Into the Daphnia vortex

Frank Moss
Chaos 14, S10 (2004)
http://link.aip.org/link/?CHAOEH/14/S10/1

Many animals perform circular-shaped motions that in swarms often lead to vortex-type structures. One only has to think of a school of fish or a flock of birds descending on a roost tree, among other examples. In some cases these motions are induced by the presence of predators. In others, the animals are responding to light, for example as moths do. But what specifically can cause animals that ordinarily move in random directions to begin circularlike motion, and when large numbers are present, as in swarms, what can cause them to begin to circle all in the same direction, that is, to form a vortex? The theory of active Brownian particles, by Werner Ebeling, Udo Erdmann, and Lutz Schimansky-Geier of Humboldt University in Berlin, successfully describes these motions. Particles, or agents, can store energy in a reservoir that they find by foraging for food. Yet the foraging motions expend energy. A further constant drain is required by the agent's metabolism. The dissipation is dependent on the agent's velocity as shown here. Two motions are the result of the active Brownian particle theory: A noisy fixed point as shown on the left and two symmetric limit cycles in the x --y plane as seen on the right. The limit cycles are the circulating motions. Clockwise and counterclockwise are equally probable. But if the conditions are right, we sometimes see that all Daphnia spontaneously decide to move in the same direction, creating a vortex motion. Swarms of large density and, of course, the light shaft favor this motion.

In the theory, vortex motion cannot occur without breaking the symmetry of the pair of limit cycles. The mechanism is unknown, but two possibilities are suggested: The first is called "avoidance." It simply means that the animals do not like to bump into one another and they try to avoid that happening. Avoidance is modeled in the theory with a short-range repulsive potential between animal pairs. The second is called "velocity alignment." It may mean that individuals like to align their velocity directions with those of their near neighbors. In this example vortex, with incipient spiral arms, both the animals and the water are moving—a process we call "biohydrodynamics." This movie shows a clockwise vortex with developing spiral arms. This movie shows a counterclockwise vortex that breaks up into two when the light shaft is moved. One of the vortices spontaneously changes direction. Simulations of the active Brownian particle theory predict these motions with either velocity alignment or avoidance as the symmetry breakers.

Category:

Science & Technology

Tags:

• chaos
• vortex
• animal-behavior

[happyorangeanimation]

Maybe this video gives a bit of an insight into what's going on inside the vase in the video I've taken?

[ZO6]

need better quality video

i could not see the vortexes

[PhilPhilUSA]

Yes, thank you! i found you by making a 'coil' picture recently (i'm a visual 'artist' although that's not for me to say) and i connected this idea to humor as it might involve vortex structure as a consequence of psychological or aspects of 'mind' that could be 'innate' to living things. i'm a heart transplant patient who years ago did several concept pieces that now seem like a predilection i find hard to dismiss. not looking for endorsement just interested...thanks again.

[SofiaBabii8]

thanks much! it has alot to do with my science Project!