Herd behavior and social contagion

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Any: 2014, Tutor: Marián BoguñaWe consider the voter model dynamics in random networks with mean- eld approach. We apply a Poisson process in the election of the neighbor whose state will be copied by an active node, which is also chosen according to the same process at each time step. For simpli cation, we consider only two possible Poisson rates distributed in two groups, a fast minority and a slow majority. We nd that, for a critical set of parameters, the system exhibit characteristic patterns, with abrupt alternation between two consensus states in the fast group. After the analysis of Langevin equation, an e ective potential for the fast group is found that models the transition between the state of two alternate consensus and another state where the fast minority oscillates around majority opinion trend

Network science for social and technological systems

This thesis contains a collection of research outcomes from the field of complex networks. The results presented here have been divided in two parts, one devoted to theoretical methods and the other to data-driven applications. Although many of the results, especially in the first part, are general enough for describing many complex systems, a special focus on social systems has been used throughout the thesis. The first part contains ideas that explore the interplay of topology and dynamics in complex systems, divided in three chapters dedicated to opinion dynamics, modular networks and weighted networks respectively. Regarding opinion dynamics, we study the emergence of self-organised leadership and herding behaviour in the voter model. Regarding modular networks, we present a generative model for networks with community structure and arbitrary bridgeness distribution. We also show how bridgeness interplays with functional behaviour in different dynamical systems. We use such interplay to define the concept of dynamical centrality, and show its applications to network dismantling under limited topological information. Finally, we demonstrate how topological uncertainty in link weights induces fluctuations on the critical threshold for multiple dynamical processes on networks. We also discuss the role of degree heterogeneity in this propagation, finding non-trivial dependencies for scale-free networks. The second part contains two applications of network analysis to real-world systems. The first application is a data study on the rail network of London and its surrounding area. We show how topological resilience measures are strongly correlated to the performance of train operators in the network. The second application contains a network-based model of armed conflict prediction at city level of analysis. We use several centrality measures as features for machine learning models, showing how network information generates very significant improvements in out-of-sample prediction performance

Resilience or robustness : identifying topological vulnerabilities in rail networks

Many critical infrastructure systems have network structure and are under stress. Despite their national importance, the complexity of large-scale transport networks means we do not fully understand their vulnerabilities to cascade failures. The research in this paper examines the interdependent rail networks in Greater London and surrounding commuter area. We focus on the morning commuter hours, where the system is under the most demand stress. There is increasing evidence that the topological shape of the network plays an important role in dynamic cascades. Here, we examine whether the different topological measures of resilience (stability) or robustness (failure) are more appropriate for understanding poor railway performance. The results show that resilience and not robustness has a strong correlation to the consumer experience statistics. Our results are a way of describing the complexity of cascade dynamics on networks without the involvement of detailed agent-based-models, showing that cascade effects are more responsible for poor performance than failures. The network science analysis hints at pathways towards making the network structure more resilient by reducing feedback loops

Gang Confrontation: The case of Medellin (Colombia)

Protracted conflict is one of the largest human challenges that have persistently undermined economic and social progress. In recent years, there has been increased emphasis on using statistical and physical science models to better understand both the universal patterns and the underlying mechanics of conflict. Whilst macroscopic power-law fractal patterns have been shown for death-toll in wars and self-excitation models have been shown for roadside ambush attacks, very few works deal with the challenge of complex dynamics between gangs at the intra-city scale. Here, based on contributions to the historical memory of the conflict in Colombia, Medellin's gang-confrontation-network is presented. It is shown that socio-economic and violence indexes are moderate to highly correlated to the structure of the network. Specifically, the death-toll of conflict is strongly influenced by the leading eigenvalues of the gangs' conflict adjacency matrix, which serves a proxy for unstable self-excitation from revenge attacks. The distribution of links based on the geographic distance between gangs in confrontation leads to the confirmation that territorial control is a main catalyst of violence and retaliation among gangs. Additionally, the Boltzmann-Lotka-Volterra (BLV) dynamic interaction network analysis is applied to quantify the spatial embeddedness of the dynamic relationship between conflicting gangs in Medellin, results suggest that more involved and comprehensive models are needed to described the dynamics of Medellin's armed conflict.Comment: 18 pages, 9 figures. Statistical analysis was largely improved. arXiv admin note: text overlap with arXiv:1107.0539 by other author

Global air transport complex network : multi-scale analysis

Almost half of the world's population is carried by airlines each year, and understanding this mode of transport is important from economic and scientific perspectives. In recent years, the increasing availability of data has led to complex network and agent interaction models which attempt to gain better understanding of the air transport network and develop forecasts. In this case study paper, we review existing research on two key approaches, namely: (i) a top-down multi-scale network science approach, and (ii) a bottom-up entropy-maximization interaction network approach. Using simple socioeconomic indicators, we were able to construct a very accurate interaction model that can predict traffic volume, and the model can forward estimate the impact of population growth or fuel cost. Using network science approaches, we were able to identify community structures and relate them to economic outputs. We also saw how hubs evolved over time to become more influential. Looking into the future, using random graph theory, it seems that reduced flight cost will lead to increased hub influence. The disseminated knowledge in this case study paper will provide both academics and industry practitioners with steps forward to co-explore the interesting research landscape

Passenger network in London area

Files describing the passenger network in the London area. The Python code to compute the resilience and robustness in also included

Polymeric nanocarriers for expected nanomedicine: Current challenges and future prospects

Polymeric nanocarriers have an increasingly growing potential for clinical applications. The current and future expectation from a polymeric nanocarrier is to exhibit both diagnostic and therapeutic functions. Living organisms are very complex systems and have many challenges for a carrier system such as biocompatibility, biodistribution, side-effects, biological barriers. Therefore, a designed polymeric nanocarrier should possess multifunctional properties to overcome these obstacles towards its target site. However, currently there are few polymeric systems that can be used for both therapy and imaging in clinic studies. In the literature, there are many studies for developing new generation polymeric nanocarriers to obtain future smart and multifunctional nanomedicine. In this review, we discuss the new generation and promising polymeric nanocarriers, which exhibit active targeting, triggered release of contents, and imaging capability for in vivo studies. © The Royal Society of Chemistry 2014

Coyuntura y problemáticas regionales de las montañas del sudoeste de Europa y restauración de hábitats mediante prácticas de herbivorismo pírico: El proyecto OPEN2PRESERVE

Le feu contrôlé est pratique dans certaines régions du sud-ouest de !'Europe pour Ia restauration des habitats et Ia prévention des grands incendies de forêt. Malgré son intérêt, il est confronté a des défis environnementaux, socio - économiques et règlementaires. Le projet Interreg SUDOE Open2preserve a mis en œuvre huit expériences sur l'herbivorie pyrique dans sept régions du territoire afin de tester et de partager les connaissances scientifiques et techniques sur l'utilisation des brulages et du pâturage dirige. Cet article justifie Ia pratique et explore Ia situation particulière de chaque région.The use of controlled fire is practised in some regions of south- western Europe for habitat restoration and prevention of large forest fires. Despite its interest, it faces many environmental, socio-economic, and regulatory challenges. The Interreg SUDOE Open2preserve project implemented eight experiments on pyric herbivory in seven regions of the territory to test and share scientific and technical knowledge on the use of burns and targeted grazing. This manuscript justifies the practice and explores the regional challenges.El uso del fuego controlado se practica en algunas regiones del suroeste de Europa para Ia restauración de hábitats y Ia prevención de grandes incendios forestales. A pesar del interés, se enfrenta a numerosos retos medioambientales, socioeconómicos y normativos. El proyecto Interreg SUDOE Open2preserve puso en marcha ocho experiencias de herbivorismo pírico en siete regiones del territorio para testar y compartir conocimientos científico-técnicos en el uso de las quemas y del pastoreo dirigido ambiental. Este articulo justifica Ia práctica y profundiza en Ia situación particular de cada región.El proyecto Open2preserve fue financiado en la segunda convocatoria de proyectos Interreg SUDOE en el eje 5 sobre Medio Ambiente y Eficiencia de los Recursos (SOE2/P5/E0804).info:eu-repo/semantics/publishedVersio