Collective versus hub activation of epidemic phases on networks

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 either ruled by a hub activation process, leading to a null threshold in the thermodynamic limit, or given by a collective activation process, corresponding to a standard phase transition with a finite threshold. We validate the proposed criterion applying it to different epidemic models, with waning immunity or heterogeneous infection rates in both synthetic and real SF networks. In particular, a waning immunity, irrespective of its strength, leads to collective activation with finite threshold in scale-free networks with large exponent, at odds with canonical theoretical approaches.Comment: Revised version accepted for publication in PR

Phase transitions with infinitely many absorbing states in complex networks

We instigate the properties of the threshold contact process (TCP), a process showing an absorbing-state phase transition with infinitely many absorbing states, on random complex networks. The finite size scaling exponents characterizing the transition are obtained in a heterogeneous mean field (HMF) approximation and compared with extensive simulations, particularly in the case of heterogeneous scale-free networks. We observe that the TCP exhibits the same critical properties as the contact process (CP), which undergoes an absorbing-state phase transition to a single absorbing state. The accordance among the critical exponents of different models and networks leads to conjecture that the critical behavior of the contact process in a HMF theory is a universal feature of absorbing state phase transitions in complex networks, depending only on the locality of the interactions and independent of the number of absorbing states. The conditions for the applicability of the conjecture are discussed considering a parallel with the susceptible-infected-susceptible epidemic spreading model, which in fact belongs to a different universality class in complex networks.Comment: 9 pages, 6 figures to appear in Phys Rev

Quantifying echo chamber effects in information spreading over political communication networks

Echo chambers in online social networks, in which users prefer to interact only with ideologically-aligned peers, are believed to facilitate misinformation spreading and contribute to radicalize political discourse. In this paper, we gauge the effects of echo chambers in information spreading phenomena over political communication networks. Mining 12 million Twitter messages, we reconstruct a network in which users interchange opinions related to the impeachment of the former Brazilian President Dilma Rousseff. We define a continuous {political position} parameter, independent of the network's structure, that allows to quantify the presence of echo chambers in the strongly connected component of the network, reflected in two well-separated communities of similar sizes with opposite views of the impeachment process. By means of simple spreading models, we show that the capability of users in propagating the content they produce, measured by the associated spreadability, strongly depends on their attitude. Users expressing pro-impeachment sentiments are capable to transmit information, on average, to a larger audience than users expressing anti-impeachment sentiments. Furthermore, the users' spreadability is correlated to the diversity, in terms of political position, of the audience reached. Our method can be exploited to identify the presence of echo chambers and their effects across different contexts and shed light upon the mechanisms allowing to break echo chambers.Comment: 9 pages, 4 figures. Supplementary Information available as ancillary fil

Irrelevance of information outflow in opinion dynamics models

The Sznajd model for opinion dynamics has attracted a large interest as a simple realization of the psychological principle of social validation. As its most salient feature, it has been claimed that the Sznajd model is qualitatively different from other ordering processes, because it is the only one featuring outflow of information as opposed to inflow. We show that this claim is unfounded by presenting a generalized zero-temperature Glauber-type of dynamics which yields results indistinguishable from those of the Sznajd model. In one-dimension we also derive an exact expression for the exit probability of the Sznajd model, that turns out to coincide with the result of an analytical approach based on the Kirkwood approximation. This observation raises interesting questions about the applicability and limitations of this approach.Comment: 5 pages, 4 figure

La declaración unilateral de independencia de Kosovo a la luz de la Opinión Consultiva de la Corte Internacional de Justicia, de 22 de julio de 2010 y de las declaraciones, opiniones individuales y disidentes a la misma

The Opinion of the International Court of Justice on the unilateral declaration of independence of Kosovo is an example of what the Court should not do. Saying only that international law does not prohibit declarations of independence and refusing to answer the matters related to this claim, the Court's opinion adopts a vacuum of legal terms and irresponsible

Voter models on weighted networks

We study the dynamics of the voter and Moran processes running on top of complex network substrates where each edge has a weight depending on the degree of the nodes it connects. For each elementary dynamical step the first node is chosen at random and the second is selected with probability proportional to the weight of the connecting edge. We present a heterogeneous mean-field approach allowing to identify conservation laws and to calculate exit probabilities along with consensus times. In the specific case when the weight is given by the product of nodes' degree raised to a power theta, we derive a rich phase-diagram, with the consensus time exhibiting various scaling laws depending on theta and on the exponent of the degree distribution gamma. Numerical simulations give very good agreement for small values of |theta|. An additional analytical treatment (heterogeneous pair approximation) improves the agreement with numerics, but the theoretical understanding of the behavior in the limit of large |theta| remains an open challenge.Comment: 21 double-spaced pages, 6 figure

Effects of local population structure in a reaction-diffusion model of a contact process on metapopulation networks

We investigate the effects of local population structure in reaction-diffusion processes representing a contact process (CP) on metapopulations represented as complex networks. Considering a model in which the nodes of a large scale network represent local populations defined in terms of a homogeneous graph, we show by means of extensive numerical simulations that the critical properties of the reaction-diffusion system are independent of the local population structure, even when this one is given by a ordered linear chain. This independence is confirmed by the perfect matching between numerical critical exponents and the results from a heterogeneous mean-field theory suited, in principle, to describe situations of local homogeneous mixing. The analysis of several variations of the reaction-diffusion process allows us to conclude the independence from population structure of the critical properties of CP-like models on metapopulations, and thus of the universality of the reaction-diffusion description of this kind of models.Postprint (published version

Nasopharyngeal angiofibroma: review of literature

Angiofibroma of nasopharynx is a highly vascular, rare and benign tumor, with a high a incidence of recurrence and local invasity which nature always defied the researchers on the subject. The controversies start on its site of origin, till therapeutical modalities, passing by clinical and diagnostic aspects. The most serious and baffling feature, however, is the occurrence of hemorrhagic outbreaks, sometimes very intense, which may lead the patient to death. In view of this, the efforts developed towards of minimizing this problematic fact have been many, aiming adequate control of the illness. The present article presents a global review on this subject and intends to discuss the main aspects related to angiofibroma of nasopharynx in a simple and didatic form.O angiofibroma de nasofaringe é um tumor benigno, raro, altamente vascularizado, com elevado índice de recorrência e invasividade local, cuja natureza sempre desafiou os estudiosos do assunto. As controvérsias vão desde o seu local de origem, até modalidades terapêuticas, passando por aspectos clínicos e diagnósticos. A característica mais grave e desconcertante, no entanto, é a ocorrência de surtos hemorrágicos, por vezes muito intensos, podendo levar o paciente à morte. Frente a esse fato, muitos foram os esforços desenvolvidos no sentido de minimizar esse problema, visando o controle adequado da doença. Esse estudo apresenta uma revisão global sobre o tema e se propõe a expor de forma simples e didática os principais aspectos relacionados ao angiofibroma nasofaríngeo.Instituto de Assistência Médica ao Servidor Público Estadual de São PauloUNIFESP-EPMHSPE FMO Departamento de OtorrinolaringologiaHospital do Servidor Público Municipal Serviço de OtorrinolaringologiaUniversidade de São Paulo Faculdade de MedicinaHospital do Servidor Público Estadual FMO Departamento de OtorrinolaringologiaUNIFESP, EPMSciEL

Degradation in AlGaN/GaN heterojunction field effect transistors upon electrical stress: Effects of field and temperature

AlGaN/GaN heterojunction field effect transistors (HFETs) with 2 μm gate length were subjected to on-state-high-field (high drain bias and drain current) and reverse-gate-bias (no drain currentand reverse gate bias) stress at room and elevated temperatures for up to 10 h. The resulting degradation of the HFETs was studied by direct current and uniquely phase noise before and after stress. A series of drain and gate voltages was applied during the on-state-high-field and reverse-gate-bias stress conditions, respectively, to examine the effect of electric field on degradation of the HFET devices passivated with SiNx. The degradation behaviors under these two types of stress conditions were analyzed and compared. In order to isolate the effect of self-heating/temperature on device degradation, stress experiments were conducted at base plate temperatures up to 150 °C. It was found that the electric field induced by reverse-gate-bias mainly generated trap(s), most likely in the AlGaN barrier, which initially were manifested as generation-recombination (G-R) peak(s) in the phase noise spectra near 103 Hz. Meanwhileelectric field induced by on-state-high-field stress mainly generated hot-electron and hot-phonon effects, which result in a nearly frequency independent increase of noise spectra. The external base plate temperatures promote trap generation as evidenced by increased G-R peak intensities