3,578 research outputs found
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.
On the splitting of nucleon effective masses at high isospin density: reaction observables
We review the present status of the nucleon effective mass splitting
in asymmetric matter, with controversial predictions within both
non-relativistic relativistic approaches to the effective in medium
interactions. Based on microscopic transport simulations we suggest some rather
sensitive observables in collisions of asymmetric (unstable) ions at
intermediate () energies: i) Energy systematics of Lane Potentials; ii)
Isospin content of fast emitted nucleons; iii) Differential Collective Flows.
Similar measurements for light isobars (like ) could be also
important.Comment: 13 pages, 10 figures; NSCL/RIA Workshop on "Reaction Mechanisms for
Rare Isotope Beams", March 2005, AIP Proc. Latex Styl
Non-Markovian source term for particle production by a self-interacting scalar field in the large-N approximation
The particle production in the self-interacting N-component complex scalar
field theory is studied at large N. A non-Markovian source term that includes
all higher order back-reaction and collision effects is derived. The kinetic
amplitudes accounting for the change in the particle number density caused by
collisions are obtained. It is shown that the production of particles is
symmetric in the momentum space. The problem of renormalization is briefly
discussed.Comment: minor changes, journal versio
Isospin Dynamics in Peripheral Heavy Ion Collisions at Fermi Energies
We present a detailed study of isospin dynamics in peripheral collisions at
Fermi energies. We consider symmetric and mixed collisions of (124,112)Sn
isotopes at 35 and 50 AMeV to study the isospin transport between the different
reaction components (residues, gas and possibly intermediate mass fragments)
and, in particular, the charge equilibration in the mixed system. We evaluate
the effects of drift terms due to asymmetry and density gradients, which are
directly related to the poorly known value and slope of the symmetry energy
below saturation density. We verify the importance of an isoscalar momentum
dependence of the mean field, which is found to influence the isospin transport
since it changes the reaction times. We finally suggest two observables
particularly sensitive to the isovector part of the nuclear equation-of-state:
the correlation between isospin equilibration and kinetic energy loss for
binary events, and the isospin content of the produced mid-rapidity fragments
for neck fragmentation events.Comment: 34 pages, 15 figures, Nucl.Phys. A, in pres
Probing the nuclear EOS with fragment production
We discuss fragmentation mechanisms and isospin transport occurring in
central collisions between neutron rich systems at Fermi energies. In
particular, isospin effects are analyzed looking at the correlations between
fragment isotopic content and kinematical properties. Simulations are based on
an approximate solution of the Boltzmann-Langevin (BL) equation. An attempt to
solve the complete BL equation, by introducing full fluctuations in phase space
is also discussed.Comment: 10 pages, 4 figures; Int.Nucl.Phys.Conf., Tokyo June 07, to appear in
Nucl.Phys.A (Elsart
Analysis of Boltzmann-Langevin Dynamics in Nuclear Matter
The Boltzmann-Langevin dynamics of harmonic modes in nuclear matter is
analyzed within linear-response theory, both with an elementary treatment and
by using the frequency-dependent response function. It is shown how the source
terms agitating the modes can be obtained from the basic BL correlation kernel
by a simple projection onto the associated dual basis states, which are
proportional to the RPA amplitudes and can be expressed explicitly. The source
terms for the correlated agitation of any two such modes can then be extracted
directly, without consideration of the other modes. This facilitates the
analysis of collective modes in unstable matter and makes it possible to asses
the accuracy of an approximate projection technique employed previously.Comment: 13 latex pages, 4 PS figure
Giant Octupole Resonance Simulation
Using a pseudo-particle technique we simulate large-amplitude isoscalar giant
octupole excitations in a finite nuclear system. Dependent on the initial
conditions we observe either clear octupole modes or over-damped octupole modes
which decay immediately into quadrupole ones. This shows clearly a behavior
beyond linear response. We propose that octupole modes might be observed in
central collisions of heavy ions
Comparison of dynamical multifragmentation models
Multifragmentation scenarios, as predicted by antisymmetrized molecular
dynamics (AMD) or momentum-dependent stochastic mean-field (BGBD) calculations
are compared. While in the BGBD case fragment emission is clearly linked to the
spinodal decomposition mechanism, i.e. to mean-field instabilities, in AMD
many-body correlations have a stronger impact on the fragmentation dynamics and
clusters start to appear at earlier times. As a consequence, fragments are
formed on shorter time scales in AMD, on about equal footing of light particle
pre-equilibrium emission. Conversely, in BGBD pre-equilibrium and fragment
emissions happen on different time scales and are related to different
mechanisms
Morphology and properties evolution upon ring-opening polymerization during extrusion of cyclic butylene terephthalate and graphene-related-materials into thermally conductive nanocomposites
In this work, the study of thermal conductivity before and after in-situ
ring-opening polymerization of cyclic butylene terephthalate into poly
(butylene terephthalate) in presence of graphene-related materials (GRM) is
addressed, to gain insight in the modification of nanocomposites morphology
upon polymerization. Five types of GRM were used: one type of graphite
nanoplatelets, two different grades of reduced graphene oxide (rGO) and the
same rGO grades after thermal annealing for 1 hour at 1700{\deg}C under vacuum
to reduce their defectiveness. Polymerization of CBT into pCBT, morphology and
nanoparticle organization were investigated by means of differential scanning
calorimetry, electron microscopy and rheology. Electrical and thermal
properties were investigated by means of volumetric resistivity and bulk
thermal conductivity measurement. In particular, the reduction of nanoflake
aspect ratio during ring-opening polymerization was found to have a detrimental
effect on both electrical and thermal conductivities in nanocomposites
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