lunedi' - 08-03-2004 (17:00 - Sala Seminari) :

Yi Zhang University, P.R. China. Cardinal invariant of symmetric groups argomento: Logica Matematica abstract: In my talk I will present two cardinal invariants in Sym(N), namely the least cardinality of maximal cofinitary groups and the cofinality of Sym(N), which were generated from the work of J.Truss, P.Cameron, P.Neumann, D.Macpherson, S.Thomas and myself. I will discuss their possible cardinalities and order relationship, and I will ask several open questions in the area.

lunedi' - 08-03-2004 (14:30 - Sala Seminari del C. di Ricerca Mat. Ennio De Giorgi palazzo Puteano) : Joao Lopes-Dias, (Instituto Superior Tecnico Lisbona Portogallo) Multidimensional continued fractions, renormalisation and KAM theory argomento: Analisi Matematica abstract: We construct a renormalisation scheme for vector fields on the d-torus and Hamiltonian flows, based on a multidimensional continued fractions algorithm of a d-dimensional vector. The convergence of this renormalisation to a trivial limit set implies some results of Kolmogorov-Arnold-Moser (KAM) type for the stability of diophantine quasi-periodic motion.

mercoledi' - 10-03-2004 (15:30 - Sala Riunioni) : Simona Settepanella

Coomologia dei gruppi delle trecce pure generalizzati e fibra di argomento: Geometria abstract: In questo seminario ci proponiamo di definire gli arrangiamenti di iperpiani, con particolare attenzione agli arrangiamenti dati dagli iperpiani di riflessione definiti dai gruppi di Coxeter finiti. Descriveremo, inoltre, un complesso algebrico, noto come "complesso di Salvetti", e ne mostreremo l'applicazione al calcolo della coomologia dei gruppi delle trecce pure.Inoltre, per ciascuno di questi gruppi, mostreremo il legame tra la sua coomologia, la coomologia del complementare M dell'arrangiamento di iperpiani ad esso associato, e la coomologia della fibra di Milnor di M. Infine daremo i risultati fino ad ora noti su queste coomologie.

giovedi' - 11-03-2004 (11:00 - Sala Riunioni) : Salma Kuhlmann

Primes and Irreducibles in Integer Parts of Exponential Fields argomento: Logica Matematica

venerdi' - 12-03-2004 (09:15 - Pisa) : Convegno

Representation of semidefinite positive functions argomento: Geometria abstract: For the polynomial rings this is known as "The Hilbert 17th problem". We want to focus on the same problem on more general spaces, in particular algebras of differentiable functions. Research on this topics was developed using both arguments from analysis in the phase space and from real and complex analytic geometry, and we want to underline these relations. Some survey talks are also scheduled to give the state of the art from several points of view.

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Tentative program

Friday, March 12.

9.15-10.15 A.Prestel: Sums of squares of polynomial functions. 10.30-11.30 J.-M.Bony: Nonnegative functions as sums of squares: the C^infinity and C^k case. 11.45-12.45 C.Andradas: Sums of squares of analytic functions.

15.00-16.00 P.W.Michor: To be annonced. 16.15-17.15 K.Schmuegden: To be confirmed. 17.45-18.45 L.Migliorini: Some analytic problems in Hodge's Theory of singular varieties.

Saturday, March 13

9.15-10.15 J.-M.Bony: The Fefferman-Phong inequality. 10.30-11.30 J.Fernando: Some advances about the 17 Hilbert problem for global analytic functions. 11.45-12.45 D.Del Santo: The Fefferman-Phong inequality in the locally tempered Weyl calculus.

15.00-15.45 F.Pieroni: Sums of squares in Quasi-analytic Denjoy-Carlemann classes. 16.00-16.45 L.Pernazza: Writing C^k functions as sums of squares of C^h functions: examples and counterexamples. 17.15-18.15 A.Parmeggiani:A natural inequality for systems: Sharp-Garding or Fefferman-Phong?

sabato - 13-03-2004 (09:15 - Pisa) : convegno

Representation of semidefinite positive functions argomento: Geometria abstract:

Saturday, March 13

9.15-10.15 J.-M.Bony: The Fefferman-Phong inequality.

10.30-11.30 J.Fernando: Some advances about the 17 Hilbert problem for global analytic functions.

11.45-12.45 D.Del Santo: The Fefferman-Phong inequality in the locally tempered Weyl calculus.

15.00-15.45 F.Pieroni: Sums of squares in Quasi-analytic Denjoy-Carlemann classes.

16.00-16.45 L.Pernazza: Writing C^k functions as sums of squares of C^h functions: examples and counterexamples.

17.15-18.15 A.Parmeggiani:A natural inequality for systems: Sharp-Garding or Fefferman-Phong?

martedi' - 16-03-2004 (15:00 - Sala Riunioni) : Andras I. Stipsicz Ozsvath--Szabo invariants and contact structures argomento:non specificato abstract: The study of tight contact structures on closed 3-manifolds turned out to be a very effective way for understanding certain geometric properties of the 3-manifold at hand. In the lecture we show a way to find such structures and prove their tightness in some particular cases. For example, we show that the result of almost any rational surgery on a positive torus knot admits a tight contact structure. Tightness will be proved by applying contact invariants recently introduced by Ozsvath and Szabo

Giulia Curciarello Segreteria Didattica tel: 050-2213219 e-mail curciare@dm.unipi.it

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