69 research outputs found
Topological Andr\'e-Quillen homology for cellular commutative -algebras
Topological Andr\'e-Quillen homology for commutative -algebras was
introduced by Basterra following work of Kriz, and has been intensively studied
by several authors. In this paper we discuss it as a homology theory on CW
-algebras and apply it to obtain results on minimal atomic -local
-algebras which generalise those of Baker and May for -local spectra and
simply connected spaces. We exhibit some new examples of minimal atomic
-algebras.Comment: Final revision, a version will appear in Abhandlungen aus dem
Mathematischen Seminar der Universitaet Hambur
The nuclear shell effects near the r-process path in the relativistic Hartree-Bogoliubov theory
We have investigated the evolution of the shell structure of nuclei in going
from the r-process path to the neutron drip line within the framework of the
Relativistic Hartree-Bogoliubov (RHB) theory. By introducing the quartic
self-coupling of meson in the RHB theory in addition to the non-linear
scalar coupling of meson, we reproduce the available data on the shell
effects about the waiting-point nucleus Zn. With this approach, it is
shown that the shell effects at N=82 in the inaccessible region of the
r-process path become milder as compared to the Lagrangian with the scalar
self-coupling only. However, the shell effects remain stronger as compared to
the quenching exhibited by the HFB+SkP approach. It is also shown that in
reaching out to the extreme point at the neutron drip line, a terminal
situation arises where the shell structure at the magic number is washed out
significantly.Comment: 18 pages (revtex), 8 ps figures, to appear in Phys. Rev.
Shape Coexistence in the Relativistic Hartree-Bogoliubov approach
The phenomenon of shape coexistence is studied in the Relativistic
Hartree-Bogoliubov framework. Standard relativistic mean-field effective
interactions do not reproduce the ground state properties of neutron-deficient
Pt-Hg-Pb isotopes. It is shown that, in order to consistently describe binding
energies, radii and ground state deformations of these nuclei, effective
interactions have to be constructed which take into account the sizes of
spherical shell gaps.Comment: 19 pages, 8 figures, accepted in Phys. Rev.
The structure of superheavy elements newly discovered in the reaction of Kr with Pb
The structure of superheavy elements newly discovered in the
Pb(Kr,n) reaction at Berkeley is systematically studied in the
Relativistic Mean Field (RMF) approach. It is shown that various usually
employed RMF forces, which give fair description of normal stable nuclei, give
quite different predictions for superheavy elements. Among the effective forces
we tested, TM1 is found to be the good candidate to describe superheavy
elements. The binding energies of the 118 nucleus and its
decay daughter nuclei obtained using TM1 agree with those of FRDM
within 2 MeV. Similar conclusion that TM1 is the good interaction is also drawn
from the calculated binding energies for Pb isotopes with the Relativistic
Continuum Hartree Bogoliubov (RCHB) theory. Using the pairing gaps obtained
from RCHB, RMF calculations with pairing and deformation are carried out for
the structure of superheavy elements. The binding energy, shape, single
particle levels, and the Q values of the decay are
discussed, and it is shown that both pairing correlation and deformation are
essential to properly understand the structure of superheavy elements. A good
agreement is obtained with experimental data on . %Especially, the
atomic number %dependence of %seems to match with the experimental
observationComment: 19 pages, 5 figure
Elevated synaptic vesicle release probability in synaptophysin/gyrin family quadruple knockouts
Synaptophysins 1 and 2 and synaptogyrins 1 and 3 constitute a major family of
synaptic vesicle membrane proteins. Unlike other widely expressed synaptic vesicle proteins such
as vSNAREs and synaptotagmins, the primary function has not been resolved. Here, we report
robust elevation in the probability of release of readily releasable vesicles with both high and low
release probabilities at a variety of synapse types from knockout mice missing all four family
members. Neither the number of readily releasable vesicles, nor the timing of recruitment to the
readily releasable pool was affected. The results suggest that family members serve as negative
regulators of neurotransmission, acting directly at the level of exocytosis to dampen connection
strength selectively when presynaptic action potentials fire at low frequency. The widespread
expression suggests that chemical synapses may play a frequency filtering role in biological
computation that is more elemental than presently envisioned
A microscopic estimate of the nuclear matter compressibility and symmetry energy in relativistic mean-field models
The relativistic mean-field plus RPA calculations, based on effective
Lagrangians with density-dependent meson-nucleon vertex functions, are employed
in a microscopic analysis of the nuclear matter compressibility and symmetry
energy. We compute the isoscalar monopole and the isovector dipole response of
Pb, as well as the differences between the neutron and proton radii for
Pb and several Sn isotopes. The comparison of the calculated excitation
energies with the experimental data on the giant monopole resonance in
Pb, restricts the nuclear matter compression modulus of structure
models based on the relativistic mean-field approximation to MeV. The isovector giant dipole resonance in Pb, and the
available data on differences between neutron and proton radii, limit the range
of the nuclear matter symmetry energy at saturation (volume asymmetry) to 32
MeV 36 MeV.Comment: 16 pages, 6 figure
Nuclear Skins and Halos in the Mean-Field Theory
Nuclei with large neutron-to-proton ratios have neutron skins, which manifest
themselves in an excess of neutrons at distances greater than the radius of the
proton distribution. In addition, some drip-line nuclei develop very extended
halo structures. The neutron halo is a threshold effect; it appears when the
valence neutrons occupy weakly bound orbits. In this study, nuclear skins and
halos are analyzed within the self-consistent Skyrme-Hartree-Fock-Bogoliubov
and relativistic Hartree-Bogoliubov theories for spherical shapes. It is
demonstrated that skins, halos, and surface thickness can be analyzed in a
model-independent way in terms of nucleonic density form factors. Such an
analysis allows for defining a quantitative measure of the halo size. The
systematic behavior of skins, halos, and surface thickness in even-even nuclei
is discussed.Comment: 22 RevTeX pages, 22 EPS figures included, submitted to Physical
Review
Cranked Relativistic Hartree-Bogoliubov Theory: Superdeformed Bands in the Region
Cranked Relativistic Hartree-Bogoliubov (CRHB) theory is presented as an
extension of Relativistic Mean Field theory with pairing correlations to the
rotating frame. Pairing correlations are taken into account by a finite range
two-body force of Gogny type and approximate particle number projection is
performed by Lipkin-Nogami method. This theory is applied to the description of
yrast superdeformed rotational bands observed in even-even nuclei of the mass region. Using the well established parameter sets NL1 for the
Lagrangian and D1S for the pairing force one obtains a very successful
description of data such as kinematic () and dynamic ()
moments of inertia without any adjustment of new parameters. Within the present
experimental accuracy the calculated transition quadrupole moments agree
reasonably well with the observed data.Comment: 6 pages including 4 PostScript figures, uses RevTex, revised version,
Phys.Rev. C, Rapid Communications, in pres
Relativistic Random-Phase Approximation with density-dependent meson-nucleon couplings
The matrix equations of the relativistic random-phase approximation (RRPA)
are derived for an effective Lagrangian characterized by density-dependent
meson-nucleon vertex functions. The explicit density dependence of the
meson-nucleon couplings introduces rearrangement terms in the residual two-body
interaction, that are essential for a quantitative description of excited
states. Illustrative calculations of the isoscalar monopole, isovector dipole
and isoscalar quadrupole response of Pb, are performed in the fully
self-consistent RRPA framework, based on effective interactions with a
phenomenological density dependence adjusted to nuclear matter and ground-state
properties of spherical nuclei. The comparison of the RRPA results on multipole
giant resonances with experimental data constrains the parameters that
characterize the isoscalar and isovector channel of the density-dependent
effective interactions.Comment: RevTeX, 8 eps figures, submitted to Phys. Rev.
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