Molybdenum, Ruthenium, and the Heavy r-process Elements in Moderately Metal-Poor Main-Sequence Turnoff Stars

The ratios of elemental abundances observed in metal-poor stars of the Galactic halo provide a unique present-day record of the nucleosynthesis products of its earliest stars. While the heaviest elements were synthesized by the r- and s-processes, dominant production mechanisms of light trans-ironic elements were obscure until recently. This work investigates further our 2011 conclusion that the low-entropy regime of a high-entropy wind (HEW) produced molybdenum and ruthenium in two moderately metal-poor turnoff stars that showed extreme overabundances of those elements with respect to iron. Only a few, rare nucleosynthesis events may have been involved. Here we determine abundances for Mo, Ru, and other trans-Fe elements for 28 similar stars by matching spectral calculations to well-exposed near-UV Keck HIRES spectra obtained for beryllium abundances. In each of the 26 turnoff stars with Mo or Ru line detections and no evidence for s-process production (therefore old), we find Mo and Ru to be three to six times overabundant. In contrast, the maximum overabundance is reduced to factors of three and two for the neighboring elements zirconium and palladium. Since the overproduction peaks sharply at Mo and Ru, a low-entropy HEW is confirmed as its origin. The overabundance level of the heavy r-process elements varies significantly, from none to a factor of four, but is uncorrelated with Mo and Ru overabundances. Despite their moderate metallicity, stars in this group trace the products of different nucleosynthetic events: possibly very few events, possibly events whose output depended on environment, metallicity, or time.Comment: Accepted April 2, 2013, for publication in the Astrophysical Journal Letters (7 pages, 3 figures

An analysis of music teaching positions in the public schools of Massachusetts.

Thesis (M.M.)--Boston Universit

Two New Settings for Examples of von Neumann Dimension

Let $G=PSL(2,\mathbb{R})$, let $\Gamma$ be a lattice in $G$, and let $\mathcal{H}$ be an irreducible unitary representation of $G$ with square-integrable matrix coefficients. A theorem in [Goodman, de la Harpe, Jones 1989] states that the von Neumann dimension of $\mathcal{H}$ as a $R\Gamma$-module is equal to the formal dimension of the discrete series representation $\mathcal{H}$ times the covolume of $\Gamma$, calculated with respect to the same Haar measure. We prove two results inspired by this theorem. First, we show there is a representation of $R\Gamma_2$ on a subspace of cuspidal automorphic functions in $L^2(\Gamma_1 \backslash G)$, where $\Gamma_1$ and $\Gamma_2$ are lattices in $G$; and this representation is unitarily equivalent to one of the representations in [Goodman, de la Harpe, Jones 1989]. Next, we calculate von Neumann dimensions when $G$ is $PGL(2,F)$, for $F$ a local non-archimedean field of characteristic $0$ with residue field of order not divisible by 2; $\Gamma$ is a torsion-free lattice in $PGL(2,F)$, which, by a theorem of Ihara, is a free group; and $\mathcal{H}$ is the Steinberg representation, or a depth-zero supercuspidal representation, each yielding a different dimension.Comment: This is the author's Ph.D. thesi

Teaching research methods: Introducing a psychogeographical approach

This paper explores teaching business students research methods using a psychogeographical approach, specifically the technique of dérive. It responds to calls for new ways of teaching in higher education and addresses the dearth of literature on teaching undergraduate business students qualitative research methods. Psychogeography challenges the dominance of questionnaires and interviews, introduces students to data variety, problematizes notions of success and illuminates the importance of observation and location. Using two studies with undergraduate students, the authors emphasize place and setting, the perception of purpose, the choice of data, criteria of success and the value of guided reflection and self-reflection in students’ learning. Additionally the data reflect on the way students perceive research about management and the nature of management itself. The paper concludes that the deployment of psychogeography to teach business research methods although complex and fraught with difficulty is nevertheless viable, educationally productive and worthy of further research