15,134 research outputs found
Analysis of a Precambrian resonance-stabilized day length
During the Precambrian era, Earth's decelerating rotation would have passed a
21-hour period that would have been resonant with the semidiurnal atmospheric
thermal tide. Near this point, the atmospheric torque would have been
maximized, being comparable in magnitude but opposite in direction to the lunar
torque, halting Earth's rotational deceleration, maintaining a constant day
length, as detailed by Zahnle and Walker (1987). We develop a computational
model to determine necessary conditions for formation and breakage of this
resonant effect. Our simulations show the resonance to be resilient to
atmospheric thermal noise but suggest a sudden atmospheric temperature increase
like the deglaciation period following a possible "snowball Earth" near the end
of the Precambrian would break this resonance; the Marinoan and Sturtian
glaciations seem the most likely candidates for this event. Our model provides
a simulated day length over time that resembles existing paleorotational data,
though further data is needed to verify this hypothesis.Comment: 7 pages, 5 figures. Accepted for publication in Geophysical Research
Letters on 10 May 201
A Guide to Disability Statistics from the National Health Interview Survey
The purpose of this paper is to examine the information on the population with disabilities in a nationally representative survey conducted by the National Center on Health Statistics called the National Health Interview Survey (NHIS). The paper provides a description of the disability information available in the NHIS and how the data may be used to assess the employment, economic well being and health of the population. Descriptive statistics from the 2002 NHIS public use files are used to illustrate the type of analysis that will be useful to researchers and policymakers
Bayesian Optimal Design for Ordinary Differential Equation Models
Bayesian optimal design is considered for experiments where it is hypothesised that the responses are described by the intractable solution to a system of non-linear ordinary differential equations (ODEs). Bayesian optimal design is based on the minimisation of an expected loss function where the expectation is with respect to all unknown quantities (responses and parameters). This expectation is typically intractable even for simple models before even considering the intractability of the ODE solution. New methodology is developed for this problem that involves minimising a smoothed stochastic approximation to the expected loss and using a state-of-the-art stochastic solution to the ODEs, by treating the ODE solution as an unknown quantity. The methodology is demonstrated on three illustrative examples and a real application involving estimating the properties of human placentas
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Approximate Strategyproofness
The standard approach of mechanism design theory insists on equilibrium behavior by participants. This assumption is captured by imposing incentive constraints on the design space. But in bridging from theory to practice, it often becomes necessary to relax incentive constraints in order to allow tradeoffs with other desirable properties. This article surveys a number of different options that can be adopted in relaxing incentive constraints, providing a current view of the state-of-the-art.Engineering and Applied Science
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