epshteyn (at) math.utah.edu)August 27
Speaker:
Eugene Mishchenko, Department of Physics and Astronomy, The University of Utah
Title: The puzzling phenomenon of minimal conductivity of graphene
Abstract: graphene is a two-dimensional crystal of carbon atoms arranged in
a honeycomb lattice. Graphene happens to be a semi-metal that can, in some
instances, display insulating properties yet reveal metallic behavior in
others. For example, conductivity of graphene is predicted by the band
theory to be metallic. In contrast, screening of Coulomb interaction
between electrons is expected to be rather weak, very much like in typical
insulators. Accordingly, one would expect interactions to be strong and
result in significant corrections to the conductivity. Surprisingly,
experiments show little such corrections, if any. I will discuss
theoretical efforts expended over the last decade to understand this
phenomenon.
September 10
Speaker:
Braxton Osting, Department of Mathematics, The University of Utah
Title: Diffusion generated methods for target-valued maps
Abstract: A variety of tasks in inverse problems and data analysis can be formulated as the variational problem of minimizing the Dirichlet energy of a function that takes values in a certain target set and possibly satisfies additional constraints. These additional constraints may be used to enforce fidelity to data or other structural constraints arising in the particular problem considered. I'll present diffusion generated methods for solving this problem for a wide class of target sets and prove some stability and convergence results. I'll give examples of how these methods can be used for the geometry processing task of generating quadrilateral meshes, finding Dirichlet partitions, constructing smooth orthogonal matrix valued functions, and solving inverse problems for target-valued maps. This is joint work with Dong Wang and Ryan Viertel.
September 24
Speaker:
Lajos Horvath, Department of Mathematics, The University of Utah
Title: Change Point Detection in the Conditional Correlation Structure of Multivariate Volatility Models
Abstract: We propose semi-parametric CUSUM tests to detect a change point in the correlation structures of non--linear multivariate models with dynamically evolving volatilities. The asymptotic distributions of the proposed statistics are derived under mild conditions. We discuss the applicability of our method to the most often used models, including constant conditional correlation (CCC), dynamic conditional correlation (DCC), BEKK, corrected DCC and factor models. Our simulations show that, our tests have good size and power properties. Also, even though the near--unit root property distorts the size and power of tests, de--volatizing the data by means of appropriate multivariate volatility models can correct such distortions. We apply the semi--parametric CUSUM tests in the attempt to date the occurrence of financial contagion from the U.S. to emerging markets worldwide during the great recession.
Joint work with Marco Barassi, Department of Economics, University of Birmingham UK and Yuqian Zhao, Department of Statistics and Actuarial Science, University of Waterloo, Canada.
October 1
Speaker:
Jia Zhao, Department of Mathematics, Utah State University
Title: Thermodynamically Consistent Models and Their Structure-Preserving Numerical
Approximations
Abstract: Generally speaking, all non-equilibrium dynamical models should be consistent with
thermodynamical principles, saying the first and second laws of thermodynamics.
Thermodynamically consistent models possess several advantages. First of all, they
are physically consistent (not breaking physical laws); secondly, they usually
possess good mathematical structures that warrant well-posedness of the governing
partial differential equations; thirdly, they provide guidance to developing stable
numerical approximations. In this talk, I will first present a general approach for
deriving thermodynamically consistent models using the generalized Onsager principle
and the variational principle. It turns out many existing models in literature are
special cases of the generalized model formulation.Then, I will introduce the newly
proposed energy quadratization (EQ) strategy to develop efficient, high-order
accurate and energy-stable numerical approximations for a class of thermodynamically
consistent models. Applications of this modeling and numerical paradigm will be
discussed.
October 15
Speaker:
Akil Narayan, Department of Mathematics and SCI, The University of Utah
Title: Low-rank multifidelity methods for parameterized scientific models
Abstract: We present an algorithm for coupling inexpensive low-fidelity model simulations with
high-fidelity simulation data of parameterized differential equations. The goal is
to grab a "free lunch": simulation accuracy of the high-fidelity model with
algorithmic complexity of only a simplified low-fidelity model. The procedure forms
an approximation with sparsely available high-fidelity simluations, and is a simple
linear algebraic construction with connections to kernel learning and column
skeletonization of matrices. We discuss theoretical results that establish accuracy
guarantees, and introduce recent analysis providing bounds on the error committed by
the algorithm.
October 22
Speaker:
Dong Wang, Department of Mathematics, The University of Utah
Title: The threshold dynamics method and its applications
Abstract: In this talk, I will review some recent work on the threshold
dynamics method for diffusion generated motion of the interface on a solid
surface. We also analyze the contact line behavior of the method from
asymptotic expansion and the contact line dynamic is derived for the
wetting problem. Applications to image segmentation, topology optimization
for fluids, and configurations of heterogeneous foams will also be
presented.
October 29
Speaker:
Ian Tobasco, Department of Mathematics, University of Michigan,
Ann Arbor
Title: The cost of crushing: curvature-driven wrinkling of thin elastic shells
Abstract: How much energy does it take to stamp a thin elastic shell flat? Motivated
by recent experiments on wrinkling patterns formed by thin floating shells,
we develop a rigorous method via Gamma-convergence for evaluating the cost
of crushing to leading order in the shell's thickness and other small
parameters. The experimentally observed patterns involve regions of
well-defined wrinkling alongside totally disordered regions in which no
single direction of wrinkling is preferred. Our goal is to explain the
appearance of such "wrinkling domains". The basic mathematical objects that
emerge in the limit are (linearly) short maps from the mid-shell into the
plane, and defect measures to describe the wrinkling patterns. To solve for
the limiting shape, one must maximize the total area covered in the plane
subject to a shortness constraint; to solve for the optimal patterns, one
must minimize the total defect subject to a curvature constraint. We
analyze these limiting problems using convex duality, and obtain a boundary
value-like problem that completely characterizes optimal defect measures.
Optimal defect measures are not in general unique. Nevertheless, in some
cases their restrictions to certain sub-domains are uniquely determined,
and explicit formulas exist.
November 5
Speaker:
Ellis Scharfenaker, Department of Economics, The University of Utah
Title: Statistical Equilibrium Economics
Abstract: In this talk I will explore some of the reasons why the problems in the
articulation of theory and measurement in economics is rooted in the standard
equilibrium concept. I will discuss how methods from statistical mechanics and
information theory offer a general approach to modeling social and economic
phenomena.
November 19
Speaker:
Brian Knaeble, Department of Mathematics, UVU
Title: Sensitivity Analysis for Causal Inference
Abstract: It is not always ethical to conduct a randomized controlled
trial. Within the field of environmental epidemiology exposure scientists
have amassed large amounts of observational data. When analyzing such data
classic sensitivity analysis may be used to support causal inference. This
talk will provide an overview of recently developed mathematical methods
for improved sensitivity analysis. We will discuss how best to apply these
methods for better interpretation of data arising from studies relating to
local population health here along the Wasatch Front.
December 3
Speaker: Qing Xia,
Department of Mathematics, The University of Utah
Title: A Domain Decomposition Approach based on Difference Potentials Method for Chemotaxis Models in 3D
Abstract: In this talk, I will present a domain decomposition
approach based on Difference Potentials Method (DPM) for approximating
the solution to the classical Patlak-Keller-Segel chemotaxis models in
3D. We employ DPM and uniform Cartesian meshes to handle sub-domains
of complex geometric shapes, without loss of accuracy near the
irregular boundaries of the sub-domains. As a result of using uniform
meshes, fast Poisson solver based on FFT is employed for better
efficiency of our numerical algorithms. In addition, our domain
decomposition approach is capable of mesh adaptivity and is suitable
for parallel computing, which further boosts the efficiency. Numerical
results from 3D simulations will be given to demonstrate the
significantly improved efficiency and similar accuracy of the domain
decomposition approach, in comparison to the single domain approach.
(Joint work with Yekaterina Epshteyn).
December 10 (Special Seminar), Room LCB 219
Speaker: Natalie Sheils,
School of Mathematics, The University of Minnesota
Title: Revivals and Fractalization in the Linear Free Space Schrodinger
Equation with Pseudoperiodic Boundary Conditions
Abstract: We consider the one-dimensional linear free space
Schrodinger equation on a bounded interval subject to homogeneous linear boundary
conditions. We prove that, in the case of pseudoperiodic boundary
conditions, the solution of the initial-boundary value problem exhibits
the phenomenon of revival at specific (``rational'') times, meaning that
it is a linear combination of a certain number of copies of the initial
datum. Equivalently, the fundamental solution at these times is a finite
linear combination of delta functions. At other (``irrational'') times,
for suitably rough initial data, e.g., a step or more general piecewise
constant function, the solution exhibits a continuous but fractal-like
profile. Further, we express the solution for general homogeneous linear
boundary conditions in terms of numerically computable eigenfunctions. (Joint work with Peter Olver and David Smith)
December 18, Room TBA
Speaker: Mikyoung Lim,
Department of Mathematical Sciences, KAIST
Title: Series solution to interface problems using the geometric function
theory
Abstract: In this talk I present a new series solution method to solve the
interface problems, the conductivity problem and the linear elasticity
problem in the presence of inclusions. For arbitrary simply connected
domain in two dimensions there exists a conformal mapping from the unit
disk to the domain. By reflecting the conformal mapping via a circle, we
have an exterior conformal mapping as well. The coefficients of the
conformal mapping fully contain the geometry information of the domain. I
will introduce a new boundary integral method to compute the conformal
mapping coefficients and a series solution for the interface problems using
the properties of the conformal mapping.
epshteyn (at) math.utah.edu).
Past lectures: Spring 2018, Fall 2017, Spring 2017, Spring 2016, Fall 2015, Spring 2015, Fall 2014, Spring 2014, Fall 2013, Spring 2013, Fall 2012, Spring 2012, Fall 2011, Spring 2011, Fall 2010, Spring 2010, Fall 2009, Spring 2009, Fall 2008, Spring 2008, Fall 2007, Spring 2007, Fall 2006, Spring 2006, Fall 2005, Spring 2005, Fall 2004, Spring 2004, Fall 2003, Spring 2003, Fall 2002, Spring 2002, Fall 2001, Spring 2001, Fall 2000, Spring 2000, Fall 1999, Spring 1999, Fall 1998, Spring 1998, Winter 1998, Fall 1997, Spring 1997, Winter 1997, Fall 1996, Spring 1996, Winter 1996, Fall 1995.