2,056 research outputs found

    Creating Community: A Quaker, Covental Approach Toward a Parallel Society

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    Within many local churches people hunger and thirst for deeper spirituality, authentic fellowship and more active ministry in the world. Sincere disciples long to know and follow Christ and participate in a community of saints who embody the values of God\u27s Kingdom in this world. Along the way, however, many of these same people often feel unfulfilled and frustrated. Hindered by social pressure and conventional values, these Christians find themselves conforming to the American social patterns and practices they often disdain. Many simply do not experience the necessary communal support to live out the gospel in the face of the prevailing culture. This phenomenon is exacerbated within the Religious Society of Friends because of the profound shift toward individualism that occurred within their religious heritage. It is further complicated by the rugged individualism that defines American culture and affects the Friends vision of spiritual experience and sense of call. The subject of this dissertation is to demonstrate creative avenues for authentic, transformational community through the use of a covenantal model in a Quaker fellowship. Sensitive to the peculiarities of Friends\u27 Faith and Practice, this model is designed to nurture and sustain the historical and present day alternative way of life of Friends. Chapter one of the dissertation includes a further examination of the problem by setting it in the context of a local congregation. Critical definitions are included to further clarify the subject of study. Chapter two identifies key biblical themes and an overarching theology of spiritual community. The third chapter provides a selected overview of communal models within church history that demonstrate a coherent and consistent thread within the long experience of the church. Chapter four examines two significant barriers to spiritual community-present day American culture and paradoxes and tensions within Friends faith. The final applied chapter of the dissertation will serve as a resource for creating a covenantal agreement within a local church. Its aim is to intentionally nurture a communal way of life that embodies the parallel cultural values of Christ\u27s Kingdom

    High-energy neutrino fluxes from AGN populations inferred from X-ray surveys

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    High-energy neutrinos and photons are complementary messengers, probing violent astrophysical processes and structural evolution of the Universe. X-ray and neutrino observations jointly constrain conditions in active galactic nuclei (AGN) jets: their baryonic and leptonic contents, and particle production efficiency. Testing two standard neutrino production models for local source Cen A \citep{KT2008,BB2009}, we calculate the high-energy neutrino spectra of single AGN sources and derive the flux of high-energy neutrinos expected for the current epoch. Assuming that accretion determines both X-rays and particle creation, our parametric scaling relations predict neutrino yield in various AGN classes. We derive redshift-dependent number densities of each class, from {\it Chandra} and {\it Swift}/BAT X-ray luminosity functions \citep{SGB2008,ACS2009}. We integrate the neutrino spectrum expected from the cumulative history of AGN (correcting for cosmological and source effects, e.g. jet orientation and beaming). Both emission scenarios yield neutrino fluxes well above limits set by {\it IceCube} (by 4\sim 4--106×10^6 \times at 1 PeV, depending on the assumed jet models for neutrino production). This implies that: (i) Cen A might not be a typical neutrino source as commonly assumed; (ii) both neutrino production models overestimate the efficiency; (iii) neutrino luminosity scales with accretion power differently among AGN classes and hence does not follow X-ray luminosity universally; (iv) some AGN are neutrino-quiet (e.g. below a power threshold for neutrino production); (v) neutrino and X-ray emission have different duty cycles (e.g. jets alternate between baryonic and leptonic flows); or (vi) some combination of the above.Comment: 16 pages, 6 figures, 3 tables, accepted for publication in MNRA

    A search for electron cyclotron maser emission from compact binaries

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    Unipolar induction (UI) is a fundamental physical process, which occurs when a conducting body transverses a magnetic field. It has been suggested that UI is operating in RX J0806+15 and RX J1914+24, which are believed to be ultra-compact binaries with orbital periods of 5.4 min and 9.6 min respectively. The UI model predicts that those two sources may be electron cyclotron maser sources at radio wavelengths. Other systems in which UI has been predicted to occur are short period extra-solar terrestrial planets with conducting cores. If UI is present, circularly polarised radio emission is predicted to be emitted. We have searched for this predicted radio emission from short period binaries using the VLA and ATCA. In one epoch we find evidence for a radio source, coincident in position with the optical position of RX J0806+15. Although we cannot completely exclude that this is a chance alignment between the position of RX J0806+15 and an artifact in the data reduction process, the fact that it was detected at a significance level of 5.8 sigma and found to be transient, suggests that it is more likely that RX J0806+15 is a transient radio source. We find an upper limit on the degree of circular polarisation to be ~50%. The inferred brightness temperature exceeds 10^18 K, which is too high for any known incoherent process, but is consistent with maser emission and UI being the driving mechanism. We did not detect radio emission from ES Cet, RX J1914+24 or Gliese 876.Comment: Accepted for publication MNRA

    The XMM-Newton Slew Survey

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    XMM-Newton, with the huge collecting area of its mirrors and the high quantum efficiency of its EPIC detectors, is the most sensitive X-ray observatory ever flown. This is strikingly evident during slew exposures, which, while yielding only at most 14 seconds of on-source exposure time, actually constitute a 2-10 keV survey ten times deeper than all other "all-sky" surveys. The current (April 2005) XMM archive contains 374 slew exposures which give a uniform coverage over around 10,000 square degrees (approx. 25% of the sky). Here we describe the results of pilot studies, the current status of the XMM-Newton Slew Survey, up-to-date results and our progress towards constructing a catalogue of slew detections in the full 0.2-12 keV energy band.Comment: 3 pages, 4 figures, XMM-Newton EPIC Consortium Meeting, Schloss Ringberg, Germany, April 2005, to appear in MPE Repor

    Extended sources in the XMM-Newton slew survey

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    The low background, good spatial resolution and great sensitivity of the EPIC-pn camera on XMM-Newton give useful limits for the detection of extended sources even during the short exposures made during slewing maneouvers. In this paper we attempt to illustrate the potential of the XMM-Newton slew survey as a tool for analysing flux-limited samples of clusters of galaxies and other sources of spatially extended X-ray emission.Comment: 2 pages, 4 figures, to appear in the proceedings of "The X-ray Universe 2005", San Lorenzo de El Escorial (Spain), 26-30 September 200

    The XMM-Newton Slew Survey: towards the XMMSL1 catalogue

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    The XMM-Newton satellite is the most sensitive X-ray observatory flown to date due to the great collecting area of its mirrors coupled with the high quantum efficiency of the EPIC detectors. It performs slewing manoeuvers between observation targets tracking almost circular orbits through the ecliptic poles due to the Sun constraint. Slews are made with the EPIC cameras open and the other instruments closed, operating with the observing mode set to the one of the previous pointed observation and the medium filter in place. Slew observations from the EPIC-pn camera in FF, eFF and LW modes provide data, resulting in a maximum of 15 seconds of on-source time. These data can be used to give a uniform survey of the X-ray sky, at great sensitivity in the hard band compared with other X-ray all-sky surveys.Comment: 2 pages, 2 figures, to appear in the proceedings of "The X-ray Universe 2005", San Lorenzo de El Escorial (Spain), 26-30 September 200

    In-orbit Vignetting Calibrations of XMM-Newton Telescopes

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    We describe measurements of the mirror vignetting in the XMM-Newton Observatory made in-orbit, using observations of SNR G21.5-09 and SNR 3C58 with the EPIC imaging cameras. The instrument features that complicate these measurements are briefly described. We show the spatial and energy dependences of measured vignetting, outlining assumptions made in deriving the eventual agreement between simulation and measurement. Alternate methods to confirm these are described, including an assessment of source elongation with off-axis angle, the surface brightness distribution of the diffuse X-ray background, and the consistency of Coma cluster emission at different position angles. A synthesis of these measurements leads to a change in the XMM calibration data base, for the optical axis of two of the three telescopes, by in excess of 1 arcminute. This has a small but measureable effect on the assumed spectral responses of the cameras for on-axis targets.Comment: Accepted by Experimental Astronomy. 26 pages, 18 figure

    Probing microscopic origins of confined subdiffusion by first-passage observables

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    Subdiffusive motion of tracer particles in complex crowded environments, such as biological cells, has been shown to be widepsread. This deviation from brownian motion is usually characterized by a sublinear time dependence of the mean square displacement (MSD). However, subdiffusive behavior can stem from different microscopic scenarios, which can not be identified solely by the MSD data. In this paper we present a theoretical framework which permits to calculate analytically first-passage observables (mean first-passage times, splitting probabilities and occupation times distributions) in disordered media in any dimensions. This analysis is applied to two representative microscopic models of subdiffusion: continuous-time random walks with heavy tailed waiting times, and diffusion on fractals. Our results show that first-passage observables provide tools to unambiguously discriminate between the two possible microscopic scenarios of subdiffusion. Moreover we suggest experiments based on first-passage observables which could help in determining the origin of subdiffusion in complex media such as living cells, and discuss the implications of anomalous transport to reaction kinetics in cells.Comment: 21 pages, 3 figures. Submitted versio

    Accretion in dipole magnetic fields: flow structure and X-ray emission of accreting white dwarfs

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    Field-channelled accretion flows occur in a variety of astrophysical objects, including T Tauri stars,magnetic cataclysmic variables and X-ray pulsars. We consider a curvilinear coordinate system and derive a general hydrodynamic formulation for accretion onto stellar objects confined by a stellar dipole magnetic field. The hydrodynamic equations are solved to determine the velocity, density and temperature profiles of the flow. We use accreting magnetic white-dwarf stars as an illustrative example of astrophysical applications. Our calculations show that the compressional heating due to the field geometry is as important as radiative cooling and gravity in determining the structure of the post-shock flow in accreting white-dwarf stars. The generalisation of the formulation to accretion flows channelled by higher-order fields and the applications to other astrophysical systems are discussed.Comment: Accepted A&
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