3,556 research outputs found
Spinodal instabilities within BUU approach
Using a recently developed method for the inclusion of fluctuation in the BUU
dynamics, we study the self-consistent propagation of inherent thermal noise of
unstable nuclear matter. The large time behaviour of the evolving system
exhibits synergism between fluctuation and non-linearities in a universal
manner which manifest in the appearance of macroscopic structure in the average
description.Comment: 12 pages Revtex. Two figures, uuencoded, are enclosed in a separate
fil
Analysis of charged particle emission sources and coalescence in E/A = 61 MeV Ar + Al, Sn and Sn collisions
Single-particle kinetic energy spectra and two-particle small angle
correlations of protons (), deuterons () and tritons () have been
measured simultaneously in 61A MeV Ar + Al, Sn and
Sn collisions. Characteristics of the emission sources have been
derived from a ``source identification plot'' (--
plot), constructed from the single-particle invariant spectra, and compared to
the complementary results from two-particle correlation functions. Furthermore,
the source identification plot has been used to determine the conditions when
the coalescence mechanism can be applied for composite particles. In our data,
this is the case only for the Ar + Al reaction, where , and are
found to originate from a common source of emission (from the overlap region
between target and projectile). In this case, the coalescence model parameter,
-- the radius of the complex particle emission source in momentum
space, has been analyzed.Comment: 20 pages, 5 figures, submitted to Nuclear Physics
Summary of EMI/EMC and vibroacoustics
The space shuttle payload bay environment data relating to vibroacoustics and electromagnetic effects are presented. Measurements were taken with low frequency accelerometers. Comparisons were made during ascent and descent
Coulomb effects on growth of instabilities in asymmetric nuclear matter
We study the effects of the Coulomb interaction on the growth of unstable
modes in asymmetric nuclear matter. In order to compare with previous
calculations we use a semiclassical approach based on the linearized Vlasov
equation. Moreover, a quantum calculation is performed within the R.P.A.. The
Coulomb effects are a slowing down of the growth and the occurrence of a
minimal wave vector for the onset of the instabilities. The quantum corrections
cause a further decrease of the growth rates.Comment: 10 pages, revtex, 4 ps figures, to appear in Phys. Rev. C e-mail:
[email protected], [email protected]
Isospin Transport at Fermi Energies
In this paper we investigate isospin transport mechanisms in semi-peripheral
collisions at Fermi energies. The effects of the formation of a low density
region (neck) between the two reaction partners and of pre-equilibrium emission
on the dynamics of isospin equilibration are carefully analyzed. We clearly
identify two main contributions to the isospin transport: isospin diffusion due
to the ratio and isospin drift due to the density gradients. Both effects
are sensitive to the symmetry part of the nuclear Equation of State (EOS), in
particular to the value and slope around saturation density.Comment: 6 pages, 6 figures, revtex4-twocolumn
Signatures of nematic quantum critical fluctuations in the Raman spectra of lightly doped cuprates
We consider the lightly doped cuprates YCaBaCuO
and LaSrCuO (with ,0.04), where the presence of a
fluctuating nematic state has often been proposed as a precursor of the stripe
(or, more generically, charge-density wave) phase, which sets in at higher
doping. We phenomenologically assume a quantum critical character for the
longitudinal and transverse nematic, and for the charge-ordering fluctuations,
and investigate the effects of these fluctuations in Raman spectra. We find
that the longitudinal nematic fluctuations peaked at zero transferred momentum
account well for the anomalous Raman absorption observed in these systems in
the channel, while the absence of such effect in the channel
may be due to the overall suppression of Raman response at low frequencies,
associated with the pseudogap. While in YCaBaCuO the
low-frequency lineshape is fully accounted by longitudinal nematic collective
modes alone, in LaSrCuO also charge-ordering modes with finite
characteristic wavevector are needed to reproduce the shoulders observed in the
Raman response. This different involvement of the nearly critical modes in the
two materials suggests a different evolution of the nematic state at very low
doping into the nearly charge-ordered state at higher doping.Comment: 12 pages with 10 figures, to appear in Phys. Rev. B 201
IMF isotopic properties in semi-peripheral collisions at Fermi energies
We study the neutron and proton dynamical behavior along the fragmentation
path in semi-peripheral collisions: 58Fe+58Fe (charge asymmetric, N/Z = 1.23)
and 58Ni+58Ni (charge symmetric, N/Z = 1.07), at 47 AMeV. We observe that
isospin dynamics processes take place also in the charge-symmetric system
58Ni+58Ni, that may produce more asymmetric fragments. A neutron enrichment of
the neck fragments is observed, resulting from the interplay between
pre-equilibrium emission and the phenomenon of "isospin-migration". Both
effects depend on the EoS (Equation of State) symmetry term. This point is
illustrated by comparing the results obtained with two different choices of the
symmetry energy density dependence.
New correlation observables are suggested, to study the reaction mechanism
and the isospin dynamics.Comment: 5 pages, 8 figures, Revtex4 Latex Styl
Nuclear fragmentation: sampling the instabilities of binary systems
We derive stability conditions of Asymmetric Nuclear Matter () and
discuss the relation to mechanical and chemical instabilities of general
two-component systems. We show that the chemical instability may appear as an
instability of the system against isoscalar-like rather than isovector-like
fluctuations if the interaction between the two constituent species has an
attractive character as in the case of . This leads to a new kind of
liquid-gas phase transition, of interest for fragmentation experiments with
radioactive beams.Comment: 4 pages (LATEX), 3 Postscript figures, improved version, added
reference
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