626 research outputs found
Transfer/Breakup Modes in the 6He+209Bi Reaction Near and Below the Coulomb Barrier
Reaction products from the interaction of 6He with 209Bi have been measured
at energies near the Coulomb barrier. A 4He group of remarkable intensity,
which dominates the total reaction cross section, has been observed. The
angular distribution of the group suggests that it results primarily from a
direct nuclear process. It is likely that this transfer/breakup channel is the
doorway state that accounts for the previously observed large sub-barrier
fusion enhancement in this system.Comment: 4 pages; 3 figure
Breakup of F on Pb near the Coulomb barrier
Angular distributions of oxygen produced in the breakup of F incident
on a Pb target have been measured around the grazing angle at beam
energies of 98 and 120 MeV. The data are dominated by the proton stripping
mechanism and are well reproduced by dynamical calculations. The measured
breakup cross section is approximately a factor of 3 less than that of fusion
at 98 MeV. The influence of breakup on fusion is discussed.Comment: 7 pages, 8 figure
Simultaneous Optical Model Analyses of Elastic Scattering, Breakup, and Fusion Cross Section Data for the He + Bi System at Near-Coulomb-Barrier Energies
Based on an approach recently proposed by us, simultaneous
-analyses are performed for elastic scattering, direct reaction (DR)
and fusion cross sections data for the He+Bi system at
near-Coulomb-barrier energies to determine the parameters of the polarization
potential consisting of DR and fusion parts. We show that the data are well
reproduced by the resultant potential, which also satisfies the proper
dispersion relation. A discussion is given of the nature of the threshold
anomaly seen in the potential
Spectroscopy of 9C via resonance scattering of protons on 8B
The structure of the neutron-deficient 9C isotope was studied via elastic
scattering of radioactive 8B on protons. An excitation function for resonance
elastic scattering was measured in the energy range from 0.5 to 3.2 MeV in the
center-of-momentum system. A new excited state in 9C was observed at an
excitation energy of 3.6 MeV. An R-matrix analysis indicates spin-parity 5/2-
for the new state. The results of this experiment are compared with Continuum
Shell Model calculations.Comment: 9 pages, 8 figures, 3 table
E2 properties of nuclei far from stability and the proton-halo problem of 8B
E2 properties of A=6--10 nuclei, including those of nuclei far from
stability, are studied by a shell-model calculation which
includes E2 core-polarization effects explicitly. The quadrupole moments and
the E2 transition strengths in A=6--10 nuclei are described quite well by the
present calculation. This result indicates that the relatively large value of
the quadrupole moment of B can be understood without introducing the
proton-halo in B. An interesting effect of the
core-polarization is found for effective charges used in the
shell model; although isoscalar effective-charges are almost constant as a
function of nucleus, appreciable variations are needed for isovector
effective-charges which play important roles in nuclei with high
isospin-values.Comment: (LaTeX, 23 pages
Fusion of light exotic nuclei at near-barrier energies : effect of inelastic excitation
The effect of inelastic excitation of exotic light projectiles (proton- as
well as neutron-rich) F and Be on fusion with heavy target has
been studied at near-barrier energies. The calculations have been performed in
the coupled channels approach where, in addition to the normal coupling of the
ground state of the projectile to the continuum, inelastic excitation of the
projectile to the bound excited state and its coupling to the continuum have
also been taken into consideration. The inclusion of these additional couplings
has been found to have significant effect on the fusion excitation function of
neutron-rich Be on Pb whereas the effect has been observed to be
nominal for the case of proton-rich F on the same target. The pronounced
effect of the channel coupling on the fusion process in case of Be is
attributed to its well-developed halo structure.Comment: 9 pages, 3 figures, Revtex.st
Protein dynamics with off-lattice Monte Carlo moves
A Monte Carlo method for dynamics simulation of all-atom protein models is
introduced, to reach long times not accessible to conventional molecular
dynamics. The considered degrees of freedom are the dihedrals at
C-atoms. Two Monte Carlo moves are used: single rotations about
torsion axes, and cooperative rotations in windows of amide planes, changing
the conformation globally and locally, respectively. For local moves Jacobians
are used to obtain an unbiased distribution of dihedrals. A molecular dynamics
energy function adapted to the protein model is employed. A polypeptide is
folded into native-like structures by local but not by global moves.Comment: 10 pages, 4 Postscript figures, uses epsf.sty and a4.sty; scheduled
tentatively for Phys.Rev.E issue of 1 March 199
A Dopaminergic Gene Cluster in the Prefrontal Cortex Predicts Performance Indicative of General Intelligence in Genetically Heterogeneous Mice
Background: Genetically heterogeneous mice express a trait that is qualitatively and psychometrically analogous to general intelligence in humans, and as in humans, this trait co-varies with the processing efficacy of working memory (including its dependence on selective attention). Dopamine signaling in the prefrontal cortex (PFC) has been established to play a critical role in animals â performance in both working memory and selective attention tasks. Owing to this role of the PFC in the regulation of working memory, here we compared PFC gene expression profiles of 60 genetically diverse CD-1 mice that exhibited a wide range of general learning abilities (i.e., aggregate performance across five diverse learning tasks). Methodology/Principal Findings: Animals â general cognitive abilities were first determined based on their aggregate performance across a battery of five diverse learning tasks. With a procedure designed to minimize false positive identifications, analysis of gene expression microarrays (comprised of <25,000 genes) identified a small number (,20) of genes that were differentially expressed across animals that exhibited fast and slow aggregate learning abilities. Of these genes, one functional cluster was identified, and this cluster (Darpp-32, Drd1a, and Rgs9) is an established modulator of dopamine signaling. Subsequent quantitative PCR found that expression of these dopaminegic genes plus one vascular gene (Nudt6) were significantly correlated with individual animalâs general cognitive performance. Conclusions/Significance: These results indicate that D1-mediated dopamine signaling in the PFC, possibly through it
- âŚ