Marta C. González

Human mobility is differentiated by time scales. While the mechanism for long time scales has been studied, the underlying mechanism on the daily scale is still unrevealed. Here, we uncover the mechanism responsible for the daily mobility patterns by analysing the temporal and spatial trajectories of thousands of persons as individual networks. Using the concept of motifs from network theory, we find only 17 unique networks are present in daily mobility and they follow simple rules. These networks, called here motifs, are sufficient to capture up to 90 per cent of the population in surveys and mobile phone datasets for different countries. Each individual exhibits a characteristic motif, which seems to be stable over several months. Consequently, daily human mobility can be reproduced by an analytically tractable framework for Markov chains by modelling periods of high-frequency trips followed by periods of lower activity as the key ingredient.

Viruses and Mobile Phones While traditional cellphones have been relatively immune to viruses, smartphones (like Palm, Blackberry, iPhone, and many Nokia brands) that can share programs and data with each other could potentially be vulnerable to virus epidemics. Why then haven't we experienced any major mobile virus outbreak so far? Wang et al. (p. 1071; published online 2 April; see the Perspective by Havlin ) believe that the answer is related to the spreading patterns possible in the current mobile phone systems. They studied the anonymized billing record of a mobile phone company, representing the calling patterns and the coordinates of the closest mobile phone tower each time a group of 6.2 million mobile phone subscribers used their phone. While a Bluetooth virus could reach all susceptible users given sufficient time, its spread, limited by human mobility, was relatively slow. In contrast, MMS viruses would have an explosive spreading pattern, but could only reach the group of individuals that know each other and carry the same phone. Thus, no major virus outbreak is likely until one operating system encompasses a larger fraction of the total smartphone market.