When a crowd needs to pass through a small doorway – an emergency exit, for example – the opening can quickly become obstructed. Recently, researchers have been using sheep to understand how they might mitigate this potentially catastrophic bottleneck effect.
The above video was shot by Iker Zuriguel and his colleagues at the University of Navarra, and depicts two experimental sheep-crowding scenarios. The researchers describe the scenarios, and the counterintuitive results:
Left: Standard door. Right: Door with an obstacle in front of it. In both cases, two cameras (one inside and the other outside the yard) are registering the flow of sheep. The charts appearing in the vertical direction are spatio-temporal diagrams constructed by taking the lines of pixels displayed by green and stacking them vertically as time evolves. The placement of the obstacle slightly increases the flow rate and, more importantly, reduces the duration of the clogs.
This particular experiment was devised not long after research on inanimate matter led to the discovery that an obstacle placed before the exit of a silo could relieve exit pressure while lowering the probability of jamming. "Although there are some works that suggest that this method is also valid to reduce the likelihood of clogging for live beings," Zuriguel and his colleagues noted back in 2012, it had not been proven one way or the other. Until this business with the sheep, that is.
This is just one of several experiments Zuriguel and his colleagues are conducting to better understand the "clogging transition of many-particle systems flowing through bottlenecks," whether the particles in question are granular materials, sheep, or people. You can read two of their recent publications on the subject here and here.