129 research outputs found

    Relative clauses in child language, pidgins and Creoles

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    Internal vs. External Factors in Socio-Historical Explanations of Change: A Fruitless Dichotomy?

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    Proceedings of the Twenty-First Annual Meeting of the Berkeley Linguistics Society: General Session and Parasession on Historical Issues in Sociolinguistics/Social Issues in Historical Linguistics (1995

    CubeX: A Compact X-ray Telescope Enables Both X-ray Fluorescence Imaging Spectroscopy and Pulsar Timing Based Navigation

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    This paper describes the miniaturized X-ray telescope payload, CubeX, in the context of a lunar mission. The first part describes the payload in detail, the second part summarizes a small satellite mission concept that utilizes its compact form factor and performance. This instrument can be used for both X-ray fluorescence (XRF) imaging spectroscopy and X-ray pulsar timing-based navigation (XNAV). It combines high angular resolution (\u3c 1 \u3earcminutes) Miniature Wolter-I X-ray optics (MiXO) with a common focal plane consisting of high spectral resolution (keV) CMOS X-ray sensors and a high timing resolution (\u3c 1 μsec) SDD X-ray sensor. This novel combination of the instruments enables both XRF measurements and XNAV operations without moving parts, in a small form factor (~1×1×6U

    SmallSat Solar Axion and Activity X-ray Imager (SSAXI)

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    Axions are a promising dark matter candidate as well as a solution to the strong charge-parity (CP) problem in quantum chromodynamics (QCD). We describe a new mission concept for SmallSat Solar Axion and Activity X-ray Imager (SSAXI) to search for solar axions or axion-like particles (ALPs) and to monitor solar activity of the entire solar disc over a wide dynamic range. SSAXI aims to unambiguously identify X-rays converted from axions in the solar magnetic field along the line of sight to the solar core, effectively imaging the solar core. SSAXI also plans to establish a statistical database of X-ray activities from Active Regions, microflares, and Quiet Sun regions to understand the origin of the solar corona heating processes. SSAXI employs Miniature lightweight Wolter-I focusing X-ray optics (MiXO) and monolithic CMOS X-ray sensors in a compact package. The wide energy range (0.5 - 6 keV) of SSAXI can easily distinguish spectra of axion-converted X-rays from typical X-ray spectra of solar activities, while encompassing the prime energy band (3 - 4.5 keV) of axion-converted X-rays. The high angular resolution (30 arcsec HPD) and large field of view (40 arcmin) in SSAXI will easily resolve the enhanced X-ray flux over the 3 arcmin wide solar core while fully covering the X-ray activity over the entire solar disc. The fast readout in the inherently radiation tolerant CMOS X-ray sensors enables high resolution spectroscopy with a wide dynamic range in a broad range of operational temperatures. SSAXI will operate in a Sun-synchronous orbit for 1 yr preferably near a solar minimum to accumulate sufficient X-ray photon statistics.Comment: 12 pages, 9 figures, 1 table, Presented at the SPIE Optics + Photonics Conference, August 2019, San Diego, C

    Cubex: A Compact X-Ray Telescope Enables Both X-Ray Fluorescence Imaging Spectroscopy and Pulsar Timing Based Navigation

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    This paper describes the miniaturized X-ray telescope payload, CubeX, in the context of a lunar mission. The first part describes the payload in detail, the second part summarizes a small satellite mission concept that utilizes its compact form factor and performance. This instrument can be used for both X-ray fluorescence (XRF) imaging spectroscopy and X-ray pulsar timing-based navigation (XNAV). It combines high angular resolution (<1 arcminutes) Miniature Wolter-I X-ray optics (MiXO) with a common focal plane consisting of high spectral resolution (<150 eV at 1 keV) CMOS X-ray sensors and a high timing resolution (< 1 Amp-microsecond) SDD X-ray sensor. This novel combination of the instruments enables both XRF measurements and XNAV operations without moving parts, in a small form factor (volume approximately 1 by 1 by 6 Units, and mass, < 6 kg). In this paper we illustrate one potential application for a lunar mission concept: The elemental composition of the Moon holds keys to understanding the origin and evolution of both the Moon and the Earth. X-ray fluorescence (XRF), induced either by solar X-ray flux or energetic ions, carries decisive signatures of surface elemental composition. In between XRF observations, CubeX also leverages the technology of high resolution X-ray imaging and time series measurements to conduct XNAV operations and evaluate their performance

    Thin-shell plastic lenses for space and laboratory applications

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    We have identified an inexpensive, readily available, mechanically stable, extremely smooth, elastic, and mechanically uniform plastic suitable for thin film X-ray optics. Polyethylene terephthalate (PET) is easily deformed without losing its elastic properties or surface smoothness. Most important, PET can be coated with mono- or multilayers that reflect X-rays at grazing incidence. We have used these properties to produce X-ray optics made either as a concentric nest of cylinders or as a spiral. We have produced accurately formed shells in precisely machined vacuum mandresl or used a pin and wheel structure to form a continuously wound spiral. The wide range of medical, industrial and scientific applications for our technology includes: a monochromatic X-ray collimater for medical diagnostics, a relay optic to transport an X-ray beam from the target in a scanning electron microscop0e to a lithium-drifted silicon and microcalorimeter detectors and a satellite mounted telescope to collect celestial X-rays. A wide variety of mono- and multilayer coatings allow X-rays up to ~100 keV to be reflected. Our paper presents data from a variety of diagnostic measurements on the properties of the PET foil and imaging results form single- and multi-shell lenses
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