8,441 research outputs found
Density Functional Calculations On First-Row Transition Metals
The excitation energies and ionization potentials of the atoms in the first
transition series are notoriously difficult to compute accurately. Errors in
calculated excitation energies can range from 1--4 eV at the Hartree-Fock
level, and errors as high as 1.5eV are encountered for ionization energies. In
the current work we present and discuss the results of a systematic study of
the first transition series using a spin-restricted Kohn-Sham
density-functional method with the gradient-corrected functionals of Becke and
Lee, Yang and Parr. Ionization energies are observed to be in good agreement
with experiment, with a mean absolute error of approximately 0.15eV; these
results are comparable to the most accurate calculations to date, the Quadratic
Configuration Interaction (QCISD(T)) calculations of Raghavachari and Trucks.
Excitation energies are calculated with a mean error of approximately 0.5eV,
compared with \sim 1\mbox{eV} for the local density approximation and 0.1eV
for QCISD(T). These gradient-corrected functionals appear to offer an
attractive compromise between accuracy and computational effort.Comment: Journal of Chemical Physics, 29, LA-UR-93-425
The sciences in America, circa 1880
For many years American science in the late 19th century was regarded as an intellectual backwater. This view derived from the assumption that the health of American science at the time was equivalent to the condition of pure science, especially pure physics. However, a closer look reveals that there was considerable vitality in American scientific research, especially in the earth and life sciences. This vitality is explainable in part by the natural scientific resources of the American continent but also in part by the energy given science from religious impulses, social reformism, and practicality. Furthermore, contrary to recent assumptions, the federal government was a significant patron of American science. The portrait of American science circa 1880 advanced in this article suggests that the nation's scientific enterprise was characterized by pluralism of institutional support and motive and that such pluralism has historically been the normal mode
Tuning density profiles and mobility of inhomogeneous fluids
Density profiles are the most common measure of inhomogeneous structure in
confined fluids, but their connection to transport coefficients is poorly
understood. We explore via simulation how tuning particle-wall interactions to
flatten or enhance the particle layering of a model confined fluid impacts its
self-diffusivity, viscosity, and entropy. Interestingly, interactions that
eliminate particle layering significantly reduce confined fluid mobility,
whereas those that enhance layering can have the opposite effect. Excess
entropy helps to understand and predict these trends.Comment: 5 pages, 3 figure
Impact of surface roughness on diffusion of confined fluids
Using event-driven molecular dynamics simulations, we quantify how the self
diffusivity of confined hard-sphere fluids depends on the nature of the
confining boundaries. We explore systems with featureless confining boundaries
that treat particle-boundary collisions in different ways and also various
types of physically (i.e., geometrically) rough boundaries. We show that, for
moderately dense fluids, the ratio of the self diffusivity of a rough wall
system to that of an appropriate smooth-wall reference system is a linear
function of the reciprocal wall separation, with the slope depending on the
nature of the roughness. We also discuss some simple practical ways to use this
information to predict confined hard-sphere fluid behavior in different
rough-wall systems
Development of non-dissipative numerical schemes for computational aeroacoustics
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76586/1/AIAA-1993-3382-851.pd
Composition and concentration anomalies for structure and dynamics of Gaussian-core mixtures
We report molecular dynamics simulation results for two-component fluid
mixtures of Gaussian-core particles, focusing on how tracer diffusivities and
static pair correlations depend on temperature, particle concentration, and
composition. At low particle concentrations, these systems behave like simple
atomic mixtures. However, for intermediate concentrations, the single-particle
dynamics of the two species largely decouple, giving rise to the following
anomalous trends. Increasing either the concentration of the fluid (at fixed
composition) or the mole fraction of the larger particles (at fixed particle
concentration) enhances the tracer diffusivity of the larger particles, but
decreases that of the smaller particles. In fact, at sufficiently high particle
concentrations, the larger particles exhibit higher mobility than the smaller
particles. Each of these dynamic behaviors is accompanied by a corresponding
structural trend that characterizes how either concentration or composition
affects the strength of the static pair correlations. Specifically, the dynamic
trends observed here are consistent with a single empirical scaling law that
relates an appropriately normalized tracer diffusivity to its pair-correlation
contribution to the excess entropy.Comment: 5 pages, 4 figure
ECONOMICALLY OPTIMAL WILDFIRE INTERVENTION REGIMES
Wildfires in the United States result in total damages and costs that are likely to exceed billions of dollars annually. Land managers and policy makers propose higher rates of prescribed burning and other kinds of vegetation management to reduce amounts of wildfire and the risks of catastrophic losses. A wildfire public welfare maximization function, using a wildfire production function estimated using a time series model of a panel of Florida counties, is employed to simulate the publicly optimal level of prescribed burning in an example county in Florida (Volusia). Evaluation of the production function reveals that prescribed fire is not associated with reduced catastrophic wildfire risks in Volusia County Florida, indicating a short-run elasticity of -0.16 and a long-run elasticity of wildfire with respect to prescribed fire of -0.07. Stochastic dominance is used to evaluate the optimal amount of prescribed fire most likely to maximize a measure of public welfare. Results of that analysis reveal that the optimal amount of annual prescribed fire is about 3 percent (9,000 acres/year) of the total forest area, which is very close to the actual average amount of prescribed burning (12,700 acres/year) between 1994-99.Resource /Energy Economics and Policy,
Detecting rare gene transfer events in bacterial populations
This Document is Protected by copyright and was first published by Frontiers. All rights reserved. it is reproduced with permissio
Accurate schemes for advection and aeroacoustics
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76639/1/AIAA-1997-2091-481.pd
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