2026 NDNS+ yearly meeting

2026 NDNS+ yearly meeting

Location

The 2026 NDNS+ yearly meeting will be a one-day, hosted by ACDC (VU Amsterdam), and funded by NDNS+. It will take place on the 13th of March 2026 in room NU-4A25 of the NU building (see here for directions) from 10:15 to 19:00.

Registration and poster submission

Registration to the event is mandatory, and available via this link (the deadline for registration is the 1st of March 2026). We solicit poster submissions, which is possible using the same form.

Talks and posters

This year's event is centred around the cluster's Special Activity Groups (SAGs). We have asked SAGs to introduce themselves and their activities, and to follow up with a thematic talk. Our SAGs are:

Schedule

Time Activity
10:15-11:00 Arrival, registration, coffee
11:00-11:05 Opening
11:05-11:40 SAG talks: Analysis of Partial Differential Equations
11:40-12:15 SAG talks: Structure-Preserving numerical methods
12:15-13:45 Lunch and posters
13:45-14:20 SAG talks: Uncertainty Quantification
14:20-14:55 SAG talks: Calculus of Variations
14:55-15:30 SAG talks: Inverse Problems
15:30-16:00 Coffee/tea break
16:00-17:45 Invited talks and NDNS+ discussion
17:45-19:00 Drinks

Titles and abstracts of the lectures will be included here in due course

Speaker 1 for SAG Analysis of Partial Differential Equations:
Koondi Mitra (TU Eindhoven)

Title: Well-posedness of a class of degenerate diffusion systems

Abstract: Nonlinear and degenerate diffusion systems are common in mathematical biology and give rise to interesting phenomenon involving free boundaries. We investigate the well-posedness of a wide class of such problems, some of them being even mixed-dimensional. By taking space and time discretised approximations that also serve as robust structure-preserving schemes, we prove the existence of solutions. Uniqueness and blow-up of such solutions are investigated subsequently. Joint work with: S. Sonner, I.S. Pop, R.K.H. Smeets, J.A. Geurts, G. Vallet.

Speaker 2 for SAG Analysis of Partial Differential Equations: Havva Yoldaş (TU Delft)

Title: TBA

Abstract: TBA

Speaker for SAG Structure-Preserving Numerical Methods: Tom Tyranowski (University of Twente)

Title: Learning deterministic and stochastic forced Hamiltonian systems

Abstract: We present a neural network architecture capable of learning the parameter-dependent flow of a Hamiltonian system subject to external forcing, while preserving the underlying Lagrange-d’Alembert structure. We demonstrate that this architecture can learn the flows of time-dependent systems—both deterministic and stochastic—and more accurately emulate the system’s energy evolution compared to general-purpose, non-structure-preserving neural networks. This results in more stable and higher-quality solutions. We also discuss prospective applications to structure-preserving model reduction of stochastic Hamiltonian systems.

Speaker for SAG Uncertainty Quantification: Wouter Edeling (CWI Amsterdam)

Title: Deep Active Subspaces for High-Dimensional Uncertainty Quantification

Abstract: The deep active subspace method is a neural-network based tool for the propagation of uncertainty through computational models with high-dimensional input spaces. Unlike the original active subspace method, it does not require access to the gradient of the model. It relies on an orthogonal projection matrix constructed with Gram-Schmidt orthogonalization, which is incorporated as a linear encoder into a neural network, and optimized using back propagation to identify the latent variables, i.e. the active subspace of the input. We assess the performance of the deep active subspace method on epidemiological models and molecular dynamics with a particular focus on uncertainties in the high-dimensional force-field parameters, which affect key quantities of interest, including macroscopic material properties and binding free energy predictions in drug discovery. We also discuss its potential for constructing efficient priors for uncertainty quantification in neural network weights.

Speaker for SAG Inverse Problems: Christoph Brune (University of Twente)

Title: Distributional Robustness and Generative Models for Reliable Inversion.

Abstract: TBA

Speaker for SAG Calculus of Variations NL: José Iglesias Martinez (University of Twente)

Title: Decomposition of functions of bounded variation: extensions and applications

Abstract: The development of the multidimensional theory of functions of bounded variation (BV) has been driven by several kinds of applications of the calculus of variations: convenient formulations of minimal surfaces, material models allowing for failure in the form of cracks and plasticity, and image processing. Something that ties together all these applications is the relevance of piecewise constant functions. Certain such functions with two values are known to constitute the extreme points of the unit ball in the space of scalar-valued BV functions, and thus play a key part in minimization problems formulated in it.

In this talk, I will give a brief overview of some developments branching from this basic result in two directions: extensions to vector-valued functions and nonlocal definitions of the variation, and numerical applications in the form of fast methods for PDE-constrained optimization problems. These stem from recent joint works with Kristian Bredies, Marcello Carioni, Giacomo Cristinelli, Leonardo del Grande, Daniel Walter and Hidde Schönberger.

Invited speaker: Carlos Pérez Arancibia (University of Twente)

Title: Maxwell à la Helmholtz: From Curl Operators to Curvature-Dependent Boundary Conditions

Abstract: Maxwell's equations stand among the greatest achievements in physics, unifying electricity, magnetism, and optics into a single elegant framework that predicted electromagnetic waves and laid the foundation for modern technology. For over 150 years, these equations—with their characteristic curl operators describing how electric and magnetic fields generate each other—have shaped everything from antenna design and radar systems to photonics and metamaterials. This talk presents a surprising result: these curl-based formulations can be completely bypassed by establishing a rigorous equivalence between Maxwell's equations and the simpler Helmholtz equation. We show that the problem of electromagnetic scattering by a smooth 3D object can be recast as two independent vector Helmholtz boundary value problems for the electric and magnetic fields, where the coupling between field components occurs solely through curvature-dependent boundary conditions that enforce the divergence constraint, effectively eliminating the need for curl operators in the formulation.

This equivalence bridges two fundamental wave models traditionally treated as distinct frameworks, unlocking the entire arsenal of boundary integral techniques and fast solvers developed for Helmholtz problems for direct application to electromagnetic scattering. We will explore the mathematical foundations of this equivalence using elementary differential geometry techniques. As a concrete application, we derive boundary integral equation formulations using only classical Helmholtz operators that are provably well-posed, frequency-robust, and free from spurious resonances. Numerical examples demonstrate the effectiveness of this approach across different geometries and frequency regimes, with implementations available in the open-source Julia package Inti.jl.

Reference: J. Burbano-Gallegos, C. Pérez-Arancibia, and C. Turc, "Maxwell à la Helmholtz: Electromagnetic Scattering by 3D Perfect Electric Conductors via Helmholtz Integral Operators," to appear in Mathematical Modelling and Numerical Analysis (2025). arXiv:2505.20440.

Invited speaker: Rafael Bailo (TU Eindhoven)

Title: Pedestrian models with congestion effects

Abstract: We study the validity of a PDE model for pedestrian dynamics derived as a generalisation of traffic models. The model uses a congestion term (a singular diffusion term) to enforce capacity constraints in the crowd density while inducing a steering behaviour. Furthermore, we introduce an asymptotic-and-structure-preserving numerical scheme which can handle the numerical solution of the model efficiently. Through this scheme, we are able to perform various simulations of the model, ultimately showing that it correctly captures crowding effects that are known empirically. This is work in collaboration with Pedro Aceves-Sanchez, Pierre Degond, and Zoe Mercier.

Invited speaker: Henk A. Dijkstra (Utrecht)

Title: Transitions of the Atlantic Meridional Overturning Circulation

Abstract: The Atlantic Meridional Overturning Circulation (AMOC) is one of the tipping elements in the climate system. The AMOC is sensitive to surface freshwater perturbations and may undergo a transition to a climate disrupting state within a few decades under continuing greenhouse gas emissions. In this talk, I will focus on determining the  probability that the onset of such an AMOC collapse occurs before the end of this century using a hierarchy of ocean models. 

Organizers