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# Events for 03/27/2015 from all calendars

## Working Seminar on Nonlinear Geometries

## Mathematical Physics and Harmonic Analysis Seminar

## Algebra and Combinatorics Seminar

## Linear Analysis Seminar

## Geometry Seminar

**Time:** 10:30AM - 11:30AM

**Location:** BLOC 220

**Speaker:** TBA

**Title:**

**Time:** 1:50PM - 2:50PM

**Location:** BLOC 628

**Speaker:** Jared Wunsch, Northwestern University

**Title:** *High frequency estimates for the Helmholtz equation with applications to boundary integral equations.*

**Abstract:** I will discuss joint work with Dean Baskin and Euan Spence on high frequency estimates for the Helmholtz equation in exterior domains as well as for the interior impedance problem. Motivations for these estimates comes from certain problems in numerical analysis.

**Time:** 3:00PM - 3:50PM

**Location:** BLOC 628

**Speaker:** Sherilyn Tamagawa, UC Santa Barbara

**Title:** *Quandles of Virtual Knots*

**Abstract:** We will explore algebraic invariants on a special class of knots, known as virtual knots. Our main focus will be on quandles, an algebraic structure which serves as a perfect knot invariant, but is usually impossible to compute. We construct new invariants by taking quotients of quandles, and introduce a variation on the Alexander polynomial.

**Time:** 4:00PM - 5:00PM

**Location:** BLOC 220

**Speaker:** Da Zheng, University of Houston

**Title:** *The Operator System Generated by Cuntz Isometries*

**Abstract:** In this talk, we will consider the operator system S_{n}, for n greater than 2, generated by isometries s_{1},...,s_{n} satisfying the Cuntz relation: s_{1}s_{1}^{*} +...+ s_{n}s_{n}^{*}=I. We will exhibit an operator system E_{n} ⊆ M_{n} living in the n by n matrices and prove that S_{n} is completely order isomorphic to a quotient of E_{n}. Next, we will study tensor products of S_{n} and examine the various notions of nuclearity of S_{n} in the category of operator systems. Finally, some open problems are discussed.

**Time:** 4:00PM - 5:00PM

**Location:** Bloc 628

**Speaker:** Martha Precup, Baylor University

**Title:** *Regular Hessenberg varieties and generalized exponents*

**Abstract:** Hessenberg varieties are closed subvarieties of the full flag variety. In this talk, we will show that regular Hessenberg varieties are irreducible. The Betti numbers of these varieties count certain subsets of positive roots. Using these subsets, we will define natural numbers that generalize the exponents of *S _{n}* in type

.