19,129 research outputs found

    Closing Thoughts

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    I Gotta Testify: Kanye West, Hip Hop, and the Church

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    The goal of this project, “I Gotta Testify: Kanye West, Hip Hop, and the Church,” is to add a new perspective to the scholarly discourse on Hip Hop and Christianity within classrooms, religious institutions, and popular culture by focusing on Kanye. We chose to focus on Kanye because he has been one of Hip Hop’s most influential artists in the past decade. Furthermore, Kanye is one of the most polarizing celebrities in America and across the globe. His music, fashion, political views, and family (which includes the Kardashians) dominate discourse on social media, blogs, television, and other forms of mass media. With the exception of Julius Bailey’s 2014 edited book, The Cultural Impact of Kanye West, there has been little scholarly work published on Kanye. Bailey’s book contained just one essay, written by Monica R. Miller, dedicated to the theme of Kanye and religion. We intended to produce a nontraditional journal issue, partly because Kanye has never adhered to traditional boundaries. We also chose this method because we wanted to provide a document suitable for both academic and popular audiences. Kanye West identifies as a Christian and primarily uses Christian themes in his music, videos, concerts, and messaging. Dr. Joshua K. Wright, Dr. Adria Y. Goldman and Dr. VaNatta S. For

    Free energy of formation of clusters of sulphuric acid and water molecules determined by guided disassembly

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    We evaluate the grand potential of a cluster of two molecular species, equivalent to its free energy of formation from a binary vapour phase, using a nonequilibrium molecular dynamics technique where guide particles, each tethered to a molecule by a harmonic force, move apart to disassemble a cluster into its components. The mechanical work performed in an ensemble of trajectories is analysed using the Jarzynski equality to obtain a free energy of disassembly, a contribution to the cluster grand potential. We study clusters of sulphuric acid and water at 300 K, using a classical interaction scheme, and contrast two modes of guided disassembly. In one, the cluster is broken apart through simple pulling by the guide particles, but we find the trajectories tend to be mechanically irreversible. In the second approach, the guide motion and strength of tethering are modified in a way that prises the cluster apart, a procedure that seems more reversible. We construct a surface representing the cluster grand potential, and identify a critical cluster for droplet nucleation under given vapour conditions. We compare the equilibrium populations of clusters with calculations reported by Henschel et al. [J. Phys. Chem. A 118, 2599 (2014)] based on optimised quantum chemical structures

    The variability of the Crab Nebula in radio: No radio counterpart to gamma-ray flares

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    We present new Jansky Very Large Array (VLA) radio images of the Crab Nebula at 5.5 GHz, taken at two epochs separated by 6 days about two months after a gamma-ray flare in 2012 July. We find no significant change in the Crab's radio emission localized to a region of <2 light-months in radius, either over the 6-day interval between our present observations or between the present observations and ones from 2001. Any radio counterpart to the flare has a radio luminosity of <~ 2×1042 \times 10^{-4} times that of the nebula. Comparing our images to one from 2001, we do however find changes in radio brightness, up to 10% in amplitude, which occur on decade timescales throughout the nebula. The morphology of the changes is complex suggesting both filamentary and knotty structures. The variability is stronger, and the timescales likely somewhat shorter, nearer the centre of the nebula. We further find that even with the excellent uv~coverage and signal-to-noise of the VLA, deconvolution errors are much larger than the noise, being up to 1.2% of peak brightness of the nebula in this particular case.Comment: Accepted to MNRAS; 13 pages, 6 figure

    Debiasing the Minimum-Mass Extrasolar Nebula: On the Diversity of Solid Disk Profiles

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    A foundational idea in the theory of in situ planet formation is the "minimum mass extrasolar nebula" (MMEN), a surface density profile (Σ\Sigma) of disk solids that is necessary to form the planets in their present locations. While most previous studies have fit a single power-law to all exoplanets in an observed ensemble, it is unclear whether most exoplanetary systems form from a universal disk template. We use an advanced statistical model for the underlying architectures of multi-planet systems to reconstruct the MMEN. The simulated physical and Kepler-observed catalogs allows us to directly assess the role of detection biases, and in particular the effect of non-transiting or otherwise undetected planets, in altering the inferred MMEN. We find that fitting a power-law of the form Σ=Σ0(a/a0)β\Sigma = \Sigma_0^* (a/a_0)^\beta to each multi-planet system results in a broad distribution of disk profiles; Σ0=336291+727\Sigma_0^* = 336_{-291}^{+727} g/cm2^2 and β=1.981.52+1.55\beta = -1.98_{-1.52}^{+1.55} encompass the 16th-84th percentiles of the marginal distributions in an underlying population, where Σ0\Sigma_0^* is the normalization at a0=0.3a_0 = 0.3 AU. Around half of inner planet-forming disks have minimum solid masses of 40M\gtrsim 40 M_\oplus within 1 AU. While transit observations do not tend to bias the median β\beta, they can lead to both significantly over- and under-estimated Σ0\Sigma_0^* and thus broaden the inferred distribution of disk masses. Nevertheless, detection biases cannot account for the full variance in the observed disk profiles; there is no universal MMEN if all planets formed in situ. The great diversity of solid disk profiles suggests that a substantial fraction (23%\gtrsim 23\%) of planetary systems experienced a history of migration.Comment: Accepted to AJ. 14 pages, 6 figures, 1 table. Accompanying code is available via SysSimPyMMEN, a pip-installable Python package (see https://syssimpymmen.readthedocs.io/en/latest/

    Testing MONDian Dark Matter with Galactic Rotation Curves

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    MONDian dark matter (MDM) is a new form of dark matter quantum that naturally accounts for Milgrom's scaling, usually associated with modified Newtonian dynamics (MOND), and theoretically behaves like cold dark matter (CDM) at cluster and cosmic scales. In this paper, we provide the first observational test of MDM by fitting rotation curves to a sample of 30 local spiral galaxies (z approximately 0.003). For comparison, we also fit the galactic rotation curves using MOND, and CDM. We find that all three models fit the data well. The rotation curves predicted by MDM and MOND are virtually indistinguishable over the range of observed radii (~1 to 30 kpc). The best-fit MDM and CDM density profiles are compared. We also compare with MDM the dark matter density profiles arising from MOND if Milgrom's formula is interpreted as Newtonian gravity with an extra source term instead of as a modification of inertia. We find that discrepancies between MDM and MOND will occur near the center of a typical spiral galaxy. In these regions, instead of continuing to rise sharply, the MDM mass density turns over and drops as we approach the center of the galaxy. Our results show that MDM, which restricts the nature of the dark matter quantum by accounting for Milgrom's scaling, accurately reproduces observed rotation curves.Comment: Preprint number IPMU13-0147. Accepted for publication in Ap
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