1,367 research outputs found
Core-periphery organization of complex networks
Networks may, or may not, be wired to have a core that is both itself densely
connected and central in terms of graph distance. In this study we propose a
coefficient to measure if the network has such a clear-cut core-periphery
dichotomy. We measure this coefficient for a number of real-world and model
networks and find that different classes of networks have their characteristic
values. For example do geographical networks have a strong core-periphery
structure, while the core-periphery structure of social networks (despite their
positive degree-degree correlations) is rather weak. We proceed to study radial
statistics of the core, i.e. properties of the n-neighborhoods of the core
vertices for increasing n. We find that almost all networks have unexpectedly
many edges within n-neighborhoods at a certain distance from the core
suggesting an effective radius for non-trivial network processes
Hierarchy Measures in Complex Networks
Using each node's degree as a proxy for its importance, the topological
hierarchy of a complex network is introduced and quantified. We propose a
simple dynamical process used to construct networks which are either maximally
or minimally hierarchical. Comparison with these extremal cases as well as with
random scale-free networks allows us to better understand hierarchical versus
modular features in several real-life complex networks. For random scale-free
topologies the extent of topological hierarchy is shown to smoothly decline
with -- the exponent of a degree distribution -- reaching its highest
possible value for and quickly approaching zero for .Comment: 4 pages, 4 figure
Popular Cultural Keystone Species are also understudied — the case of the camphor tree (Dryobalanops aromatica)
Along with landscape degradation and loss of biodiversity there is also a co-occurring loss of cultural and linguistic diversity. When species become rare, there is a corresponding loss of cultural practices and linguistic elements associated with that species. Although cultural assessments of tree species can help in identifying Cultural Keystone Species (CKS) and be used to enhance the cultural relevance of conservation actions, such information is typically lacking for endangered species were the cultural connections may have been lost. Here, we review historic written accounts to assess the cultural status of the critically endangered camphor tree, Dryobalanops aromatica, native to Southeast Asia which is recognized for its camphor and crystals forming in the wood. We found that despite centuries of use, the importance of the tree for specific cultures has not been fully understood. Published literature indicate that it could be a CKS to multiple communities. The tree was once culturally significant for many cultures in its native range and beyond, but contemporary data is lacking, especially with respect to persistence and memory of use in relation to cultural change. By virtue of being a culturally recognized tree species, as well as having a distinct ecological role within its natural distribution, we propose D. aromatica as a flagship species for conservation and restoration of the habitat it defines. Our review highlights the usability of historic accounts as starting points for identifying CKS and effective conservation of biocultural diversity, especially concerning endangered species. We propose that future research should pay attention to inter and intra-community dynamics of local knowledge on the species, and causes and consequences of varying cultural importance across temporal and spatial scale
Nonequilibrium phase transition in the coevolution of networks and opinions
Models of the convergence of opinion in social systems have been the subject
of a considerable amount of recent attention in the physics literature. These
models divide into two classes, those in which individuals form their beliefs
based on the opinions of their neighbors in a social network of personal
acquaintances, and those in which, conversely, network connections form between
individuals of similar beliefs. While both of these processes can give rise to
realistic levels of agreement between acquaintances, practical experience
suggests that opinion formation in the real world is not a result of one
process or the other, but a combination of the two. Here we present a simple
model of this combination, with a single parameter controlling the balance of
the two processes. We find that the model undergoes a continuous phase
transition as this parameter is varied, from a regime in which opinions are
arbitrarily diverse to one in which most individuals hold the same opinion. We
characterize the static and dynamical properties of this transition
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