2,415 research outputs found
Betweenness Centrality of Fractal and Non-Fractal Scale-Free Model Networks and Tests on Real Networks
We study the betweenness centrality of fractal and non-fractal scale-free
network models as well as real networks. We show that the correlation between
degree and betweenness centrality of nodes is much weaker in fractal
network models compared to non-fractal models. We also show that nodes of both
fractal and non-fractal scale-free networks have power law betweenness
centrality distribution . We find that for non-fractal
scale-free networks , and for fractal scale-free networks , where is the dimension of the fractal network. We support
these results by explicit calculations on four real networks: pharmaceutical
firms (N=6776), yeast (N=1458), WWW (N=2526), and a sample of Internet network
at AS level (N=20566), where is the number of nodes in the largest
connected component of a network. We also study the crossover phenomenon from
fractal to non-fractal networks upon adding random edges to a fractal network.
We show that the crossover length , separating fractal and
non-fractal regimes, scales with dimension of the network as
, where is the density of random edges added to the network.
We find that the correlation between degree and betweenness centrality
increases with .Comment: 19 pages, 6 figures. Submitted to PR
Betweenness Centrality in Large Complex Networks
We analyze the betweenness centrality (BC) of nodes in large complex
networks. In general, the BC is increasing with connectivity as a power law
with an exponent . We find that for trees or networks with a small loop
density while a larger density of loops leads to . For
scale-free networks characterized by an exponent which describes the
connectivity distribution decay, the BC is also distributed according to a
power law with a non universal exponent . We show that this exponent
must satisfy the exact bound . If the scale
free network is a tree, then we have the equality .Comment: 6 pages, 5 figures, revised versio
Benchmarking Measures of Network Influence
Identifying key agents for the transmission of diseases (ideas, technology,
etc.) across social networks has predominantly relied on measures of centrality
on a static base network or a temporally flattened graph of agent interactions.
Various measures have been proposed as the best trackers of influence, such as
degree centrality, betweenness, and -shell, depending on the structure of
the connectivity. We consider SIR and SIS propagation dynamics on a
temporally-extruded network of observed interactions and measure the
conditional marginal spread as the change in the magnitude of the infection
given the removal of each agent at each time: its temporal knockout (TKO)
score. We argue that the exhaustive approach of the TKO score makes it an
effective benchmark measure for evaluating the accuracy of other, often more
practical, measures of influence. We find that none of the common network
measures applied to the induced flat graphs are accurate predictors of network
propagation influence on the systems studied; however, temporal networks and
the TKO measure provide the requisite targets for the hunt for effective
predictive measures
Structure and Dynamics of Brain Lobes Functional Networks at the Onset of Anesthesia Induced Loss of Consciousness
Anesthetic agents are neurotropic drugs able to induce dramatic alterations
in the thalamo-cortical system, promoting a drastic reduction in awareness and
level of consciousness. There is experimental evidence that general anesthesia
impacts large scale functional networks leading to alterations in the brain
state. However, the way anesthetics affect the structure assumed by functional
connectivity in different brain regions have not been reported yet. Within this
context, the present study has sought to characterize the functional brain
networks respective to the frontal, parietal, temporal and occipital lobes. In
this experiment, electro-physiological neural activity was recorded through the
use of a dense ECoG-electrode array positioned directly over the cortical
surface of an old world monkey of the species Macaca fuscata. Networks were
serially estimated over time at each five seconds, while the animal model was
under controlled experimental conditions of an anesthetic induction process. In
each one of the four cortical brain lobes, prominent alterations on distinct
properties of the networks evidenced a transition in the networks architecture,
which occurred within about one and a half minutes after the administration of
the anesthetics. The characterization of functional brain networks performed in
this study represents important experimental evidence and brings new knowledge
towards the understanding of neural correlates of consciousness in terms of the
structure and properties of the functional brain networks.Comment: 41 pages; 30 figures; 30 tables. arXiv admin note: substantial text
overlap with arXiv:1604.0000
Characterization of Large Scale Functional Brain Networks During Ketamine-Medetomidine Anesthetic Induction
Several experiments evidence that specialized brain regions functionally
interact and reveal that the brain processes and integrates information in a
specific and structured manner. Networks can be used to model brain functional
activities constituting a way to characterize and quantify this structured form
of organization. Reports state that different physiological states or even
diseases that affect the central nervous system may be associated to
alterations on those networks, that might reflect in graphs of different
architectures. However, the relation of their structure to different states or
conditions of the organism is not well comprehended. Thus, experiments that
involve the estimation of functional neural networks of subjects exposed to
different controlled conditions are of great relevance. Within this context,
this research has sought to model large scale functional brain networks during
an anesthetic induction process. The experiment was based on intra-cranial
recordings of neural activities of an old world macaque of the species Macaca
fuscata. Neural activity was recorded during a Ketamine-Medetomidine anesthetic
induction process. Networks were serially estimated in time intervals of five
seconds. Changes were observed in various networks properties within about one
and a half minutes after the administration of the anesthetics. These changes
reveal the occurrence of a transition on the networks architecture. During
general anesthesia a reduction in the functional connectivity and network
integration capabilities were verified in both local and global levels. It was
also observed that the brain shifted to a highly specific and dynamic state.
The results bring empirical evidence and report the relation of the induced
state of anesthesia to properties of functional networks, thus, they contribute
for the elucidation of some new aspects of neural correlates of consciousness.Comment: 28 pages , 9 figures, 7 tables; - English errors were corrected;
Figures 1,3,4,5,6,8 and 9 were replaced by (exact the same)figures of higher
resolution; Three(3) references were added on the introduction sectio
Modeling Minneapolis Skyway Network
Adopting an agent-based approach, this paper explores the topological evolution of the Minneapolis Skyway System from a microscopic perspective. Under a decentralized decision-making mechanism, skyway segments are built by self-interested building owners. We measure the accessibility for the blocks from 1962 to 2002 using the size of office space in each block as an indicator of business opportunities. By building skyway segments, building owners desire to increase their buildingsÕ value of accessibility, and thus potential business revenue. The skyway network in equilibrium generated from the agent model displays similarity to the actual skyway system. The network topology is evaluated by multiple centrality measures (e.g., degree centrality, closeness centrality, and betweenness centrality) and a measure of road contiguity, roadness. Sensitivity tests such parameters as distance decay parameter and construction cost per unit length of segments are performed. Our results disclose that the accessibility- based agent model can provide unique insights for the dynamics of the skyway network growth.skyway network, network growth, agent-based modeling
Generalized Erdos Numbers for network analysis
In this paper we consider the concept of `closeness' between nodes in a
weighted network that can be defined topologically even in the absence of a
metric. The Generalized Erd\H{o}s Numbers (GENs) satisfy a number of desirable
properties as a measure of topological closeness when nodes share a finite
resource between nodes as they are real-valued and non-local, and can be used
to create an asymmetric matrix of connectivities. We show that they can be used
to define a personalized measure of the importance of nodes in a network with a
natural interpretation that leads to a new global measure of centrality and is
highly correlated with Page Rank. The relative asymmetry of the GENs (due to
their non-metric definition) is linked also to the asymmetry in the mean first
passage time between nodes in a random walk, and we use a linearized form of
the GENs to develop a continuum model for `closeness' in spatial networks. As
an example of their practicality, we deploy them to characterize the structure
of static networks and show how it relates to dynamics on networks in such
situations as the spread of an epidemic
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