Applied Mathematics Seminar, Spring 2019

Mondays 4:00 PM - 5:00 PM, LCB 215

• This seminar can be taken for credit: Students can get 1-3 credits by registering to the Applied Math Seminar class Math 7875 Section 010 for Spring 2019. Students should talk to the seminar organizer before taking it for a credit. Grading is based on attendance and giving a talk by presenting an applied-mathematics paper (not necessarily your own). Student talks will be appropriately labeled to distinguish them from visitor talks. The seminar organizer is available to review your slides, for dry-runs etc.
• Please direct questions or comments about the seminar (or its class) to Yekaterina Epshteyn (epshteyn (at) math.utah.edu)
• Talks are announced through the applied-math mailing list. Please ask the seminar organizer for information about how to subscribe to this list.

January 11, Friday (Special Seminar), Room LCB 219. Time 3pm - 4pm
Speaker: William Feldman, Department of Mathematics, University of Chicago
Title: Recent developments in stochastic homogenization of Hamilton-Jacobi equations
Abstract: I will describe some background and some new developments in the theory homogenization of Hamilton-Jacobi equations in random environments. The primary difficulties in this field have been around understanding the roles of convexity and coercivity (controllability). Many interesting problems, especially involving interface motions, lack one or both of these properties. I will discuss some positive results and some counter-examples where homogenization does not hold.

January 18, Friday (Special Seminar), Room LCB 215. Time 4pm - 5pm.
Speaker: Ian Tobasco, Department of Mathematics, University of Michigan, Ann Arbor
Title: Optimal design of wall-bounded heat transport
Abstract: Flowing a fluid is a familiar and efficient way to cool: fans cool electronics, water cools nuclear reactors, and the atmosphere cools the surface of the Earth. In this talk, we discuss a class of problems from fluid dynamics which ask for the design of incompressible wall-bounded flows achieving optimal rates of heat transport for a given flow intensity budget. Guided by a perhaps unexpected connection between this optimal design problem and various "energy-driven pattern formation" problems from materials science, we construct flows achieving nearly optimal rates of heat transport in their scaling with respect to a prescribed intensity budget. The resulting flows share striking similarities with self-similar elastic wrinkling patterns, such as can be seen in the shape of a hanging drape or nearby the edge of a torn plastic sheet. They also remind of (carefully designed versions) of the complex multi-scale patterns seen in turbulent fluids. Nevertheless, we prove that in certain cases natural buoyancy-driven convection is not capable of achieving optimal rates of cooling. This is joint work with Charlie Doering.

March 1, Time 3pm, Room LCB 219, Joint Stochastics and Applied Math seminar
Speaker: Greg Rice, Department of Statistics and Actuarial Science, University of Waterloo
Title: Change point analysis with functional time series
Abstract: We consider methods for detecting and dating changes in both the level and variability of a time series of curves or functional data objects. Regarding level shifts, we propose a new detection and dating procedure that is fully functional", in the sense that it does not rely on dimension reduction techniques. To test for changes in variability, we consider methods based on measuring the fluctuations of eigenvalues of the sequential estimates of the empirical covariance operator. A thorough asymptotic theory is developed for each procedure that highlights their relative strengths and weaknesses when compared to existing methods. An application to annual temperature curves illustrates the practical use of the proposed methods.

March 4
Speaker: Piotr Kokoszka, Department of Statistics, Colorado State University
Title: Fundamental concepts of functional data analysis and an application to global cooling
Abstract: The talk will consist of two parts. In the first part I will review the basic concepts of functional data analysis (FDA), mostly by showing relevant graphical displays. In FDA, a single observation is a curve rather than a number. The curves exist as mathematical objects, but are never fully observed. For example, a child has a height at any time point, but it is generally recorded about once a year. In the second part of the talk, I will focus on the problem of testing if there is a global cooling trend in the ionosphere. It has been conjectured almost 30 years ago that green house gases should radiate heat into space once they enter the ionosphere. This should result in its thermal contraction. The height of the ionosphere can be approximately measured only directly over a terrestrial observatory. These observatories are unevenly spaced and have operated over different time periods. I will explain how the data collected by them can be used to test the conjecture of the thermal contraction of the ionosphere. The talk will be accessible to anyone with an undergraduate background in statistics.

April 1 (reserved)
Speaker: TBA
Title: TBA
Abstract: TBA

April 8
Speaker: Petia Vlahovska, School of Engineering, Northwestern University
Title: Electrohydrodynamic fluid instabilities: droplet tumbling, surface vortices, equatorial streaming
Abstract: A classic result due to G.I.Taylor is that a weakly conducting drop bearing zero net charge placed in a uniform electric field adopts a prolate or oblate spheroidal shape, the flow and shape being axisymmetrically aligned with the applied field. In this talk, I will discuss some intriguing symmetry--breaking instabilities related to the Quincke rotation effect: drop steady tilt or tumbling, and appearance of vortices along the drop equator. If time permits I will also present a related instability - the streaming from the drop equator that creates visually striking "Saturn-rings" around the drop.

April 15
Speaker Christian Kern, Institute of Applied Physics, KIT
Title: On the Hall Effect in Composites
Abstract: The Hall effect describes the appearance of a transversal voltage, the so-called Hall voltage, in a current-carrying slab of material that is subject to a magnetic field. The corresponding material property, which relates the Hall voltage to the current, magnetic field, and thickness of the slab, is the so-called Hall coefficient. In composites, very unusual values of the effective Hall coefficient can be realized by tailoring their microscopic structure. In this talk, based on the work of Marc Briane and Graeme Milton, I will show that the effective Hall coefficient of a single-constituent porous composite can be sign-inverted with respect to the Hall coefficient of the constituent material and how we were able to demonstrate this effect experimentally. Furthermore, I will discuss structures with lower symmetry, which are described by a rank-two tensor instead of a scalar Hall coefficient. Finally, I will elaborate on corresponding bounds and show how the theory can be extended to account for non-trivial distributions of the magnetic permeability. Joint work with Graeme Milton, Muamer Kadic, and Martin Wegener.

Seminar organizer: Yekaterina Epshteyn (epshteyn (at) math.utah.edu).

155 South 1400 East, Room 233, Salt Lake City, UT 84112-0090, T:+1 801 581 6851, F:+1 801 581 4148