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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:''' [http://www.math.wisc.edu/~spagnolie Saverio Spagnolie] and [http://www.math.wisc.edu/~jeanluc Jean-Luc Thiffeault]
*'''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],
*'''To join the ACMS mailing list:''' Send mail to [mailto:acms+join@g-groups.wisc.edu acms+join@g-groups.wisc.edu].


<br>
<br>  


== Spring 2013 Semester ==
== Spring 2024  ==


{| cellpadding="8"
{| cellpadding="8"
Line 17: Line 18:
!align="left" | host(s)
!align="left" | host(s)
|-
|-
|'''Feb 15, 4pm, B239'''
| Feb 2
|[http://maeresearch.ucsd.edu/lauga/ Eric Lauga] (UCSD)
|[https://people.math.wisc.edu/~chr/ Chris Rycroft] (UW)
|''Optimization in fluid-based locomotion''
|''The reference map technique for simulating complex materials and multi-body interactions''
|'''Colloquium'''
|
|-
| Feb 9
|[https://users.flatironinstitute.org/~sweady/ Scott Weady] (Flatiron Institute)
|''Entropy methods in active suspensions''
|Saverio and Laurel
|-
| Feb 16
|[http://stokeslet.ucsd.edu/ David Saintillan] (UC San Diego)
|''[[Applied/ACMS/absS24#David Saintillan (UC San Diego)|Hydrodynamics of active nematic surfaces]]''
|Saverio and Tom
|-
|-
|March 1
| Feb 23
|[http://fsisg.ucsd.edu/ Kourosh Shoele] (RE Vision Consulting)
|[https://cersonsky-lab.github.io/website/ Rose Cersonsky] (UW)
|''[[Applied/ACMS/absS13#Kourosh_Shoele_(RE Vision Consulting)|Fluid interaction with structures, from fish fins to hydrokinetic devices]]''
|''Data-driven approaches to chemical and materials sciences''
|Saverio
|Chris
|-
|-
|March 8
| Mar 1 [4:00pm Colloquium]
|[http://www.math.wisc.edu/~zlatos/ Andrej Zlatoš] (UW)
|[https://users.oden.utexas.edu/~pgm/ Per-Gunnar Martinsson] (UT Austin)
|''[[Applied/ACMS/absS13#Andrej_Zlatos_(UW)|TBA]]''
|''[[Applied/ACMS/absS24#Per-Gunnar Martinsson (UT-Austin)|TBA]]''
|Jean-Luc, Saverio
|Li
|-
|-
|March 15
| Mar 8
|[http://home.physics.wisc.edu/~cbforest/ Cary Forest] (UW)
|[https://www.physics.wisc.edu/directory/jorge-rogerio/ Rogerio Jorge] (UW-Madison)
|''[[Applied/ACMS/absS13#Cary_Forest_(UW)|Stirring Magnetized Plasma]]''
|''The Direct Optimization Framework in Stellarator Design: Transport and Turbulence Optimization''
|Jean-Luc, Saverio
|Li
|-
|-
|March 22
| Mar 15
|[https://mywebspace.wisc.edu/mjohnston3/web/index.html Matthew Johnston] (UW)
|[https://www.math.purdue.edu/~qi117/personal.html/ Di Qi] (Purdue University)
|''[[Applied/ACMS/absS13#Matthew_Johnston_(UW)|TBA]]''
|[[Applied/ACMS#diqi|Statistical Reduced-Order Models and Random Batch Method for Complex Multiscale Systems]]
|Jean-Luc, Saverio
|Chen
|-
|-
|April 5
| Mar 22
|[http://www.math.wisc.edu/~boston/ Nigel Boston] (UW)
|''[[Applied/ACMS/absS13#Nigel_Boston_(UW)|TBA]]''
|Jean-Luc, Saverio
|
|
|-
|April 12
|[http://geoscience.wisc.edu/geoscience/people/faculty/shanan-peters/ Shanan Peters] (UW)
|''[[Applied/ACMS/absS13#Shanan_Peters_(UW)|TBA]]''
|Jean-Luc, Saverio
|
|
|-
|April 19
|[https://sites.google.com/a/brown.edu/fluids/home Shreyas Mandre] (Brown)
|''[[Applied/ACMS/absS13#Shreyas_Mandre_(Brown)|TBA]]''
|Jean-Luc, Saverio
|
|
|-
|-
|April 26
| Mar 29
|[http://pages.cs.wisc.edu/~brecht/ Ben Recht] (UW)
|Spring break
|''[[Applied/ACMS/absS13#Ben_Recht_(UW)|TBA]]''
|Jean-Luc, Saverio
|
|
|-
|May 10
|[http://www-personal.umich.edu/~alben/ Silas Alben] (Michigan)
|''[[Applied/ACMS/absS13#Silas_Alben_(Michigan)|TBA]]''
|Jean-Luc, Saverio
|
|
|}
<br>
== Fall 2012 Semester ==
{| cellpadding="8"
!align="left" | date
!align="left" | speaker
!align="left" | title
!align="left" | host(s)
|-
|-
|Sept 14
| Apr 5
|[http://mechse.illinois.edu/research/dstn David Saintillan] (U. Illinois)
|[https://www.jinlongwu.org/ Jinlong Wu] (UW)
|''[[Applied/ACMS/absF12#David_Saintillan_(U._Illinois)|Living fluids: modeling and simulation of biologically active suspensions]]''
|''[[Applied/ACMS/absS24#Jinlong Wu (UW)|TBA]]''
|Jean-Luc, Saverio
|Saverio
|-
|-
|'''<strike>Thu Sept 20, 4pm, B239</strike>'''
| Apr 12
|[http://www-stat.stanford.edu/~cgates/PERSI/ Persi Diaconis] (Stanford)
|[https://zayascaban.labs.wisc.edu/ Gabriel Zayas-Caban] (UW)
|''CANCELLED''
|''[[Applied/ACMS/absS24#Gabriel Zayas-Caban (UW)|TBA]]''
|Jean-Luc
|Li
|-
|-
|Sept 21
| Apr 19
|[http://www.math.wisc.edu/~roch Sebastien Roch] (UW)
|[https://www.nist.gov/people/anthony-j-kearsley Tony Kearsley] (NIST)
|''[[Applied/ACMS/absF12#Sebastien_Roch_(UW)|Assembling the tree of life: theory beyond the substitution-only model of sequence evolution]]''
|''[[Applied/ACMS/absS24#Tony Kearsley (NIST)|TBA]]''
|local
|Fabien
|-
|-
|'''Sept 21, 4pm, B239'''
| Apr 26
|[http://eaton.math.rpi.edu/faculty/J.McLaughlin/mclauj.html Joyce McLaughlin] (RPI)
|[https://math.oregonstate.edu/directory/malgorzata-peszynska Malgorzata Peszynska] (Oregon State)
|''Mathematics for imaging biomechanical parameters in dynamic elastography''
|''[[Applied/ACMS/absS24#Malgorzata Peszynska (Oregon State)|TBA]]''
|'''Colloquium'''
|Fabien
|-
|-
|'''Sept 28, 1:20pm'''
|
|[http://engineering.purdue.edu/~mboutin/ Mireille Boutin] (Purdue)
|''[[Geometry_and_Topology_Seminar#Mirielle Boutin (Purdue)|The Pascal triangle of a discrete Image: definition, properties, and application to object segmentation]]''
|'''Geometry seminar'''
|-
|Sept 28
|[http://caos.cims.nyu.edu/object/skeating Shane Keating] (NYU)
|''[[Applied/ACMS/absF12#Shane_Keating_(NYU)|Models and measures of turbulent mixing in the ocean]]''
|Jean-Luc
|-
|Oct 5
|[http://www.astro.wisc.edu/~zweibel Ellen Zweibel] (UW)
|''[[Applied/ACMS/absF12#Ellen_Zweibel_(UW)|The fluid dynamics of stellar interiors]]''
|Jean-Luc
|-
|Oct 12
|[http://m.njit.edu/~muratov Cyrill Muratov]  (NJIT)
|''[[Applied/ACMS/absF12#Cyrill_Muratov_(NJIT)|Gamma-convergence for pattern forming systems with competing interactions]]''
|Sasha Kiselev
|-
|Oct 19
|[http://www.math.cmu.edu/~gautam Gautam Iyer] (CMU)
|''[[Applied/ACMS/absF12#Gautam_Iyer_(CMU)|Time discrete approximations to the Navier&ndash;Stokes equations:
    Existence, stability and coercivity]]''
|Sasha Kiselev
|-
|Oct 26
|[http://www.math.drexel.edu/~tyu Thomas Yu] (Drexel U.)
|''[[Applied/ACMS/absF12#Thomas_Yu_(Drexel)|Subdivision methods in scientific computing]]''
|Shi Jin
|-
|'''Tues Oct 30, 4pm, B239'''
|[http://www.math.nyu.edu/faculty/majda/ Andrew Majda] (Courant)
|''[[Applied/ACMS/absF12#Andrew_Majda_(NYU)|Data driven methods for complex turbulent systems]]''
|Smith, Stechmann (Colloquium)
|-
|'''Thu Nov 1, 4pm, B239'''
|[http://math.uchicago.edu/~ryzhik Lenya Ryzhik] (Chicago)
|''The role of a drift in elliptic and parabolic equations''
|'''Colloquium'''
|-
|'''Nov 2, 4pm, B239'''
|[http://www.math.umn.edu/~sverak Vladimir Sverak] (Minnesota)
|''On scale-invariant solutions of the Navier-Stokes equations''
|'''Colloquium'''
|-
|Nov 9
|[http://www.biochem.wisc.edu/faculty/weibel Doug Weibel] (UW)
|''[[Applied/ACMS/absF12#Douglas_Weibel_(UW)|Insight into the mechanism(s) of Proteus mirabilis community structure]]''
|Jean-Luc, Saverio
|-
|Nov 16
|[http://www.math.colostate.edu/~yzhou Yongcheng Zhou] (Colorado State)
|''[[Applied/ACMS/absF12#xxxx|Multiscale modeling and numerics for surface electrodiffusion]]''
|Julie
|-
|Nov 30, '''B211'''
|[http://129.81.170.14/~kurganov Alexander Kurganov] (Tulane)
|''[[Applied/ACMS/absF12#Alexander_Kurganov_(Tulane)|Central-upwind schemes for shallow water models]]''
|Shi Jin
|
|
|}
|}


<br>
== Abstracts ==
 
==== Chris Rycroft (UW–Madison) ====
Title: The reference map technique for simulating complex materials and multi-body interactions
 
Conventional computational methods often create a dilemma for fluid–structure interaction problems. Typically, solids are simulated using a Lagrangian approach with grid that moves with the material, whereas fluids are simulated using an Eulerian approach with a fixed spatial grid, requiring some type of interfacial coupling between the two different perspectives. Here, a fully Eulerian method for simulating structures immersed in a fluid will be presented [1]. By introducing a reference map variable to model finite-deformation constitutive relations in the structures on the same grid as the fluid, the interfacial coupling problem is highly simplified. The method is particularly well suited for simulating soft, highly-deformable materials and many-body contact problems [2], and several examples in two and three dimensions [3] will be presented.
 
# K. Kamrin, C. H. Rycroft, and J.-C. Nave, J. Mech. Phys. Solids '''60''', 1952–1969 (2012). [https://doi.org/10.1016/j.jmps.2012.06.003 <nowiki>[DOI link]</nowiki>]
# C. H. Rycroft ''et al.'', J. Fluid Mech. '''898''', A9 (2020). [https://doi.org/10.1017/jfm.2020.353 <nowiki>[DOI link]</nowiki>]
# Y. L. Lin, N. J. Derr, and C. H. Rycroft, Proc. Natl. Acad. Sci. '''119''', e2105338118 (2022). [https://doi.org/10.1073/pnas.2105338118 <nowiki>[DOI link]</nowiki>]
 
 
==== Scott Weady (Flatiron Institute) ====
 
Title: Entropy methods in active suspensions
 
Collections of active particles, such as suspensions of E. coli or mixtures of microtubules and molecular motors, can exhibit rich non-equilibrium dynamics due to a combination of activity, hydrodynamic interactions, and steric stresses. Continuum kinetic theories, which characterize the set of particle configurations through a continuous distribution function, provide a powerful framework for analyzing such systems and connecting their micro- to macroscopic dynamics. The probabilistic formulation of kinetic theories leads naturally to a characterization in terms of entropy, whether thermodynamic or information-theoretic. In equilibrium systems, entropy strictly increases and always tends towards steady state. This no longer holds in active systems, however entropy still has a convenient mathematical structure. In this talk, we use entropy methods, specifically variational principles involving the relative entropy functional, to study the nonlinear dynamics and stability of active suspensions in the context of the Doi-Saintillan-Shelley kinetic theory. We first present a class of moment closures that arise as constrained minimizers of the relative entropy, and show these closures preserve the kinetic theory's stability and entropic structure while admitting efficient numerical simulation. We then derive variational bounds on relative entropy fluctuations for apolar active suspensions that are closely related to the moment closures. These bounds provide conditions for global stability and yield estimates of time-averaged order parameters. Finally, we discuss applications of these methods to polar active suspensions.
 


==== David Saintillan (UC San Diego) ====


== How to join the ACMS mailing list ==
Title: Hydrodynamics of active nematic surfaces
See [https://lists.math.wisc.edu/listinfo/acms mailing list] website


<br>
The dynamics of biological surfaces often involves the coupling of internal active processes with in-plane orientational order and hydrodynamic flows. Such active surfaces play a key role in various biological processes, from cytokinesis to tissue morphogenesis. In this talk, I will discuss two approaches for the modeling and simulation of active nematic surfaces. In a first model, we analyze the spontaneous dynamics of a freely-suspended viscous drop with surface nematic activity and its coupling with bulk fluid mechanics. Using a spectral boundary integral solver for Stokes flow coupled with a hydrodynamic evolution equation for the nematic tensor, numerical simulations reveal a complex interplay between the flow inside and outside the drop, the surface transport of the nematic field and surface deformations, giving rise to a sequence of self-organized behaviors and symmetry-breaking phenomena of increasing complexity, consistent with experimental observations. In the second part of the talk, I will present a novel computational approach for the simulation of active nematic fluids confined to Riemannian manifolds. The fluid velocity and nematic order parameter are represented as sections of the complex line bundle of a two-manifold. Using a geometric approach based on the Levi-Civita connection, we introduce a coordinate-free discretization method that preserves the continuous local-to-global theorems in differential geometry. Furthermore, we establish a nematic Laplacian on complex functions that can accommodate fractional topological charges through the covariant derivative on the complex nematic representation. Advection of the nematic field is formulated based on the Lie derivative, resulting in a stable geometric semi-Lagrangian discretization scheme for transport by the flow. The proposed surface-based method offers an efficient and stable means to investigate the influence of local curvature and topology on the hydrodynamics of active nematic systems, and we illustrate its capabilities by simulating active flows on a range of surfaces of increasing complexity.
 
 
 
'''Rose Cersonsky (UW–Madison)'''
 
Title: Data-driven approaches to chemical and materials sciences: the importance of data selection, representation, and interpretability
 
Like many other fields, there has been a recent and overwhelming wave of machine learning and artificial intelligence methods being employed in the chemical sciences. While these methods have the undoubted ability to drive innovation and capabilities, their application to chemical sciences requires a nuanced understanding of molecular representations and structure-property relationships.
 
In this talk, I will discuss the role of molecular featurization – how we transform atoms and molecules into mathematical signals appropriate for machine-learning thermodynamic quantities – and unsupervised analyses that allow us to easily understand and assess these so-called “featurizations” in the context of complex machine learning tasks. In doing so, I will demonstrate how linear methods – that constitute the simplest, most robust, and most transparent approaches to automatically processing large amounts of data – can be leveraged to understand molecular crystallization and aid in pharmaceutical engineering.
 
All methods discussed are available through the open-source [https://scikit-matter.readthedocs.io scikit-matter] software, an official scikit-learn companion that implement methods born out of the materials and chemistry communities.
 
 
==== Rogerio Jorge (UW-Madison) ====
 
Title: The Direct Optimization Framework in Stellarator Design: Transport and Turbulence Optimization
 
Abstract:
When it comes to magnetic confinement nuclear fusion, high-quality magnetic fields are crucial for sustaining high-heat plasmas and managing plasma density, fast particles, and turbulence. Transport and turbulence are particularly important factors in this process. Traditional designs of stellarator machines, like those seen in the HSX and W7-X experiments, typically optimize magnetic fields and coils separately. This approach can result in limited engineering tolerances and often overlooks turbulent transport during the optimization process. Moreover, the process is highly dependent on the initial conditions, requiring multiple restarts with relaxed requirements, which can make it inefficient and compromise the optimal balance between alpha particles, neoclassical transport, and turbulence. However, recent breakthroughs in the optimization of stellarator devices are able to overcome such barriers. Direct near-axis designs, integrated plasma-coil optimization algorithms, precise quasisymmetric and quasi-isodynamic fields, and direct turbulence optimization are among the innovations that are revolutionizing the way these machines are designed. By taking into account transport and turbulence from the start, these advancements allow for more efficient fusion devices and greater control over the plasma. In this presentation, we will discuss the main outcomes of these advancements and the prospects for even more efficient and effective fusion devices.
 
 
==== Di Qi (Purdue) ====
Title: [[#diqi|Statistical Reduced-Order Models and Random Batch Method for Complex Multiscale Systems]]
 
Abstract: The capability of using imperfect stochastic and statistical reduced-order models to capture key statistical features in multiscale nonlinear dynamical systems is investigated. A systematic framework is proposed using a high-order statistical closure enabling accurate prediction of leading-order statistical moments and probability density functions in multiscale complex turbulent systems. A new efficient ensemble forecast algorithm is developed dealing with the nonlinear multiscale coupling mechanism as a characteristic feature in high-dimensional turbulent systems. To address challenges associated with closely coupled spatio-temporal scales in turbulent states and expensive large ensemble simulation for high-dimensional complex systems, we introduce efficient computational strategies using the so-called random batch method. It is demonstrated that crucial principal statistical quantities in the most important large scales can be captured efficiently with accuracy using the new reduced-order model in various dynamical regimes of the flow field with distinct statistical structures. Finally, the proposed model is applied for a wide range of problems in uncertainty quantification, data assimilation, and control.
 
== Future semesters ==
 
*[[Applied/ACMS/Fall2024|Fall 2024]]


== Archived semesters ==
== Archived semesters ==
*[[Applied/ACMS/Fall2023|Fall 2023]]
*[[Applied/ACMS/Spring2023|Spring 2023]]
*[[Applied/ACMS/Fall2022|Fall 2022]]
*[[Applied/ACMS/Spring2022|Spring 2022]]
*[[Applied/ACMS/Fall2021|Fall 2021]]
*[[Applied/ACMS/Spring2021|Spring 2021]]
*[[Applied/ACMS/Fall2020|Fall 2020]]
*[[Applied/ACMS/Spring2020|Spring 2020]]
*[[Applied/ACMS/Fall2019|Fall 2019]]
*[[Applied/ACMS/Spring2019|Spring 2019]]
*[[Applied/ACMS/Fall2018|Fall 2018]]
*[[Applied/ACMS/Spring2018|Spring 2018]]
*[[Applied/ACMS/Fall2017|Fall 2017]]
*[[Applied/ACMS/Spring2017|Spring 2017]]
*[[Applied/ACMS/Fall2016|Fall 2016]]
*[[Applied/ACMS/Spring2016|Spring 2016]]
*[[Applied/ACMS/Fall2015|Fall 2015]]
*[[Applied/ACMS/Spring2015|Spring 2015]]
*[[Applied/ACMS/Fall2014|Fall 2014]]
*[[Applied/ACMS/Spring2014|Spring 2014]]
*[[Applied/ACMS/Fall2013|Fall 2013]]
*[[Applied/ACMS/Spring2013|Spring 2013]]
*[[Applied/ACMS/Fall2012|Fall 2012]]
*[[Applied/ACMS/Spring2012|Spring 2012]]
*[[Applied/ACMS/Spring2012|Spring 2012]]
*[[Applied/ACMS/Fall2011|Fall 2011]]
*[[Applied/ACMS/Fall2011|Fall 2011]]

Latest revision as of 02:20, 6 March 2024


Applied and Computational Mathematics Seminar


Spring 2024

date speaker title host(s)
Feb 2 Chris Rycroft (UW) The reference map technique for simulating complex materials and multi-body interactions
Feb 9 Scott Weady (Flatiron Institute) Entropy methods in active suspensions Saverio and Laurel
Feb 16 David Saintillan (UC San Diego) Hydrodynamics of active nematic surfaces Saverio and Tom
Feb 23 Rose Cersonsky (UW) Data-driven approaches to chemical and materials sciences Chris
Mar 1 [4:00pm Colloquium] Per-Gunnar Martinsson (UT Austin) TBA Li
Mar 8 Rogerio Jorge (UW-Madison) The Direct Optimization Framework in Stellarator Design: Transport and Turbulence Optimization Li
Mar 15 Di Qi (Purdue University) Statistical Reduced-Order Models and Random Batch Method for Complex Multiscale Systems Chen
Mar 22
Mar 29 Spring break
Apr 5 Jinlong Wu (UW) TBA Saverio
Apr 12 Gabriel Zayas-Caban (UW) TBA Li
Apr 19 Tony Kearsley (NIST) TBA Fabien
Apr 26 Malgorzata Peszynska (Oregon State) TBA Fabien

Abstracts

Chris Rycroft (UW–Madison)

Title: The reference map technique for simulating complex materials and multi-body interactions

Conventional computational methods often create a dilemma for fluid–structure interaction problems. Typically, solids are simulated using a Lagrangian approach with grid that moves with the material, whereas fluids are simulated using an Eulerian approach with a fixed spatial grid, requiring some type of interfacial coupling between the two different perspectives. Here, a fully Eulerian method for simulating structures immersed in a fluid will be presented [1]. By introducing a reference map variable to model finite-deformation constitutive relations in the structures on the same grid as the fluid, the interfacial coupling problem is highly simplified. The method is particularly well suited for simulating soft, highly-deformable materials and many-body contact problems [2], and several examples in two and three dimensions [3] will be presented.

  1. K. Kamrin, C. H. Rycroft, and J.-C. Nave, J. Mech. Phys. Solids 60, 1952–1969 (2012). [DOI link]
  2. C. H. Rycroft et al., J. Fluid Mech. 898, A9 (2020). [DOI link]
  3. Y. L. Lin, N. J. Derr, and C. H. Rycroft, Proc. Natl. Acad. Sci. 119, e2105338118 (2022). [DOI link]


Scott Weady (Flatiron Institute)

Title: Entropy methods in active suspensions

Collections of active particles, such as suspensions of E. coli or mixtures of microtubules and molecular motors, can exhibit rich non-equilibrium dynamics due to a combination of activity, hydrodynamic interactions, and steric stresses. Continuum kinetic theories, which characterize the set of particle configurations through a continuous distribution function, provide a powerful framework for analyzing such systems and connecting their micro- to macroscopic dynamics. The probabilistic formulation of kinetic theories leads naturally to a characterization in terms of entropy, whether thermodynamic or information-theoretic. In equilibrium systems, entropy strictly increases and always tends towards steady state. This no longer holds in active systems, however entropy still has a convenient mathematical structure. In this talk, we use entropy methods, specifically variational principles involving the relative entropy functional, to study the nonlinear dynamics and stability of active suspensions in the context of the Doi-Saintillan-Shelley kinetic theory. We first present a class of moment closures that arise as constrained minimizers of the relative entropy, and show these closures preserve the kinetic theory's stability and entropic structure while admitting efficient numerical simulation. We then derive variational bounds on relative entropy fluctuations for apolar active suspensions that are closely related to the moment closures. These bounds provide conditions for global stability and yield estimates of time-averaged order parameters. Finally, we discuss applications of these methods to polar active suspensions.


David Saintillan (UC San Diego)

Title: Hydrodynamics of active nematic surfaces

The dynamics of biological surfaces often involves the coupling of internal active processes with in-plane orientational order and hydrodynamic flows. Such active surfaces play a key role in various biological processes, from cytokinesis to tissue morphogenesis. In this talk, I will discuss two approaches for the modeling and simulation of active nematic surfaces. In a first model, we analyze the spontaneous dynamics of a freely-suspended viscous drop with surface nematic activity and its coupling with bulk fluid mechanics. Using a spectral boundary integral solver for Stokes flow coupled with a hydrodynamic evolution equation for the nematic tensor, numerical simulations reveal a complex interplay between the flow inside and outside the drop, the surface transport of the nematic field and surface deformations, giving rise to a sequence of self-organized behaviors and symmetry-breaking phenomena of increasing complexity, consistent with experimental observations. In the second part of the talk, I will present a novel computational approach for the simulation of active nematic fluids confined to Riemannian manifolds. The fluid velocity and nematic order parameter are represented as sections of the complex line bundle of a two-manifold. Using a geometric approach based on the Levi-Civita connection, we introduce a coordinate-free discretization method that preserves the continuous local-to-global theorems in differential geometry. Furthermore, we establish a nematic Laplacian on complex functions that can accommodate fractional topological charges through the covariant derivative on the complex nematic representation. Advection of the nematic field is formulated based on the Lie derivative, resulting in a stable geometric semi-Lagrangian discretization scheme for transport by the flow. The proposed surface-based method offers an efficient and stable means to investigate the influence of local curvature and topology on the hydrodynamics of active nematic systems, and we illustrate its capabilities by simulating active flows on a range of surfaces of increasing complexity.


Rose Cersonsky (UW–Madison)

Title: Data-driven approaches to chemical and materials sciences: the importance of data selection, representation, and interpretability

Like many other fields, there has been a recent and overwhelming wave of machine learning and artificial intelligence methods being employed in the chemical sciences. While these methods have the undoubted ability to drive innovation and capabilities, their application to chemical sciences requires a nuanced understanding of molecular representations and structure-property relationships.

In this talk, I will discuss the role of molecular featurization – how we transform atoms and molecules into mathematical signals appropriate for machine-learning thermodynamic quantities – and unsupervised analyses that allow us to easily understand and assess these so-called “featurizations” in the context of complex machine learning tasks. In doing so, I will demonstrate how linear methods – that constitute the simplest, most robust, and most transparent approaches to automatically processing large amounts of data – can be leveraged to understand molecular crystallization and aid in pharmaceutical engineering.

All methods discussed are available through the open-source scikit-matter software, an official scikit-learn companion that implement methods born out of the materials and chemistry communities.


Rogerio Jorge (UW-Madison)

Title: The Direct Optimization Framework in Stellarator Design: Transport and Turbulence Optimization

Abstract: When it comes to magnetic confinement nuclear fusion, high-quality magnetic fields are crucial for sustaining high-heat plasmas and managing plasma density, fast particles, and turbulence. Transport and turbulence are particularly important factors in this process. Traditional designs of stellarator machines, like those seen in the HSX and W7-X experiments, typically optimize magnetic fields and coils separately. This approach can result in limited engineering tolerances and often overlooks turbulent transport during the optimization process. Moreover, the process is highly dependent on the initial conditions, requiring multiple restarts with relaxed requirements, which can make it inefficient and compromise the optimal balance between alpha particles, neoclassical transport, and turbulence. However, recent breakthroughs in the optimization of stellarator devices are able to overcome such barriers. Direct near-axis designs, integrated plasma-coil optimization algorithms, precise quasisymmetric and quasi-isodynamic fields, and direct turbulence optimization are among the innovations that are revolutionizing the way these machines are designed. By taking into account transport and turbulence from the start, these advancements allow for more efficient fusion devices and greater control over the plasma. In this presentation, we will discuss the main outcomes of these advancements and the prospects for even more efficient and effective fusion devices.


Di Qi (Purdue)

Title: Statistical Reduced-Order Models and Random Batch Method for Complex Multiscale Systems

Abstract: The capability of using imperfect stochastic and statistical reduced-order models to capture key statistical features in multiscale nonlinear dynamical systems is investigated. A systematic framework is proposed using a high-order statistical closure enabling accurate prediction of leading-order statistical moments and probability density functions in multiscale complex turbulent systems. A new efficient ensemble forecast algorithm is developed dealing with the nonlinear multiscale coupling mechanism as a characteristic feature in high-dimensional turbulent systems. To address challenges associated with closely coupled spatio-temporal scales in turbulent states and expensive large ensemble simulation for high-dimensional complex systems, we introduce efficient computational strategies using the so-called random batch method. It is demonstrated that crucial principal statistical quantities in the most important large scales can be captured efficiently with accuracy using the new reduced-order model in various dynamical regimes of the flow field with distinct statistical structures. Finally, the proposed model is applied for a wide range of problems in uncertainty quantification, data assimilation, and control.

Future semesters

Archived semesters



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