21,101 research outputs found
Covariant description of shape evolution and shape coexistence in neutron-rich nuclei at N\approx60
The shape evolution and shape coexistence phenomena in neutron-rich nuclei at
, including Kr, Sr, Zr, and Mo isotopes, are studied in the
covariant density functional theory (DFT) with the new parameter set PC-PK1.
Pairing correlations are treated using the BCS approximation with a separable
pairing force. Sharp rising in the charge radii of Sr and Zr isotopes at N=60
is observed and shown to be related to the rapid changing in nuclear shapes.
The shape evolution is moderate in neighboring Kr and Mo isotopes. Similar as
the results of previous Hartree-Fock-Bogogliubov (HFB) calculations with the
Gogny force, triaxiality is observed in Mo isotopes and shown to be essential
to reproduce quantitatively the corresponding charge radii. In addition, the
coexistence of prolate and oblate shapes is found in both Sr and
Zr. The observed oblate and prolate minima are related to the low
single-particle energy level density around the Fermi surfaces of neutron and
proton respectively. Furthermore, the 5-dimensional (5D) collective Hamiltonian
determined by the calculations of the PC-PK1 energy functional is solved for
Sr and Zr. The resultant excitation energy of state and
E0 transition strength are in rather good
agreement with the data. It is found that the lower barrier height separating
the two competing minima along the deformation in Zr gives
rise to the larger than that in Sr.Comment: 1 table, 11 figures, 23 page
Channel Parameters Estimation Algorithm Based on The Characteristic Function under Impulse Noise Environment
Under communication environments, such as wireless sensor networks, the noise observed usually exhibits impulsive as well as Gaussian characteristics. In the initialization of channel iterative decoder, such as low density parity check codes, it is required in advance to estimate the channel parameters to obtain the prior information from the received signals. In this paper, a blind channel parameters estimator under impulsive noise environment is proposed, which is based on the empirical characteristic function in MPSK/MQAM higher-order modulation system. Simulation results show that for various MPSK/MQAM modulations, the estimator can obtain a more accurate unbiased estimation even though we do not know which kind of higher-order modulation is used
Solving Dirac equations on a 3D lattice with inverse Hamiltonian and spectral methods
A new method to solve the Dirac equation on a 3D lattice is proposed, in
which the variational collapse problem is avoided by the inverse Hamiltonian
method and the fermion doubling problem is avoided by performing spatial
derivatives in momentum space with the help of the discrete Fourier transform,
i.e., the spectral method. This method is demonstrated in solving the Dirac
equation for a given spherical potential in 3D lattice space. In comparison
with the results obtained by the shooting method, the differences in single
particle energy are smaller than ~MeV, and the densities are almost
identical, which demonstrates the high accuracy of the present method. The
results obtained by applying this method without any modification to solve the
Dirac equations for an axial deformed, non-axial deformed, and octupole
deformed potential are provided and discussed.Comment: 18 pages, 6 figure
Energy-dependent Lorentz covariant parameterization of the NN interaction between 50 and 200 MeV
For laboratory kinetic energies between 50 and 200 MeV, we focus on
generating an energy-dependent Lorentz covariant parameterization of the
on-shell nucleon-nucleon (NN) scattering amplitudes in terms of a number of
Yukawa-type meson exchanges in first-order Born approximation. This
parameterization provides a good description of NN scattering observables in
the energy range of interest, and can also be extrapolated to energies between
40 and 300 MeV.Comment: 18 pages, 7 figures, Final version accepted by Physics Review
Nuclear quantum shape-phase transitions in odd-mass systems
Microscopic signatures of nuclear ground-state shape phase transitions in
odd-mass Eu isotopes are explored starting from excitation spectra and
collective wave functions obtained by diagonalization of a core-quasiparticle
coupling Hamiltonian based on energy density functionals. As functions of the
physical control parameter -- the number of nucleons -- theoretical low-energy
spectra, two-neutron separation energies, charge isotope shifts, spectroscopic
quadrupole moments, and reduced transition matrix elements accurately
reproduce available data, and exhibit more pronounced discontinuities at
neutron number , compared to the adjacent even-even Sm and Gd isotopes.
The enhancement of the first-order quantum phase transition in odd-mass systems
can be attributed to a shape polarization effect of the unpaired proton which,
at the critical neutron number, starts predominantly coupling to Gd core nuclei
that are characterized by larger quadrupole deformation and weaker proton
pairing correlations compared to the corresponding Sm isotopes.Comment: 6 pages, 4 figure
Microscopic Analysis of Order Parameters in Nuclear Quantum Phase Transitions
Microscopic signatures of nuclear ground-state shape phase transitions in Nd
isotopes are studied using excitation spectra and collective wave functions
obtained by diagonalization of a five-dimensional Hamiltonian for quadrupole
vibrational and rotational degrees of freedom, with parameters determined by
constrained self-consistent relativistic mean-field calculations for triaxial
shapes. As a function of the physical control parameter -- the number of
nucleons, energy gaps between the ground state and the excited vibrational
states with zero angular momentum, isomer shifts, and monopole transition
strengths, exhibit sharp discontinuities at neutron number N=90, characteristic
of a first-order quantum phase transition.Comment: 5 pages, 4 figures, accepted for publication as a Rapid Communication
in Physical Review
Low-lying states in Mg: a beyond relativistic mean-field investigation
The recently developed model of three-dimensional angular momentum projection
plus generator coordinate method on top of triaxial relativistic mean-field
states has been applied to study the low-lying states of Mg. The effects
of triaxiality on the low-energy spectra and E0 and E2 transitions are
examined.Comment: 6 pages, 3 figures, 1 table, talk presented at the 17th nuclear
physics conference "Marie and Pierre Curie" Kazimierz Dolny, 22-26th
September 2010, Polan
New parametrization for the nuclear covariant energy density functional with point-coupling interaction
A new parametrization PC-PK1 for the nuclear covariant energy density
functional with nonlinear point-coupling interaction is proposed by fitting to
observables for 60 selected spherical nuclei, including the binding energies,
charge radii and empirical pairing gaps. The success of PC-PK1 is illustrated
in its description for infinite nuclear matter and finite nuclei including the
ground-state and low-lying excited states. Particularly, PC-PK1 improves the
description for isospin dependence of binding energy along either the isotopic
or the isotonic chains, which makes it more reliable for application in exotic
nuclei. The predictive power of PC-PK1 is also illustrated for the nuclear
low-lying excitation states in a five-dimensional collective Hamiltonian in
which the parameters are determined by constrained calculations for triaxial
shapes.Comment: 32 pages, 12 figures, 4 tables, accepted by Phys. Rev.
- …