mercoledi' 22-03-2006 (18:00) - Sala delle riunioni Davide Ferrario (Universita' di Milano Bicocca.) : Variational methods and symmetric orbits for the n-body problem.

Argomento: Analisi Matematica

Abstract: Periodic and quasi-periodic orbits for the $n$-body problem can be found as critical points of the action functional constrained to the space of equivariant loops. Without strong-force assumptions, existence and properties of symmetric collisionless (quasi-)periodic orbits can be proved to exist by such equivariant variational methods, provided the symmetry group fulfills some simple assumptions. As a consequence, global and local optimization numerical techniques can be used to determine and visualize approximations of such periodic orbits.

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giovedi' 23-03-2006 (11:00) - Sala Seminari Carlo Traverso (Dip. di Matematica - Pisa) :

INTRODUZIONE AI METODI ARITMETICI DELLA CRITTOGRAFIA

Argomenti:

Generalità sulla crittografia a chiave pubblica. Protocolli RSA e Diffie-Hellmann.

Algoritmi per la fattorizzazione: rho di Pollard, p-1 di Pollard,crivello quadratico.

Algoritmi per il logaritmo discreto: baby step-giant step, rho di Pollard, Pohlig-Hellmann, index calculus.

Curve ellittiche: fattorizzazione con curve ellittiche, Diffie-Hellmann su curve ellittiche.

Il corso consisterà in (presumibilmente) tre seminari di 90 minuti. L'orario successivo sarà deciso nella prima riunione (la seconda sarà probabilmente venerdì 24 alle 12 ma non si escludono cambiamenti).

E' possibile che vi sia una seconda serie di seminari con argomenti più avanzati (number field sieve, conteggio dei punti delle curve ellittiche, algoritmi per il logaritmo discreto sulle curve ellittiche, crittografia iperellittica) con inviti di specialisti.

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venerdi' 24-03-2006 (16:00) - Sala Riunioni Petar Popivanov (Institute of Mathematics, Bulgarian Academy of Sciences Bulgaria) :

Local properties of the solutions and characteristic Dirichlet problem for a class of degenerate parabolic operators

seminario PDE

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mercoledi' 29-03-2006 (24:00) - Sala Seminari Priska Jahnke (Bayreuth) :

Terminal Fano threefolds and their smoothings

Argomento: Geometria

Abstract:

Let X be a Gorenstein Fano threefold with at most canonical singularities. It is known, that there are only finitely many deformation families of such X, so one may ask for a complete classification as was done in thesmooth case by Iskovskikh, Mori and Mukai. An important question is under which conditions X arises as a degeneration of a smooth Fano threefold, and if that is the case, how X and its "smoothing" are related. In 1997 Namikawa proved the existence of a smoothing, if X has only terminal singularities, i.e., X is the special fiber of a flat family Z -> D with general fiber Z_t a smooth Fano threefold. Here Z is an irreducible complex space, not necessarily smooth. We show that the Picard groups of X and Z_t are isomorphic in the terminal case and give some examples concerning canonical singularities. Here a smoothing need notexist, and even if it exists, the Picard number may jump.

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Segreteria Didattica Giulia Curciarello tel- 050 2213219

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