The Mathematics Department holds regular seminars on a variety of topics. Please see below for further details.
Seminar  Meeting Details  Title & Abstract 

Geometry and Topology Seminar  Sphere's theorem on Warped product submanifolds Speaker: Jaewon Lee (Gyeongsang National University) 

Differential Equations Seminar  Transmission of fast solitons for the NLS with an external potential We consider the dynamics of a boosted soliton evolving under the cubic NLS with an external potential. We show that for sufficiently large velocities, the soliton is effectively transmitted through the potential. This result extends work of Holmer, Marzuola, and Zworski, who considered the case of a delta potential with no bound states in their 2007 paper “Fast soliton scattering by delta impurities,” and the work of Datchev and Holmer, who considered the case of the delta potential with a linear bound state in their 2009 paper “Fast soliton scattering by attractive delta impurities.” This is joint work with Jason Murphy. Speaker: Christopher Horgan (MS&T) 

Analysis Seminar  Questions related to Ulam's floating body problem and to centroid bodies Abstract: Croft, Falconer and Guy posed a series of questions generalizing Ulam's floating body problem, as follows. Given a convex body K in R^3, we consider its plane sections with certain given properties,
(V): Plane sections which cut off a given constant volume
(I) Plane sections which have equal constant principal moments of inertia
Ulam's floating body problem is equivalent to problem (V,I): If all plane sections of the body K which cut off equal volumes have equal constant moments of inertial, must K be an Euclidean ball?
We give a negative answer to problem (V,A) following Ryabogin's counterexample to Ulam's floating body problem. We also give a positive answer to problem (A,I) in the class of bodies of revolution.
In addition, we prove several local fixed point results for the centroid body (the surface of buoyancy associated to Ulam's floating body problem when the density of K is 1/2).
This is joint work with Gulnar Aghabalayeva and Chase Reuter. Speaker: Maria Alfonseca (North Dakota State University) 

Algebra Seminar  Wilf’s Conjecture and More (and Less) Wilf’s conjecture establishes an inequality that relates three fundamental invariants of a numerical semigroup: the minimal number of generators (or the embedding dimension), the Frobenius number, and the number of gaps. Based on a preprint by Srinivasan and S, the talk will discuss the past, present, and future of this conjecture. We prove that this Wilf inequality is preserved under gluing of numerical semigroups. If the numerical semigroups minimally generated by \(A = \{ a_1, \ldots, a_p\}\) and \(B = \{ b_1, \ldots, b_q\}\) satisfy the Wilf inequality, then so does their gluing which is minimally generated by \(C =k_1A\sqcup k_2B\). We discuss the extended Wilf's Conjecture in higher dimensions and prove an analogous result. Speaker: Srishti Singh, University of Missouri 

Differential Equations Seminar  Desingularization of hollow vortices A hollow vortex is a region of constant pressure bounded by a vortex sheet and suspended inside a perfect fluid — think of it as a spinning bubble of air in water. In this talk, I will describe a general method for desingularizing nondegenerate translating, rotating, or stationary point vortex configurations into collections of steady hollow vortices. Through global bifurcation theory, moreover, these families can be extended to maximal curves of solutions that continue until the onset of a singularity. As specific applications, this machinery gives the first existence theory for corotating hollow vortex pairs and stationary hollow vortex tripoles, as well as a new construction of Pocklington’s classical cotranslating hollow vortex pairs. All of these families extend into the nonperturbative regime, and we obtain a rather complete characterization of the limiting behavior along the global bifurcation curve. This is joint work with Ming Chen (University of Pittsburgh) and Miles H. Wheeler (University of Bath). Speaker: Samuel Walsh (University of Missouri) 

Differential Equations Seminar  New results on global bifurcation of traveling periodic water waves While the research on water waves modeled by Euler's equations has a long history, mainly in the last two decades traveling periodic rotational waves have been constructed rigorously by means of bifurcation theorems. After introducing the problem, I will present a new reformulation in two dimensions in the puregravity case, where the problem is equivalently cast into the form “identity plus compact”, which is amenable to Rabinowitz's global bifurcation theorem. The main advantages (and the novelty) of this new reformulation are that no simplifying restrictions on the geometry of the surface profile and no simplifying assumptions on the vorticity distribution (and thus no assumptions regarding the absence of stagnation points or critical layers) have to be made. Within the scope of this new formulation, global families of solutions, bifurcating from laminar flows with a flat surface, are constructed. Moreover, I will discuss the possible alternatives for the global set of solutions, as well as their nodal properties. This is joint work with Erik Wahlén. Speaker: Jörg Weber (Lund University) 

Astro/Relativity Seminar  Astro/Relativity Seminars Please see the schedule here. 

Preprint Algebra Seminar  Asymptotic multiplicities of graded families of ideals and linear series, Part II Speaker: Stephen Landsittel 

Differential Equations Seminar  Antiplane shear equilibria in the large In this talk, we discuss antiplane shear deformations on a semiinfinite slab with a nonlinear mixed traction displacement boundary condition. We apply global bifurcation theoretic methods and deduce extreme behavior at the terminal end solution curves. It is shown that arbitrarily large strains are encountered for a class of idealized materials. We also consider degenerate materials, prove that ellipticity breaks down, and show that a concurrent blowup in the second derivative occurs. Speaker: Thomas Hogancamp (University of Missouri) 

Preprint Algebra Seminar  Asymptotic multiplicities of graded families of ideals and linear series, by Cutkosky (Part I) Speaker: Stephen Landsittel 