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Exploring patterns of empirical networks
Umeå University, Faculty of Science and Technology, Department of Physics. (IceLab)
2011 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Utforska mönster av empiriska nätverk (Swedish)
Abstract [en]

We are constantly struggling to understand how nature works, trying to identify recurrent events and looking for analogies and relations between objects or individuals. Knowing patterns of behavior is powerful and fundamental for survival of any species. In this thesis, datasets of diverse systems related to transportation, economics, sexual and social contacts, are characterized by using the formalisms of time series and network theory. Part of the results consists on the collection and analyzes of original network data, the rest focuses on the simulation of dynamical processes on these networks and to study how they are affected by the particular structures. The majority of the thesis is about temporal networks, i.e. networks whose structure changes in time. The new temporal dimension reveals structural dynamical properties that help to understand the feedback mechanisms responsible to make the network structure to adapt and to understand the emergence and inhibition of diverse phenomena in dynamic systems, as epidemics in sexual and contact networks.

Abstract [sv]

Vi är ständigt kämpar för att förstå hur naturen fungerar, försöker identifier återkommande evenemang och söker analogier och relationer mellan objekt eller individer. Veta beteendemönster är kraftfull och grundläggande för överlevnad av arter. I denna avhandling, dataset av olika system i samband med transporter är ekonomi, sexuella och sociala kontakter, som kännetecknas av att använda formalismer av tidsserier och nätverk teori. En del av resultatet utgörs av insamling och analys av ursprungliga nätdata, fokuserar resten på simulering av dynamiska processer i dessa nätverk och att studera hur de påverkas av de särskilda strukturer. Huvuddelen av avhandlingen handlar om tidsmässiga nät, i.e. nät vars struktur förändringar i tid. Den nya tidsdimensionen avslöjar strukturella dynamiska egenskaper som hjälper till att förstå den feedback mekanismer som ansvarar för att göra nätverksstruktur att anpassa sig och förstå uppkomsten och hämning av olika företeelser i dynamiska system, epidemier i sexuella och kontaktnät.

Abstract [pt]

Constantemente nos esforçamos para entender como a natureza funciona, tentando identificar eventos recorrentes e procurando por analogias e relações entre objetos ou indivíduos. Conhecer padrões de comportamento é algo poderoso e fundamental para a sobrevivência de qualquer espécie. Nesta tese, dados de sistemas diversos, relacionados a transporte, economia, contatos sexuais e sociais, são caracterizados usando o formalismo de séries temporais e teoria de redes. Uma parte dos resultados consiste na coleta e análise de dados de redes originais, a outra parte concentra-se na simulação de processos dinâmicos nessas redes e no estudo de como esses processos são afetados por determinadas estruturas. A maior parte da tese é sobre redes temporais, ou seja, redes cuja estrutura varia no tempo. A nova dimensão temporal revela propriedades estruturais dinâmicas que contribuem para o entendimento dos mecanismos de resposta responsáveis pela adaptação da rede, e para o entendimento da emergência e inibição de fenômenos diversos em sistemas dinâmicos, como epidemias em redes sexuais e de contato pessoal.

Place, publisher, year, edition, pages
Umeå: Umeå University, Department of Physics , 2011. , 66 p.
Keyword [en]
complex systems, complex networks, network analysis, empirical networks, air transportation, consumer complaints, information technology, sexual contacts, epidemics, vaccination
National Category
Other Physics Topics Other Physics Topics Other Social Sciences not elsewhere specified Public Health, Global Health, Social Medicine and Epidemiology Computer and Information Science
Research subject
Physics; Statistics; Epidemiology; Economics
Identifiers
URN: urn:nbn:se:umu:diva-46588ISBN: 978-91-7459-241-2 (print)OAI: oai:DiVA.org:umu-46588DiVA: diva2:439205
Public defence
2011-09-30, Naturvetarhuset, N300, Umeå universitet, Umeå, 13:30 (English)
Opponent
Supervisors
Available from: 2011-09-08 Created: 2011-09-06 Last updated: 2011-09-08Bibliographically approved
List of papers
1. Structural evolution of the Brazilian airport network
Open this publication in new window or tab >>Structural evolution of the Brazilian airport network
2009 (English)In: Journal of Statistical Mechanics: Theory and Experiment, ISSN 1742-5468, E-ISSN 1742-5468, 04020- p.Article in journal (Refereed) Published
Abstract [en]

The aviation sector is profitable, but sensitive to economic fluctuations, geopolitical constraints and governmental regulations. As for other means of transportation, the relation between origin and destination results in a complex map of routes, which can be complemented with information associated with the routes themselves, for instance, frequency, traffic load and distance. The theory of networks provides a natural framework for investigating the dynamics on the resulting structure. Here, we investigate the structure and evolution of the Brazilian airport network (BAN) as regards several quantities: routes, connections, passengers and cargo. Some structural features are in accordance with previous results for other airport networks. The analysis of the evolution of the BAN shows that its structure is dynamic, with changes in the relative relevance of some airports and routes. The results indicate that the connections converge to specific routes. The network shrinks at the route level but grows in number of passengers and amount of cargo, which more than doubled during the period studied.

Place, publisher, year, edition, pages
Bristol: Institute of Physics, 2009
Keyword
complex systems, complex networks, airports, Brazil
National Category
Other Physics Topics Environmental Analysis and Construction Information Technology
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-22241 (URN)10.1088/1742-5468/2009/04/P04020 (DOI)
Available from: 2009-05-03 Created: 2009-05-03 Last updated: 2017-12-13Bibliographically approved
2. The network organisation of consumer complaints
Open this publication in new window or tab >>The network organisation of consumer complaints
2010 (English)In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 91, no 2, 28005-28011 p.Article in journal (Refereed) Published
Abstract [en]

Interaction between consumers and companies can create conflict. When a consensus is unreachable there are legal authorities to resolve the case. This letter is a study of data from the Brazilian Department of Justice from which we build a bipartite network of categories of complaints linked to the companies receiving those complaints. We find the complaint categories organised in an hierarchical way where companies only get complaints of lower degree if they already got complaints of higher degree. The fraction of resolved complaints for a company appears to be nearly independent of the equity of the company but is positively correlated with the total number of complaints received. We construct feature vectors based on the edge-weight —the weight of an edge represents the times complaints of a category have been filed against that company— and use these vectors to study the similarity between the categories of complaints. From this analysis, we obtain trees mapping the hierarchical organisation of the complaints. We also apply principal component analysis to the set of feature vectors concluding that a reduction of the dimensionality of these from 8827 to 27 gives an optimal hierarchical representation.

Keyword
complex system, complex network, complaints, consumers, company, management
National Category
Other Physics Topics
Identifiers
urn:nbn:se:umu:diva-35245 (URN)10.1209/0295-5075/91/28005 (DOI)000282189500021 ()
Available from: 2010-08-11 Created: 2010-08-11 Last updated: 2017-12-12Bibliographically approved
3. Information dynamics shape the sexual networks of Internet-mediated prostitution
Open this publication in new window or tab >>Information dynamics shape the sexual networks of Internet-mediated prostitution
2010 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 107, no 13, 5706-5711 p.Article in journal (Refereed) Published
Abstract [en]

Like many other social phenomena, prostitution is increasingly coordinated over the Internet. The online behavior affects the offline activity; the reverse is also true. We investigated the reported sexual contacts between 6,624 anonymous escorts and 10,106 sex buyers extracted from an online community from its beginning and six years on. These sexual encounters were also graded and categorized (in terms of the type of sexual activities performed) by the buyers. From the temporal, bipartite network of posts, we found a full feedback loop in which high grades on previous posts affect the future commercial success of the sex worker, and vice versa. We also found a peculiar growth pattern in which the turnover of community members and sex workers causes a sublinear preferential attachment. There is, moreover, a strong geographic influence on network structure—the network is geographically clustered but still close to connected, the contacts consistent with the inverse-square law observed in trading patterns. We also found that the number of sellers scales sublinearly with city size, so this type of prostitution does not, comparatively speaking, benefit much from an increasing concentration of people.

Place, publisher, year, edition, pages
National Academy of Sciences, 2010
Keyword
complex networks, sexual contacts, sexual network, information spreading, feedback process, online/offline activity
National Category
Information Science Communication Studies
Identifiers
urn:nbn:se:umu:diva-32704 (URN)10.1073/pnas.0914080107 (DOI)000276159500005 ()
Available from: 2010-03-22 Created: 2010-03-22 Last updated: 2017-12-12Bibliographically approved
4. Simulated epidemics in an empirical spatiotemporal network of 50,185 sexual contacts
Open this publication in new window or tab >>Simulated epidemics in an empirical spatiotemporal network of 50,185 sexual contacts
2011 (English)In: PloS Computational Biology, ISSN 1553-734X, E-ISSN 1553-7358, Vol. 7, no 3, e1001109- p.Article in journal (Refereed) Published
Abstract [en]

Sexual contact patterns, both in their temporal and network structure, can influence the spread of sexually transmitted infections (STI). Most previous literature has focused on effects of network topology; few studies have addressed the role of temporal structure. We simulate disease spread using SI and SIR models on an empirical temporal network of sexual contacts in high-end prostitution. We compare these results with several other approaches, including randomization of the data, classic mean-field approaches, and static network simulations. We observe that epidemic dynamics in this contact structure have well-defined, rather high epidemic thresholds. Temporal effects create a broad distribution of outbreak sizes, even if the per-contact transmission probability is taken to its hypothetical maximum of 100%. In general, we conclude that the temporal correlations of our network accelerate outbreaks, especially in the early phase of the epidemics, while the network topology (apart from the contact-rate distribution) slows them down. We find that the temporal correlations of sexual contacts can significantly change simulated outbreaks in a large empirical sexual network. Thus, temporal structures are needed alongside network topology to fully understand the spread of STIs. On a side note, our simulations further suggest that the specific type of commercial sex we investigate is not a reservoir of major importance for HIV.

National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-43120 (URN)10.1371/journal.pcbi.1001109 (DOI)
Funder
Swedish Research Council, 2009-3536
Available from: 2011-04-18 Created: 2011-04-18 Last updated: 2017-12-11Bibliographically approved
5. Exploiting temporal network structures of human interaction to effectively immunize populations
Open this publication in new window or tab >>Exploiting temporal network structures of human interaction to effectively immunize populations
(English)Manuscript (preprint) (Other academic)
Abstract [en]

If we can lower the number of people needed to vaccinate for a community to be immune against contagious diseases, we can save resources and life. A key to reach such a lower threshold of immunization is to find and vaccinate people who, through their behavior, are more likely to become infected and effective to spread the disease than the average. Fortunately, the very behavior that makes these people important to vaccinate can help us finding them. People you have met recently are more likely to be socially active and thus central in the contact pattern, and important to vaccinate. We propose two immunization schemes exploiting temporal contact patterns. Both of these rely only on obtainable, local information and could implemented in practice. We show that these schemes outperform benchmark protocols in four real data sets under various epidemic scenarios. The data sets are dynamic, which enables us to make more realistic evaluations than other studies - we use information only about the past to perform the vaccination and the future to simulate disease outbreaks. We also use models to elucidate the mechanisms behind how the temporal structures make our immunization protocols efficient.

Keyword
vaccination protocol, epidemics, contact network
National Category
Public Health, Global Health, Social Medicine and Epidemiology Other Physics Topics
Research subject
Epidemiology; Public health
Identifiers
urn:nbn:se:umu:diva-46587 (URN)
Available from: 2011-09-06 Created: 2011-09-06 Last updated: 2013-09-06Bibliographically approved

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