58 research outputs found
Long-Range Connections in Transportation Networks
Since its recent introduction, the small-world effect has been identified in
several important real-world systems. Frequently, it is a consequence of the
existence of a few long-range connections, which dominate the original regular
structure of the systems and implies each node to become accessible from other
nodes after a small number of steps, typically of order .
However, this effect has been observed in pure-topological networks, where the
nodes have no spatial coordinates. In this paper, we present an alalogue of
small-world effect observed in real-world transportation networks, where the
nodes are embeded in a hree-dimensional space. Using the multidimensional
scaling method, we demonstrate how the addition of a few long-range connections
can suubstantially reduce the travel time in transportation systems. Also, we
investigated the importance of long-range connections when the systems are
under an attack process. Our findings are illustrated for two real-world
systems, namely the London urban network (streets and underground) and the US
highways network enhanced by some of the main US airlines routes
The simplicity of planar networks
Shortest paths are not always simple. In planar networks, they can be very
different from those with the smallest number of turns - the simplest paths.
The statistical comparison of the lengths of the shortest and simplest paths
provides a non trivial and non local information about the spatial organization
of these graphs. We define the simplicity index as the average ratio of these
lengths and the simplicity profile characterizes the simplicity at different
scales. We measure these metrics on artificial (roads, highways, railways) and
natural networks (leaves, slime mould, insect wings) and show that there are
fundamental differences in the organization of urban and biological systems,
related to their function, navigation or distribution: straight lines are
organized hierarchically in biological cases, and have random lengths and
locations in urban systems. In the case of time evolving networks, the
simplicity is able to reveal important structural changes during their
evolution.Comment: 8 pages, 4 figure
On time-varying collaboration networks
The patterns of scientific collaboration have been frequently investigated in
terms of complex networks without reference to time evolution. In the present
work, we derive collaborative networks (from the arXiv repository)
parameterized along time. By defining the concept of affine group, we identify
several interesting trends in scientific collaboration, including the fact that
the average size of the affine groups grows exponentially, while the number of
authors increases as a power law. We were therefore able to identify, through
extrapolation, the possible date when a single affine group is expected to
emerge. Characteristic collaboration patterns were identified for each
researcher, and their analysis revealed that larger affine groups tend to be
less stable
Mapping road network communities for guiding disease surveillance and control strategies
Human mobility is increasing in its volume, speed and reach, leading to the
movement and introduction of pathogens through infected travelers. An
understanding of how areas are connected, the strength of these connections and
how this translates into disease spread is valuable for planning surveillance
and designing control and elimination strategies. While analyses have been
undertaken to identify and map connectivity in global air, shipping and
migration networks, such analyses have yet to be undertaken on the road
networks that carry the vast majority of travellers in low and middle income
settings. Here we present methods for identifying road connectivity
communities, as well as mapping bridge areas between communities and key
linkage routes. We apply these to Africa, and show how many highly-connected
communities straddle national borders and when integrating malaria prevalence
and population data as an example, the communities change, highlighting regions
most strongly connected to areas of high burden. The approaches and results
presented provide a flexible tool for supporting the design of disease
surveillance and control strategies through mapping areas of high connectivity
that form coherent units of intervention and key link routes between
communities for targeting surveillance.Comment: 11 pages, 5 figures, research pape
The relationship between structure and function in locally observed complex networks
Recently, studies looking at the small scale interactions taking place in complex networks have started to unveil the wealth of interactions that occur between groups of nodes. Such findings make the claim for a new systematic methodology to quantify, at node level, how dynamics are influenced (or differentiated) by the structure of the underlying system. Here we define a new measure that, based on the dynamical characteristics obtained for a large set of initial conditions, compares the dynamical behavior of the nodes present in the system. Through this measure, we find that the geographic and Barabasi-Albert' models have a high capacity for generating networks that exhibit groups of nodes with distinct dynamics compared to the rest of the network. The application of our methodology is illustrated with respect to two real systems. In the first we use the neuronal network of the nematode Caenorhabditis elegans to show that the interneurons of the ventral cord of the nematode present a very large dynamical differentiation when compared to the rest of the network. The second application concerns the SIS epidemic model on an airport network, where we quantify how different the distribution of infection times of high and low degree nodes can be, when compared to the expected value for the network.FAPESP (05/00587-5, 2011/22639-8, 2010/16310-0)CNPq (301303/06-1, 573583/2008-0
How Many Nodes are Effectively Accessed in Complex Networks?
The measurement called accessibility has been proposed as a means to quantify
the efficiency of the communication between nodes in complex networks. This
article reports important results regarding the properties of the
accessibility, including its relationship with the average minimal time to
visit all nodes reachable after steps along a random walk starting from a
source, as well as the number of nodes that are visited after a finite period
of time. We characterize the relationship between accessibility and the average
number of walks required in order to visit all reachable nodes (the exploration
time), conjecture that the maximum accessibility implies the minimal
exploration time, and confirm the relationship between the accessibility values
and the number of nodes visited after a basic time unit. The latter
relationship is investigated with respect to three types of dynamics, namely:
traditional random walks, self-avoiding random walks, and preferential random
walks.Comment: 8 pages and 7 figure
Mitochondrial Network Size Scaling in Budding Yeast
Mitochondria must grow with the growing cell to ensure proper cellular physiology and inheritance upon division. We measured the physical size of mitochondrial networks in budding yeast and found that mitochondrial network size increased with increasing cell size and that this scaling relation occurred primarily in the bud. The mitochondria-to-cell size ratio continually decreased in aging mothers over successive generations. However, regardless of the mother's age or mitochondrial content, all buds attained the same average ratio. Thus, yeast populations achieve a stable scaling relation between mitochondrial content and cell size despite asymmetry in inheritance.Sandler Postdoctoral FellowshipSandler Postdoctoral FellowshipHerbert Boyer Junior Faculty Endowed Chair AwardHerbert Boyer Junior Faculty Endowed Chair AwardNIHNIH [R01GM097017, R01GM070808, R01GM026259, P50Gm081879, 5RO1GM097213-02]NIH National Research Service Award fellowshipNIH National Research Service Award fellowshipFundacao de Amparo a Pesquisa do Estado de Sao PauloFundacao de Amparo a Pesquisa do Estado de Sao Paulo [05/00587-5, 07/50882-9]Conselho Nacional de Desenvolvimento Cientifico e Tecnologico [301303/06-1]Conselho Nacional de Desenvolvimento Cientifico e TecnologicoPackard FellowshipPackard FellowshipChina Scholarship Council (CSC) scholarshipChina Scholarship Council (CSC) scholarshipBoyer Postdoctoral FellowshipBoyer Postdoctoral Fellowshi
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