# Colloquia/Fall18

## Contents

# Mathematics Colloquium

All colloquia are on Fridays at 4:00 pm in Van Vleck B239, **unless otherwise indicated**. The calendar for spring 2019 can be found here.

## Fall 2018

date | speaker | title | host(s) | |
---|---|---|---|---|

Sep 12 | Gunther Uhlmann (Univ. of Washington) Distinguished Lecture series | Harry Potter's Cloak via Transformation Optics | Li | |

Sep 14 | Gunther Uhlmann (Univ. of Washington) Distinguished Lecture series | Journey to the Center of the Earth | Li | |

Sep 21 | Andrew Stuart (Caltech) LAA lecture | The Legacy of Rudolph Kalman | Jin | |

Sep 28 | Gautam Iyer (CMU) | TBA | Thiffeault | |

Oct 5 | Eyal Subag (Penn State) | Symmetries of the hydrogen atom and algebraic families | Gurevich | |

Oct 12 | Arie Levit (Yale) | TBA | Gurevich | |

Oct 19 | Jeremy Teitelbaum (U Connecticut) | TBA | Boston | |

Oct 26 | Douglas Ulmer (Arizona) | TBA | Yang | |

Nov 2 | Reserved for job talk | TBA | hosting faculty | |

Nov 9 | Reserved for job talk | TBA | hosting faculty | |

Nov 16 | Reserved for job talk | TBA | hosting faculty | |

Nov 30 | Reserved for job talk | TBA | hosting faculty | |

Dec 7 | Reserved for job talk | TBA | hosting faculty |

## Abstracts

### Sep 12: Gunther Uhlmann (Univ. of Washington)

Harry Potter's Cloak via Transformation Optics

Can we make objects invisible? This has been a subject of human fascination for millennia in Greek mythology, movies, science fiction, etc. including the legend of Perseus versus Medusa and the more recent Star Trek and Harry Potter. In the last fifteen years or so there have been several scientific proposals to achieve invisibility. We will introduce in a non-technical fashion one of them, the so-called "traansformation optics" in a non-technical fashion n the so-called that has received the most attention in the scientific literature.

### Sep 14: Gunther Uhlmann (Univ. of Washington)

Journey to the Center of the Earth

We will consider the inverse problem of determining the sound speed or index of refraction of a medium by measuring the travel times of waves going through the medium. This problem arises in global seismology in an attempt to determine the inner structure of the Earth by measuring travel times of earthquakes. It has also several applications in optics and medical imaging among others.

The problem can be recast as a geometric problem: Can one determine the Riemannian metric of a Riemannian manifold with boundary by measuring the distance function between boundary points? This is the boundary rigidity problem. We will also consider the problem of determining the metric from the scattering relation, the so-called lens rigidity problem. The linearization of these problems involve the integration of a tensor along geodesics, similar to the X-ray transform.

We will also describe some recent results, join with Plamen Stefanov and Andras Vasy, on the partial data case, where you are making measurements on a subset of the boundary. No previous knowledge of Riemannian geometry will be assumed.

### Sep 21: Andrew Stuart (Caltech)

The Legacy of Rudolph Kalman

In 1960 Rudolph Kalman published what is arguably the first paper to develop a systematic, principled approach to the use of data to improve the predictive capability of mathematical models. As our ability to gather data grows at an enormous rate, the importance of this work continues to grow too. The lecture will describe this paper, and developments that have stemmed from it, revolutionizing fields such space-craft control, weather prediction, oceanography and oil recovery, and with potential for use in new fields such as medical imaging and artificial intelligence. Some mathematical details will be also provided, but limited to simple concepts such as optimization, and iteration; the talk is designed to be broadly accessible to anyone with an interest in quantitative science.

### Oct 5: Eyal Subag (Penn State)

Symmetries of the hydrogen atom and algebraic families

The hydrogen atom system is one of the most thoroughly studied examples of a quantum mechanical system. It can be fully solved, and the main reason why is its (hidden) symmetry. In this talk I shall explain how the symmetries of the Schrödinger equation for the hydrogen atom, both visible and hidden, give rise to an example in the recently developed theory of algebraic families of Harish-Chandra modules. I will show how the algebraic structure of these symmetries completely determines the spectrum of the Schrödinger operator and sheds new light on the quantum nature of the system. No prior knowledge on quantum mechanics or representation theory will be assumed.