9,204 research outputs found
Research on new techniques for the analysis of manual control systems Progress report, 16 Jun. - 15 Dec. 1968
Parameter estimation for continuous input-output systems with internal sampling in human controller model
Black Hole Motion as Catalyst of Orbital Resonances
The motion of a black hole about the centre of gravity of its host galaxy
induces a strong response from the surrounding stellar population. We treat the
case of a harmonic potential analytically and show that half of the stars on
circular orbits in that potential shift to an orbit of lower energy, while the
other half receive a positive boost and recede to a larger radius. The black
hole itself remains on an orbit of fixed amplitude and merely acts as a
catalyst for the evolution of the stellar energy distribution function f(E). We
show that this effect is operative out to a radius of approx 3 to 4 times the
hole's influence radius, R_bh. We use numerical integration to explore more
fully the response of a stellar distribution to black hole motion. We consider
orbits in a logarithmic potential and compare the response of stars on circular
orbits, to the situation of a `warm' and `hot' (isotropic) stellar velocity
field. While features seen in density maps are now wiped out, the kinematic
signature of black hole motion still imprints the stellar line-of-sight mean
velocity to a magnitude ~18% the local root mean-square velocity dispersion
sigma.Comment: revised version, typos fixed, added references, 20 pages MN styl
Research on new techniques for the analysis of manual control systems Progress report, 15 Dec. 1968 - 15 Jun. 1969
Decision processes of human manual controllers, neuromuscular system, and stochastic processe
Gravitational waves from galaxy encounters
We discuss the emission of gravitational radiation produced in encounters of
dark matter galactic halos. To this aim we perform a number of numerical
simulations of typical galaxy mergers, computing the associated gravitational
radiation waveforms as well as the energy released in the processes. Our
simulations yield dimensionless gravitational wave amplitudes of the order of
and gravitational wave frequencies of the order of Hz,
when the galaxies are located at a distance of 10 Mpc. These values are of the
same order as those arising in the gravitational radiation originated by strong
variations of the gravitational field in the early Universe, and therefore,
such gravitational waves cannot be directly observed by ground-based detectors.
We discuss the feasibility of an indirect detection by means of the B-mode
polarization of the Cosmic Microwave Background (CMB) induced by such waves.
Our results show that the gravitational waves from encounters of dark matter
galactic halos leave much too small an imprint on the CMB polarization to be
actually observed with ongoing and future missions.Comment: 9 pages with revtex style, 3 ps figures; to be published in Physical
Review
Instability of the Gravitational N-Body Problem in the Large-N Limit
We use a systolic N-body algorithm to evaluate the linear stability of the
gravitational N-body problem for N up to 1.3 x 10^5, two orders of magnitude
greater than in previous experiments. For the first time, a clear ~ln
N-dependence of the perturbation growth rate is seen. The e-folding time for N
= 10^5 is roughly 1/20 of a crossing time.Comment: Accepted for publication in The Astrophysical Journa
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Effect of a Fruit and Vegetable Prescription Program on Children's Fruit and Vegetable Consumption.
IntroductionMost children in families with low income do not meet dietary guidance on fruit and vegetable consumption. Fruit and vegetable prescription programs improve access to and affordability of health-supporting foods for adults, but their effect on dietary behavior among children is not known. The objective of this study was to describe the extent to which exposure to a fruit and vegetable prescription program was associated with changes in consumption among participants aged 2 to 18.MethodsWe used data from a modified National Cancer Institute screener to calculate fruit and vegetable intake among 883 children who were overweight or had obesity and participated in a 4- to 6-month fruit and vegetable prescription program at federally qualified health centers during 4 years (2012-2015). Secondary analyses in 2017 included paired t tests to compare change in fruit and vegetable consumption (cups/day) between first and last visits and multivariable linear regressions, including propensity dose-adjusted models, to model this change as a function of sociodemographic and program-specific covariates, such as number of clinical visits and value of prescription redemption.ResultsWe found a dose propensity-adjusted increase of 0.32 cups (95% confidence interval, 0.19-0.45 cups) for each additional visit while holding constant the predicted number of visits and site. An equal portion of the change-score increase was attributed to vegetable consumption and fruit consumption (β = 0.16 for each).ConclusionFruit and vegetable prescription programs in clinical settings may increase fruit and vegetable consumption among children in low-income households. Future research should use a comparison group and consider including qualitative analysis of site-specific barriers and facilitators to success
An asynchronous pulse-amplitude pulse-width model of the human operator
Asynchronous pulse amplitude pulse width model of human operato
115 DEGRADATION TO SYNTHESIS RATIOS OF TYPE II COLLAGEN BIOMARKERS IN SYNOVIAL FLUID AND SERUM IN THOROUGHBRED RACEHORSES
Arthropod Fauna Associated with Wild and Cultivated Cranberries in Wisconsin
The cranberry (Vaccinium macrocarpon Aiton) is an evergreen, trailing shrub native to North American peatlands. It is cultivated commercially in the US and Canada, with major production centers in Wisconsin, Massachusetts, New Jersey, Washington, Québec, and British Columbia. Despite the agricultural importance of cranberry in Wisconsin, relatively little is known of its arthropod associates, particularly the arachnid fauna. Here we report preliminary data on the insect and spider communities associated with wild and cultivated cranberries in Wisconsin. We then compare the insect and spider communities of wild cranberry systems to those of cultivated cranberries, indexed by region. Approximately 7,400 arthropods were curated and identified, spanning more than 100 families, across 11 orders. The vast majority of specimens and diversity derived from wild ecosystems. In both the wild and cultivated systems, the greatest numbers of families were found among the Diptera (midges, flies) and Hymenoptera (bees, ants, wasps), but numerically, the Hymenoptera and Araneae (spiders) were dominant. Within the spider fauna, 18 new county records, as well as a new Wisconsin state record (Linyphiidae: Ceratinopsis laticeps (Em.)), were documented. While more extensive sampling will be needed to better resolve arthropod biodiversity in North American cranberry systems, our findings represent baseline data on the breadth of arthropod diversity in the Upper Midwest, USA
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