8,194,939 research outputs found

    Iron K-alpha Emission from X-ray Reflection: Predictions for Gamma-Ray Burst Models

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    Recent observations of several gamma-ray burst (GRB) afterglows have shown evidence for a large amount of X-ray line emitting material, possibly arising from ionized iron. A significant detection of an X-ray spectral feature, such as that found in the Chandra observation of GRB 991216, may provide important constraints on the immediate environment of the burst and hence on progenitor models. The large Fe K-alpha equivalent widths inferred from the X-ray observations favor models in which the line is produced when the primary X-ray emission from the source strikes Thomson-thick material and Compton scatters into our line of sight. We present such reflection spectra here, computed in a fully self-consistent manner, and discuss the range of ionization parameters that may be relevant to different models of GRBs. We argue that the presence of a strong hydrogen-like K-alpha line is unlikely, because Fe-XXVI photons would be trapped resonantly and removed from the line core by Compton scattering. In contrast, a strong narrow emission line from He-like Fe-XXV is prominent in the model spectra. We briefly discuss how these constraints may affect the line energy determination in GRB 991216.Comment: 8 pages, 3 figures, Ap.J. Letters accepte

    Exploding bridgewire detonator simulator

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    Tests indicate that electric detonator simulators of the exploding bridgewire type will not fire as a result of the application of a direct current power of one watt for 5 minutes. The detonator also will not fire if the protective gap fails and the firing stimulus is inadvertently applied

    Solar energy modulator

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    A module is described with a receiver having a solar energy acceptance opening and supported by a mounting ring along the optic axis of a parabolic mirror in coaxial alignment for receiving solar energy from the mirror, and a solar flux modulator plate for varying the quantity of solar energy flux received by the acceptance opening of the module. The modulator plate is characterized by an annular, plate-like body, the internal diameter of which is equal to or slightly greater than the diameter of the solar energy acceptance opening of the receiver. Slave cylinders are connected to the modulator plate for supporting the plate for axial displacement along the axis of the mirror, therby shading the opening with respect to solar energy flux reflected from the surface of the mirror to the solar energy acceptance opening

    Generalised leptonic colour

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    It is conceivable that there is an SU(N)SU(N)_{\ell} `colour' gauge group for leptons, analogous to the gauged SU(3)qSU(3)_q colour group of the quarks. The standard model emerges as the low energy effective theory when the leptonic colour is spontaneously broken. The simplest such generalised leptonic colour models are constructed. We show that the see-saw mechanism for small neutrino masses, along with the theoretical constraint of electric charge quantisation, suggests that the models with N=3,5,7N = 3, 5, 7 are the theoretically most promising cases. A striking feature of generalized leptonic colour is the physics associated with the extra leptonic degrees of freedom -- the liptons. These particles can potentially be discovered at future colliders, such as the LHC, making the idea testable in the near future.Comment: about 7 page

    Connected Learning Journeys in Music Production Education

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    The field of music production education is a challenging one, exploring multiple creative, technical and entrepreneurial disciplines, including music composition, performance electronics, acoustics, musicology, project management and psychology. As a result, students take multiple ‘learning journeys’ on their pathway towards becoming autonomous learners. This paper uniquely evaluates the journey of climbing Bloom’s cognitive domain in the field of music production and gives specific examples that validate teaching music production in higher education through multiple, connected ascents of the framework. Owing to the practical nature of music production, Kolb’s Experiential Learning Model is also considered as a recurring function that is necessary for climbing Bloom’s domain, in order to ensure that learners are equipped for employability and entrepreneurship on graduation. The authors’ own experiences of higher education course delivery, design and development are also reflected upon with reference to Music Production pathways at both the University of Westminster (London, UK) and York St John University (York, UK)

    Time Dependence of Particle Creation from Accelerating Mirrors

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    Particle production due to a quantized, massless, minimally coupled scalar field in two-dimensional flat spacetime with an accelerating mirror is investigated, with a focus on the time dependence of the process. We analyze first the classes of trajectories previously investigated by Carlitz and Willey and by Walker and Davies. We then analyze four new classes of trajectories, all of which can be expressed analytically and for which several ancillary properties can be derived analytically. The time dependence is investigated through the use of wave packets for the modes of the quantized field that are in the out vacuum state. It is shown for most of the trajectories studied that good time resolution of the particle production process can be obtained.Comment: 21 pages, 5 figure
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