Virus Propagation on Time-Varying Networks: Theory and Immunization Algorithms

Abstract. Given a contact network that changes over time (say, day vs night connectivity), and the SIS (susceptible/infected/susceptible, flu like) virus propagation model, what can we say about its epidemic threshold? That is, can we determine when a small infection will “take-off ” and create an epidemic? Consequently then, which nodes should we immunize to prevent an epidemic? This is a very real problem, since, e.g. people have different connections during the day at work, and during the night at home. Static graphs have been studied for a long time, with numerous analytical results. Time-evolving networks are so hard to analyze, that most existing works are simulation studies [5]. Specifically, our contributions in this paper are: (a) we formulate the problem by approximating it by a Non-linear Dynamical system (NLDS), (b) we derive the first closed formula for the epidemic threshold of timevarying graphs under the SIS model, and finally (c) we show the usefulness of our threshold by presenting efficient heuristics and evaluate the effectiveness of our methods on synthetic and real data like the MIT reality mining graphs.

Organizing and the Search for Excellence: Making Sense of the Times in Theory and Practice

This paper seeks to draw out commonalities between the organizational/practitioners' and academic agenda and to explore the idea that academe may not only reflect the times but also help to create them. In so doing, it examines the extent to which In Search of Excellence, a significant and timely exemplar of the organizational agenda, in effect operationalized The Social Psychology of Organizing. If, it concludes, sensemaking is retrospective, then how can it help us to think about current issues that require action and shape our conversations and sensemaking about time future? To this end, much of academic management treats much of management practice as beyond the pale and, for that reason, what matters in this paper is not just a consideration of how to break out of Hambrick's closed loop, but also how others can be encouraged to break in. We see this as part of an ongoing conversation that matters.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68948/2/10.1177_135050849961006.pd