2,051 research outputs found
Cascade control and defense in complex networks
Complex networks with heterogeneous distribution of loads may undergo a
global cascade of overload failures when highly loaded nodes or edges are
removed due to attacks or failures. Since a small attack or failure has the
potential to trigger a global cascade, a fundamental question regards the
possible strategies of defense to prevent the cascade from propagating through
the entire network. Here we introduce and investigate a costless strategy of
defense based on a selective further removal of nodes and edges, right after
the initial attack or failure. This intentional removal of network elements is
shown to drastically reduce the size of the cascade.Comment: 4 pages, 2 figures, Revte
Modularity and community structure in networks
Many networks of interest in the sciences, including a variety of social and
biological networks, are found to divide naturally into communities or modules.
The problem of detecting and characterizing this community structure has
attracted considerable recent attention. One of the most sensitive detection
methods is optimization of the quality function known as "modularity" over the
possible divisions of a network, but direct application of this method using,
for instance, simulated annealing is computationally costly. Here we show that
the modularity can be reformulated in terms of the eigenvectors of a new
characteristic matrix for the network, which we call the modularity matrix, and
that this reformulation leads to a spectral algorithm for community detection
that returns results of better quality than competing methods in noticeably
shorter running times. We demonstrate the algorithm with applications to
several network data sets.Comment: 7 pages, 3 figure
Factor eight inhibitor bypass activity (FEIBA) in the management of bleeds in hemophilia patients with high-titer inhibitors
The development of high-titer inhibitors to FVIII and less often to other coagulation factors are the most serious complication of hemophilia therapy and makes treatment of bleeds very challenging. At present, bypassing agents, such as factor eight inhibitor bypass activity (FEIBA) and activated recombinant factor VII (rFVIIa) are the only coagulation factor concentrates available for the treatment of bleeds in inhibitor patients. Both products are effective and safe, and their efficacy has been found to be comparable (approximately 80%) in a recent prospective study. A significant number of patients report a better effect of one or the other of the products, and in a minority of the patients none of the products are particularly effective. The hemostatic efficacy of bypassing agents is not considered equal to that of coagulation factor replacement in patients without inhibitors by most physicians. An improvement in hemostatic efficacy may be achieved by optimizing the dosing of by passing agents. However, the lack of standardized and validated laboratory assays reflecting the hemostatic efficacy of the bypassing agents is an obstacle to this achievement
Network dynamics of ongoing social relationships
Many recent large-scale studies of interaction networks have focused on
networks of accumulated contacts. In this paper we explore social networks of
ongoing relationships with an emphasis on dynamical aspects. We find a
distribution of response times (times between consecutive contacts of different
direction between two actors) that has a power-law shape over a large range. We
also argue that the distribution of relationship duration (the time between the
first and last contacts between actors) is exponentially decaying. Methods to
reanalyze the data to compensate for the finite sampling time are proposed. We
find that the degree distribution for networks of ongoing contacts fits better
to a power-law than the degree distribution of the network of accumulated
contacts do. We see that the clustering and assortative mixing coefficients are
of the same order for networks of ongoing and accumulated contacts, and that
the structural fluctuations of the former are rather large.Comment: to appear in Europhys. Let
Signatures of currency vertices
Many real-world networks have broad degree distributions. For some systems,
this means that the functional significance of the vertices is also broadly
distributed, in other cases the vertices are equally significant, but in
different ways. One example of the latter case is metabolic networks, where the
high-degree vertices -- the currency metabolites -- supply the molecular groups
to the low-degree metabolites, and the latter are responsible for the
higher-order biological function, of vital importance to the organism. In this
paper, we propose a generalization of currency metabolites to currency
vertices. We investigate the network structural characteristics of such
systems, both in model networks and in some empirical systems. In addition to
metabolic networks, we find that a network of music collaborations and a
network of e-mail exchange could be described by a division of the vertices
into currency vertices and others.Comment: to appear in Journal of the Physical Society of Japa
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
Nonlocal evolution of weighted scale-free networks
We introduce the notion of globally updating evolution for a class of
weighted networks, in which the weight of a link is characterized by the amount
of data packet transport flowing through it. By noting that the packet
transport over the network is determined nonlocally, this approach can explain
the generic nonlinear scaling between the strength and the degree of a node. We
demonstrate by a simple model that the strength-driven evolution scheme
recently introduced can be generalized to a nonlinear preferential attachment
rule, generating the power-law behaviors in degree and in strength
simultaneously.Comment: 4 pages, 4 figures, final version published in PR
Vertex similarity in networks
We consider methods for quantifying the similarity of vertices in networks.
We propose a measure of similarity based on the concept that two vertices are
similar if their immediate neighbors in the network are themselves similar.
This leads to a self-consistent matrix formulation of similarity that can be
evaluated iteratively using only a knowledge of the adjacency matrix of the
network. We test our similarity measure on computer-generated networks for
which the expected results are known, and on a number of real-world networks
Information dynamics shape the networks of Internet-mediated prostitution
Like many other social phenomena, prostitution is increasingly coordinated
over the Internet. The online behavior affects the offline activity; the
reverse is also true. We investigated the reported sexual contacts between
6,624 anonymous escorts and 10,106 sex-buyers extracted from an online
community from its beginning and six years on. These sexual encounters were
also graded and categorized (in terms of the type of sexual activities
performed) by the buyers. From the temporal, bipartite network of posts, we
found a full feedback loop in which high grades on previous posts affect the
future commercial success of the sex-worker, and vice versa. We also found a
peculiar growth pattern in which the turnover of community members and sex
workers causes a sublinear preferential attachment. There is, moreover, a
strong geographic influence on network structure-the network is geographically
clustered but still close to connected, the contacts consistent with the
inverse-square law observed in trading patterns. We also found that the number
of sellers scales sublinearly with city size, so this type of prostitution does
not, comparatively speaking, benefit much from an increasing concentration of
people
The global migration network of sex-workers
Differences in the social and economic environment across countries encourage
humans to migrate in search of better living conditions, including job
opportunities, higher salaries, security and welfare. Quantifying global
migration is, however, challenging because of poor recording, privacy issues
and residence status. This is particularly critical for some classes of
migrants involved in stigmatised, unregulated or illegal activities. Escorting
services or high-end prostitution are well-paid activities that attract workers
all around the world. In this paper, we study international migration patterns
of sex-workers by using network methods. Using an extensive international
online advertisement directory of escorting services and information about
individual escorts, we reconstruct a migrant flow network where nodes represent
either origin or destination countries. The links represent the direct routes
between two countries. The migration network of sex-workers shows different
structural patterns than the migration of the general population. The network
contains a strong core where mutual migration is often observed between a group
of high-income European countries, yet Europe is split into different network
communities with specific ties to non-European countries. We find
non-reciprocal relations between countries, with some of them mostly offering
while others attract workers. The GDP per capita is a good indicator of country
attractiveness for incoming workers and service rates but is unrelated to the
probability of emigration. The median financial gain of migrating, in
comparison to working at the home country, is 15.9%. Only sex-workers coming
from 77% of the countries have financial gains with migration and average gains
decrease with the GDPc of the country of origin. Our results shows that
high-end sex-worker migration is regulated by economic, geographic and cultural
aspects.Comment: Comments and feedback welcomed. Two tables and 6 figures including S
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