Namur Institute For Complex Systems

Federico Andres Stasyszyn (IATE & OAC, National University of Córdoba, Argentina)
2021-06-10 13:00 - 14:00 (Europe/Paris)
Title: Overview on Cosmic Magnetism Issues

We summarize some open questions around cosmic magnetic fields, from the theoretical and observational point of view. The use of Smoothed Particle Magneto Hydrodynamics (SPMHD) is getting nowadays more and more common to tackle these problems. From galaxy clusters to neutron stars, there are multiple applications already existing in the literature. I will quickly review some of the common methods used to evolve the MF, highlighting the successful approach of using vector potentials to describe them. Finally, I select a few applied astrophysical examples that will shed light on these issues in the near future.

Link to the seminar here
People outside Université de Namur with a Microsoft Teams account may join. For any questions, write to riccardo.muolo@unamur.be

Thomas Durt (Institut Fresnel, Ecole Centrale Marseille, France)
2021-06-03 13:00 - 14:00
Title: Applications of the Heisenberg-Weyl group to quantum state tomography with focus on dimensions 2 (quits) and 3 (qutrits)
Quantum state tomography aims at estimating an a priori unknown quantum state with maximal efficiency.The Heisenberg-Weyl group is obtained by composing phase-space displacements in position (translations) and momentum (boosts); it is a representation of the Galilei group. Heisenberg-Weyl displacement operators are intimately associated to the Wigner operators which are quantum localisation operators in phase-space. Mutually Unbiased Bases (MUBs) and Symmetric Informationally Complete POVMs (SICs) play a central role in relation with the tomographic applications associated to the aforementioned operators.Our goal is to define these objects, to describe the elegant symmetries and geometric structures associated to them, and to emphasize their relevance in the framework of quantum state tomography.
Link to the seminar here
People outside Université de Namur with a Microsoft Teams account may join. For any questions, write to riccardo.muolo@unamur.be

Horizon Europe by ADRE (event in French)
2021-05-25 12:30 - 13:15
Le nouveau programme-cadre de l’Union européenne pour la recherche et l’innovation “Horizon Europe” a été lancé depuis janvier 2021. Il représente un budget de 95 milliard € qui seront investis dans la recherche pour la période allant de 2021 à 2027.
Nous (ADRE) pensons que ce programme est une opportunité pour mettre en évidences les compétences de l’Université de Namur, en particulier celles de l’institut NAXYS. Nous proposons donc de vous en donner un aperçu et parcourir ensemble quelques opportunités pour NAXYS.
Points abordés :

Enjeux majeurs et nouveautés par rapport à Horizon 2020

Taux de financement des activités pour les Universités et autres partenaires

Au-delà de l’excellence scientifique, les autres aspects à prendre en compte pour une proposition réussie

Quelles opportunités pour NAXYS ?

Support ADRE et incitants institutionnels

La réunion aura lieu sur Teams le mardi 25/05 de 12h30 à 13h15 et sera accessible via ce lien

Carolina Charalambous (Université de Namur)
2021-05-20 13:00 - 14:00
Title: Dynamical analysis of resonant multi-planet systems
Throughout this seminar, I intend to cover some of the general problems observed in the extrasolar population as a consequence of their dynamical evolution.
For this purpose, I will first present some planetary features and discuss in which context the planets were formed to obtain the currently observed architectures.
The focus will be on systems with 3-planets. The interest comes after the discovery of the TRAPPIST-1 system.
To carry out this investigation, we used N-body numerical simulations to study in detail the evolution of planetary systems during the early stages of planet formation, that is, when there was still gas in the protoplanetary disk. We make dynamical maps from grids of initial conditions for systems with planets of different masses and compare the results of the N-body simulations with the analytical modeling to understand the evolutionary paths, on which parameters of the disk depend, and other physical characteristics. We dynamically analyze the TRAPPIST-1 planetary system that lies in a very complex resonant configuration. Results are consistent with the fact that systems were not formed in-situ but had to migrate to reach their current positions, without having to suppose ad-hoc dissipative effects, such as tidal effects by the star.

Link to the seminar here
People outside Université de Namur with a Microsoft Teams account may join. For any questions, write to riccardo.muolo@unamur.be

Ana Paula Millán Vidal (Amsterdam UMC, Netherlands)
2021-04-27 13:00 - 14:00
Title: Brain network models of epilepsy propagation and surgery
Clinical network neuroscience aims to apply the knowledge and tools from network science to study brain network topology in neurological and psychiatric diseases. This idea stems from the description of the brain as a complex network whose underlying structure and dynamics give rise to the emergent behaviour leading to cognition. How is this structure altered in different brain disorders [1]? And how can we apply this information to every-day clinical practice [2]? Here we will discuss the case of epilepsy, a neurological disorder that affects between 4 and 10 per 1000 people worldwide [3]. There is not one single cause of epilepsy: it often occurs as an associated symptom of an underlying disease, but many other times it is produced by unknown causes [4]. For patients who do not respond to medication (roughly 1 out of 3 people), epilepsy surgery is the treatment of choice if a focal origin can be found. However, seizure-freedom is currently achieved in only 2/3 of the patients after surgery. Brain networks in patients with epilepsy have been found to deviate significantly from the healthy brain, even when seizures have a local origin. In order to study how alterations in the underlying network and dynamics can lead and promote seizure propagation, computational models are used to mimic seizure generation and propagation. These allow us to test in silico different resections before the actual surgery, with the ultimate goal to improve surgery outcome and reduce side-effects. The choice of the network and dynamical model is the first step on this analysis. Simpler models allow for more computational tractability and theoretical analysis. In particular, we have modelled seizure propagation as an epidemic spreading process. Fitted with patient specific data, the model can capture the fundamental aspects of clinically observed seizure propagation, and can be used to test virtual resections in silico. Combined with optimization algorithms, smaller or alternative resection strategies, that are individually targeted for each patient, can be determined with the ultimate goal to improve surgery outcome.
[1] C. J. Stam. Nature Reviews Neuroscience 15.10 (2014), 683-695.
[2] L. Douw et al. Network Neuroscience 3.4 (2019), 969-993.
[3] P. N. Banerjee, D. Filippi, and W. A. Hauser. Epilepsy Research 85.1 (2009), 31-45.
[4] A. T. Berg et al. Epilepsia 51.4 (2010), 676-685.

Link to the seminar here
People outside Université de Namur with a Microsoft Teams account may join. For any questions, write to riccardo.muolo@unamur.be

Luca Gamberi (King's College London, UK)
2021-04-15 13:00 - 14:00
Title: Maximal modularity and the optimal size of parliaments: how big should your parliament be?
An important question in representative democracies is how to determine the optimal parliament size of a given country. According to an old conjecture, known as the cubic root law, there is a fairly universal power-law relation, with a 1/3 exponent, between the size of an elected parliament and the country’s population. Empirical data in modern European countries support such universality but are consistent with a larger exponent. In this seminar, I will introduce the audience to this intriguing regularity and discuss the current state of social science research on the topic. I will then move on to introducing our model, which is derived from fundamental complex network theory. We will see how modelling the population of a democratic country as a random network, drawn from a “clustered” growth model, enable us to determine an optimal number of constituencies – and thus of representatives – for a given population. In particular, I will briefly show how the modularity of the population can be calculated analytically and that its functional relation with the number of constituencies is strongly non-monotonic, exhibiting a maximum that depends on the population size. following a criterion of maximal modularity allows we are able to predict that the number of representatives and show that it naturally scales as a power-law in the size of the population – a finding that is qualitatively confirmed by the empirical analysis of real-world data.

Link to the seminar here
People outside Université de Namur with a Microsoft Teams account may join. For any questions, write to riccardo.muolo@unamur.be

Valentin Delchevalerie (Université de Namur)
2021-03-25 13:00 - 14:00
Title: Accelerating t-SNE using the Particle-Mesh Algorithm from Physics
t-Distributed Stochastic Neighbor Embedding (t-SNE) is a well-known dimensionality reduction technique used for the visualization of high-dimensional data. However, despite several improvements, t-SNE is not well-suited to handle large datasets. Indeed, for large datasets, the computation time required to obtain the visualizations is still too high to incorporate it in an interactive data exploration process. Since t-SNE can be seen as an N-body problem, this work presents a new variant of t-SNE based on a popular algorithm used in physics called Particle-Mesh (PM). The problem is solved by first computing a potential in space and deriving from it the force exerted on each body. As the potential can be computed efficiently using Fast Fourier Transforms (FFTs), this leads to a significant speed up.
Link to the seminar here
People outside Université de Namur with a Microsoft Teams account may join. For any questions, write to riccardo.muolo@unamur.be

François Lamoline (University of Luxembourg, Luxembourg)
2021-03-04 13:00 - 14:00
Title: Gene expression modelling from cell population snapshot data using optimal mass transport
Modelling gene expression is a central problem in systems biology. Accurate predictive models provide powerful tools for understanding cellular mechanisms and exploring the regulatory relations between genes. Perturbations of these regulatory structures affect the cellular functions. The ability to predict the effects of these perturbations is critical for finding sources of complex diseases and developing new treatments. Recently, single-cell techniques have enabled to perform sequencing at the level of individual cells for a large number of cells at a time. Unfortunately, the cells are destroyed in the measurement process, and so the data consist of population snapshots at different times. Traditional methods aim at modelling from time series data and cannot utilise the full information in the richer single-cell data. Therefore, these new sequencing techniques have raised the need of tailored computational methods for modelling the gene expression from single-cell data. In this talk we introduce new methods based on the 18th century problem of optimal mass transport. The idea consists in tracking the evolution of the distribution of cells over time and finding the dynamical system that minimises the transport cost between consecutive time points. The performance of the methods is compared in numerical experiments.
Link to the seminar here
People outside Université de Namur with a Microsoft Teams account may join. For any questions, write to riccardo.muolo@unamur.be

Maxime Lucas (Aix-Marseille University, France)
2021-02-18 13:00 - 14:00
Title: The cell cycle as a temporal network of protein interactions
Biological systems often operate over multiple timescales and their temporal organisation is often crucial to their functioning. The cell cycle illustrates this well: before dividing into two cells, the cell must go through 4 consecutive phases. Each of these phases corresponds to specific and well-timed physiological processes, driven by protein-protein interactions (PPIs), necessary to the cycle progression. Any deviation from this temporal organisation can indicate a change in cell fate, behaviour, or a malfunction which can lead to diseases. Identifying, predicting, and understanding this temporal organisation can thus yield important insight into their behaviour.
Here, we infer phases of the cell cycle by modelling it as a temporal network of protein-protein interactions and clustering the network’s snapshots. First, we build our temporal network by integrating time series of protein concentrations to a static PPI network. Second, we group snapshots at different times that have a similar structure by clustering them. We show that the obtained clusters recover the 4 known phases of the cell cycle. Moreover, we identify the temporal organisation across a range of timescales by clustering the snapshots for different number of clusters. Results are in agreement with biological knowledge, and we show how robust they are against method changes. Finally, we explore how the input time series affect the results. For example, we investigate the effect of having only partial temporal information in the networks, i.e. not for all edges, which is a common situation in biology. Finally, we show that gene expression data from RNA-seq, widely available for many biological systems, can be used too. This method can be used to further our understanding of the multiscale temporal organisation of many biological networks.
Link to the seminar here
People outside Université de Namur with a Microsoft Teams account may join. For any questions, write to riccardo.muolo@unamur.be

International Day of Women and Girls in Science at UNamur
2021-02-11 14:00 - 17:00
Join to the online scientific & outreach conferences held at UNamur in the framework of the International Day of Women and Girls in Science to attend the scientific presentations of two naXys members, Morgane Dumont and Anne-Sophie Libert.
The International Day of Women and Girls in Science takes place every 11th of February, following the declaration by the General Assembly of the United Nations on 22nd of December 2015. It aims at promoting the access of women and girls to science and technology as well as their full and fair participation. This event reminds the important role of women in the scientific community. It constitutes a great opportunity to encourage girls and young women to participate in scientific developments. This year, the University of Namur takes fully part in this day. In this context, a scientific conference [in English] will highlight the research contributions of women from UNamur and promote the interaction among them and our fellow colleagues.
Check out our invited speakers. The programme is available online: https://cds.unamur.be/activites/femmesenscience/university
Please take a minute to register (it’s free!) in order to help us in terms of logistics: https://www.billetweb.fr/womeninscience
In the evening, an outreach conference [in French] is organised in collaboration with Confluent des Savoirs: https://cds.unamur.be/activites/femmesenscience/public. Do not hesitate to spread the word, specifically to non-scientists and younger generations!
Looking forward to welcoming you to our conferences!
An initiative by Lorena Ballesteros Ferraz, Aishwarya Saxena, and Sébastien R. Mouchet from the Faculty of Sciences with the support of Confluent des Savoirs (CDS) and Unité d’Appui à la Recherche (UAR).

Rodrigo Martínez (University of the Balearic Islands, Spain)
2021-02-04 13:00 - 14:00
Title: Dynamical Phase Transitions in Quantum Reservoir Computing
Closed quantum systems may exhibit different dynamical regimes, such as Many-Body Localization or thermalization, that can affect their ability to process information. Specifically, we establish the role of dynamical phases of Ising spin networks in the field of quantum reservoir computing.
Reservoir computing is an unconventional computing paradigm that consists in exploiting classical or quantum dynamical systems to solve nonlinear and temporal tasks. We observe that the thermal phase of the spin model is naturally adapted to the requirements of reservoir computing while the localized phase is detrimental for the purposes of this computational approach, finding an improved performance for linear and mildly nonlinear tasks in the transition regime. We uncover the physical mechanisms behind optimal information processing capabilities of the spin networks, essential for future experimental implementations.

Link to the teams group “naXys Seminars” (unamur members) here
Link to the seminar here

Jean Teyssandier (Université de Namur)
2020-12-17 13:00 - 14:00
Title: An overview of astrophysical disc dynamics
Astrophysical discs appear at all scales in the Universe, from rings around planets to galactic discs. Despite the differences in scales and building blocks, they all share similar underlying physical processes. In this talk I will review some of these processes and explain the origin of certain features, such as the spiral arms of galaxies, the fine structures in the rings of Saturn, or the recent observations of gaseous discs where planetary systems are born.
Link to the teams group “naXys Seminars” (unamur members) here
Link to the seminar here

Greta Malaspina (University of Novi Sad, Serbia)
2020-12-03 13:00
Title: A modified Levenberg-Maquardt method for large scale network adjustment
We present a numerical optimization approach for the solution of large scale Network Adjustment Problems that arise in localization problems such as GPS positioning, surveying and large scale Wireless Sensors Networks localization. We consider a modification of Levenberg Marquardt method that attempts to deal with the non-convex nature of the objective function and the large number of variables.
At each iteration of the classical method the search direction is computed by solving a linear system of equations, which is an expensive procedure when the number of unknowns in the problem that we consider is large, and represents the major obstacle to the solution of realistic, large scale, problems. We develop a scheme for the decomposition of the linear system, which consist in computing an approximation of the Levenberg Marquardt direction by solving a number of independent linear systems of smaller size, and we propose a correction strategy of the right sides that improves the quality of the approximated direction while retaining separability of the linear systems. The convergence analysis of the resulting method is studied under standard regularity assumptions of the objective function. Moreover, the algorithm we propose is tested on realistic adjustment problems and compared with Levenberg Marquardt in terms of both accuracy and computational cost.
Link to the teams group “naXys Seminars” (unamur members) here
Link to the seminar here

Benedetta Franceschiello (University of Lausanne, Switzerland)
2020-11-19 13:00 - 14:00 | Online Event
Title: MIME – Magnetic resonance Imaging of the Moving Eye
Abstract: Vision is arguably the most important of our senses and it relies on the synchronous functioning of the eyes and the brain. These organs are highly interdependent: pathologies of the eyes can impact brain functionality [1], and brain impairments affect how the visual information is encoded at the eye-level [2], [3]. While nowadays ophthalmic biomedical devices are able to extract high-resolution anatomical measurements and behavioral measurements of the eyes, no technology is able to perform anatomical assessments of the eye while it moves, yet eye-movements are a behavioral readout encompassing valuable biomarkers in brain disorders [4], [5]. Magnetic Resonance Imaging (MRI) is a particularly promising non-invasive and versatile technique because it provides measurements related both to the tissue/organ structure and to the regional neural activity. However, the image artefacts arising from eye motion prevent the applicability of MR techniques to eye imaging, therefore impeding the investigation of the interplay between anatomical structures and their motion.
In this talk I will present our patented structural MRI protocol [6], [7] that allows dynamic acquisitions of the eye while it moves during quasi-naturalistic vision. To test the efficacy of this method, eye-movements and eye-axial lengths – as extracted from the MR images – were compared with eye-tracker measurements and optical biometry, respectively. This new non-invasive technology can estimate the rotation axes from the MR images with up to 97% accuracy with respect to the eye-tracker hardware. The high-resolution MRI scans of the human eye (1 mm3) – acquired during natural movement – permit to quantify the optical axial length with an accuracy having the same order of magnitude of the one obtained with ocular biometry. Finally, I will discuss the possible applications of this technique and the new frontiers it opens both in the field of ophthalmic MRI and vision neuroscience.
[1] Zheng, D. D. et al. Longitudinal Associations Between Visual Impairment and Cognitive Functioning. JAMA Ophthalmol. 136, 989 (2018).
[2] Ciuffreda, K. J. et al. Occurrence of oculomotor dysfunctions in acquired brain injury: A retrospective analysis. Optom. – J. Am. Optom. Assoc. 78, 155–161 (2007).
[3] DeBuc, D. C. et al. Seeing the Brain Through the Eye: What Is Next for Neuroimaging and Neurology Applications. in OCT and Imaging in Central Nervous System Diseases 55–82 (Springer International Publishing, 2020). doi: 10.1007/978-3-030-26269-3_5
[4] MacAskill, M. R. & Anderson, T. J. Eye movements in neurodegenerative diseases. Curr. Opin. Neurol. 29, 61–68 (2016).
[5] Anderson, T. J. & MacAskill, M. R. Eye movements in patients with neurodegenerative disorders. Nat. Rev. Neurol. 9, 74–85 (2013).
[6] Franceschiello, B. et al. 3-Dimensional magnetic resonance imaging of the freely moving human eye. Prog. Neurobiol. 101885 (2020). doi:10.1016/j.pneurobio.2020.101885
[7] Franceschiello, B. et al. WO2020178397 – Magnetic Resonance Imaging Methods and device. (2020). Available at: https://patentscope.wipo.int/search/en/detail.jsf?docId=WO2020178397&tab=PCTBIBLIO.
Benedetta Franceschiello
Laboratory for Investigative Neurophysiology,
Ophthalmology Department, Fondation Asile des aveugles, Lausanne, Switzerland
Radiology Department, University Hospital Center and University of Lausanne, Switzerland
Link to the teams group “naXys Seminars” (unamur members) here
Link to the seminar here

Delivering your presentation remotely by Principiae
2020-11-13 14:00 - 16:00 | Online Event
Abstract: When circumstances oblige you to deliver your presentation remotely from your office, your home, or even a hotel room, you face additional challenges, technological and otherwise. This remote lecture discusses and demonstrates the necessary adaptations to your tools, your environment, and your delivery so as to focus the attention of the audience, minimize distractions, and get your message across optimally.
Speaker: An engineer (UCLouvain) and PhD in applied physics (Stanford), Jean-luc Doumont is acclaimed worldwide for his no-nonsense approach, his highly applicable, often life-changing recommendations on a wide range of topics, and Trees, maps, and theorems, his book about “effective communication for rational minds.” For additional information, visit www.principiae.be.
Registration
Registration is free but mandatory through the following web form.
PhD students will receive a certificate with ECTS mention for their doctoral training.

Joseph O'Brien (MACSI, University of Limerick, Ireland)
2020-11-05 13:00 - 14:00 | Online Event
Title: Branching Processes and their Application to Popularity Dynamics
Abstract: Arising from a desire to understand the likelihood of a family name becoming extinct, branching processes have a rich history and have been shown to be applicable to a wide range of domains. The simplest description of these processes is the case where a parent has a random number of children during their lifetime who themselves proceed to have a similarly distributed number of children. In this talk I demonstrate how the processes may be used to describe social spreading phenomena whereby the parents are now online pieces of information (tweets, online threads, …) while their children correspond to interactions with these pieces (retweets, comments,…) and as such may represent social contagion dynamics. Two specific examples will be considered in detail, the first being a mathematical model of online spreading across multiple social media platforms and the effect said network structure has upon the dynamics [2]. Second, I will demonstrate how a branching process approach can allow a unified understanding of the well-studied Hawkes process (which has itself been shown to accurately describe social spreading features [3]) and may in fact allow one to make predictions regarding future dynamics of such processes [4].
[1] K. B. Athreya and P. E. Ney, Branching Processes (Springer Science + Business Media, New York, 2013).
[2] J. D. O’Brien, I. K. Dassios, and J. P. Gleeson. Spreading of memes on multiplex networks. New Journal of Physics, 21(2):025001, 2019.
[3] A. N. Medvedev, R. Lambiotte, and J.-C. Delvenne. The anatomy of Reddit: An overview of academic research. In Dynamics on and of Complex Networks, pages 183–204. Springer, 2017.
[4] J. D. O’Brien, A. Aleta, Y. Moreno, and J. P. Gleeson. Quantifying uncertainty in a predictive model for popularity dynamics. Physical Review E, 101(6):62311, 2020.

Link to the teams group “naXys Seminars” (unamur members) here
Link to the seminar here
For any problem with the links, write to riccardo.muolo@unamur.be

Principiae - POSTPONED
2020-05-14 14:00 - 16:00

Carlos Ordas (Université Laval, Canada) - POSTPONED
2020-04-30 13:00 - 14:00 | E25

Philippe Naveau (LSCE, Saclay) - POSTPONED
2020-04-23 13:00 - 14:00 | E25

Keven Bluteau (UGhent & HEC Montréal) - POSTPONED
2020-04-02 13:00 - 14:00 | E25
Title: The Concern in Climate Change News: A Driver of Flight-to-Green Investment Episodes?
Abstract: Climate change can have a negative economic, social, and environmental impact. Investors can help in fighting climate change is buying “Green” firms and selling “Brown” firms. Several studies, however, indicate that green assets underperform brown assets, therefore incurring a cost for being a green investor. The recent asset pricing model of Pastor et al. (2020), however, suggests that green assets can outperform brown assets when concern about climate change is unusually large among investors. We empirically study this result by deriving climate change concerns indices using news articles from highly read US newspapers. We evaluate if a high value of climate change concern is associated with a higher abnormal return of a green minus brown portfolio from the S&P 500 universe between 2003 to 2017. Overall, our results indicate that high (low) climate change concern implies higher (lower) abnormal returns in a green minus brown portfolio. Furthermore, we demonstrate that not all topics surrounding the climate change discussion in the media drive concern among investors.

Justin Buhendwa Nyenyezi (ISP-Bukavu, DRC) - POSTPONED
2020-03-26 13:00 - 14:00 | E25
Title: A Low-rank tensor based preconditioner for accelerating deformable 3D medical image registration
Abstract: Modeled as a variational problem, the deformable 3D image registration problem needs to solve a sequence of linear systems during the optimization process. Although these linear systems are sparse and structured, they are very large and ill conditioned. This leads to low convergence rate of the algorithms used to solve the problem or to inaccurate solutions.
Since it is observed that much of the time is spent in the solution of these linear systems, there is a need to provide efficient system solvers. Let N be the number of voxels in the image. Algorithms with linear complexity O(N ) based on fast Discrete Cosine Transforms or additive spliting operator are yet available. However, this linear complexity may be far too large for large 3D medical images. In our current study, we examine the contribution of a specific Low-rank preconditioner in a tensor-train format. We argue that, this preconditioner offers the most compromise between complexity and precision, since it allows to replace this linear
complexity by a logarithmic complexity O(log N ).
For this purpose, we first propose to use a compressed representation of data with a given accuracy ε using tensor train format. Then, within this tensor train format, we propose this low-rank preconditioner build with spectral information to speedup and stabilize the system solver. A benchmark of some registration algorithms on a large set of 3D medical images and different from their linear system solvers is provided. The benchmark relies on the perfomance profile based on the earlier decrease of the function value.

Jérôme Daquin (UNamur)
2020-03-12 13:00 - 14:00 | E22
Title: Aspects of the secular dynamics of terrestrial orbits
Abstract: The threat raised by space debris has vivified long-term studies of terrestrial orbits. To apprehend the motion on long time scales, the Astrodynamics community has translated, deployed and adapted many tools coming from Dynamical System theory and Celestial Mechanics: from the construction of effective averaged models more amenable to analytical and/or numerical investigations to the construction of resonant normal forms, including modern dynamical chaos indicator to visualise the template of the phase-space. Those efforts contributed to foster the `passive debris removal ideology’, where natural perturbations are ‘surfed’ rather than `counteracted’. In this talk, I will review and discuss some aspects of the long-term dynamics of terrestrial orbits, especially in the range of medium altitude. I will then present recent results obtained by the author and collaborators on the 2g+h lunisolar resonance where a (normally hyperbolic) manifold structure has been identified.

2020 international FRANCQUI Chair – Spatially extended systems
2020-02-19 16:30 - 18:30 | E25
Guest lecturer: Pr. Duccio Fanelli

2020 international FRANCQUI Chair – Impact of the noise
2020-02-18 16:30 - 18:30 | E25

Giovanni Reina (University of Sheffield, UK)
2020-02-18 13:00 - 14:00 | E25
Title: Collective Decision Making: From Bees to Robots via Multiscale Modelling
Abstract: I will give an overview of my studies on collective decision making in distributed systems of the last seven years. Such systems, found in biology, sociology, and engineering, are composed of a large number of interacting individuals that coordinate in order to reach a consensus. The main phases of the collective decision making process consist of identifying the available options, estimating their quality, and selecting the best option or any of them. I will present the main results of my research in understanding and designing each of these phases. Collective systems are inherently difficult to analyse as the stochastic nonlinear interactions between individuals can give rise to complex emergent dynamics. Therefore, I employ a collection of advanced techniques, commonly defined as multiscale modelling. Relying on a set of methods, rather than a single one, gives the benefit of having complementary techniques addressing one another’s limitations. In fact, through multiscale modelling, it is possible to analyse the systems at various levels of complexity and detail, from macroscopic group-level dynamics to microscopic individual-level behaviour, and from noise-free deterministic models to stochastic spatial descriptions. I finally shed a light on the recently developed opensource software for automated multiscale modelling.

William Polycarpe (IMCCE, France)
2020-02-17 11:00 - 12:00 | E25
Title: Iapetus, the key to the whole system ?
Abstract : Iapetus possesses all the attributes and characteristics of the whole system of Saturn. It is mysterious and very complex. In my doctoral study I have been runing numerical and semi-analytical simulations of a past mean motion resonance between Titan and Iapetus. The goal was to expose the consequences of a fast tidal migration for Titan and find an explanation for the eccentricity and the inclination of Iapetus’ orbit. The outcomes of simulations depend on the rate of migration and, consequently, there are constraints on the quality factor of Saturn at Titan’s frequency. The resonance allows Iapetus to pass from a circular orbit to an eccentric orbit and from its local Laplace plane to a tilted orbit. A few simulations show consistency in the orbital elements of Iapetus today.
A long semi-analytic expansion was performed to run fast simulations but alternative approaches can be taken. Inverting the order of Taylor and, eventually Fourier, expansions of the direct part of the disturbing function yields a series which is more suited to the resonance with Titan and the inclined orbit of Iapetus. More work is waiting to be done and the goal would be to obtain a universal formalism for the expansion.
The migration of Titan is becoming a reality today and, here again, further studies need to be carried out concerning, for example, the rotation of Iapetus.

2020 international FRANCQUI Chair - Master equation
2020-02-06 16:30 - 18:30 | E25

2020 international FRANCQUI Chair - Stochastic processes
2020-02-05 16:30 - 18:30 | E25

INAUGURAL FRANCQUI CHAIR LECTURE. Complex systems: physics beyond physics
2020-02-04 17:00 - 18:00 | E13, 8 Rempart de la Vierge, Namur, Belgium
Guest lecturer: Pr. Duccio Fanelli
Macroscopic order from microscopic disorder:
from endogenous noise to topology driven instability
More info: https://www.unamur.be/sciences/mathematique/chairfrancqui2020

EDT FNRS Doctoral School
2020-02-04 13:00 - 16:00 | E25
