The Science of Complex Systems is an emergent discipline rather successful in the last years. However, further progress in the physics is hampered by the lack of deep knowledge about how multi-level complex systems organize and operate. Preliminary results show that interactions at different levels behave in a significantly different way than in an isolated...

Concerning again the complex patterns of interactions that have been found in many natural, social and technological systems, we have studied the interplay between dynamics and topology. In particular:

1. Hierarchically organized networks: We have focused our research on the way topology, in terms of the communities that are formed at different scales, affects the...

We have studied different aspects of human mobility. The increased pervasiveness of information and communication technologies is enabling the tracking of human mobility at an unprecedented scale. Massive call detail records from mobile phone activities and the use of global positioning systems (GPS) in large vehicle fleets for instance, are generating extraordinary quantities of positional...

We are currently collaborating with historians, archaeologists, and computer scientists to set up an innovative framework to investigate the political and economic mechanisms that characterized the dynamics of the commercial trade system during the Roman Empire. It is a project funded by the European Research Council and our contribution is to introduce network theory as...

Statistical properties of binary complex networks are well understood and recently many attempts have been made to extend this knowledge to weighted ones. There are, however, subtle yet important considerations to be made regarding the nature of the weights used in this generalization. Weights can be either continuous or discrete magnitudes, and in the latter...

At first instance, Human kind relies on food to survive as biological specie. Given our cognitive capabilities and neuronal complexity, along history we have been evolving preferences in the way we select food. Besides survival, we may have developed food preferences based on several other factors such as: food caloric value, taste, texture, appearance, psychological...

Our interest in this subject is focused on the behavior of complex structures formed by elements (or agents) that interact with each other via communication processes. This framework is specially adequate to study e.g. Internet flow, traffic networks, river networks, and even communication flows in organizations.

We have proposed a simple model that includes only the...

Various physical, social, and biological systems generate complex fluctuations with correlations across multiple time scales. In physiologic systems, these long-range correlations are altered with disease and aging. Such correlated fluctuations in living systems have been attributed to the interaction of multiple control systems; however, the mechanisms underlying this behavior remain unknown. Here, we show that...

During the last years we have been collaborating with Prof. Fernando Vega-Redondo, an economist from the University of Alicante. 

As physicists our contribution in this subject has been to apply concepts and tools widely used in nonequilibrium statistical mechanics, as those described above, to the study of the complex behavior of interacting economic agents. 

We have...

We have also the statistical properties of different social networks. The examples are:

1. The Web of trust: we investigate the creation of social capital in the “web of trust” formed by the users of the “Pretty-Good-Privacy” (PGP) encryption system. The PGP program is used in digital communications both to encrypt messages—so that only...

One of the central points of our research has been the study of biological rhythms, together with other dynamical aspects related to the cooperative behavior of extended populations. Particularly, our analysis has been emphasized on the study of the mechanisms that are behind phenomena like synchronization of the activity of these populations as well as...

The phenomenon known as self-organized criticality is related to systems which spontaneously (self organized) evolve towards a stationary state without time and length characteristic scales; it is named critical because their analogies with critical phenomena, widely studied in equilibrium. The main differences are that now one deals with non-equilibrium systems, and hence equilibrium statistical mechanics...