8,429 research outputs found

    Development and use of an extensometer for determining the mechanical compliance of crack toughness test specimens

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    Extensometer for determining mechanical compliance of crack toughness test specimen

    Investigation of the reactivity of organic materials in liquid oxygen

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    Measurements of impact-ignition sensitivity and studies of the relative reactivity of t-butoxy and t-butyl peroxy radicals toward a variety of organic compounds reveal improved methods of selection of materials for safe use in a liquid oxygen environment

    Are dwarf spheroidal galaxies dark matter dominated or remnants of disrupted larger satellite galaxies? -- A possible test

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    The failure of standard cosmolocical models in accounting for the statistics of dwarf satellites and the rotation curve of gas-rich dwarf galaxies in detail has led us to examine whether earlier non-equilibrium models of dwarf spheroidal satellites without any dark matter should be reconsidered in more detail. Such models can explain the high dispersion of the dwarf spheroids by the projection of disrupted tidal debris. We show in the case of Milky Way satellites, that these models predict a significant spread in the apparent magnitude of horizontal branch stars which is correlated with sky position and velocity. In particular, the models produce a strong correlation of radial velocity with the long axis of the dwarf. Current data do not set strong enough constraints on the models, but we suggest that photometric and spectroscopic surveys of extra-tidal stars of nearby dwarf spheroids in the Milky Way and Andromeda can falsify these models without dark matter.Comment: 7 pages, 5 figures, accepted for publication in Ap

    A Search for Additional Bodies in the GJ 1132 Planetary System from 21 Ground-based Transits and a 100 Hour Spitzer Campaign

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    We present the results of a search for additional bodies in the GJ 1132 system through two methods: photometric transits and transit timing variations of the known planet. We collected 21 transit observations of GJ 1132b with the MEarth-South array since 2015. We obtained 100 near-continuous hours of observations with the SpitzerSpitzer Space Telescope, including two transits of GJ 1132b and spanning 60\% of the orbital phase of the maximum period at which bodies coplanar with GJ 1132b would pass in front of the star. We exclude transits of additional Mars-sized bodies, such as a second planet or a moon, with a confidence of 99.7\%. When we combine the mass estimate of the star (obtained from its parallax and apparent KsK_s band magnitude) with the stellar density inferred from our high-cadence SpitzerSpitzer light curve (assuming zero eccentricity), we measure the stellar radius of GJ 1132 to be 0.21050.0085+0.0102R0.2105^{+0.0102}_{-0.0085} R_\odot, and we refine the radius measurement of GJ 1132b to 1.130±0.056R1.130 \pm 0.056 R_\oplus. Combined with HARPS RV measurements, we determine the density of GJ 1132b to be 6.2±2.06.2 \pm 2.0\ g cm3^{-3}, with the mass determination dominating this uncertainty. We refine the ephemeris of the system and find no evidence for transit timing variations, which would be expected if there was a second planet near an orbital resonance with GJ 1132b.Comment: 29 pages, 4 Tables, 8 Figures, Submitted to ApJ. Comments welcom

    Effect of a thin AlO_x layer on transition-edge sensor properties

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    We have studied the physics of transition-edge sensor (TES) devices with an insulating AlOx layer on top of the device to allow implementation of more complex detector geometries. By comparing devices with and without the insulating film, we have observed significant additional noise apparently caused by the insulator layer. In addition, AlOx was found to be a relatively good thermal conductor. This adds an unforeseen internal thermal feature to the system.Comment: 6 pages, 5 figures, Low Temperature Detectors 14 conferenc