13,661 research outputs found
Extracting (n,g) direct capture cross sections from Coulomb dissociation: application to C(n,)C
A methodology for extracting neutron direct capture rates from Coulomb
dissociation data is developed and applied to the Coulomb dissociation of 15C
on 208Pb at 68 MeV/nucleon. Full Continuum Discretized Coupled Channel
calculations are performed and an asymptotic normalization coefficient is
determined from a fit to the breakup data. Direct neutron capture calculations
using the extracted asymptotic normalization coefficient provide
cross sections consistent with direct measurements. Our results show that the
Coulomb Dissociation data can be reliably used for extracting the cross section
for 14C(n,g)15C if the appropriate reaction theory is used. The resulting error
bars are of comparable magnitude to those from the direct measurement. This
procedure can be used more generally to extract capture cross sections from
breakup reactions whenever the desired capture process is fully peripheral.Comment: submitted to Phys. Rev. C (R
Testing linear-theory predictions of galaxy formation
The angular momentum of galaxies is routinely ascribed to a process of tidal
torques acting during the early stages of gravitational collapse, and is
predicted from the initial mass distribution using second-order perturbation
theory and the Zel'dovich approximation. We have tested this theory for a flat
hierarchical cosmogony using a large N-body simulation with sufficient dynamic
range to include tidal fields, allow resolution of individual galaxies, and
thereby expand on previous studies. We find relatively good correlation between
the predictions of linear theory and actual galaxy evolution. While structure
formation from early times is a complex history of hierarchical merging,
salient features are well described by the simple spherical-collapse model.
Most notably, we test several methods for determining the turnaround epoch, and
find that turnaround is succesfully described by the spherical collapse model.
The angular momentum of collapsing structures grows linearly until turnaround,
as predicted, and continues quasi-linearly until shell crossing. The predicted
angular momentum for well-resolved galaxies at turnaround overestimates the
true turnaround and final values by a factor of ~3 with a scatter of ~70
percent, and only marginally yields the correct direction of the angular
momentum vector. We recover the prediction that final angular momentum scales
as mass to the 5/3 power. We find that mass and angular momentum also vary
proportionally with peak height.Comment: 20 pages, 16 figures, Accepted for publication in MNRA
Can Inter-Industry Wage Differentials Justify Strategic Trade Policy?
This paper examines the relationship between labor market imperfections and trade policies. The available evidence suggests that pervasive industry wage differentials of up to 20 percent remain even after controlling for differences in observed measures of workers' skill and the effects of unions. Theoretical analysis indicates that given non-competitive wage differentials of this magnitude policies directed at encouraging employment in high-wage sectors could significantly enhance allocative efficiency. For the United States and other developed countries, such policies are more likely to involve export promotion than import substitution. Increased international trade flows (at least through 1984) have been associated with increased employment in high-wage U.S. manufacturing industries relative to low-wage U.S. manufacturing industries.
Theoretical and material studies on thin-film electroluminescent devices
A theoretical study of resonant tunneling in multilayered heterostructures is presented based on an exact solution of the Schroedinger equation under the application of a constant electric field. By use of the transfer matrix approach, the transmissivity of the structure is determined as a function of the incident electron energy. The approach presented is easily extended to many layer structures where it is more accurate than other existing transfer matrix or WKB models. The transmission resonances are compared to the bound state energies calculated for a finite square well under bias using either an asymmetric square well model or the exact solution of an infinite square well under the application of an electric field. The results show good agreement with other existing models as well as with the bound state energies. The calculations were then applied to a new superlattice structure, the variablly spaced superlattice energy filter, (VSSEP) which is designed such that under bias the spatial quantization levels fully align. Based on these calculations, a new class of resonant tunneling superlattice devices can be designed
Performance characteristics of high-earning minority banks
An abstract for this article is not available.Banks and banking
Design, fabrication, and bench testing of a solar chemical receiver
Solar thermal energy can be effectively collected, transported, stored, and utilized by means of a chemical storage and transport system employing the reversible SO2 oxidation reaction. A solar chemical receiver for SO3 thermal decomposition to SO2 and oxygen was analyzed. Bench tests of a ten foot section of a receiver module were conducted with dissociated sulfuric acid (SO3 and H2O) in an electrical furnace. Measured percent conversion of SO3 was 85% of the equilibrium value. Methods were developed to fabricate and assemble a complete receiver module. These methods included applying an aluminide coating to certain exposed surfaces, assembling concentric tubes with a wire spacer, applying a platinum catalyst to the tubing wall, and coiling the entire assembly into the desired configuration
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