Prof. Matthew Turner: From animal to thermodynamic swarms

Pred predavanjem vse udeležence vabimo na čaj!  

Povzetek:

    From animal to thermodynamic swarms 

    Prof. Matthew S.Turner, Physics Department, University of Warwick, Coventry, UK

The controlling interactions in bird flocks, insect swarms and fish shoals are still not well understood. Some authors have proposed interactions that are local in space, either in a metric-based or topological sense. We discuss the evidence for non-local interactions and suggest a natural choice for these that is consistent with the cognitive limitations of a bird's vision. We study the global character of the flocks that emerge from this model and their various phenotypes. Most significantly, an emergent state arises in which the probability that a typical bird can see out (sky) in any direction divided by the probability that its view is blocked by other bird(s) is O(1). We refer to this state as being marginally opaque and present experimental data supporting this prediction. Finally, I will draw an analogy with thermodynamic ’swarms' of thermophoretic colloids that are heated by a focussed external light source. We analyse how this system undergoes a first order transition from a disperse to compact state as the light intensity is increased. Intriguingly, we find that the same state of marginal opacity emerges: no compact state with a density below marginal opacity is stable. This reveals a previously unidentified connection between animal and thermodynamic swarms.