12,074 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
Galaxy Tracers and Velocity Bias
This paper examines several methods of tracing galaxies in N-body simulations
and their effects on the derived galaxy statistics, especially measurements of
velocity bias. Using two simulations with identical initial conditions, one
following dark matter only and the other following dark matter and baryons,
both collisionless and collisional methods of tracing galaxies are compared to
one another and against a set of idealized criteria. None of the collisionless
methods proves satisfactory, including an elaborate scheme developed here to
circumvent previously known problems. The main problem is that galactic
overdensities are both secularly and impulsively disrupted while orbiting in
cluster potentials. With dissipation, the baryonic tracers have much higher
density contrasts and much smaller cross sections, allowing them to remain
distinct within the cluster potential. The question remains whether the
incomplete physical model introduces systematic biases. Statistical measures
determined from simulations can vary significantly based solely on the galaxy
tracing method utilized. The two point correlation function differs most on
sub-cluster scales with generally good agreement on larger scales. Pairwise
velocity dispersions show less uniformity on all scales addressed here. All
tracing methods show a velocity bias to varying degrees, but the predictions
are not firm: either the tracing method is not robust or the statistical
significance has not been demonstrated. Though theoretical arguments suggest
that a mild velocity bias should exist, simulation results are not yet
conclusive.Comment: ApJ, in press, 23 pages, plain TeX, 8 of 13 figures included, all
PostScript figures (4.8 MB) available via anonymous ftp from
ftp://astro.princeton.edu/summers/tracers . Also available as POPe-616 on
http://astro.princeton.edu/~library/prep.htm
Sensitivity of 8B breakup cross section to projectile structure in CDCC calculations
Given the Astrophysical interest of BeB, there have been
several experiments applying the Coulomb dissociation method for extracting the
capture rate. Measurements at Michigan State are dominated by
contributions but have a small component. On the other hand, a lower
energy measurement at Notre Dame has a much stronger contribution. The
expectation was that the two measurements would tie down the and thus
allow for an accurate extraction of the relevant for the capture process.
The aim of this brief report is to show that the factor in breakup
reactions does not translate into a scaling of the contribution in the
corresponding capture reaction. We show that changes to the B single
particle parameters, which are directly related to the component in the
capture reaction, do not effect the corresponding breakup reactions, using the
present reaction theory.Comment: 4 pages, 6 figures, revtex
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