NCSU Differential Equations/Nonlinear Analysis Seminar Schedule 2024-2025

Wednesday, Sep 11, 15:00-16:00, Zoom meeting: Link

Speaker: Giovanni Gravina
Title: Collision and self-contact for viscoelastic solids with Lipschitz boundaries
Abstract: In this talk, we will examine the time evolution of viscoelastic solids within a framework that allows for collisions and self-contact. In the static and quasi-static regimes, corresponding existence results have been shown through variational descriptions of the problem. For the fully dynamical case, however, collisions have so far either been ignored or handled using a simplified model (for example, using repulsive terms). In contrast to this, by employing a newly developed variational technique, we are able to prove the existence of solutions for arbitrary times. In the second part of the talk, we will delve into the latest developments concerning solids with Lipschitz boundaries and discuss technical and conceptual difficulties that arise due to the presence of corners.  —————————————————————————————————————————————–

Wednesday, Sep 25, 15:00-16:00, Zoom meeting: Link

Speaker: Jone Apraiz, Universidad del País Vasco
Title: Inverse problem for a one-dimensional fluid-solid interaction model
Abstract: In this talk we will first briefly review some geometric inverse problems
we have studied for the one-dimensional heat, wave and Burgers equations.
Then, we will consider a one-dimensional fluid-solid interaction model gov-
erned by the Burgers equation with a time varying interface. This is a
preliminary simplified version of other more complicate and more realistic
models in higher dimensions. We will see the results we have obtained for
the inverse problem of determining the shape of the interface from Dirichlet
and Neumann data at one end point of the spatial interval. In particular, we
will show uniqueness results and some conditional stability estimates. For
the proofs, it will be seen that some lateral estimates have been used and
adapted, which rely on appropriate Carleman and interpolation inequalities.
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Wednesday, Oct 09, 15:00-16:00, Zoom meeting: Link

Speaker: Silvia Villa, Università di Genova
Title: Structured stochastic zeroth order optimization
Abstract: In the framework of black-box optimization, I will present new algorithms, 
based on the stochastic estimation of the gradient via  finite differences with structured
directions. I will describe their convergence properties under various assumptions and
show some numerical results.
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Wednesday, Oct 16, 15:00-16:00, COX 306

Speaker: Ziad Musslimani, Florida State University
Title: Space-time nonlocal integrable systems
Abstract: n this talk I will review past and recent results pertaining to the emerging topic of integrable space-time nonlocal integrable nonlinear evolution equations. In particular, we will discuss blow-up in finite time for solitons and the physical derivations of many integrable nonlocal systems.
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Wednesday, Oct 23, 15:00-16:00, Zoom meeting: Link

Speaker: Emilio Vilches Gutiérrez, Universidad de O’Higgins, Chile
Title: Recent Developments in Moreau’s Sweeping Processes
Abstract: The sweeping process is a first-order differential inclusion involving the normal cone to a family of moving sets. It was introduced by J.J. Moreau in the early seventies to address an elastoplastic problem. Since then, it has been used to model constrained dynamical systems, nonsmooth electrical circuits, crowd motion, mechanical problems, and other applications. The aim of this talk is twofold. On the one hand, we will provide the main insights into the well-posedness of the sweeping process, and on the other hand, we will present the latest developments in the subject, such as optimal control and numerical approximation.
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Wednesday, Oct 30, 15:00-16:00, Room: SAS 4201

Speaker: Stefania Patrizi, The University of Texas at Austin
Title: The discrete dislocation dynamics of multiple dislocation loops
Abstract: We consider a nonlocal reaction-diffusion equation that physically arises from the classical Peierls–Nabarro model for dislocations in crystalline structures. Our initial configuration corresponds to multiple slip loop dislocations in $\mathbb R^n$, $n\geq 2$. After suitably rescaling the equation with a small phase parameter $\epsilon>0$, the rescaled solution solves a fractional Allen–Cahn equation. We show that, as $\epsilon \to 0$, the limiting solution exhibits multiple interfaces evolving independently and according to their mean curvature. 

This is a joint work with Mary Vaughan  (University of Western Australia).
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Wednesday, Jan 22, 15:00-16:00, Zoom meeting: Link

Speaker: David Salas, Universidad de O’Higgins, Chile
Title: The Bayesian approach for bilevel programming
Abstract: In this talk, we present the Bayesian approach for bilevel programming problems, first introduced by Mallozzi and Morgan [1] under the name of intermediate Stackelberg games, and rediscovered in [3]. The main idea of this approach is to treat the (possibly not single-valued) response set of the follower as an uncertainty set, and treat the actual response as a random variable following a decision-dependent distribution. This distribution models the belief of the leader, hence the name of the approach. In the first part of the talk we will explore the well-posedness of the model, focusing on sufficient conditions to guarantee the existence of optimal solutions. In particular, we will show that in the linear setting, the existence of solutions is guaranteed for a large family of beliefs derived from the natural adaptation of the uniform distribution. In the second part, we will study an application to stochastic linear bilevel optimization, where we leverage on the polyhedral structure of the problem which is revealed under the lens of the Bayesian approach. We will finish discussing some open problems and new directions of research in this topic. The talk is based on the recent contributions with A. Svensson and G. Muñoz  [2,3].

References:
[1] L. Mallozzi and J. Morgan. Hierarchical Systems with Weighted Reaction Set, pages 271–282. Springer US, Boston, MA, 1996.
[2] G. Muñoz, D. Salas, and A. Svensson. Exploiting the polyhedral geometry of stochastic linear bilevel programming. Math. Program., pages 1–36, 2024.
[3] D. Salas and A. Svensson. Existence of solutions for deterministic bilevel games under a general Bayesian approach. SIAM J. Optim., 33(3):2311–2340, 2023.
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Wednesday, Jan 29, 15:00-16:00, Zoom meeting: Link

Speaker: Michael Goldman, CMAP, Ecole Polytechnique.
Title: Recent progress on the optimal matching problem
Abstract: In this talk I will review some recent progress in the understanding of the (random) optimal matching problem. While the work of Ajtai-Komlos-Tusnady in the 80’s on this classical optimization problem attracted a lot of attention from the probability community (see the book by Talagrand), this problem has seen a renewed interest from the PDE community thanks to the ansatz proposed by Caracciolo Lucibello, Parisi and Sicuro in 2014. I will explain to which extent this ansatz can be rigorously justified and show how it leads to a deeper understanding of this problem.
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Wednesday, Feb 12, 15:00-16:00, SAS 4201

Speaker: Ryan Murray, NC State University
Title:  A variational approach to studying dimension reduction algorithms
Abstract: Dimension reduction algorithms, such as principal component analysis (PCA), multidimensional scaling (MDS), and stochastic neighbor embeddings (SNE and tSNE), are an important tool for data exploration, visualization, and subgroup identification. While these algorithms see broad application across many scientific fields, our theoretical understanding of non-linear dimension reduction algorithms remains limited. This talk will describe new results that identify large data limits for MDS and tSNE using tools from the Calculus of Variations. Along the way, we will showcase situations where standard libraries give outputs that are misleading, and propose new computational algorithms to mitigate these issues and improve efficiency. Connections with the celebrated Gromov-Wasserstein distance and manifold learning will also be highlighted. This talk will aim to be accessible to a broad mathematical audience.
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Wednesday, Feb 19, 15:00-16:00, Zoom meeting: Link

Speaker: Sorin PoP, Hasselt University
Title: TBA
Abstract: TBA
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Wednesday, Feb 26, 15:00-16:00, Zoom meeting: Link

Speaker: Roberto Guglielmi, University of Waterloo
Title: TBA
Abstract: TBA
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Wednesday, Mar 05, 15:00-16:00, Zoom meeting: Link

Speaker: Kerrek Stinson, University of Utah
Title: TBA
Abstract: TBA
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Wednesday, Mar 19, 15:00-16:00, SAS 4201

Speaker: Piermarco Cannarsa, Tor Vergata University of Rome
Title: TBA
Abstract: TBA
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Wednesday, Mar 26, 15:00-16:00, 15:00-16:00, SAS 4201

Speaker: Wonjun Lee, University of Minnesota
Title: TBA
Abstract: TBA
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Wednesday, April 02, 15:00-16:00, Zoom meeting: Link

Speaker: Loc Nguyen, UNCC
Title: TBA
Abstract: TBA
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Wednesday, April 09, 15:00-16:00, Zoom meeting: Link

Speaker: Tarek M Elgindi, Duke University
Title: TBA
Abstract: TBA
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Wednesday, April 16, 15:00-16:00, Zoom meeting: Link

Speaker: Arunima Bhattacharya, UNC
Title: TBA
Abstract: TBA
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Monday, April 21, 1:45 PM – 2:45PM, SAS 4201

Speaker: Fabio Ancona, University of Padova
Title: TBA
Abstract: TBA