Ray tracing of Jovian low frequency radiation

The radio emission from Jupiter in the decametric range (2 to 40 MHz) has been studied for three decades. It is known that this emission is correlated with particular longitude regions on the planet and with the position of the satellite Io. The Planetary Radio Astronomy experiment on the Voyager 1 and 2 spacecraft observed this emission, obtaining valuable new information. The objectives of this study are as follows: (1) calculate raypaths for decametric wavelength radiation in Jupiter's magnetosphere; (2) compare the model-dependent raypaths with the Voyager observations; and (3) deduce characteristics of the source regions and the influence of propagation effects

Workplace Accommodations for Persons with Musculoskeletal Disorders

This brochure is one of a series on human resources practices and workplace accommodations for persons with disabilities edited by Susanne M. Bruyère, Ph.D., CRC, Director, Employment and Disability Institute, Cornell University ILR School. The original was written by Frank N. Morosky, M.S., P.T., the coordinator of the Cornell University Back Injury Prevention Program, Ithaca, NY. It was revised and updated in 2000, and again in 2010, by Sheryl Ulin, Ph.D., CPE, Research Investigator, The University of Michigan Center for Ergonomics. It recieved legal review in 2011 by Beth Reiter, an independent legal consultant from Ithaca, N.Y., with assistance from Sara Furguson, a Cornell University Employment and Disability Institute student research assistant

CURRENT ISSUES IN FOOD DISTRIBUTION

The most serious problem in food distribution is productivity.Agribusiness,

Is Social Security behind the Collapse of Personal Saving?

This paper considers the quantitative role of growth in the size of the social security program in contributing to the collapse of personal saving in the U.S. over the last few decades. Using a calibrated, general equilibrium life-cycle model this paper shows that social security may not be to blame. Specifically, the model predicts that a 50-percent increase in the social security tax rate (as in the U.S. over the last half century) produces a modest decline in the personal saving rate from 10 percent down to 9.6 percent. This result runs counter to some popular opinion.NIPA personal saving rate, social security, life-cycle permanent-income model, general equilibrium calibration

Destabilization of rotating flows with positive shear by azimuthal magnetic fields

According to Rayleigh's criterion, rotating flows are linearly stable when their specific angular momentum increases radially outward. The celebrated magnetorotational instability opens a way to destabilize those flows, as long as the angular velocity is decreasing outward. Using a short-wavelength approximation we demonstrate that even flows with very steep positive shear can be destabilized by azimuthal magnetic fields which are current-free within the fluid. We illustrate the transition of this instability to a rotationally enhanced kink-type instability in case of a homogeneous current in the fluid, and discuss the prospects for observing it in a magnetized Taylor-Couette flow.Comment: 4 pages, 4 figur

Standard and helical magnetorotational instability: How singularities create paradoxal phenomena in MHD

The magnetorotational instability (MRI) triggers turbulence and enables outward transport of angular momentum in hydrodynamically stable rotating shear flows, e.g., in accretion disks. What laws of differential rotation are susceptible to the destabilization by axial, azimuthal, or helical magnetic field? The answer to this question, which is vital for astrophysical and experimental applications, inevitably leads to the study of spectral and geometrical singularities on the instability threshold. The singularities provide a connection between seemingly discontinuous stability criteria and thus explain several paradoxes in the theory of MRI that were poorly understood since the 1950s.Comment: 25 pages, 10 figures. A tutorial paper. Invited talk at SPT 2011, Symmetry and Perturbation Theory, 5 - 12 June 2011, Otranto near Lecce (Italy

Extending the range of the inductionless magnetorotational instability

The magnetorotational instability (MRI) can destabilize hydrodynamically stable rotational flows, thereby allowing angular momentum transport in accretion disks. A notorious problem for MRI is its questionable applicability in regions with low magnetic Prandtl number, as they are typical for protoplanetary disks and the outer parts of accretion disks around black holes. Using the WKB method, we extend the range of applicability of MRI by showing that the inductionless versions of MRI, such as the helical MRI and the azimuthal MRI, can easily destabilize Keplerian profiles ~ 1/r^(3/2) if the radial profile of the azimuthal magnetic field is only slightly modified from the current-free profile ~ 1/r. This way we further show how the formerly known lower Liu limit of the critical Rossby number, Ro=-0.828, connects naturally with the upper Liu limit, Ro=+4.828.Comment: Growth rates added, references modified; submitted to Physical Review Letter

Input window size and neural network predictors

Neural network approaches to time series prediction are briefly discussed, and the need to specify an appropriately sized input window identified. Relevant theoretical results from dynamic systems theory are briefly introduced, and heuristics for finding the correct embedding dimension, and hence window size, are discussed. The method is applied to two time series and the resulting generalisation performance of the trained feedforward neural network predictors is analysed. It is shown that the heuristics can provide useful information in defining the appropriate network architectur

The effect of massed compared with massed followed by evenly spaced practice on the learning of a motor skill

Thesis (Ed.M.)--Boston Universit