11,753 research outputs found

    Ionization state, excited populations and emission of impurities in dynamic finite density plasmas: I. The generalized collisional-radiative model for light elements

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    The paper presents an integrated view of the population structure and its role in establishing the ionization state of light elements in dynamic, finite density, laboratory and astrophysical plasmas. There are four main issues, the generalized collisional-radiative picture for metastables in dynamic plasmas with Maxwellian free electrons and its particularizing to light elements, the methods of bundling and projection for manipulating the population equations, the systematic production/use of state selective fundamental collision data in the metastable resolved picture to all levels for collisonal-radiative modelling and the delivery of appropriate derived coefficients for experiment analysis. The ions of carbon, oxygen and neon are used in illustration. The practical implementation of the methods described here is part of the ADAS Project

    Remarks on Causality in Relativistic Quantum Field Theory

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    It is shown that the correlations predicted by relativistic quantum field theory in locally normal states between projections in local von Neumann algebras \cA(V_1),\cA(V_2) associated with spacelike separated spacetime regions V1,V2V_1,V_2 have a (Reichenbachian) common cause located in the union of the backward light cones of V1V_1 and V2V_2. Further comments on causality and independence in quantum field theory are made.Comment: 10 pages, Latex, Quantum Structures 2002 Conference Proceedings submission. Minor revision of the order of definitions on p.

    The Quest for Understanding in Relativistic Quantum Physics

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    We discuss the status and some perspectives of relativistic quantum physics.Comment: Invited contribution to the Special Issue 2000 of the Journal of Mathematical Physics, 38 pages, typos corrected and references added, as to appear in JM

    The second law of thermodynamics, TCP, and Einstein causality in anti-de Sitter space-time

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    If the vacuum is passive for uniformly accelerated observers in anti-de Sitter space-time (i.e. cannot be used by them to operate a "perpetuum mobile"), they will (a) register a universal value of the Hawking-Unruh temperature, (b) discover a TCP symmetry, and (c) find that observables in complementary wedge-shaped regions are commensurable (local) in the vacuum state. These results are model independent and hold in any theory which is compatible with some weak notion of space-time localization.Comment: 8 pages, slightly improved results, minor changes in the expository part, new title; to appear in "Classical and Quantum Gravity

    A structural evaluation of the tungsten isotopes via thermal neutron capture

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    Total radiative thermal neutron-capture γ\gamma-ray cross sections for the 182,183,184,186^{182,183,184,186}W isotopes were measured using guided neutron beams from the Budapest Research Reactor to induce prompt and delayed γ\gamma rays from elemental and isotopically-enriched tungsten targets. These cross sections were determined from the sum of measured γ\gamma-ray cross sections feeding the ground state from low-lying levels below a cutoff energy, Ecrit_{\rm crit}, where the level scheme is completely known, and continuum γ\gamma rays from levels above Ecrit_{\rm crit}, calculated using the Monte Carlo statistical-decay code DICEBOX. The new cross sections determined in this work for the tungsten nuclides are: σ0(182W)=20.5(14)\sigma_{0}(^{182}{\rm W}) = 20.5(14) b and σ11/2+(183Wm,5.2s)=0.177(18)\sigma_{11/2^{+}}(^{183}{\rm W}^{m}, 5.2 {\rm s}) = 0.177(18) b; σ0(183W)=9.37(38)\sigma_{0}(^{183}{\rm W}) = 9.37(38) b and σ5(184Wm,8.33μs)=0.0247(55)\sigma_{5^{-}}(^{184}{\rm W}^{m}, 8.33 \mu{\rm s}) = 0.0247(55) b; σ0(184W)=1.43(10)\sigma_{0}(^{184}{\rm W}) = 1.43(10) b and σ11/2+(185Wm,1.67min)=0.0062(16)\sigma_{11/2^{+}}(^{185}{\rm W}^{m}, 1.67 {\rm min}) = 0.0062(16) b; and, σ0(186W)=33.33(62)\sigma_{0}(^{186}{\rm W}) = 33.33(62) b and σ9/2+(187Wm,1.38μs)=0.400(16)\sigma_{9/2^{+}}(^{187}{\rm W}^{m}, 1.38 \mu{\rm s}) = 0.400(16) b. These results are consistent with earlier measurements in the literature. The 186^{186}W cross section was also independently confirmed from an activation measurement, following the decay of 187^{187}W, yielding values for σ0(186W)\sigma_{0}(^{186}{\rm W}) that are consistent with our prompt γ\gamma-ray measurement. The cross-section measurements were found to be insensitive to choice of level density or photon strength model, and only weakly dependent on Ecrit_{\rm crit}. Total radiative-capture widths calculated with DICEBOX showed much greater model dependence, however, the recommended values could be reproduced with selected model choices. The decay schemes for all tungsten isotopes were improved in these analyses.Comment: 25 pages, 15 figures, 15 table

    There are No Causality Problems for Fermi's Two Atom System

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    A repeatedly discussed gedanken experiment, proposed by Fermi to check Einstein causality, is reconsidered. It is shown that, contrary to a recent statement made by Hegerfeldt, there appears no causality paradoxon in a proper theoretical description of the experiment.Comment: 6 pages, latex, DESY 94-02

    Using Co-operative Inquiry to embed Education for Sustainable Development (ESD) across all programmes offered by Plymouth Institute of Education (PIoE)

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    Our aim is to embed Education for Sustainable Development across all of our courses, ensuring that all students benefit from an education where social, economic and environmental sustainability is woven into the very fabric of their learning experience, thereby producing graduates who take this learning forward and embed it in their own teaching. To achieve this, the aims of the projects were: To embed elements of ESD in all PIoE programmes utilising a co-operative inquiry approach (Heron and Reason 2001) • To critically evaluate co-operative inquiry (CI) as an effective mechanism for the implementation of ESD in HE.PedRI

    Inflammation and changes in cytokine levels in neurological feline infectious peritonitis.

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    Feline infectious peritonitis (FIP) is a progressive, fatal, predominantly Arthus-type immune-mediated disease that is triggered when cats are infected with a mutant enteric coronavirus. The disease presents variably with multiple organ failure, seizures, generalized effusion, or shock. Neurological FIP is clinically and pathologically more homogeneous than systemic 'wet' or 'dry' FIP; thus, comparison of cytokine profiles from cats with neurological FIP, wet FIP, and non-FIP neurological disease may provide insight into some baseline characteristics relating to the immunopathogenesis of neurological FIP. This study characterizes inflammation and changes in cytokines in the brain tissue of FIP-affected cats. Cellular infiltrates in cats with FIP included lymphocytes, plasma cells, neutrophils, macrophages, and eosinophils. IL-1 beta, IL-6, IL-12, IL-18, TNF-alpha, macrophage inhibitory protein (MIP)-1 alpha, and RANTES showed no upregulation in the brains of control cats, moderate upregulation in neurological FIP cats, and very high upregulation in generalized FIP cats. Transcription of IFN-gamma appeared upregulated in cats with systemic FIP and slightly downregulated in neurological FIP. In most cytokines tested, variance was extremely high in generalized FIP and much less in neurological FIP. Principal components analysis was performed in order to find the least number of 'components' that would summarize the cytokine profiles in cats with neurological FIP. A large component of the variance (91.7%) was accounted for by levels of IL-6, MIP-1 alpha, and RANTES. These findings provide new insight into the immunopathogenesis of FIP and suggest targets for immune therapy of this disease
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