A recurring theme in the study of society is the concentration of influence and power that is driven through unequal membership of groups and associations. In some instances, these bodies constitute a small world while in others they are fragmented into distinct cliques. This paper presents a...

Modern economies rely heavily on their infrastructure networks. These networks face threats ranging from natural disasters to human attacks. As networks are pervasive, the investments needed to protect them are very large; this motivates the study of targeted defense. What are the 'key' nodes to...