2,055 research outputs found
Asymmetry Effects on Nuclear Fragmentation
We show the possibility of extracting important information on the symmetry
term of the Equation of State () directly from multifragmentation
reactions using stable isotopes with different charge asymmetries. We study
n-rich and n-poor collisions at using a new stochastic
transport approach with all isospin effects suitably accounted for. For central
collisions a chemical component in the spinodal instabilities is clearly seen.
This effect is reduced in the neck fragmentation observed for semiperipheral
collisions, pointing to a different nature of the instability. In spite of the
low asymmetry tested with stable isotopes the results are showing an
interesting and promising dependence on the stiffness of the symmetry term,
with an indication towards an increase of the repulsion above normal density.Comment: 8 pages (Latex), 7 Postscript figures, CRIS2000 Conference,
Acicastello, Italy, May 22-26, (2000), Nucl. Phys. A (in press
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
Symmetry Energy Effects on the Mixed Hadron-Quark Phase at High Baryon Density
The phase transition of hadronic to quark matter at high baryon and isospin
density is analyzed. Relativistic mean field models are used to describe
hadronic matter, and the MIT bag model is adopted for quark matter. The
boundaries of the mixed phase and the related critical points for symmetric and
asymmetric matter are obtained. Due to the different symmetry term in the two
phases, isospin effects appear to be rather significant. With increasing
isospin asymmetry the binodal transition line of the (T,\rho_B) diagram is
lowered to a region accessible through heavy ion collisions in the energy range
of the new planned facilities, e.g. the FAIR/NICA projects. Some observable
effects are suggested, in particular an "Isospin Distillation" mechanism with a
more isospin asymmetric quark phase, to be seen in charged meson yield ratios,
and an onset of quark number scaling of the meson/baryon elliptic flows. The
presented isospin effects on the mixed phase appear to be robust with respect
to even large variations of the poorly known symmetry term at high baryon
density in the hadron phase. The dependence of the results on a suitable
treatment of isospin contributions in effective QCD Lagrangian approaches, at
the level of explicit isovector parts and/or quark condensates, is finally
discussed.Comment: 14 two column pages, 14 figures, new results with other hadron EoS.
Accepted for publication in Phys.Rev.
Hadron-quark phase transition in asymmetric matter with dynamical quark masses
The two-Equation of State (EoS) model is used to describe the hadron-quark
phase transition in asymmetric matter formed at high density in heavy-ion
collisions. For the quark phase, the three-flavor Nambu--Jona-Lasinio (NJL)
effective theory is used to investigate the influence of dynamical quark mass
effects on the phase transition. At variance to the MIT-Bag results, with fixed
current quark masses, the main important effect of the chiral dynamics is the
appearance of an End-Point for the coexistence zone. We show that a first order
hadron-quark phase transition may take place in the region T=(50-80)MeV and
\rho_B=(2-4)\rho_0, which is possible to be probed in the new planned
facilities, such as FAIR at GSI-Darmstadt and NICA at JINR-Dubna. From isospin
properties of the mixed phase somepossible signals are suggested. The
importance of chiral symmetry and dynamical quark mass on the hadron-quark
phase transition is stressed. The difficulty of an exact location of
Critical-End-Point comes from its appearance in a region of competition between
chiral symmetry breaking and confinement, where our knowledge of effective QCD
theories is still rather uncertain.Comment: 13 pages, 16 figures (revtex
Low density instability in a nuclear Fermi liquid drop
The instability of a Fermi-liquid drop with respect to bulk density
distortions is considered. It is shown that the presence of the surface
strongly reduces the growth rate of the bulk instability of the finite
Fermi-liquid drop because of the anomalous dispersion term in the dispersion
relation. The instability growth rate is reduced due to the Fermi surface
distortions and the relaxation processes. The dependence of the bulk
instability on the multipolarity of the particle density fluctuations is
demonstrated for two nuclei and .Comment: 12 pages, latex, 3 ps-figures, submitted to Phys. Rev.
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]
Development of RT-semi-nested PCR for detection of hepatitis A virus in stool in epidemic conditions.
The purpose of this study was to determine the efficiency of semi-nested PCR in detecting hepatitis A virus (HAV) RNA. During a 2-year period (1990-1991), HAV RNA was searched for in shellfish from the French Brittany coasts using cRNA and vRNA probes. In January 1992, at the time of a hepatitis A outbreak, 28 stool samples were collected from infected patients (18 adults, 10 children) with anti-HAV IgM. Four samples from subjects with negative HAV serology were used as negative controls. Nucleic acid amplification (reverse-transcription-semi-nested PCR) was performed to detect HAV in stool. HAV RNA was purified by phenol-chloroform extraction and converted to cDNA using reverse transcriptase (Mu-MLV). After amplification, PCR products were visualized on an ethidium-bromide-stained gel and confirmed by hybridization with a specific digoxigenin-labelled oligoprobe. Samples were also studied by molecular hybridization with cRNA and vRNA probes. After onset of the illness, HAV RNA was detected over a longer time period by semi-nested PCR (16/28) than by hybridization (0/28). Even though biological diagnosis of hepatitis A will continue to rely on the detection of anti-HAV IgM, PCR should be useful in certain clinical cases (diagnosis of relapse) and for epidemiological and environmental monitoring of viruses
Isospin Dynamics in Heavy Ion Collisions: from Coulomb Barrier to Quark Gluon Plasma
Heavy Ion Collisions (HIC) represent a unique tool to probe the in-medium
nuclear interaction in regions away from saturation. In this report we present
a selection of new reaction observables in dissipative collisions particularly
sensitive to the symmetry term of the nuclear Equation of State (Iso-EoS). We
will first discuss the Isospin Equilibration Dynamics. At low energies this
manifests via the recently observed Dynamical Dipole Radiation, due to a
collective neutron-proton oscillation with the symmetry term acting as a
restoring force. At higher beam energies Iso-EoS effects will be seen in
Imbalance Ratio Measurements, in particular from the correlations with the
total kinetic energy loss. For fragmentation reactions in central events we
suggest to look at the coupling between isospin distillation and radial flow.
In Neck Fragmentation reactions important information can be obtained
from the correlation between isospin content and alignement. The high density
symmetry term can be probed from isospin effects on heavy ion reactions at
relativistic energies (few AGeV range). Rather isospin sensitive observables
are proposed from nucleon/cluster emissions, collective flows and meson
production. The possibility to shed light on the controversial neutron/proton
effective mass splitting in asymmetric matter is also suggested. A large
symmetry repulsion at high baryon density will also lead to an "earlier"
hadron-deconfinement transition in n-rich matter. A suitable treatment of the
isovector interaction in the partonic EoS appears very relevant.Comment: 18 pages, 12 figures, lecture at the 2008 Erice School on Nuclear
Physics, to appear in Progress in Particle and Nuclear Physic
Isotopic Composition of Fragments in Nuclear Multifragmentation
The isotope yields of fragments, produced in the decay of the quasiprojectile
in Au+Au peripheral collisions at 35 MeV/nucleon and those coming from the
disassembly of the unique source formed in Xe+Cu central reactions at 30
MeV/nucleon, were measured. We show that the relative yields of neutron-rich
isotopes increase with the excitation energy in multifragmentation reaction. In
the framework of the statistical multifragmentation model which fairly well
reproduces the experimental observables, this behaviour can be explained by
increasing N/Z ratio of hot primary fragments, that corresponds to the
statistical evolution of the decay mechanism with the excitation energy: from a
compound-like decay to complete multifragmentation.Comment: 10 pages. 4 Postscript figures. Submitted to Physical Review C, Rapid
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