1,758 research outputs found
Two-body correlation functions in nuclear matter with condensate
The density, spin and isospin correlation functions in nuclear matter with a
neutron-proton () condensate are calculated to study the possible
signatures of the BEC-BCS crossover in the low-density region. It is shown that
the criterion of the crossover (Phys. Rev. Lett. {\bf 95}, 090402 (2005)),
consisting in the change of the sign of the density correlation function at low
momentum transfer, fails to describe correctly the density-driven BEC-BCS
transition at finite isospin asymmetry or finite temperature. As an unambiguous
signature of the BEC-BCS transition, there can be used the presence (BCS
regime) or absence (BEC regime) of the singularity in the momentum distribution
of the quasiparticle density of states.Comment: Prepared with RevTeX4, 5p., 4 figure
The strength of nuclear shell effects at N=126 in the r-process region
We have investigated nuclear shell effects across the magic number N=126 in
the region of the r-process path. Microscopic calculations have been performed
using the relativistic Hartree-Bogoliubov approach within the framework of the
RMF theory for isotopic chains of rare-earth nuclei in the r-process region.
The Lagrangian model NL-SV1 with the inclusion of the vector self-coupling of
omega meson has been employed. The RMF results show that the shell effects at
N=126 remain strong and exhibit only a slight reduction in the strength in
going from the r-process path to the neutron drip line. This is in striking
contrast to a systematic weakening of the shell effects at N=82 in the
r-process region predicted earlier in the similar approach. In comparison the
shell effects with microscopic-macroscopic mass formulae show a near constancy
of shell gaps leading to strong shell effects in the region of r-process path
to the drip line. A recent analysis of solar-system r-process abundances in a
prompt supernova explosion model using various mass formulae including the
recently introduced mass tables based upon HFB approach shows that whilst mass
formulae with weak shell effects at N=126 give rise to a spread and an
overproduction of nuclides near the third abundance peak at A~190, mass tables
with droplet models showing stronger shell effects are able to reproduce the
abundance features near the third peak appropriately. In comparison, several
analyses of the second r-process peak at A~130 have required weakened shell
effects at N=82. Our predictions in the RMF theory with NL-SV1, which exhibit
weaker shell effects at N=82 and stronger one at N=126 in the r-process region,
support the conjecture that a different nature of the shell effects at the
magic numbers may be at play in r-process nucleosynthesis of heavy nuclei.Comment: 14 pages, 8 figures; submitted to Physical Review C. Part of this
work was presented at Nuclear Physics in Astrophysics II, 20th International
Nuclear Physics Divisional Conference of the European Physical Society, at
Debrecen, Hungary, May 16-20, 200
On the Origin of the Early Solar System Radioactivities. Problems with the AGB and Massive Star Scenarios
Recent improvements in stellar models for intermediate-mass and massive stars
are recalled, together with their expectations for the synthesis of radioactive
nuclei of lifetime Myr, in order to re-examine the origins
of now extinct radioactivities, which were alive in the solar nebula. The
Galactic inheritance broadly explains most of them, especially if -process
nuclei are produced by neutron star merging according to recent models.
Instead, Al, Ca, Cs and possibly Fe require
nucleosynthesis events close to the solar formation. We outline the persisting
difficulties to account for these nuclei by Intermediate Mass Stars (2
M/M). Models of their final stages now
predict the ubiquitous formation of a C reservoir as a neutron capture
source; hence, even in presence of Al production from Deep Mixing or Hot
Bottom Burning, the ratio Al/Pd remains incompatible with
measured data, with a large excess in Pd. This is shown for two recent
approaches to Deep Mixing. Even a late contamination by a Massive Star meets
problems. In fact, inhomogeneous addition of Supernova debris predicts
non-measured excesses on stable isotopes. Revisions invoking specific low-mass
supernovae and/or the sequential contamination of the pre-solar molecular cloud
might be affected by similar problems, although our conclusions here are
weakened by our schematic approach to the addition of SN ejecta. The limited
parameter space remaining to be explored for solving this puzzle is discussed.Comment: Accepted for publication on Ap
Longâterm impact of childhood selective dorsal rhizotomy on pain, fatigue, and function: a caseâcontrol study
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138232/1/dmcn13481_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/138232/2/dmcn13481.pd
Closed shells at drip-line nuclei
The shell structure of magic nuclei far from stability is discussed in terms
of the self-consistent spherical Hartree-Fock-Bogoliubov theory. In particular,
the sensitivity of the shell-gap sizes and the two-neutron separation energies
to the choice of particle-hole and particle-particle components of the
effective interaction is investigated.Comment: 19 pages, LaTeX, 8 uuencoded figures available upon reques
The Ubiquity of the Rapid Neutron-Capture Process
To better characterize the abundance patterns produced by the r-process, we
have derived new abundances or upper limits for the heavy elements zinc (Zn),
yttrium (Y), lanthanum (La), europium (Eu), and lead (Pb). Our sample of 161
metal-poor stars includes new measurements from 88 high resolution and high
signal-to-noise spectra obtained with the Tull Spectrograph on the 2.7m Smith
Telescope at McDonald Observatory, and other abundances are adopted from the
literature. We use models of the s-process in AGB stars to characterize the
high Pb/Eu ratios produced in the s-process at low metallicity, and our new
observations then allow us to identify a sample of stars with no detectable
s-process material. In these stars, we find no significant increase in the
Pb/Eu ratios with increasing metallicity. This suggests that s-process material
was not widely dispersed until the overall Galactic metallicity grew
considerably, perhaps even as high as [Fe/H]=-1.4. We identify a dispersion of
at least 0.5 dex in [La/Eu] in metal-poor stars with [Eu/Fe]<+0.6 attributable
to the r-process, suggesting that there is no unique "pure" r-process elemental
ratio among pairs of rare earth elements. We confirm earlier detections of an
anti-correlation between Y/Eu and Eu/Fe bookended by stars strongly enriched in
the r-process (e.g., CS 22892-052) and those with deficiencies of the heavy
elements (e.g., HD 122563). We can reproduce the range of Y/Eu ratios using
simulations of high-entropy neutrino winds of core-collapse supernovae that
include charged-particle and neutron-capture components of r-process
nucleosynthesis. The heavy element abundance patterns in most metal-poor stars
do not resemble that of CS 22892-052, but the presence of heavy elements such
as Ba in nearly all metal-poor stars without s-process enrichment suggests that
the r-process is a common phenomenon.Comment: Accepted for publication in the Astrophysical Journal. 25 pages, 13
figure
Measures for the Assessment of Pain in Adults
Peer reviewedPublisher PD
Religiosity, Alcohol Use Attitudes, and Alcohol Use in a National Sample of Adolescents
The purpose of this study was to investigate alcohol use attitudes as a mediator of the
relationship between religiosity and the frequency of past month alcohol use in a national sample of adolescents. Data were drawn from 18,314 adolescents who participated in the 2006 and 2007 National Survey on Drug Use and Health. Variables included religiosity, alcohol use attitudes, and past month frequency of alcohol use. Structural equation modeling was used to test alcohol use attitudes as a mediator of the relationship between religiosity and frequency of alcohol use and to test model invariance across 4 racial/ethnic groups. Results suggest that alcohol use attitudes partially mediate the relationship between religiosity and frequency of alcohol use.
Furthermore, while the pattern of these relationships is similar across racial/ethnic groups, the magnitude of alcohol use attitudes on frequency of alcohol use differed. Implications for prevention programs include targeting alcohol use attitudes in a variety of settings
The beta-delayed neutron emission in 78Ni region
A systematic study of the total -decay half-lives and -delayed
neutron emission probabilities is performed. The -strength function is
treated within the self-consistent density-functional + continuum-QRPA
framework including the Gamow-Teller and first-forbidden transitions. The
experimental total -decay half-lives for the Ni isotopes with 76
are described satisfactorily. The half-lives predicted from =70 up to =86
reveal fairly regular -behaviour which results from simultaneous account for
the Gamow-Teller and first-forbidden transitions. For 28 nuclei, a
suppression of the delayed neutron emission probability is found when the
=50 neutron closed shell is crossed. The effect originates from the
high-energy first-forbidden transitions to the states outside the -window in the daughter nuclei.
PACS numbers: 23.40.Bw,21.60.Jz,25.30.Pt,26.30.+kComment: LaTeX, 13 pages, 5 figure
First decay study of the very neutron-rich isotope Br-93
The decay of the mass-separated, very neutron-rich isotope Br-93 has been
studied by gamma-spectroscopy. A level scheme of its daughter Kr-93 has been
constructed. Level energies, gamma-ray branching ratios and multipolarities
suggest spins and parities which are in accord with a smooth systematics of the
N=57 isotones for Z less-equal 40, suggesting the N=56 shell closure still to
be effective in Kr isotopes. So far, there is no indication of a progressive
onset of deformation in neutron-rich Kr isotopes.Comment: 17 pages, 3 figures, Phys. Rev. C, in prin
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