Writing While Black: The Black Tax on African American Graduate Writers

In Souls of Black Folk, W. E. B. Du Bois states that African American identity contains a “double consciousness” of being both black and American (45). According to Du Bois, African Americans are constantly aware of their dual identities because their existence is a constant struggle to reconcile those two selves in a society that scorns them. As Du Bois writes, “He simply wishes to make it possible for a man to be both a Negro and an American, without being cursed and spit upon by his fellows, without having the doors of Opportunity closed roughly in his face” (46). As a result, African Americans have to see themselves in relation to how white Americans view them, while struggling to encounter a world that they anticipate will eventually—and hopefully—view them without contempt.University Writing Cente

Results From Core-Collapse Simulations with Multi-Dimensional, Multi-Angle Neutrino Transport

We present new results from the only 2D multi-group, multi-angle calculations of core-collapse supernova evolution. The first set of results from these calculations was published in Ott et al. (2008). We have followed a nonrotating and a rapidly rotating 20 solar mass model for ~400 ms after bounce. We show that the radiation fields vary much less with angle than the matter quantities in the region of net neutrino heating. This obtains because most neutrinos are emitted from inner radiative regions and because the specific intensity is an integral over sources from many angles at depth. The latter effect can only be captured by multi-angle transport. We then compute the phase relationship between dipolar oscillations in the shock radius and in matter and radiation quantities throughout the postshock region. We demonstrate a connection between variations in neutrino flux and the hydrodynamical shock oscillations, and use a variant of the Rayleigh test to estimate the detectability of these neutrino fluctuations in IceCube and Super-K. Neglecting flavor oscillations, fluctuations in our nonrotating model would be detectable to ~10 kpc in IceCube, and a detailed power spectrum could be measured out to ~5 kpc. These distances are considerably lower in our rapidly rotating model or with significant flavor oscillations. Finally, we measure the impact of rapid rotation on detectable neutrino signals. Our rapidly rotating model has strong, species-dependent asymmetries in both its peak neutrino flux and its light curves. The peak flux and decline rate show pole-equator ratios of up to ~3 and ~2, respectively.Comment: 13 pages, 9 figures, ApJ accepted. Replaced with accepted versio

GRB Energetics in the Swift Era

We examine the rest frame energetics of 76 gamma-ray bursts (GRBs) with known redshift that were detected by the Swift spacecraft and monitored by the satellite's X-ray Telescope (XRT). Using the bolometric fluence values estimated in Butler et al. 2007b and the last XRT observation for each event, we set a lower limit the their collimation corrected energy Eg and find that a 68% of our sample are at high enough redshift and/or low enough fluence to accommodate a jet break occurring beyond the last XRT observation and still be consistent with the pre-Swift Eg distribution for long GRBs. We find that relatively few of the X-ray light curves for the remaining events show evidence for late-time decay slopes that are consistent with that expected from post jet break emission. The breaks in the X-ray light curves that do exist tend to be shallower and occur earlier than the breaks previously observed in optical light curves, yielding a Eg distribution that is far lower than the pre-Swift distribution. If these early X-ray breaks are not due to jet effects, then a small but significant fraction of our sample have lower limits to their collimation corrected energy that place them well above the pre-Swift Eg distribution. Either scenario would necessitate a much wider post-Swift Eg distribution for long cosmological GRBs compared to the narrow standard energy deduced from pre-Swift observations. We note that almost all of the pre-Swift Eg estimates come from jet breaks detected in the optical whereas our sample is limited entirely to X-ray wavelengths, furthering the suggestion that the assumed achromaticity of jet breaks may not extend to high energies.Comment: 30 pages, 10 figures, Accepted to Ap

Strong Water Absorption in the Dayside Emission Spectrum of the Planet HD 189733b

Recent observations of the extrasolar planet HD 189733b did not reveal the presence of water in the emission spectrum of the planet. Yet models of such 'Hot Jupiter' planets predict an abundance of atmospheric water vapour. Validating and constraining these models is crucial for understanding the physics and chemistry of planetary atmospheres in extreme environments. Indications of the presence of water in the atmosphere of HD 189733b have recently been found in transmission spectra, where the planet's atmosphere selectively absorbs the light of the parent star, and in broadband photometry. Here we report on the detection of strong water absorption in a high signal-to-noise, mid-infrared emission spectrum of the planet itself. We find both a strong downturn in the flux ratio below 10 microns and discrete spectral features that are characteristic of strong absorption by water vapour. The differences between these and previous observations are significant and admit the possibility that predicted planetary-scale dynamical weather structures might alter the emission spectrum over time. Models that match the observed spectrum and the broadband photometry suggest that heat distribution from the dayside to the night side is weak. Reconciling this with the high night side temperature will require a better understanding of atmospheric circulation or possible additional energy sources.Comment: 11 pages, 1 figure, published in Natur

Multi-Dimensional Explorations in Supernova Theory

In this paper, we bring together various of our published and unpublished findings from our recent 2D multi-group, flux-limited radiation hydrodynamic simulations of the collapse and explosion of the cores of massive stars. Aided by 2D and 3D graphical renditions, we motivate the acoustic mechanism of core-collapse supernova explosions and explain, as best we currently can, the phases and phenomena that attend this mechanism. Two major foci of our presentation are the outer shock instability and the inner core g-mode oscillations. The former sets the stage for the latter, which damp by the generation of sound. This sound propagates outward to energize the explosion and is relevant only if the core has not exploded earlier by some other means. Hence, it is a more delayed mechanism than the traditional neutrino mechanism that has been studied for the last twenty years since it was championed by Bethe and Wilson. We discuss protoneutron star convection, accretion-induced-collapse, gravitational wave emissions, pulsar kicks, the angular anisotropy of the neutrino emissions, a subset of numerical issues, and a new code we are designing that should supercede our current supernova code VULCAN/2D. Whatever ideas last from this current generation of numerical results, and whatever the eventual mechanism(s), we conclude that the breaking of spherical symmetry will survive as one of the crucial keys to the supernova puzzle.Comment: To be published in the "Centennial Festschrift for Hans Bethe," Physics Reports (Elsevier: Holland), ed. G.E. Brown, E. van den Heuvel, and V. Kalogera, 200

Epitaxial growth and surface reconstruction of CrSb(0001)

Smooth CrSb(0001) films have been grown by molecular beam epitaxy on MnSb(0001) – GaAs(111) substrates. CrSb(0001) shows (2 × 2), triple domain (1 × 4) and (√3×√3)R30° reconstructed surfaces as well as a (1 × 1) phase. The dependence of reconstruction on substrate temperature and incident fluxes is very similar to MnSb(0001)

Mu and Tau Neutrino Thermalization and Production in Supernovae: Processes and Timescales

We investigate the rates of production and thermalization of $\nu_\mu$ and $\nu_\tau$ neutrinos at temperatures and densities relevant to core-collapse supernovae and protoneutron stars. Included are contributions from electron scattering, electron-positron annihilation, nucleon-nucleon bremsstrahlung, and nucleon scattering. For the scattering processes, in order to incorporate the full scattering kinematics at arbitrary degeneracy, the structure function formalism developed by Reddy et al. (1998) and Burrows and Sawyer (1998) is employed. Furthermore, we derive formulae for the total and differential rates of nucleon-nucleon bremsstrahlung for arbitrary nucleon degeneracy in asymmetric matter. We find that electron scattering dominates nucleon scattering as a thermalization process at low neutrino energies ($\epsilon_\nu\lesssim 10$ MeV), but that nucleon scattering is always faster than or comparable to electron scattering above $\epsilon_\nu\simeq10$ MeV. In addition, for $\rho\gtrsim 10^{13}$ g cm$^{-3}$, $T\lesssim14$ MeV, and neutrino energies $\lesssim60$ MeV, nucleon-nucleon bremsstrahlung always dominates electron-positron annihilation as a production mechanism for $\nu_\mu$ and $\nu_\tau$ neutrinos.Comment: 29 pages, LaTeX (RevTeX), 13 figures, submitted to Phys. Rev. C. Also to be found at anonymous ftp site http://www.astrophysics.arizona.edu; cd to pub/thompso

Science Fictioning Singularities: The Diagrammatic Imaginaries of Physics

Data Loam focuses on the future of knowledge systems in texts about artificial intelligence, cybernetics, and cryptoeconomics – as a means of counteracting end-of-the-world fears