21,392 research outputs found
Cold neutrons trapped in external fields
The properties of inhomogeneous neutron matter are crucial to the physics of
neutron-rich nuclei and the crust of neutron stars. Advances in computational
techniques now allow us to accurately determine the binding energies and
densities of many neutrons interacting via realistic microscopic interactions
and confined in external fields. We perform calculations for different external
fields and across several shells to place important constraints on
inhomogeneous neutron matter, and hence the large isospin limit of the nuclear
energy density functionals that are used to predict properties of heavy nuclei
and neutron star crusts. We find important differences between microscopic
calculations and current density functionals; in particular the isovector
gradient terms are significantly more repulsive than in traditional models, and
the spin-orbit and pairing forces are comparatively weaker.Comment: 5 pages, 4 figures, final version. Additional material reference
added in the published versio
Electron densities and temperatures in the f-region from backscatter measurements at arecibo
Diurnal variation in electron densities and temperatures in F region from backscatter measurements over Puerto Ric
Quantum Monte Carlo study of inhomogeneous neutron matter
We present an ab-initio study of neutron drops. We use Quantum Monte Carlo
techniques to calculate the energy up to 54 neutrons in different external
potentials, and we compare the results with Skyrme forces. We also calculate
the rms radii and radial densities, and we find that a re-adjustment of the
gradient term in Skyrme is needed in order to reproduce the properties of these
systems given by the ab-initio calculation. By using the ab-initio results for
neutron drops for close- and open-shell configurations, we suggest how to
improve Skyrme forces when dealing with systems with large isospin-asymmetries
like neutron-rich nuclei.Comment: 8 pages, 6 figures, talk given at Horizons on Innovative Theories,
Experiments, and Supercomputing in Nuclear Physics 2012, (HITES2012), New
Orleans, Louisiana, June 4-7, 2012; to appear in Journal of Physics:
Conference Series (JPCS
Baryon Resonance Analysis from MAID
The unitary isobar model MAID2007 has been used to analyze the recent data of
pion electroproduction. The model contains all four-star resonances in the
region below W=2 GeV and both single-Q^2 and Q^2 dependent transition form
factors could be obtained for the Delta, Roper, D13(1520), S11(1535),
S31(1620), S11(1650), D15(1675), F15(1680) and P13(1720). From the complete
world data base, including also pi- data on the neutron, also Q^2 dependent
neutron form factors are obtained. For all transition form factors we also give
convenient numerical parameterizations that can be used in other reactions.
Furthermore, we show how the transition form factors can be used to obtain
empirical transverse charge densities and our first results are given for the
Roper, the S11 and D13 resonances.Comment: 8 pages, 11 figures, 4 tables, Proc. of NSTAR2009, Beijin
Lithological maps of selected Apollo 14 Breccia samples
A booklet of mapped surfaces of some Apollo 14 samples was prepared as an intermediate step towards the preparation of a new Apollo 14 sample catalog. It contains recently obtained observations and pictures of some of the largest and less well documented Apollo breccia samples. Some of the samples (14303, 14305, 14306, and 14311) were chosen because they have large sawn surfaces. These were dusted and mapped using a binocular microscope through the window of the nitrogen cabinet
Scaling and Duality in Semi-exclusive Processes
We discuss extending scaling and duality studies to semi-exclusive processes.
We show that semi-exclusive hard pion photoproduction should exhibit scaling
behavior in kinematic regions where the photon and pion both interact directly
with the same quark. We show that such kinematic regions exist. We also show
that the constancy with changing momentum transfer of the resonance
peak/scaling curve ratio, familiar for many resonances in deep inelastic
scattering, is also expected in the semi-exclusive case.Comment: 8 pages, 4 figures, submitted to Phys.Rev.
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