705 research outputs found

    The gradient of potential vorticity, quaternions and an orthonormal frame for fluid particles

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    The gradient of potential vorticity (PV) is an important quantity because of the way PV (denoted as qq) tends to accumulate locally in the oceans and atmospheres. Recent analysis by the authors has shown that the vector quantity \bdB = \bnabla q\times \bnabla\theta for the three-dimensional incompressible rotating Euler equations evolves according to the same stretching equation as for \bom the vorticity and \bB, the magnetic field in magnetohydrodynamics (MHD). The \bdB-vector therefore acts like the vorticity \bom in Euler's equations and the \bB-field in MHD. For example, it allows various analogies, such as stretching dynamics, helicity, superhelicity and cross helicity. In addition, using quaternionic analysis, the dynamics of the \bdB-vector naturally allow the construction of an orthonormal frame attached to fluid particles\,; this is designated as a quaternion frame. The alignment dynamics of this frame are particularly relevant to the three-axis rotations that particles undergo as they traverse regions of a flow when the PV gradient \bnabla q is large.Comment: Dedicated to Raymond Hide on the occasion of his 80th birthda

    Complex circular subsidence structures in tephra deposited on large blocks of ice: Varða tuff cone, Öræfajökull, Iceland

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    Several broadly circular structures up to 16 m in diameter, into which higher strata have sagged and locally collapsed, are present in a tephra outcrop on southwest Öræfajökull, southern Iceland. The tephra was sourced in a nearby basaltic tuff cone at Varða. The structures have not previously been described in tuff cones, and they probably formed by the melting out of large buried blocks of ice emplaced during a preceding jökulhlaup that may have been triggered by a subglacial eruption within the Öræfajökull ice cap. They are named ice-melt subsidence structures, and they are analogous to kettle holes that are commonly found in proglacial sandurs and some lahars sourced in ice-clad volcanoes. The internal structure is better exposed in the Varða examples because of an absence of fluvial infilling and reworking, and erosion of the outcrop to reveal the deeper geometry. The ice-melt subsidence structures at Varða are a proxy for buried ice. They are the only known evidence for a subglacial eruption and associated jökulhlaup that created the ice blocks. The recognition of such structures elsewhere will be useful in reconstructing more complete regional volcanic histories as well as for identifying ice-proximal settings during palaeoenvironmental investigations

    Developing a Standard Set of Patient-centred Outcomes for Adult Oral Health - An International, Cross-disciplinary Consensus.

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    OBJECTIVE: To develop a minimum Adult Oral Health Standard Set (AOHSS) for use in clinical practice, research, advocacy and population health. MATERIALS AND METHODS: An international oral health working group (OHWG) was established, of patient advocates, researchers, clinicians and public health experts to develop an AOHSS. PubMed was searched for oral health clinical and patient-reported measures and case-mix variables related to caries and periodontal disease. The selected patient-reported outcome measures focused on general oral health, and oral health-related quality of life tools. A consensus was reached via Delphi with parallel consultation of subject matter content experts. Finally, comments and input were elicited from oral health stakeholders globally, including patients/consumers. RESULTS: The literature search yielded 1,453 results. After inclusion/exclusion criteria, 959 abstracts generated potential outcomes and case-mix variables. Delphi rounds resulted in a consensus-based selection of 80 individual items capturing 31 outcome and case-mix concepts. Global reviews generated 347 responses from 87 countries, and the patient/consumer validation survey elicited 129 responses. This AOHSS includes 25 items directed towards patients (including demographics, the impact of their oral health on oral function, a record of pain and oral hygiene practices, and financial implications of care) and items for clinicians to complete, including medical history, a record of caries and periodontal disease activity, and types of dental treatment delivered. CONCLUSION: In conclusion, utilising a robust methodology, a standardised core set of oral health outcome measures for adults, with a particular emphasis on caries and periodontal disease, was developed

    The importance of creep strain in linking together the Wilshire equations for minimum creep rates and times to various strains (including the rupture strain): An illustration using 1CrMoV rotor steel

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    This paper highlights the observation that the Wilshire equations for failure times and times to various strains, as reported in the original literature, may not be the most appropriate ones for all materials—including the one selected in this study. Further, such appropriateness can be determined by looking at the consistencies between the parameter estimates obtained using minimum creep rates in comparison to using failure times. It is shown, using 1CrMoV steel as an illustration, that the parameter consistency can be achieved by generalising the Monkman–Grant relation so that it contains a temperature correction. Indeed, the ability of the Wilshire equations to produce meaningful physical parameters, such as the activation energy, is shown to be highly dependent upon a valid specification for the Monkman–Grant relation. It is shown that variations in the measured values for some of the Wilshire parameters (w and k 3) with strain indicate that the causes of deformation are different at different strains and different stresses. Finally, the measured variations in the parameters of the Monkman–Grant relation with strain enable accurate interpolated and extrapolated creep curves to be calculated for any test condition

    A technique to train new oculomotor behavior in patients with central macular scotomas during reading related tasks using scanning laser ophthalmoscopy: immediate functional benefits and gains retention

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    BACKGROUND: Reading with a central scotoma involves the use of preferred retinal loci (PRLs) that enable both letter resolution and global viewing of word. Spontaneously developed PRLs however often privilege spatial resolution and, as a result, visual span is commonly limited by the position of the scotoma. In this study we designed and performed the pilot trial of a training procedure aimed at modifying oculomotor behavior in subjects with central field loss. We use an additional fixation point which, when combined with the initial PRL, allows the fulfillment of both letter resolution and global viewing of words. METHODS: The training procedure comprises ten training sessions conducted with the scanning laser ophthalmoscope (SLO). Subjects have to read single letters and isolated words varying in length, by combining the use of their initial PRL with the one of an examiner's selected trained retinal locus (TRL). We enrolled five subjects to test for the feasibility of the training technique. They showed stable maculopathy and persisting major reading difficulties despite previous orthoptic rehabilitation. We evaluated ETDRS visual acuity, threshold character size for single letters and isolated words, accuracy for paragraphed text reading and reading strategies before, immediately after SLO training, and three months later. RESULTS: Training the use of multiple PRLs in patients with central field loss is feasible and contributes to adapt oculomotor strategies during reading related tasks. Immediately after SLO training subjects used in combination with their initial PRL the examiner's selected TRL and other newly self-selected PRLs. Training gains were also reflected in ETDRS acuity, threshold character size for words of different lengths and in paragraphed text reading. Interestingly, subjects benefited variously from the training procedure and gains were retained differently as a function of word length. CONCLUSION: We designed a new procedure for training patients with central field loss using scanning laser ophthalmoscopy. Our initial results on the acquisition of newly self-selected PRLs and the development of new oculomotor behaviors suggest that the procedure aiming primarily at developing an examiner's selected TRL might have initiated a more global functional adaptation process

    Simultaneous Analysis of All SNPs in Genome-Wide and Re-Sequencing Association Studies

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    Testing one SNP at a time does not fully realise the potential of genome-wide association studies to identify multiple causal variants, which is a plausible scenario for many complex diseases. We show that simultaneous analysis of the entire set of SNPs from a genome-wide study to identify the subset that best predicts disease outcome is now feasible, thanks to developments in stochastic search methods. We used a Bayesian-inspired penalised maximum likelihood approach in which every SNP can be considered for additive, dominant, and recessive contributions to disease risk. Posterior mode estimates were obtained for regression coefficients that were each assigned a prior with a sharp mode at zero. A non-zero coefficient estimate was interpreted as corresponding to a significant SNP. We investigated two prior distributions and show that the normal-exponential-gamma prior leads to improved SNP selection in comparison with single-SNP tests. We also derived an explicit approximation for type-I error that avoids the need to use permutation procedures. As well as genome-wide analyses, our method is well-suited to fine mapping with very dense SNP sets obtained from re-sequencing and/or imputation. It can accommodate quantitative as well as case-control phenotypes, covariate adjustment, and can be extended to search for interactions. Here, we demonstrate the power and empirical type-I error of our approach using simulated case-control data sets of up to 500 K SNPs, a real genome-wide data set of 300 K SNPs, and a sequence-based dataset, each of which can be analysed in a few hours on a desktop workstation

    The Effects of Governmental Protected Areas and Social Initiatives for Land Protection on the Conservation of Mexican Amphibians

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    Traditionally, biodiversity conservation gap analyses have been focused on governmental protected areas (PAs). However, an increasing number of social initiatives in conservation (SICs) are promoting a new perspective for analysis. SICs include all of the efforts that society implements to conserve biodiversity, such as land protection, from private reserves to community zoning plans some of which have generated community-protected areas. This is the first attempt to analyze the status of conservation in Latin America when some of these social initiatives are included. The analyses were focused on amphibians because they are one of the most threatened groups worldwide. Mexico is not an exception, where more than 60% of its amphibians are endemic. We used a niche model approach to map the potential and real geographical distribution (extracting the transformed areas) of the endemic amphibians. Based on remnant distribution, all the species have suffered some degree of loss, but 36 species have lost more than 50% of their potential distribution. For 50 micro-endemic species we could not model their potential distribution range due to the small number of records per species, therefore the analyses were performed using these records directly. We then evaluated the efficiency of the existing set of governmental protected areas and established the contribution of social initiatives (private and community) for land protection for amphibian conservation. We found that most of the species have some proportion of their potential ecological niche distribution protected, but 20% are not protected at all within governmental PAs. 73% of endemic and 26% of micro-endemic amphibians are represented within SICs. However, 30 micro-endemic species are not represented within either governmental PAs or SICs. This study shows how the role of land conservation through social initiatives is therefore becoming a crucial element for an important number of species not protected by governmental PAs

    Methods for calculating Protection Equality for conservation planning

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    Protected Areas (PAs) are a central part of biodiversity conservation strategies around the world. Today, PAs cover c15% of the Earth’s land mass and c3% of the global oceans. These numbers are expected to grow rapidly to meet the Convention on Biological Diversity’s Aichi Biodiversity target 11, which aims to see 17% and 10% of terrestrial and marine biomes protected, respectively, by 2020. This target also requires countries to ensure that PAs protect an “ecologically representative” sample of their biodiversity. At present, there is no clear definition of what desirable ecological representation looks like, or guidelines of how to standardize its assessment as the PA estate grows. We propose a systematic approach to measure ecological representation in PA networks using the Protection Equality (PE) metric, which measures how equally ecological features, such as habitats, within a country’s borders are protected. Extending research in Barr et al. (2011), we present an R package and two Protection Equality (PE) measures; proportional to area PE, and fixed area PE, which measure the representativeness of a country’s PA network. We illustrate the PE metrics with two case studies: coral reef protection across countries and ecoregions in the Coral Triangle, and representation of ecoregions of six of the largest countries in the world. Our results provide repeatable transparency to the issue of representation in PA networks and provide a starting point for further discussion, evaluation and testing of representation metrics. They also highlight clear shortcomings in current PA networks, particularly where they are biased towards certain assemblage types or habitats. Our proposed metrics should be used to report on measuring progress towards the representation component of Aichi Target 11. The PE metrics can be used to measure the representation of any kind of ecological feature including: species, ecoregions, processes or habitats
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