arXiv subjects

Arianna Bottinelli

Publications and source records attributed to Arianna Bottinelli.

5 recordsLinked to original sources

arXiv2019

Efficiency and shrinking in evolving networks

Characterizing the spatio-temporal evolution of networks is a central topic in many disciplines. While network expansion has been studied thoroughly, less is known about how empirical networks behave when shrinking. For transportation networks, this is especially relevant on account of their connection with the socio-economical substrate, and we focus here on the evolution of the French railway network from its birth in 1840 to 2000, in relation to the country's demographic dynamics. The network evolved in parallel with technology (e.g., faster trains) and under strong constraints, such as preserving a good population coverage and balancing cost and efficiency. We show that the shrinking phase that started in 1930 decreased the total length of the network while preserving efficiency and population coverage: efficiency and robustness remain remarkably constant while the total length of the network shrinks by $50\%$ between 1930 and 2000, and the total travel time and time-diameter decreased by more than $75\%$ during the same period. Moreover, shrinking the network did not affect the overall accessibility, with an average travel time that decreases steadily since its formation. This evolution leads naturally to an increase of transportation multimodality (such as a massive use of cars) and shows the importance of considering together transportation modes acting at different spatial scales. More generally, our results suggest that shrinking is not necessarily associated with a decay in performance and functions, but can be beneficial in terms of design goals and can be part of the natural evolution of an adaptive network.

physics.soc-ph↗

arXiv2018

Can high-density human collective motion be forecasted by spatiotemporal fluctuations?

Concerts, protests, and sporting events are occurring with increasing frequency and magnitude. The extreme physical conditions common to these events are known to cause injuries and loss-of-life due to the emergence of collective motion such as crowd crush, turbulence, and density waves. Mathematical models of human crowds aimed at enhancing crowd safety by understanding these phenomena are developed with input from a variety of disciplines. However, model validation is challenged by a lack of high-quality empirical data and ethical constraints surrounding human crowd research. Consequently, generalized model-based approach for real-time monitoring/risk-assessment of crowd collective motion remains an open problem. Here, we take a model-free approach to crowd analysis and show that emergent collective motion can be forecasted directly from video data. We use mode analysis methods from material science and concepts from non-equilibrium physics to study footage of a human crowd at an Oasis rock concert. We analyze the attendees positional fluctuations during a period of crowd turbulence to predict the spatial patterns of an emergent human density wave. In addition to predicting spatial patterns of collective motion, we also identify and measure temporal patterns that precede the density wave and forecast its appearance by 1~s. Looking ahead, widening this forecasting window beyond 1~s will enable new computer vision technologies for real-time risk-assessment of emergent human collective motion.

physics.soc-ph↗

arXiv2016

Balancing building and maintenance costs in growing transport networks

The costs associated to the length of links impose unavoidable constraints to the growth of natural and artificial transport networks. When future network developments can not be predicted, building and maintenance costs require competing minimization mechanisms, and can not be optimized simultaneously. Hereby, we study the interplay of building and maintenance costs and its impact on the growth of transportation networks through a non-equilibrium model of network growth. We show cost balance is a sufficient ingredient for the emergence of tradeoffs between the network's total length and transport effciency, of optimal strategies of construction, and of power-law temporal correlations in the growth history of the network. Analysis of empirical ant transport networks in the framework of this model suggests different ant species may adopt similar optimization strategies.

physics.soc-ph↗

arXiv2016

Emergent Structural Mechanisms for High-Density Collective Motion Inspired by Human Crowds

Collective motion of large human crowds often depends on their density. In extreme cases like heavy metal concerts and Black Friday sales events, motion is dominated by physical interactions instead of conventional social norms. Here, we study an active matter model inspired by situations when large groups of people gather at a point of common interest. Our analysis takes an approach developed for jammed granular media and identifies Goldstone modes, soft spots, and stochastic resonance as structurally-driven mechanisms for potentially dangerous emergent collective motion.

physics.soc-ph↗

arXiv2012

Influence of homology and node-age on the growth of protein-protein interaction networks

Proteins participating in a protein-protein interaction network can be grouped into homology classes following their common ancestry. Proteins added to the network correspond to genes added to the classes, so that the dynamics of the two objects are intrinsically linked. Here, we first introduce a statistical model describing the joint growth of the network and the partitioning of nodes into classes, which is studied through a combined mean-field and simulation approach. We then employ this unified framework to address the specific issue of the age dependence of protein interactions, through the definition of three different node wiring/divergence schemes. Comparison with empirical data indicates that an age-dependent divergence move is necessary in order to reproduce the basic topological observables together with the age correlation between interacting nodes visible in empirical data. We also discuss the possibility of nontrivial joint partition/topology observables.

q-bio.MN↗