5,887 research outputs found
Correlations derived from Modern Nucleon-Nucleon Potentials
Various modern nucleon-nucleon (NN) potentials yield a very accurate fit to
the nucleon-nucleon scattering phase shifts. The differences between these
interactions in describing properties of nuclear matter are investigated.
Various contributions to the total energy are evaluated employing the Hellmann
- Feynman theorem. Special attention is paid to the two-nucleon correlation
functions derived from these interactions. Differences in the predictions of
the various interactions can be traced back to the inclusion of non-local
terms.Comment: 7 pages, 4 figures include
A Sensitivity Study on the Effects of Particle Chemistry, Asphericity and Size on the Mass Extinction Efficiency of Mineral Dust in the Earth's Atmosphere: From the Near to Thermal IR
To determine a plausible range of mass extinction efficiencies (MEE) of terrestrial atmospheric dust from the near to thermal IR, sensitivity analyses are performed over an extended range of dust microphysical and chemistry perturbations. The IR values are subsequently compared to those in the near-IR, to evaluate spectral relationships in their optical properties. Synthesized size distributions consistent with measurements, model particle size, while composition is defined by the refractive indices of minerals routinely observed in dust, including the widely used OPAC/Hess parameterization. Single-scattering properties of representative dust particle shapes are calculated using the T-matrix, Discrete Dipole Approximation and Lorenz-Mie light-scattering codes. For the parameterizations examined, MEE ranges from nearly zero to 1.2 square meters per gram, with the higher values associated with non-spheres composed of quartz and gypsum. At near-IR wavelengths, MEE for non-spheres generally exceeds those for spheres, while in the thermal IR, shape-induced changes in MEE strongly depend on volume median diameter (VMD) and wavelength, particularly for MEE evaluated at the mineral resonant frequencies. MEE spectral distributions appear to follow particle geometry and are evidence for shape dependency in the optical properties. It is also shown that non-spheres best reproduce the positions of prominent absorption peaks found in silicates. Generally, angular particles exhibit wider and more symmetric MEE spectral distribution patterns from 8-10 micrometers than those with smooth surfaces, likely due to their edge-effects. Lastly, MEE ratios allow for inferring dust optical properties across the visible-IR spectrum. We conclude the MEE of dust aerosol are significant for the parameter space investigated, and are a key component for remote sensing applications and the study of direct aerosol radiative effects
Effective range function below threshold
We demonstrate that the kernel of the Lippmann-Schwinger equation, associated
with interactions consisting of a sum of the Coulomb plus a short range nuclear
potential, below threshold becomes degenerate. Taking advantage of this fact,
we present a simple method of calculating the effective range function for
negative energies. This may be useful in practice since the effective range
expansion extrapolated to threshold allows to extract low-energy scattering
parameters: the Coulomb-modified scattering length and the effective range.Comment: 14 pages, 1 figur
Isoscalar Hamiltonians for light atomic nuclei
The charge-dependent realistic nuclear Hamiltonian for a nucleus, composed of
neutrons and protons, can be successfully approximated by a charge-independent
one. The parameters of such a Hamiltonian, i.e., the nucleon mass and the NN
potential, depend upon the mass number A, charge Z and isospin quantum number T
of state of the studied nucleus.Comment: REVTeX, 22 pages, 3 eps figures, to appear in PR
On the effects of the final state interaction in the electro-disintegration of the deuteron at intermediate and high energies
The role of the final state interactions (FSI) in the inclusive quasi-elastic
disintegration of the deuteron is investigated treating the two-nucleon final
state within the exact continuum solutions of the non-relativistic Schroedinger
equation, as well as within the Glauber multiple scattering approach. It is
shown that for values of the Bjorken scaling variable both
approaches provide similar results, unless the case , where
they appreciably disagree. It is demonstrated that present experimental data,
which are mostly limited to a region of four-momentum transfer () where the Center-of-Mass energy of the final state is below the
pion threshold production, can be satisfactorily reproduced by the approach
based on the exact solution of the Schroedinger equation and not by the Glauber
approach. It is also pointed out that the latter, unlike the former, does not
satisfy the inelastic Coulomb sum rule, the violation being of the order of
about 20%.Comment: 16 LaTeX pages, 10 eps-figures, 1 tabl
Skyrmions and the Nuclear Force
The derivation of the nucleon-nucleon force from the Skyrme model is
reexamined. Starting from previous results for the potential energy of
quasistatic solutions, we show that a calculation using the Born-Oppenheimer
approximation properly taking into account the mixing of nucleon resonances,
leads to substantial central attraction. We obtain a potential that is in
qualitative agreement with phenomenological potentials. We also study the
non-adiabatic corrections, such as the velocity dependent transition
potentials, and discuss their importance.Comment: 24 pages, UPR-0124M
Globular Cluster Distance Determinations
The present status of the distance scale to Galactic globular clusters is
reviewed. Six distance determination techniques which are deemed to be most
reliable are discussed in depth. These different techniques are used to
calibrate the absolute magnitude of the RR Lyrae stars. The various
calibrations fall into three groups. Main sequence fitting using Hipparcos
parallaxes, theoretical HB models and the RR Lyrae in the LMC all favor a
bright calibration, implying a `long' globular cluster distance scale. White
dwarf fitting and the astrometric distances yield a somewhat fainter RR Lyrae
calibration, while the statistical parallax solution yields faint RR Lyrae
stars implying a `short' distance scale to globular clusters. Various secondary
distance indicators discussed all favor the long distance scale. The `long' and
`short' distance scales differ by (0.31+/-0.16) mag. Averaging together all of
the different distance determinations yields Mv(RR) = (0.23+/-0.04)([Fe/H] +
1.6) + (0.56+/-0.12) mag.Comment: Invited review article to appear in: `Post-Hipparcos Cosmic Candles',
A. Heck & F. Caputo (Eds), Kluwer Academic Publ., Dordrecht, in pres
Femtometer Toroidal Structures in Nuclei
The two-nucleon density distributions in states with isospin , spin
=1 and projection =0 and 1 are studied in H, He,
Li and O. The equidensity surfaces for =0 distributions are
found to be toroidal in shape, while those of =1 have dumbbell shapes
at large density. The dumbbell shapes are generated by rotating tori. The
toroidal shapes indicate that the tensor correlations have near maximal
strength at fm in all these nuclei. They provide new insights and simple
explanations of the structure and electromagnetic form factors of the deuteron,
the quasi-deuteron model, and the , and =2 (-wave)
components in He, He and Li. The toroidal distribution has a
maximum-density diameter of 1 fm and a half-maximum density thickness of
0.9 fm. Many realistic models of nuclear forces predict these values,
which are supported by the observed electromagnetic form factors of the
deuteron, and also predicted by classical Skyrme effective Lagrangians, related
to QCD in the limit of infinite colors. Due to the rather small size of this
structure, it could have a revealing relation to certain aspects of QCD.Comment: 35 pages in REVTeX, 25 PostScript figure
Correlation Between the Deuteron Characteristics and the Low-energy Triplet np Scattering Parameters
The correlation relationship between the deuteron asymptotic normalization
constant, , and the triplet np scattering length, , is
investigated. It is found that 99.7% of the asymptotic constant is
determined by the scattering length . It is shown that the linear
correlation relationship between the quantities and
provides a good test of correctness of various models of nucleon-nucleon
interaction. It is revealed that, for the normalization constant and
for the root-mean-square deuteron radius , the results obtained with the
experimental value recommended at present for the triplet scattering length
are exaggerated with respect to their experimental counterparts. By
using the latest experimental phase shifts of Arndt et al., we obtain, for the
low-energy scattering parameters (, , ) and for the
deuteron characteristics (, ), results that comply well with
experimental data.Comment: 19 pages, 1 figure, To be published in Physics of Atomic Nucle
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