19,714 research outputs found
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
Book Review (M. Ray & J. Ramsfield, Legal Writing: Getting It Right and Getting It Written (1987))
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 , let be a lattice in , and let
be an irreducible unitary representation of with
square-integrable matrix coefficients. A theorem in [Goodman, de la Harpe,
Jones 1989] states that the von Neumann dimension of as a
-module is equal to the formal dimension of the discrete series
representation times the covolume of , calculated with
respect to the same Haar measure. We prove two results inspired by this
theorem. First, we show there is a representation of on a subspace
of cuspidal automorphic functions in , where
and are lattices in ; 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 is ,
for a local non-archimedean field of characteristic with residue field
of order not divisible by 2; is a torsion-free lattice in ,
which, by a theorem of Ihara, is a free group; and 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
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