201 research outputs found
SOLUTIONS OF THE LANDAU-VLASOV EQUATION IN NUCLEAR PHYSICS
The properties of Vlasov equation solutions obtained by projection on coherent state basis are discussed. Such solutions satisfy stationarity conditions and satisfactorily describe the average diffusivity of nuclear phase space and reproduce the bulk properties of nuclei. Sampling methods and their effects on dynamics are discussed for the study of heavy ion reactions at intermediate energies. The non-local Gogny force is easily computable on this basis which allows to use it for dynamical nuclear studies
PHASE SPACE DYNAMICS OF HEAVY ION NUCLEAR COLLISIONS IN THE FERMI ENERGY DOMAIN
No abstract availabl
Macroscopic dynamics of the fusion process
A macroscopic dynamical model has been used to calculate fusion cross sections for a wide number of systems ranging from 16O + 27Al to 40Ar + 165Ho. This model takes into account the reorganization of the densities and the nucleon exchanges. The possible reaction mechanisms after capture of the system into the pocket of the interaction potential are discussed Two processes contribute to fusion : compound nucleus formation and fast fission phenomenon. The calculated fusion cross sections are in overall agreement with the data
LOW AND INTERMEDIATE ENERGY HEAVY ION COLLISIONS IN THE SEMI-CLASSICAL MICROSCOPIC DESCRIPTION
It is shown how peripheral and central heavy-ion collisions can be described by Landau-Vlasov dynamics. For peripheral collisions at intermediate energies, mass-mass correlations, ejectile mean energies and angular distributions are obtained and compared with fragmentation data. For central collisions, one shows that the collision term destroys the TDHF property of transparency at low impact parameters for collisions close from the Coulomb barrier. Above 20 MeV/u incomplete fusion is described with associated linear momentum transfer and nuclear deformations. One exhibits how coupling to the continuum is obtained in Vlasov and Landau-Vlasov dynamics. Coulomb interaction being taken into account, we present also results concerning the isospin transfer and the excitation of the isovector dipole mode near and well above the Coulomb barrier. Some perspectives to further studies of physical observables are finally drawn
A STUDY ON THE FUSION REACTION 139La + 12C AT 50 MeV/u WITH THE VUU EQUATION
Recently Bownan et al. found that in the reaction 139La + 12C at 50 MeV/u a compound nucleus is formed. We simulate this reaction with a numerical solution of the VUU equation and indeed find that for a central collision the system fuses and equilibrates after 90 fm/c
Isospin non-equilibrium in heavy-ion collisions at intermediate energies
We study the equilibration of isospin degree of freedom in intermediate
energy heavy-ion collisions using an isospin-dependent BUU model. It is found
that there exists a transition from the isospin equilibration at low energies
to non-equilibration at high energies as the beam energy varies across the
Fermi energy in central, asymmetric heavy-ion collisions. At beam energies
around 55 MeV/nucleon, the composite system in thermal equilibrium but isospin
non-equilibrium breaks up into two primary hot residues with N/Z ratios closely
related to those of the target and projectile respectively. The decay of these
forward-backward moving residues results in the strong isospin asymmetry in
space and the dependence of the isotopic composition of fragments on the N/Z
ratios of the target and projectile. These features are in good agreement with
those found recently in experiments at NSCL/MSU and TAMU, implications of these
findings are discussed.Comment: 9 pages, latex, + 3 figures available upon reques
Isospin Physics in Heavy-Ion Collisions at Intermediate Energies
In nuclear collisions induced by stable or radioactive neutron-rich nuclei a
transient state of nuclear matter with an appreciable isospin asymmetry as well
as thermal and compressional excitation can be created. This offers the
possibility to study the properties of nuclear matter in the region between
symmetric nuclear matter and pure neutron matter. In this review, we discuss
recent theoretical studies of the equation of state of isospin-asymmetric
nuclear matter and its relations to the properties of neutron stars and
radioactive nuclei. Chemical and mechanical instabilities as well as the
liquid-gas phase transition in asymmetric nuclear matter are investigated. The
in-medium nucleon-nucleon cross sections at different isospin states are
reviewed as they affect significantly the dynamics of heavy ion collisions
induced by radioactive beams. We then discuss an isospin-dependent transport
model, which includes different mean-field potentials and cross sections for
the proton and neutron, and its application to these reactions. Furthermore, we
review the comparisons between theoretical predictions and available
experimental data. In particular, we discuss the study of nuclear stopping in
terms of isospin equilibration, the dependence of nuclear collective flow and
balance energy on the isospin-dependent nuclear equation of state and cross
sections, the isospin dependence of total nuclear reaction cross sections, and
the role of isospin in preequilibrium nucleon emissions and subthreshold pion
production.Comment: 101 pages with embedded epsf figures, review article for
"International Journal of Modern Physics E: Nuclear Physics". Send request
for a hard copy to 1/author
ÉTUDE EXPÉRIMENTALE ET THÉORIQUE DES NOYAUX DE TRANSITION 68,70,72,74Ge
Les isotopes de 68,70,72,74Ge ont été étudiés avec une haute résolution en énergie au moyen de la réaction (p, t). Un grand nombre de nouveaux niveaux 0+, 2+ et 4+ à basse énergie ont été mis en évidence. Des calculs semi-microscopiques de surfaces d'énergie potentielle et de spectres ont été effectués et des conclusions sont données sur la structure des noyaux Ge
Removing critical gaps in chemical test methods by developing new assays for the identification of thyroid hormone system-disrupting chemicals—the athena project
The test methods that currently exist for the identification of thyroid hormone system-disrupting chemicals are woefully inadequate. There are currently no internationally validated in vitro assays, and test methods that can capture the consequences of diminished or enhanced thyroid hormone action on the developing brain are missing entirely. These gaps put the public at risk and risk assessors in a difficult position. Decisions about the status of chemicals as thyroid hormone system disruptors currently are based on inadequate toxicity data. The ATHENA project (Assays for the identification of Thyroid Hormone axis-disrupting chemicals: Elaborating Novel Assessment strategies) has been conceived to address these gaps. The project will develop new test methods for the disruption of thyroid hormone transport across biological barriers such as the blood–brain and blood–placenta barriers. It will also devise methods for the disruption of the downstream effects on the brain. ATHENA will deliver a testing strategy based on those elements of the thyroid hormone system that, when disrupted, could have the greatest impact on diminished or enhanced thyroid hormone action and therefore should be targeted through effective testing. To further enhance the impact of the ATHENA test method developments, the project will develop concepts for better international collaboration and development in the area of thyroid hormone system disruptor identification and regulation
Notch and Prospero Repress Proliferation following Cyclin E Overexpression in the Drosophila Bristle Lineage
Understanding the mechanisms that coordinate cell proliferation, cell cycle arrest, and cell differentiation is essential to address the problem of how “normal” versus pathological developmental processes take place. In the bristle lineage of the adult fly, we have tested the capacity of post-mitotic cells to re-enter the cell cycle in response to the overexpression of cyclin E. We show that only terminal cells in which the identity is independent of Notch pathway undergo extra divisions after CycE overexpression. Our analysis shows that the responsiveness of cells to forced proliferation depends on both Prospero, a fate determinant, and on the level of Notch pathway activity. Our results demonstrate that the terminal quiescent state and differentiation are regulated by two parallel mechanisms acting simultaneously on fate acquisition and cell cycle progression
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