120 research outputs found

    Maser radiation from collisionless shocks

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    Funding: UK Engineering and Physical Sciences Research Council (grant Nos. EP/N014472/1, EP/R004773/1 and EP/N013298/1) and the Science and Technologies Facilities Council of the United Kingdom. F.C. and L.O.S. acknowledge support from the European Research Council (InPairs ERC-2015-AdG 695088) and FCT Portugal (grant No. PD/BD/114307/2016).This paper describes a model of electron energization and cyclotron-maser emission applicable to astrophysical magnetized collisionless shocks. It is motivated by the work of Begelman, Ergun and Rees [Astrophys. J. 625 , 51 (2005)] who argued that the cyclotron-maser instability occurs in localized magnetized collisionless shocks such as those expected in blazar jets. We report on recent research carried out to investigate electron acceleration at collisionless shocks and maser radiation associated with the accelerated electrons. We describe how electrons accelerated by lower-hybrid,waves at collisionless shocks generate cyclotron-maser radiation when the accelerated electrons move into regions of stronger magnetic fields. The electrons are accelerated along the magnetic field and magnetically compressed leading to the formation of an electron velocity distribution having a horseshoe shape due to conservation of the electron magnetic moment. Under certain conditions the horseshoe electron velocity distribution function is unstable to the cyclotron-maser instability [Bingham and Cairns, Phys. Plasmas 7, 3089 (2000); Melrose, Rev. Mod. Plasma Phys. 1 , 5 (2017)].Publisher PDFPeer reviewe

    T2K ECAL Test–beam Proposal

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    The T2K experiment will search for the last unknown element of the neutrino mixing matrix. An crucial component of the near detector for this experiment is the electromagnetic calorimeter which is being built in the UK. Testbeam time is requested to test the full ECAL system, validate calibration techniques, and determine the hadronic and electromagnetic energy scale of the calorimeter

    Autistic Development, Trauma and Personhood: Beyond the Frame of the Neoliberal Individual

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    This chapter critically explores notions of childhood development, particularly in regard to autism, reactions to traumatic events and the meaning of ‘personhood’. The construction of the neoliberal individual is contrasted with that of personhood as experienced by an autistic person. Person-centred methods of engagement as outlined in this chapter can give opportunities for opening up a respectful discursive space where autistic development is not framed from the outset as ‘disordered’

    Global Increase in Climate-Related Disasters

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    Intense climate-related disasters - floods, storms, droughts, and heat waves - have been on the rise worldwide. At the same time and coupled with an increasing concentration of greenhouse gases in the atmosphere, temperatures, on average, have been rising, and are becoming more variable and more extreme. Rainfall has also been more variable and more extreme. Is there an ominous link between the global increase of these hydrometeorological and climatological events on the one side and anthropogenic climate change on the other? This paper considers three main disaster risk factors - rising population exposure, greater population vulnerability, and increasing climate-related hazards - behind the increased frequency of intense climate-related natural disasters. In a regression analysis within a model of disaster risk determination for 1971-2013, population exposure measured by population density and people's vulnerability measured by socioeconomic variables are positively linked to the frequency of these intense disasters. Importantly, the results show that precipitation deviations are positively related to hydrometeorological events, while temperature and precipitation deviations have a negative association with climatological events. Moreover, global climate change indicators show positive and highly significant effects. Along with the scientific association between greenhouse gases and the changes in the climate, the findings in this paper suggest a connection between the increasing number of natural disasters and man-made emissions of greenhouse gases in the atmosphere. The implication is that climate mitigation and climate adaptation should form part of actions for disaster risk reduction

    The electromagnetic calorimeter for the T2K near detector ND280

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    The T2K experiment studies oscillations of an off-axis muon neutrino beam between the J-PARC accelerator complex and the Super-Kamiokande detector. Special emphasis is placed on measuring the mixing angle θ 13 by observing ν e appearance via the sub-dominant νμ ν e oscillation and searching for CP violation in the lepton sector. The experiment includes a sophisticated, off-axis, near detector, the ND280, situated 280 m downstream of the neutrino production target in order to measure the properties of the neutrino beam and to understand better neutrino interactions at the energy scale below a few GeV. The data collected with the ND280 are used to study charged- and neutral-current neutrino interaction rates and kinematics prior to oscillation, in order to reduce uncertainties in the oscillation measurements by the far detector. A key element of the near detector is the ND280 electromagnetic calorimeter (ECal), consisting of active scintillator bars sandwiched between lead sheets and read out with multi-pixel photon counters (MPPCs). The ECal is vital to the reconstruction of neutral particles, and the identification of charged particle species. The ECal surrounds the Pi-0 detector (PØD) and the tracking region of the ND280, and is enclosed in the former UA1/NOMAD dipole magnet. This paper describes the design, construction and assembly of the ECal, as well as the materials from which it is composed. The electronic and data acquisition (DAQ) systems are discussed, and performance of the ECal modules, as deduced from measurements with particle beams, cosmic rays, the calibration system, and T2K data, is described.© 2013 IOP Publishing Ltd and Sissa Medialab srl.The ECal detector has been built and is operated using funds provided by the Science and Technology Facilities Council U.K. Important support was also provided by the collaborating institutions. Individual researchers have been supported by the Royal Society and the European Research Council
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