Preface iii Conventions v * * * * * * PLK thanks Genja, Lyuba, Dana, and other members of his family for things that have nothing to do with statistical physics. SR thanks his children Rebecca and Gabriel, and his wife Anita, for their forebearance, support, and love during the preparation of this book. EB thanks his loving family, Ellen, Micha, Daniel, and Talia, for everything.

No abstract

We study an opinion dynamics model in which agents reach compromise via pairwise interactions. When the opinions of two agents are sufficiently close, they both acquire the average of their initial opinions; otherwise, they do not interact. Generically, the system reaches a steady state with a finite number of isolated, noninteracting opinion clusters ("parties"). As the initial opinion range increases, the number of such parties undergoes a periodic sequence of bifurcations. Both major and minor parties emerge, and these are organized in alternating pattern. This behavior is illuminated by considering discrete opinion states.

We study steady-state properties of inelastic gases in two-dimensions in the presence of an energy source. We generalize previous hydrodynamic treatments to situations where high and low density regions coexist. The theoretical predictions compare well with numerical simulations in the nearly elastic limit. It is also seen that the system can achieve a nonequilibrium steady-state with asymmetric velocity distributions, and we discuss the conditions under which such situations occur.