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Combinatorial aspects of excedances and the Frobenius complex

In this talk, we will first discuss the topology of the Frobenius complex, the order complex of a poset motivated by the classical Frobenius problem. Specifically, we will determine the homotopy type of the Frobenius complex in certain cases using discrete Morse theory. In the second half of the talk, we will extend the classical excedancestatistic of the symmetric group to the affine symmetric group and determine the generating function of its distribution. The proof involves enumerating lattice points in a skew version of the root polytope of type $A$.

There will be a reception for Eric at 4:00 p.m. in POT 745.

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The Andrew-Curtis Conjecture

A cornerstone theorem of free groups is the Nielsen-Schreier theorem - that every subgroup of a free group is itself free. In this talk we'll explore this result via Nielsen's proof and then discuss the statement of the Andrew-Curtis conjecture. This is an open problem that is a natural extension of the tools developed by Nielsen to prove the Nielsen-Schreier theorem, yet a proof has eluded mathematicians for nearly 50 years (and continues to do so!) The talk should be accessible to everyone with an interest in algebra.

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A Culture of Disaster Prepardeness: UK Students Study Tsunami Mitigation in Japan

In the aftermath of the earthquake and ensuing tsunami on March 11, Japan has experienced devastation the likes of which few places have ever felt. To UK geography professor Pradyumna Karan, this disaster feels personal.

“I have been leading UK Summer Field Seminars in Japan along with professor Todd Stradford for many years. My students and I have many friends in each region that we will have for the rest of our lives.”

The importance of being equivalent: The Ubiquity of equivalence relations in mathematics, K-16+

Equivalence relations show up at all levels in mathematics from kindergarten to graduate school: regrouping in addition and subtraction; equivalent fractions; equivalent algebraic expressions and equations; vectors; modular arithmetic; row reduction in matrices; cardinality; etc. I hypothesize that one reason students have difficulties with these topics is the subtle difference between "equivalent" and "equal" in these settings. In spite of the centrality of equivalence relations to understanding so many math topics, we don't explicitly talk about this to students, even to math majors and prospective math teachers, until late in their education, if at all.

I will talk about the mathematics that underlies the various uses of equivalence relations in these diverse settings. There will be something here for everyone who teaches math, or who prepares math teachers, at all grade levels.

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Image Reconstruction in Thermoacoustic Tomography

Thermoacoustic tomography (TAT) is an emerging modality of medical imaging which produces high resolution, high contrast tomographic images without exposing patients to dangerous ionizing radiation. In a TAT scan, pulsed radio frequency energy applied to a tissue sample causes rapid thermoelastic expansion and contraction, propagating a pressure wave through the sample. Transducers arranged around the patient's body record this ultrasonic pressure data and there are several reconstruction regimes available to recover a tomographic image from this information. In this talk, I will describe the standard wave equation model for thermoacoustic signal generation and highlight several of the image reconstruction techniques discovered in the past twenty years. I will then present a new Neumann series exact solution due to P. Stefanov and G. Uhlmann. This very elegant method motivates and theoretically justifies wave equation time reversal methods for TAT reconstruction and I will outline some promising numerical algorithms of this type.

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