880 research outputs found
Nuclear fragmentation by tunneling
Fragmentation of nuclear system by tunneling is discussed in a molecular
dynamics simulation coupled with imaginary time method. In this way we obtain
informations on the fragmenting systems at low densities and temperatures.
These conditions cannot be reached normally (i.e. above the barrier) in
nucleus-nucleus or nucleon-nucleus collisions. The price to pay is the small
probability of fragmentation by tunneling but we obtain observables which can
be a clear signature of such phenomena.Comment: Phys.Rev.C (submitted
On The Expansion and Fate Of The Universe
The evolution of the universe from an initial dramatic event, the Big-Bang,
is firmly established. Hubble's law [1] (HL) connects the velocity of galactic
objects and their relative distance: v(r)=Hr, where H is the Hubble constant.
In this work we suggest that HL is not valid at large distances because of
total energy conservation. We propose that the velocity can be expanded in
terms of their relative distance and produce a better fit to the available
experimental data. Using a simple 'dust' universe model, we can easily
calculate under which conditions an (unstable) equilibrium state can be reached
and we can estimate the values of the matter present in the universe as well as
the 'dark energy'. We do not need to invoke any 'dark energy', its role being
played by the kinetic correction. The resulting picture is that the universe
might reach an unstable equilibrium state whose fate will be decided by
fluctuations: either collapse or expand forever
Density and Temperature of Bosons from Quantum Fluctuations
A method to determine the density and temperature of a system is proposed
based on quantum fluctuations typical of Bosons in the limit where the reached
temperature T is close to the critical temperature for a Bose condensate
at a given density . Quadrupole and particle multiplicity fluctuations
relations are derived in terms of . This method is valid for
weakly interacting infinite and finite Boson systems.
As an example, we apply it to heavy ion collisions using the Constrained
Molecular Dynamics (CoMD) approach which includes the Fermi statistics. The
model shows some clusterization into deuteron and clusters which
could suggest a Bose condensate. However, our approach demonstrates that in the
model there is no Bose condensate but it gives useful informations to be tested
experimentally. We stress the differences with methods based on classical
approximations. The derived 'quantum' temperatures are systematically higher
than the corresponding 'classical' ones. The role of the Coulomb charge of
fragments is discussed
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