Edmilson Roque

We study the percolation in coupled networks with both inner-dependency and inter-dependency links, where the inner- and inter-dependency links represent the dependencies between nodes in the same or different networks, respectively. We find that when most of dependency links are inner- or inter-ones, the coupled networks system is fragile and makes a discontinuous percolation transition. However, when the numbers of two types of dependency links are close to each other, the system is robust and makes a continuous percolation transition. This indicates that the high density of dependency links could not always lead to a discontinuous percolation transition as the previous studies. More interestingly, although the robustness of the system can be optimized by adjusting the ratio of the two types of dependency links, there exists a critical average degree of the networks for coupled random networks, below which the crossover of the two types of percolation transitions disappears, and the system will always demonstrate a discontinuous percolation transition. We also develop an approach to analyze this model, which is agreement with the simulation results well.

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In this work we present a method to study phase transitions based on the complex zeros of a polynomial with coefficients determined by the energy probability distribution. This is a general method that brings advantages over the conventional Fisher zeros approach since it does not require the knowledge of the full density of states and allows the obtention of essentially the same informations. Indeed, only the energy histogram at a given temperature is used, the polynomial degree can be safely reduced and the polynomial coefficients spans over a reduced range of values, facilitating the zeros finder task as compared to the Fisher zeros. The method was applied to the 2D Ising, Potts and XY models and to a homopolymer model, showing its power in determining the phase transition properties of systems with first, second and infinity order phase transitions as well as systems with multiple phase transitions. Our strategy can easily be adapted to any model, classical or quantum, once we are able to build the corresponding energy probability distribution.

We discuss the transition paths in a coupled bistable system consisting of interacting multiple identical bistable motifs. We propose a simple model of coupled bistable gene circuits as an example, and show that its transition paths are bifurcating. We then derive a criterion to predict the bifurcation of transition paths in a generalized coupled bistable system. We confirm the validity of the theory for the example system by numerical simulation. We also demonstrate in the example system that, if the steady states of individual gene circuits are not changed by the coupling, the bifurcation pattern is not dependent on the number of gene circuits. We further show that the transition rate exponentially decreases with the number of gene circuits when the transition path does not bifurcate, while a bifurcation softens this decrease. Finally we show that multiplicative noises facilitate the bifurcation of transition paths.

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Policy: Urban physics

Nature. doi:10.1038/531S64a

Author: Kevin Pollock

Cities are complex environments. Planning interventions that borrow principles from theoretical physics could help to improve peoples' lives.

Advisory network: Six principles for EU peer review

Nature 531, 7594 (2016). doi:10.1038/531305c

Authors: William Cockburn & Hubert Deluyker

The European Union Agencies Network for Scientific Advice (EU-ANSA) is a group of 11 EU agencies that provides scientific information for institutions and national authorities in Europe. It has recently assessed its peer-review practices and drawn up guidelines that we hope will support the agencies'

Author(s): Justus A. Kromer, Lutz Schimansky-Geier, and Alexander B. Neiman

We study the emergence and coherence of stochastic oscillations in star networks of excitable elements in which peripheral nodes receive independent random inputs. A biophysical model of a distal branch of sensory neuron in which peripheral nodes of Ranvier are coupled to a central node by myelinate…

[Phys. Rev. E] Published Fri Mar 11, 2016

Author(s): Robert Großmann, Fernando Peruani, and Markus Bär

We study an ensemble of random walkers carrying internal noisy phase oscillators which are synchronized among the walkers by local interactions. Due to individual mobility, the interaction partners of every walker change randomly, hereby introducing an additional, independent source of fluctuations,…

[Phys. Rev. E] Published Fri Mar 11, 2016

We present analytical results for the distribution of shortest path lengths between random pairs of nodes in configuration model networks. The results, which are based on recursion equations, are shown to be in good agreement with numerical simulations for networks with degenerate, binomial and power-law degree distributions. The mean, mode and variance of the distribution of shortest path lengths are also evaluated. These results provide expressions for central measures and dispersion measures of the distribution of shortest path lengths in terms of moments of the degree distribution, illuminating the connection between the two distributions.

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It is known that the stationary distribution of the random walk process is dependent on the structure of the network. This could provide us a solution of the network reconstruction. However, the stationary distribution of the random walk process can only reflect the relative size of node degrees directly, how to infer the real connection is still a problem. In this paper, we will propose a method to reconstruct network by the random walk process, which can reconstruct the total number of links, degree sequence and links sequentially. In our method, only the stationary distribution is used, and no data of the evolution process is needed, such as the first passage time. We perform our method on some network models and real-world network, the results indicate our method can reconstruct networks accurately, even when we can not get the exact stationary distribution.

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We present analytical results for the distribution of shortest path lengths between random pairs of nodes in configuration model networks. The results, which are based on recursion equations, are shown to be in good agreement with numerical simulations for networks with degenerate, binomial and power-law degree distributions. The mean, mode and variance of the distribution of shortest path lengths are also evaluated. These results provide expressions for central measures and dispersion measures of the distribution of shortest path lengths in terms of moments of the degree distribution, illuminating the connection between the two distributions.

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A comparative study is done of interdisciplinary citations in 2013 between physics, chemistry, and molecular biology, in Brazil, South Korea, Turkey, and USA. Several surprising conclusions emerge from our tabular and graphical analysis: The cross-science citation rates are in general strikingly similar, between Brazil, South Korea, Turkey, and USA. One apparent exception is the comparatively more tenuous relation between molecular biology and physics in Brazil and USA. Other slight exceptions are the higher amount of citing of physicists by chemists in South Korea, of chemists by molecular biologists in Turkey, and of molecular biologists by chemists in Brazil and USA. Chemists are, by a sizable margin, the most cross-science citing scientists in this group of three sciences. Physicist are, again by a sizable margin, the least cross-science citing scientists in this group of three sciences. In all four countries, the strongest cross-science citation is from chemistry to physics and the weakest cross-science citation is from physics to molecular biology. Our findings are consistent with a V-shaped backbone connectivity, as opposed to a Delta connectivity, as also found in a previous study of earlier citation years.

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Several expressions for the $j$-th component $\left( x_{k}\right)_{j}$ of the $k$-th eigenvector $x_{k}$ of a symmetric matrix $A$ belonging to eigenvalue $\lambda_{k}$ and normalized as $x_{k}^{T}x_{k}=1$ are presented. In particular, the expression \[ \left( x_{k}\right)_{j}^{2}=-\frac{1}{c_{A}^{\prime}\left( \lambda_{k}\right) }\det\left( A_{\backslash\left\{ j\right\} }-\lambda_{k}I\right) \] where $c_{A}\left( \lambda\right) =\det\left( A-\lambda I\right) $ is the characteristic polynomial of $A$, $c_{A}^{\prime}\left( \lambda\right) =\frac{dc_{A}\left( \lambda\right) }{d\lambda}$ and $A_{\backslash\left\{ j\right\} }$ is obtained from $A$ by removal of row $j$ and column $j$, suggests us to consider the square eigenvector component as a graph centrality metric for node $j$ that reflects the impact of the removal of node $j$ from the graph at an eigenfrequency/eigenvalue $\lambda_{k}$ of a graph related matrix (such as the adjacency or Laplacian matrix). Removal of nodes in a graph relates to the robustness of a graph. The set of such nodal centrality metrics, the squared eigenvector components $\left( x_{k}\right)_{j}^{2}$ of the adjacency matrix over all eigenvalue $\lambda_{k}$ for each node $j$, is 'ideal' in the sense of being complete, \emph{almost} uncorrelated and mathematically precisely defined and computable. Fundamental weights (column sum of $X$) and dual fundamental weights (row sum of $X$) are introduced as spectral metrics that condense information embedded in the orthogonal eigenvector matrix $X$, with elements $X_{ij}=\left( x_{j}\right)_{i}$.

In addition to the criterion {\em If the algebraic connectivity is positive, then the graph is connected}, we found an alternative condition: {\em If $\min_{1\leq k\leq N}\left( \lambda_{k}^{2}(A)\right) =d_{\min}$, then the graph is disconnected.}

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Author(s): N. Azimi-Tafreshi

The spread of one disease, in some cases, can stimulate the spreading of another infectious disease. Here, we treat analytically a symmetric co-infection model for spreading of two diseases on a 2-layer multiplex network. We allow layer overlapping, but we assume that each layer is random and locall…

[Phys. Rev. E] Published Mon Mar 14, 2016

Author(s): Marc Wiedermann, Jonathan F. Donges, Jürgen Kurths, and Reik V. Donner

Networks with nodes embedded in a metric space have gained increasing interest in recent years. The effects of spatial embedding on the networks' structural characteristics, however, are rarely taken into account when studying their macroscopic properties. Here, we propose a hierarchy of null models…

[Phys. Rev. E] Published Mon Mar 14, 2016

Author(s): Tommaso Coletta and Philippe Jacquod

We investigate the influence that adding a new coupling has on the linear stability of the synchronous state in coupled oscillators networks. Using a simple model we show that, depending on its location, the new coupling can lead to enhanced or reduced stability. We extend these results to electric …

[Phys. Rev. E] Published Mon Mar 14, 2016

Author(s): Iryna Omelchenko, Oleh E. Omel’chenko, Anna Zakharova, Matthias Wolfrum, and Eckehard Schöll

We propose a control scheme which can stabilize and fix the position of chimera states in small networks. Chimeras consist of coexisting domains of spatially coherent and incoherent dynamics in systems of nonlocally coupled identical oscillators. Chimera states are generally difficult to observe in …

[Phys. Rev. Lett. 116, 114101] Published Mon Mar 14, 2016

Author(s): Carl P. Dettmann and Orestis Georgiou

In the original (1961) Gilbert model of random geometric graphs, nodes are placed according to a Poisson point process, and links formed between those within a fixed range. Motivated by wireless ad hoc networks “soft” or “probabilistic” connection models have recently been introduced, involving a “c…

[Phys. Rev. E 93, 032313] Published Mon Mar 14, 2016

Author(s): Silvio C. Ferreira, Renan S. Sander, and Romualdo Pastor-Satorras

We consider a general criterion to discern the nature of the threshold in epidemic models on scale-free (SF) networks. Comparing the epidemic lifespan of the nodes with largest degrees with the infection time between them, we propose a general dual scenario, in which the epidemic transition is eithe…

[Phys. Rev. E 93, 032314] Published Mon Mar 14, 2016

Author(s): Ginestra Bianconi and Christoph Rahmede

Network geometry is attracting increasing attention because it has a wide range of applications, ranging from data mining to routing protocols in the Internet. At the same time advances in the understanding of the geometrical properties of networks are essential for further progress in quantum gravi…

[Phys. Rev. E 93, 032315] Published Mon Mar 14, 2016

Author(s): Albert Solé-Ribalta, Sergio Gómez, and Alex Arenas

Multiplex networks are representations of multilayer interconnected complex networks where the nodes are the same at every layer. They turn out to be good abstractions of the intricate connectivity of multimodal transportation networks, among other types of complex systems. One of the most important…

[Phys. Rev. Lett. 116, 108701] Published Thu Mar 10, 2016

The eigenvector centrality equation $\lambda x = A \, x$ is a successful compromise between simplicity and expressivity. It claims that central actors are those connected with central others. For at least 70 years, this equation has been explored in disparate contexts, including econometrics, sociometry, bibliometrics, Web information retrieval, and network science. We propose an equally elegant counterpart: the power equation $x = A x^{\div}$, where $x^{\div}$ is the vector whose entries are the reciprocal of those of $x$. It asserts that power is in the hands of those connected with powerless others. It is meaningful, for instance, in bargaining situations, where it is advantageous to be connected to those who have few options. We tell the parallel, mostly unexplored story of this intriguing equation.

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The self-consistent probabilistic approach has proven itself powerful in studying the percolation behavior of interdependent or multiplex networks without tracking the percolation process through each cascading step. In order to understand how directed dependency links impact criticality, we employ this approach to study the percolation properties of networks with both undirected connectivity links and directed dependency links. We find that when a random network with a given degree distribution undergoes a second-order phase transition, the critical point and the unstable regime surrounding the second-order phase transition regime are determined by the proportion of nodes that do not depend on any other nodes. Moreover, we also find that the triple point and the boundary between first- and second-order transitions are determined by the proportion of nodes that depend on no more than one node. This implies that it is maybe general for multiplex network systems, some important properties of phase transitions can be determined only by a few parameters. We illustrate our findings using Erdos-Renyi (ER) networks.

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Author(s): Tomomichi Nakamura, Toshihiro Tanizawa, and Michael Small

We describe a method for constructing networks from multivariate nonlinear time series. We approach the interaction between the various scalar time series from a deterministic dynamical system perspective and provide a generic and algorithmic test for whether the interaction between two measured tim…

[Phys. Rev. E] Published Fri Mar 11, 2016

Author(s): Vivek Kohar, Behnam Kia, John F. Lindner, and William L. Ditto

We illustrate through theory and numerical simulations that redundant coupled dynamical systems can be extremely robust against local noise in comparison to uncoupled dynamical systems evolving in the same noisy environment. Previous studies have shown that the noise robustness of redundant coupled …

[Phys. Rev. E 93, 032213] Published Fri Mar 11, 2016

Author(s): Ping Li, Xian Sun, Kai Zhang, Jie Zhang, and Jürgen Kurths

Structural holes are channels or paths spanned by a group of indirectly connected nodes and their intermediary in a network. In this work we emphasize the interesting role of structural holes as brokers for information propagation. Based on the distribution of the structural hole numbers associated …

[Phys. Rev. E 93, 032312] Published Fri Mar 11, 2016

A Liga Árabe passou a classificar, nesta sexta (11), o Hizbullah como organização terrorista. Leia mais (03/11/2016 - 16h06)

Speaker recognition is a forensic field with a checkered history that is trying to find solid scientific ground. Past methods to compare recordings of human voices were often highly subjective and have been discredited. More objective alternatives have emerged and they are reliable when comparing standard sentences clearly spoken into a microphone, but real-world recordings are often still problematic. To improve accuracy, scientists are studying how factors like inebriation, emotional state, and recording device influence voice samples. They are also testing how well existing systems perform and developing standards for things like data selection and the presentation of results. Author: Nala Rogers

The so-called El Niño-southern oscillation (ENSO) is the most important and influential climate phenomenon of contemporary climate variability, in which oceanic wave dynamics plays an important role. Here we develop and apply an approach based on network theory to quantify the characteristics of El-Niño related oceanic waves using the satellite dataset. We associate the majority of dominant long distance (≥500 km) links of the network with several kinds of oceanic waves, i.e. equatorial Kelvin, Rossby, and tropical instability waves. Notably, we find that the location of the out-going ( ##IMG## [http://ej.iop.org/images/1367-2630/18/3/033021/njpaa1835ieqn1.gif] {$\sim 180^\circ {\rm{E}}$} ) and in-coming hubs ( ##IMG## [http://ej.iop.org/images/1367-2630/18/3/033021/njpaa1835ieqn2.gif] {$\sim 140^\circ {\rm{W}}$} ) of the climate network coincide with the locations of the wave initiation and dissipation, respectively. We also find that thi...

Group dynamics: A lab of their own

Nature (2016). doi:10.1038/nj7593-263a

Author: Chris Woolston

The make-up of a lab is crucial to success in publishing its research — and now, scientists are exploring how to compose the best research group possible.