The Control of Dynamical Systems - Recovering Order from Chaos -

Following a brief historical introduction of the notions of chaos in dynamical systems, we will present recent developments that attempt to profit from the rich structure and complexity of the chaotic dynamics. In particular, we will demonstrate the ability to control chaos in realistic complex environments. Several applications will serve to illustrate the theory and to highlight its advantages and weaknesses. The presentation will end with a survey of possible generalizations and extensions of the basic formalism as well as a discussion of applications outside the field of the physical sciences. Future research avenues in this rapidly growing field will also be addressed.Comment: 18 pages, 9 figures. Invited Talk at the XXIth International Conference on the Physics of Electronic and Atomic Collisions (ICPEAC), July 22-27, 1999 (Sendai, Japan

Bases, Bullets, and Ballots: The Effect of U.S. Military Aid on Political Conflict in Colombia

Does foreign military assistance strengthen or further weaken fragile states facing internal confict? We address this question by estimating how U.S. military aid affects violence and electoral participation in Colombia. We exploit the allocation of U.S. military aid to Colombian military bases, and compare how aid affects municipalities with and without bases. Using detailed political violence data, we find that U.S. military aid leads to differential increases in attacks by paramilitaries (who collude with the military), but has no effect on guerilla attacks. Aid increases also result in more paramilitary (but not guerrilla) homicides during election years. Moreover, when military aid rises, voter turnout falls more in base municipalities, especially those that are politically contested. Our results are robust to an instrument based on worldwide increases in U.S. military aid (excluding Latin America). The findings suggest that foreign military assistance may strengthen armed non-state actors, undermining domestic political institutions.military aid; conflict; democracy; elections

Conserved Dynamics and Interface Roughening in Spontaneous Imbibition : A Critical Overview

Imbibition phenomena have been widely used experimentally and theoretically to study the kinetic roughening of interfaces. We critically discuss the existing experiments and some associated theoretical approaches on the scaling properties of the imbibition front, with particular attention to the conservation law associated to the fluid, to problems arising from the actual structure of the embedding medium, and to external influences such as evaporation and gravity. Our main conclusion is that the scaling of moving interfaces includes many crossover phenomena, with competition between the average capillary pressure gradient and its fluctuations setting the maximal lengthscale for roughening. We discuss the physics of both pinned and moving interfaces and the ability of the existing models to account for their properties.Comment: 9 pages, Late