63,107 research outputs found
Statistical properties of antisymmetrized molecular dynamics for non-nucleon-emission and nucleon-emission processes
Statistical properties of the antisymmetrized molecular dynamics (AMD) are
classical in the case of nucleon emission processes, while they are quantum
mechanical for the processes without nucleon emission. We first clarify that
there coexist mutually opposite two statistics in the AMD framework: One is the
classical statistics of the motion of wave packet centroids and the other is
the quantum statistics of the motion of wave packets which is described by the
AMD wave function. We prove the classical statistics of wave packet centroids
by using the framework of the microcanonical ensemble of the nuclear system. We
show that the quantum statistics of wave packets emerges from the classical
statistics of wave packet centroids. It is emphasized that the temperature of
the classical statistics of wave packet centroids is different from the
temperature of the quantum statistics of wave packets. We then explain that the
statistical properties of AMD for nucleon emission processes are classical
because nucleon emission processes in AMD are described by the motion of wave
packet centroids. When we improve the description of the nucleon emission
process so as to take into account the momentum fluctuation due to the wave
packet spread, the AMD statistical properties for nucleon emission processes
change drastically into quantum statistics. Our study of nucleon emission
processes can be conversely regarded as giving another kind of proof of the
fact that the statistics of wave packets is quantum mechanical while that of
wave packet centroids is classical.Comment: 20 pages, LaTeX with revtex and epsf, uuenocded postscript figures,
postscript version available at http://pearl.scphys.kyoto-u.ac.jp/~ono
Multifragmentation and Symmetry Energy Studied with AMD
The antisymmetrized molecular dynamics (AMD) simulations suggest that the
isospin composition of fragments produced dynamically in multifragmentation
reactions is basically governed by the symmetry energy of low-density uniform
nuclear matter rather than the symmetry energy for the ground-state finite
nuclei. After the statistical secondary decay of the excited fragments, the
symmetry energy effect still remains in the fragment isospin composition,
though the effect in the isoscaling parameter seems a very delicate problem.Comment: Proceedings for VI Latin American Symposium on Nuclear Physics and
Applications, Iguazu, Argentina (2005). To be published in Acta Phys. Hung.
First-principles calculation of scattering potentials of Si-Ge and Sn-Ge dimers on Ge(001) surfaces
The scattering potential of the defects on Ge(001) surfaces is investigated
by first-principles methods. The standing wave in the spatial map of the local
density of states obtained by wave function matching is compared to the image
of the differential conductance measured by scanning tunneling spectroscopy.
The period of the standing wave and its phase shift agree with those in the
experiment. It is found that the scattering potential becomes a barrier when
the electronegativity of the upper atom of the dimer is larger than that of the
lower atom, while it acts as a well in the opposite case.Comment: to be published in Phys. Rev.
Dynamics of clusters and fragments in heavy-ion collisions
A review is given on the studies of formation of light clusters and heavier
fragments in heavy-ion collisions at incident energies from several tens of
MeV/nucleon to several hundred MeV/nucleon, focusing on dynamical aspects and
on microscopic theoretical descriptions. Existing experimental data already
clarify basic characteristics of expanding and fragmenting systems typically in
central collisions, where cluster correlations cannot be ignored. Cluster
correlations appear almost everywhere in excited low-density nuclear many-body
systems and nuclear matter in statistical equilibrium where the properties of a
cluster may be influenced by the medium. On the other hand, transport models to
solve the time evolution have been developed based on the single-nucleon
distribution function. Different types of transport models are reviewed putting
emphasis both on theoretical features and practical performances in the
description of fragmentation. A key concept to distinguish different models is
how to consistently handle single-nucleon motions in the mean field,
fluctuation or branching induced by two-nucleon collisions, and localization of
nucleons to form fragments and clusters. Some transport codes have been
extended to treat light clusters explicitly. Results indicate that cluster
correlations can have strong impacts on global collision dynamics and
correlations between light clusters should also be taken into account.Comment: review article, 64 pages, 27 figure
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