Fall 2015
Wednesdays 12:55 - 1:45
LCB 225

Pizza and discussion after each talk
Past Colloquia

August 26    No Talk

September 2     Andrejs Treibergs
Analysis Meets Topology: Gauss Bonnet Theorem
Abstract: This talk is about one of the most important results about the geometry of surfaces. The Gauss Bonnet Theorem equates the integral of the curvature, which is an analytic invariant with the Euler Characteristic, which is a topological invariant. We begin by describing some calculus of surfaces from an intrinsic point of view. We assume we have a Riemannian metric so that we can measure lengths and angles of vectors. We explain how to differentiate vector fields, compute the geodesic curvature which tells how much a curve turns, and the Gauss curvature which gives the shape of the surface. By applying Green's Theorem, we relate Gauss curvature to the angles and geodesic curvature of a curvilinear triangle. This generalizes the fact that the interior angles of a Euclidean triangle add up to pi. By combining the formulas for triangles that subdivide a surface yields the result. Some applications will be mentioned.

Slides for the talk are available: www.math.utah.edu/~treiberg/GaussBonnetSlides.pdf

September 9     Jon Chaika
Metric number theory, continued fractions and dynamics.
Abstract: As you probably know, the rational numbers are dense. However, if you only consider rationals with denominator at most n you do not get a dense set. Given an irrational number, a natural object to consider is the sequence of rational numbers closest to it and a natural question is how close a point in this sequence is to the irrational number when compared to the size of its denominator. This talk will discuss this and other questions.

September 16     Karl Schwede - Director of Graduate Studies
Applying for and attending graduate school
• Should I apply to graduate school?
• How do I apply to graduate school?
• What will it be like when I'm in graduate school?
There will be a short presentation followed by a panel discussion. Faculty, postdocs and current graduate students from all areas of the department will be there to give their points of view and to answer your questions. This discussion should be useful both for students who will be applying this fall and students who are just starting to think about going to graduate school and may be applying in future years.

September 23     Liz Fedak
Interdisciplinary Model Building: Constructing, Validating and Analyzing ODE Models For Tumor-Immune System Interaction
Abstract: Mathematical oncologists seek to describe how tumor cells and the immune system interact over time, then use such knowledge to gain insight that would benefit clinicians. As useful as they are, understanding these models requires one to be well-versed in both mathematical and biological methodology, and are often intimidatingly complex to the layperson. Liz Fedak's talk attempts to rectify this by demystifying large systems of ODEs piece by piece. By drawing on previous works by local researchers, recent advances in the field, and her own previous and current research, she hopes to provide her audience with the specialized knowledge needed to parse models of this type. The first part of the talk will focus on the origin of terms in a simple ODE model of tumor-immune system interaction, while the second part includes a thorough description on how these models are built, validated, and analyzed. Afterwards, attendees will be given the chance to demonstrate what they have learned.

This talk is intended for an audience familiar with systems of ODEs, and further alludes to immunology, numerical analysis, and dynamical systems analysis.

September 30     Peter Alfeld
Hotel Infinity
Abstract: You are the owner of Hotel Infinity. It has infinitely many rooms, and it's full. A new guest arrives and insists you give her a room. How do you accommodate her? The next day, a family with infinitely many members arrives, each of whom wants a private room. The next day infinitely many families, each with infinitely many members, arrive. Each family member insists on a private room. You can do it! Infinity is different.

The Weird and Wonderful Chemistry of the Look-and-Say Sequence
Abstract: 1,11,21,1211,111221,312211,13112221,... Do you see the pattern? The defining rule can be explained to children and is a great off-the-wall example for Calc II students. Despite a simple definition, this sequence has surprising mathematical properties. We'll talk about eigenvalues of large matrices, roots of degree 71 polynomial equations, and something John Conway calls the "Cosmological Theorem." In the spirit of Calc II we might even do the ratio test!

A PDF of Conway's paper can be found at: http://www.math.utah.edu/~boocher/writings/ConwayLook.pdf

October 14     No Talk - Fall Break

October 21     Sean McAfee
Abstract: The word "paradox" is used in a mathematical sense to describe a statement that is extremely counterintuitive but true. For example, the Banach-Tarski paradox states that a 3-dimensional ball can be decomposed into five disjoint subsets which can be reassembled to form two balls, each having the same volume as the original ball! We will discuss this and other historical paradoxes such as Zeno's Paradox, Gabriel's Horn, and the Potato Paradox.

October 28     Christopher Miles
How the Zebra Got its Stripes: The Mathematics of Pattern Formation
Abstract: Although found prevalently throughout nature, patterns are a uniquely complex and diverse phenomenon. For instance, seashells have a distinctly different pattern than cheetahs, which also have different patterns than zebras or cacti. Can a single mathematical theory explain how all of these patterns arise? In 1952, Alan Turing answered this question​, particularly in the context of developmental biology​. In this talk, we'll discuss the primary mechanism proposed by Turing: a reaction-diffusion system. ​ By looking at an example, the Gierer-Meinhardt model, ​we'll attempt to develop intuition for how these partial differential equations behave and why this mechanism does such a good job explaining pattern formation. Along the way, we'll hopefully ​see some math and pretty pictures.

Slides for the talk are available: slides.com/cmiles/undergrad_colloq_2015#/

November 4     Anna Macquarie Romanova
A Glimpse of the Fourth Dimension: Exploring Higher Dimensional Polytopes
Abstract: Platonic solids are the most symmetric objects that we can construct in three dimensions. Built from regular polyhedra, they look the same at each vertex. One of the major revelations of classical Greek mathematics was that the fact that there are only five solids possessing this maximal symmetry - the tetrahedron, the cube, the octahedron, the dodecahedron, and the icosahedron. But what happens if we expand our view to four dimensions? In this talk, I will introduce the four dimensional analogues to the platonic solids and discuss how we can understand objects that we cannot see. Along the way, we'll encounter the princess of polytopes, a hypercube of monkeys, and the view from inside a hyperdodecahedron. Bring your iOS or Android devices for full immersion.

Slides for the talk are available: http://www.math.utah.edu/~romanova/talks/polytopes.svg

November 11     Shiang Tang
Continued fractions and music theory
Abstract: Continued fraction is an alternative way of expressing a number as opposed to decimal expansion. It provides better rational approximation to real numbers. In this talk, I will show you how to express some important irrational numbers by continued fraction and an application to piano theory. No preliminary knowledge is required other than elementary algebra.

November 18     Ian Shipman
Sometimes you just get lucky
Abstract: The probabilistic method is a technique that can be used to prove existence results in a wide variety of discrete contexts by analyzing a random example. I will explain the technique through examples from graph theory, elementary number theory, coding, and discrete geometry.

Notes from Ian's talk are available: Lecture Notes

November 25     Damon Toth
Stochastic branching process theory and Ebola
Abstract: Stochastic branching processes describe the probabilistic propagation of offspring across generations and are well suited for modeling outbreaks of diseases that spread from person to person. In most countries, incoming travelers infected with Ebola caused only small outbreaks. I will show how data from these extinguished Ebola outbreaks can be represented by a "subcritical" branching process model, in which outbreaks will eventually extinguish with probability 1, but perhaps not before a large number of transmissions occur. I will derive the final outbreak size distribution equations and show how they can be used by public health officials to assess the risk of "worst-case scenario" outbreaks after an Ebola introduction under different conditions.

December 2     Michael Elifritz, Actuary & Math Department Alumnus