Décembre 2017

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Vendredi 1 Décembre
Heure: 10:00 - 13:00
Lieu: TBA
Résumé: [soutenance]
Description: Thomas Rubiano
Heure: 14:30 - 17:00
Lieu: Amphi Fermat, Université de Villetaneuse
Résumé: [Soutenance] Types inductifs, fonctionnels et non-linéaires en ludique
Description: Alice Pavaux
Lundi 4 Décembre
Heure: 15:00 - 16:00
Lieu: Salle A303, bâtiment A, campus de Villetaneuse
Résumé: Séminaire SV : Hiba Ouni
Description: Hiba Ouni
Titre : Parallel Symbolic Observation Graph

Model checking is a powerful technique for verifying and analyzing complex systems in many application fields. The analysis process of complex and concurrent systems often requires large computation resources which represents a real challenge. Even with simple configurations, the well-known state explosion problem is faced as the generated state space of such systems grows exponentially with the number of the system components. Numerous methods and techniques have been developed to overcome this problem including parallel and distributed-memory processing. In this work, we aim at improving the performances of the so called Symbolic Observation Graph (SOG) construction by using parallelization techniques. A SOG is a hybrid structure where the transitions of a system are divided into observed and unobserved ones. The nodes of this graph are then defined as sets of states linked with unobserved transitions (and encoded symbolically with a BDD) and edges are labeled with observed transitions only (and are explicitly represented). We propose two parallel algorithms to build the SOG. The first algorithm is dedicated for shared memory architectures, and is based on the distribution of the SOG construction on several threads using a dynamic load balancing scheme. The second algorithm is proposed for distributed memory architectures, and distributes the SOG construction on processes using a static load balancing scheme.
These two algorithms are implemented and their performances are studied and compared to each other and to the sequential construction of the SOG.
Mardi 5 Décembre
Heure: 12:45 - 15:30
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: soutenance de thèse
Description: Quentin de Mourgues
Mercredi 6 Décembre
Heure: 10:00 - 13:00
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Axel Bacher, Kilian Raschel, Arvind Singh et Niccolò Torri
Description: Journée mathstic
Vendredi 8 Décembre
Heure: 14:00 - 17:00
Lieu: TBA
Résumé: Réduction et Approximations Linéaires
Description: Luc Pellissier TBA
Mardi 12 Décembre
Heure: 14:00 - 17:00
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Analysis of the Brun GCD Algorithm. TBA
Description: Loïck Lhote
Heure: 15:00 - 18:00
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: A graph-based method to randomly generate subgroups of free groups
Description: Pascal Weil The study of random algebraic objects sheds a different light on these objects, which complements the algebraic and the algorithmic points of view. When it comes to finitely generated subgroups of free groups, we have a remarkable graphical representation calledthe Stallings graph: the Stallings graph of a subgroup H is a finite labeled graph uniquely associated with H, efficiently computed from a set of generators of H (say, given as reduced words), and from which one can efficiently compute many invariants of H.I will discuss enumerating and randomly generating finitely generated subgroups of free groups, for the distribution given by Stallings graphs: for each positive integer n, one considers the finite number of subgroups whose Stallings graph has n vertices, and oneconsiders the uniform distribution on that set. This requires understanding the combinatorial structure of Stallings graphs, which are interesting objects per se. I will also exhibit natural properties of subgroups which are `generic' for this distribution.This is joint work with F. Bassino (LIPN) and C. Nicaud (LIGM)
Jeudi 14 Décembre
Heure: 12:15 - 13:30
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Flots de liens pour la modélisation des interactions temporelles
Description: Matthieu Latapy Etudier la structure et la dynamique des interactions revêt un caractère crucial pour la compréhension de nombreux phénomènes et pour de nombreuses applications (détection d'événements dans du trafic, détection de fraudes, recommandation de produits, optimisation de réseaux, etc). La structure de telles interactions est étudiée en utilisant des graphes ou des réseaux (ensembles de noeuds et de liens) ; leur dynamique est étudiée en utilisant des signaux ou des séries temporelles (variations d'une propriété au cours du temps) ; pour étudier la dynamique de leur structure, on utilise des séquences de graphes. Toutefois, ces approches ne capturent que de façon très limitée la nature à la fois structurelle et temporelle des interactions, qui nécessite un cadre spécifique. Nous présentons ici une généralisation des graphes, que nous appelons des flots de liens, permettant un traitement cohérent des deux aspects. Nous obtenons un langage pour l'étude directe des séquences d'interactions, similaire à celui des graphes pour l'étude des relations.
Vendredi 15 Décembre
Heure: 11:00 - 14:00
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Soutenance d'HDR: Computer algebra for lattice path combinatorics
Description: Alin Bostan
Lundi 18 Décembre
Heure: 12:30 - 14:00
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Semantic similarity on transcriptional regulation literature
Description: Oscar Lithgow Experimentally generated biological information needs to be organized and structured in order to become meaningful knowledge. However, the rate at which new information is being published makes manual curation increasingly unable to cope. Therefore, new curation strategies based on natural language processing are promising alternatives.

Particularly, nowadays is improbable to consider all related research and reference every single piece of knowledge contained in the publication. Here is where we believe that computers and specifically, automatic natural language processing can help to inter-connect similar conveyed ideas among a collection of articles through discover ing semantically related sentences within a set of scientific articles and delivering those meaningful relations to the end user.

Given our interest in applying such approaches to the benefit of curation of the biomedical literature, specifically about gene regulation in microbial organisms, we decided to also build a corpus with graded textual similarity evaluated by curators, and designed specifically oriented to our purposes.
Mardi 19 Décembre
Heure: 12:30 - 13:30
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Characterization of the Flexibility of an Energy Consumer and Optimization of its Energy Usage
Description: Claude Le Pape The exploitation of flexibility in energy production and consumption is essential to avoid costly reinforcements of the power system and maintain security of supply while increasing the penetration of renewable (and intermittent) sources of energy. Let us focus on the "demand" side, i.e., on actors which are mostly consumers of energy: manufacturing plants, water networks, commercial buildings (or even elements in a building such as an HVAC (Heating, Ventilation and Air Conditioning) system, an elevator or a pool of elevators), and aggregations of those, such as a district. These actors use energy for their own needs, i.e., manufacture and deliver products to their own customers, deliver drinkable water to their customers, provide a comfortable work place to the employees and visitors of the building, etc. They may also produce energy, either as part of the process they manage (e.g., cogeneration in an industrial plant, elevator braking energy recovery) or with energy product
ion resources installed for cost reduction and security reasons. Finally, they may also have energy storage resources, which could have been installed to build flexibility or for any other reason. Part or all of the stored energy capacity can then be used to reduce operational costs.

Incentives to reduce or shift energy consumption in time must be considered with respect to the main objectives (and other cost factors) of the consuming organization. The very first thing to do is to characterize the available or potential sources of flexibility and how they could be used to make gains in terms of energy, revenues and cost savings, or environmental impact.

• First, there may exist options for definitive savings of energy with no significant impact on the process for which the energy is used. In general, such savings will be doable provided they have an "acceptable" impact on the process or on its outcome. For example, the capacity to slightly dim lights in an elevator enables direct and definitive energy savings. Such dimming is acceptable if it does not occur too often.
• Delays in consumption are possible when a given activity can be delayed (or performed in advance) or, more generally, when savings are possible at a given time but at the expense of further consumption before or after this time. For example, if enough water is available in a water tower, one can delay for a while the pumping of water into the water tower. At some point, however, pumping will be needed to ensure the water tower gets enough water to serve the local customers. Similarly, highly consuming activities in a manufacturing plant might be avoided during a given interval of time, provided these activities are not time-critical and the corresponding products are available in stock. At some point, however, it will become necessary to perform these activities, and consume the corresponding amount of energy to replenish the stock.
• If energy storage (e.g., in batteries, in the form of hot water, etc.) is possible, then the stored energy can be used to provide an apparent consumption flexibility. For example, part of the energy stored in the battery of an elevator can be used to temporarily operate the elevator with no other impact on the elevator’s process.

Considered separately, such sources of flexibility induce very different optimization models: multi-criteria regulation; scheduling with energy resource constraints and costs; energy flow optimization. Things get more complex when these sources of flexibility coexist and when multiple actors, each with its own constraints and objectives, share the same energy network. Practical optimization problems will be presented, using examples from two European projects (Arrowhead and Ambassador) and from the two PhD theses of Chloé Desdouits "Reduction of electricity consumption peaks and optimization problems induced on the demand side" and Peter Pflaum "Energy management strategies for smart grids".
Heure: 14:00 - 17:00
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Phase transition for the hard-core model in the 2-dimensional lattice
Description: Juan Vera Lizcano The hard-core gas model is a natural combinatorial problem that has played an important role in the design of new approximate counting algorithms and for understanding computational connections to statistical physics phase transitions. For a graph G = (V, E) and afugacity t > 0, the hard-core model is defined on the set of independent sets of G where each independent set I has weight w(I) = |I|^t . The equilibrium state of the system is described by the Gibbs distribution in which each independent set I has probability ~w(I). A long-standing open problem to establish the critical fugacity t* for the hard-core gas model on the 2-dimensional integer lattice Z^2. In particular, t* is the conjectured critical point for the phase transition between uniqueness of infinite-volume Gibbsmeasures on Z^2 when t < t* and non-uniqueness when t > t*. Empirical results identified the critical point t* ~ 3.79. The best known bounds show 2.538 < t* < 5.3646.In this talk the techniques to obtain these bounds will be discussed. Special emphasis will be given to the lower bound, which is based on connections between the decay of correlations on the lattice and on its self-avoiding walk tree.
Heure: 15:30 - 18:30
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: pot de clôture, agrémenté de gâteaux et de False Beliefs in mathematics
Description: thé combinatoire