Seminars and Colloquia by Series

Novel metrics of entanglement of open curves in 3-space and their applications to proteins

Series
School of Mathematics Colloquium
Time
Thursday, September 25, 2025 - 11:00 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Eleni PanagiotouArizona State University

Filamentous materials may exhibit structure-dependent material properties and function that depend on their entanglement. Even though intuitively entanglement is often understood in terms of knotting or linking, many of the filamentous systems in the natural world are not mathematical knots or links. In this talk, we will introduce a novel and general framework in knot theory that can characterize the complexity of open curves in 3-space. This leads to new metrics of entanglement of open curves in 3-space that generalize classical topological invariants, like for example, the Jones polynomial and Vassiliev invariants. For open curves, these are continuous functions of the curve coordinates and converge to topological invariants of classical knots and links when the endpoints of the curves tend to coincide. These methods provide an innovative approach to advance important questions in knot theory. As an example, we will see how the theory of linkoids enables the first, to our knowledge, parallel algorithm for computing the Jones polynomial.

Importantly, this approach opens exciting applications to systems that can be modeled as open curves in 3-space, such as polymers and proteins, for which new quantitative relationships between their structure and material properties become evident. As an example, we apply our methods to proteins to understand the interplay between their structures and functions. By analyzing almost all protein structures in the Protein Data Bank, we derive for the first time a quantitative representation of the topology/geometry of the Topological Landscape of proteins. We show that 3 topological and geometrical parameters alone can predict the biological classifications of proteins with high accuracy. Moreover, preliminary results show that our proposed topological metrics based on static protein structures alone correlate with protein dynamics and protein function. The methods and results represent a new framework for advancing knot theory, as well as its applications to filamentous materials, which can be validated by experimental data and integrated into machine-learning algorithms.

Volume Polynomials

Series
School of Mathematics Colloquium
Time
Friday, September 19, 2025 - 11:00 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
June HuhPrinceton University

Volume polynomials constitute a distinguished class of log-concave polynomials with remarkable analytic and combinatorial properties arising from convex bodies and projective varieties. I will introduce new entropy inequalities satisfied by volume polynomials, discuss applications to the combinatorics of algebraic matroids, introduce the new class of analytic matroids, and pose several open questions (based on joint with Lukas Grund, Mateusz Michalek, Henrik Süss, and Botong Wang).

How Mathematics Can Drive Innovation in Artificial Intelligence

Series
School of Mathematics Colloquium
Time
Thursday, August 28, 2025 - 11:00 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Talitha WashingtonHoward University

Mathematics is at the core of artificial intelligence, from the linear algebra that powers deep learning to the probability and optimization driving new algorithms. We will explore how mathematical ideas can open new directions for AI innovation and how recent U.S. AI policy trends are shaping research priorities. Together, these perspectives reveal opportunities for mathematicians to influence the design and future of AI technologies.

Random matrices and logarithmically correlated fields

Series
School of Mathematics Colloquium
Time
Thursday, April 17, 2025 - 11:00 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Paul BourgadeNYU

The Liouville quantum gravity measure is a properly normalized exponential of 2d log-correlated fields, such as the Gaussian free field. It is the volume form for the scaling limit of random planar maps and numerous statistical physics models. I will explain how this random measure naturally appears in random matrix theory either in space time from random matrix dynamics, or in space from the characteristic polynomial of random normal matrices. A 3d log-correlated field also naturally emerges in random matrix theory, from dynamics on non-Hermitian matrices.

Local-to-global in thin orbits

Series
School of Mathematics Colloquium
Time
Thursday, March 27, 2025 - 11:00 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Kate StangeUniversity of Colorado, Boulder

Primitive integral Apollonian circle packings are fractal arrangements of tangent circles with integer curvatures.  The curvatures form an orbit of a 'thin group,' a subgroup of an algebraic group having infinite index in its Zariski closure.  The curvatures that appear must fall into a restricted class of residues modulo 24. The twenty-year-old local-global conjecture states that every sufficiently large integer in one of these residue classes will appear as a curvature in the packing. We prove that this conjecture is false for many packings, by proving that certain quadratic and quartic families are missed. The new obstructions are a property of the thin Apollonian group (and not its Zariski closure), and are a result of quadratic and quartic reciprocity, reminiscent of a Brauer-Manin obstruction. Based on computational evidence, we formulate a new conjecture.  This is joint work with Summer Haag, Clyde Kertzer, and James Rickards.  Time permitting, I will discuss some new results, joint with Rickards, that extend these phenomena to certain settings in the study of continued fractions.

Theory of valuations and geometric inequalities

Series
School of Mathematics Colloquium
Time
Thursday, March 13, 2025 - 11:00 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Semyon AleskerTel Aviv University and Kent State University

Valuations are finitely additive measures on convex compact sets. In the last two decades a number of structures (e.g. product and convolution)  with non-trivial properties were discovered on the space of valuations. One such recently discovered property is an analogue of the classical Hodge-Riemann bilinear relations known in algebraic/Kaehler geometry. In special cases, they lead to new inequalities for convex bodies, to be discussed in the talk. No familiarity with valuations theory and algebraic/Kaehler geometry is assumed.

Towards an algorithmic model of the neuron for Neuroscience and AI

Series
School of Mathematics Colloquium
Time
Thursday, March 6, 2025 - 11:00 for 1 hour (actually 50 minutes)
Location
Skiles 005 and Zoom: https://gatech.zoom.us/j/98474702488?pwd=2CiHNben05BqfpbikKkCuzzdr0MjdZ.1
Speaker
Dmitri Chklovskii NYU and the Flatiron Institute

Modern Artificial Intelligence (AI) systems, such as ChatGPT, rely on artificial neural networks (ANNs), which are historically inspired by the human brain. Despite this inspiration, the similarity between ANNs and biological neural networks is largely superficial. For instance, the foundational McCulloch-Pitts-Rosenblatt unit of ANNs drastically oversimplifies the complexity of real neurons.Recognizing the intricate temporal dynamics in biological neurons and the ubiquity of feedback loops in natural networks, we suggest reimagining neurons as feedback controllers. A practical implementation of such controllers within biological systems is made feasible by the recently developed Direct Data-Driven Control (DD-DC). We find that DD-DC neuron models can explain various neurophysiological observations, affirming our theory.

Dual Lyapunov exponents and sharp arithmetic spectral transitions for quasiperiodic operators

Series
School of Mathematics Colloquium
Time
Thursday, March 6, 2025 - 09:30 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Svetlana JitomirskayaUC Berkeley

We will describe a recently discovered object, dual Lyapunov exponents, that has emerged as a powerful tool in the spectral analysis of  quasiperiodic operators with analytic potentials, leading to solutions of several long outstanding problems. Based on papers joint with L. Ge, J. You, and Q. Zhou

Local-to-global in thin orbits

Series
School of Mathematics Colloquium
Time
Thursday, February 27, 2025 - 11:00 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Kate StangeUniversity of Colorado, Boulder

Primitive integral Apollonian circle packings are fractal arrangements of tangent circles with integer curvatures.  The curvatures form an orbit of a 'thin group,' a subgroup of an algebraic group having infinite index in its Zariski closure.  The curvatures that appear must fall into a restricted class of residues modulo 24. The twenty-year-old local-global conjecture states that every sufficiently large integer in one of these residue classes will appear as a curvature in the packing. We prove that this conjecture is false for many packings, by proving that certain quadratic and quartic families are missed. The new obstructions are a property of the thin Apollonian group (and not its Zariski closure), and are a result of quadratic and quartic reciprocity, reminiscent of a Brauer-Manin obstruction. Based on computational evidence, we formulate a new conjecture.  This is joint work with Summer Haag, Clyde Kertzer, and James Rickards.  Time permitting, I will discuss some new results, joint with Rickards, that extend these phenomena to certain settings in the study of continued fractions.

No Equations, No Variables, No Space and No Time: Data and the Modeling of Complex Systems

Series
School of Mathematics Colloquium
Time
Thursday, January 30, 2025 - 11:00 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Yannis KevrekidisJohns Hopkins University

I will give an overview of a research path in data driven modeling of complex systems over the last 30 or so years – from the early days of shallow neural networks and autoencoders for nonlinear dynamical system identification, to the more recent derivation of data driven “emergent” spaces in which to better learn generative PDE laws. In all illustrations presented, I will try to point out connections between the “traditional” numerical analysis we know and love, and the more modern data-driven tools and techniques we now have – and some mathematical questions they hopefully make possible for us to answer.

Bio: Yannis Kevrekidis studied Chemical Engineering at the National Technical University in Athens. He then followed the steps of many alumni of that department to the University of Minnesota, where he studied with Rutherford Aris and Lanny Schmidt (as well as Don Aronson and Dick McGehee in Math). He was a Director's Fellow at the Center for Nonlinear Studies in Los Alamos in 1985-86 (when the Soviet Union still existed and research funds were plentiful). He then had the good fortune of joining the faculty at Princeton, where he taught Chemical Engineering and also Applied and Computational Mathematics for 31 years; seven years ago he became Emeritus and started fresh at Johns Hopkins (where he somehow is also Professor of Urology). His work always had to do with nonlinear dynamics (from instabilities and bifurcation algorithms to spatiotemporal patterns to data science in the 90s, nonlinear identification, multiscale modeling, and back to data science/ML); and he had the additional good fortune to work with several truly talented experimentalists, like G. Ertl's group in Berlin. Currently -on leave from Hopkins- he works with the Defense Sciences Office at DARPA. When young and promising he was a Packard Fellow, a Presidential Young Investigator and the Ulam Scholar at Los Alamos National Laboratory. He holds the Colburn, CAST Wilhelm and Walker awards of the AIChE, the Crawford and the Reid prizes of SIAM, he is a member of the NAE, the American Academy of Arts and Sciences, and the Academy of Athens.

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