29,018 research outputs found
Intra-group diffuse light in compact groups of galaxies. HCG 79, HCG 88 and HCG 95
Deep and images of three Hickson Compact Groups, HCG 79, HCG 88 and
HCG 95, were analyzed using a new wavelet technic to measure possible
intra-group diffuse light present in these systems. The method used, OV\_WAV,
is a wavelet technic particularly suitable to detect low-surface brightness
extended structures, down to a per pixel, which corresponds to a
5--detection level in wavelet space. The three groups studied are in
different evolutionary stages, as can be judged by their very different
fractions of the total light contained in their intra-group halos: %
for HCG 79 and % for HCG 95, in the band, and HCG 88 had no
component detected down to a limiting surface brightness of . For HCG 95 the intra-group light is red, similar to the mean
colors of the group galaxies themselves, suggesting that it is formed by an old
population with no significant on-going star formation. For HCG 79, however,
the intra-group material has significantly bluer color than the mean color of
the group galaxies, suggesting that the diffuse light may, at least in part,
come from stripping of dwarf galaxies which dissolved into the group potential
well.Comment: Two suggested references added to the introductio
Gravity with extra dimensions and dark matter interpretation: A straightforward approach
Any connection between dark matter and extra dimensions can be cognizably
evinced from the associated effective energy-momentum tensor. In order to
investigate and test such relationship, a higher dimensional spacetime endowed
with a factorizable general metric is regarded to derive a general expression
for the stress tensor -- from the Einstein-Hilbert action -- and to elicit the
effective gravitational potential. A particular construction for the case of
six dimensions is provided, and it is forthwith revealed that the missing mass
phenomenon may be explained, irrespective of the dark matter existence.
Moreover, the existence of extra dimensions in the universe accrues the
possibility of a straightforward mechanism for such explanation. A
configuration which density profile coincides with the Newtonian potential for
spiral galaxies is constructed, from a 4-dimensional isotropic metric plus
extra-dimensional components. A Miyamoto-Nagai \emph{ansatz} is used to solve
Einstein equations. The stable rotation curves associated to such system are
computed, in full compliance to the observational data, without fitting
techniques. The density profiles are reconstructed and compared to that ones
obtained from the Newtonian potential.Comment: 13 pages, 6 figure
Stability of switched linear differential systems
We study the stability of switched systems where the dynamic modes are
described by systems of higher-order linear differential equations not
necessarily sharing the same state space. Concatenability of trajectories at
the switching instants is specified by gluing conditions, i.e. algebraic
conditions on the trajectories and their derivatives at the switching instant.
We provide sufficient conditions for stability based on LMIs for systems with
general gluing conditions. We also analyse the role of positive-realness in
providing sufficient polynomial-algebraic conditions for stability of two-modes
switched systems with special gluing conditions
A Generalized Approach to Complex Networks
This work describes how the formalization of complex network concepts in
terms of discrete mathematics, especially mathematical morphology, allows a
series of generalizations and important results ranging from new measurements
of the network topology to new network growth models. First, the concepts of
node degree and clustering coefficient are extended in order to characterize
not only specific nodes, but any generic subnetwork. Second, the consideration
of distance transform and rings are used to further extend those concepts in
order to obtain a signature, instead of a single scalar measurement, ranging
from the single node to whole graph scales. The enhanced discriminative
potential of such extended measurements is illustrated with respect to the
identification of correspondence between nodes in two complex networks, namely
a protein-protein interaction network and a perturbed version of it. The use of
other measurements derived from mathematical morphology are also suggested as a
means to characterize complex networks connectivity in a more comprehensive
fashion.Comment: 10 pages, 2 figur
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