82,499 research outputs found
Hybrid geared traction transmissions
The basic configuration of geared traction drives, geometric and structural factors to be considered in their construction, and current work on hybrid helicopter transmissions rated at 500 and 3000 hp are discussed
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The area around the Orion Nebula observed in the CO (J = 1- 0) transition
An area 1 deg2 around the Orion Nebula has been surveyed with a 2.6 km s-1 wide single-channel receiver. The map shows considerable structure in the east including a bright spot 24' (2.8 pc) from the main CO peak
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Navigating the Turbulent Waters of School Reform Guided by Complexity Theory
The goal of this research study has been to develop, implement, and evaluate a school reform design experiment at a continuation high school with low-income, low-performing underrepresented minority students. The complexity sciences served as a theoretical framework for this design experiment. Treating an innovative college preparatory program as a nested complex adaptive system within a larger complex adaptive system, the school, we used features of complex adaptive systems (equilibrium, emergence, self-organization, and feedback loops) as a framework to design a strategy for school reform. The goal was to create an environment for change by pulling the school far from equilibrium using a strategy we call “purposeful perturbations” to disrupt the stable state of the school in a purposeful way. Over the four years of the study, several tipping points were reached, and we developed agent-based simulation models that capture important dynamic properties of the reform at these points. The study draws upon complexity theory in multiple ways that have supported improved education for low-achieving students
Topological Change in Mean Convex Mean Curvature Flow
Consider the mean curvature flow of an (n+1)-dimensional, compact, mean
convex region in Euclidean space (or, if n<7, in a Riemannian manifold). We
prove that elements of the m-th homotopy group of the complementary region can
die only if there is a shrinking S^k x R^(n-k) singularity for some k less than
or equal to m. We also prove that for each m from 1 to n, there is a nonempty
open set of compact, mean convex regions K in R^(n+1) with smooth boundary for
which the resulting mean curvature flow has a shrinking S^m x R^(n-m)
singularity.Comment: 19 pages. This version includes a new section proving that certain
kinds of mean curvature flow singularities persist under arbitrary small
perturbations of the initial surface. Newest update (Oct 2013) fixes some
bibliographic reference
Detection of coherent beam-beam modes with digitized beam position monitor signals
A system for bunch-by-bunch detection of transverse proton and antiproton
coherent oscillations in the Fermilab Tevatron collider is described. It is
based on the signal from a single beam-position monitor located in a region of
the ring with large amplitude functions. The signal is digitized over a large
number of turns and Fourier-analyzed offline with a dedicated algorithm. To
enhance the signal, band-limited noise is applied to the beam for about 1 s.
This excitation does not adversely affect the circulating beams even at high
luminosities. The device has a response time of a few seconds, a frequency
resolution of in fractional tune, and it is sensitive to
oscillation amplitudes of 60 nm. It complements Schottky detectors as a
diagnostic tool for tunes, tune spreads, and beam-beam effects. Measurements of
coherent mode spectra are presented and compared with models of beam-beam
oscillations.Comment: 7 pages, 4 figures. Submitted to the Proceedings of the ICFA
Mini-Workshop on Beam-beam Effects in Hadron Colliders (BB2013), Geneva,
Switzerland, 18-22 March 201
Resolving the virial discrepancy in clusters of galaxies with modified Newtonian dynamics
A sample of 197 X-ray emitting clusters of galaxies is considered in the
context of Milgrom's modified Newtonian dynamics (MOND). It is shown that the
gas mass, extrapolated via an assumed model to a fixed radius of 3 Mpc,
is correlated with the gas temperature as predicted by MOND (). The observed temperatures are generally consistent with the inferred
mass of hot gas; no substantial quantity of additional unseen matter is
required in the context of MOND. However, modified dynamics cannot resolve the
strong lensing discrepancy in those clusters where this phenomenon occurs. The
prediction is that additional baryonic matter may be detected in the central
regions of rich clusters.Comment: Submitted to A&A, 4 pages, 3 figures, A&A macro
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