Swarming is a conspicuous behavioural trait observed throughout the animal kingdom. It is thought to improve collective awareness and over protection from predators. Self propelled particle (SPP) models are often compared with animal swarms and involve the hypothesis that information coordinating motion is exchanged between neighbours. We identify that minimal models for swarming must achieve a few key properties such as, polarisation, the global alignment of velocities, cohesion, high density that is robust to perturbation. These constraints still leave considerable freedom in the structure of these models. To tackle this degeneracy, and better distinguish between candidate models for polarisation, we first study swarms of SPPs circulating in channels where we permit information to pass through windows between neighbouring channels. Co-alignment between particles then couples the channels so that they tend to counter-rotate. We study channels arranged to mimic a geometrically frustrated antiferromagnet and show how the effects of this frustration allow us to better distinguish between SPP models. There is now experimental evidence that nearest-neighbour interactions in many swarms are metric free, but the models that control density rely on attractive and repulsive forces with associated length scales. We propose a solution that involves a metric-free motional bias on those individuals that are topologically identified to be on the surface of the swarm. We and a novel power-law scaling of the real-space density with the number of individuals N as well as a familiar order-to-disorder transition. We argue that local interactions alone are insufficient to explain the organisation of large flocks of birds and expand the strictly metric free model to mimic the information set and abilities of a starling in a murmuration. We postulate that large flocks self-organise to the maximum density at which a typical individual is still able to see out of the flock in many directions; such flocks are marginally opaque. The emergence of marginal opacity constrains how individuals interact with each other within swarms. It also provides a mechanism for global interactions: An individual can respond to the projection of the flock that it sees. We then present evidence for marginal opacity in starling murmurations observed around the UK.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:640945 |
| Date | January 2014 |
| Creators | Pearce, Daniel J. G. |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/66438/ |
Page generated in 0.0017 seconds