45,220 research outputs found
Random walks in directed modular networks
Because diffusion typically involves symmetric interactions, scant attention
has been focused on studying asymmetric cases. However, important networked
systems underlain by diffusion (e.g. cortical networks and WWW) are inherently
directed. In the case of undirected diffusion, it can be shown that the
steady-state probability of the random walk dynamics is fully correlated with
the degree, which no longer holds for directed networks. We investigate the
relationship between such probability and the inward node degree, which we call
efficiency, in modular networks. Our findings show that the efficiency of a
given community depends mostly on the balance between its ingoing and outgoing
connections. In addition, we derive analytical expressions to show that the
internal degree of the nodes do not play a crucial role in their efficiency,
when considering the Erd\H{o}s-R\'enyi and Barab\'asi-Albert models. The
results are illustrated with respect to the macaque cortical network, providing
subsidies for improving transportation and communication systems
Modeling the International-Trade Network: A Gravity Approach
This paper investigates whether the gravity model (GM) can explain the
statistical properties of the International Trade Network (ITN). We fit data on
international-trade flows with a GM specification using alternative fitting
techniques and we employ GM estimates to build a weighted predicted ITN, whose
topological properties are compared to observed ones. Furthermore, we propose
an estimation strategy to predict the binary ITN with a GM. We find that the GM
successfully replicates the weighted-network structure of the ITN, only if one
fixes its binary architecture equal to the observed one. Conversely, the GM
performs very badly when asked to predict the presence of a link, or the level
of the trade flow it carries, whenever the binary structure must be
simultaneously estimated
Introduction to Focus Issue : Dynamics in Systems Biology
Peer reviewedPublisher PD
Network of recurrent events for the Olami-Feder-Christensen model
We numerically study the dynamics of a discrete spring-block model introduced
by Olami, Feder and Christensen (OFC) to mimic earthquakes and investigate to
which extent this simple model is able to reproduce the observed spatiotemporal
clustering of seismicty. Following a recently proposed method to characterize
such clustering by networks of recurrent events [Geophys. Res. Lett. {\bf 33},
L1304, 2006], we find that for synthetic catalogs generated by the OFC model
these networks have many non-trivial statistical properties. This includes
characteristic degree distributions -- very similar to what has been observed
for real seismicity. There are, however, also significant differences between
the OFC model and earthquake catalogs indicating that this simple model is
insufficient to account for certain aspects of the spatiotemporal clustering of
seismicity.Comment: 11 pages, 16 figure
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China’s rise in a liberal world order in transition – introduction to the FORUM
In a time of great uncertainty about the future and resilience of the liberal world order this Forum focuses on China’s rise and interplay with the foundations of that liberal order. The key question is the extent to and variegated ways in which China - with its (re)ascendance to power and potential global leadership – is adapting to and perhaps even strengthening liberal institutions and rules of the game, confronting them, or developing alternative paths. In this introduction to the Forum we advance three key points based on the contributions. First, contrasting the orthodox binary scenarios of either inevitable conflict or co-optation offered in the mainstream IR debate, the Forum highlights the possibility of a third scenario of China’s interplay with the liberal world and its key actors, institutions, and rules. A hybrid and variegated scenario that entails both conflict and adaptation, differently entangled in different issue areas. Second, it stresses the need to conceptualize and empirically comprise the essentially interlinked nature of domestic state-society models and the global political economy. Third, we argue for a perspective that incorporates underlying economic and social structures and the power relations embedded therein
Network communities within and across borders
We investigate the impact of borders on the topology of spatially embedded
networks. Indeed territorial subdivisions and geographical borders
significantly hamper the geographical span of networks thus playing a key role
in the formation of network communities. This is especially important in
scientific and technological policy-making, highlighting the interplay between
pressure for the internationalization to lead towards a global innovation
system and the administrative borders imposed by the national and regional
institutions. In this study we introduce an outreach index to quantify the
impact of borders on the community structure and apply it to the case of the
European and US patent co-inventors networks. We find that (a) the US
connectivity decays as a power of distance, whereas we observe a faster
exponential decay for Europe; (b) European network communities essentially
correspond to nations and contiguous regions while US communities span multiple
states across the whole country without any characteristic geographic scale. We
confirm our findings by means of a set of simulations aimed at exploring the
relationship between different patterns of cross-border community structures
and the outreach index.Comment: Scientific Reports 4, 201
A multiscale model for collagen alignment in wound healing
It is thought that collagen alignment plays a significant part in scar tissue formation during dermal wound healing. We present a multiscale model for collagen deposition and alignment during this process. We consider fibroblasts as discrete units moving within an extracellular matrix of collagen and fibrin modelled as continua. Our model includes flux induced alignment of collagen by fibroblasts, and contact guidance of fibroblasts by collagen fibres. We can use the model to predict the effects of certain manipulations, such as varying fibroblast speed, or placing an aligned piece of tissue in the wound. We also simulate experiments which alter the TGF-β concentrations in a healing dermal wound and use the model to offer an explanation of the observed influence of this growth factor on scarring
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