Discrete CATS Seminar
##
**
UNIVERSITY OF KENTUCKY **

DEPARTMENT OF MATHEMATICS COLLOQUIUM

####

#
"From tensegrities to distance geometry"

Professor Robert Connelly

Cornell University

###
Thursday, March 20, 2008

4:00 pm, 219 CB

Refreshments at 3:30 pm in 745 POT

####
Abstract:

Some years ago a young artist, Kenneth Snelson, connected some sticks
with string in such a way that they were rigidly held in place, as if
by magic. Since then he has made several large sculptures out of
large metal tubes and steel cables. Why do these structures hold
together? Secrets will be revealed. The key deals with things
called stress matrices. As a bonus, stress matrices can also be used
to determine when a configuration of points in space are determined
uniquely by some subset of their pairwise distances. Some models of
tensegrities will be shown, so the audience can test their integrity
themselves.

*
*

*
Bio of Robert Connelly
*

Robert Connelly is a professor at Cornell University who
specializes in discrete geometry with interests in rigid structures
and circle arrangements. He has held visiting positions at
I.H.E.S. in France, Syracuse, New York, University of Bielefeld in
Germany, Universite de Montreal, Canada, University of Seattle,
Washington, and Cambridge University, UK. He has proved some very
stunning results, including the first proof (with Erik Demaine and
Gunter Rote) of the Carpenter's Rule Conjecture (all embedded open
polygons in the plane can be continuously straightened without
overlap keeping the edge lengths fixed), the Kneser-Poulsen
Conjecture in the plane (with Karoly Bezdek) (if any finite
collection of circular disks in the plane are repositioned such
that their centers don't move apart, then the area of the union
does not decrease), and the first construction of a nonconvex
surface which flexes. A model of this is in the Smithsonian at the
National Museum of American History.