Buffalo Geometry and Topology Seminar

Spring 2012

Unless noted, all seminars are Friday at 4pm, in Mathematics 122.

Date Speaker Organization Title Abstract

January 20th Milena Pabiniak Cornell University Lower bounds for Gromov width in the unitary and special orthogonal coadjoint orbits Every Lie group acts on the dual of its Lie algebra by the coadjoint action. It is known that the coadjoint orbits of that action are canonically symplectic manifolds. We investigate their Gromov widths using the notion of the Gelfand-Tsetlin system of action coordinates.

January 25th (WEDNESDAY, Room 250) Sang-hyun Kim KAIST Inclusions Between Right-angled Artin Groups Despite their simple presentations, Right-angled Artin groups (RAAGs) are known to have very rich subgroup structures. In particular, we study the question of when there exists an embedding from a RAAG into another RAAG. We give a combinatorial characterization when either (1) the target is two-dimensional, or (2) the source is a three-manifold group. Some interesting consequences are related with surface subgroups and RAAGs defined by cycles.
Key ingredients are Koberda's theorem on groups generated by high-powers of Dehn twists, and the action of pseudo-Anosov maps on the curve complex of a surface. This is a joint work with Thomas Koberda.

January 27th

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February 20th (MONDAY) Laurent Siebenmann Université de PARIS-SUD TBA

February 24th Jason DeBlois University of Pittsburgh Tessellations of hyperbolic surfaces A discrete set S in the plane canonically determines a Delaunay tessellation, a decomposition into convex polygons such that each has its vertices in S and is inscribed in a circle containing no other points of S. For some sets there are Delaunay polygons with "large aspect ratio" -- circumcircle radius much larger than some or all of their edge lengths -- and this may obstruct extracting geometric information about S from its Delaunay tessellation. In this talk I will describe a way of surmounting the aspect ratio problem by coarsening the tessellation and, time permitting, give some applications to the geometry of closed hyperbolic surfaces.

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March 26th No seminar (Spring break)

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April 13 Ian Biringer Yale TBA

April 17--19 (Myhill Lectures) Mladen Bestvina University of Utah TBA

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Old seminar pages:

Spring 2007

Fall 2007

Fall 2011

Last modified 21 November 2011

Date	Speaker	Organization	Title	Abstract
January 20th	Milena Pabiniak	Cornell University	Lower bounds for Gromov width in the unitary and special orthogonal coadjoint orbits	Every Lie group acts on the dual of its Lie algebra by the coadjoint action. It is known that the coadjoint orbits of that action are canonically symplectic manifolds. We investigate their Gromov widths using the notion of the Gelfand-Tsetlin system of action coordinates.
January 25th (WEDNESDAY, Room 250)	Sang-hyun Kim	KAIST	Inclusions Between Right-angled Artin Groups	Despite their simple presentations, Right-angled Artin groups (RAAGs) are known to have very rich subgroup structures. In particular, we study the question of when there exists an embedding from a RAAG into another RAAG. We give a combinatorial characterization when either (1) the target is two-dimensional, or (2) the source is a three-manifold group. Some interesting consequences are related with surface subgroups and RAAGs defined by cycles. Key ingredients are Koberda's theorem on groups generated by high-powers of Dehn twists, and the action of pseudo-Anosov maps on the curve complex of a surface. This is a joint work with Thomas Koberda.
January 27th
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February 20th (MONDAY)	Laurent Siebenmann	Université de PARIS-SUD	TBA
February 24th	Jason DeBlois	University of Pittsburgh	Tessellations of hyperbolic surfaces	A discrete set S in the plane canonically determines a Delaunay tessellation, a decomposition into convex polygons such that each has its vertices in S and is inscribed in a circle containing no other points of S. For some sets there are Delaunay polygons with "large aspect ratio" -- circumcircle radius much larger than some or all of their edge lengths -- and this may obstruct extracting geometric information about S from its Delaunay tessellation. In this talk I will describe a way of surmounting the aspect ratio problem by coarsening the tessellation and, time permitting, give some applications to the geometry of closed hyperbolic surfaces.
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March 26th	No seminar (Spring break)
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April 13	Ian Biringer	Yale	TBA
April 17--19 (Myhill Lectures)	Mladen Bestvina	University of Utah	TBA
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