15,389 research outputs found
Nonequilibrium flow computations. 1: An analysis of numerical formulations of conservation laws
Modern numerical techniques employing properties of flux Jacobian matrices are extended to general, nonequilibrium flows. Generalizations of the Beam-Warming scheme, Steger-Warming and van Leer Flux-vector splittings, and Roe's approximate Riemann solver are presented for 3-D, time-varying grids. The analysis is based on a thermodynamic model that includes the most general thermal and chemical nonequilibrium flow of an arbitrary gas. Various special cases are also discussed
The Supplemental Nutrition Assistance Program and Nutrient Intakes
The socioeconomic determinants of Food Stamp Program participation and the effects of program participation on nutrient intakes are investigated, using data from the 2003–04 and 2005–06 National Health and Nutrition Examination Survey (NHANES). An endogenous switching regression system of equations is estimated, which includes protein, vitamin A, vitamin C, calcium and iron. Participation in the FSP is found to play an important role in nutrient intakes. Socio-demographic variables such as income, household size and presence of children are also found to affect individuals’ decisions on program participation and nutrient intakes.Food Consumption/Nutrition/Food Safety, Food Security and Poverty,
Optimal Tests of Treatment Effects for the Overall Population and Two Subpopulations in Randomized Trials, using Sparse Linear Programming
We propose new, optimal methods for analyzing randomized trials, when it is
suspected that treatment effects may differ in two predefined subpopulations.
Such sub-populations could be defined by a biomarker or risk factor measured at
baseline. The goal is to simultaneously learn which subpopulations benefit from
an experimental treatment, while providing strong control of the familywise
Type I error rate. We formalize this as a multiple testing problem and show it
is computationally infeasible to solve using existing techniques. Our solution
involves a novel approach, in which we first transform the original multiple
testing problem into a large, sparse linear program. We then solve this problem
using advanced optimization techniques. This general method can solve a variety
of multiple testing problems and decision theory problems related to optimal
trial design, for which no solution was previously available. In particular, we
construct new multiple testing procedures that satisfy minimax and Bayes
optimality criteria. For a given optimality criterion, our new approach yields
the optimal tradeoff? between power to detect an effect in the overall
population versus power to detect effects in subpopulations. We demonstrate our
approach in examples motivated by two randomized trials of new treatments for
HIV
Tradeoff between Smoother and Sooner "Little Rip"
There exists dark energy models that predict the occurrence of "little rip".
At the point of little rip the Hubble rate and its cosmic time derivative
approach infinity, which is quite similar to the big rip singularity except
that the former happens at infinite future while the latter at a finite cosmic
time; both events happen in the future and at high energies. In the case of the
big rip, a combination of ultra-violet and infra-red effects can smooth its
doomsday. We therefore wonder if the little rip can also be smoothed in a
similar way. We address the ultra-violet and infra-red effects in general
relativity through a brane-world model with a Gauss-Bonnet term in the bulk and
an induced gravity term on the brane. We find that the little rip is
transformed in this case into a sudden singularity, or a "big brake". Even
though the big brake is smoother than the little rip in that the Hubble rate is
finite at the event, the trade-off is that it takes place sooner, at a finite
cosmic time. In our estimate, the big brake would happen at roughly 1300Gyr.Comment: 9 pages, 4 figures. RevTex4-1. Title modified and discussion
expanded. Version accepted in European Physical Journal
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