258 research outputs found
Rich-club vs rich-multipolarization phenomena in weighted networks
Large scale hierarchies characterize complex networks in different domains.
Elements at their top, usually the most central or influential, may show
multipolarization or tend to club forming tightly interconnected communities.
The rich-club phenomenon quantified this tendency based on unweighted network
representations. Here, we define this metric for weighted networks and discuss
the appropriate normalization which preserves nodes' strengths and discounts
structural strength-strength correlations if present. We find that in some real
networks the results given by the weighted rich-club coefficient can be in
sharp contrast to the ones in the unweighted approach. We also discuss that the
scanning of the weighted subgraphs formed by the high-strength hubs is able to
unveil features contrary to the average: the formation of local alliances in
rich-multipolarized environments, or a lack of cohesion even in the presence of
rich-club ordering. Beyond structure, this analysis matters for understanding
correctly functionalities and dynamical processes relying on hub
interconnectedness.Comment: 12 pages, 2 figure
Essential plasticity and redundancy of metabolism unveiled by synthetic lethality analysis
We unravel how functional plasticity and redundancy are essential mechanisms
underlying the ability to survive of metabolic networks. We perform an
exhaustive computational screening of synthetic lethal reaction pairs in
Escherichia coli in a minimal medium and we find that synthetic lethal pairs
divide in two different groups depending on whether the synthetic lethal
interaction works as a backup or as a parallel use mechanism, the first
corresponding to essential plasticity and the second to essential redundancy.
In E. coli, the analysis of pathways entanglement through essential redundancy
supports the view that synthetic lethality affects preferentially a single
function or pathway. In contrast, essential plasticity, the dominant class,
tends to be inter-pathway but strongly localized and unveils Cell Envelope
Biosynthesis as an essential backup for Membrane Lipid Metabolism. When
comparing E. coli and Mycoplasma pneumoniae, we find that the metabolic
networks of the two organisms exhibit a large difference in the relative
importance of plasticity and redundancy which is consistent with the conjecture
that plasticity is a sophisticated mechanism that requires a complex
organization. Finally, coessential reaction pairs are explored in different
environmental conditions to uncover the interplay between the two mechanisms.
We find that synthetic lethal interactions and their classification in
plasticity and redundancy are basically insensitive to medium composition, and
are highly conserved even when the environment is enriched with nonessential
compounds or overconstrained to decrease maximum biomass formation.Comment: 22 pages, 4 figure
Navigability of temporal networks in hyperbolic space
Information routing is one of the main tasks in many complex networks with a
communication function. Maps produced by embedding the networks in hyperbolic
space can assist this task enabling the implementation of efficient navigation
strategies. However, only static maps have been considered so far, while
navigation in more realistic situations, where the network structure may vary
in time, remain largely unexplored. Here, we analyze the navigability of real
networks by using greedy routing in hyperbolic space, where the nodes are
subject to a stochastic activation-inactivation dynamics. We find that such
dynamics enhances navigability with respect to the static case. Interestingly,
there exists an optimal intermediate activation value, which ensures the best
trade-off between the increase in the number of successful paths and a limited
growth of their length. Contrary to expectations, the enhanced navigability is
robust even when the most connected nodes inactivate with very high
probability. Finally, our results indicate that some real networks are
ultranavigable and remain highly navigable even if the network structure is
extremely unsteady. These findings have important implications for the design
and evaluation of efficient routing protocols that account for the temporal
nature of real complex networks.Comment: 10 pages, 4 figures. Includes Supplemental Informatio
- …