16,025 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
Antisymmetrized molecular dynamics with quantum branching processes for collisions of heavy nuclei
Antisymmetrized molecular dynamics (AMD) with quantum branching processes is
reformulated so that it can be applicable to the collisions of heavy nuclei
such as Au + Au multifragmentation reactions. The quantum branching process due
to the wave packet diffusion effect is treated as a random term in a
Langevin-type equation of motion, whose numerical treatment is much easier than
the method of the previous papers. Furthermore a new approximation formula,
called the triple-loop approximation, is introduced in order to evaluate the
Hamiltonian in the equation of motion with much less computation time than the
exact calculation. A calculation is performed for the Au + Au central
collisions at 150 MeV/nucleon. The result shows that AMD almost reproduces the
copious fragment formation in this reaction.Comment: 24 pages, 5 figures embedde
Antisymmetrized molecular dynamics of wave packets with stochastic incorporation of Vlasov equation
On the basis of the antisymmetrized molecular dynamics (AMD) of wave packets
for the quantum system, a novel model (called AMD-V) is constructed by the
stochastic incorporation of the diffusion and the deformation of wave packets
which is calculated by Vlasov equation without any restriction on the one-body
distribution. In other words, the stochastic branching process in molecular
dynamics is formulated so that the instantaneous time evolution of the averaged
one-body distribution is essentially equivalent to the solution of Vlasov
equation. Furthermore, as usual molecular dynamics, AMD-V keeps the many-body
correlation and can naturally describe the fluctuation among many channels of
the reaction. It is demonstrated that the newly introduced process of AMD-V has
drastic effects in heavy ion collisions of 40Ca + 40Ca at 35 MeV/nucleon,
especially on the fragmentation mechanism, and AMD-V reproduces the
fragmentation data very well. Discussions are given on the interrelation among
the frameworks of AMD, AMD-V and other microscopic models developed for the
nuclear dynamics.Comment: 26 pages, LaTeX with revtex and epsf, embedded postscript figure
Nucleon Flow and Fragment Flow in Heavy Ion Reactions
The collective flow of nucleons and that of fragments in the 12C + 12C
reaction below 150 MeV/nucleon are calculated with the antisymmetrized version
of molecular dynamics combined with the statistical decay calculation. Density
dependent Gogny force is used as the effective interaction. The calculated
balance energy is about 100 MeV/nucleon, which is close to the observed value.
Below the balance energy, the absolute value of the fragment flow is larger
than that of nucleon flow, which is also in accordance with data. The
dependence of the flow on the stochastic collision cross section and its origin
are discussed. All the results are naturally understood by introducing the
concept of two components of flow: the flow of dynamically emitted nucleons and
the flow of the nuclear matter which contributes to both the flow of fragments
and the flow of nucleons due to the statistical decay.Comment: 20 pages, PostScript figures, LaTeX with REVTeX and EPSF, KUNS 121
Flexible control of the Peierls transition in metallic C polymers
The metal-semiconductor transition of peanut-shaped fullerene (C)
polymers is clarified by considering the electron-phonon coupling in the uneven
structure of the polymers. We established a theory that accounts for the
transition temperature reported in a recent experiment and also suggests
that is considerably lowered by electron doping or prolonged irradiation
during synthesis. The decrease in is an appealing phenomenon with regard
to realizing high-conductivity C-based nanowires even at low
temperatures.Comment: 3 pages, 3 figure
Fragmentation paths in dynamical models
We undertake a quantitative comparison of multi-fragmentation reactions, as
modeled by two different approaches: the Antisymmetrized Molecular Dynamics
(AMD) and the momentum-dependent stochastic mean-field (SMF) model. Fragment
observables and pre-equilibrium (nucleon and light cluster) emission are
analyzed, in connection to the underlying compression-expansion dynamics in
each model. Considering reactions between neutron-rich systems, observables
related to the isotopic properties of emitted particles and fragments are also
discussed, as a function of the parametrization employed for the isovector part
of the nuclear interaction. We find that the reaction path, particularly the
mechanism of fragmentation, is different in the two models and reflects on some
properties of the reaction products, including their isospin content. This
should be taken into account in the study of the density dependence of the
symmetry energy from such collisions.Comment: 11 pages, 13 figures, submitted to Phys. Rev.
A critical examination of discrete lattice and dispersed barrier hardening
Critical assessment of discrete lattice and dispersed barrier hardening theories of thermally activated deformation of metal
Short timescale behavior of colliding heavy nuclei at intermediate energies
An Antisymmetrized Molecular Dynamics model is used to explore the collision
of Cd projectiles with Mo target nuclei at E/A=50 MeV over a
broad range in impact parameter. The atomic number (Z), velocity, and emission
pattern of the reaction products are examined as a function of the impact
parameter and the cluster recognition time. The non-central collisions are
found to be essentially binary in character resulting in the formation of an
excited projectile-like fragment (PLF) and target-like fragment (TLF).
The decay of these fragments occurs on a short timescale, 100t300
fm/c. The average excitation energy deduced for the PLF and TLF
`saturates for mid-central collisions, 3.5b6 fm, with its magnitude
depending on the cluster recognition time. For short cluster recognition times
(t=150 fm/c), an average excitation energy as high as 6 MeV is
predicted. Short timescale emission leads to a loss of initial correlations and
results in features such as an anisotropic emission pattern of both IMFs and
alpha particles emitted from the PLF and TLF in peripheral collisions.Comment: 19 pages, 17 figure
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