## Colloquia

Colloquia for the Department of Mathematics and Statistics are normally held in University Hall 4010 on Fridays at 4:00 p.m. Any departures from this are indicated below. Light refreshments are served before the colloquia in 2040 University Hall. Driving directions, parking information and maps are available on the university website.

**For the 2021-2022 academic year the colloquia will be held online due to COVID-19.**

Here is the link: Blackboard Collaborate Colloquia Meeting Room

## 2021-2022 Colloquia

Below is a list of speakers, talk titles and abstracts for the current academic year. Abstracts for the talks are also posted in the hallways around the departmental offices.

**Spring Semester**

**January 21**

Yun Kang (Arizona State University)*How Does Mathematics Save Honeybees?*

Abstract: The honeybee, Apis mellifera, is not only crucial in maintaining biodiversity by pollinating 85% plant species but also is the most economically valuable pollinator of agricultural crops worldwide with value between $15 and $20 billion annually as commercial pollinators in the U.S. Unfortunately, the recent sharp declines in honeybee population have been considered a global crisis. In this talk, we will demonstrate how we develop different types of mathematical trackable models to explore how the crucial feedback mechanisms linking disease, parasitism, nutrition, and foraging behavior might be responsible for the colony growth dynamics and survival in a dynamical environment. Rigorous mathematics from those models that use nonlinear nonautonomous and/or delayed differential equations within metapopulation frameworks have been integrated with data to explore the contributing factors to the mysterious and dramatic loss of honeybees as well as provide a basis for new strategies for controlling Varroa and reducing colony losses for beekeepers, and benefit land managers.

**Fall Semester**

**December 10**

Mingji Zhang (New Mexico Institute of Mining and Technology)*Qualitative properties of ionic flows via Poisson-Nernst-Planck models with nonzero
but small permanent charges and multiple cations*

Abstract: A quasi-one-dimensional Poisson-Nernst-Planck system for ionic flow through a membrane channel is studied. Nonzero but small permanent charge, the major structural quantity of an ion channel, is included in the model. The system includes three ion species, two cations with the same valences and one anion, which provides more correlations/interactions between ions compared to the case included only two oppositely charged particles. The cross-section area of the channel is included in the system, which provides certain information of the geometry of the three-dimensional channel. This is crucial for our analysis. Under the framework of geometric singular perturbation theory, more importantly, the specific structure of the model, the existence and local uniqueness of solutions to the system for small permanent charges is established. Furthermore, treating the permanent charge as a small parameter, through regular perturbation analysis, we are able to derive approximations of the individual fluxes and current-voltage relations explicitly, and this allows us to examine the small permanent charge effects on ionic flows in detail.

**December 3**

Radakrishnan 'Kit' Nair (University of Liverpool, UK)*On Weyl’s theorem on uniform distribution of polynomials*

Suppose $P(x) = \alpha _k x^k + \ldots + \alpha _1 x + \alpha$ is a polynomial with one of $\alpha _k , \ldots , \alpha _1$ irrational. Suppose $( k_l )_{l\geq 1}$ is a class of highly regular sequences of natural numbers, to be specified. Then if a function $f: [0,1) \to \Bbb{C}$ is continuous, we have $$ \lim _{l\to \infty}{1\over l}\sum _{i=1}^{l}f(P({k_l})) = \int _0^1f(t)dt. $$ In the case of $k_l=l \ (l=1,2, \ldots )$ this is a seminal theorem of Herman Weyl, that underlies much of modern analytic number theory ergodic theory. We will prove this theorem and give some arithmetic applications.

**November 5**

Emil Straube (Texas A&M University)*d-bar methods in complex analysis*

Abstract: In this lecture, we will indicate some typical applications of $\overline{\partial}$-methods in complex analysis of one and several variables. We start with the solution of the inhomogeneous $\overline{\partial}$-equation in a planar domain, which lends itself to a simple proof of the Mittag--Leffler theorem on holomorphic functions with prescribed poles. Next, we describe how one variable methods give the solution of the inhomogeneous Cauchy-Riemann equations in $\mathbb{C}^{2}$ when the right hand side has compact support, and how this simple observation already leads to a phenomenon that is radically different from the one variable case: holomorphic functions in certain domains automatically extend holomorphically to a bigger domain. This leads to the question of domains of existence of holomorphic functions, and we indicate how these domains are characterized by the solvability of the inhomogeneous $\overline{\partial}$- equations. Finally, we add some remarks about solving the inhomogeneous equations with regularity estimates up to the boundary (time permitting).

**October 29**

Hoi Nguyen (The Ohio State University)*Random matrices: universality of the spectrum and cokernels *

Abstract: Random Matrix Theory is a rich area with many applications. In this talk I will give a brief survey on some recent developments in the area, focusing mainly on the universality aspect of the spectrum and cokernels.

**October 22**

Pablo Roldan (Yeshiva University)*Continuation of relative equilibria in the n–body problem to spaces of constant curvature*

Abstract: The curved n–body problem is a natural extension of the planar Newtonian n–body problem to surfaces of non-zero constant curvature. We prove that all non-degenerate relative equilibria of the planar problem can be continued to spaces of constant curvature k, positive or negative, for small enough values of this parameter. We also compute the extension of some classical relative equilibria to curved spaces using numerical continuation. For example, we extend Lagrange’s triangle configuration with different masses to both positive and negative curvature spaces.

**October 8**

Vladimir Retakh (Rutgers)*Noncommutative versions of classical and semi-classical problems*

Abstract: I will talk about the Gelfand program on noncommutative versions of some classical problems based on "down-to-Earth" approach. In particular, I will discuss factorizations of polynomials, noncommutative symmetric functions, noncommutative versions of Plücker coordinates, Ptolemy identity and noncommutative Laurent phenomenon for triangulated surfaces.

**October 1**

Jo Nelson (Rice)*Contact Invariants and Reeb Dynamics*

Abstract: Contact topology is the study of certain geometric structures on odd dimensional smooth manifolds. A contact structure is a hyperplane field specified by a one form which satisfies a maximum nondegeneracy condition called complete non- integrability. The associated one form is called a contact form and uniquely determines a Hamiltonian-like vector field called the Reeb vector field on the manifold. I will give some background on this subject, including motivation from classical mechanics. I will also explain how to generalize Morse theoretic constructions using J-holomorphic curves to obtain a Floer theoretic contact invariant, contact homology, whose chain complex is generated by closed Reeb orbits. This talk will feature numerous graphics to acclimate people to the realm of contact geometry.