454 research outputs found
Quantifying long-range correlations in complex networks beyond nearest neighbors
We propose a fluctuation analysis to quantify spatial correlations in complex
networks. The approach considers the sequences of degrees along shortest paths
in the networks and quantifies the fluctuations in analogy to time series. In
this work, the Barabasi-Albert (BA) model, the Cayley tree at the percolation
transition, a fractal network model, and examples of real-world networks are
studied. While the fluctuation functions for the BA model show exponential
decay, in the case of the Cayley tree and the fractal network model the
fluctuation functions display a power-law behavior. The fractal network model
comprises long-range anti-correlations. The results suggest that the
fluctuation exponent provides complementary information to the fractal
dimension
Dynamic Critical approach to Self-Organized Criticality
A dynamic scaling Ansatz for the approach to the Self-Organized Critical
(SOC) regime is proposed and tested by means of extensive simulations applied
to the Bak-Sneppen model (BS), which exhibits robust SOC behavior. Considering
the short-time scaling behavior of the density of sites () below the
critical value, it is shown that i) starting the dynamics with configurations
such that one observes an {\it initial increase} of the
density with exponent ; ii) using initial configurations with
, the density decays with exponent . It is
also shown that he temporal autocorrelation decays with exponent . Using these, dynamically determined, critical exponents and suitable
scaling relationships, all known exponents of the BS model can be obtained,
e.g. the dynamical exponent , the mass dimension exponent , and the exponent of all returns of the activity , in excellent agreement with values already accepted and obtained
within the SOC regime.Comment: Rapid Communication Physical Review E in press (4 pages, 5 figures
Irreversible phase transitions induced by an oscillatory input
A novel kind of irreversible phase transitions (IPT's) driven by an
oscillatory input parameter is studied by means of computer simulations. Second
order IPT's showing scale invariance in relevant dynamic critical properties
are found to belong to the universality class of directed percolation. In
contrast, the absence of universality is observed for first order IPT's.Comment: 18 pages (Revtex); 8 figures (.ps); submitted to Europhysics Letters,
December 9th, 199
Vertex routing models
A class of models describing the flow of information within networks via
routing processes is proposed and investigated, concentrating on the effects of
memory traces on the global properties. The long-term flow of information is
governed by cyclic attractors, allowing to define a measure for the information
centrality of a vertex given by the number of attractors passing through this
vertex. We find the number of vertices having a non-zero information centrality
to be extensive/sub-extensive for models with/without a memory trace in the
thermodynamic limit. We evaluate the distribution of the number of cycles, of
the cycle length and of the maximal basins of attraction, finding a complete
scaling collapse in the thermodynamic limit for the latter. Possible
implications of our results on the information flow in social networks are
discussed.Comment: 12 pages, 6 figure
Crispr/cas9 editing for gaucher disease modelling
Gaucher disease (GD) is an autosomal recessive lysosomal storage disorder caused by mutations in the acid \u3b2-glucosidase gene (GBA1). Besides causing GD, GBA1 mutations constitute the main genetic risk factor for developing Parkinson\u2019s disease. The molecular basis of neurological manifestations in GD remain elusive. However, neuroinflammation has been proposed as a key player in this process. We exploited CRISPR/Cas9 technology to edit GBA1 in the human monocytic THP-1 cell line to develop an isogenic GD model of monocytes and in glioblastoma U87 cell lines to generate an isogenic GD model of glial cells. Both edited (GBA1 mutant) cell lines presented low levels of mutant acid \u3b2-glucosidase expression, less than 1% of residual activity and massive accumulation of substrate. Moreover, U87 GBA1 mutant cells showed that the mutant enzyme was retained in the ER and subjected to proteasomal degradation, triggering unfolded protein response (UPR). U87 GBA1 mutant cells displayed an increased production of interleukin-1\u3b2, both with and without inflammosome activation, \u3b1-syn accumulation and a higher rate of cell death in comparison with wild-type cells. In conclusion, we developed reliable, isogenic, and easy-to-handle cellular models of GD obtained from commercially accessible cells to be employed in GD pathophysiology studies and high-throughput drug screenings
Statistics of Cycles: How Loopy is your Network?
We study the distribution of cycles of length h in large networks (of size
N>>1) and find it to be an excellent ergodic estimator, even in the extreme
inhomogeneous case of scale-free networks. The distribution is sharply peaked
around a characteristic cycle length, h* ~ N^a. Our results suggest that h* and
the exponent a might usefully characterize broad families of networks. In
addition to an exact counting of cycles in hierarchical nets, we present a
Monte-Carlo sampling algorithm for approximately locating h* and reliably
determining a. Our empirical results indicate that for small random scale-free
nets of degree exponent g, a=1/(g-1), and a grows as the nets become larger.Comment: Further work presented and conclusions revised, following referee
report
Portraits of Complex Networks
We propose a method for characterizing large complex networks by introducing
a new matrix structure, unique for a given network, which encodes structural
information; provides useful visualization, even for very large networks; and
allows for rigorous statistical comparison between networks. Dynamic processes
such as percolation can be visualized using animations. Applications to graph
theory are discussed, as are generalizations to weighted networks, real-world
network similarity testing, and applicability to the graph isomorphism problem.Comment: 6 pages, 9 figure
High incidence of autoantibodies in Fabry disease patients
Fabry disease (FD) is an X-linked disorder of glycosphingolipid catabolism that results from a deficiency of the lysosomal enzyme α-galactosidase A. This defect leads to the accumulation of its substrates, mainly globotriaosylceramide, in lysosomes of cells of different tissues. Different studies have shown the involvement of immunopathologies in different sphingolipidoses. The coexistence of FD and immune disorders such as systemic lupus erythematosus, rheumatoid arthritis and IgA nephropathy, has been described in the literature. The aim of this study was to evaluate the prevalence of a group of autoantibodies in a series of Argentine FD patients. Autoantibodies against extractable nuclear antigens (ENAs), double-stranded DNA, anticardiolipin and phosphatidylserine were assayed by ELISA. Lupus anticoagulants were also tested. Fifty-seven per cent of the samples showed reactivity with at least one autoantigen. Such reactivities were more frequent among males than among females. Antiphospholipid autoantibodies were detected in 45% of our patients. The high rate of thrombosis associated with FD could be related, at least in part, to the presence of antiphospholipid autoantibodies in Fabry patients. We found the presence of ENAs, which are a characteristic finding of rheumatological diseases, previous a frequent misdiagnosis of FD, in around 39% of the cases. The detection of a high level of autoantibodies must be correlated clinically to determine the existence of an underlying autoimmune disease. With the recent development of therapy, the life expectancy in FD will increase and autoimmune diseases might play an important role in the morbidity of FD.Facultad de Ciencias ExactasLaboratorio de Investigaciones del Sistema Inmun
Anomalous behavior of trapping on a fractal scale-free network
It is known that the heterogeneity of scale-free networks helps enhancing the
efficiency of trapping processes performed on them. In this paper, we show that
transport efficiency is much lower in a fractal scale-free network than in
non-fractal networks. To this end, we examine a simple random walk with a fixed
trap at a given position on a fractal scale-free network. We calculate
analytically the mean first-passage time (MFPT) as a measure of the efficiency
for the trapping process, and obtain a closed-form expression for MFPT, which
agrees with direct numerical calculations. We find that, in the limit of a
large network order , the MFPT behaves superlinearly as with an exponent 3/2 much larger than 1, which is in sharp contrast
to the scaling with , previously obtained
for non-fractal scale-free networks. Our results indicate that the degree
distribution of scale-free networks is not sufficient to characterize trapping
processes taking place on them. Since various real-world networks are
simultaneously scale-free and fractal, our results may shed light on the
understanding of trapping processes running on real-life systems.Comment: 6 pages, 5 figures; Definitive version accepted for publication in
EPL (Europhysics Letters
High Dimensional Apollonian Networks
We propose a simple algorithm which produces high dimensional Apollonian
networks with both small-world and scale-free characteristics. We derive
analytical expressions for the degree distribution, the clustering coefficient
and the diameter of the networks, which are determined by their dimension
- …