# Events for November 8, 2017 from General and Seminar calendars

## Postdoc Lunch Time Talks

**Time:** 12:00PM - 12:20PM

**Location:** BLOC 220

**Speaker:** Rick Lynch, Texas A&M University

**Description:**Title: Preserving a certain operator property under subgaussian maps

Abstract: In this talk, I will discuss the following result. As long as an operator $\mathbf{D}$ stays bounded away from zero in norm on $S$ and a provided map ${\boldsymbol \Phi}$ comprised of i.i.d. subgaussian rows has number of measurements at least proportional to the square of $w(\mathbf{D}S)$, the Gaussian width of the related set $\mathbf{D}S$, then with high probability the composition ${\boldsymbol \Phi} \mathbf{D}$ also stays bounded away from zero in norm on $S$ with bound proportional to $w(\mathbf{D}S)$. The null space property is preserved w.h.p. under such subgaussian maps as a consequence, and there might be other potential applications in dimension reduction analysis. This is joint work with Peter G. Casazza (University of Missouri) and Xuemei Chen (University of San Francisco).

## Postdoc Lunch Time Talks

**Time:** 12:35PM - 12:55PM

**Location:** BLOC 220

**Speaker:** Laura Saavedra

**Description:**Title: A stabilized Lagrange-Galerkin method for the simulation of turbulent flows.

Abstract: We present stabilized Lagrange-Galerkin method to integrate the incompressible Navier Stokes equations at high Reynolds numbers. The stabilization of the conventional Lagrange-Galekin method is done via a local projection technique for inf-sup stable finite elements. We prove that the stabilized method has the same accuracy as the standard one. The numerical results shows that our method is stable and can predict the behavior of high Reynolds flows.

## Student Working Seminar in Groups and Dynamics

**Time:** 1:00PM - 2:00PM

**Location:** BLOC 628

**Speaker:** Justin Cantu

**Title:** *Fragmentations and Periodicity of Tree-like Groups*

**Abstract:**We introduce the notion of a tree-like action of a group generated by homeomorphisms of the Cantor set with period 2. Under some conditions, we can produce an orbit-equivalent action by a infinite finitely generated periodic group.

## Noncommutative Geometry Seminar

**Time:** 2:00PM - 2:50PM

**Location:** BLOC 628

**Speaker:** Rufus Willett, University of Hawaii

**Title:** *Finite dynamical complexity and controlled K-theory*

**Abstract:**I’ll discuss a notion of finite dynamical complexity introduced in joint work in Erik Guentner and Guoliang Yu. This notion applies for topological dynamical systems (and more generally for étale groupoids). I’ll sketch connections to amenability and the earlier idea of finite decomposition complexity (introduced by Guentner, Tessera, and Yu), and applications to computing K-theory.

## Numerical Analysis Seminar

**Time:** 3:00PM - 4:00PM

**Location:** BLOC 628

**Speaker:** Diane Guignard, TAMU

**Title:** *A posteriori error estimation for PDEs with random input data*

**Abstract:**In this talk, we perform a posteriori error analysis for partial differential equations with uncertain input data characterized using random variables. Considering first small uncertainties, we use a perturbation approach expanding the solution of the problem with respect to a parameter ε that controls the amount of uncertainty. We derive residual-based a posteriori error estimates that control the two sources of error: the finite element discretization and the truncation in the expansion. The methodology is presented first on an elliptic equation with random coefficients and then on the steady-state Navier-Stokes equations on random domains. In the case of large uncertainties, we use instead the stochastic collocation method for the random space approximation. We present a residual-based a posteriori error estimate that provides an upper bound for the total error, which is composed of the finite element and the stochastic collocation errors. The stochastic error estimator is then used to drive an adaptive sparse grid algorithm. Several numerical examples are presented to illustrate the theoretical findings.

## Groups and Dynamics Seminar

**Time:** 3:00PM - 4:00PM

**Location:** BLOC 220

**Speaker:** Ben Ben Liao, Texas A&M

**Title:** *Noncommutative maximal inequalities for group actions*

**Abstract:**Let $G$ be a finitely generated group, and $M$ a semi-finite von Neumann algebra on which $G$ acts. When the group $G$ has polynomial growth, we obtain strong type $(p,p),p>1,$ and weak type $(1,1)$ maximal inequalities for $G$ acting on $M$. This extends the results of Yeadon and Junge-Xu for the integer group. Based on joint work with Guixiang Hong and Simeng Wang.

## Postdoc Colloquium Series

**Time:** 4:00PM - 5:00PM

**Location:** Bloc 220

**Speaker:** Cecilia Mondaini, TAMU

**Title:** *Analysis of a feedback-control based data assimilation algorithm*

**Abstract:**Forecasts of the future state of a complex physical system (e.g., the atmosphere) that are purely generated from a theoretical model are commonly affected by the limitations of the model inadequately representing reality. Data assimilation is the technique that combines the theoretical model with information from physical observations in order to obtain a better prediction of the future state of the system. In this talk, I will show some analytical results concerning a certain data assimilation algorithm based on feedback control. This is based on joint works with A. Biswas, C. Foias and E. S. Titi.

## AMUSE

**Time:** 6:00PM - 7:00PM

**Location:** BLOC 220

**Speaker:** Dr. Kamran Entesari, Texas A&M University, Department of Electrical and Computer

**Title:** *Mathematical Analysis of Signal and Noise In Digital Wireless Communication Channels*

**Abstract:**This talk describes the mathematical representation of fundamental concepts behind signal transmission and reception in digital wireless communication channels including frequency domain and modulation theory. It also explains the concept of stochastic process and channel noise to calculate signal to noise ratio and bit-error rate in digital receivers. The talk is concluded with an example of a real-world digital wireless communication system.