# Events for December 6, 2017 from General and Seminar calendars

## Inverse Problems Seminar

Time: 12:00PM - 1:00PM

Location: BLOC 628

Speaker: Dr. Matthew Lewis, UT Southwest Medical Center, Radiology Department

Title: Secrets of Spectral Computed Tomography

Abstract: In the past ten years, all three major vendors of clinical CT have released different kinds of CT systems that exploit the energy-dependence of X-ray attenuation. In this talk, I will discuss the dimensionality of X-ray contrast and how these different CT systems work. Examples of artifacts of unknown origin will be presented and related to model non-linearities. Model errors due to K-edges will also be presented, with a question to applied mathematicians: how can we exploit these singularities in novel ways? Lastly, I will conclude with a discussion of next generation photon-counting spectral CT.

## Number Theory Seminar

Time: 1:45PM - 2:45PM

Location: BLOC 220

Speaker: Shin Hattori, Kyushu University

Title: Duality of Drinfeld modules and P-adic properties of Drinfeld modular forms

Abstract: Let p be a rational prime, q>1 a p-power and P a non-constant irreducible polynomial in F_q[t]. The notion of Drinfeld modular form is an analogue over F_q(t) of that of elliptic modular form. On the other hand, following the analogy with p-adic elliptic modular forms, Vincent defined P-adic Drinfeld modular forms as the P-adic limits of Fourier expansions of Drinfeld modular forms. Numerical computations suggest that Drinfeld modular forms should enjoy deep P-adic structures comparable to the elliptic analogue, while at present their P-adic properties are far less well understood than the p-adic elliptic case. In this talk, I will explain how basic properties of P-adic Drinfeld modular forms are obtained from the duality theories of Taguchi for Drinfeld modules and finite v-modules.

## Noncommutative Geometry Seminar

Time: 2:00PM - 2:50PM

Location: BLOC 628

Speaker: Xin Ma, TAMU

Title: Dynamics and classification of crossed product C*-algebras

Abstract: In this talk I will talk about some dynamical properties and their relation to classification program of crossed products by Elliott invariant. These properties include dimensions, almost finiteness, comparison, and the small boundary property. In addition, I will talk about some recent classification results for crossed products.

## Numerical Analysis Seminar

Time: 3:00PM - 4:00PM

Location: BLOC 628

Speaker: Chris Kees, Coastal and Hydraulics Laboratory, US Army ERDC

Title: A two-scale computational framework for air-water-sediment dynamics

Abstract: A better understanding of sediment erosion and deposition processes is critical to the mission of the US Army Corps of Engineers. Long-term engineering of the Mississippi river, beach nourishment projects for coastal communities, and design of levees, breakwaters, and dunes for flood and storm protection all turn on the interaction of fluids with granular materials. Hunter Rouse, the father of modern hydraulics'' wrote in 1939 that, neither mathematical tools nor physical understanding of their use can be considered sufficiently far advanced to cope with so intricate a problem at the present time''. Today, the state of practice in computational modeling of sediment dynamics still relies heavily on empirical relationships. In recent decades, however, much progress has been made on the development of numerical methods capable of obtaining qualitatively correct solutions of fluid-grain dynamics at the microscale and on thermodynamically correct averaging methods to obtain practical computational models at the macroscale. This presentation will describe a combination of level set and immersed boundary methods for simulating microscale air-water-solid dynamics, averaging methods for deriving a 3D air-water-sediment model, and an incremental projection scheme for the three-phase Navier-Stokes system that arises at the macroscale.

## Hiring Candidate - Laura Escobar

Time: 4:00PM - 5:00PM

Location: BLOC 220

Speaker: Laura Escobar , University of Illinois at Urbana-Champaign

Description:
Title: Bott-Samelson varieties and combinatorics

Abstract:

Schubert varieties parametrize families of linear spaces intersecting certain hyperplanes in C^n in a predetermined way. In the 1970’s Hansen and Demazure independently constructed resolutions of singularities for Schubert varieties: the Bott-Samelson varieties. In this talk I will describe their relation with associahedra. I will also discuss joint work with Pechenick-Tenner-Yong linking Magyar’s construction of these varieties as configuration spaces with Elnitsky’s rhombic tilings. Finally, based on joint work with Wyser-Yong, I will give a parallel for the Barbasch-Evens desingularizations of certain families of linear spaces which are constructed using symmetric subgroups of the general linear group.