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 timecritical 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 elevators process.
Considered separately, such sources of flexibility induce very different optimization models: multicriteria 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 hardcore model in the 2dimensional lattice 
Description: 
Juan Vera Lizcano The hardcore 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 hardcore 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 longstanding open problem to establish the critical fugacity t* for the hardcore gas model on the 2dimensional integer lattice Z^2. In particular, t* is the conjectured critical point for the phase transition between uniqueness of infinitevolume Gibbsmeasures on Z^2 when t < t* and nonuniqueness 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 selfavoiding 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 

