1,059 research outputs found
Dynamical Evolution of an Unstable Gravastar with Zero Mass
Using the conventional gravastar model, that is, an object constituted by two
components where one of them is a massive infinitely thin shell and the other
one is a de Sitter interior spacetime, we physically interpret a solution
characterized by a zero Schwarzschild mass. No stable gravastar is formed and
it collapses without forming an event horizon, originating what we call a
massive non-gravitational object. The most surprise here is that the collapse
occurs with an exterior de Sitter vacuum spacetime. This creates an object
which does not interact gravitationally with an outside test particle and it
may evolve to a point-like topological defect.Comment: 8 pages, 10 figures, to appear in Astrophysics and Space Scienc
Border trees of complex networks
The comprehensive characterization of the structure of complex networks is
essential to understand the dynamical processes which guide their evolution.
The discovery of the scale-free distribution and the small world property of
real networks were fundamental to stimulate more realistic models and to
understand some dynamical processes such as network growth. However, properties
related to the network borders (nodes with degree equal to one), one of its
most fragile parts, remain little investigated and understood. The border nodes
may be involved in the evolution of structures such as geographical networks.
Here we analyze complex networks by looking for border trees, which are defined
as the subgraphs without cycles connected to the remainder of the network
(containing cycles) and terminating into border nodes. In addition to
describing an algorithm for identification of such tree subgraphs, we also
consider a series of their measurements, including their number of vertices,
number of leaves, and depth. We investigate the properties of border trees for
several theoretical models as well as real-world networks.Comment: 5 pages, 1 figure, 2 tables. A working manuscript, comments and
suggestions welcome
Dressing a Naked Singularity: an Example
Considering the evolution of a perfect fluid with self-similarity of the
second kind, we have found that an initial naked singularity can be trapped by
an event horizon due to collapsing matter. The fluid moves along time-like
geodesics with a self-similar parameter . Since the metric
obtained is not asymptotically flat, we match the spacetime of the fluid with a
Schwarzschild spacetime. All the energy conditions are fulfilled until the
naked singularity.Comment: 14 pages, 1 figure. This version corrects an error in the calculus of
the pressure and in the conclusion
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