25,509 research outputs found
On the momentum-dependence of -nuclear potentials
The momentum dependent -nucleus optical potentials are obtained based
on the relativistic mean-field theory. By considering the quarks coordinates of
meson, we introduced a momentum-dependent "form factor" to modify the
coupling vertexes. The parameters in the form factors are determined by fitting
the experimental -nucleus scattering data. It is found that the real
part of the optical potentials decrease with increasing momenta, however
the imaginary potentials increase at first with increasing momenta up to
MeV and then decrease. By comparing the calculated mean
free paths with those from / scattering data, we suggested that the
real potential depth is MeV, and the imaginary potential parameter
is MeV.Comment: 9 pages, 4 figure
The Carriers of the Interstellar Unidentified Infrared Emission Features: Constraints from the Interstellar C-H Stretching Features at 3.2-3.5 Micrometers
The unidentified infrared emission (UIE) features at 3.3, 6.2, 7.7, 8.6, and
11.3 micrometer, commonly attributed to polycyclic aromatic hydrocarbon (PAH)
molecules, have been recently ascribed to mixed aromatic/aliphatic organic
nanoparticles. More recently, an upper limit of <9% on the aliphatic fraction
(i.e., the fraction of carbon atoms in aliphatic form) of the UIE carriers
based on the observed intensities of the 3.4 and 3.3 micrometer emission
features by attributing them to aliphatic and aromatic C-H stretching modes,
respectively, and assuming A_34./A_3.3~0.68 derived from a small set of
aliphatic and aromatic compounds, where A_3.4 and A_3.3 are respectively the
band strengths of the 3.4 micrometer aliphatic and 3.3 micrometer aromatic C-H
bonds.
To improve the estimate of the aliphatic fraction of the UIE carriers, here
we analyze 35 UIE sources which exhibit both the 3.3 and 3.4 micrometer C-H
features and determine I_3.4/I_3.3, the ratio of the power emitted from the 3.4
micrometer feature to that from the 3.3 micrometer feature. We derive the
median ratio to be ~ 0.12. We employ density functional theory
and second-order perturbation theory to compute A_3.4/A_3.3 for a range of
methyl-substituted PAHs. The resulting A_3.4/A_3.3 ratio well exceeds 1.4, with
an average ratio of ~1.76. By attributing the 3.4 micrometer
feature exclusively to aliphatic C-H stretch (i.e., neglecting anharmonicity
and superhydrogenation), we derive the fraction of C atoms in aliphatic form to
be ~2%. We therefore conclude that the UIE emitters are predominantly aromatic.Comment: 14 pages, 5 figures, 1 table; accepted for publication in The
Astrophysical Journa
The properties of kaonic nuclei in relativistic mean-field theory
The static properties of some possible light and moderate kaonic nuclei, from
C to Ti, are studied in the relativistic mean-field theory. The 1s and 1p state
binding energies of are in the range of MeV and
MeV, respectively. The binding energies of 1p states increase monotonically
with the nucleon number A. The upper limit of the widths are about
MeV for the 1s states, and about MeV for the 1p states. The lower
limit of the widths are about MeV for the 1s states, and
MeV for the 1p states. If MeV, the discrete bound states
should be identified in experiment. The shrinkage effect is found in the
possible kaonic nuclei. The interior nuclear density increases obviously, the
densest center density is about .Comment: 9 pages, 2 tables and 1 figure, widths are considered, changes a lo
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