1,154 research outputs found
The equation of state and symmetry energy of low density nuclear matter
The symmetry energy of nuclear matter is a fundamental ingredient in the
investigation of exotic nuclei, heavy-ion collisions and astrophysical
phenomena. A recently developed quantum statistical (QS) approach that takes
the formation of clusters into account predicts low density symmetry energies
far above the usually quoted mean field limits. A consistent description of the
symmetry energy has been developed that joins the correct low-density limit
with values calculated from quasi-particle approaches valid near the saturation
density. The results are confronted with experimental values for free symmetry
energies and internal symmetry energies, determined at sub-saturation densities
and temperatures below 10 MeV using data from heavy-ion collisions. There is
very good agreement between the experimental symmetry energy values and those
calculated in the QS approachComment: 16 pages, 10 figures. arXiv admin note: text overlap with
arXiv:0908.234
Two-step Doppler cooling of a three-level ladder system with an intermediate metastable level
Doppler laser cooling of a three-level ladder system using two near-resonant
laser fields is analyzed in the case of the intermediate level being metastable
while the upper level is short-lived. Analytical as well as numerical results
for e.g. obtainable scattering rates and achievable temperatures are presented.
When appropriate, comparisons with two-level single photon Doppler laser
cooling is made. These results are relevant to recent experimental Doppler
laser cooling investigations addressing intercombination lines in alkali-earth
metal atoms and quadrupole transitions in alkali-earth metal ions.Comment: accepted by Phys Rev
Constrained Molecular Dynamics II: a N-body approach to nuclear systems
In this work we illustrate the basic development of the constrained molecular
dynamics applied to the N-body problem in nuclear physics. The heavy
computational taskes related to quantum effects, to the presence of the "hard
core" repulsive interaction have been worked out by defining a set of
transformations based on the concept of impulsive forces. In particular in the
implemented version II of the Constrained Molecular Dynamics model the problem
related to the non conservation of the total angular momentum has been solved.
This problem can affect others semiclassical microscopic approaches as due to
the "hard core" repulsive interaction or to the use of stochastic forces. The
effect of the restored conservation law on the fusion cross section for
40Ca+40Ca system is also briefly discussed.Comment: Tex version 3.1459 (Web2C 7.3.1);main text+fig.cap in .tex 13 page;
+4 figures .ps;the order and the numerical label of the figure files reflect
the figure numbers in the main tex and captions, Submited to Journal of
computational physic
Nucleation and cluster formation in low-density nucleonic matter: A mechanism for ternary fission
Ternary fission yields in the reaction 241Pu(nth,f) are calculated using a
new model which assumes a nucleation-time moderated chemical equilibrium in the
low density matter which constitutes the neck region of the scissioning system.
The temperature, density, proton fraction and fission time required to fit the
experimental data are derived and discussed. A reasonably good fit to the
experimental data is obtained. This model provides a natural explanation for
the observed yields of heavier isotopes relative to those of the lighter
isotopes, the observation of low proton yields relative to 2H and 3H yields and
the non-observation of 3He, all features which are shared by similar thermal
neutron induced and spontaneous fissioning systems.Comment: 6 pages, 3 figure
Long-Term Stability of Planets in Binary Systems
A simple question of celestial mechanics is investigated: in what regions of
phase space near a binary system can planets persist for long times? The
planets are taken to be test particles moving in the field of an eccentric
binary system. A range of values of the binary eccentricity and mass ratio is
studied, and both the case of planets orbiting close to one of the stars, and
that of planets outside the binary orbiting the system's center of mass, are
examined. From the results, empirical expressions are developed for both 1) the
largest orbit around each of the stars, and 2) the smallest orbit around the
binary system as a whole, in which test particles survive the length of the
integration (10^4 binary periods). The empirical expressions developed, which
are roughly linear in both the mass ratio mu and the binary eccentricity e, are
determined for the range 0.0 <= e <= 0.7-0.8 and 0.1 <= mu <= 0.9 in both
regions, and can be used to guide searches for planets in binary systems. After
considering the case of a single low-mass planet in binary systems, the
stability of a mutually-interacting system of planets orbiting one star of a
binary system is examined, though in less detail.Comment: 19 pages, 5 figures, 7 tables, accepted by the Astronomical Journa
Terahertz frequency standard based on three-photon coherent population trapping
A scheme for a THz frequency standard based on three-photon coherent
population trapping in stored ions is proposed. Assuming the propagation
directions of the three lasers obey the phase matching condition, we show that
stability of few 10 at one second can be reached with a precision
limited by power broadening to in the less favorable case. The
referenced THz signal can be propagated over long distances, the useful
information being carried by the relative frequency of the three optical
photons.Comment: article soumis a PRL le 21 mars 2007, accepte le 10 mai, version 2
(24/05/2007
Irreversible Magnetization Deep in the Vortex-Liquid State of a 2D Superconductor at High Magnetic Fields
The remarkable phenomenon of weak magnetization hysteresis loops, observed
recently deep in the vortex-liquid state of a nearly two-dimensional (2D)
superconductor at low temperatures, is shown to reflect the existence of an
unusual vortex-liquid state, consisting of collectively pinned crystallites of
easily sliding vortex chains.Comment: 5 pages, 4 figure
Constraint Molecular Dynamics approach to Fermionic systems
We propose a Constraint Molecular Dynamics model for Fermionic system. In
this approach the equations of motion of wave packets for the nuclear many-body
problem are solved by imposing that the one-body occupation probability
can assume only values less or equal to 1. This condition
reflects the Fermionic nature of the studied systems and it is implemented with
a fast algorithm which allows also the study of the heaviest colliding system.
The parameters of the model have been chosen to reproduce the average binding
energy and radii of nuclei in the mass region . Some comparison
to data is given.Comment: 11 pages and 6 figure
Symmetry energy of dilute warm nuclear matter
The symmetry energy of nuclear matter is a fundamental ingredient in the
investigation of exotic nuclei, heavy-ion collisions and astrophysical
phenomena. New data from heavy-ion collisions can be used to extract the free
symmetry energy and the internal symmetry energy at subsaturation densities and
temperatures below 10 MeV. Conventional theoretical calculations of the
symmetry energy based on mean-field approaches fail to give the correct
low-temperature, low-density limit that is governed by correlations, in
particular by the appearance of bound states. A recently developed quantum
statistical (QS) approach that takes the formation of clusters into account
predicts symmetry energies that are in very good agreement with the
experimental data. A consistent description of the symmetry energy is given
that joins the correct low-density limit with quasiparticle approaches valid
near the saturation density.Comment: 4 pages, 2 figures, 1 tabl
Density determinations in heavy ion collisions
The experimental determination of freeze-out temperatures and densities from
the yields of light elements emitted in heavy ion collisions is discussed.
Results from different experimental approaches are compared with those of model
calculations carried out with and without the inclusion of medium effects.
Medium effects become of relevance for baryon densities above fm. A quantum statistical (QS) model incorporating medium
effects is in good agreement with the experimentally derived results at higher
densities. A densitometer based on calculated chemical equilibrium constants is
proposed.Comment: 5 pages, 3 figure
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