Physics & Astronomy

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Now showing 1 - 5 of 58
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    X-ray Spectroscopy of the O Supergiant ζ Puppis Indicates Surprising Variation in the Wind Mass-loss Rate on Years Timescales
    (2022) Wang, Jiaming; Cohen, David H.
    We apply two mass-loss rate diagnostics described in the thesis on Chandra and XMM-Newton X-ray spectroscopic measurements of ζ Pup, one of the most luminous stars in the Milky Way and one of the closest O stars to Earth. Emission line profile analysis from new long Chandra grating observations taken during 2018 and 2019 indicates a significant 40% increase in ζ Pup’s wind mass-loss rate as compared to data taken in Chandra’s first observation cycle in 2000. Broadband spectral modeling of 20 years of XMM observations also reveal non-periodic wind mass-loss rate variation at a 40% level on timescales of months to years. These results are surprising as the mass-loss rates of massive stars are predicted to be constant.
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    DeepCIP: Probing Compensated Isocurvature Perturbations in the CMB using deep neural nets
    (2021) Mebratu, Matiwos A.; Smith, Tristan
    It is almost unbelievable to realize that just a century ago we did not know that galaxies outside Milky Way exist let alone the Universe is expanding. After Einstein formulated his theory of General Relativity, it became apparent to him, the theory does not seem to describe the static universe most scientists at the time thought we lived in. This prompted him to introduce a cosmological constant in his equations to make the Universe, as described by his equations, static [1]. Alexander Friedmann and Georges Lemaıtre, from solving Einstein’s equations, independently predicted that the Universe is expanding and the recession velocity of galaxies is proportional to the distance between them [2, 3]. This prediction was later confirmed by Edwin Hubble who measured the distance from Earth to multiple galaxies by measuring the distance to Cepheid variable stars in those galaxies [4].
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    Measurement of Angular Correlation of Two Protons in Quasielastic Neutrino-Nucleus Cross-Section
    (2020) Chalifour, Matthieu; Crouch, Catherine; McFarland, Kevin
    We search in the MINERvA scintillator detector for multiple proton emission in quasielastic like charged current neutrino scattering. The number of such observable events in MINERvA is predicted to be far greater than currently available samples. We measure the total number of such events, and study the distribution of laboratory frame angles between the multiple protons and the muon, which is sensitive to the production mechanism for such events. We find significant disagreement of signal events between data and Monte-Carlo simulation.
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    A Theory for Allosteric Temperature-Sensitive Transcription Factors
    (2018) Zhang, Zechen; Phillips, Rob; Crouch, Catherine
    We propose a theory for temperature-sensitive transcription factors under the allostery framework. We show that the allostery theory due to excess vibrational entropy and conformational energy difference can produce a thermal switch behavior that is experimentally observed in the literature. The theory paves the way for a complete model of a tunable thermal bioswitch.