Engineering analysis should match an underlying designed shape and not restrict the quality of the shape. I.e. one would like finite elements matching the geometric space optimized for generically good shape. Since the 1980s, classic tensor-product splines have been used both to define good shape geometry and analysis functions (finite elements) on the geometry. Polyhedral-net splines (PnS) generalize tensor-product splines by allowing additional control net patterns required for free-form surfaces: isotropic patterns, such as n quads surrounding a vertex, an n-gon surrounded by quads, polar configurations where many triangles join, and preferred direction patterns, that adjust parameter line density, such as T-junctions. PnS2 generalize C1 bi-2 splines, generate C1 surfaces and can be output bi-3 Bezier pieces. There are two instances of PnS2 in the public domain: a Blender add-on and a ToMS distribution with output in several formats. PnS3 generalize C2 bi-3 splines for high-end design. PnS generalize the use of higher-order isoparametric approach from tensor-product splines. A web interface offers solving elliptic PDEs on PnS2 surfaces and using PnS2 finite elements.[-]

Real-analytic manifolds are studied very much in the last century until the time when people found the partition of unity on smooth manifolds makes the manifold theory very tractable. The group of real-analytic diffeomorphisms is the natural automorphism group of the real-analytic manifold. Because of the analytic continuation, there are no partition of unity by functions with support in balls. The germ at a point of a real-analytic diffeomorphism determines the diffeomorphism and hence the group of them looks rigid. However, the group of real-analytic diffeomorphisms is dense in the group of smooth diffeomorphisms and diffeomorphisms can exhibit all kinds of smooth stable dynamics. I would like to convince the audience that the group of real-analytic diffeomorphisms is a really interesting object.In the first course, I would like to review the theorem by Herman which says the identity component of the group of real analytic diffeomorphisms of the n-torus is simple, which gives a motivation to study the group for other manifolds. We also review several fundamental facts in the real analytic category.In the second course, we introduce the regimentation lemma which can play in the real analytic category the role of the partition of unity in the smooth category. For manifolds with nontrivial circle actions, we show that any real analytic diffeomorphism isotopic to the identity is homologous to a diffeomorphism which is an orbitwise rotation.In the third course, we state a lemma which says that the multiple actions of the standard action on the plane is a final (terminal) object in the category of circle actions. This lemma would imply that the identity component of the group of real analytic diffeomorphisms is perfect.[-]

Real-analytic manifolds are studied very much in the last century until the time when people found the partition of unity on smooth manifolds makes the manifold theory very tractable. The group of real-analytic diffeomorphisms is the natural automorphism group of the real-analytic manifold. Because of the analytic continuation, there are no partition of unity by functions with support in balls. The germ at a point of a real-analytic diffeomorphism determines the diffeomorphism and hence the group of them looks rigid. However, the group of real-analytic diffeomorphisms is dense in the group of smooth diffeomorphisms and diffeomorphisms can exhibit all kinds of smooth stable dynamics. I would like to convince the audience that the group of real-analytic diffeomorphisms is a really interesting object.In the first course, I would like to review the theorem by Herman which says the identity component of the group of real analytic diffeomorphisms of the n-torus is simple, which gives a motivation to study the group for other manifolds. We also review several fundamental facts in the real analytic category.In the second course, we introduce the regimentation lemma which can play in the real analytic category the role of the partition of unity in the smooth category. For manifolds with nontrivial circle actions, we show that any real analytic diffeomorphism isotopic to the identity is homologous to a diffeomorphism which is an orbitwise rotation.In the third course, we state a lemma which says that the multiple actions of the standard action on the plane is a final (terminal) object in the category of circle actions. This lemma would imply that the identity component of the group of real analytic diffeomorphisms is perfect.[-]

We study a notion of shuffle for trees which extends the usual notion of a shuffle for two natural numbers. Our notion of shuffle is motivated by the theory of operads and occurs in the theory of dendroidal sets. We give several equivalent descriptions of the shuffles, and prove some algebraic and combinatorial properties. In addition, we characterize shuffles in terms of open sets in a topological space associated to a pair of trees. This is a joint work with Ieke Moerdijk.[-]

Given an automorphism of the free group, we consider the mapping torus defined with respect to the automorphism. If the automorphism is atoroidal, then the resulting free-by-cyclic group is hyperbolic by work of Brinkmann. In addition, if the automorphism is fully irreducible, then work of Kapovich-Kleiner proves the boundary of the group is homeomorphic to the Menger curve. However, their proof is very general and gives no tools to further study the boundary and large-scale geometry of these groups. In this talk, I will explain how to construct explicit embeddings of non-planar graphs into the boundary of these groups whenever the group is hyperbolic. Along the way, I will illustrate how our methods distinguish free-by-cyclic groups which are the fundamental group of a 3-manifold. This is joint work with Yael Algom-Kfir and Arnaud Hilion.[-]

(joint work with Michael Handel) $Out(F_{n}) := Aut(F_{n})/Inn(F_{n})$ denotes the outer automorphism group of the rank n free group $F_{n}$. An element $f$ of $Out(F_{n})$ is polynomially growing if the word lengths of conjugacy classes in Fn grow at most polynomially under iteration by $f$. The existence in $Out(F_{n}), n > 2$, of elements with non-linear polynomial growth is a feature of $Out(F_{n})$ not shared by mapping class groups of surfaces.
To avoid some finite order behavior, we restrict attention to the subset $UPG(F_{n})$ of $Out(F_{n})$ consisting of polynomially growing elements whose action on $H_{1}(F_{n}, Z)$ is unipotent. In particular, if $f$ is polynomially growing and acts trivially on $H_{1}(F_{n}, Z_{3})$ then $f $ is in $UPG(F_{n})$ and further every polynomially growing element of $Out(F_{n})$ has a power that is in $UPG(F_{n})$. The goal of the talk is to describe an algorithm to decide given $f,g$ in $UPG(F_{n})$ whether or not there is h in $Out(F_{n})$ such that $hf h^{-1} = g$.
The conjugacy problem for linearly growing elements of $UPG(F_{n})$ was solved by Cohen-Lustig. Krstic-Lustig-Vogtmann solved the case of linearly growing elements of $Out(F_{n})$.
A key technique is our use of train track representatives for elements of $Out(F_{n})$, a method pioneered by Bestvina-Handel in the early 1990s that has since been ubiquitous in the study of $Out(F_{n})$.[-]

Using a very recent result of Calderon and Salter, we relate small type Artin groups defined by Coxeter diagram which are trees to mapping class groups. This gives information on both the Artin groups with respect to commensurability and hyperbolicity of the parabolic subgroup graph as well as information on the mapping class group and its associated geometric spaces, namely generating sets of finite index subgroups and fundamental groups of strata of abelian differentials. I'll try to highlight the many ways in which this reflects various aspects of Mladen's work.[-]