668 research outputs found
SU(4) flavor symmetry breaking in D-meson couplings to light hadrons
The validity of SU(4)-flavor symmetry relations of couplings of charmed
mesons to light mesons and baryons is examined with the use of
quark-pair creation model and nonrelativistic quark model wave functions. We
focus on the three-meson couplings , and and
baryon-baryon-meson couplings , and . It is
found that SU(4)-flavor symmetry is broken at the level of 30% in the
tree-meson couplings and 20% in the baryon-baryon-meson couplings. Consequences
of these findings for DN cross sections and existence of bound states D-mesons
in nuclei are discussed.Comment: 5 pages, 3 figure
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
A Fast and Accurate Nonlinear Spectral Method for Image Recognition and Registration
This article addresses the problem of two- and higher dimensional pattern
matching, i.e. the identification of instances of a template within a larger
signal space, which is a form of registration. Unlike traditional correlation,
we aim at obtaining more selective matchings by considering more strict
comparisons of gray-level intensity. In order to achieve fast matching, a
nonlinear thresholded version of the fast Fourier transform is applied to a
gray-level decomposition of the original 2D image. The potential of the method
is substantiated with respect to real data involving the selective
identification of neuronal cell bodies in gray-level images.Comment: 4 pages, 3 figure
Relativistic model for the nonmesonic weak decay of single-lambda hypernuclei
Having in mind its future extension for theoretical investigations related to
charmed nuclei, we develop a relativistic formalism for the nonmesonic weak
decay of single- hypernuclei in the framework of the
independent-particle shell model and with the dynamics represented by the
one-meson-exchange model. Numerical results for the
one-nucleon-induced transition rates of are
presented and compared with those obtained in the analogous nonrelativistic
calculation. There is satisfactory agreement between the two approaches, and
the most noteworthy difference is that the ratio is
appreciably higher and closer to the experimental value in the relativistic
calculation. Large discrepancies between ours and previous relativistic
calculations are found, for which we do not encounter any fully satisfactory
explanation. The most recent experimental data is well reproduced by our
results. In summary, we have achieved our purpose to develop a reliable model
for the relativistic calculation of the nonmesonic weak decay of
-hypernuclei, which can now be extended to evaluate similar processes
in charmed nuclei
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Strategic CSR shifts towards adaptive food governance under environmental change: A comparison between South African and Brazilian retailers
Governance in the food system has become a key topic of discussion in light of the 2007-08 food price crisis. Of special importance has been the shift to include the role that non-state actors are likely to play in achieving food security under global environmental change (GEC). This paper aims to compare private sector food system governance trends in two emerging economies, Brazil and South Africa. It focuses on practices around adaptation, an area largely neglected in climate change discussion, yet a critical factor in coping with the societal consequences of GEC. This study identifies several processes, particularly within the retail sector, that could indicate normative mechanisms through which 'good governance' can be translated into practice
Learning about knowledge: A complex network approach
This article describes an approach to modeling knowledge acquisition in terms
of walks along complex networks. Each subset of knowledge is represented as a
node, and relations between such knowledge are expressed as edges. Two types of
edges are considered, corresponding to free and conditional transitions. The
latter case implies that a node can only be reached after visiting previously a
set of nodes (the required conditions). The process of knowledge acquisition
can then be simulated by considering the number of nodes visited as a single
agent moves along the network, starting from its lowest layer. It is shown that
hierarchical networks, i.e. networks composed of successive interconnected
layers, arise naturally as a consequence of compositions of the prerequisite
relationships between the nodes. In order to avoid deadlocks, i.e. unreachable
nodes, the subnetwork in each layer is assumed to be a connected component.
Several configurations of such hierarchical knowledge networks are simulated
and the performance of the moving agent quantified in terms of the percentage
of visited nodes after each movement. The Barab\'asi-Albert and random models
are considered for the layer and interconnecting subnetworks. Although all
subnetworks in each realization have the same number of nodes, several
interconnectivities, defined by the average node degree of the interconnection
networks, have been considered. Two visiting strategies are investigated:
random choice among the existing edges and preferential choice to so far
untracked edges. A series of interesting results are obtained, including the
identification of a series of plateaux of knowledge stagnation in the case of
the preferential movements strategy in presence of conditional edges.Comment: 18 pages, 19 figure
CO013. PREVALÊNCIA DE SÍNDROME METABÓLICA EM CRIANÇAS E ADOLESCENTES COM DIABETES MELLITUS TIPO 1
https://nsuworks.nova.edu/nsudigital_harrison/3368/thumbnail.jp
Performance of networks of artificial neurons: The role of clustering
The performance of the Hopfield neural network model is numerically studied
on various complex networks, such as the Watts-Strogatz network, the
Barab{\'a}si-Albert network, and the neuronal network of the C. elegans.
Through the use of a systematic way of controlling the clustering coefficient,
with the degree of each neuron kept unchanged, we find that the networks with
the lower clustering exhibit much better performance. The results are discussed
in the practical viewpoint of application, and the biological implications are
also suggested.Comment: 4 pages, to appear in PRE as Rapid Com
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