Speaker:

Joseph Paulsen, Associate Professor, Department of Physics, Syracuse University

Title:

Computing with a pile of sand: Understanding amorphous solids that “count” modulo n

Abstract:

In a perfect crystalline solid, the location of its ~1023 atoms can be determined from the whereabouts of just a handful of them. This highly symmetric structure underlies our modern theories of the solid state. By contrast, amorphous solids appear to be a jumbled mess — their lack of symmetry complicates predictions of their mechanical properties and can lead to unusual behaviors. Here we consider an intriguing response seen in simulations of amorphous solids under repeated shearing: the solid may repeatedly visit two distinct configurations at the end of each driving cycle; one at the end of each “even” cycle and one at the end of each “odd” cycle. We build a phenomenological model based on localized rearrangements in the material, which we show can form a faithful picture of this “multiperiodic” response. Beyond elucidating the physics of randomly-packed grains, our results provide a bonus: We obtain a set of design principles for mechanical metamaterials that can “count” the number of times they are disturbed.

Speaker Bio:

Joseph Paulsen earned a bachelor's degrees in Mathematics and Physics from St. Olaf College in Northfield, MN, and he completed his PhD in Physics at the University of Chicago with Sidney Nagel. He won a National Science Foundation CAREER Award for his work that studies connections between geometry and mechanics in thin materials. Outside of science, one of his passions is trying to squirrel away as much time as possible to ski with his 7-year-old daughter (his son and his wife are not skiers... yet).

Location:

In person: Chambers Hall, 600 Foster Street, Lower Level
Remote option: https://northwestern.zoom.us/j/94291553667
Passcode: NICO2024

About the Speaker Series:

Wednesdays@NICO is a vibrant weekly seminar series focusing broadly on the topics of complex systems, data science and network science. It brings together attendees ranging from graduate students to senior faculty who span all of the schools across Northwestern, from applied math to sociology to biology and every discipline in-between. Please visit: https://bit.ly/WedatNICO for information on future speakers.

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