Browsing by Author "Vespignani, Alessandro"

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Comment on “Self-organized criticality and absorbing states: Lessons from the Ising model”
(2008) Alava, Mikko J.; Laurson, Lasse; Vespignani, Alessandro; Zapperi, Stefano
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
According to Pruessner and Peters [G. Pruessner and O. Peters, Phys. Rev. E 73, 025106(R) (2006)], the finite-size scaling exponents of the order parameter in sandpile models depend on the tuning of driving and dissipation rates with system size. We point out that the same is not true for avalanches in the slow driving limit.
Comment on "Self-organized criticality and absorbing states: Lessons from the Ising model"
(2008) Alava, Mikko J.; Laurson, Lasse; Vespignani, Alessandro; Zapperi, Stefano
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
According to Pruessner and Peters [G. Pruessner and O. Peters, Phys. Rev. E 73, 025106(R) (2006)], the finite-size scaling exponents of the order parameter in sandpile models depend on the tuning of driving and dissipation rates with system size. We point out that the same is not true for avalanches in the slow driving limit.
Critical behavior of a one-dimensional fixed-energy stochastic sandpile
(2001) Dickman, Ronald; Alava, Mikko J.; A. Muñoz, Miguel; Peltola, Jarkko; Vespignani, Alessandro; Zapperi, Stefano
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
We study a one-dimensional fixed-energy version (that is, with no input or loss of particles) of Manna’s stochastic sandpile model. The system has a continuous transition to an absorbing state at a critical value of the particle density, and exhibits the hallmarks of an absorbing-state phase transition, including finite-size scaling. Critical exponents are obtained from extensive simulations, which treat stationary and transient properties, and an associated interface representation. These exponents characterize the universality class of an absorbing-state phase transition with a static conserved density in one dimension; they differ from those expected at a linear-interface depinning transition in a medium with point disorder, and from those of directed percolation.
Give more data, awareness and control to individual citizens, and they will help COVID-19 containment
(2020-04-01) Nanni, Mirco; Andrienko, Gennady; Barabàsi, Albert Làszlò; Boldrini, Chiara; Bonchi, Francesco; Cattuto, Ciro; Chiaromonte, Francesca; Comandé, Giovanni; Conti, Marco; Coté, Mark; Dignum, Frank; Dignum, Virginia; Domingo-Ferrer, Josep; Ferragina, Paolo; Giannotti, Fosca; Guidotti, Riccardo; Helbing, Dirk; Kaski, Kimmo; Kertesz, Janos; Lehmann, Sune; Lepri, Bruno; Lukowicz, Paul; Matwin, Stan; Jiménez, Davidmegìas; Monreale, Anna; Morik, Katharina; Oliver, Nuria; Passarella, Andrea; Passerini, Andrea; Pedreschi, Dino; Pentland, Alex; Pianesi, Fabio; Pratesi, Francesca; Rinzivillo, Salvatore; Ruggieri, Salvatore; Siebes, Arno; Torra, Vicenҫ; Trasarti, Roberto; Van Den Hoven, Jeroen; Vespignani, Alessandro
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The rapid dynamics of COVID-19 calls for quick and effective tracking of virus transmission chains and early detection of outbreaks, especially in the “phase 2” of the pandemic, when lockdown and other restriction measures are progressively withdrawn, in order to avoid or minimize contagion resurgence. For this purpose, contact-tracing apps are being proposed for large scale adoption by many countries. A centralized approach, where data sensed by the app are all sent to a nation-wide server, raises concerns about citizens’ privacy and needlessly strong digital surveillance, thus alerting us to the need to minimize personal data collection and avoiding location tracking. We advocate the conceptual advantage of a decentralized approach, where both contact and location data are collected exclusively in individual citizens’ “personal data stores”, to be shared separately and selectively (e.g., with a backend system, but possibly also with other citizens), voluntarily, only when the citizen has tested positive forCOVID-19, and with a privacy preserving level of granularity. This approach better protects the personal sphere of citizens and affords multiple benefits: It allows for detailed information gathering for infected people in a privacy-preserving fashion; and, in turn this enables both contact tracing, and, the early detection of outbreak hotspots on more finely-granulated geographic scale. The decentralized approach is also scalable to large populations, in that only the data of positive patients need be handled at a central level. Our recommendation is two-fold. First to extend existing decentralized architectures with a light touch, in order to manage the collection of location data locally on the device, and allowthe user to share spatio-temporal aggregates-if and when they want and for specific aims-with health authorities, for instance. Second, we favour a longerterm pursuit of realizing a Personal Data Store vision, giving users the opportunity to contribute to collective good in the measure they want, enhancing self-awareness, and cultivating collective efforts for rebuilding society.
Give more data, awareness and control to individual citizens, and they will help COVID-19 containment
(2021-11) Nanni, Mirco; Andrienko, Gennady; Barabási, Albert László; Boldrini, Chiara; Bonchi, Francesco; Cattuto, Ciro; Chiaromonte, Francesca; Comandé, Giovanni; Conti, Marco; Coté, Mark; Dignum, Frank; Dignum, Virginia; Domingo-Ferrer, Josep; Ferragina, Paolo; Giannotti, Fosca; Guidotti, Riccardo; Helbing, Dirk; Kaski, Kimmo; Kertesz, Janos; Lehmann, Sune; Lepri, Bruno; Lukowicz, Paul; Matwin, Stan; Jiménez, David Megías; Monreale, Anna; Morik, Katharina; Oliver, Nuria; Passarella, Andrea; Passerini, Andrea; Pedreschi, Dino; Pentland, Alex; Pianesi, Fabio; Pratesi, Francesca; Rinzivillo, Salvatore; Ruggieri, Salvatore; Siebes, Arno; Torra, Vicenc; Trasarti, Roberto; Hoven, Jeroen van den; Vespignani, Alessandro
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The rapid dynamics of COVID-19 calls for quick and effective tracking of virus transmission chains and early detection of outbreaks, especially in the “phase 2” of the pandemic, when lockdown and other restriction measures are progressively withdrawn, in order to avoid or minimize contagion resurgence. For this purpose, contact-tracing apps are being proposed for large scale adoption by many countries. A centralized approach, where data sensed by the app are all sent to a nation-wide server, raises concerns about citizens’ privacy and needlessly strong digital surveillance, thus alerting us to the need to minimize personal data collection and avoiding location tracking. We advocate the conceptual advantage of a decentralized approach, where both contact and location data are collected exclusively in individual citizens’ “personal data stores”, to be shared separately and selectively (e.g., with a backend system, but possibly also with other citizens), voluntarily, only when the citizen has tested positive for COVID-19, and with a privacy preserving level of granularity. This approach better protects the personal sphere of citizens and affords multiple benefits: it allows for detailed information gathering for infected people in a privacy-preserving fashion; and, in turn this enables both contact tracing, and, the early detection of outbreak hotspots on more finely-granulated geographic scale. The decentralized approach is also scalable to large populations, in that only the data of positive patients need be handled at a central level. Our recommendation is two-fold. First to extend existing decentralized architectures with a light touch, in order to manage the collection of location data locally on the device, and allow the user to share spatio-temporal aggregates—if and when they want and for specific aims—with health authorities, for instance. Second, we favour a longer-term pursuit of realizing a Personal Data Store vision, giving users the opportunity to contribute to collective good in the measure they want, enhancing self-awareness, and cultivating collective efforts for rebuilding society.
Time varying networks and the weakness of strong ties
(2014-02-10) Karsai, Márton; Perra, Nicola; Vespignani, Alessandro
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
In most social and information systems the activity of agents generates rapidly evolving time-varying networks. The temporal variation in networks' connectivity patterns and the ongoing dynamic processes are usually coupled in ways that still challenge our mathematical or computational modelling. Here we analyse a mobile call dataset and find a simple statistical law that characterize the temporal evolution of users' egocentric networks. We encode this observation in a reinforcement process defining a time-varying network model that exhibits the emergence of strong and weak ties. We study the effect of time-varying and heterogeneous interactions on the classic rumour spreading model in both synthetic, and real-world networks. We observe that strong ties severely inhibit information diffusion by confining the spreading process among agents with recurrent communication patterns. This provides the counterintuitive evidence that strong ties may have a negative role in the spreading of information across networks.