13,577 research outputs found
The black-white education-scaled test-score gap in grades k-7
We measure the black-white achievement gap from kindergarten through seventh grade on an interval scale created by tying each grade/test score combination to average eventual education. After correcting for various sources of test measurement error, some of which are unique to forward-looking scales, we find no racial component in the evolution of the achievement gap through the first eight years of schooling. Further, most, if not all, of the gap can be explained by socioeconomic differences. Our results suggest that the rising racial test gap in previous studies probably reflects excessive measurement error in testing in the early grades.Accepted manuscrip
Constraints on dark energy and cosmic topology
A non-trivial spatial topology of the Universe is a potentially observable
attribute, which can be probed through the circles-in-the-sky for all locally
homogeneous and isotropic universes with no assumptions on the cosmological
parameters. We show how one can use a possible circles-in-the-sky detection of
the spatial topology of globally homogeneous universes to set constraints on
the dark energy equation of state parameters.Comment: 6 pages, 1 figure. To appear in Int. J. Mod. Phys. A (2009). From a
talk presented at the Seventh Alexander Friedmann International Seminar on
Gravitation and Cosmolog
How Filaments are Woven into the Cosmic Web
Observations indicate galaxies are distributed in a filament-dominated
web-like structure. Numerical experiments at high and low redshift of viable
structure formation theories also show filament-dominance. We present a simple
quantitative explanation of why this is so, showing that the final-state web is
actually present in embryonic form in the overdensity pattern of the initial
fluctuations, with nonlinear dynamics just sharpening the image. The web is
largely defined by the position and primordial tidal fields of rare events in
the medium, with the strongest filaments between nearby clusters whose tidal
tensors are nearly aligned. Applications of the cosmic web theory to
observations include probing cluster-cluster bridges by weak gravitational
lensing, X-rays, and the Sunyaev-Zeldovich effect and probing high redshift
galaxy-galaxy bridges by low column density Lyman alpha absorption lines.Comment: 9 pages, gzipped uuencoded postscript file, 4 figures in separate
files. The text + figures are also available from anonymous ftp site:
ftp://ftp.cita.utoronto.ca/ftp/cita/bond/bkp_natur
CMB Polarization Experiments
We discuss the analysis of polarization experiments with particular emphasis
on those that measure the Stokes parameters on a ring on the sky. We discuss
the ability of these experiments to separate the and contributions to
the polarization signal. The experiment being developed at Wisconsin university
is studied in detail, it will be sensitive to both Stokes parameters and will
concentrate on large scale polarization, scanning a degree ring. We will
also consider another example, an experiment that measures one of the Stokes
parameters in a ring. We find that the small ring experiment will be able
to detect cosmological polarization for some models consistent with the current
temperature anisotropy data, for reasonable integration times. In most
cosmological models large scale polarization is too small to be detected by the
Wisconsin experiment, but because both and are measured, separate
constraints can be set on and polarization.Comment: 27 pages with 12 included figure
Separating the effects of experimental noise from inherent system variability in voltammetry: the Fe(CN) process
Recently, we have introduced the use of techniques drawn from Bayesian
statistics to recover kinetic and thermodynamic parameters from voltammetric
data, and were able to show that the technique of large amplitude ac
voltammetry yielded significantly more accurate parameter values than the
equivalent dc approach. In this paper we build on this work to show that this
approach allows us, for the first time, to separate the effects of random
experimental noise and inherent system variability in voltammetric experiments.
We analyse ten repeated experimental data sets for the Fe(CN)
process, again using large-amplitude ac cyclic voltammetry. In each of the ten
cases we are able to obtain an extremely good fit to the experimental data and
obtain very narrow distributions of the recovered parameters governing both the
faradaic (the reversible formal faradaic potential, , the standard
heterogeneous charge transfer rate constant , and the charge transfer
coefficient ) and non-faradaic terms (uncompensated resistance, ,
and double layer capacitance, ). We then employ hierarchical Bayesian
methods to recover the underlying "hyperdistribution" of the faradaic and
non-faradaic parameters, showing that in general the variation between the
experimental data sets is significantly greater than suggested by individual
experiments, except for where the inter-experiment variation was
relatively minor. Correlations between pairs of parameters are provided, and
for example, reveal a weak link between and (surface activity of
a glassy carbon electrode surface). Finally, we discuss the implications of our
findings for voltammetric experiments more generally.Comment: 30 pages, 6 figure
EXPLORING SUCCESS AND CHALLENGES OF BLACK STUDENTS TAKING AN ENGLISH COURSE ONLINE AT AN URBAN COMMUNITY COLLEGE
Community colleges have expanded access to higher education and were early adopters of online courses. Among literature on online course performance, Black students are least successful in online learning despite being one of the growing populations at community colleges. This case study investigated the experiences of Black community college students taking an online English course for the first time. These experiences were particularly unique because the students participated during the Covid-19 pandemic. The findings indicate that students navigate multiple priorities outside of school, technology challenges, and desire for increased preparation, representation, and support from the campus community. This study assists in expanding the limited research on Black community college students\u27 experiences online. Growing technology adaptation within education necessitates conversation around online learning structure and supports so virtual spaces can be a tool to address existing inequities, so all students reach success
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