5,287 research outputs found
Influence of pairing correlations on the radius of neutron-rich nuclei
The influence of pairing correlations on the neutron root mean square (rms)
radius of nuclei is investigated in the framework of self-consistent Skyrme
Hartree-Fock-Bogoliubov calculations. The continuum is treated appropriately by
the Green's function techniques. As an example the nucleus Zr is
treated for a varying strength of pairing correlations. We find that, as the
pairing strength increases, the neutron rms radius first shrinks, reaches a
minimum and beyond this point it expands again. The shrinkage is due to the the
so-called `pairing anti-halo effect', i. e. due to the decreasing of the
asymptotic density distribution with increasing pairing. However, in some
cases, increasing pairing correlations can also lead to an expansion of the
nucleus due to a growing occupation of so-called `halo' orbits, i.e. weakly
bound states and resonances in the continuum with low- values. In this
case, the neutron radii are extended just by the influence of pairing
correlations, since these `halo' orbits cannot be occupied without pairing. The
term `anti-halo effect' is not justified in such cases. For a full
understanding of this complicated interplay self-consistent calculations are
necessary.Comment: 18 pages, 5 figure
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Optimization of bus stop locations for on-demand public bus service
This paper proposes an optimization model formulation for the design of bus stop spacing of on-demand public bus (ODPB) service. The objective of this model is to minimize the total travel time of all the passengers. To capture the unique characteristics of ODPB service, model constraints such as the length of segment, the configuration of shed line, minimum stop spacing, vehicle capacity limitation, are explicitly considered. Numerical results show that the optimal bus stop spacing for ODPB is very different from a conventional bus. Factors like passenger density, travel time perception weight ratio, access/egress walking speed, and the time loss near/at the stop would affect the ODPB stop spacing significantly
Effects of tensor forces in nuclear spin-orbit splittings from ab initio calculations
A systematic and specific pattern due to the effects of the tensor forces is
found in the evolution of spin-orbit splittings in neutron drops. This result
is obtained from relativistic Brueckner-Hartree-Fock theory using the bare
nucleon-nucleon interaction. It forms an important guide for future microscopic
derivations of relativistic and nonrelativistic nuclear energy density
functionals.Comment: 14 pages, 3 figure
Fully self-consistent relativistic Brueckner-Hartree-Fock theory for finite nuclei
Starting from the relativistic form of the Bonn potential as a bare
nucleon-nucleon interaction, the full Relativistic Brueckner-Hartree-Fock
(RBHF) equations are solved for finite nuclei in a fully self-consistent basis.
This provides a relativistic ab initio calculation of the ground state
properties of finite nuclei without any free parameters and without three-body
forces. The convergence properties for the solutions of these coupled equations
are discussed in detail at the example of the nucleus O. The binding
energies, radii, and spin-orbit splittings of the doubly magic nuclei He,
O, and Ca are calculated and compared with the earlier RBHF
calculated results in a fixed Dirac Woods-Saxon basis and other
non-relativistic ab initio calculated results based on pure two-body forces.Comment: 22 pages, 13 figure
Relativistic Brueckner-Hartree-Fock theory for neutron drops
Neutron drops confined in an external field are studied in the framework of
relativistic Brueckner-Hartree-Fock theory using the bare nucleon-nucleon
interaction. The ground state energies and radii of neutron drops with even
numbers from to are calculated and compared with results
obtained from other nonrelativistic \textit{ab initio} calculations and from
relativistic density functional theory. Special attention has been paid to the
magic numbers and to the sub-shell closures. The single-particle energies are
investigated and the monopole effect of the tensor force on the evolutions of
the spin-orbit and the pseudospin-orbit splittings is discussed. The results
provide interesting insight of neutron rich systems and can form an important
guide for future density functionals.Comment: 31 pages, 12 figure
Dark viscous fluid described by a unified equation of state in cosmology
We generalize the CDM model by introducing a unified EOS to describe
the Universe contents modeled as dark viscous fluid, motivated by the fact that
a single constant equation of state (EOS) () reproduces the
CDM model exactly. This EOS describes the perfect fluid term, the
dissipative effect, and the cosmological constant in a unique framework and the
Friedmann equations can be analytically solved. Especially, we find a relation
between the EOS parameter and the renormalizable condition of a scalar field.
We develop a completely numerical method to perform a minimization to
constrain the parameters in a cosmological model directly from the Friedmann
equations, and employ the SNe data with the parameter measured
from the SDSS data to constrain our model. The result indicates that the
dissipative effect is rather small in the late-time Universe.Comment: 4 pages, 2 figures. v2: new materials added. v3: matches the version
to appear in IJMP
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