8,757 research outputs found
Using membrane computing for obtaining homology groups of binary 2D digital images
Membrane Computing is a new paradigm inspired from cellular communication. Until now, P systems have been used in research areas like modeling chemical process, several ecosystems, etc. In this paper, we apply P systems to Computational Topology within the context of the Digital Image. We work with a variant of P systems called tissue-like P systems to calculate in a general maximally parallel manner the homology groups of 2D images. In fact, homology computation for binary pixel-based 2D digital images can be reduced to connected component labeling of white and black regions. Finally, we use a software called Tissue Simulator to show with some examples how these systems wor
Pressure effect in the X-ray intrinsic position resolution in noble gases and mixtures
A study of the gas pressure effect in the position resolution of an
interacting X- or gamma-ray photon in a gas medium is performed. The intrinsic
position resolution for pure noble gases (Argon and Xenon) and their mixtures
with CO2 and CH4 were calculated for several gas pressures (1-10bar) and for
photon energies between 5.4 and 60.0 keV, being possible to establish a linear
match between the intrinsic position resolution and the inverse of the gas
pressure in that energy range. In order to evaluate the quality of the method
here described, a comparison between the available experimental data and the
calculated one in this work, is done and discussed. In the majority of the
cases, a strong agreement is observed
Solar System experiments do not yet veto modified gravity models
The dynamical equivalence between modified and scalar-tensor gravity theories
is revisited and it is concluded that it breaks down in the limit to general
relativity. A gauge-independent analysis of cosmological perturbations in both
classes of theories lends independent support to this conclusion. As a
consequence, the PPN formalism of scalar-tensor gravity and Solar System
experiments do not veto modified gravity, as previously thought.Comment: 7 pages, latex, submitted to Phys. Rev.
Internal space structure generalization of the quintom cosmological scenario
We introduce the Lagrangian for a multi-scalar field configuration in a
-dimensional internal space endowed with a constant metric and
generalize the quintom cosmological scenario. We find the energy momentum
tensor of the model and show that the set of dual transformations, that
preserve the form of the Einstein equations in the Friedmann-Robertson-Walker
(FRW) cosmology, is enlarged. We show that the stability of the power law
solutions leads to an exponential potential which is invariant under linear
transformations in the internal space. Moreover, we obtain the general exact
solution of the Einstein-Klein-Gordon equations for that potential. There exist
solutions that cross the phantom divide and solutions that blow up at a finite
time, exhibiting a superaccelerated behavior and ending in a big rip. We show
that the quintom model with a separable potential can be identified with a
mixture of several fluids. This framework includes the CDM model, a
bouncing model, and a setting sourced by a cosmic string network plus a
cosmological constant. The we concentrate on the case where the dimension of
the internal quintessence sector exceeds the dimension of the internal
phantom sector . For the dark energy density
derived from the 3-scalar field crosses the phantom divide and its negative
component plays the role of the negative part of a classical Dirac Field.Comment: 10 pages, 2 figure
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