7,833 research outputs found
Transition from small to large world in growing networks
We examine the global organization of growing networks in which a new vertex
is attached to already existing ones with a probability depending on their age.
We find that the network is infinite- or finite-dimensional depending on
whether the attachment probability decays slower or faster than .
The network becomes one-dimensional when the attachment probability decays
faster than . We describe structural characteristics of these
phases and transitions between them.Comment: 5 page
Flexible construction of hierarchical scale-free networks with general exponent
Extensive studies have been done to understand the principles behind
architectures of real networks. Recently, evidences for hierarchical
organization in many real networks have also been reported. Here, we present a
new hierarchical model which reproduces the main experimental properties
observed in real networks: scale-free of degree distribution (frequency
of the nodes that are connected to other nodes decays as a power-law
) and power-law scaling of the clustering coefficient
. The major novelties of our model can be summarized as
follows: {\it (a)} The model generates networks with scale-free distribution
for the degree of nodes with general exponent , and arbitrarily
close to any specified value, being able to reproduce most of the observed
hierarchical scale-free topologies. In contrast, previous models can not obtain
values of . {\it (b)} Our model has structural flexibility
because {\it (i)} it can incorporate various types of basic building blocks
(e.g., triangles, tetrahedrons and, in general, fully connected clusters of
nodes) and {\it (ii)} it allows a large variety of configurations (i.e., the
model can use more than copies of basic blocks of nodes). The
structural features of our proposed model might lead to a better understanding
of architectures of biological and non-biological networks.Comment: RevTeX, 5 pages, 4 figure
Preferential attachment of communities: the same principle, but a higher level
The graph of communities is a network emerging above the level of individual
nodes in the hierarchical organisation of a complex system. In this graph the
nodes correspond to communities (highly interconnected subgraphs, also called
modules or clusters), and the links refer to members shared by two communities.
Our analysis indicates that the development of this modular structure is driven
by preferential attachment, in complete analogy with the growth of the
underlying network of nodes. We study how the links between communities are
born in a growing co-authorship network, and introduce a simple model for the
dynamics of overlapping communities.Comment: 7 pages, 3 figure
Diluted antiferromagnet in a ferromagnetic enviroment
The question of robustness of a network under random ``attacks'' is treated
in the framework of critical phenomena. The persistence of spontaneous
magnetization of a ferromagnetic system to the random inclusion of
antiferromagnetic interactions is investigated. After examing the static
properties of the quenched version (in respect to the random antiferromagnetic
interactions) of the model, the persistence of the magnetization is analysed
also in the annealed approximation, and the difference in the results are
discussed
Spectral transitions in networks
We study the level spacing distribution p(s) in the spectrum of random
networks. According to our numerical results, the shape of p(s) in the
Erdos-Renyi (E-R) random graph is determined by the average degree , and
p(s) undergoes a dramatic change when is varied around the critical point
of the percolation transition, =1. When > 1, the p(s) is described by
the statistics of the Gaussian Orthogonal Ensemble (GOE), one of the major
statistical ensembles in Random Matrix Theory, whereas at =1 it follows the
Poisson level spacing distribution. Closely above the critical point, p(s) can
be described in terms of an intermediate distribution between Poisson and the
GOE, the Brody-distribution. Furthermore, below the critical point p(s) can be
given with the help of the regularised Gamma-function. Motivated by these
results, we analyse the behaviour of p(s) in real networks such as the
Internet, a word association network and a protein protein interaction network
as well. When the giant component of these networks is destroyed in a node
deletion process simulating the networks subjected to intentional attack, their
level spacing distribution undergoes a similar transition to that of the E-R
graph.Comment: 11 pages, 5 figure
Carnitine partially improves oxidative stress, acrosome integrity, and reproductive competence in doxorubicin-treated rats
Doxorubicin has been largely used in anticancer therapy in adults, adolescents, and children. The efficacy of l-carnitine as an antioxidant substance has been confirmed both in humans and rats. Carnitine, present in testis and epididymis, is involved in sperm maturation. It is also effective in infertility treatment. As a continuation of a previous study, we evaluated whether some spermatic qualitative parameters, DNA integrity, chromatin structure, and fertility status, could be ameliorated by the carnitine treatment in adult rats, which were subsequently exposed to doxorubicin at pre-puberty. Pre-pubertal male rats were distributed into four groups: Sham ControlDoxorubicinl-carnitinel-carnitine+Doxorubicin (l-carnitine injected 1h before doxorubicin). At 100days of age, all groups were reassigned into two sets: One set was submitted to the evaluation of sperm motility, acrosome integrity, mitochondrial activity, sperm chromatin structure analysis (SCSA), and evaluation of the oxidative stress. The other set of rats was destined to the evaluation of reproductive competence. The percentage of spermatozoa with intact acrosome integrity was higher in the Carnitine+Doxorubicin group when compared with the Doxorubicin group. However, sperm motility and mitochondrial activity were not improved by carnitine pre-treatment. Both values of malondialdehyde and nitrite (indirect measurement of nitric oxide) concentrations were statistically higher in the only doxorubicin-treated group when compared to the Carnitine+Doxorubicin group. Fertility index and implantation rate were lower in Doxorubicin group, when compared to Carnitine+Doxorubicin group. Moreover, the percentage of spermatozoa with damaged DNA was higher in the Doxorubicin-treated group when compared to the Carnitine+Doxorubicin group. l-carnitine, when administered before doxorubicin, partially preserved the acrosome integrity, an important feature related to sperm fertilization ability that positively correlated with the reproductive competence and sperm DNA integrity at adulthood. In conclusion, l-carnitine attenuated the long-term alterations caused by doxorubicin in the germ cells and improved male reproductive capacity in adulthood.National Council for the Improvement of Higher Education (CAPES/Brazil)Fed Univ Sao Paulo UNIFESP, Lab Dev Biol, Dept Morphol & Genet, Botucatu St 740,Leitao da Cunha Bldg,2nd Floor, BR-04023900 Sao Paulo, SP, BrazilFed Univ Sao Paulo UNIFESP, Lab Dev Biol, Dept Morphol & Genet, Botucatu St 740,Leitao da Cunha Bldg,2nd Floor, BR-04023900 Sao Paulo, SP, BrazilWeb of Scienc
Multi-camera person re-identification based on trajectory data
This study presents a trajectory-based person re-identification algorithm, embedded in a tool to detect and track customers present in a large retail store, in a multi-camera environment. The customer trajectory data are obtained from video surveillance images captured by multiple cameras, and customers are detected and tracked along the frames that compose the videos. Due to the characteristics of a multi-camera environment or the occurrence of occlusions, caused by objects such as shelves or counters, different identifiers are assigned to each person when, in fact, they should be identified with a unique identifier. Thus, the proposed tool tries to solve this problem in a scenario where there are constraints in using images of people due to data privacy concerns. The results show that our method was able to correctly re-identify the customers present in the store with a re-identification rate of 82%.info:eu-repo/semantics/publishedVersio
Constraints on the IR behavior of the gluon propagator in Yang-Mills theories
We present rigorous upper and lower bounds for the zero-momentum gluon
propagator D(0) of Yang-Mills theories in terms of the average value of the
gluon field. This allows us to perform a controlled extrapolation of lattice
data to infinite volume, showing that the infrared limit of the Landau-gauge
gluon propagator in SU(2) gauge theory is finite and nonzero in three and in
four space-time dimensions. In the two-dimensional case we find D(0) = 0, in
agreement with Ref. [1]. We suggest an explanation for these results. We note
that our discussion is general, although we only apply our analysis to pure
gauge theory in Landau gauge. Simulations have been performed on the IBM
supercomputer at the University of Sao Paulo.Comment: 4 pages, 3 figures, 1 tabl
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