27,367 research outputs found
Innovative Opportunities for Elementary and Middle School Teachers to Maintain Currency in Mathematics and Science: A Community College-School System Partnership
Since 1992 the Manassas Campus of Northern Virginia Community College – in response to requests from local school systems – has developed four innovative methods of assisting elementary, secondary and middle school teachers to enhance their content knowledge in science and mathematics, as well as integrate curriculum units for classroom presentation. These methods are based on the assumptions that: - While teachers at this level have fundamental understanding of math and science, if they wish to incorporate new concepts or technologies from these fields, graduate level content courses are generally beyond their background level. - Community College faculty can often provide a bridge that connects advanced content in science and mathematics with the applications that can be adapted to elementary/middle school curriculum. - Presenting content to a mixed audience of teachers from K-8 allows teachers to see how content can be adapted to grade levels above and below. - Content delivery methods must be interactive and must be responsive to the multiple demands on these teachers’ time. This requires flexibility in scheduling and course requirements
MOSFIRE Absorption Line Spectroscopy of z > 2 Quiescent Galaxies: Probing a Period of Rapid Size Growth
Using the MOSFIRE near-infrared multi-slit spectrograph on the Keck 1
Telescope, we have secured high signal-to-noise ratio absorption line spectra
for six massive galaxies with redshift 2 < z < 2.5. Five of these galaxies lie
on the red sequence and show signatures of passive stellar populations in their
rest-frame optical spectra. By fitting broadened spectral templates we have
determined stellar velocity dispersions and, with broad-band HST and Spitzer
photometry and imaging, stellar masses and effective radii. Using this enlarged
sample of galaxies we confirm earlier suggestions that quiescent galaxies at z
> 2 have small sizes and large velocity dispersions compared to local galaxies
of similar stellar mass. The dynamical masses are in very good agreement with
stellar masses (log Mstar/Mdyn = -0.02 +/- 0.03), although the average
stellar-to-dynamical mass ratio is larger than that found at lower redshift
(-0.23 +/- 0.05). By assuming evolution at fixed velocity dispersion, not only
do we confirm a surprisingly rapid rate of size growth but we also consider the
necessary evolutionary track on the mass-size plane and find a slope alpha =
dlogR / dlogM > ~2 inconsistent with most numerical simulations of minor
mergers. Both results suggest an additional mechanism may be required to
explain the size growth of early galaxies.Comment: Updated to match the published versio
Gluino Condensation in Strongly Coupled Heterotic String Theory
Strongly coupled heterotic string theory, compactified to
four dimensions on a large Calabi-Yau manifold , may represent a
viable candidate for the description of low-energy particle phenomenology. In
this regime, heterotic string theory is adequately described by low-energy
-theory on , with the two
's supported at the two boundaries of the world. In this paper we study
the effects of gluino condensation, as a mechanism for supersymmetry breaking
in this -theory regime. We show that when a gluino condensate forms in
-theory, the conditions for unbroken supersymmetry can still be satisfied
locally in the orbifold dimension . Supersymmetry is then
only broken by the global topology of the orbifold dimension, in a mechanism
similar to the Casimir effect. This mechanism leads to a natural hierarchy of
scales, and elucidates some aspects of heterotic string theory that might be
relevant to the stabilization of moduli and the smallness of the cosmological
constant.Comment: 22 pages, harvmac, no figure
A Gauge-invariant Analysis of Magnetic Fields in General Relativistic Cosmology
We provide a fully general-relativistic treatment of cosmological
perturbations in a universe permeated by a large-scale primordial magnetic
field, using the Ellis-Bruni gauge-invariant formalism. The exact non-linear
equations for general relativistic magnetohydrodynamic evolution are derived. A
number of applications are made: the behaviour of small perturbations to
Friedmann universes are studied; a comparison is made with earlier Newtonian
treatments of cosmological perturbations and some effects of inflationary
expansion are examined.Comment: 31 pages, Latex, Submitted to Classical and Quantum Gravit
Image restoration and superresolution as probes of small scale far-IR structure in star forming regions
Far-infrared continuum studies from the Kuiper Airborne Observatory are described that are designed to fully exploit the small-scale spatial information that this facility can provide. This work gives the clearest picture to data on the structure of galactic and extragalactic star forming regions in the far infrared. Work is presently being done with slit scans taken simultaneously at 50 and 100 microns, yielding one-dimensional data. Scans of sources in different directions have been used to get certain information on two dimensional structure. Planned work with linear arrays will allow us to generalize our techniques to two dimensional image restoration. For faint sources, spatial information at the diffraction limit of the telescope is obtained, while for brighter sources, nonlinear deconvolution techniques have allowed us to improve over the diffraction limit by as much as a factor of four. Information on the details of the color temperature distribution is derived as well. This is made possible by the accuracy with which the instrumental point-source profile (PSP) is determined at both wavelengths. While these two PSPs are different, data at different wavelengths can be compared by proper spatial filtering. Considerable effort has been devoted to implementing deconvolution algorithms. Nonlinear deconvolution methods offer the potential of superresolution -- that is, inference of power at spatial frequencies that exceed D lambda. This potential is made possible by the implicit assumption by the algorithm of positivity of the deconvolved data, a universally justifiable constraint for photon processes. We have tested two nonlinear deconvolution algorithms on our data; the Richardson-Lucy (R-L) method and the Maximum Entropy Method (MEM). The limits of image deconvolution techniques for achieving spatial resolution are addressed
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Rice marketing in Indonesia: Methodology, results and implications of a research study
There is a continuing trend in developing countries, as elsewhere, to devolve activities which have hitherto been performed by the public sector to the private sector, and to less regulated markets. The marketing of staple foods is no exception to this trend, but it raises important issues about national food security, price stability, and the protection of poor people from price rises which could mean malnutrition or starvation. Rice Marketing in Indonesia describes a research project which explores these issues in depth for a staple food commodity in a large developing country. The research focuses on seasonal rice price formation, on storage and sales decisions by farmers and traders, and on competition and efficiency in marketing channels. The research approach, which involves tracing marketing chains from sample farmers, is likely to be of interest to all those concerned with studying the liberalization of food markets in developing countries
Flavor and Spin Contents of the Nucleon in the Quark Model with Chiral Symmetry
A simple calculation in the framework of the chiral quark theory of Manohar
and Georgi yields results that can account for many of the ''failures'' of the
naive quark model: significant strange quark content in the nucleon as
indicated by the value of the -
asymmetry in the nucleon as measured by the deviation from Gottfried sum rule
and by the Drell-Yan process, as well as the various quark contributions to the
nucleon spin as measured by the deep inelastic polarized lepton-nucleon
scatterings.Comment: figure has been separated from tex file. No other changes. Preprint
CMU-HEP94-3
Stability of attitude control systems acted upon by random perturbations
Mathematical models on stability of attitude control systems acted upon by random perturbation processe
Lensing and caustic effects on cosmological distances
We consider the changes which occur in cosmological distances due to the
combined effects of some null geodesics passing through low-density regions
while others pass through lensing-induced caustics. This combination of effects
increases observed areas corresponding to a given solid angle even when
averaged over large angular scales, through the additive effect of increases on
all scales, but particularly on micro-angular scales; however angular sizes
will not be significantly effected on large angular scales (when caustics
occur, area distances and angular-diameter distances no longer coincide). We
compare our results with other works on lensing, which claim there is no such
effect, and explain why the effect will indeed occur in the (realistic)
situation where caustics due to lensing are significant. Whether or not the
effect is significant for number counts depends on the associated angular
scales and on the distribution of inhomogeneities in the universe. It could
also possibly affect the spectrum of CBR anisotropies on small angular scales,
indeed caustics can induce a non-Gaussian signature into the CMB at small
scales and lead to stronger mixing of anisotropies than occurs in weak lensing.Comment: 28 pages, 6 ps figures, eps
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