The asymptotic dimension of metric spaces is an important notion in geometric group theory. The metric spaces considered in this talk are the ones whose underlying spaces are the vertex-sets of (edge-)weighted graphs and whose metrics are the distance functions in weighted graphs. A standard compactness argument shows that it suffices to consider the asymptotic dimension of classes of finite weighted graphs. We prove that the asymptotic dimension of any minor-closed family of weighted graphs, any class of weighted graphs of bounded tree-width, and any class of graphs of bounded layered tree-width are at most 2, 1, and 2, respectively. The first result solves a question of Fujiwara and Papasoglu; the second and third results solve a number of questions of Bonamy, Bousquet, Esperet, Groenland, Pirot and Scott. These bounds for asymptotic dimension are optimal and generalize and improve some results in the literature, including results for Riemann surfaces and Cayley graphs of groups with a forbidden minor.

The problem of finding minimal free resolutions of monomial ideals in polynomial rings has been central to commutative algebra ever since Kaplansky raised the problem in the 1960s and his student, Diana Taylor, produced the first general construction in 1966. The ultimate goal along these lines is a construction of free resolutions that is universal -- that is, valid for arbitrary monomial ideals -- canonical, combinatorial, and minimal. This talk describes a solution to the problem valid in characteristic 0 and almost all positive characteristics.

This talk is based on joint work with Sala Lamboglia and Faye Pasley Simon. During the first part of the talk we will focus on the tropical convex hull of convex sets and polyhedral complexes. We will introduce results on the tropical convex hull of a line segment and a ray, show that for sets in two dimensions tropical convex hull and ordinary convex hull commute, and give a characterization of tropically convex polyhedra. In the second part of the talk we will use these results to show that the dimension of a tropically convex fan depends on the coordinates of its rays and give a lower bound on the degree of a fan tropical curve using only tropical techniques. The talk will be based on the work in this paper: https://arxiv.org/abs/1912.01253v2.