7,044 research outputs found
Dismal Science: The Shortcomings of U.S. School Choice Research and How to Address Them
Pressing questions about the merits of market accountability in K-12 education have spawned a large scholarly literature. Unfortunately, much of that literature is of limited relevance, and some of it is misleading. The studies most widely cited in the United States used intense scrutiny of a few small-scale, restriction-laden U.S. programs -- and a handful of larger but still restriction-laden foreign school choice expansions -- to assert general conclusions about the effects of "choice," "competition," and "markets." The most intensely studied programs lack most or all of the key elements of market systems, including profit, price change, market entry, and product differentiation -- factors that are normally central to any discussion of market effects. In essence, researchers have drawn conclusions about apples by studying lemons. To address the need for credible evidence on the effects of genuine education markets, economists should look to simulation models, indirect evidence such as outcomes in similar industries, and school systems abroad that enjoy varying degrees of market accountability
The Merrifield-Simmons conjecture holds for bipartite graphs
Let be a graph and the number of independent
(vertex) sets in . Then the Merrifield-Simmons conjecture states that the
sign of the term only depends on the parity of the distance of the vertices
in . We prove that the conjecture holds for bipartite graphs by
considering a generalization of the term, where vertex subsets instead of
vertices are deleted.Comment: 8 page
Buckling Bars and Boxy Bulges
It has been suggested that the peanut-shaped bulges seen in some edge-on disk
galaxies are produced when bars in these galaxies buckle. This paper reviews
the modelling which seeks to show how bars buckle, and I present a very simple
new model which captures the essential physics of this process. I then discuss
the problems in establishing observationally the connection between
peanut-shaped bulges and bars: confirmation of the link has proved difficult
because boxy bulges are only apparent in edge-on galaxies whereas bars are only
easily detectable in more face-on systems. Finally, I present a new technique
which avoids this difficulty by searching for the distinctive kinematic
signature of an edge-on bar; application of this method to spectra of
peanut-shaped bulges reveals that they are, indeed, associated with hidden
bars.Comment: uuencoded compressed postcript, 9 pages. Invited talk at IAU
Colloquium #157: Barred Galaxies. The figures (some of which are rather
large) are available over the WWW from our preprint server at
http://www.astro.soton.ac.uk/pubs/Publications.htm
Dark Matter on Galactic Scales (or the Lack Thereof)
This paper presents a brief review of the evidence for dark matter in the
Universe on the scales of galaxies. In the interests of critically and
objectively testing the dark matter paradigm on these scales, this evidence is
weighed against that from the only other game in town, modified Newtonian
dynamics. The verdict is not as clear cut as one might have hoped.Comment: 10 pages, 5 figures. Invited review talk presented at IDM2004 5th
International Workshop on the Identification of Dark Matter, Edinburgh,
Scotland, September 200
Does Money Matter? The Impact of State Political Context on the Relationship between Race/Ethnicity and Campaign Finance
Despite increasing campaign-finance legislation aimed at equalizing barriers in political campaigns, a fundraising gap persists across racial/ethnic lines. In the era of modern campaigning, with the expenses of advertising and polling, among others, ample funds are necessary but not accessible to all candidates. This study addresses the relationship between candidate race/ethnicity and campaign fundraising, and the possible moderating effect of three dimensions of the state political context: state legislative professionalism, state Republican party strength, and state culture (South vs. non-South). I evaluate fundraising totals across 15 states for more than 3,000 candidates in the 2006 state legislative elections. Ultimately, the findings suggest that after controlling for other candidate characteristics, as well as for district and state context, there is a negative statistically significant relationship between candidate race/ethnicity and fundraising. In addition, the effect of race/ethnicity is moderated by two features of the state context: legislative professionalization and state culture. This study finds that nonwhite candidates continue to fundraise less than their white counterparts and that state context is important in understanding the race/ethnicity gap in campaign finance
The Kinematics of Galactic Stellar Disks
The disks of galaxies are primarily stellar systems, and fundamentally
dynamical entities. Thus, to fully understand galactic disks, we must study
their stellar kinematics as well as their morphologies. Observational
techniques have now advanced to a point where quite detailed stellar-kinematic
information can be extracted from spectral observations. This review presents
three illustrative examples of analyses that make use of such information to
study the formation and evolution of these systems: the derivation of the
pattern speed of the bar in NGC 936; the calculation of the complete velocity
ellipsoid of random motions in NGC 488; and the strange phenomenon of
counter-rotation seen in NGC 3593.Comment: 11 pages, LaTeX (including 7 figures), uses paspconf.sty and
epsf.sty, to be published in Proceedings of the EC Summer School on
'Astrophysical Discs', eds J. A. Sellwood and J. Goodman, ASP Conf. Serie
- …