[MEGA Star] Alison Patteson: Life in suspense, Patterns from chaos
September 15, 2016, Dr. Alison Patteson became the most recent Doctor of Philosophy graduated from Prof. Paulo Arratia's Lab, after defending a culminating thesis that draws on years of research and joyfully popping two bottles of champagne. Her research focuses on the fluid dynamics and nonequilibrium physics of living and active soft matter.
In the first episode of MEGA star, where we feature the life stories and cutting-edge research projects of rock-star MEAM graduate students, we will go on a tour-de-force with Alison Patteson. She will take us to the world of living and active matter, where spontaneous patterns and collective motions can arise from simple or random individual behavior.
One intriguing example of collective motion is the "tuna tornado" formed by Jack-fish schools. The whirlwind pattern emerges not by a central command, but from the spontaneous action of each individual.[Source: Youtube]
Another example is the nebulous dance of the murmuring starlings. These collective behaviors occur at large length scales, often tens of meters. [source: Youtube]
The microscopic world, however, is where collective motion and spontaneous patterns truly shines. Order often emerges from chaos. Shown above is the chaotic flows generated by a dense suspension of active microtubules, an example of active fluid. Yet over long range, we see the formation of a percolating network. These microtubules, fueled by ATP, are cell's ingenious molecular motors that drive cell motility, division and replication. [Source: Sanchez et al, Nature 491,431–434,2012]
This is where Alison's research comes in. She tries to shed light on the physics of active matter and collective behavior by studying an interesting system: a dense soup of bacteria. By investigating how Escherichia coli, the bug that swims and roams in your gut, is able to move large boulders like the ones in the movie, she found that surprisingly, E. coli can move large particles (3-50 micron) much better than smaller ones. This size dependency may play an important role in the transport of nutrients and the spread of toxins in microbial environments.[Source: Patteson, Alison E., et al. "Particle diffusion in active fluids is non-monotonic in size." Soft matter 12.8 (2016): 2365-2372.]
Alison also found that fluid dynamics is critical to the collective behavior in active fluids. This time she creates her own man-made active system to study such effect. She suspends a layer of paramagnetic particles in water, and then turns on a cyclic external magnetic field, which causes the particles to magnetize, move, and eventually cluster. Watch their action in the movie. Alison found that fluid viscous stresses hinder collective aggregation. Higher fluid resistance (or smaller Mason number, Mn) produces smaller clusters, and significantly decreases the rate of cluster formation. [Source: Koser, Alison E. et al, "Structure and dynamics of self-assembling colloidal monolayers in oscillating magnetic fields." Physical Review E 88.6 (2013): 062304]
By studying active matter and collective behavior, Dr. Alison Patteson and Prof. Paulo Arratia provide fundamental insights on how to engineer smart materials that are controllable and adaptive. These insights can also be applied to design bottom-up systems, like swarms of micro-robots, that are capable of accomplishing tasks autonomously without central coordination.
Dr. Patteson is currently a post-doc in Prof. Paul Jamney's Lab at Penn.
Episode editor: Boyang Qin, 2016 Oct.
To be featured on MEGA star, contact mega@seas.upenn.edu
© Copyright 2016-17. Mechanical Engineering Graduate Association, University of Pennsylvania.