Stabilizing Heegaard splittings of toroidal 3-manifolds

Let $T$ be a separating incompressible torus in a 3-manifold $M$. Assuming that a genus $g$ Heegaard splitting $V \cup_S W$ can be positioned nicely with respect to $T$ (e.g. $V \cup_S W$ is strongly irreducible), we obtain an upper bound on the number of stabilizations required for $V \cup_S W$ to become isotopic to a Heegaard splitting which is an amalgamation along $T$. In particular, if $T$ is a canonical torus in the JSJ decomposition of $M$, then the number of necessary stabilizations is at most $4g-4$. As a corollary, this establishes an upper bound on the number of stabilizations required for $V \cup_S W$ and any Heegaard splitting obtained by a Dehn twist of $V \cup_S W$ along $T$ to become isotopic.Comment: 21 pages, 18 figures. Version for publication. Generalization of the main theorem and minor changes in style and forma

Degeneration of Heegaard genus, a survey

We survey known (and unknown) results about the behavior of Heegaard genus of 3-manifolds constructed via various gluings. The constructions we consider are (1) gluing together two 3-manifolds with incompressible boundary, (2) gluing together the boundary components of surface times I, and (3) gluing a handlebody to the boundary of a 3-manifold. We detail those cases in which it is known when the Heegaard genus is less than what is expected after gluing.Comment: This is the version published by Geometry & Topology Monographs on 3 December 200

Lengths of Geodesics on Klein’s Quartic Curve

A well-known and much studied Riemann surface is Klein’s quartic curve. This surface is interesting since it is the smallest complex curve with maximal symmetry. In addition to this high degree of symmetry, Klein’s quartic curve can be tiled by triangles,giving rise to a tiling group generated by reflections. Using the tiling group and the universal cover of the tiling group we are able to compile a list of the lengths of the short,simple,closed geodesics on this surface. In particular,w e are able to determine whether the geodesic loops generated by the tiling are the systoles,i.e.,the shortest closed geodesics

Learning that Matters is Messy: Experiments Revealing Hidden Potential in Higher Education

Why are some learning experiences so profound that they alter our worlds, whereas others don’t end up sticking at all? The author investigates this question in the context of undergraduate education, recounting several educational experiments that highlight subtle but powerful aspects of the student learning experience. By exploring a different approach to teaching a math course, an alternative framework for academic specialization instead of traditional majors, and a radical approach to designing new institutions, an encounter with the hidden, ontological dimension of learning becomes possible. Accessing the ontological experience of the learner opens up new possibilities for meaningful, deep, and transformative learning experiences in higher education

Stabilization, amalgamation, and curves of intersection of Heegaard splittings

We address a special case of the Stabilization Problem for Heegaard splittings, establishing an upper bound on the number of stabilizations required to make a Heegaard splitting of a Haken 3-manifold isotopic to an amalgamation along an essential surface. As a consequence we show that for any positive integer $n$ there are 3-manifolds containing an essential torus and a Heegaard splitting such that the torus and splitting surface must intersect in at least $n$ simple closed curves. These give the first examples of lower bounds on the minimum number of curves of intersection between an essential surface and a Heegaard surface that are greater than one.Comment: Version for publication. To appear in Algebraic and Geometric Topolog