566 research outputs found
Layer degradation triggers an abrupt structural transition in multiplex networks
Network robustness is a central point in network science, both from a
theoretical and a practical point of view. In this paper, we show that layer
degradation, understood as the continuous or discrete loss of links' weight,
triggers a structural transition revealed by an abrupt change in the algebraic
connectivity of the graph. Unlike traditional single layer networks, multiplex
networks exist in two phases, one in which the system is protected from link
failures in some of its layers and one in which all the system senses the
failure happening in one single layer. We also give the exact critical value of
the weight of the intra-layer links at which the transition occurs for
continuous layer degradation and its relation to the value of the coupling
between layers. This relation allows us to reveal the connection between the
transition observed under layer degradation and the one observed under the
variation of the coupling between layers.Comment: 8 pages, and 8 figures in Revtex style. Submitted for publicatio
A polynomial eigenvalue approach for multiplex networks
We explore the block nature of the matrix representation of multiplex
networks, introducing a new formalism to deal with its spectral properties as a
function of the inter-layer coupling parameter. This approach allows us to
derive interesting results based on an interpretation of the traditional
eigenvalue problem. More specifically, we reduce the dimensionality of our
matrices but increase the power of the characteristic polynomial, i.e, a
polynomial eigenvalue problem. Such an approach may sound counterintuitive at
first glance, but it allows us to relate the quadratic problem for a 2-Layer
multiplex system with the spectra of the aggregated network and to derive
bounds for the spectra, among many other interesting analytical insights.
Furthermore, it also permits to directly obtain analytical and numerical
insights on the eigenvalue behavior as a function of the coupling between
layers. Our study includes the supra-adjacency, supra-Laplacian, and the
probability transition matrices, which enable us to put our results under the
perspective of structural phases in multiplex networks. We believe that this
formalism and the results reported will make it possible to derive new results
for multiplex networks in the future.Comment: 15 pages including figures. Submitted for publicatio
On degree-degree correlations in multilayer networks
We propose a generalization of the concept of assortativity based on the
tensorial representation of multilayer networks, covering the definitions given
in terms of Pearson and Spearman coefficients. Our approach can also be applied
to weighted networks and provides information about correlations considering
pairs of layers. By analyzing the multilayer representation of the airport
transportation network, we show that contrasting results are obtained when the
layers are analyzed independently or as an interconnected system. Finally, we
study the impact of the level of assortativity and heterogeneity between layers
on the spreading of diseases. Our results highlight the need of studying
degree-degree correlations on multilayer systems, instead of on aggregated
networks.Comment: 8 pages, 3 figure
A process of rumor scotching on finite populations
Rumor spreading is a ubiquitous phenomenon in social and technological
networks. Traditional models consider that the rumor is propagated by pairwise
interactions between spreaders and ignorants. Spreaders can become stiflers
only after contacting spreaders or stiflers. Here we propose a model that
considers the traditional assumptions, but stiflers are active and try to
scotch the rumor to the spreaders. An analytical treatment based on the theory
of convergence of density dependent Markov chains is developed to analyze how
the final proportion of ignorants behaves asymptotically in a finite
homogeneously mixing population. We perform Monte Carlo simulations in random
graphs and scale-free networks and verify that the results obtained for
homogeneously mixing populations can be approximated for random graphs, but are
not suitable for scale-free networks. Furthermore, regarding the process on a
heterogeneous mixing population, we obtain a set of differential equations that
describes the time evolution of the probability that an individual is in each
state. Our model can be applied to study systems in which informed agents try
to stop the rumor propagation. In addition, our results can be considered to
develop optimal information dissemination strategies and approaches to control
rumor propagation.Comment: 13 pages, 11 figure
The flying man’s journey : evolution of the multimedia market
In the year 1999 and 2000, Nikon and Canon launched the first digital
single-lens reflex camera (DSLR’s), and some years later the first DSRL shooting
full high definition (HD) video was on the market at an extremely affordable price.
Along with the Internet boom and the era of social networks, the
multimedia market suffered a dramatic change. Knowledge and equipment
became much more accessible, and companies started to see innovative and
creative multimedia projects done by individual young enthusiasts that reached
larger audiences with extremely low budgets, through the electronic word of
mouth on the Internet. Web Marketing became one of the most important
marketing tools available for companies.
This dissertation focuses on the evolution of the multimedia market, and
how Internet and technology affected it, by creating a new market for online
content. By making a parallel of a young business student’s path and his market
research efforts, the study concludes that there is an open space on Web
marketing market and investigates how can the student capitalize on his skills by
properly introducing a new brand and concept into the market.No ano de 1999 e 2000, a marca Nikon e Canon lançam no mercado a
primeira câmara digital reflex de lente única ( DSLR’s ), e uns anos mais tarde é
lançada a primeira DSLR a filmar em alta definição (HD) a um preço
extremamente acessível.
A era da Internet e das redes sócias veio revolucionar o mercado
multimédia. O equipamento e o “know-how”, que eram anteriormente difíceis de
obter, tornaram-se baratos e acessíveis, e as empresas começaram a ver
projetos inovadores no mercado produzidos por jovens criativos com poucos
meios, mas que se tornavam extremamente eficazes atingindo um público
enorme e com orçamentos baixos devido à estrutura dos produtores. No entanto
mostravam-se eficientes e eficazes parte devido a partilhas e a boca a boca
electrónica nas redes sociais. O Web marketing tornou-se uma das ferramentas
de marketing mais importantes e utilizadas pelas empresas
Esta dissertação centra-se na evolução do mercado de multimédia, e
como a Internet e evolução da tecnologia o afetou , através da criação de um
novo mercado de conteúdos online. Utilizando o exemplo do progresso de um
jovem estudante de gestão como metáfora e fazendo um paralelo com o seu
estudo de mercado, a tese visa encontrar a melhor maneira de capitalizar as
habilitações do jovem com uma devida introdução da sua marca e conceito no
mercado
Gamification Design with a Domain-Driven Engineering Approach
Companies use a variety of methods and processes to improve the quality of their services, which, in turn, would increase the satisfaction of their users and hence their popularity. One of the enhancements that have been used in recent years is known as gamification. With the benefit of being virtually independent of business types, one of the goals of gamification is to solve user engagement issues. Even so, companies fail to achieve their goals after instantiating gamification into their services, and one cause is related to poor gamification design. The main objective of the developed project was to acquire and develop a possible solution to this problem through the use of a specific set of methods, technologies and the Model-Driven Engineering (MDE) approach. In this sense, in-depth research was done into previous gamification applications and other previous attempts to solve the problem at hand. Several gamification concepts were analyzed, gathering as much data as possible about the subject before the conceptualization of the solution’s domain through an MDE approach.As empresas usam uma variedade de métodos e processos para melhorar a qualidade dos seus serviços, o que por sua vez aumentaria a satisfação de seus utilizadores e, consequentemente, sua popularidade. Um exemplo do mesmo que tem sido utilizado nos últimos anos é conhecido como gamification. Com o benefício de ser praticamente independente dos tipos de negócios, um dos objetivos de gamification é resolver problemas relacionados com a interação entre o serviço e o utilizador. Mesmo assim, as empresas não conseguem atingir os seus objetivos após a adição de gamification nos seus serviços, e uma das causas está relacionada a mau design de gamification. O principal objetivo do projeto é desenvolver uma possível solução para o problema através do uso de um conjunto específico de métodos, tecnologias e da abordagem Model-Driven Engineering (MDE). Nesse sentido, uma pesquisa rigorosa foi realizada sobre aplicações existentes de gamification, como também sobre outras tentativas de resolver o problema em questão. Vários conceitos de gamification foram analisados, de forma a reunir o máximo de informação possível sobre o assunto antes da conceituação do domínio para a solução através da abordagem MDE
On the temporal resolution limits of numerical simulations in complex systems
In this paper we formalize, using the Nyquist-Shannon theorem, a fundamental
temporal resolution limit for numerical experiments in complex systems. A
consequence of this limit is aliasing, the introduction of spurious frequencies
due to sampling. By imposing these limits on the uncertainty principle in
harmonic analysis, we show that by increasing the sampling interval ,
we can also artificially stretch the temporal behavior of our numerical
experiment. Importantly, in limiting cases, we could even observe a new
artificially created absorbing state. Our findings are validated in
deterministic and stochastic simulations. In deterministic systems, we analyzed
the Kuramoto model in which aliasing could be observed. In stochastic
simulations, we formalized and compared different simulation approaches and
showed their temporal limits. Gillespie-like simulations fully capture the
continuous-time Markov chain processes, being lossless. Asynchronous cellular
automata methods capture the same transitions as the continuous-time process
but lose the temporal information about the process. Finally, synchronous
cellular automata simulations solve a sampled chain. By comparing these
methods, we show that if is not small enough, the cellular automata
approach fails to capture the original continuous-time Markov chain since the
sampling is already built into the simulation method. Our results point to a
fundamental limitation that cannot be overcome by traditional methods of
numerical simulations
The 2011 Tohoku earthquake : the impact on the energy sector
The purpose of this paper is to study the impact caused by the Tohoku 2011 earthquake, within the energy sector across the World. In order to measure results, a couple of methodologies that resorted to abnormal returns were undertaken and multiple significance tests were made to verify statistical relevancy on the findings. It has been possible to observe a positive reaction on the “Nuclear Energy” companies, as well as a negative impact on the “Renewable Energy” group, with the most prominent results coming from the second methodology. However, due to the lack of statistical significance across most of the data under study, conclusions tend to be inevitably limited
Disease Localization in Multilayer Networks
We present a continuous formulation of epidemic spreading on multilayer
networks using a tensorial representation, extending the models of monoplex
networks to this context. We derive analytical expressions for the epidemic
threshold of the SIS and SIR dynamics, as well as upper and lower bounds for
the disease prevalence in the steady state for the SIS scenario. Using the
quasi-stationary state method we numerically show the existence of disease
localization and the emergence of two or more susceptibility peaks, which are
characterized analytically and numerically through the inverse participation
ratio. Furthermore, when mapping the critical dynamics to an eigenvalue
problem, we observe a characteristic transition in the eigenvalue spectra of
the supra-contact tensor as a function of the ratio of two spreading rates: if
the rate at which the disease spreads within a layer is comparable to the
spreading rate across layers, the individual spectra of each layer merge with
the coupling between layers. Finally, we verified the barrier effect, i.e., for
three-layer configuration, when the layer with the largest eigenvalue is
located at the center of the line, it can effectively act as a barrier to the
disease. The formalism introduced here provides a unifying mathematical
approach to disease contagion in multiplex systems opening new possibilities
for the study of spreading processes.Comment: Revised version. 25 pages and 18 figure
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