6,909 research outputs found
A double-helix neutron detector using micron-size B-10 powder
A double-helix electrode configuration is combined with a B powder
coating technique to build large-area (9 in 36 in) neutron detectors.
The neutron detection efficiency for each of the four prototypes is comparable
to a single 2-bar He drift tube of the same length (36 in). One unit has
been operational continuously for 18 months and the change of efficiency is
less than 1%. An analytic model for pulse heigh spectra is described and the
predicted mean film thickness agrees with the experiment to within 30%. Further
detector optimization is possible through film texture, power size, moderator
box and gas. The estimated production cost per unit is less than 3k US\$ and
the technology is thus suitable for deployment in large numbers
AN ANALYSIS OF CONSUMER CHARACTERISTICS CONCERNING DIRECT MARKETING OF FRESH PRODUCE IN DELAWARE: A CASE STUDY
Consumer/Household Economics, Marketing,
AN ANALYSIS OF CONSUMERS' VIEWS AND PREFERENCES REGARDING FARMER TO CONSUMER DIRECT MARKETS IN DELAWARE
Consumer/Household Economics,
AN ANALYSIS OF HOUSEHOLD CONSUMPTION OF FRESH POTATOES IN DELAWARE
Food Consumption/Nutrition/Food Safety,
CONSUMER, WHOLESALER AND RETAILER PERCEPTIONS ABOUT SELECTED MARKETING ISSUES CONCERNING FRESH FISH AND SEAFOOD PRODUCTS
Consumer/Household Economics, Marketing,
Boom and Bust Carbon-Nitrogen Dynamics during Reforestation
Legacies of historical land use strongly shape contemporary ecosystem dynamics. In old-field secondary forests, tree growth embodies a legacy of soil changes affected by previous cultivation. Three patterns of biomass accumulation during reforestation have been hypothesized previously, including monotonic to steady state, non-monotonic with a single peak then decay to steady state, and multiple oscillations around the steady state. In this paper, the conditions leading to the emergence of these patterns is analyzed. Using observations and models, we demonstrate that divergent reforestation patterns can be explained by contrasting time-scales in ecosystem carbon-nitrogen cycles that are influenced by land use legacies. Model analyses characterize non-monotonic plant-soil trajectories as either single peaks or multiple oscillations during an initial transient phase controlled by soil carbon-nitrogen conditions at the time of planting. Oscillations in plant and soil pools appear in modeled systems with rapid tree growth and low initial soil nitrogen, which stimulate nitrogen competition between trees and decomposers and lead the forest into a state of acute nitrogen deficiency. High initial soil nitrogen dampens oscillations, but enhances the magnitude of the tree biomass peak. These model results are supported by data derived from the long-running Calhoun Long-Term Soil-Ecosystem Experiment from 1957 to 2007. Observed carbon and nitrogen pools reveal distinct tree growth and decay phases, coincident with soil nitrogen depletion and partial re-accumulation. Further, contemporary tree biomass loss decreases with the legacy soil C:N ratio. These results support the idea that non-monotonic reforestation trajectories may result from initial transients in the plant-soil system affected by initial conditions derived from soil changes associated with land-use history
Renormalization of Molecular Electronic Levels at Metal-Molecule Interfaces
The electronic structure of benzene on graphite (0001) is computed using the
GW approximation for the electron self-energy. The benzene quasiparticle energy
gap is predicted to be 7.2 eV on graphite, substantially reduced from its
calculated gas-phase value of 10.5 eV. This decrease is caused by a change in
electronic correlation energy, an effect completely absent from the
corresponding Kohn-Sham gap. For weakly-coupled molecules, this correlation
energy change is seen to be well described by a surface polarization effect. A
classical image potential model illustrates trends for other conjugated
molecules on graphite.Comment: 4 pages, 3 figures, 2 table
AN ANALYSIS OF CONSUMER PREFERENCES FOR DELAWARE FARMER DIRECT MARKETS
Consumer/Household Economics,
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