Math Calendar

Monday, May 26, 2025
13:00-14:30
Ruppert 0.33
MI Institute meeting
Institute meeting for full professors, associate professors and assistant professors, as well as support staff of the MI.
15:00-20:00
Colour Kitchen Zuilen
MI Spring Outing
Please let us know whether you'll attend.
Tuesday, May 27, 2025
09:45-10:45
HFG-611AB
MSc thesis presentation - Martijn Brouwer
Machine Learning based lesion detection using 18F-FDG PET/MR

Supervisors: prof. dr. Tristan van Leeuwen & dr. Palina Salanevich

Other supervisors: dr. Gyula Kotek (EMC), dr. Jukka Hirvasniemi(EMC), dr. Frans Vos (TU Delft)

Abstract:

Inthis thesis presentation for both my Mathematics and Physics degrees, I presenta novel pipeline for simulating anatomically realistic lesions in 18F-FDGPET/MR scans to overcome the scarcity of annotated data. Using dimensionalityreduction (PCA) and probabilistic sampling (GMM), synthetic lesions aregenerated and inserted at clinically relevant locations. These datasets arethen used to train nnU-NetV2 models, which outperform those trained on reallesions alone. 

Experimentally,I identified which features influence lesion detectability – revealing thatbesides intensity, shape-based features like convexity affect detectability –and demonstrated how radiomics can be used to interpret the AI’sdecision-making. 

Ialso introduce a method for generating diverse anatomical variations throughdeformation fields, enabling scalable data augmentation without manualannotation. This work strengthens the foundation for automated lesion detectionin PET/MR and supports future applications in diagnostic imaging and treatmentplanning.

10:00-11:00
HFG 707
AG Seminar
Haowen Zhang (Leiden University) on "Strong approximation and Brauer-Manin obstruction for homogeneous spaces"
For an algebraic variety X over a number field k, strong approximation studies the density of rational points inside the set X(A_k^S) of adelic points away from a finite set S of primes, generalizing the Chinese Remainder Theorem. When strong approximation fails, we want to understand the closure of rational points inside X(A_k^S). For X a homogeneous space under a semisimple simply connected group with commutative stabilizers, we give conditions showing when the closure of the rational points is equal to the set of adelic points cut out by certain elements from the Brauer group.
16:00-17:00
HFG 611
MI talk
Aaron Gootjes-Dreesbach - Blown-up jet configuration spaces for non-local h-principles

Blowing up the diagonal of M^2 for a manifold M yields a configuration space that remembers the collision axis of collided configurations. Fulton and MacPherson famously generalized this construction to configurations of more than two points. As part of my thesis advised by Á. del Pino, we build configuration spaces for jets of maps in the same spirit, but adapted to the main structure on jet space: The Cartan distribution and the Lie filtration it generates. Higher jet orders necessitate the use of weighted blow-ups, which we tackle within the differential-geometric framework of weightings due to Loizides and Meinrenken. In this talk, I first want to intuitively illustrate this construction and then motivate why it is natural to consider when studying h-principles for differential constraints involving multiple points. 

Wednesday, May 28, 2025
14:00-16:00
HFG 7.07
Six-functor formalism seminar
Sven van Nigtevecht - Examples
Tuesday, June 3, 2025
10:00-11:00
HFG 707
AG Seminar
Nicolo Piazzalunga (Rutgers University)
15:00-16:30
HFG707
Category Theory Seminar
TBA - TBA
TBA
16:00-17:00
HFG 611
MI Seminar
Dusan Dragutinovic
Wednesday, June 4, 2025
14:00-16:00
HFG 7.07
Six-functor formalism seminar
Vignesh Subramanian - Norms in motivic homotopy theory
Tuesday, June 10, 2025
10:00-11:00
HFG 707
AG Seminar
Finn Bartsch (Radboud University Nijmegen)
Monday, June 16, 2025
12:00-13:00
Bring Your Own Lunch
Tuesday, June 17, 2025
10:00-11:00
HFG 707
AG Seminar
Victoria Hoskins (Radboud University Nijmegen)
15:00-16:30
HFG707
Category Theory Seminar
TBA - TBA
TBA
16:00-17:00
HFG 611
MI Seminar
Sven Nigtevecht
Friday, June 20, 2025
11:00-12:00
HFG 611
Special lecture
Gunther Uhlmann (University of Washington) - Seeing through space-time
We will consider the question of whether we can determine the structure of space-time by making measurements near the worldline of an observer. We will consider both active and passive measurements. For the case of passive measurements one measures the fronts of light sources near the observer. For the case of active measurements we couple Einstein equations with matter or electromagnetic fields and formulate the question of recovering the metric from observations of waves near the observer. The method applies to several other inverse problems for nonlinear equations, for example, nonlinear acoustic and elastic equations. No previous knowledge of Einstein's equations or Lorentzian geometry will be assumed.
Tuesday, June 24, 2025
10:00-11:00
HFG 707
AG Seminar
Giuseppe Ancona (IRMA Strasbourg)
16:00-17:00
HFG 611
MI Seminar
Max Blans
16:15-17:15
Utrecht University Hall
PhD defense Dusan Dragutinovic
Tuesday, July 1, 2025
10:00-11:00
HFG 707
AG Seminar
Maximilian Schimpf (University Heidelberg)
15:00-16:30
HFG707
Category Theory Seminar
TBA - TBA
TBA
Tuesday, July 8, 2025
10:00-11:00
HFG 707
AG Seminar
Arkadij Bojko (SIMIS and Fudan Uni.)
Thursday, July 10, 2025
14:15-15:15
Academiegebouw
PhD Defense Slade Sanderson
Tuesday, July 15, 2025
15:00-16:30
HFG707
Category Theory Seminar
TBA - TBA
TBA
Tuesday, July 29, 2025
15:00-16:30
HFG707
Category Theory Seminar
TBA - TBA
TBA
Tuesday, August 12, 2025
15:00-16:30
HFG707
Category Theory Seminar
TBA - TBA
TBA
Tuesday, August 26, 2025
15:00-16:30
HFG707
Category Theory Seminar
TBA - TBA
TBA
Tuesday, September 9, 2025
15:00-16:30
HFG707
Category Theory Seminar
TBA - TBA
TBA
Tuesday, September 16, 2025
14:15-15:15
PhD defense Boaz Moerman
Thursday, September 18, 2025
13:00-14:00
Applied mathematics seminar - Alef Sterk (RUG)
Host: Wioletta Ruszel 
Title: Extremes in dynamical systems: max-stable and max-semistable laws

Abstract:
Extreme value theory for chaotic, deterministic dynamical systems is a rapidly expanding area of research. Given a dynamical system and a real-valued observable defined on its state space, extreme value theory studies the limit probabilistic laws for asymptotically large values attained by the observable along orbits of the system. Under suitable mixing conditions the extreme value laws are the same as those for stochastic processes of i.i.d. random variables. 

Max-stable laws typically arise for probability distributions with regularly varying tails. However, in the context of dynamical systems, where the underlying invariant measure can be irregular, max-semistable distributions also have a natural place in studying extremal behaviour. In this talk I will first discuss a family of autoregressive processes with marginal distributions resembling the Cantor function. The resulting extreme value law can be proven to be a max-semistable distribution. Alternatively, we can describe the autoregressive process in terms of an iterated map with an invariant measure. Further examples of extreme value laws in dynamical systems are discussed as well.
Tuesday, September 23, 2025
15:00-16:30
HFG707
Category Theory Seminar
TBA - TBA
TBA
Monday, September 29, 2025
14:15-15:15
Academiegebouw
PhD Defense Yann Guggisberg
Tuesday, October 7, 2025
15:00-16:30
HFG707
Category Theory Seminar
TBA - TBA
TBA
Tuesday, October 21, 2025
15:00-16:30
HFG707
Category Theory Seminar
TBA - TBA
TBA
Tuesday, November 4, 2025
15:00-16:30
HFG707
Category Theory Seminar
TBA - TBA
TBA
Tuesday, November 18, 2025
15:00-16:30
HFG707
Category Theory Seminar
TBA - TBA
TBA