,6-pentakisphosphate 2-kinase is a distant IPK member with a singular inositide binding site for axial 2-OH recognition

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    Inositol phosphates (InsPs) are signaling molecules with multiple roles in cells. In particular Graphic (InsP6) is involved in mRNA export and editing or chromatin remodeling among other events. InsP6 accumulates as mixed salts (phytate) in storage tissues of plants and plays a key role in their physiology. Human diets that are exclusively grain-based provide an excess of InsP6 that, through chelation of metal ions, may have a detrimental effect on human health. Ins(1,3,4,5,6)P5 2-kinase (InsP5 2-kinase or Ipk1) catalyses the synthesis of InsP6 from InsP5 and ATP, and is the only enzyme that transfers a phosphate group to the axial 2-OH of the myo-inositide. We present the first structure for an InsP5 2-kinase in complex with both substrates and products. This enzyme presents a singular structural region for inositide binding that encompasses almost half of the protein. The key residues in substrate binding are identified, with Asp368 being responsible for recognition of the axial 2-OH. This study sheds light on the unique molecular mechanism for the synthesis of the precursor of inositol pyrophosphates

    Coefficient of restitution for elastic disks

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    We calculate the coefficient of restitution, ϵ\epsilon, starting from a microscopic model of elastic disks. The theory is shown to agree with the approach of Hertz in the quasistatic limit, but predicts inelastic collisions for finite relative velocities of two approaching disks. The velocity dependence of ϵ\epsilon is calculated numerically for a wide range of velocities. The coefficient of restitution furthermore depends on the elastic constants of the material via Poisson's number. The elastic vibrations absorb kinetic energy more effectively for materials with low values of the shear modulus.Comment: 25 pages, 12 Postscript figures, LaTex2

    "They think we're OK and we know we're not". A qualitative study of asylum seekers' access, knowledge and views to health care in the UK

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    <i>Background</i>: The provision of healthcare for asylum seekers is a global issue. Providing appropriate and culturally sensitive services requires us to understand the barriers facing asylum seekers and the facilitators that help them access health care. Here, we report on two linked studies exploring these issues, along with the health care needs and beliefs of asylum seekers living in the UK. <i>Methods</i>: Two qualitative methods were employed: focus groups facilitated by members of the asylum seeking community and interviews, either one-to-one or in a group, conducted through an interpreter. Analysis was facilitated using the Framework method. <i>Results</i>: Most asylum seekers were registered with a GP, facilitated for some by an Asylum Support nurse. Many experienced difficulty getting timely appointments with their doctor, especially for self-limiting symptoms that they felt could become more serious, especially in children. Most were positive about the health care they received, although some commented on the lack of continuity. However, there was surprise and disappointment at the length of waiting times both for hospital appointments and when attending accident and emergency departments. Most had attended a dentist, but usually only when there was a clinical need. The provision of interpreters in primary care was generally good, although there was a tension between interpreters translating verbatim and acting as patient advocates. Access to interpreters in other settings, e.g. in-patient hospital stays, was problematic. Barriers included the cost of over-the-counter medication, e.g. children's paracetamol; knowledge of out-of-hours medical care; and access to specialists in secondary care. Most respondents came from countries with no system of primary medical care, which impacted on their expectations of the UK system. <i>Conclusion</i>: Most asylum seekers were positive about their experiences of health care. However, we have identified issues regarding their understanding of how the UK system works, in particular the role of general practitioners and referral to hospital specialists. The provision of an Asylum Support nurse was clearly a facilitator to accessing primary medical care. Initiatives to increase their awareness and understanding of the UK system would be beneficial. Interpreting services also need to be developed, in particular their role in secondary care and the development of the role of interpreter as patient advocate

    UK export performance research - review and implications

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    Previous research on export performance has been criticized for being a mosaic of autonomous endeavours and for a lack of theoretical development. Building upon extant models of export performance, and a review and analysis of research on export performance in the UK for the period 1990-2005, an integrated model of export performance is developed and theoretical explanations of export performance are put forward. It is suggested that a multi-theory approach to explaining export performance is viable. Management and policy implications for the UK emerging from the review and synthesis of the literature and the integrated model are discussed

    Astrophysical evidence for the existence of black holes

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    Following a short account of the history of the idea of black holes, we present a review of the current status of the search for observational evidence of their existence aimed at an audience of relativists rather than astronomers or astrophysicists. We focus on two different regimes: that of stellar-mass black holes and that of black holes with the masses of galactic nuclei.Comment: 23 pages, 3 figures, TeX forma

    Companions of Stars: From Other Stars to Brown Dwarfs to Planets: The Discovery of the First Methane Brown Dwarf

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    The discovery of the first methane brown dwarf provides a framework for describing the important advances in both fundamental physics and astrophysics that are due to the study of companions of stars. I present a few highlights of the history of this subject along with details of the discovery of the brown dwarf Gliese 229B. The nature of companions of stars is discussed with an attempt to avoid biases induced by anthropocentric nomenclature. With the newer types of remote reconnaissance of nearby stars and their systems of companions, an exciting and perhaps even more profound set of contributions to science is within reach in the near future. This includes an exploration of the diversity of planets in the universe and perhaps soon the first solid evidence for biological activity outside our Solar System.Comment: 31 pages, 13 figure

    Safe Parallelism: Compiler Analysis Techniques for Ada and OpenMP

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    There is a growing need to support parallel computation in Ada to cope with the performance requirements of the most advanced functionalities of safety-critical systems. In that regard, the use of parallel programming models is paramount to exploit the benefits of parallelism. Recent works motivate the use of OpenMP for being a de facto standard in high-performance computing for programming shared memory architectures. These works address two important aspects towards the introduction of OpenMP in Ada: the compatibility of the OpenMP syntax with the Ada language, and the interoperability of the OpenMP and the Ada runtimes, demonstrating that OpenMP complements and supports the structured parallelism approach of the tasklet model. This paper addresses a third fundamental aspect: functional safety from a compiler perspective. Particularly, it focuses on race conditions and considers the fine-grain and unstructured capabilities of OpenMP. Hereof, this paper presents a new compiler analysis technique that: (1) identifies potential race conditions in parallel Ada programs based on OpenMP or Ada tasks or both, and (2) provides solutions for the detected races.This work was supported by the Spanish Ministry of Science and Innovation under contract TIN2015-65316-P, and by the FCT (Portuguese Foundation for Science and Technology) within the CISTER Research Unit (CEC/04234).Peer ReviewedPostprint (author's final draft

    Primary skin fibroblasts as a model of Parkinson's disease

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    Parkinson's disease is the second most frequent neurodegenerative disorder. While most cases occur sporadic mutations in a growing number of genes including Parkin (PARK2) and PINK1 (PARK6) have been associated with the disease. Different animal models and cell models like patient skin fibroblasts and recombinant cell lines can be used as model systems for Parkinson's disease. Skin fibroblasts present a system with defined mutations and the cumulative cellular damage of the patients. PINK1 and Parkin genes show relevant expression levels in human fibroblasts and since both genes participate in stress response pathways, we believe fibroblasts advantageous in order to assess, e.g. the effect of stressors. Furthermore, since a bioenergetic deficit underlies early stage Parkinson's disease, while atrophy underlies later stages, the use of primary cells seems preferable over the use of tumor cell lines. The new option to use fibroblast-derived induced pluripotent stem cells redifferentiated into dopaminergic neurons is an additional benefit. However, the use of fibroblast has also some drawbacks. We have investigated PARK6 fibroblasts and they mirror closely the respiratory alterations, the expression profiles, the mitochondrial dynamics pathology and the vulnerability to proteasomal stress that has been documented in other model systems. Fibroblasts from patients with PARK2, PARK6, idiopathic Parkinson's disease, Alzheimer's disease, and spinocerebellar ataxia type 2 demonstrated a distinct and unique mRNA expression pattern of key genes in neurodegeneration. Thus, primary skin fibroblasts are a useful Parkinson's disease model, able to serve as a complement to animal mutants, transformed cell lines and patient tissues
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