Namur Institute For Complex Systems

Francesco Piazza (University of Orléans)
2017-04-25 13:00 - 14:00 (Europe/Paris) | Seminar room, Rempart de la Vierge 8, Namur, 1170
Title: Diffusion of small ligands in complex confining and reactive landscapes:
the geometry of chemoreception.
Abstract:
The rate constant that describes the diffusive encounter/reaction between a particle
and a large sphere can be computed easily by solving the stationary diffusion
(i.e. Laplace) equation for the particle density with appropriate boundary conditions
imposed on the surface of the sphere. In one classic, text-book example, this calculation is
used to estimate the binding rate constant of a ligand to a receptor-covered cell.
But what happens if the particles are diffusing in the presence of many reactive boundaries
of different strength (intrinsic reaction rate), which compete for the same ligands and amidst
a landscape of inert obstacles? In spite of the apparent overwhelming complexity, the same mathematical framework as the two-body problem can be used to solve the N-body problem exactly, by resorting to addition theorems for the appropriate fundamental solutions of the Laplace equation.
This powerful mathematical framework allows one to investigate fundamental issues
that are central in cell biology and modern nano-sciences, such as how the specific geometric
configurations of many reactive boundaries shape the overall reaction rate constant.
We will illustrate several examples, including applications to the study of ligand binding
to arrays of receptors on the surface of a cell and the action of many nano-catalysts embedded within a core-shell nano-reactor.

William Polycarpe (Paris Observatory)
2017-04-04 13:00 - 14:00 | Seminar room, Rempart de la Vierge 8, Namur, 1170
Title: Is Titan responsible for Iapetus’ orbit ?

Abstract: Latest astrometrical results on Saturnian moons show evidence for high migration rates (Lainey et al. 2012; 2016). The tidal dissipation in the planet is responsible for those large orbital expansions and should therefore be much stronger than usually expected. The idea of significant tidal dissipation in the massive core (Remus et al. 2012) and the convective envelope (Le Guenel et al. 2015; Fuller et al. 2016) of the planet has been brought forward as a likely explanation.
Nevertheless, high changes in semi-major axes of the moons shuffle up the ideas we had on the past evolution of the system of Saturn. In particular, depending on tidal mechanisms at play, several Mean Motion Resonances could have been crossed just a few million years ago.
In the frame of high tidal migration, we investigate the consequences of the past 5:1 mean motion resonance between Titan and Iapetus, which could have happened between 5 and 500 million years ago. Numerical simulations show that the most common outcome for Iapetus is to be ejected, as Titan migrates through the resonance. However, if Titan has a very high recession (Q <2000), Iapetus may survive the resonance and come out of it with an eccentricity consistent with today’s value. The effect on Iapetus’ inclination is still under investigation.

Hands-on session with GIT.
2017-03-30 08:00 - 17:00 | Brussels
The train to Brussels costs will be re-imbursed by Naxys. The training itself is free of charge. Agenda will be send around well in advance.
Registration is free vut mandatory on: http://doodle.com/poll/bdq4aetpkk6kav9w

Tarik Roukny (UGent)
2017-03-28 13:00 - 14:00 | Seminar room, Rempart de la Vierge 8, Namur, 1170
Title: Compressing Over-the-counter Markets

Abstract: In this talk, we show both theoretically and empirically that the size of over-the-counter (OTC) markets can be reduced without affecting individual net positions. First, we find that the networked nature of these markets generates an excess of notional obligations between the aggregate gross amount and the minimum amount required to satisfy each individual net position. Second, we show conditions under which such excess can be removed while preserving individual net positions. We refer to this operation as compression and identify feasibility and efficiency criteria, highlighting intermediation as the key element for excess levels. We show that a trade-off exists between the amount of notional that can be removed from the system and the conservation of trading relationships. Third, we apply our theoretical framework to a unique and comprehensive transaction-level dataset on OTC derivatives. We document large levels of excess across all markets and time. Finally, we show that compression – when applied at a global level – can reduce a considerable fraction of total notional even under relationship constrained approaches.

Ryota Kobayashi (NII, Tokyo): Inferring synaptic connections from spike data of multiple neurons
2017-03-21 11:00 - 12:00
Inferring synaptic connections from spike data of multiple neurons:
Abstract: Correlations in electric activity among neurons are defined as “functional connections”. It is still unclear how the functional connectivity is related to underlying (physiological) synaptic connectivity. Here, we develop a method for estimating synaptic connections from spike data of multiple neurons. Estimation performance of the proposed method was evaluated by using simulated data generated by a realistic cortical network model (Kitano & Fukai, 2007). This is joint work with Katsunori Kitano.
The meeting will take place at 11H00 in the 4th floor, Room Camille Joset (401).

Malbor Asllani (FNRS & NaXys)
2017-03-14 13:00 - 14:00 | Seminar room, Rempart de la Vierge 8, Namur, 1170
Title: Desynchronization of the Kuramoto oscillators. A neurostimulation method for controlling epilepsy seizures

Abstract:
Many coordination phenomena are based on a synchronization process, whose global behavior emerges from the interactions among the individual parts. Often in nature, such self-organized mechanism allows the system to behave as a whole and thus grounding its very first existence, or expected functioning, on such process. There are however cases where synchronization acts against the stability of the system; for instance in some neurodegenerative diseases or epilepsy or the famous case of Millennium Bridge where the crowd synchronization of the pedestrians seriously endangered the stability of the structure. In this talk we propose an innovative control method to tackle the synchronization process based on the application of the Hamiltonian control theory, by adding a small control term to the system we are able to impede the onset of the synchronisation. We illustrate the effectiveness of our method applying it to control the epileptic seizures.

Introduction to GIT
2017-03-09 08:00 - 17:00 | Namur
Contact Frederik de Laender (frederik.delaender@unamur.be) for details.
Registration is free, but mandatory on: http://doodle.com/poll/bdq4aetpkk6kav9w
Precise schedule to be confirmed.

Seminar of Melaine Saillenfest
2017-02-07 13:00 - 14:00 | Seminar room, Rempart de la Vierge 8, Namur, 1170
Affiliations: IMCCE – Observatoire de Paris and Dipartimento di Matematica – Università di Pisa
Titre : Secular representations for the long-term dynamics beyond Neptune
Abstract: I will present the development and the application of semi-analytical secular models, designed to describe generically the long-term dynamics of transneptunian objects. One-degree-of-freedom systems are obtained in both the non-resonant and resonant cases, allowing to represent every possible trajectory by the level curves of the Hamiltonian. The application to known objects reveals pathways to high perihelion distances. In particular, distant resonant objects can be tracked back to their resonance capture.

SQLfast : langage et environnement logiciel pour la manipulation de données par des utilisateur non experts
2016-11-08 12:00 - 13:00
