
Benoît Naegel
Connected operators and maxtree in mathematical morphology
2 février 2023  09:00Salle de conférences IRMA
Mathematical morphology is a discipline that was developed in 1964 by Georges Matheron and Jean Serra, with the objective of characterizing and quantifying objects and structures in images by the means of sets, and more generally complete lattices. Since then, mathematical morphology can be seen as a convenient toolkit providing many operators to solve practical image processing problems. In this context, connected operators are a class of operators having the property to preserve image contours: a contour is either retained or removed, but cannot be moved.
In this talk, I will present hierarchical data structures enabling to design and compute efficiently connected operators. In particular, the maxtree, or componenttree, is a structure that is built from the levelsets of an image by storing in its nodes the connected components of the threshold sets and their inclusion relationship in its edges. On this basis, I will present an extension of this concept to color and multivalued images that we have called "componentgraph". I will also present some recent results in the field of semantic segmentation involving maxtrees, deeplearning and topological constraints. These concepts will be illustrated on biomedical applications.
The seminar will be also broadcasted via BBB: https://bbb.unistra.fr/b/hum51dsufmzq
Benoît Naegel is a professor in Computer Science. He obtained his PhD in the field of mathematical morphology applied to medical image analysis in 2004. From 2005 to 2007 he was a postdoctoral fellow at the University of Applied Sciences of Western Switzerland in Geneva where he worked on several biomedical projects in collaboration with the Hospital of Geneva. From 2007 to 2011 he was with the LORIA laboratory, Nancy, in the QGAR team dedicated to document processing. He is a member of ICube laboratory since 2011 where he conducts research in mathematical morphology and deep learning applied to biomedical imaging.

Pierre Guillot
Addition chains from computer science to astrochemistry
9 février 2023  09:00Salle de conférences IRMA
I will start with the wellknown subject of addition chains, which describe the best possible ways of raising an element to a certain power, in any group (or even monoid). These are used by all computer algebra packages, when you request them to compute a high power of a large matrix, for example. Then I will say a word about the more general problem of computing in other groups, facing questions such as: when A and B are matrices, how many multiplications do you need to compute ABABABABABABABABABABABABABABABAB ? (Answer: just 4.) Very little is known in general. Finally, I will explain how similar ideas can be used to describe the "assembly index" of any object, as was recently exploited by chemists. It turns out that the assembly index of molecules can be measured experimentally rather than computed, and this opens up the possibility of detecting the presence of life on other planets. Accordingly, the talk will end with pictures of aliens.
The seminar will be also broadcasted via BBB: https://bbb.unistra.fr/b/hum51dsufmzq
Pierre Guillot is a reader in mathematics at the university of Strasbourg, and a researcher at IRMA. He obtained his PhD at the university of Cambridge (UK) in 2004, was a postdoctoral fellow in Lille and Nice before being appointed lecturer at Strasbourg. His research interests include group cohomology, Galois theory, algebraic topology and computational algebra. 
Clément Stahl
A nonGaussian Universe?
16 mars 2023  09:00Salle de conférences IRMA
In this talk, I will present a (nonexhaustive) review of the stateoftheart of our current standard cosmological model. I will show how we manipulate stochastic (quasi)Gaussian random fields living on a curved spacetime and how we evolve them through cosmic history. I will then show that for the final stages of the cosmic evolution, when the evolution becomes too nonlinear, a numerical approach prevails. I will then present you how some of the (high performance computing) simulations that we are currently developing at the observatory, with nonGaussian initial conditions, could (perhaps) be a game changer for the field of galaxy formation.
The seminar will be also broadcasted via BBB: https://bbb.unistra.fr/b/hum51dsufmzq
Clément Stahl is a postdoc in the GALHECOS team at Strasbourg Observatory since 2021. He obtained his PhD at the University of La Sapienza (Rome) in 2017. Before, he was a postdoctoral fellow in Valparaiso (Chile) and at the Laboratoire Astroparticules & Cosmologie (APC, Paris). His research interests include inflation, large scale structure, dark matter and dark energy both from a theoretical and numerical point of view. 
Adrien Wanko
Ecological engineering and modelling for urban waters sustainable management
13 avril 2023  09:00Salle de conférences IRMA
L’Eau, ressource indispensable à la vie sur Terre, est de nos jours, sujette à de multiples pressions naturelles et anthropiques qui modifient voire altèrent ses états. Répondre en qualité et quantité aux besoins en eau de l’humanité sans nuire à la pérennité de la ressource et des écosystèmes nécessite une gestion intégrée à une échelle spatiale judicieusement déterminée. Face à l’urgence climatique inspirée des recommandations du GIEC (2013) et considérant l’accélération des transformations urbaines, les collectivités territoriales mènent de front des stratégies d’adaptation et d’atténuation. Ces stratégies intègrent l’implémentation des Solutions Fondées sur la Nature (SFN) qui sont des dispositifs relevant de l’ingénierie écologique. La compréhension de la trajectoire de ces SFN, des processus en jeu, de leurs fonctions écologiques et des services qu’elles offrent sont au cœur des recherches que je présenterais. Après des généralités, je ferai un focus sur différentes applications pour lesquels des modèles mathématiques ont permis de clarifier la compréhension des processus clés au sein des écosystèmes complexes.
Le séminaire sera retransmis par BBB : https://bbb.unistra.fr/b/hum51dsufmzq
Adrien Wanko est professeur en sciences de l’eau et génie de l’environnement à l’ENGEES, coresponsable de l’équipe Mécanique des Fluides d’ICube et animateur de la thématique « Eau & durabilité » de la Zone Atelier Environnemental Urbaine (Zaeu), labellisée par l'Institut écologie et environnement (INEE) du Centre national de la recherche scientifique (CNRS). Thèmes de recherche : transferts de matière en milieux poreux, modélisation du couplage hydrodynamique et transferts réactifs en ingénierie écologique, phytoremédiation des eaux, phytoremédiation des sols, hydrologie urbaine durable. 
Katarina Kraljic
Complete characterisation of the (largescale) structure of the Universe  Minkowski functionals
25 mai 2023  09:00Salle de conférences IRMA
Since their introduction into cosmology, Minkowski functionals have been applied to various problems regarding the morphology of the largescale structure of the Universe, but also the smallerscale objects such as galaxy clusters and dark matter halos. Minkowski functionals represent a complete family of morphological measures describing the content, shape and connectivity of the underlying density field. In this talk, I will give a short comprehensible introduction into integral geometry alongside the interpretation of the Minkowski functionals in 3 dimensional Euclidean space. I will then show some applications of all four Minkowski functionals in different configurations, namely the distribution of observed galaxies in our Universe, and the distribution of matter in simulations with different initial conditions or ingredients. These morphological descriptors incorporate correlations of arbitrary order and therefore provide a complementary look at largescale structure that could potentially reveal the presence of (primordial) nonGaussianities, but also provide constraints on poorly known baryonic processes such as stellar or black hole feedback.
The seminar will be also broadcasted via BBB: https://bbb.unistra.fr/b/hum51dsufmzq
Katarina Kraljic is a CNRS researcher in the GALHECOS team at Strasbourg Observatory since 2022. After finishing her PhD at CEASaclay in 2014, she moved to Marseille for a postdoctoral appointment. She then spent 3 years as a postdoctoral fellow at the Royal Observatory in Edinburgh, before returning to Marseille in 2020 and then Strasbourg in 2022. Her research focuses on the formation and evolution of galaxies, the largescale structure of the Universe, the internal structure of galaxies and their interstellar medium, with the aim to better understand the complete cosmic baryon cycle, both from a theoretical and observational perspective. 
Laure Marêché
Kinetically Constrained Models: Universality Results
15 juin 2023  09:00Salle de conférences IRMA
Kinetically constrained models are a class of mathematical models introduced by physicists to describe the behavior of glass. Each element of Z^2 is in state 0 or 1, and can change state at random times, but only when a constraint of the form "there are enough zeros around the element" is satisfied. There is an infinite number of possible constraints, and the properties of a model sharply depend on the constraint chosen. Therefore a very important question is that of universality: can this infinite number of models be divided into a finite number of classes depending on their behavior ? The answer is yes, and in this talk we will explain how.
The seminar will also be broadcasted online at https://bbb.unistra.fr/b/hum51dsufmzq
Laure Marêché has been an assistant professor in mathematics at Université de Strasbourg and a researcher at IRMA since 2020. She obtained her PhD in 2019 at Université Paris Diderot. After that, she did a postdoc at École Polytechnique Fédérale de Lausanne. She works in the field of probability, more precisely in statistical mechanics. 
Arthur Charguéraud
Interactive Program Verification
21 septembre 2023  09:00Salle de conférences IRMA
Formal Verification enables one to prove that a program does not contain any bug. In this talk, I will present stateoftheart techniques for formally verifying the implementation of a nontrivial algorithm or data structure. First, I will explain how to formulate as a mathematical theorem a statement of the form: "this program behaves as intended". Second, I will explain how to leverage an "interactive proof assistant", a tool for developing machinechecked mathematical proofs, for reasoning about the behavior of the source code of the program. Finally, I will give a survey of complex programs that have been formally verified in the past decade, assessing the progress made since the pioneering work by HoareFloydDijkstra in the late 60's.
The seminar will be also broadcasted via BBB: https://bbb.unistra.fr/b/hum51dsufmzq
Arthur Charguéraud is an Inria researcher, member of the ICube lab since 2016. He completed his PhD in 2010 at Inria ParisRocquencourt, then spent 18 months as a postdoc at the Max Plank Institute for Software Systems in Kaiserslautern. He was recruited at Inria Saclay in 2012, then moved to Strasbourg in 2016. His research is focused on program verification and program optimization. 
Xiaolin Zeng
The harmonic oscillator and the free field
19 octobre 2023  09:00Salle de conférences IRMA
In this talk we will discuss Euclidean Quantum Field Theory (EQFT) on the example of the harmonic oscillator. We will also explore a few classical probabilistic models, e.g. the free field and the OrnsteinUhlenbeck process.
The seminar will be broadcasted on BBB: https://bbb.unistra.fr/b/hum51dsufmzq
Xiaolin Zeng is a McF in mathematics at IRMA and maths department of the University of Strasbourg. He obtained his PhD at the University of Lyon 1 in 2015, was a postdoctoral fellow in TelAviv before being appointed in Strasbourg in 2018. His research interests include probability, statistics, and mathematical physics.

Florent Renaud
From stars to galaxies: modeling collisions in collisionless simulations
23 novembre 2023  09:00Salle de conférences IRMA
Star clusters are dense and old groups of stars held together by selfgravitation, typically orbiting around (larger and less dense) galaxies. They are actually amongst the densest and oldest astrophysical structures of the Universe. Formed more than 10 billion years ago, they have witnessed and survived all the steps along the evolution of the galaxies around which they orbit. Therefore, they constitute unique probes of the history of the Universe, and in particular of our home galaxy, the Milky Way. Yet, the improvement of the observational techniques and ressources of the last decade has revealed that decoding the story told by clusters is more challenging than previously thought. Numerical simulations to the rescue! This problem is however notoriously complex, being the posterchild example of a multiphysics and multiscale topic: up to 13 orders of magnitudes in time and spatial scales must be captured by simulations to reach a predictive nature. This multiscale bottleneck can be, somehow seamlessly, overcome with increased computational power. But the multiphysics aspect, where complex hydrodynamics must be solved jointly with starbystar gravitation is the real challenge. To date, no numerical technique allows to model jointly the formation and evolution of a star cluster together with its host galaxy, which hinders theoretical progress in this field. In this talk, after an introduction of the problem and the state of the art, I will present our curent efforts to add a collisional treatment in the Boltzmann equation to solve the starbystar dynamics within the dense star clusters, while maintaining a much faster collisionless and hydrodynamical description for the rest of the galaxy. I will illustrate how our new method paves the way to a new generation of astrophysical simulations, by tackling longlasting questions in the field.
The seminar will also be broadcasted on BBB at https://bbb.unistra.fr/b/hum51dsufmzq
Florent Renaud is a CNRS researcher in the GALHECOS team at Strasbourg Observatory since October 2023. After completing his PhD between Vienna and Strasbourg back in 2010, he moved to CEASaclay, Surrey (UK) and Lund (Sweden) for various postdoctoral appointments. He then became staff in Lund from 2019 to 2023. He recently obtained a fellowship from the Institute for Advanced Studies of the University of Strasbourg (USIAS) in 2023 and was concomitantly hired as a Research Director of the CNRS at Strasbourg Observatory. His research focuses on the formation and evolution of galaxies, their internal structure and their interstellar medium, with the aim to better understand the complete cosmic baryon cycle.

Paul Viville
Meshes: how to make them and what they are good for
21 décembre 2023  09:00Salle de conférences IRMA
Meshes have become ubiquitous in our modern times, from video game environments and CGI characters for cartoons, to high precision simulation of physical phenomena in science and engineering. In spite of their usefulness in this wide variety of fields, representing meshes and generating them can be challenging. Each field will have its own needs and criteria, its own data structure. This talk will go over the main types of representations for meshes, 2D and 3D, and how they are used in various industries. The main focus will then be on a specific hexahedral mesh generation method for objects that are represented by their skeleton, to show some of the challenges present and a solution offered.
The seminar will be also broadcasted via BBB: https://bbb.unistra.fr/b/hum51dsufmzq
Paul Viville is a postdoctoral researcher at the University of Strasbourg in the computer science department, and the ICube Laboratory in the computer graphics and geometry team (IGG). He graduated with a Ph.D at the same university in late 2022. His research focuses on geometric modeling, volumetric mesh generation, and animation.