Speaker
Prof.
Pierre Desesquelles
(Universita’ di Paris Sud ( Orsay))
Description
Many physical systems evolve by brutal fragmentation or, on the contrary, by aggregation and coalescence. Unlike the processes of reactions at equilibrium (chemical reactions, nuclear fission, for example) that are well understood, the processes of fragmentation are often puzzling. In the nineties, great efforts have been invested in the frame of nuclear physics to describe and understand the process of nuclear multifragmentation. The statistical tools developed at this time are now spreading to many different domains including biology, geology, chemistry, matter physics etc.
The physical information on such fragmenting systems can be inferred from the probabilities of their partitions (that is the set of thesizes of all the fragments). These probabilities are also conditioned by the constraints of finite size or conservation and combinatorialconstraints related for example to the indistinguishablity of their constituents or the density of states of the fragments. We presentstatistical methods that discriminate physical correlations, carrying information on the system, from trivial correlations due to thecombinatorial constraints or conservation laws. This work has led us to solve exactly the model of Random Graphs. We show examples of applicative works, done in collaboration with different laboratories of the Paris-Sud Faculty of Sciences, that have led to the identification of physical effects from systems consisting of sets of nucleons (nuclear spinodale decomposition) of atoms (cluster fragmentation), of molecules (thermal clusters of H2O) and from the topology of insect nests (cubitermes).
NB:Anche se il titolo inquadra un agomento molto specifico , il seminario servira’ ad introdurre alcune delle le attivita’ che vengono svolte a Orsay nella Facolta’ di Scienze. E’ quindi destinato non solo ai colleghi ma anche agli studenti ( almeno quelli della Laurea Magistrale e del Dottorato ) al fine di offrire opportunita’ per nuove collaborazioni scientifiche e Tesi di Laurea Specialistiche e di Dottorato.
Seguira’ alle ore 11.15-11.30 un rinfresco che sara’ organizzato nella cucina del IV piano.
