Past Seminars

Magnets, Criticality and Collective Intelligence

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Speaker: Dr Julianne Halley
Institution: School of Biological Sciences, Monash University
Date: Sat 18 Jun 2005
Time: 3:15 pm
Location: Theatre 1, Old Geology Building, The University of Melbourne

Abstract: There is abundant evidence that natural selection is a dominant force in evolution, but a growing number of researchers suggest that it acts in concert with self-organization. From the smallest to largest scales, self-organization can be found in most (if not all) levels of biology, and parallels the ubiquity of self-organization in the non-biological world. In this seminar, a brief overview of the history of the study of self-organization in general and self-organized criticality in particular will be provided. I then discuss groups of feeding Argentine ants, showing how self-organization to an almost critical state enables a group to collectively balance foraging efficiency with the need to avoid excessive mortality. A new type of self-organized criticality, which I call rapid self-organized criticality, will also be introduced.

Granular complexities: from everyday materials to the extraterrestrial kind

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Speaker: Antoinette Tordesillas and Maya Muthuswamy
Institution: Department of Mathematics & Statistics, University of Melbourne
Date: Sat 11 Jun 2005
Time: 3:15 pm
Location: Theatre 1, Old Geology Building, The University of Melbourne

Abstract: In 1987, Per Bak, Chao Taug, and Kurt Wiesenfeld published a now famous paper in Physical Review Letters, proposing the theory of self-organized criticality, in which they used an all-too-common sight - a sand pile - as a paradigm for complex systems out of equilibrium (e.g. an outbreak of a war, a stock market crash, forest fires). Sand, M&Ms, powders, pharmaceutical pills, grains and other granular materials exhibit a vast range of complex phenomena that defy our usual classification of matter into a solid, liquid or gas. Take, for example, vacuum-packed coffee: under pressure, it is a solid-like material as hard as a brick, but when opened and poured into a container, it flows like water. In common with other complex systems, the simplest unit in a granular assembly, i.e. the interaction of two particles in contact, is well understood;† the complexity emerges from the collective behaviour of the whole assembly. In this talk, we will highlight challenges in our quest to develop rheological models of dry granular assemblies using two methodologies: micromechanical continuum theory and discrete element method. And if that's not complex enough, wait till you see the challenges that await those involved in the exploration and settlement of the all-granular lunar and Martian surface!