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Upcoming Seminars

Memorial Union on sunny day

Join us for an upcoming seminar featuring mathematics faculty and invited speakers on one of our seven research topics. You may also see upcoming seminars by topic:

Effective Resistance for Connection Graph Laplacian

Kidd 280
Geometry and Topology Seminar

Speaker: Zhengchao Wan

We investigate the concept of effective resistance in connection graphs, expanding its traditional application from undirected graphs. We propose a robust definition of effective resistance in connection graphs by focusing on the duality of Dirichlet-type and Poisson-type problems on connection graphs. Additionally, we delve into random walks, taking into account both node transitions and vector rotations. This approach introduces novel concepts of effective conductance and resistance matrices for connection graphs, capturing mean rotation matrices corresponding to random walk transitions. Thereby, it provides new theoretical insights for network analysis and optimization.This is based on a joint work with Alexander Cloninger, Gal Mishne, Andreas Oslandsbotn, Sawyer Jack Robertson and Yusu Wang. Read more.

Abelian dynamical Galois groups associated to postcritically finite rational functions

On line
Algebra and Number Theory Seminar

Speaker: Chifan Leung

Andrews and Petsche formulated a conjecture that an arboreal Galois extension is abelian if and only if the polynomial is conjugate to a powering map or a Chebyshev map and the base point is a root of unity in a number field. In this talk, we will discuss if a rational function is postcritically finite, and the base point is not preperiodic, then the arboreal Galois tower is not abelian. This uses two deep theorems, a result by Benedetto-Ingram-Jones-Levy on attracting cycles, as well as an equidistribution result by Baker-Rumely, Favre-Rivera-Letelier and Chambert Loir. This work is jointly by me and my advisor Clayton Petsche. Read more.

Identified vaccine efficacy for binary post-infection outcomes under misclassification without monotonicity

Kidder 238
Probability and Data Science Seminar

Speaker: Robert Trangucci

Abstract: To meet regulatory approval, pharmaceutical companies often must demonstrate that new vaccines reduce the total risk of a post-infection outcome like transmission, symptomatic disease, or severe illness in randomized, placebo-controlled trials. Given that infection is necessary for a postinfection outcome, one can use principal stratification to partition the total causal effect of vaccination into two causal effects: vaccine efficacy against infection, and the principal effect of vaccine efficacy against a post-infection outcome in always-infected patients. Despite the importance of such principal effects to policymakers, these estimands are generally unidentifiable, even under strong assumptions that are rarely satisfied in real-world trials. We develop a novel method to nonparametrically point identify these principal effects while eliminating the monotonicity assumption and allowing for measurement error. Moreover, our results readily generalize to multiple treatments.… Read more.

Evaluating Genetic Engineering Trade-offs Through Whole-cell Modeling of Escherichia coli

Kidder 237
Mathematical Biology Seminar

Speaker: Riley Juenemann

Genetically engineered bacteria are utilized to produce compounds that are difficult, expensive, or impractical to synthesize chemically. These compounds have potential applications ranging from medicine to sustainability. However, metabolic pathway introduction, extensive feedback mechanisms in the cell, and evolutionary forces complicate the engineering of bacterial strains that are well-suited for the task. We need tools that will enable us to anticipate these challenges, as well as increase efficiency and enable novel design. A recently published large-scale model of Escherichia coli has enabled us to simulate many distinct cellular processes and capture their complex interactions on a system-wide level. We now introduce components related to genetic engineering, with an initial focus on chromosome modification. In this presentation, I will give an overview of whole-cell modeling and describe preliminary work analyzing the trade-offs between maximizing compound production and… Read more.

Some theoretical results on finite convergence property and temporary stalling behavior of Anderson acceleration on linear systems

STAG 113
Applied Mathematics and Computation Seminar

Speaker: Yunhui He

ABSTRACT: In this talk, we consider Anderson acceleration with window size $m$ (AA(m)) applied to fixed-point iteration for linear systems. We explore some conditions on the $m+1$ initial guesses of AA(m), aiming for the residuals $r_{m+1}=0$. We propose the sufficient and necessary conditions on the $m+1$ initial guesses for $r_{m+1}=0$. These findings can help us better understand the performance between original fixed-point iteration and Anderson acceleration. Meanwhile, it may give us some guidance on the choice of good initial guesses. Moreover, we give examples to show the temporary stalling behavior of Anderson acceleration applied to solving linear systems. BIO: Yunhui He is currently an Assistant Professor in the Department of Mathematics at the University of Houston. During 2021-2023 she was a Postdoctoral Research Fellow in the Department of Computer Science at the University of British Columbia. In 2018, She obtained her PhD after three years' study from Memorial… Read more.

Wave propagation and its failure in lattice equations

STAG 113
Applied Mathematics and Computation Seminar

Speaker: Brian Moore

ABSTRACT: Lattice equations are used to model physical processes or to approximate solutions for continuous models. Various techniques, including Fourier transforms, Jacobi operator theory, and backward error analysis, provide means to construct and study the behavior of traveling-wave-like solutions for discrete reaction-diffusion equations and discrete semi-linear wave equations. The results supply waves speed estimates and necessary and sufficient conditions for fronts and pulses to fail to propagate due to inhomogeneities in the medium, as well as confirmation that certain discretizations reproduce the qualitative solution behavior of the corresponding partial differential equations.BIO: After completing an M.S. degree in mathematical and computer sciences at Colorado School of Mines, Brian Moore earned his Ph.D. in mathematics at the University of Surrey in the United Kingdom in 2003. He held a postdoctoral research position at McGill University in Quebec, followed by a visiting… Read more.

Improving the accuracy of coupled physics packages in Earth system models

STAG 112
Applied Mathematics and Computation Seminar

Speaker: Sean Santos

ABSTRACT: Earth system models solve exceedingly complicated multiphysics problems by breaking down the Earth system hierarchically into smaller sub-models (e.g. atmosphere, ocean, land, and sea ice), which are composed of smaller components themselves. This decomposition of an Earth system model (which may require millions of lines of code in its software implementation) into many small modules is a vital part of model development. However, naïve coupling of modular physics packages using first-order methods can significantly reduce model accuracy, or even produce numerical instability. This talk covers two examples from the Energy Exascale Earth System Model (E3SM). First, we will see that “sequential” (Lie-Trotter) splitting is a major source of error for E3SM’s cloud and precipitation physics. We will discuss our evaluation of several proposed alternatives, including Strang splitting and multirate methods. Second, we will see that E3SM is prone to spurious “oscillations” in winds… Read more.