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*'''When:''' Fridays at 2:25pm (except as otherwise indicated)
*'''When:''' Fridays at 2:25pm (except as otherwise indicated)
*'''Where:''' 901 Van Vleck Hall
*'''Where:''' 901 Van Vleck Hall
*'''Organizers:''' [https://math.wisc.edu/staff/fabien-maurice/ Maurice Fabien], [https://people.math.wisc.edu/~rycroft/ Chris Rycroft], and [https://www.math.wisc.edu/~spagnolie/ Saverio Spagnolie],
*'''Organizers:''' [https://www.math.wisc.edu/~spagnolie/ Saverio Spagnolie], [https://people.math.wisc.edu/~rycroft/ Chris Rycroft], and [https://sites.google.com/view/laurel-ohm-math Laurel Ohm]  
*'''To join the ACMS mailing list:''' Send mail to [mailto:acms+join@g-groups.wisc.edu acms+subscribe@g-groups.wisc.edu].
*'''To join the ACMS mailing list:''' Send mail to [mailto:acms+join@g-groups.wisc.edu acms+subscribe@g-groups.wisc.edu].


<br>   
<br>   


== '''Spring 2025''' ==
== '''Fall 2025''' ==
{| cellpadding="8"
{| cellpadding="8"
! align="left" |Date
! align="left" |Date
Line 17: Line 17:
! align="left" |Host(s)
! align="left" |Host(s)
|-
|-
|Jan 31
|Sep 19*
|[https://people.math.wisc.edu/~tgchandler/ Thomas Chandler] (UW)
|[https://www.anl.gov/profile/zichao-di Zichao (Wendy) Di] (Argonne National Laboratory)
|[[#Chandler|''Fluid–structure interactions in active complex fluids'']]
|Multimodal Inverse Problems and Multilevel Optimization for X-ray Imaging Science
|Rycroft/Li
|-
|Sep 26
|[https://scholar.google.com/citations?user=Imuw5CMAAAAJ&hl=en&oi=ao Pouria Behnoudfar] (UW)
|TBD
|Spagnolie
|Spagnolie
|-
|-
|Feb 7
|Oct 3
|[https://afraser3.github.io/ Adrian Fraser] (Colorado)
|
|[[#Fraser|''Destabilization of transverse waves by periodic shear flows'']]
|
|
|-
|Oct 10*
|[https://www.alexandriavolkening.com Alexandria Volkening] (Purdue)
|TBD
|Rycroft
|-
|Oct 17*
|[https://www.nickderr.me/ Nick Derr] (UW)
|TBD
|Spagnolie
|Spagnolie
|-
|-
|Feb 14
|Oct 24
|[https://jrluedtke.github.io/ Jim Luedtke] (UW)
|[https://cims.nyu.edu/~oneil/ Mike O'Neil] (Courant)
|[[#Luedtke|Using integer programming for verification of binarized neural networks]]
|TBD
|Spagnolie
|Spagnolie
|-
|-
|Feb 21
|Oct 31
|[https://zhdankin.physics.wisc.edu/ Vladimir Zhdankin] (UW)
|[https://people.math.wisc.edu/~hhong78/ Hyukpyo Hong] (UW)
|[[#Zhdankin|Exploring astrophysical plasma turbulence with particle-in-cell methods]]
|TBD
|Spagnolie
|Spagnolie
|-
|-
|Feb 28
|Nov 7*
|[https://nmboffi.github.io/ Nick Boffi] (CMU)
|[https://thales.mit.edu/bush/ John Bush] (MIT)
|[[#Boffi|Generative modeling with stochastic interpolants]]
|TBD
|Li
|Spagnolie
|-
|-
|Mar 7
|Nov 14
|[https://sites.lsa.umich.edu/shankar-lab/ Suraj Shankar] (Michigan)
|[https://sites.google.com/andrew.cmu.edu/yukunyue/home Yukun Yue] (UW)
|[[#Shankar|TBA]]
|TBD
|Spagnolie
|Spagnolie
|-
|-
|Mar 14
|Nov 21*
|[https://lu.seas.harvard.edu/ Yue Lu] (Harvard) '''[Colloquium]'''
|[https://jesnial.github.io/ Jessie Levillain] (CNES/INSA Toulouse)
|[[#Lu|TBA]]
|TBD
|Li
|Ohm
|-
|Mar 21
|[https://people.llnl.gov/vogman1 Genia Vogman] (LLNL)
|[[#Vogman|TBA]]
|Li
|-
|Mar 28
|''Spring Break''
|
|
|-
|-
|Apr 4
|Nov 28
|TBA
|Thanksgiving
|
|
|
|
|-
|-
|Apr 11
|Dec 5
|[https://meche.mit.edu/people/faculty/pierrel@mit.edu Pierre Lermusiaux] (MIT)
|[https://mesomod.weebly.com/ Jiamian Hu] (UW; Engineering)
|[[#Lermusiaux|TBA]]
|TBD
|Chen
|Chen
|-
|-
|Apr 18
|Dec 12
|[https://www.math.uci.edu/~jxin/ Jack Xin] (UC Irvine) '''[Colloquium]'''
|[https://sites.google.com/a/brandeis.edu/tfai/home Thomas Fai] (Brandeis)
|[[#Xin|TBA]]
|TBD
|
|Rycroft
|-
|Apr 25
|[https://www-users.cse.umn.edu/~bcockbur/ Bernardo Cockburn] (Minnesota)
|[[#Cockburn|''Transforming stabilization into spaces'']]
| Stechmann, Fabien
|-
|May 2
|[https://sylviaherbert.com/ Sylvia Herbert] (UCSD)
|[[#Herbert|TBA]]
|Chen
|}
|}
''[Dates marked with an asterisk are close to weekends with a home game for the [https://uwbadgers.com/sports/football/schedule UW Badgers football team]. Hotel availability around these dates is often limited if booked on short notice.]''


==Abstracts==
==Abstract==


<div id="Chandler">
<div id="Chandler">
====Thomas G. J. Chandler (UW)====
'''Zichao (Wendy) Di (Argonne National Laboratory)'''
Title: Fluid-structure interactions in active complex fluids
 
Fluid anisotropy is central to many biological systems, from rod-like bacteria that self-assemble into dense swarms that function as fluids, to the cell cytoskeleton where the active alignment of stiff biofilaments is crucial to cell division. Nematic liquid crystals provide a powerful model for studying these complex environments. However, large immersed bodies elastically frustrate these fluids, leading to intricate interactions. This frustration can be alleviated through body deformations, at the cost of introducing internal stresses. Additionally, active stresses, arising from particle motility or molecular activity, disrupt nematic order by driving flows. In this presentation, I will demonstrate how complex variables enable analytical solutions to a broad range of problems, offering key insights into the roles of body geometry, anchoring conditions, interaction dynamics, activity-induced flows, and body deformations in many biological settings.
 
<div id="Fraser">
====Adrian Fraser (Colorado)====
Title: Destabilization of transverse waves by periodic shear flows
 
Periodic shear flows have the peculiar property that they are unstable to large-scale, transverse perturbations, and that this instability proceeds via a negative-eddy-viscosity mechanism (Dubrulle & Frisch, 1991). In this talk, I will show an example where this property causes transverse waves to become linearly unstable: a sinusoidal shear flow in the presence of a uniform, streamwise magnetic field in the framework of incompressible MHD. This flow is unstable to a KH-like instability for sufficiently weak magnetic fields, and uniform magnetic fields permit transverse waves known as Alfvén waves. Under the right conditions, these Alfvén waves become unstable, presenting a separate branch of instability that persists for arbitrarily strong magnetic fields which otherwise suppress the KH-like instability. After characterizing these waves with the help of a simple asymptotic expansion, I will show that they drive soliton-like waves in nonlinear simulations. With time permitting, I will discuss other fluid systems where similar dynamics are or may be found, including stratified flows and plasma drift waves.
 
<div id="Luedtke">
====Jim Luedtke (UW)====
Title: Using integer programming for verification of binarized neural networks
 
Binarized neural networks (BNNs) are neural networks in which the weights are binary and the activation functions are the sign function. Verification of BNNs against input perturbation is one way to measure robustness of BNNs. BNN verification can be formulated as an integer linear optimization problem and hence can in theory be solved by state-of-the art methods for integer programming such as the branch-and-cut algorithm implemented in solvers like Gurobi. Unfortunately, the natural formulation is often difficult to solve in practice, even by the best such solvers, due to large integrality gap induced by its so-called "big-M" constraints. We present simple but effective techniques for improving the ability of the integer programming approach to solve the verification problem for BNNs. Along the way, we hope to illustrate more generally some of the strategies integer programmers use to attack difficult problems like this. We find that our techniques enable verifying BNNs against a higher range of input perturbation than using the natural formulation directly.
 
This is joint work with Woojin Kim, Mathematics PhD student at UW-Madison.
 
<div id="Zhdankin">
====Vladimir Zhdankin (UW)====
Title: Exploring astrophysical plasma turbulence with particle-in-cell methods
 
Plasmas throughout the universe (as well as in the laboratory) tend to exist in turbulent, nonequilibrium states due to their "collisionless" nature. Described by the Vlasov-Maxwell equations in a six-dimensional phase space (of position and momentum), the basic physics of such plasmas is difficult to model from first principles. There remain open questions about entropy production, nonthermal particle acceleration, energy partition amongst different particle species, and more. Particle-in-cell simulations are a numerical tool that allow us to explore in depth the rich dynamics and statistical mechanics of collisionless plasmas, validating analytical speculation. I will describe some of the results from my group's work on this topic.
 
 
<div id="Boffi">
====Nick Boffi (CMU)====
Title: Generative modeling with stochastic interpolants


We introduce a class of generative models that unifies flows and diffusions. These models are built using a continuous-time stochastic process called a stochastic interpolant, which exactly connects two arbitrary probability densities in finite time. We show that the time-dependent density of the stochastic interpolant satisfies both a first-order transport equation and an infinite family of forward and backward Fokker-Planck equations with tunable diffusion coefficients. This viewpoint yields deterministic and stochastic generative models built dynamically from an ordinary or stochastic differential equation with an adjustable noise level. To formulate a practical algorithm, we discuss how the resulting drift functions can be characterized variationally and learned efficiently over flexible parametric classes such as neural networks. Empirically, we highlight the advantages of our formalism -- and the tradeoffs between deterministic and stochastic sampling -- through numerical examples in image generation, inverse imaging, probabilistic forecasting, and accelerated sampling.
Title: Multimodal Inverse Problems and Multilevel Optimization for X-ray Imaging Science


<div id="Cockburn">
X-ray imaging experiments generate vast datasets that are often incomplete or ill-posed when considered in isolation. One way forward is multimodal data analysis, where complementary measurement modalities are fused to reduce ambiguity and improve reconstructions. A key question, both mathematically and practically, is how to identify which modalities to combine and how best to integrate them within an inverse problem framework.
====Bernardo Cockburn (Minnesota)====
Title: Transforming stabilization into spaces


In the framework of finite element methods for ordinary differential equations, we consider the continuous Galerkin method (introduced in 72) and the discontinuous Galerkin method (introduced in 73/74). We uncover the fact that both methods discretize the time derivative in exactly the same form, and discuss a few of its consequences. We end by briefly describing our ongoing work on the extension of this result to some Galerkin methods for partial differential equations.
A second line of work focuses on the computational challenge: even for single-modality inverse problems, the resulting optimization problems are large-scale, nonlinear, and nonconvex. Here, I will discuss multilevel optimization and stochastic sampling strategies that accelerate convergence by exploiting hierarchical structure in both parameter and data spaces.


Although developed separately, these two directions point toward a common goal: building scalable, optimization-based frameworks that make the best use of diverse data to enable new discoveries in X-ray imaging science.<div id="Fraser"><div id="Luedtke"><div id="Zhdankin"><div id="Boffi"><div id="Shankar"><div id="Loevbak">
<div id="Lu"><div id="Vogman"><div id="Cockburn">
== Archived semesters ==
== Archived semesters ==


*[[Applied/ACMS/Spring2025|Spring 2025]]
*[[Applied/ACMS/Fall2024|Fall 2024]]
*[[Applied/ACMS/Fall2024|Fall 2024]]
*[[Applied/ACMS/Spring2024|Spring 2024]]
*[[Applied/ACMS/Spring2024|Spring 2024]]

Latest revision as of 02:58, 5 September 2025


Applied and Computational Mathematics Seminar


Fall 2025

Date Speaker Title Host(s)
Sep 19* Zichao (Wendy) Di (Argonne National Laboratory) Multimodal Inverse Problems and Multilevel Optimization for X-ray Imaging Science Rycroft/Li
Sep 26 Pouria Behnoudfar (UW) TBD Spagnolie
Oct 3
Oct 10* Alexandria Volkening (Purdue) TBD Rycroft
Oct 17* Nick Derr (UW) TBD Spagnolie
Oct 24 Mike O'Neil (Courant) TBD Spagnolie
Oct 31 Hyukpyo Hong (UW) TBD Spagnolie
Nov 7* John Bush (MIT) TBD Spagnolie
Nov 14 Yukun Yue (UW) TBD Spagnolie
Nov 21* Jessie Levillain (CNES/INSA Toulouse) TBD Ohm
Nov 28 Thanksgiving
Dec 5 Jiamian Hu (UW; Engineering) TBD Chen
Dec 12 Thomas Fai (Brandeis) TBD Rycroft

[Dates marked with an asterisk are close to weekends with a home game for the UW Badgers football team. Hotel availability around these dates is often limited if booked on short notice.]

Abstract

Zichao (Wendy) Di (Argonne National Laboratory)

Title: Multimodal Inverse Problems and Multilevel Optimization for X-ray Imaging Science

X-ray imaging experiments generate vast datasets that are often incomplete or ill-posed when considered in isolation. One way forward is multimodal data analysis, where complementary measurement modalities are fused to reduce ambiguity and improve reconstructions. A key question, both mathematically and practically, is how to identify which modalities to combine and how best to integrate them within an inverse problem framework.

A second line of work focuses on the computational challenge: even for single-modality inverse problems, the resulting optimization problems are large-scale, nonlinear, and nonconvex. Here, I will discuss multilevel optimization and stochastic sampling strategies that accelerate convergence by exploiting hierarchical structure in both parameter and data spaces.

Although developed separately, these two directions point toward a common goal: building scalable, optimization-based frameworks that make the best use of diverse data to enable new discoveries in X-ray imaging science.
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