81 research outputs found
Effect of pairing correlations on incompressibility and symmetry energy in nuclear matter and finite nuclei
The role of superfluidity in the incompressibility and in the symmetry energy
is studied in nuclear matter and finite nuclei. Several pairing interactions
are used: surface, mixed and isovector dependent. Pairing has a small effect on
the nuclear matter incompressibility at saturation density, but the effects are
significant at lower densities. The pairing effect on the centroid energy of
the isoscalar Giant Monopole Resonance (GMR) is also evaluated for Pb and Sn
isotopes by using a microscopic constrained-HFB approach, and found to change
at most by 10% the nucleus incompressibility . It is shown by using the
Local Density Approximation (LDA) that most of the pairing effect on the GMR
centroid come from the low-density nuclear surface.Comment: 9 pages, 6 figure
Effects of the Tensor Force on the Multipole Response in Finite Nuclei
We present a thorough analysis of the effects of the tensor interaction on
the multipole response of magic nuclei, using the fully self-consistent Random
Phase Approximation (RPA) model with Skyrme interactions. We disentangle the
modifications to the static mean field induced by the tensor terms, and the
specific features of the residual particle-hole (p-h) tensor interaction, for
quadrupole (2+), octupole (3-), and also magnetic dipole (1+) responses. It is
pointed out that the tensor force has a larger effect on the magnetic dipole
states than on the natural parity states 2+ and 3-, especially at the mean
field level. Perspectives for a better assessment of the tensor force
parameters are eventually discussed
Effect of the tensor force on the charge-exchange spin-dipole excitations of 208Pb
The charge-exchange spin-dipole (SD) excitations of 208Pb are studied by
using a fully self-consistent Skyrme Hartree-Fock plus Random Phase
Approximation (HF+RPA) formalism which includes the tensor interaction. It is
found, for the first time, that the tensor correlations have a unique,
multipole-dependent effect on the SD excitations, that is, they produce
softening of 1- states, but hardening of 0- and 2- states. This paves the way
to a clear assessment of the strength of the tensor terms. We compare our
results with a recent measurement, showing that our choice of tensor terms
improves the agreement with experiment. The robustness of our results is
supported by the analytic form of the tensor matrix elements.Comment: 4 pages, 1 figure, 2 table
On Properties of the Isoscalar Giant Dipole Resonance
Main properties (strength function, energy-dependent transition density,
branching ratios for direct nucleon decay) of the isoscalar giant dipole
resonance in several medium-heavy mass spherical nuclei are described within a
continuum-RPA approach, taking into account the smearing effect. All model
parameters used in the calculations are taken from independent data.
Calculation results are compared with available experimental data.Comment: 12 pages, 2 figure
Attractive and repulsive contributions of medium fluctuations to nuclear superfluidity
Oscillations of mainly surface character (S=0 modes) give rise, in atomic
nuclei, to an attractive (induced) pairing interaction, while spin (S=1) modes
of mainly volume character generate a repulsive interaction, the net effect
being an attraction which accounts for a sizeable fraction of the experimental
pairing gap. Suppressing the particle-vibration coupling mediated by the proton
degrees of freedom, i.e., mimicking neutron matter, the total surface plus
spin-induced pairing interaction becomes repulsive
SprayâDried Mesoporous Mixed CuâNi Oxide@Graphene Nanocomposite Microspheres for High Power and Durable LiâIon Battery Anodes
Exfoliated grapheneâwrapped mesoporous CuâNi oxide (CNO) nanocast composites are developed using a straightforward nanostructure engineering strategy. The synergistic effect of hierarchical mesoporous CNO nanobuilding blocks that are homogeneously wrapped by graphene nanosheets (GNSs) using a rapid spray drying technique effectively preserves the electroactive species against the volume changes resulting from the charge/discharge process. Owing to the intriguing structural/morphological features arising from the caging effect of exfoliated graphene sheets, these 3D/2D CNO@GNS nanocomposite microspheres are promising as highâperformance Liâion battery anode materials. They exhibit unprecedented electrochemical behavior, such as high reversible specific capacity (initial discharge capacities exceeding 1700 mAh gâ1 at low 0.1 mA gâ1, stable 850 and 730 mAh gâ1 at 1 and 5 mA gâ1 after 800 and 1300 cycles, respectively, and higher than 400 mAh gâ1 at very high current density of 10 mA gâ1 after more than 2000 cycles), excellent coulombic efficiency and longâterm stability (more than 3000 cycles with >55% capacity retention) at high current density that are remarkable compared to most transition metal oxides and nanocomposites prepared by conventional techniques. This simple, yet innovative, material design is inspiring to develop advanced conversion materials for Liâion batteries or other energy storage devices
Determination of local energy density functionals from Brueckner-Hartree-Fock calculations
Generator Coordinate Method Calculations for Ground and First Excited Collective States in He, O and Ca Nuclei
The main characteristics of the ground and, in particular, the first excited
monopole state in the He, O and Ca nuclei are studied
within the generator coordinate method using Skyrme-type effective forces and
three construction potentials, namely the harmonic-oscillator, the square-well
and Woods-Saxon potentials. Calculations of density distributions, radii,
nucleon momentum distributions, natural orbitals, occupation numbers and
depletions of the Fermi sea, as well as of pair density and momentum
distributions are carried out. A comparison of these quantities for both ground
and first excited monopole states with the available empirical data and with
the results of other theoretical methods are given and discussed in detail.Comment: 15 pages, LaTeX, 6 Postscript figures, submitted to EPJ
Electron-phonon interaction in C70
The matrix elements of the deformation potential of C are calculated
by means of a simple, yet accurate solution of the electron-phonon coupling
problem in fullerenes, based on a parametrization of the ground state
electronic density of the system in terms of hybridized orbitals.
The value of the calculated dimensionless total electron-phonon coupling
constant is , an order of magnitude smaller than in
C, consistent with the lack of a superconducting phase transition in
CA fullerite, and in overall agreement with measurements of the
broadening of Raman peaks in CK. We also calculate the photoemission
cross section of C, which is found to display less structure than that
associated with C, in overall agreement with the experimental
findings.Comment: To be published in Phys. Rev.
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