313 research outputs found

    Ground calibration of the Silicon Drift Detectors for NICER

    Get PDF
    The Neutron star Interior Composition ExploreR (NICER) is set to be deployed on the International Space Station (ISS) in early 2017. It will use an array of 56 Silicon Drift Detectors (SDDs) to detect soft X-rays (0.2 - 12 keV) with 100 nanosecond timing resolution. Here we describe the effort to calibrate the detectors in the lab primarily using a Modulated X-ray Source (MXS). The MXS that was customized for NICER provides more than a dozen emission lines spread over the instrument bandwidth, providing calibration measurements for detector gain and spectral resolution. In addition, the fluorescence source in the MXS was pulsed at high frequency to enable measurement of the delay due to charge collection in the silicon and signal processing in the detector electronics. A second chamber, designed to illuminate detectors with either 55 Fe, an optical LED, or neither, provided additional calibration of detector response, optical blocking, and effectiveness of background rejection techniques. The overall ground calibration achieved total operating time that was generally in the range of 500-1500 hours for each of the 56 detectors. Keywords: Silicon Drift Detectors; X-rays; timing spectroscopy; calibrationUnited States. National Aeronautics and Space Administration (Contract NNG14PJ13C

    Detection of Reflection Features in the Neutron Star Low-Mass X-Ray Binary Serpens X-1 with NICER

    Get PDF
    We present Neutron Star Interior Composition Explorer (NICER) observations of the neutron star (NS) low-mass X-ray binary Serpens X-1 during the early mission phase in 2017. With the high spectral sensitivity and low-energy X-ray passband of NICER, we are able to detect the Fe L line complex in addition to the signature broad, asymmetric Fe K line. We confirm the presence of these lines by comparing the NICER data to archival observations with XMM-Newton/Reflection Grating Spectrometer (RGS) and NuSTAR. Both features originate close to the innermost stable circular orbit (ISCO). When modeling the lines with the relativistic line model relline, we find that the Fe L blend requires an inner disk radius of 1.4 [superscript +0.2][subscript -0.01] R ISCO and Fe K is at 1.03[superscript +0.13][subscript -0.03]R ISCO (errors quoted at 90%). This corresponds to a position of 17.3[superscript +2.5][subscript -0.1] km and 12.7[superscript +1.6][subscript -0.04] km for a canonical NS mass (M[subscript NS] = 1.4 M[superscript ⨀]) and dimensionless spin value of a = 0. Additionally, we employ a new version of the relxill model tailored for NSs and determine that these features arise from a dense disk and supersolar Fe abundance

    The Sir Jimmy Savile Scandal: Child Sexual Abuse and Institutional Denial at the BBC

    Get PDF
    This study advances research on scandal through an empirical examination of one of the most extraordinary UK institutional child sexual abuse (CSA) scandals in the post-war period. Sir Jimmy Savile (1926–2011) was a BBC celebrity, showbiz friend of the establishment and philanthropist. In October 2012, one year after his death, an ITV documentary alleged that Savile was also a prolific sexual predator who for decades had exploited his BBC status to abuse teenage girls. As we demonstrate, this incendiary documentary triggered a news media feeding frenzy that in less than one week destroyed Savile’s reputation and thrust the BBC – the institution that made him a star – into a multi-faceted, globally reported CSA scandal. This study has four purposes. First, we propose a model of institutional CSA scandals that can account for critical transitions between key phases in the scandal process. Second, we apply this model to analyse the transition between the ‘latent’ and ‘activated’ phases of the Savile scandal. This transition corresponded with a dramatic transformation in the inferential structuring of Savile from ‘national treasure’, who had devoted decades to working with children, to ‘prolific sexual predator’, who spent decades abusing them. Third, we demonstrate how the BBC’s denial of responsibility for Savile’s sexual offending and its subsequent institutional cover-up triggered a ‘trial by media’ which in turn initiated the next phase in the scandal’s development – ‘amplification’. Finally, we consider the significance of our analysis of the Sir Jimmy Savile scandal for understanding the activation and development of scandals more generally

    TOM40 Mediates Mitochondrial Dysfunction Induced by α-Synuclein Accumulation in Parkinson's Disease.

    Get PDF
    Alpha-synuclein (α-Syn) accumulation/aggregation and mitochondrial dysfunction play prominent roles in the pathology of Parkinson's disease. We have previously shown that postmortem human dopaminergic neurons from PD brains accumulate high levels of mitochondrial DNA (mtDNA) deletions. We now addressed the question, whether alterations in a component of the mitochondrial import machinery -TOM40- might contribute to the mitochondrial dysfunction and damage in PD. For this purpose, we studied levels of TOM40, mtDNA deletions, oxidative damage, energy production, and complexes of the respiratory chain in brain homogenates as well as in single neurons, using laser-capture-microdissection in transgenic mice overexpressing human wildtype α-Syn. Additionally, we used lentivirus-mediated stereotactic delivery of a component of this import machinery into mouse brain as a novel therapeutic strategy. We report here that TOM40 is significantly reduced in the brain of PD patients and in α-Syn transgenic mice. TOM40 deficits were associated with increased mtDNA deletions and oxidative DNA damage, and with decreased energy production and altered levels of complex I proteins in α-Syn transgenic mice. Lentiviral-mediated overexpression of Tom40 in α-Syn-transgenic mice brains ameliorated energy deficits as well as oxidative burden. Our results suggest that alterations in the mitochondrial protein transport machinery might contribute to mitochondrial impairment in α-Synucleinopathies

    The Neutron star Interior Composition Explorer (NICER): design and development

    Get PDF
    During 2014 and 2015, NASA's Neutron star Interior Composition Explorer (NICER) mission proceeded successfully through Phase C, Design and Development. An X-ray (0.2-12 keV) astrophysics payload destined for the International Space Station, NICER is manifested for launch in early 2017 on the Commercial Resupply Services SpaceX-11 flight. Its scientific objectives are to investigate the internal structure, dynamics, and energetics of neutron stars, the densest objects in the universe. During Phase C, flight components including optics, detectors, the optical bench, pointing actuators, electronics, and others were subjected to environmental testing and integrated to form the flight payload. A custom-built facility was used to co-align and integrate the X-ray "concentrator" optics and silicon-drift detectors. Ground calibration provided robust performance measures of the optical (at NASA's Goddard Space Flight Center) and detector (at the Massachusetts Institute of Technology) subsystems, while comprehensive functional tests prior to payload-level environmental testing met all instrument performance requirements. We describe here the implementation of NICER's major subsystems, summarize their performance and calibration, and outline the component-level testing that was successfully applied

    Semi-Dense 3D Reconstruction with a Stereo Event Camera

    Full text link
    Event cameras are bio-inspired sensors that offer several advantages, such as low latency, high-speed and high dynamic range, to tackle challenging scenarios in computer vision. This paper presents a solution to the problem of 3D reconstruction from data captured by a stereo event-camera rig moving in a static scene, such as in the context of stereo Simultaneous Localization and Mapping. The proposed method consists of the optimization of an energy function designed to exploit small-baseline spatio-temporal consistency of events triggered across both stereo image planes. To improve the density of the reconstruction and to reduce the uncertainty of the estimation, a probabilistic depth-fusion strategy is also developed. The resulting method has no special requirements on either the motion of the stereo event-camera rig or on prior knowledge about the scene. Experiments demonstrate our method can deal with both texture-rich scenes as well as sparse scenes, outperforming state-of-the-art stereo methods based on event data image representations.Comment: 19 pages, 8 figures, Video: https://youtu.be/Qrnpj2FD1e

    Innate recognition of apoptotic cells:novel apoptotic cell-associated molecular patterns revealed by crossreactivity of anti-LPS antibodies

    Get PDF
    Cells dying by apoptosis are normally cleared by phagocytes through mechanisms that can suppress inflammation and immunity. Molecules of the innate immune system, the pattern recognition receptors (PRRs), are able to interact not only with conserved structures on microbes (pathogen-associated molecular patterns, PAMPs) but also with ligands displayed by apoptotic cells. We reasoned that PRRs might therefore interact with structures on apoptotic cells-apoptotic cell-associated molecular patterns (ACAMPs)-that are analogous to PAMPs. Here we show that certain monoclonal antibodies raised against the prototypic PAMP, lipopolysaccharide (LPS), can crossreact with apoptotic cells. We demonstrate that one such antibody interacts with a constitutively expressed intracellular protein, laminin-binding protein, which translocates to the cell surface during apoptosis and can interact with cells expressing the prototypic PRR, mCD14 as well as with CD14-negative cells. Anti-LPS cross reactive epitopes on apoptotic cells colocalised with annexin V-and C1q-binding sites on vesicular regions of apoptotic cell surfaces and were released associated with apoptotic cell-derived microvesicles (MVs). These results confirm that apoptotic cells and microbes can interact with the immune system through common elements and suggest that anti-PAMP antibodies could be used strategically to characterise novel ACAMPs associated not only with apoptotic cells but also with derived MVs

    Testing and characterization of the TESS CCDs

    Get PDF
    The Transiting Exoplanet Survey Satellite (TESS) is an Explorer-class mission dedicated to finding planets around bright, nearby stars so that more detailed follow-up studies can be done. TESS is due to launch in 2017 and careful characterization of the detectors will need to be completed on ground before then to ensure that the cameras will be within their photometric requirement of 60ppm/hr. TESS will fly MITLincoln Laboratories CCID-80s as the main scientific detector for its four cameras. They are 100μm deep depletion devices which have low dark current noise levels and can operate at low light levels at room temperature. They also each have a frame store region, which reduces smearing during readout and allows for near continuous integration. This paper describes the hardware and methodology that were developed for testing and characterizing individual CCID-80s. A dark system with no stimuli was used to measure the dark current. Fe 55 and Cd 109 X-ray sources were used to establish gain at low signal levels and its temperature dependence. An LED system that generates a programmable series of pulses was used in conjunction with an integrating sphere to measure pixel response non-uniformity (PRNU) and gain at higher signal levels. The same LED system was used with a pinhole system to evaluate the linearity and charge conservation capability of the CCID-80s.United States. National Aeronautics and Space Administration (contract number NNG14FC03C
    • …
    corecore