5,904 research outputs found
Shell structure in neutron-rich Ca and Ni nuclei under semi-realistic mean fields
Shell structure in the neutron-rich Ca and Ni nuclei is investigated by the
spherical Hartree-Fock calculations with the semi-realistic interactions.
Specific ingredients of the effective interaction, particularly the tensor
force, often play a key role in the dependence of the neutron shell
structure. Such examples are found in N=32 and N=40; N=32 becomes magic or
submagic in Ca while its magicity is broken in Ni, and N=40 is
submagic (though not magic) in Ni but not in Ca. Comments are
given on the doubly magic nature of Ni. We point out that the loose
binding can lead to a submagic number N=58 in Ni, assisted by the weak
pair coupling.Comment: 14 pages including 5 figures, to appear in Physical Review C (Rapid
Communication
Level Densities by Particle-Number Reprojection Monte Carlo Methods
A particle-number reprojection method is applied in the framework of the
shell model Monte Carlo approach to calculate level densities for a family of
nuclei using Monte Carlo sampling for a single nucleus. In particular we can
also calculate level densities of odd-even and odd-odd nuclei despite a new
sign problem introduced by the projection on an odd number of particles. The
method is applied to level densities in the iron region using the complete
-shell. The single-particle level density parameter and the
backshift parameter are extracted by fitting the microscopically
calculated level densities to the backshifted Bethe formula. We find good
agreement with experimental level densities with no adjustable parameters in
the microscopic calculations. The parameter is found to vary smoothly with
mass and does not show odd-even effects. The calculated backshift parameter
displays an odd-even staggering effect versus mass and is in better
agreement with the experimental data than are the empirical values.Comment: To be published in the proceedings of the Tenth International
Symposium on Capture Gamma-Ray Spectroscopy and Related Topics, S. Wender,
ed., AIP Conference Proceedings (2000
Spin projection in the shell model Monte Carlo method and the spin distribution of nuclear level densities
We introduce spin projection methods in the shell model Monte Carlo approach
and apply them to calculate the spin distribution of level densities for
iron-region nuclei using the complete -shell. We compare the
calculated distributions with the spin-cutoff model and extract an
energy-dependent moment of inertia. For even-even nuclei and at low excitation
energies, we observe a significant suppression of the moment of inertia and
odd-even staggering in the spin dependence of level densities.Comment: 4 pages, 4 figure
Gastrointestinal motility in the immediate postoperative period after intestinal transplantation, with special reference to acute rejection
Particle-Number Reprojection in the Shell Model Monte Carlo Method: Application to Nuclear Level Densities
We introduce a particle-number reprojection method in the shell model Monte
Carlo that enables the calculation of observables for a series of nuclei using
a Monte Carlo sampling for a single nucleus. The method is used to calculate
nuclear level densities in the complete -shell using a good-sign
Hamiltonian. Level densities of odd-A and odd-odd nuclei are reliably extracted
despite an additional sign problem. Both the mass and the dependence of
the experimental level densities are well described without any adjustable
parameters. The single-particle level density parameter is found to vary
smoothly with mass. The odd-even staggering observed in the calculated
backshift parameter follows the experimental data more closely than do
empirical formulae.Comment: 14 pages, 4 eps figures included, RevTe
Relation of SiO maser emission to IR radiation in evolved stars based on the MSX observation
Based on the space MSX observation in bands A(8m), C(12m),
D(15m) and E(21m), and the ground SiO maser observation of evolved
stars by the Nobeyama 45-m telescope in the v=1 and v=2 J=1-0 transitions, the
relation between SiO maser emission and mid-IR continuum radiation is analyzed.
The relation between SiO maser emission and the IR radiation in the MSX bands
A, C, D and E is all clearly correlated. The SiO maser emission can be
explained by a radiative pumping mechanism according to its correlation with
infrared radiation in the MSX band A.Comment: 11 pages, 4 figures, to appear in ApJ
Intestinal neuromuscular function after preservation and transplantation
While it is well known that prolonged preservation of the intestinal graft causes severe mucosal damage after transplantation, little is known about the effect on neuromuscular function. The entire small intestine of adult hound dogs was flushed and preserved with cold lactated Ringer's solution and autotransplanted either immediately (n = 6) or after 24 hr (n = 6). Animals undergoing sham operation (n = 4) were used as a control. Fasting motility and the response of the intestinal smooth muscle and enteric nerves to bethanechol (100 ÎŒg/kg/0.5 hr, iv) and cisapride (0.5 mg/kg, iv) were determined by a multiple strain gauge method on Postoperative Days 2, 4, 7, 14, 21, and 28. Compared to the control, immediately transplanted grafts and those preserved for 24 hr developed delayed reappearance of migrating myoelectric complexes (MMC), hypercontractile activity, and reduced response to bethanechol and cisapride administration. Animals in the preservation group developed more abnormal fasting motility after transplantation, but responses to bethanechol and cisapride stimulation were not markedly different from those of the immediate group. The reappearance of MMC occurred 3 weeks postoperatively in the preservation group compared to 2 days in the immediate group. The results of our study indicate that intestinal dysmotility is augmented in prolonged-preservation grafts compared to those with brief preservation. The dysmotility was transient and normalized 3 to 4 weeks after surgery. Preservation and reperfusion injury to the neuromuscular system of intestinal grafts are reversible and are attenuated by simple hypothermia
Controlling edge states of zigzag carbon nanotubes by the Aharonov-Bohm flux
It has been known theoretically that localized states exist around zigzag
edges of a graphite ribbon and of a carbon nanotube, whose energy eigenvalues
are located between conduction and valence bands. We found that in metallic
single-walled zigzag carbon nanotubes two of the localized states become
critical, and that their localization length is sensitive to the mean curvature
of a tube and can be controlled by the Aharonov-Bohm flux. The curvature
induced mini-gap closes by the relatively weak magnetic field. Conductance
measurement in the presence of the Aharonov-Bohm flux can give information
about the curvature effect and the critical states.Comment: 5 pages, 4 figure
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