78 research outputs found
Topological characterization of neutron star crusts
Neutron star crusts are studied using a classical molecular dynamics model
developed for heavy ion reactions. After the model is shown to produce a
plethora of the so-called "pasta" shapes, a series of techniques borrowed from
nuclear physics, condensed matter physics and topology are used to craft a
method that can be used to characterize the shape of the pasta structures in an
unequivocal way
Fragmentation of Neutron Star Matter
Background: Neutron stars are astronomical systems with nucleons submitted to
extreme conditions. Due to the long range coulomb repulsion between protons,
the system has structural inhomogeneities. These structural inhomogeneities
arise also in expanding systems, where the fragment distribution is highly
dependent on the thermodynamic conditions (temperature, proton fraction, ...)
and the expansion velocity.
Purpose: We aim to find the different regimes of fragment distribution, and
the existence of infinite clusters.
Method: We study the dynamics of the nucleons with a semiclassical molecular
dynamics model. Starting with an equilibrium configuration, we expand the
system homogeneously until we arrive to an asymptotic configuration (i. e. very
low final densities). We study the fragment distribution throughout this
expansion.
Results: We found the typical regimes of the asymptotic fragment distribution
of an expansion: u-shaped, power law and exponential. Another key feature in
our calculations is that, since the interaction between protons is long range
repulsive, we do not have always an infinite fragment. We found that, as
expected, the faster the expansion velocity is, the quicker the infinite
fragment disappears.
Conclusions: We have developed a novel graph-based tool for the
identification of infinite fragments, and found a transition from U-shaped to
exponential fragment mass distribution with increasing expansion rate
Alternative approach to community detection in networks
The problem of community detection is relevant in many disciplines of science
and modularity optimization is the widely accepted method for this purpose. It
has recently been shown that this approach presents a resolution limit by which
it is not possible to detect communities with sizes smaller than a threshold
which depends on the network size. Moreover, it might happen that the
communities resulting from such an approach do not satisfy the usual
qualitative definition of commune, i.e., nodes in a commune are more connected
among themselves than to nodes outside the commune. In this article we
introduce a new method for community detection in complex networks. We define
new merit factors based on the weak and strong community definitions formulated
by Radicchi et al (Proc. Nat. Acad. Sci. USA 101, 2658-2663 (2004)) and we show
that this local definitions avoid the resolution limit problem found in the
modularity optimization approach.Comment: 17 pages, 6 figure
Dynamical aspects of fragmentation
In this short communication we address the problem of reducibility in a
highly excited Lennard-Jones system. We show that the probability of emitting
fragments can be described in terms of a single probability through the
binomial expression. However, the Arrhenius law does not hold and the process
can be viewed as a mixture of sequential and simultaneous fragmentation events.Comment: Proceedings for VI Latin American Symposium on Nuclear Physics and
Applications, Iguazu, Argentina (2005). To be published in Acta Phys. Hung.
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