Edmilson Roque

University jobs: Germany to fund tenure-track posts

Nature (2016). doi:10.1038/nj7610-190a

Author: Amber Dance

Federal government will create 1,000 professorships.

Back to the thesis

Nature 535, 7610 (2016). http://www.nature.com/doifinder/10.1038/535022a

Authors: Kerri Smith & Noah Baker

Late nights, typos, self-doubt and despair. Three leading scientists dust off their theses, and reflect on what the PhD was like for them.

The past, present and future of the PhD thesis

Nature 535, 7610 (2016). doi:10.1038/535007a

Writing a PhD thesis is a personal and professional milestone for many researchers. But the process needs to change with the times.

We investigate the emergence of different kinds of imperfect synchronized states and chimera states in two interacting populations of nonlocally coupled Stuart-Landau oscillators. We find that the complete synchronization in population-I and existence of solitary oscillators which escape from the synchronized group in population-II lead to imperfect synchronized states for sufficiently small values of nonisochronicity parameter. Interestingly, on increasing the strength of this parameter further there occurs an onset of mixed imperfect synchronized states where the solitary oscillators occur from both the populations. Synchronized oscillators from both the populations are locked to a common average frequency. In both the cases of imperfect synchronized states synchronized oscillators exhibit periodic motion while the solitary oscillators are quasi-periodic in nature. In this region, for spatially prepared initial conditions, we can observe the mixed chimera states where the coexistence of synchronized and desynchronized oscillations occur from both the populations. On the other hand, imperfect synchronized states are not always stable, and they can drift aperiodically due to instability caused by an increase of nonisochronicity parameter. We observe that these states are robust to the introduction of frequency mismatch between the two populations.

We investigate synchronization in networks of Kuramoto oscillators with inertia. More specifically, we introduce a rewiring algorithm consisting basically in a {\em hill climb} scheme in which the edges of the network are swapped in order to enhance its synchronization capacity. We show that the the synchrony-optimized networks generated by our algorithm have some interesting topological and dynamical properties. In particular, they typically exhibit an anticipation of the synchronization onset and are more robust against certain types of perturbations. We consider synthetic random networks and also a network with a topology based in an approximated model of the (high voltage) power grid of Spain, since networks of Kuramoto oscillators with inertia have been used recently as simplified models for power grids, for which synchronization is obviously a crucial issue. Despite the extreme simplifications adopted in these models, our results, among others recently obtained in the literature, may provide interesting principles to guide the future growth and development of real-world grids, specially in the case of a change of the current paradigm of centralized towards distributed generation power grids.

We investigate synchronization in networks of Kuramoto oscillators with inertia. More specifically, we introduce a rewiring algorithm consisting basically in a {\em hill climb} scheme in which the edges of the network are swapped in order to enhance its synchronization capacity. We show that the the synchrony-optimized networks generated by our algorithm have some interesting topological and dynamical properties. In particular, they typically exhibit an anticipation of the synchronization onset and are more robust against certain types of perturbations. We consider synthetic random networks and also a network with a topology based in an approximated model of the (high voltage) power grid of Spain, since networks of Kuramoto oscillators with inertia have been used recently as simplified models for power grids, for which synchronization is obviously a crucial issue. Despite the extreme simplifications adopted in these models, our results, among others recently obtained in the literature, may provide interesting principles to guide the future growth and development of real-world grids, specially in the case of a change of the current paradigm of centralized towards distributed generation power grids.

Author(s): Dhagash Mehta, Jianxu Chen, Danny Z. Chen, Halim Kusumaatmaja, and David J. Wales

Network theory is used to find the minimum energy of N identical charges constrained on a sphere. Solutions are found relatively easily for N≤150 due to the easily accessible global minimum of the energy landscape.

[Phys. Rev. Lett. 117, 028301] Published Wed Jul 06, 2016

Author(s): Vladimir Klinshov, Dmitry Shchapin, Serhiy Yanchuk, and Vladimir Nekorkin

Rings of oscillators with delayed pulse coupling are studied analytically, numerically, and experimentally. The basic regimes observed in such rings are rotating waves with constant interspike intervals and phase lags between the neighbors. We show that these rotating waves may destabilize leading t…

[Phys. Rev. E 94, 012206] Published Wed Jul 06, 2016

Author(s): Gareth J. Baxter, Ginestra Bianconi, Rui A. da Costa, Sergey N. Dorogovtsev, and José F. F. Mendes

We develop the theory of sparse multiplex networks with partially overlapping links based on their local treelikeness. This theory enables us to find the giant mutually connected component in a two-layer multiplex network with arbitrary correlations between connections of different types. We find th…

[Phys. Rev. E 94, 012303] Published Wed Jul 06, 2016

Author(s): Jason Hindes and Ira B. Schwartz

We consider epidemic extinction in finite networks with a broad variation in local connectivity. Generalizing the theory of large fluctuations to random networks with a given degree distribution, we are able to predict the most probable, or optimal, paths to extinction in various configurations, inc…

[Phys. Rev. Lett. 117, 028302] Published Wed Jul 06, 2016

An old branch of mathematics, Topology, has opened the road to the discovery of new phases of matter. A hidden topology in the energy spectrum is the key for novel conducting/insulating properties of topological matter.

DONATE to arXiv: One hundred percent of your contribution will fund improvements and new initiatives to benefit arXiv's global scientific community. Please join the Simons Foundation and our generous member organizations and research labs in supporting arXiv. https://goo.gl/QIgRpr

Author(s): S. A. Plotnikov, J. Lehnert, A. L. Fradkov, and E. Schöll

We study synchronization in heterogeneous FitzHugh-Nagumo networks. It is well known that heterogeneities in the nodes hinder synchronization when becoming too large. Here we develop a controller to counteract the impact of these heterogeneities. We first analyze the stability of the equilibrium poi…

[Phys. Rev. E 94, 012203] Published Tue Jul 05, 2016

Author(s): Xiyun Zhang, Hongjie Bi, Shuguang Guan, Jinming Liu, and Zonghua Liu

Global synchronization and partial synchronization are the two distinctive forms of synchronization in coupled oscillators and have been well studied in recent decades. Recent attention on synchronization is focused on the chimera state (CS) and explosive synchronization (ES), but little attention h…

[Phys. Rev. E 94, 012204] Published Tue Jul 05, 2016

Author(s): Clara Stegehuis, Remco van der Hofstad, and Johan S. H. van Leeuwaarden

Most random graph models are locally tree-like—do not contain short cycles—rendering them unfit for modeling networks with a community structure. We introduce the hierarchical configuration model (HCM), a generalization of the configuration model that includes community structures, while properties …

[Phys. Rev. E 94, 012302] Published Tue Jul 05, 2016

Nature Physics. doi:10.1038/nphys3812

Authors: Kaj-Kolja Kleineberg, Marián Boguñá, M. Ángeles Serrano & Fragkiskos Papadopoulos

We study systems of identical coupled oscillators introducing a distribution of delay times in the coupling. For arbitrary network topologies, we show that the frequency and stability of the fully synchronized states depend only on the mean of the delay distribution. However, synchronization dynamics is sensitive to the shape of the distribution. In the presence of coupling delays, the synchronization rate can be maximal for a specific value of the coupling strength.

DONATE to arXiv: One hundred percent of your contribution will fund improvements and new initiatives to benefit arXiv's global scientific community. Please join the Simons Foundation and our generous member organizations and research labs in supporting arXiv. https://goo.gl/QIgRpr

Many studies have explored spreading and diffusion through complex networks. The following study examines a specific case of spreading of opinions in modern society through two spreading schemes —defined as being either through “word of mouth” (WOM), or through online search engines (WEB). We apply both modelling and real experimental results and compare the opinions people adopt through an exposure to their friend's opinions, as opposed to the opinions they adopt when using a search engine based on the PageRank algorithm. A simulated study shows that when members in a population adopt decisions through the use of the WEB scheme, the population ends up with a few dominant views, while other views are barely expressed. In contrast, when members adopt decisions based on the WOM scheme, there is a far more diverse distribution of opinions in that population. The simulative results are further supported by an online experiment which finds that people searching information through a ...

Author(s): Yu Terada and Toshio Aoyagi

A large variety of rhythms are observed in nature. Rhythms such as electroencephalogram signals in the brain can often be regarded as interacting. In this study, we investigate the dynamical properties of rhythmic systems in two populations of phase oscillators with different frequency distributions…

[Phys. Rev. E] Published Thu Jun 30, 2016

Author(s): Alex Roxin and Albert Compte

Bistability between attracting fixed points in neuronal networks has been hypothesized to underly persistent activity observed in several cortical areas during working memory tasks. In network models this kind of bistability arises due to strong recurrent excitation, sufficient to generate a state o…

[Phys. Rev. E] Published Thu Jun 30, 2016

Publication date: 13 September 2016
Source:Physics Reports, Volume 650
Author(s): Linyuan Lü, Duanbing Chen, Xiao-Long Ren, Qian-Ming Zhang, Yi-Cheng Zhang, Tao Zhou
Real networks exhibit heterogeneous nature with nodes playing far different roles in structure and function. To identify vital nodes is thus very significant, allowing us to control the outbreak of epidemics, to conduct advertisements for e-commercial products, to predict popular scientific publications, and so on. The vital nodes identification attracts increasing attentions from both computer science and physical societies, with algorithms ranging from simply counting the immediate neighbors to complicated machine learning and message passing approaches. In this review, we clarify the concepts and metrics, classify the problems and methods, as well as review the important progresses and describe the state of the art. Furthermore, we provide extensive empirical analyses to compare well-known methods on disparate real networks, and highlight the future directions. In spite of the emphasis on physics-rooted approaches, the unification of the language and comparison with cross-domain methods would trigger interdisciplinary solutions in the near future.

Author(s): K. Premalatha, V. K. Chandrasekar, M. Senthilvelan, and M. Lakshmanan

We investigate the emergence of different kinds of imperfect synchronized states and chimera states in two interacting populations of nonlocally coupled Stuart-Landau oscillators. We find that the complete synchronization in population-I and existence of solitary oscillators which escape from the sy…

[Phys. Rev. E] Published Thu Jun 30, 2016

Author(s): Nadezhda Semenova, Anna Zakharova, Vadim Anishchenko, and Eckehard Schöll

We demonstrate that chimera behavior can be observed in nonlocally coupled networks of excitable systems in the presence of noise. This phenomenon is distinct from classical chimeras, which occur in deterministic oscillatory systems, and it combines temporal features of coherence resonance, i.e., th…

[Phys. Rev. Lett. 117, 014102] Published Fri Jul 01, 2016

Author(s): Pavel V. Kuptsov and Sergey P. Kuznetsov

We develop a numerical test of hyperbolicity of chaotic dynamics in time-delay systems. The test is based on the angle criterion and includes computation of angle distributions between expanding, contracting, and neutral manifolds of trajectories on the attractor. Three examples are tested. For two …

[Phys. Rev. E 94, 010201(R)] Published Fri Jul 01, 2016

Author: Melanie L. Blanchette

Author(s): Heetae Kim, Sang Hoon Lee, and Petter Holme

Given a power grid and a transmission (coupling) strength, basin stability is a measure of synchronization stability for individual nodes. Earlier studies have focused on the basin stability's dependence of the position of the nodes in the network for single values of transmission strength. Basin st…

[Phys. Rev. E 93, 062318] Published Thu Jun 30, 2016

Author(s): Daniel Jung and Stefan Kettemann

Local changes in the topology of electricity grids can cause overloads far away from the disturbance , making the prediction of the robustness against changes in the topology - for example caused by power outages or grid extensions - a challenging task. The impact of single-line additions on the lon…

[Phys. Rev. E] Published Wed Jun 29, 2016

Clustering algorithms for large networks typically use modularity values to test which partitions of the vertex set better represent structure in the data. The modularity of a graph is the maximum modularity of a partition. We consider the modularity of two kinds of graphs.

For $r$-regular graphs with a given number of vertices, we investigate the minimum possible modularity, the typical modularity, and the maximum possible modularity. In particular, we see that for random cubic graphs the modularity is usually in the interval $(0.666, 0.804)$, and for random $r$-regular graphs with large $r$ it usually is of order $1/\sqrt{r}$. These results help to establish baselines for statistical tests on regular graphs.

The modularity of cycles and low degree trees is known to be close to 1: we extend these results to `treelike' graphs, where the product of treewidth and maximum degree is much less than the number of edges. This yields for example the (deterministic) lower bound $0.666$ mentioned above on the modularity of random cubic graphs.

Nature Physics 12, 631 (2016). doi:10.1038/nphys3821

Author: Abigail Klopper