4,840 research outputs found
Perturbative HFB model for many-body pairing correlations
We develop a perturbative model to treat the off-diagonal components in the
Hartree-Fock-Bogoliubov (HFB) transformation matrix, which are neglected in the
BCS approximation. Applying the perturbative model to a weakly bound nucleus
Ni, it is shown that the perturbative approach reproduces well the
solutions of the HFB method both for the quasi-particle energies and the radial
dependence of quasi-particle wave functions. We find that the non-resonant part
of the continuum single-particle state can acquire an appreciable occupation
probability when there exists a weakly bound state close to the Fermi surface.
This result originates from the strong coupling between the continuum particle
state and the weakly bound state, and is absent in the BCS approximation. The
limitation of the BCS approximation is pointed out in comparison with the HFB
and the present perturbative model.Comment: 6 pages, 5 eps figure
Reducing the hypoxic fraction of a tumour model by growth in low glucose.
The question of whether growth under low glucose conditions leads to a reduced amount of cell hypoxia was investigated using an in vitro tumour analogue, the sandwich system. In this multicellular system, the interplay between diffusion and consumption of oxygen and nutrients results in spatial gradients of these environmental factors. Gradients in the environment lead to biological heterogeneity within the cell population. A necrotic centre, surrounded by a viable cell border, subsequently develops. Cells adjacent to the necrotic centre in sandwiches are hypoxic and are in an environment somewhat analogous to that of cells adjacent to necrotic regions in solid tumours. Using sandwiches of the 9L and V79 cell lines, the effects of growth under low glucose conditions on the degree of hypoxia in regions adjacent to the necrotic centre were investigated. Per-cell binding of 3H-misonidazole, assessed by autoradiography, was used as an indicator of oxygen deprivation. It was found that the extent of the hypoxic region and the severity of hypoxia were considerably reduced by growing sandwiches in a glucose concentration of 0.6 mM rather than 6.5 mM. This reduction was found in conjunction with a smaller viable border; it occurred despite the fact that the average per-cell oxygen consumption is higher in the low glucose sandwiches. The data are qualitatively consistent with a joint oxygen-glucose deprivation model for cell necrosis
Pairing correlations in nuclei on the neutron-drip line
Paring correlations in weakly bound nuclei on the edge of neutron drip line
is studied by using a three-body model. A density-dependent contact interaction
is employed to calculate the ground state of halo nuclei He and
Li, as well as a skin nucleus O. Dipole excitations in these
nuclei are also studied within the same model. We point out that the di-neutron
type correlation plays a dominant role in the halo nuclei He and
Li having the coupled spin of the two neutrons =0, while the
correlation similar to the BCS type is important in O. Contributions of
the spin =1 and S=0 configurations are separately discussed in the low
energy dipole excitations.Comment: 6 pages, 12 eps figure
Imaginary-time method for radiative capture reaction rate
We propose a new computational method for astrophysical reaction rate of
radiative capture process. In the method, an evolution of a wave function is
calculated along the imaginary-time axis which is identified as the inverse
temperature. It enables direct evaluation of reaction rate as a function of
temperature without solving any scattering problem. The method is tested for
two-body radiative capture reaction, , showing that it gives identical results to that calculated by the
ordinary procedure. The new method will be suited for calculation of
triple-alpha radiative capture rate for which an explicit construction of the
scattering solution is difficult.Comment: 8 pages, 7 figure
Nuclear Excitations Described by Randomly Selected Multiple Slater Determinants
We propose a new stochastic method to describe low-lying excited states of
finite nuclei superposing multiple Slater determinants without assuming
generator coordinates a priori. We examine accuracy of our method by using
simple BKN interaction.Comment: Talk at International Symposium on Correlation Dynamics in Nuclei,
Tokyo, Japan, 31 Jan.-- 4 Feb. 200
Strong dineutron correlation in 8He and 18C
We study the spatial structure of four valence neutrons in the ground state
of He and C nuclei using a core+4 model. For this purpose, we
employ a density-dependent contact interaction among the valence neutrons, and
solve the five-body Hamiltonian in the Hartree-Fock-Bogoliubov (HFB)
approximation. We show that two neutrons with the coupled spin of =0 exhibit
a strong dineutron correlation around the surface of these nuclei, whereas the
correlation between the two dineutrons is much weaker. Our calculation
indicates that the probability of the (1p and [(1p
(p] configurations in the ground state wave function of He
nucleus is 34.9% and 23.7%, respectively. This is consistent with the recent
experimental finding with the He(He reaction, that is, the ground
state wave function of He deviates significantly from the pure
(1p structure.Comment: 10 pages, 9 figures, 3 table
Systematic study of nuclear matrix elements in neutrinoless double-beta decay with a beyond mean-field covariant density functional theory
We report a systematic study of nuclear matrix elements (NMEs) in
neutrinoless double-beta decays with a state-of-the-art beyond mean-field
covariant density functional theory. The dynamic effects of particle-number and
angular-momentum conservations as well as quadrupole shape fluctuations are
taken into account with projections and generator coordinate method for both
initial and final nuclei. The full relativistic transition operator is adopted
to calculate the NMEs. The present systematic studies show that in most of the
cases there is a much better agreement with the previous non-relativistic
calculation based on the Gogny force than in the case of the nucleus Nd
found in Song et al. [Phys. Rev. C 90, 054309 (2014)]. In particular, we find
that the total NMEs can be well approximated by the pure axial-vector coupling
term with a considerable reduction of the computational effort.Comment: 9 pages with 7 figures and 3 table
Relativistic quasiparticle time blocking approximation. II. Pygmy dipole resonance in neutron-rich nuclei
Theoretical studies of low-lying dipole strength in even-even spherical
nuclei within the relativistic quasiparticle time blocking approximation
(RQTBA) are presented. The RQTBA developed recently as an extension of the
self-consistent relativistic quasiparticle random phase approximation (RQRPA)
enables one to investigate effects of coupling of two-quasiparticle excitations
to collective vibrations within a fully consistent calculation scheme based on
covariant energy density functional theory. Dipole spectra of even-even
Sn -- Sn and Ni -- Ni isotopes calculated within
both RQRPA and RQTBA show two well separated collective structures: the
higher-lying giant dipole resonance (GDR) and the lower-lying pygmy dipole
resonance (PDR) which can be identified by a different behavior of the
transition densities of states in these regions.Comment: 28 pages, 13 figure
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