Tales from the ArXiv: "A Nudge Framework"

A new paper that just appeared on arXiv this evening is called "Steering the aggregative behavior of noncooperative agents: a nudge framework". I come from a Jewish family, so I am very familiar with this strategy.

Tales from the ArXiv: "Sheep Soliton"

You had me at "sheep soliton".

Yes, under a suitable approximation, it appears that you can gave a soliton description of certain types of collective behavior in sheep.

Below are the title and abstract. (I was hoping for an intriguing picture from the experimental data, but alas the visuals in this article are run-of-the-mill.) In other contexts, when sheep (a type of 'active matter') behave like a fluid, there are obvious jokes to tell about "shearing instabilities".

Title: Sheep Soliton

Abstract: Monitoring small groups of sheep in spontaneous evolution in the field, we decipher behavioral rules that sheep follow at the individual scale in order to sustain collective motion. Individuals alternate grazing mode at null speed and moving mode at walking speed, so cohesive motion stems from synchronizing when they decide to switch between the two modes. We propose a model for the individual decision making process and parametrize it from data. Next, we translate this individual-based model into its density-flow equations counterpart, considering 1D-motion along the group trajectory. Numerical solving these equations display a solitary wave propagating at constant speed. Coupling individual and collective levels, groups motion can then be seen as a wave propagating at some fraction of the individual walking speed even though each individual is at any moment either stopped or walking. Considering the minimal model embedded in these equations, we show analytically that it has the Korteweg-De Vries (KdV) Soliton as a steady regime solution. This soliton emerges from the non linear coupling of start/stop individual decisions which compensate exactly for diffusion and promotes a steady ratio of walking / stopped individuals, which in turn determines the wave speed. The convergence to only one solitary wave from any initial condition, and which can recover from perturbation, gives a high robustness to this biological system.

Update (12/18/17): I forgot to make a snarky remark along the following lines: One first needs to do a continuum approximation to get a relevant nonlinear wave equation.

For the actual sheep, one would think that there is some energy shedding as the wave propagates. :)

Cow Magnetization

Here is a cool video of what I will call cow magnetization. Maybe we should bring out the spin models after all? :)

(Tip of the cap to Erik Bollt.)

A Video of My Seminar on "A Simple Generative Model of Collective Online Behavior"

On Friday 27 May, I gave a talk at the Oxford Internet Institute on "A Simple Generative Model of Collective Online Behavior". The video was posted online today. My talk, which took place at the Oxford Internet Institute, was part of an event for the Computational Social Science Initiative London.

I spoke about this paper, which I like to call our "Small Data" paper.

You may also be interested in videos of some of my other presentations.

Teaching Complex Systems: Building Evacuation Edition

Today I gave my first lecture for my course on complex systems. After about the first hour (of the 2 hours), the fire alarm rang, and we had to evacuate the building.

So I did what any self-respecting person in complex systems would do: briefly as we walked outside and much more once outside and as we watched others leaving the building through the door, while we were outside being drizzled on, I gave a brief description of the work of people like Dirk Helbing on that exact problem.

(And then after we got back inside, I showed them the video of sheep moving through a bottleneck.)

New Article in Physical Review E: "Flow and Clogging of a Sheep Herd Passing Through a Bottleneck"

Yes, really.

The first person who told me about this granular sheep project, which has finally appeared in published form, is Karen Daniels, who points out that there are all sorts of wonderful (baaaaaaaad?) puns that one can make about shearing forces, sheared sheep, and so on.

The Physics of Ants

Apparently, a collection of fire ants can act either as a fluid or as a solid. Check out the video in the New York Times article to which I just linked. It's way cool.

(Tip of the cap to whoever posts for APS Physics on Facebook.)

Update (12/21/13): As Jimmy Lin points out, you can also make some really cool sculptures by pouring molten aluminum down anthills. Seeing this makes me want data from Anthill Art to complement our study of a rabbit warren in this paper. Notice that the depicted fire ant colonies have a much more complicated network structure than the carpenter ant colonies.