1,898 research outputs found
Quasi-free (p,2p) and (p,pn) reactions with unstable nuclei
We study (p,2p) and (p,pn) reactions at proton energies in the range of 100
MeV -- 1 GeV. Our purpose is to explore the most sensitive observables in
unpolarized reactions with inverse kinematics involving radioactive nuclei. We
formulate a model based on the eikonal theory to describe total cross sections
and momentum distributions of the recoiled residual nucleus. The model is
similar to the one adopted for knockout reactions with heavy ions. We show that
momentum distributions are sensitive to the angular momentum of the ejected
nucleon which can be used as an spectroscopic tool. The total cross sections
are sensitive to the nucleon separation energies and to multiple scattering
effects. Our calculations also indicate that a beam energy around 500
MeV/nucleon has a smaller dependence on the anisotropy of the nucleon-nucleon
elastic scattering.Comment: 17 pages, 12 figures, Accepted for publication in the Physical review
Sum Rules of the Multiple Giant Dipole States
Various sum rules for multiple giant dipole resonance states are derived. For
the triple giant dipole resonance states, the energy-weighted sum of the
transition strengths requires a model to be related to those of the single and
double giant dipole resonance states. It is also shown that the non-diagonal
matrix elements of the double commutator between the dipole operator and the
nuclear Hamiltonian give useful identities for the excitation energy and
transition strength of each excited state. Using those identities, the
relationship between width of the single dipole state and those of the multiple
ones is qualitatively discussed.Comment: 8 pages, 1 figure, using PTPTeX styl
Anharmonicities of giant dipole excitations
The role of anharmonic effects on the excitation of the double giant dipole
resonance is investigated in a simple macroscopic model.Perturbation theory is
used to find energies and wave functions of the anharmonic ascillator.The cross
sections for the electromagnetic excitation of the one- and two-phonon giant
dipole resonances in energetic heavy-ion collisions are then evaluated through
a semiclassical coupled-channel calculation.It is argued that the variations of
the strength of the anharmonic potential should be combined with appropriate
changes in the oscillator frequency,in order to keep the giant dipole resonance
energy consistent with the experimental value.When this is taken into
account,the effects of anharmonicities on the double giant dipole resonance
excitation probabilities are small and cannot account for the well-known
discrepancy between theory and experiment
Comparison of exact and approximate cross-sections in relativistic Coulomb excitation
We present a new method of obtaining time-dependent matrix elements of the
electromagnetic pulse produced by a highly-relativistic projectile. These
matrix elements are used in a coupled-channel calculation to predict the
cross-sections for population of 1- and 2-phonon states of the giant dipole
resonance. Comparisons are made with the predictions of the long-wavelength and
Born approximations.Comment: 26 pages, LaTex2
Shared Information -- New Insights and Problems in Decomposing Information in Complex Systems
How can the information that a set of random variables
contains about another random variable be decomposed? To what extent do
different subgroups provide the same, i.e. shared or redundant, information,
carry unique information or interact for the emergence of synergistic
information?
Recently Williams and Beer proposed such a decomposition based on natural
properties for shared information. While these properties fix the structure of
the decomposition, they do not uniquely specify the values of the different
terms. Therefore, we investigate additional properties such as strong symmetry
and left monotonicity. We find that strong symmetry is incompatible with the
properties proposed by Williams and Beer. Although left monotonicity is a very
natural property for an information measure it is not fulfilled by any of the
proposed measures.
We also study a geometric framework for information decompositions and ask
whether it is possible to represent shared information by a family of posterior
distributions.
Finally, we draw connections to the notions of shared knowledge and common
knowledge in game theory. While many people believe that independent variables
cannot share information, we show that in game theory independent agents can
have shared knowledge, but not common knowledge. We conclude that intuition and
heuristic arguments do not suffice when arguing about information.Comment: 20 page
Soft Dipole Modes in Neutron-rich Ni-isotopes in QRRPA
The soft dipole modes in neutron rich even-even Ni-isotopes are investigated
in the quasiparticle relativistic random phase approximation. We study the
evolution of strengths distribution, centroid energies of dipole excitation in
low-lying and normal GDR regions with the increase of the neutron excess. It is
found in the present study that the centroid energies of the soft dipole
strengths strongly depend on the thickness of neutron skin along with the
neutron rich even-even Ni-isotopes.Comment: 14 pages, 7 figure
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