46,961 research outputs found
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
The effect of massed compared with massed followed by evenly spaced practice on the learning of a motor skill
Thesis (Ed.M.)--Boston Universit
Modelling fat and protein concentration curves for Irish dairy cows
peer-reviewedThe objective of this study was to acquire a well-fitting, single-equation model that would represent the fat and protein concentration curves of milk from Irish dairy cows. The dataset consisted of 16,086 records from both spring and autumn calving cows from both experimental and commercial herds. Many models cited in the literature to represent milk yield were examined for their suitability to model constituent curves. Models were tested for goodness-of-fit, adherence to the assumptions of regression analysis, and their ability to predict total fat and protein concentration for an entire lactation. Wilmink’s model best satisfied these criteria. It had the best Mean Square Prediction Error (goodness-of-fit) value, it satisfied the assumptions of regression analysis (multicollinearity, heteroskedasticity, autocorrelation and normality of distribution), and it predicted the actual concentration of the constituents to within 0.01 percentage point
- …