Week of November 14, 2021

Mon Nov 15, 2021
12:00pm to 1:00pm - Zoom - UCI Mathematics Alumni Lectures
Daniel Agress - (The Aerospace Corporation)
Mathematics at the Aerospace Corporation

Daniel will describe his path through internships, job applications, and the interview process. He will also give a brief introduction to The Aerospace Corporation and the role mathematicians and mathematics play at Aerospace and in the space industry in general.

Register to obtain a Zoom link. Seminar flyer.

4:00pm to 5:00pm - Zoom - https://uci.zoom.us/j/97796361534 - Applied and Computational Mathematics
Jiahua Jiang - (ShanghaiTech University)
Hybrid projection methods with recycling for inverse problems

Abstract: Iterative hybrid projection methods have proven to be very effective for solving large linear inverse problems due to their inherent regularizing properties as well as the added flexibility to select regularization parameters adaptively. In this work, we develop Golub-Kahan-based hybrid projection methods that can exploit compression and recycling techniques in order to solve a broad class of inverse problems where memory requirements or high computational cost may otherwise be prohibitive.  For problems that have many unknown parameters and require many iterations, hybrid projection methods with recycling can be used to compress and recycle the solution basis vectors to reduce the number of solution basis vectors that must be stored, while obtaining a solution accuracy that is comparable to that of standard methods. If reorthogonalization is required, this may also reduce computational cost substantially.  In other scenarios, such as streaming data problems or inverse problems with multiple datasets, hybrid projection methods with recycling can be used to efficiently integrate previously computed information for faster and better reconstruction. Additional benefits of the proposed methods are that various subspace selection and compression techniques can be incorporated, standard techniques for automatic regularization parameter selection can be used, and the methods can be applied multiple times in an iterative fashion. Theoretical results show that, under reasonable conditions, regularized solutions for our proposed recycling hybrid method remain close to regularized solutions for standard hybrid methods and reveal important connections among the resulting projection matrices. Numerical examples from image processing show the potential benefits of combining recycling with hybrid projection methods.

Tue Nov 16, 2021
1:00pm to 2:00pm - Zoom - Dynamical Systems
Paul Carter - (UC Irvine)
Pulse replication and slow absolute spectrum in the FitzHugh-Nagumo system

Traveling waves arise in partial differential equations in a broad range of applications. The notion of stability of a traveling wave solution concerns its resilience to small perturbations and can frequently be inferred from an eigenvalue problem obtained by linearizing the PDE about the solution. I will discuss these ideas in the context of the FitzHugh--Nagumo system, a simplified model of nerve impulse propagation. I will present existence and stability results for (multi)pulse solutions, and I will describe a phenomenon whereby unstable eigenvalues accumulate as a single pulse is continuously deformed into a double pulse.

4:00pm - NS2 1201 - Differential Geometry
Connor Mooney - (UC Irvine)
Solutions to the Monge-Ampere equation with polyhedral and Y-shaped singularities

The Monge-Ampere equation det(D^2 u) = 1 arises in prescribed
curvature problems and in optimal transport. An interesting feature of the
equation is that it admits singular solutions. We will discuss new examples
of convex functions on R^n that solve the Monge-Ampere equation away from
finitely many points, but contain polyhedral and Y-shaped singular
structures. Along the way we will discuss geometric and applied motivations
for constructing such examples, as well as their connection to a certain
obstacle problem.

Wed Nov 17, 2021
2:00pm to 3:00pm - 510R - Combinatorics and Probability
Thomas Mountford - (EPFL)
An invariance principle for Markov cookie random walks.

 

 

In joint work with E Kosygina and J Peterson, the

"natural" diffusive scaling is considered for the recurrent case

and the convergence to Brownian motion perturbed at extrema is shown.  The key ideas are coarse graining and

the Ray Knight approach.

Thu Nov 18, 2021
9:00am to 10:00am - Zoom - Inverse Problems
Fernando Guevara Vasquez - (University of Utah)
Active thermal cloaking and mimicking

https://sites.uci.edu/inverse/

11:00am - zoom ID: 949 5980 5461. Password: the last four digits of the zoom ID in the reverse order - Harmonic Analysis
Alex Samorodnitsky - (The Hebrew University of Jerusalem)
A moment ratio bound for polynomials on the boolean cube

We prove an almost tight upper bound on the ratio ||f||_p / ||f||_2, when f is a polynomial of a given degree on the Boolean cube {0,1}^n and describe some applications.  In particular, we describe a family of hypercontractive inequalities for functions on {0,1}^n which take into account the concentration of a function.

3:00pm to 3:50pm - https://uci.zoom.us/j/96138712994 - Number Theory
Vivian Kuperberg - (Stanford)
Odd moments in the distribution of primes

In 2004, Montgomery and Soundararajan showed (conditionally) that the distribution of the number of primes in appropriately sized intervals is approximately Gaussian and has a somewhat smaller variance than you might expect from modeling the primes as a purely random sequence. Their work depends on evaluating sums of certain arithmetic constants that generalize the twin prime constant, known as singular series. In particular, these sums exhibit square-root cancellation in each term if they have an even number of terms, but if they have an odd number of terms, there should be slightly more than square-root cancellation. I will discuss sums of singular series with an odd number of terms, including tighter bounds for small cases and the function field analog. I will also explain how this problem is connected to a simple problem about adding fractions.