Stanley's proof of the g-conjecture for
simplicial convex polytopes, parts I and II
29 Nov. & 6 Dec. 2011
- Title:
- Stanley's proof of the g-conjecture for
simplicial convex polytopes, parts I and II
- Speaker:
- Stavros Papadakis
- Abstract:
- For a simplicial complex D, the f-vector of D is
the finite sequence with entries the number of vertices,
1-faces, 2 faces, ... of D. For fixed n, the g-conjecture
characterizes the possible number of f-vectors for simplicial
complexes D triangulating the sphere $S^n$. We will sketch
Stanley's celebrated proof, using toric geometry and the
hard Lefschetz theorem, of the g-conjecture for the case
when D is the boundary of a simplicial convex polytope.
- References:
- Billera, Louis J.; Lee, Carl W., A proof of the sufficiency of
McMullen's conditions for $f$-vectors of simplicial convex polytopes.
J. Combin. Theory Ser. A 31 (1981), no. 3, 237-255.
Stanley, Richard P., The number of faces of a simplicial
convex polytope. Adv. in Math. 35 (1980), no. 3, 236-238.
Fulton, William, Introduction to toric varieties.
Annals of Mathematics Studies, 131.
The William H. Roever Lectures in Geometry.
Princeton University Press, Princeton, NJ, 1993. xii+157 pp.
ISBN: 0-691-00049-2
Existence of KAM tori for degenerate Hamiltonian Systems
22 Nov. 2011
- Title:
- Existence of KAM tori for degenerate Hamiltonian Systems
- Speaker:
- Hassan Najafi Alishah
- Abstract:
- I will start with a brief reminder of the talk I gave last semester, then try to explain the beautiful technic that been used to extend the results of non-degenerate systems to degenerate ones. I will state some facts from Riemannian geometry used in this technic and talk a bit about Whitney differentiability.
- References:
- Chong-Qing Cheng, Yi-Sui Sun, Existence of KAM tori in Degenerate Hamiltonian Systems. J. Differential Equations, 114-1 (1994), pp. 288-335
H. Whitney, Analytical extensions of differentiable functions defined in closed sets, Trans. Amer. Math. Soc. 36(1934), 63-89
***I can provide hard copies of the above papers upon request***
Natural (and less natural) deduction systems for classical (and less classical) logics
15 Nov. 2011
- Title:
- Natural (and less natural) deduction systems for classical (and less classical) logics
- Speaker:
- Marco Volpe
- Abstract:
- In this introductory talk, we will describe a calculus for logical reasoning called "natural deduction". We will present it in the case of classical logic and have a look at possible variants in order to capture some non-classical logics.
Stability of the Steiner symmetrization of convex sets
25 OCt. & 8 Nov. 2011
- Title:
- Stability of the Steiner symmetrization of convex sets
- Speaker:
- Filippo Cagnetti
- Abstract:
- The goal of the talk is the study
of the isoperimetric inequality
for the Steiner symmetrization in any codimension.
First, we give a characterization of the cases of equality.
Then, we will prove a quantitative version
of the inequality, in the case of convex sets.
This is a joint work with Marco Barchiesi and Nicola Fusco.
Open books and pseudo-Anosov maps II
18 Oct. 2011
Again, due to the informality of the seminar we will have the rest of Sinan's unfinished talk.
Open books and pseudo-Anosov maps I
Introduction to the McKay Correspondence II
4 Oct. 2011
Due to the informality of talks:-), we will continue with Stavros's unfinished talk.
This is a video which gives you an intuition about blowup that Stavros was talking about last week.
Introduction to the Mckey correspondenc I
27 Sept. 2011
- Title:
-
Introduction to the McKay Correspondence
- Speaker:
- Stavros Papadakis
- Abstract:
-
The talk will be a gentle introduction to the McKay correspondence. Let $\mathbb C$ be the field of complex numbers. In its simplest form, McKay correspondence relates for a finite subgroup $G\subset SL(2,\mathbb C)$ the geometry of the quotient space $\mathbb C^2 / G$ with the representation theory of $G$.
- References:
- Dolgachev, I., McKay correspondence, Lecture note is available
here.
Reid, M., La correspondance de McKay. Sêminaire Bourbaki,
Vol. 1999/2000. Astêrisque No. 276 (2002), 53-72. A copy is available
here
Closed forms on fiber bundles
20 Sept. 2011
- Title:
- Closed forms on fiber bundles
- Speaker:
- Olivier Brahic
- Abstract:
- Given a 3-form defined on the total space of a fibration, I will explain how to interpret geometrically the equations for it to be closed in geometric terms. Namely we have Courant algebroid structures defined fiberwise, and preserved by a higher analogue of a connection.
Hopf Algebras and Hopf-Galois Extensions
13 Sept. 2011
- Title:
- Hopf Algebras and Hopf-Galois Extensions
- Speaker:
- Marcin Szamotulski
- Abstract:
- I will deliver an introduction to Hopf algebras, Hopf-Galois extensions, and try to justify the notions. I will present some basic examples, and a way to present classical Galois theory in an 'extravagant' way. If time permits I'll try to present some of my results. Quite soon I will give a more advanced Version of this talk at UL.