One special feature for the Ricci flow in dimension 3 is the
Hamilton-Ivey estimate. The curvature pinching estimate provides a lot of
information about the ancient solution and plays a crucial role in the
singularity formation of the flow in dimension 3. We study the pinching
estimate on 3 dimensional expanding and 4 dimensional steady gradient Ricci
solitons. A sufficient condition for a 3-dimensional expanding soliton to
have positive curvature is established. This condition is satisfied by a
large class of conical expanders. As an application, we show that any
3-dimensional gradient Ricci expander C^2 asymptotic to certain cones is
rotationally symmetric. We also prove that the norm of the curvature tensor
is bounded by the scalar curvature on 4 dimensional non Ricci flat steady
soliton singularity model and derive a quantitative lower bound of the
curvature operator for 4-dimensional steady solitons with linear scalar
curvature decay and proper potential function. This talk is based on a joint
work with Zilu Ma and Yongjia Zhang.

A 7D minimal and locally-stable hypersurface will in general have a discrete singular set, provided it has no singularities modeled on a union of half-planes. We show in this talk that the geometry/topology/singular set of these surfaces has uniform control, in the following sense: if $M_i$ is a sequence of 7D minimal hypersurfaces with uniformly bounded index and area, and discrete singular set, then up to a subsequence all the $M_i$ are bi-Lipschitz equivalent, with uniform Lipschitz bounds on the maps. As a consequence, we prove the space of $C^2$ embedded minimal hypersurfaces in a fixed $8$-manifold, having index $\leq I$, area $\leq \Lambda$, and discrete singular set, divides into finitely-many diffeomorphism types.

Asymptotically conical Calabi-Yau manifolds are non-compact Ricci-flat Kähler manifolds that are modeled on a Ricci-flat Kähler cone at infinity. I will present a classification result for such manifolds. This is joint work with Hans-Joachim Hein (Fordham/Muenster).

Understanding moduli spaces is one of the central questions in
algebraic geometry. This talk will survey one of the main aspects of
research in moduli theory — the compactification problem. Roughly speaking,
most naturally occurring moduli spaces are not compact and so the goal is to
come up with geometrically meaningful compactifications. We will begin by
looking at the case of algebraic curves (i.e. Riemann surfaces) and progress
to higher dimensions, where the theory is usually divided into three main
categories: general type (i.e. negatively curved), Calabi-Yau (i.e. flat),
and Fano (i.e. positively curved, where the theory is connected to the
existence of KE metrics). Time permitting, we will use this motivation to
discuss moduli spaces of K3 surfaces (simply connected compact complex
surfaces with a no-where vanishing holomorphic 2-form).

(A joint seminar with the Geometry & Topology Seminar series.)