Homepage
Research
Teaching
News
Personal
Photos

Research Papers

Dave Futer

  1. Angled Triangulations of Link Complements. Ph.D. Thesis (2005). [PDF]

    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.

  2. 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..

  3. 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.

  4. 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.


[Home] [Research] [Teaching] [News] [Personal] [Photos]

dfuter at math stanford edu
Last modified: Tue Apr 19 18:15:42 PDT 2005