3,394 research outputs found

    Biot-Savart-like law in electrostatics

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    The Biot-Savart law is a well-known and powerful theoretical tool used to calculate magnetic fields due to currents in magnetostatics. We extend the range of applicability and the formal structure of the Biot-Savart law to electrostatics by deriving a Biot-Savart-like law suitable for calculating electric fields. We show that, under certain circumstances, the traditional Dirichlet problem can be mapped onto a much simpler Biot-Savart-like problem. We find an integral expression for the electric field due to an arbitrarily shaped, planar region kept at a fixed electric potential, in an otherwise grounded plane. As a by-product we present a very simple formula to compute the field produced in the plane defined by such a region. We illustrate the usefulness of our approach by calculating the electric field produced by planar regions of a few nontrivial shapes.Comment: 14 pages, 6 figures, RevTex, accepted for publication in the European Journal of Physic

    The impact of free access to swimming pools on children's participation in swimming:A comparative regression discontinuity study

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    Objective: Investigating the extent to which providing children with free swimming access during school holidays increased participation in swimming and whether this effect differed according to the socioeconomic deprivation of the neighbourhoods in which children lived. Setting: A highly disadvantaged local authority (LA) in North West England. Intervention: Provision of children with free swimming during the summer holidays. Outcome measures: Number of children swimming, and the number of swims, per 100 population in 2014. Design: Comparative regression discontinuity investigating the extent to which participation rates amongst children aged 5-15 were greater in the intervention LA compared to a similar control LA. We estimated the differential effect of the intervention across five groups, defined by quintiles of area deprivation. Results: Free swimming during the summer holidays was associated with an additional 6% of children swimming (95% CI: 4-9%) and an additional 33 swims per 100 children per year (95% CI: 21-44). The effects were greatest in areas with intermediate levels of deprivation (quintiles 3 and 4) within this deprived LA. Conclusion: Providing free facilities for children in disadvantaged areas is likely to increase swimming participation and may help reduce inequalities in physical activity

    Pregnancy and childbirth in English prisons : institutional ignominy and the pains of imprisonment

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    © 2020 The Authors. Sociology of Health & Illness published by John Wiley & Sons Ltd on behalf of Foundation for SHIL.With a prison population of approximately 9000 women in England, it is estimated that approximately 600 pregnancies and 100 births occur annually. Despite an extensive literature on the sociology of reproduction, pregnancy and childbirth among women prisoners is under‐researched. This article reports an ethnographic study in three English prisons undertaken in 2015‐2016, including interviews with 22 prisoners, six women released from prison and 10 staff members. Pregnant prisoners experience numerous additional difficulties in prison including the ambiguous status of a pregnant prisoner, physical aspects of pregnancy and the degradation of the handcuffed or chained prisoner during visits to the more public setting of hospital. This article draws on Erving Goffman's concepts of closed institutions, dramaturgy and mortification of self, Crewe et al.'s work on the gendered pains of imprisonment and Crawley's notion of ‘institutional thoughtlessness’, and proposes a new concept of institutional ignominy to understand the embodied situation of the pregnant prisoner.Peer reviewe

    Using conceptual metaphor and functional grammar to explore how language used in physics affects student learning

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    This paper introduces a theory about the role of language in learning physics. The theory is developed in the context of physics students' and physicists' talking and writing about the subject of quantum mechanics. We found that physicists' language encodes different varieties of analogical models through the use of grammar and conceptual metaphor. We hypothesize that students categorize concepts into ontological categories based on the grammatical structure of physicists' language. We also hypothesize that students over-extend and misapply conceptual metaphors in physicists' speech and writing. Using our theory, we will show how, in some cases, we can explain student difficulties in quantum mechanics as difficulties with language.Comment: Accepted for publication in Phys. Rev. ST:PE

    Epidemiology of Leptospirosis in Africa: A Systematic Review of a Neglected Zoonosis and a Paradigm for 'One Health' in Africa.

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    Leptospirosis is an important but neglected bacterial zoonosis that has been largely overlooked in Africa. In this systematic review, we aimed to summarise and compare current knowledge of: (1) the geographic distribution, prevalence, incidence and diversity of acute human leptospirosis in Africa; and (2) the geographic distribution, host range, prevalence and diversity of Leptospira spp. infection in animal hosts in Africa. Following Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines, we searched for studies that described (1) acute human leptospirosis and (2) pathogenic Leptospira spp. infection in animals. We performed a literature search using eight international and regional databases for English and non-English articles published between January 1930 to October 2014 that met out pre-defined inclusion criteria and strict case definitions. We identified 97 studies that described acute human leptospirosis (n = 46) or animal Leptospira infection (n = 51) in 26 African countries. The prevalence of acute human leptospirosis ranged from 2 3% to 19 8% (n = 11) in hospital patients with febrile illness. Incidence estimates were largely restricted to the Indian Ocean islands (3 to 101 cases per 100,000 per year (n = 6)). Data from Tanzania indicate that human disease incidence is also high in mainland Africa (75 to 102 cases per 100,000 per year). Three major species (Leptospira borgpetersenii, L. interrogans and L. kirschneri) are predominant in reports from Africa and isolates from a diverse range of serogroups have been reported in human and animal infections. Cattle appear to be important hosts of a large number of Leptospira serogroups in Africa, but few data are available to allow comparison of Leptospira infection in linked human and animal populations. We advocate a 'One Health' approach to promote multidisciplinary research efforts to improve understanding of the animal to human transmission of leptospirosis on the African continent

    Convergence of the Optimized Delta Expansion for the Connected Vacuum Amplitude: Zero Dimensions

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    Recent proofs of the convergence of the linear delta expansion in zero and in one dimensions have been limited to the analogue of the vacuum generating functional in field theory. In zero dimensions it was shown that with an appropriate, NN-dependent, choice of an optimizing parameter \l, which is an important feature of the method, the sequence of approximants ZNZ_N tends to ZZ with an error proportional to e−cN{\rm e}^{-cN}. In the present paper we establish the convergence of the linear delta expansion for the connected vacuum function W=ln⁡ZW=\ln Z. We show that with the same choice of \l the corresponding sequence WNW_N tends to WW with an error proportional to e−cN{\rm e}^{-c\sqrt N}. The rate of convergence of the latter sequence is governed by the positions of the zeros of ZNZ_N.Comment: 20 pages, LaTeX, Imperial/TP/92-93/5

    On the Divergence of Perturbation Theory. Steps Towards a Convergent Series

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    The mechanism underlying the divergence of perturbation theory is exposed. This is done through a detailed study of the violation of the hypothesis of the Dominated Convergence Theorem of Lebesgue using familiar techniques of Quantum Field Theory. That theorem governs the validity (or lack of it) of the formal manipulations done to generate the perturbative series in the functional integral formalism. The aspects of the perturbative series that need to be modified to obtain a convergent series are presented. Useful tools for a practical implementation of these modifications are developed. Some resummation methods are analyzed in the light of the above mentioned mechanism.Comment: 42 pages, Latex, 4 figure

    Closing in on the picture : analyzing interactions in video recordings

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    This paper provides a detailed account of the processing and analysing of data, obtained through video recording during reflective practitioner research. It sets out five stages in the analysis of video recordings of classroom interactions during a series of educational drama lessons: from decisions relating to the selection of data for close analysis, to the seeking of themes, and finally to the presentation of conclusions. The researcher adapted and synthesised several processes derived from discourse analysis (Wells, 2001; Spiers, 2004; Gee, 2005) to produce a range of instruments for use in transcription and analysis of verbal and non-verbal discourse. These include: a simple transcription key; classifications for verbal and non-verbal discourse; and a template for a transcription and analysis matrix
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