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== '''Fall 2024''' ==
== '''Spring 2025''' ==
{| class="wikitable"
{| cellpadding="8"
|+
! align="left" |Date
!Date
! align="left" |Speaker
!Speaker
! align="left" |Title
!Title
! align="left" |Host(s)
!Host(s)
|-
|-
|Sep 13*
|Jan 31
|[https://people.math.wisc.edu/~nchen29/ Nan Chen] (UW)
|[https://people.math.wisc.edu/~tgchandler/ Thomas Chandler] (UW)
|Intro. to Uncertainty Quantification (UQ) (tutorial)
|[[#Chandler|''Fluid–structure interactions in active complex fluids'']]
|
|-
|Feb 7
|[https://www.colorado.edu/aps/adrian-fraser Adrian Fraser] (Colorado)
|[[#Fraser|''Destabilization of transverse waves by periodic shear flows'']]
|Spagnolie
|Spagnolie
|-
|-
|Sep 20
|Feb 14
|[https://knewhall.web.unc.edu Katie Newhall] (UNC Chapel Hill)
|TBA
|Energy landscapes, metastability, and transition paths
|
|Rycroft
|
|-
|-
|Sep 27
|Feb 21
|[https://ptg.ukzn.ac.za Indresan Govender] (Mintek / Univ. of KwaZulu-Natal, South Africa)
|TBA
|Granular flow modeling and visualization using nuclear imaging
|
|Rycroft
|
|-
|Oct 4*
|[https://sse.tulane.edu/math/people/hongfei-chen Hongfei Chen] (Tulane)
|Investigating Hydrodynamics of Choanoflagellate Colonies: A Reduced Model Approach
|Jean-Luc
|-
|-
|Oct 11 '''Colloquium in B239 at 4:00pm'''
|Feb 28
|[https://people.math.ethz.ch/~imikaela/ Mikaela Iacobelli] (ETH/IAS)
|[https://nmboffi.github.io/ Nick Boffi] (CMU)
|[[# TBA| TBA ]]
|[[#Boffi|TBA]]
|Li
|Li
|-
|-
|Oct 18 '''Colloquium in B239 at 4:00pm'''
|Mar 7
|[https://galton.uchicago.edu/~guillaumebal/ Guillaume Bal] (U Chicago)
|[https://sites.lsa.umich.edu/shankar-lab/ Suraj Shankar] (Michigan)
|[[# TBA| TBA ]]
|[[#Shankar|TBA]]
| Li, Stechmann
|Spagnolie
|-
|-
|Oct 23 ('''Wednesday''')
|Mar 14
|[https://www.sandia.gov/ccr/staff/teresa-portone/ Teresa Portone] (Sandia)
|[https://lu.seas.harvard.edu/ Yue Lu] (Harvard) '''[Colloquium]'''
|[[# Beyond parametric uncertainty: quantifying model-form uncertainty in model predictions | Beyond parametric uncertainty: quantifying model-form uncertainty in model predictions ]]
|[[#Lu|TBA]]
|Stechmann
|Li
|-
|-
|Oct 25
|Mar 21
|[https://www.cs.cornell.edu/~damle/ Anil Damle] (Cornell)
|[https://people.llnl.gov/vogman1 Genia Vogman] (LLNL)
|Fine-grained Theory and Hybrid Algorithms for Randomized Numerical Linear Algebra
|[[#Vogman|TBA]]
|Li
|Li
|-
|-
| Nov 1
|Mar 28
|[https://research-hub.nrel.gov/en/persons/michael-sprague Michael Sprague] (NREL)
|''Spring Break''
|[[# TBA|  TBA  ]]
|
|Spagnolie
|
|-
|-
| Nov 8
|Apr 4
|[https://personal.math.ubc.ca/~holmescerfon/ Miranda Holmes-Cerfon] (UBC)
|TBA
|
|
|Stechmann
|-
| Nov 15*
| [http://sun-yue.com Yue Sun] (UW–Madison)
|
|
| Rycroft
|-
|-
| Nov 22
|Apr 11
|[https://ibd.uchicago.edu/joinus/yenfellowship/ Ondrej Maxian] (U Chicago)
|[https://meche.mit.edu/people/faculty/pierrel@mit.edu Pierre Lermusiaux] (MIT)
|[[# TBA| TBA ]]
|[[#Lermusiaux|TBA]]
|Ohm & Spagnolie
|Chen
|-
|-
| Nov 29*
|Apr 18
|''Thanksgiving''
|[https://www.math.uci.edu/~jxin/ Jack Xin] (UC Irvine) '''[Colloquium]'''
|
|[[#Xin|TBA]]
|
|
|-
|-
| Dec 6
|Apr 25
|[https://www.simonsfoundation.org/people/ido-lavi/ Ido Lavi] (Flatiron)
|[https://www-users.cse.umn.edu/~bcockbur/ Bernardo Cockburn] (Minnesota)
|[[# TBA| TBA ]]
|[[#Cockburn|''Transforming stabilization into spaces'']]
|Spagnolie
| Stechmann, Fabien
|-
|May 2
|[https://sylviaherbert.com/ Sylvia Herbert] (UCSD)
|[[#Herbert|TBA]]
|Chen
|}
|}


Dates marked with an asterisk correspond to [https://uwbadgers.com/sports/football/schedule home football games of the UW–Madison Badgers]. On these dates it can be difficult to get a hotel room close to campus at short notice.
==Abstracts==


== Abstracts ==
<div id="Chandler">
====Thomas G. J. Chandler (UW)====
Title: Fluid-structure interactions in active complex fluids


===Nan Chen (UW–Madison)===
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.


Title: Taming Uncertainty in a Complex World: The Rise of Uncertainty Quantification -- A Tutorial for Beginners
<div id="Fraser">
====Adrian Fraser (Colorado)====
Title: Destabilization of transverse waves by periodic shear flows


I will provide a tutorial about uncertainty quantification (UQ) for those who have no background but are interested in learning more about this area. The talk will exploit many elementary examples, which are understandable to graduate students and senior undergraduates, to present the ideas of UQ. Topics include characterizing uncertainties using information theory, UQ in linear and nonlinear dynamical systems, UQ via data assimilation, the role of uncertainty in diagnostics, and UQ in advancing efficient modeling. The surprisingly simple examples in each topic explain why and how UQ is essential. Both Matlab and Python codes have been made available for these simple examples.
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.


===Katie Newhall (UNC Chapel Hill)===
<div id="Cockburn">
====Bernardo Cockburn (Minnesota)====
Title: Transforming stabilization into spaces


Title: Energy landscapes, metastability, and transition paths
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.


The concept of an energy landscape emerged in the 1930’s as a way to calculate chemical reaction rate constants via Henry Eyring’s transition state theory. Its use has expanded since then, remaining central to quantifying metastability (infrequent jumps between deterministically-stable, energy minimizing, states) that arises in noisy systems when the thermal energy is small relative to the energy barrier separating two states. In this talk, I will present extensions of this theory that I have developed and applied to physical and biological systems. The first is an infinite dimensional system for which I prove metastability is present in the absence of an energy barrier; I extend transition state theory to compute mean transition times. In the second, I derive a model for a spatially-extended magnetic system with spatially-correlated noise designed to sample the Gibbs distribution relative to a defined energy functional. In the third, I show a quasi-potential can be found and used to describe metastable transitions between stable clusters in a bead-spring polymer model of chromosome dynamics with additional stochastic binding pushing the system out of equilibrium.
== Archived semesters ==
 
===Indresan Govender (Mintek / Univ. of KwaZulu Natal, South Africa)===
 
Title: Granular flow modeling and visualization using nuclear imaging
 
Despite its ubiquity, a complete theory to describe the underlying rheology of granular flows remains elusive. Central to this problem is the lack of detailed, in-situ measurements of the granular flow field. To this end, we present two non-invasive imaging techniques currently employed to measure the flow of individual grains within granular flow systems that span simple mono-sized flows of plastic beads to complex industrial mixture flows of rocks and slurry. The first technique employs diagnostic X-rays operated in biplanar mode to triangulate the motion of low-density granules in simplified flow systems to within a 3D spatial accuracy of 0.15 mm at tracking frequencies up to 100 Hz. The second—arguably the workhorse of our research operation—is the nuclear imaging technique of Positron Emission Particle Tracking (PEPT) which triangulates the back-to-back gamma rays emanating from radiolabeled particles to within a millimeter in 3D space at a millisecond timing resolution. PEPT can track the motion of any particle with a diameter greater than ∼20 microns. Both techniques are well suited to studying the flow of granular materials after the data is cast into volume and time averages consistent with the continuum framework. In this talk I will explore the many interesting analysis techniques employed to mapping out the complex flow regimes found in typical granular systems, and the insights they offer towards better understanding their rheological character. Examples explored will include rotating drum flows (wet and dry), shear cells and their industrial counterpart the IsaMill<sup>TM</sup>, hydrocyclone separator flows, and the motivation for tracking of multiple particles. The validation offered to numerical schemes like the Discrete Element Method will also be explored wherein we highlight the complimentary role that measurement and simulation play in unravelling the secrets of granular flows. Finally, and deviating somewhat from the imaging world, I will present our efforts towards utilizing granular flow modeling in real-time control of complex industrial flows encountered in mineral processing.
 
===Hongfei Chen (Tulane)===
 
Title: Investigating Hydrodynamics of Choanoflagellate Colonies: A Reduced Model Approach
 
Abstract: Choanoflagellates, eukaryotes with a distinctive cellular structure consisting of a cell body, a flagellum, and a collar of microvilli, exhibit fascinating biological behavior. While many species exist as single cells, some form colonies, with the species ''C. Flexa'' standing out for its ability to dynamically transition its flagella between positions inside and outside the colony.
 
Modeling the hydrodynamics of these colonies ideally requires detailed representations of each cell’s flagellum, microvilli, and body. However, the computational cost of simulating colonies with hundreds of cells makes this approach very expensive. To address this, we propose a reduced modeling framework that simplifies each cell to a force dipole while retaining key hydrodynamic features.
 
Our force dipole model is calibrated against detailed computational simulations that account for the complete cellular structure. We show that this reduced model closely matches experimental data for non-deforming, free-swimming colonies. We further investigate how colony swimming and feeding performance depend on the flagellar position relative the colony, cell density, and overall colony shape. Finally, we explore the impact of the wall for flagella-in colonies, which are frequently observed in laboratory settings.
 
<div id="Portone">
===Teresa Portone (Sandia)===
Title: Beyond parametric uncertainty: quantifying model-form uncertainty in model predictions
 
Uncertainty quantification (UQ) is the science of characterizing, quantifying, and reducing
uncertainties in mathematical models. It is critical for informing decisions, because it provides a measure
of confidence in model predictions, given the uncertainties present in the model. While approaches to
characterize uncertainties in model parameters, boundary and initial conditions are well established, it is
less clear how to address uncertainties arising when the equations of a mathematical model are
themselves uncertain—that is, when there is model-form uncertainty. Model-form uncertainty often
arises in models of complex physical phenomena where (1) simplifications for computational tractability
or (2) lack of knowledge lead to unknowns in the governing equations for which appropriate
mathematical forms are unknown or may not exist. In this talk, I briefly introduce major concepts in UQ,
then I discuss approaches to characterize model-form uncertainty and its impact on model predictions.
 
=== Anil Damle (Cornell)===
Title: Fine-grained Theory and Hybrid Algorithms for Randomized Numerical Linear Algebra
 
Randomized algorithms have gained increased prominence within numerical linear algebra and they play a key role in an ever-expanding range of problems driven by a breadth of scientific applications. In this talk we will explore two aspects of randomized algorithms by (1) providing experiments and accompanying theoretical analysis that demonstrate how their performance depends on matrix structures beyond singular values (such as coherence of singular subspaces), and (2) showing how to leverage those insights to build hybrid algorithms that blend favorable aspects of deterministic and randomized methods. A focus of this talk will be on methods that approximate matrices using subsets of columns. Relevant motivating applications will be discussed and numerical experiments will illuminate directions for further research.
 
== Future semesters ==


*[[Applied/ACMS/Fall2024|Fall 2024]]
*[[Applied/ACMS/Fall2024|Fall 2024]]
*[[Applied/ACMS/Spring2025|Spring 2025]]
== Archived semesters ==
*[[Applied/ACMS/Spring2024|Spring 2024]]
*[[Applied/ACMS/Spring2024|Spring 2024]]
*[[Applied/ACMS/Fall2023|Fall 2023]]
*[[Applied/ACMS/Fall2023|Fall 2023]]

Latest revision as of 22:02, 25 January 2025


Applied and Computational Mathematics Seminar


Spring 2025

Date Speaker Title Host(s)
Jan 31 Thomas Chandler (UW) Fluid–structure interactions in active complex fluids
Feb 7 Adrian Fraser (Colorado) Destabilization of transverse waves by periodic shear flows Spagnolie
Feb 14 TBA
Feb 21 TBA
Feb 28 Nick Boffi (CMU) TBA Li
Mar 7 Suraj Shankar (Michigan) TBA Spagnolie
Mar 14 Yue Lu (Harvard) [Colloquium] TBA Li
Mar 21 Genia Vogman (LLNL) TBA Li
Mar 28 Spring Break
Apr 4 TBA
Apr 11 Pierre Lermusiaux (MIT) TBA Chen
Apr 18 Jack Xin (UC Irvine) [Colloquium] TBA
Apr 25 Bernardo Cockburn (Minnesota) Transforming stabilization into spaces Stechmann, Fabien
May 2 Sylvia Herbert (UCSD) TBA Chen

Abstracts

Thomas G. J. Chandler (UW)

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.

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.

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.

Archived semesters


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