Research Interests

The underlying structure that governs many natural and man-made systems can often be well represented by networks. For instance, in society, interpersonal ties in large interrelated groups are represented by social networks. Networks also have interesting applications in economics: the relationship between various entities (or "agents") can be represented by networks of firms, banks, or countries. Networks play a particularly important role as substrates in which complex flows occur. Thus, social networks serve as the medium in which epidemics or information propagate, and banking networks the medium for inter-bank lending.

My broad interest is in the mathematical, empirical, and numerical study of such flow processes on networks because, ultimately, most networks emerge for the purpose of being carriers of those flows. In recent years, I have particularly focused on more social and economic systems, although I continue to develop my broad interest in network theory. A related interest is the search for quantitative laws in social, economic, and technological systems.

Labor networks: Together with my colleagues Omar Guerrero and Rob Axtell, I have developed a mathematical framework that changes the way in which workforce mobility is understood. This Labor Flow Network framework establishes a new way to develop microfoundations of job search and matching process that is specific down to the level of firms and individuals, and has the potential to change the way in which economic shocks and policy incentives relevant to employment are understood. For more details see subpage here.

Social Networks and Human Communication Patterns: My work in human communication also focuses on persistent temporal patterns. In this context, together with my colleagues Jari Saramäki, Robin Dunbar, Felix Reed-Tsochas, and others, I have introduced the concept of social signatures and identified some of its temporal properties of change of social ties but persistence in the allocation of attention to ranked alters. This work has led to some media attention that has interpreted the work with a "one-in one-out rule", meaning that when one of our friends drops out of our communication pattern, another one takes her/his place receiving a similar amount of communication as the one that left. For more details see subpage here.

Flow, Percolation, and Network Theory: As part of my larger agenda of understanding flow on complex networks, I have worked extensively on the concept of connectivity and percolation in networks and hypergraphs. This work is concerned with the theoretical aspects of network structure and network flow, and asks questions about the efficiency of network flows, the robustness of a network to local disruption, etc. In this area, I have collaborated with Gene Stanley, Shlomo Havlin, Sergey Buldyrev, and Lidia Braunstein, among others, addressing many different challenging and interesting problems. For more details see subpage here.