]
Abstract: The goal of this thesis is to relate the
projection diagram of a knot or link in S3 to the
geometry and
topology of the link complement. We use the diagram of a link K to
obtain a Dehn surgery description
of K from a hyperbolic link L. The simple geometry of S3-L
allows us to decompose it into ideal hyperbolic polyhedra, whose dihedral angles provide a lot of
combinatorial information. One consequence of this approach is a mild condition on the original
diagram that ensures K is hyperbolic and all its non-trivial Dehn fillings are hyperbolike.
Another, closely related, consequence is a diagrammatic lower bound on the genus of K.
(See [2].)
When K is an arborescent link, we use the correspondence between the link and a
weighted tree to simplify the projection diagram into a particularly nice form. This simplified
diagram then allows us to subdivide the link complement into hyperbolic polyhedra and tetrahedra
whose dihedral angles fit together in a consistent fashion. An angled decomposition of this type
implies that K is hyperbolic and provides a robust combinatorial framework for more
detailed investigations into its geometry.
Links with no exceptional surgeries. With
Jessica Purcell (2004).
[PS],
[PDF],
[ArXiv].
Abstract: If Thurston's Geometrization Conjecture is
true, then a closed 3-manifold is hyperbolic whenever it satisfies a
topological condition, called "hyperbolike". This paper proves a
mild diagrammatic condition on a knot or link in S3
under which any
non-trivial Dehn filling gives a hyperbolike closed manifold. For a
knot K, a non-trivial Dehn filling of K will be hyperbolike
whenever a prime, twist-reduced diagram of K has at least 4 twist
regions and at least 6 crossings per twist region; the statement for
links is similar.
We prove this result using two arguments, one geometric and one
combinatorial. The combinatorial argument also proves that every
link with at least 2 twist regions and at least 6 crossings per
twist region is hyperbolic and gives a lower bound for the genus of a link..
Involutions of knots that fix unknotting tunnels (2004).
[PS],
[PDF],
[ArXiv].
Abstract: Let K be a knot that has an unknotting tunnel
tau. This paper proves that K admits a strong involution that
fixes tau pointwise if and only if K is a two-bridge knot and
tau its upper or lower tunnel. One result obtained along the way is
a version of the Smith conjecture for handlebodies: the fixed-point
set of an orientation-preserving, periodic diffeomorphism of a
handlebody is either empty or boundary-parallel.
Cost-minimizing networks among immiscible fluids in R2. With
Andrei Gnepp, David McMath,
Brian Munson,
Ting Ng,
Sang-Hyoun Pahk, and
Cara Yoder.
Pacific Journal of Mathematics 196 (2000), no. 2, 395-414.
[PS],
[PDF],
[Web].
Abstract: We model interfaces between immiscible fluids
as cost-minimizing networks, where "cost" is a weighted length. We
consider conjectured necessary and sufficient conditions for when a planar
cone is minimizing. In some cases we give a proof; in other cases we
provide a counterexample.