Events
Past Event
WED@NICO SEMINAR: Richard Lueptow, McCormick School of Engineering "Mixing by Cutting and Shuffling: Remarkably Persistent Structures"
Northwestern Institute on Complex Systems (NICO)
12:00 PM
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Lower Level Chambers Hall
Details
Mixing by Cutting and Shuffling: Remarkably Persistent Structures
Speaker:
Richard Lueptow - Professor of Mechanical Engineering and Senior Associate Dean for Research, McCormick School of Engineering
Talk Abstract:
Engineers and scientists think of mixing in terms of diffusion, chaotic advection (stirring), or turbulence. However, mixing can also be accomplished by cutting and shuffling, like that used to mix a deck of cards or the colors of a Rubik's Cube. While other means of mixing have long been studied, mixing by cutting and shuffling is not well explored or understood. Unlike the stretching and folding characteristic of chaotic advection, cutting and shuffling maps do not stretch the material and exhibit no chaotic behavior in the usual sense—yet they can mix quite efficiently under certain conditions. In a 3D geometry, a physical model of cutting and shuffling is a spherical tumbler that is half-filled with a granular material undergoing a bi-axial rotation protocol—a rotation about one axis followed by a rotation about another axis for each iteration. X-ray visualization of the flowing granular material reveals non-mixing regions. Simulations of the granular system confirm the non-mixing regions. To further explore cutting and shuffling of a hemisphere, the problem can be mathematically formulated as a Piecewise Isometries (PWIs) transformation that cuts an object into a finite number of pieces and rearranges them into the object's original shape. Computationally recording the cut locations from the PWI on the hemispherical shell yields beautifully intricate complex patterns. However, the PWI transformation requires the assumption of a non-physical granular flow. Hence, it is remarkable that non-mixing regions identified using PWIs correspond to surprisingly persistent non-mixing regions and global barriers to mixing that occur in both experiments and continuum model simulations. This extraordinary merging of the mathematics of PWIs, traditional dynamical systems approaches, and physical applications is leading toward a novel paradigm for understanding and predicting mixing in physical systems based on cutting and shuffling. Funded by NSF Grant #CMMI-1435065.
Live Stream:
To join the Meeting: bluejeans.com/8474912527
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Time
Wednesday, January 18, 2017 at 12:00 PM - 1:00 PM
Location
Lower Level Chambers Hall Map
Contact
Calendar
Northwestern Institute on Complex Systems (NICO)
WED@NICO SEMINAR: Mayank Agrawal, Proof of Human "The Invisible Turing Test for the Internet"
Northwestern Institute on Complex Systems (NICO)
12:00 PM
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Lower Level, Chambers Hall
Details
Speaker:
Mayank Agrawal, Co-founder and CEO, Proof of Human
Title:
Proof of Human: the Invisible Turing Test for the Internet
Abstract:
This presentation introduces the Process Turing Test, a new framework for distinguishing humans from AI that goes beyond linguistic output to analyze behavioral dynamics. As LLMs routinely pass text-based Turing Tests, we need methods that probe the underlying architecture of intelligence through perception, control, and decision-making patterns. Using process tracing data from canonical cognitive tasks, we demonstrate how behavioral embeddings capture computational signatures unique to human cognition. This provides robust proof-of-personhood that resists adversarial attacks while revealing fundamental principles about how humans and machines process information differently.
Speaker Bio:
Mayank Agrawal is the co-founder and CEO of Proof of Human, a research and deployment company building the proof-of-human layer in digital identity. The company develops high-impact research and translates that work into systems for bot detection, fraud prevention, and continuous authentication. Mayank’s work focuses on new approaches to distinguishing humans from AI through behavioral and cognitive signals. He earned his PhD in Psychology and Neuroscience from Princeton University, where he studied computational models of human decision-making with Jonathan Cohen, Tom Griffiths, and Nathaniel Daw. His research spans cognitive science, machine learning, and artificial intelligence, with work published in Science, PNAS, and Psychological Review. He previously studied Computer Science and Philosophy at Swarthmore College.
Location:
In person: Chambers Hall, 600 Foster Street, Lower Level
Remote option: https://northwestern.zoom.us/j/96392420891
About the Speaker Series:
Wednesdays@NICO is a vibrant weekly seminar series focusing broadly on the topics of complex systems, networks, and artificial intelligence. 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.
Time
Wednesday, November 11, 2026 at 12:00 PM - 1:00 PM
Location
Lower Level, Chambers Hall Map
Contact
Calendar
Northwestern Institute on Complex Systems (NICO)