21,949 research outputs found
Baryon number conservation and statistical production of antibaryons
The statistical production of antibaryons is considered within the canonical ensemble formulation. We demonstrate that the antibaryon suppression in small systems due to the exact baryon number conservation is rather different in the baryon-free (B=0) and baryon-rich (B>1) systems. At constant values of temperature and baryon density in the baryon-rich systems the density of the produced antibaryons is only weakly dependent on the size of the system. For realistic hadronization conditions this dependence appears to be close to B/(B+1) which is in agreement with the preliminary data of the NA49 Collaboration for the antiproton/pion ratio in nucleus-nucleus collisions at the CERN SPS energies. However, a consistent picture of antibaryon production within the statistical hadronization model has not yet been achieved. This is because the condition of constant hadronization temperature in the baryon-free systems leads to a contradiction with the data on the antiproton/pion ratio in e+e- interactions
The mass distribution of the Fornax dSph: constraints from its globular cluster distribution
Uniquely among the dwarf spheroidal (dSph) satellite galaxies of the Milky
Way, Fornax hosts globular clusters. It remains a puzzle as to why dynamical
friction has not yet dragged any of Fornax's five globular clusters to the
centre, and also why there is no evidence that any similar star cluster has
been in the past (for Fornax or any other dSph). We set up a suite of 2800
N-body simulations that sample the full range of globular-cluster orbits and
mass models consistent with all existing observational constraints for Fornax.
In agreement with previous work, we find that if Fornax has a large dark-matter
core then its globular clusters remain close to their currently observed
locations for long times. Furthermore, we find previously unreported behaviour
for clusters that start inside the core region. These are pushed out of the
core and gain orbital energy, a process we call 'dynamical buoyancy'. Thus a
cored mass distribution in Fornax will naturally lead to a shell-like globular
cluster distribution near the core radius, independent of the initial
conditions. By contrast, CDM-type cusped mass distributions lead to the rapid
infall of at least one cluster within \Delta t = 1-2Gyr, except when picking
unlikely initial conditions for the cluster orbits (\sim 2% probability), and
almost all clusters within \Delta t = 10Gyr. Alternatively, if Fornax has only
a weakly cusped mass distribution, dynamical friction is much reduced. While
over \Delta t = 10Gyr this still leads to the infall of 1-4 clusters from their
present orbits, the infall of any cluster within \Delta t = 1-2Gyr is much less
likely (with probability 0-70%, depending on \Delta t and the strength of the
cusp). Such a solution to the timing problem requires that in the past the
globular clusters were somewhat further from Fornax than today; they most
likely did not form within Fornax, but were accreted.Comment: 12 pages, 8 figures, 3 tables, submitted to MNRA
Superheavies: Theoretical incitements and predictions
It is well known that in fusion reactions one may get only neutron deficient
superheavy nuclei located far from the island of stability. The multi-nucleon
transfer reactions allow one to produce more neutron enriched new heavy nuclei
but the corresponding cross sections are rather low. Neutron capture process is
considered here as alternative method for production of long-lived neutron rich
superheavy nuclei. Strong neutron fluxes might be provided by nuclear reactors
and nuclear explosions in laboratory frame and by supernova explosions in
nature. All these cases are discussed in the paper.Comment: 7 FIGURE
Decorrelating a compressible turbulent flow: an experiment
Floating particles that are initially distributed uniformly on the surface of
a turbulent fluid, subsequently coagulate, until finally a steady state is
reached. This being so, they manifestly form a compressible system. In this
experiment, the information dimension D_1, and the Lyapunov exponents of the
coagulated floaters, are measured. The trajectories and the velocity fields of
the particles are captured in a sequence of rapidly acquired images. Then the
velocity sequence is randomly shuffled in time to generate new trajectories.
This analysis mimics the Kraichnan ensemble and yields properties of a velocity
correlation function that is delta-correlated in time (but not in space). The
measurements are compared with theoretical expectations and with simulations of
Boffetta et al., that closely mimic the laboratory experiment reported here.Comment: 6 pages, 5 figure
Discrete integrable systems generated by Hermite-Pad\'e approximants
We consider Hermite-Pad\'e approximants in the framework of discrete
integrable systems defined on the lattice . We show that the
concept of multiple orthogonality is intimately related to the Lax
representations for the entries of the nearest neighbor recurrence relations
and it thus gives rise to a discrete integrable system. We show that the
converse statement is also true. More precisely, given the discrete integrable
system in question there exists a perfect system of two functions, i.e., a
system for which the entire table of Hermite-Pad\'e approximants exists. In
addition, we give a few algorithms to find solutions of the discrete system.Comment: 20 page
Formation of light exotic nuclei in low-energy multinucleon transfer reactions
Low-energy multinucleon transfer reactions are shown to be very effective
tool for the production and spectroscopic study of light exotic nuclei. The
corresponding cross sections are found to be significantly larger as compared
with high energy fragmentation reactions. Several optimal reactions for the
production of extremely neutron rich isotopes of elements with Z=6-14 are
proposed.Comment: 8 figure
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