2,297 research outputs found
SUPPLY RESPONSE AND IMPACT OF GOVERNMENT-SUPPORTED CROPS ON THE TEXAS VEGETABLE INDUSTRY
Supply functions, elasticity estimates, and nonjointness test results consistently indicated that few commodities compete economically in the production of six major Texas vegetables (cabbage, cantaloupes, carrots, onions, potatoes, and watermelons). Significant bias effects caused by government-supported commodities, fixed inputs, and technological change were observed and measured. Nonnested test results for the hypothesis of sequential decision making by vegetable producers were inconclusive, but they gave greater likelihood support to sequential than to contemporaneous decision making.Demand and Price Analysis,
A model based framework for air quality indices and population risk evaluation, with an application to the analysis of Scottish air quality data
The paper is devoted to the development of a statistical framework for air quality assessment at the country level and for the evaluation of the ambient population exposure and risk with respect to airborne pollutants. The framework is based on a multivariate space–time model and on aggregated indices defined at different levels of aggregation in space and time. The indices are evaluated, uncertainty included, by considering both the model outputs and the information on the population spatial distribution. The framework is applied to the analysis of air quality data for Scotland for 2009 referring to European and Scottish air quality legislation
Biexciton recombination rates in self-assembled quantum dots
The radiative recombination rates of interacting electron-hole pairs in a
quantum dot are strongly affected by quantum correlations among electrons and
holes in the dot. Recent measurements of the biexciton recombination rate in
single self-assembled quantum dots have found values spanning from two times
the single exciton recombination rate to values well below the exciton decay
rate. In this paper, a Feynman path-integral formulation is developed to
calculate recombination rates including thermal and many-body effects. Using
real-space Monte Carlo integration, the path-integral expressions for realistic
three-dimensional models of InGaAs/GaAs, CdSe/ZnSe, and InP/InGaP dots are
evaluated, including anisotropic effective masses. Depending on size, radiative
rates of typical dots lie in the regime between strong and intermediate
confinement. The results compare favorably to recent experiments and
calculations on related dot systems. Configuration interaction calculations
using uncorrelated basis sets are found to be severely limited in calculating
decay rates.Comment: 11 pages, 4 figure
Molecular Dynamics Simulations of a Pressure-induced Glass Transition
We simulate the compression of a two-component Lennard-Jones liquid at a
variety of constant temperatures using a molecular dynamics algorithm in an
isobaric-isothermal ensemble. The viscosity of the liquid increases with
pressure, undergoing a broadened transition into a structurally arrested,
amorphous state. This transition, like the more familiar one induced by
cooling, is correlated with a significant increase in icosahedral ordering. In
fact, the structure of the final state, as measured by an analysis of the
bonding, is essentially the same in the glassy, frozen state whether produced
by squeezing or by cooling under pressure. We have computed an effective
hard-sphere packing fraction at the transition, defining the transition
pressure or temperature by a cutoff in the diffusion constant, analogous to the
traditional laboratory definition of the glass transition by an arbitrary, low
cutoff in viscosity. The packing fraction at this transition point is not
constant, but is consistently higher for runs compressed at higher temperature.
We show that this is because the transition point defined by a constant cutoff
in the diffusion constant is not the same as the point of structural arrest, at
which further changes in pressure induce no further structural changes, but
that the two alternate descriptions may be reconciled by using a thermally
activated cutoff for the diffusion constant. This enables estimation of the
characteristic activation energy for diffusion at the point of structural
arrest.Comment: Latex using Revtex macro
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