932 research outputs found

    X-ray Searches for Axions from Super Star Clusters

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    Axions may be produced in abundance inside stellar cores and then convert into observable X-rays in the Galactic magnetic fields. We focus on the Quintuplet and Westerlund 1 super star clusters, which host large numbers of hot, young stars including Wolf-Rayet stars; these stars produce axions efficiently through the axion-photon coupling. We use Galactic magnetic field models to calculate the expected X-ray flux locally from axions emitted from these clusters. We then combine the axion model predictions with archival Nuclear Spectroscopic Telescope Array (NuSTAR) data from 10 - 80 keV to search for evidence of axions. We find no significant evidence for axions and constrain the axion-photon coupling gaγγ≲3.6×10−12g_{a\gamma\gamma} \lesssim 3.6 \times 10^{-12} GeV−1^{-1} for masses ma≲5×10−11m_a \lesssim 5 \times 10^{-11} eV at 95\% confidence.Comment: 8+18 pages, 3+21 figures, version published in PRL. Supplementary Data at https://github.com/bsafdi/axionSS

    Flipping an Agricultural Teaching Methods Course at a Non-Land Grant University

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    The purpose of this study was to analyze undergraduate students’ perceptions of experiencing a flipped classroom in a teaching methods course at a Non-Land Grant Public Institution. The flipped classroom moves lectures and online videos outside of the classroom and uses class time for learning activities that promote problem-solving and discussion. Basic qualitative methods were used to provide flexibility, rich description, and the emergence of common patterns and themes. Participants reported the online lectures were beneficial and provided order and structure to the learning process. Personal responsibility emerged as a subtheme with mixed responses. Some participants felt it was the responsibility of the students to watch the videos and make sure they understood, while others felt it was too much responsibility on the students. All participants acknowledged that online lectures were a valuable tool for delivering content knowledge. All participants reported the online lectures, combined with the learning activities during class meetings, deepened their knowledge of teaching and learning application and skill development. Overall, participants felt the flipped classroom approach was a confidence booster due to the use of class time to practice their teaching skills. Participants recognized the flipped classroom as an effective teaching approach

    Timing of extension in the Pioneer metamorphic core complex with implications for the spatial-temporal pattern of Cenozoic extension and exhumation in the northern U.S. Cordillera

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    The Pioneer core complex (PCC) in central Idaho lies along a transition between Early Eocene and ca. 40 Ma core complexes to the north and south, respectively. Thus, the age of extensional development of the PCC is important in understanding the spatial-temporal patterns of core-complex development in the North American Cordillera. New results, including structural observations and U-Pb zircon (SHRIMP and ICPMS) geochronology, constrain the early extensional history of the footwall for the first time. High-temperature strain with a top-WNW shear-sense is pervasive throughout metamorphic rocks of the northwestern footwall. An isoclinally folded dike yields a crystallization age of ∼48-47 Ma, whereas a crosscutting dike yielded an age of 46 Ma. Metamorphic rocks are also intruded by the ∼50-48 Ma Pioneer intrusive suite (PIS), a W-dipping granodiorite sheet displaying a magmatic fabric. Northwest-trending lineations are locally visible and also defined by anisotropy of magnetic susceptibility, indicating that during emplacement, the PIS was undergoing similarly oriented extensional strain as the enclosing metamorphic rocks. Therefore, WNW-directed extension spanning this structural section occurred between ∼50 and 46 Ma. Following emplacement of crosscutting 46 Ma dikes, deformation was partitioned into the WNW-directed Wildhorse detachment. Motion on the detachment occurred between ∼38 and 33 Ma, as documented by previous 40Ar/ 39Ar thermochronology. It is not clear, however, whether extension was continuous through the interval between these two time periods. Although Early Eocene extension in the PCC was synchronous with extension in core complexes to the north, rates of footwall exhumation in central Idaho were much lower. This southward slowing is compatible with N-S differences in inferred subduction zone geometry/kinematics and in the internal character of the orogenic wedge

    Design and Preliminary Testing of the International Docking Adapter's Peripheral Docking Target

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    The International Docking Adapter's Peripheral Docking Target (PDT) was designed to allow a docking spacecraft to judge its alignment relative to the docking system. The PDT was designed to be compatible with relative sensors using visible cameras, thermal imagers, or Light Detection and Ranging (LIDAR) technologies. The conceptual design team tested prototype designs and materials to determine the contrast requirements for the features. This paper will discuss the design of the PDT, the methodology and results of the tests, and the conclusions pertaining to PDT design that were drawn from testing
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