Archives: 2011 | 2012 | 2013 | 2014 | 2015 | 2016 | 2017

• #### Speaker: Addison Bohannon (UMD) -

When: Mon, March 27, 2017 - 12:00pm
Where: Kirwan Hall 1311
• #### Speaker: Michael Robinson (American University) -

When: Mon, March 27, 2017 - 1:00pm
Where: Kirwan Hall 3206
• #### Speaker: Yoshihiro Ishikawa (Okayama University, JAPAN) - http://www.math.okayama-u.ac.jp/staff.html

When: Mon, March 27, 2017 - 2:00pm
Where: Kirwan Hall 1311

### View Abstract

Abstract:
We introduce Harder type periods as the difference of two rational
structures attached to the zeta integral of Gelbart-Piatetski-Shapiro.
One is obtained from Whittaker model of our generic cohomological cuspidal
representation $\pi$. The other comes from the cohomological interpretation
of the integral, by using Mahnkopf cycles on Picard modular surface. We show
the cuspidality preservation of $Aut(\C)$-action on $\pi$, looking at the
structure of the automorphic spectrum on U(3). The non vanishing problem of
archimedean integral is cleared by my Whittaker new vectors. So we get our
rationality of the critical values of $L$-function for quasi-split $U(3)$.

• #### Speaker: Christian Rosendal (University of Maryland ) - http://homepages.math.uic.edu/~rosendal/

When: Mon, March 27, 2017 - 3:15pm
Where: Kirwan Hall 1313

### View Abstract

Abstract: We show how every topological group is canonically equipped with a coarse geometric structure. For a compact manifold M, the coarse structure on the identity component of the homeomorphism group, Homeo_0(M), is induced by the so called fragmentation metric. We connect the non-triviality of the geometry to the size of the fundamental group of M and also show how it relates to the group of lifts to a normal cover. (Part of the talk is based on joint work with K. Mann.)
• #### Speaker: Livio Flaminio (Universite de Lille 1, France) - http://math.univ-lille1.fr/~flaminio/

When: Tue, March 28, 2017 - 2:00pm
Where: MTH B0427

### View Abstract

Abstract: We prove that any ergodic affine unipotent diffeomorphisms of a compact
nilmanifold enjoys the property of asymptotically orthogonal
powers (AOP). Two consequences follow: (i) Sarnak's conjecture on
M\"obius orthogonality holds in every uniquely ergodic model of an
ergodic affine unipotent diffeomorphism; (ii) For ergodic affine
unipotent diffeomorphisms themselves, the M\"obius orthogonality holds
on so called typical short intervals.

(Joint work with K.\ Fr\k{a}czek, J.\ Ku\l aga-Przymus and
M.\ Lema\'nczyk.)
• #### Speaker: Clifton Cunningham (University of Calgary) - http://math.ucalgary.ca/math_unitis/profiles/clifton-cunningham

When: Tue, March 28, 2017 - 2:00pm
Where: Kirwan Hall 1311

### View Abstract

Abstract: This talk will explain how to adapt the approach developed by Adams-Barbasch-Vogan to Arthur packets from Real groups to p-adic groups, and will illustrate this adaptation with several examples. We will also sketch a proof showing that Arthur packets are p-adic ABV packets for unipotent representations of p-adic special orthogonal groups.

Joint with: Bin Xu, Ahmed Moussaoui, Andrew Fiori, James Mracek
• #### Speaker: David Sherman (University of Virginia) -

When: Tue, March 28, 2017 - 3:30pm
Where: Kirwan Hall 1311

### View Abstract

Abstract: Historically, model theory has not had much influence on functional analysis. One reason is that the ultrapowers appropriate for analysis do not quite have the same model theoretic significance as their classical counterparts. An elegant recent solution -- not the first -- is to switch to a logic in which truth values are drawn from the interval [0,1]. This "continuous model theory" is natural for analysts and has opened up a flurry of interaction between the two fields. I will try to explain what this approach is, where it came from, and what kinds of things happen when model theorists start playing with Banach spaces, C*-algebras, etc.
• #### Speaker: Xiaoye (Sherry) Li (Lawrence Berkeley Laboratory) - http://crd-legacy.lbl.gov/~xiaoye/

When: Tue, March 28, 2017 - 3:30pm
Where: 3258 AV Williams

### View Abstract

Abstract: Many extreme-scale simulation codes encompass multiphysics components in multiple spatial and length scales. The resulting discretized sparse linear systems can be highly indefinite, nonsymmetric and extremely ill-conditioned. For such problems, factorization based algorithms are often the most robust algorithmic choices among many alternatives. We present our recent research on novel parallel factorization algorithms that are efficient for solving such problems. From algorithm side, we incorporate data-sparse low-rank structures, such as hierarchical matrix algebra, to achieve lower arithmetic and communication complexity as well as robust preconditioner. From parallelization side, we exploit sparse data structures represented by DAGs and trees to schedule coarse-grained tasks and SIMD/SIMT for fine-grained parallelism. We will illustrate both theoretical and practical aspects of the methods, and demonstrate their performance on manycore architectures including GPU clusters and the latest Intel Xeon Phi KNL platforms, using a variety of real world problems.
• #### Speaker: Xiaofeng Sun (Lehigh) -

When: Tue, March 28, 2017 - 4:30pm
Where: Ames 218 (Johns Hopkins)

### View Abstract

Abstract: In this talk we will describe a new necessary and sufficient condition on the existence of KE metrics on all small deformation of a Fano KE manifold with nontrivial automorphism group. We will also describe a canonical extension of pluri-anticanonical forms from a Fano KE manifold to its small deformations which leads to simultaneous embedding of a family of Fano manifolds into projective spaces with effective control. We will also discuss a construction of plurisubharmonic functions on Teichmuller spaces of KE manifolds of general type by using energy of equivariant harmonic maps.
• #### Speaker: Michael Salins (Boston University) - http://math.bu.edu/people/msalins/index.html

When: Wed, March 29, 2017 - 11:00am
Where: Kirwan Hall 3206

### View Abstract

Abstract: We develop provably efficient importance sampling methods for estimating rare events for linear stochastic partial differential equations exposed to small noise. We use a spectral method to identify a one-dimensional linear span where the rare event likely occurs and we project our change of measure onto that direction. The scheme we develop works well for a wide variety of different intensities of noise, time horizons, and finite dimensional Galerkin approximations of the infinite dimensional system. Simulations support the theoretical results.
• #### Speaker: Prof. Kayo Ide (University of Maryland)

When: Wed, March 29, 2017 - 2:00pm
Where: CSIC 4122

### View Abstract

Abstract: Data assimilation is a method to estimate and predict evolution of physical system by integrating computational models and observations sampled from the evolving system. Prediction can be extremely challenging when the underlying physical system is highly nonlinear, corresponding model is high-dimensional and complex, and observations are not only nonlinear but also heterogeneous and inhomogeneous. In the context of data assimilation, impact of selected sets of observations on the optimal estimation can be quantified by information theory. The concept can be extended to evaluate the impact on forecast skill. In other words, forecast skill can be traced back to the observations used in the state estimate using an adjoint technique that can be either explicit or ensemble based. Forecast Sensitivity to Observations (FSO) is a diagnostic tool that complements traditional data denial of the observing system experiments. In this talk, we will present the FSO in the operational numerical weather prediction. We will also discuss the effect of observation and model biases on FSO.
• #### Speaker: Nicolas Arancibia (Paris) -

When: Wed, March 29, 2017 - 2:00pm
Where: Kirwan Hall 1311

### View Abstract

Abstract: The objective of this talk is to give an introduction to the Local Arthur Conjecture (LAC). In a first time I will introduce the LAC for any local field of characteristic zero, then I will specialize to the Archimedean case and introduce the packets of irreducible unitary cohomological representations defined by J. Adams and J. Johnson in 1987 and the work of C. Moeglin and D. Renard on complex classical groups. If time allows me I will end the talk with a short exposition of the work of J. Adams, D. Barbasch and D. Vogan on the local Arthur conjecture.
• #### Speaker: Stephen Gilles (UMCP) -

When: Wed, March 29, 2017 - 2:00pm
Where: Math 2300
• #### Speaker: Daniel Orr (Virginia Tech) - https://www.math.vt.edu/people/dorr/

When: Wed, March 29, 2017 - 3:15pm
Where: MTH 0403

### View Abstract

Abstract: Hall-Littlewood symmetric functions and their transition coefficients
with Schur functions, the Kostka-Foulkes polynomials, have multiple
realizations in representation theory, geometry, and combinatorics.
These realizations reveal deep properties such as the positivity of
the Kostka-Foulkes polynomials.

I will discuss joint work with Mark Shimozono in which we define a
family of Hall-Littlewood functions for any quiver. Our functions form
a basis for a tensor power of symmetric functions over a field with
several parameters, one for each arrow in the quiver. For the Jordan
quiver, with a single vertex and single loop arrow, our functions are
the usual (modified) Hall-Littlewood functions. For a cyclic quiver
with more than one vertex, they are modified versions of functions
defined by Shoji. The general quiver Hall-Littlewood functions are
defined via creation operators and also admit a geometric
interpretation.

We conjecture that the quiver Hall-Littlewood functions are
Schur-positive for arbitrary quivers. In the context of cyclic quivers
we propose an explicit combinatorial formula for the multiparameter
Kostka-Shoji polynomials, which were introduced and studied recently
by Finkelberg and Ionov.
• #### Speaker: Tom Antonsen (Department of Physics - University of Maryland) - http://www.umerc.umd.edu/faculty/antonsen

When: Thu, March 30, 2017 - 12:30pm
Where: ERF 1207

### View Abstract

Abstract:
Physicists and engineers frequently encounter situations where calculations of the governing equations of a system of interest appear to need to be repeated many times to describe or optimize the system. It is often the case that only a particular state dependent quantity or metric needs to be determined. In this case a computational savings can be achieved if an âadjoint problemâ can be found that produces the desired information without requiring multiple computations. A simple example is the design of a receiving antenna. One wishes to know and optimize the signal received as a function of the incident angle and polarization of incoming waves. It might appear that solution of Maxwellâs field equations would have to be repeated for each possible incident direction and polarization. However, due to the reciprocal property of the governing equations, the desired information is obtained by treating the antenna as a transmitter and calculating the far field radiation pattern. Thus, one computation replaces many. In this talk I will review some problems from the area of charged particle dynamics where adjoint methods have proven useful. A new example is the optimization of electron beam optics in beam sources used in microwave and millimeter wave amplifiers.

• #### Speaker: Ilya Vinogradov (Princeton University) - https://web.math.princeton.edu/~ivinogra/

When: Thu, March 30, 2017 - 2:00pm
Where: Kirwan Hall 1311

### View Abstract

Abstract: The study of randomness of fixed objects is an area of active
research with many exciting developments in the last few years. We will
discuss recent results about sequences in the unit interval specializing to
directions in affine lattices, \sqrt n modulo 1, and directions in hyperbolic lattices.
Theorems about these sequences address convergence of moments as well as rates of convergence, and their proofs showcase a beautiful interplay between dynamical systems and number theory. I plan to focus on hyperbolic lattices for the more technical part of the talk.
• #### Speaker: Alpar Meszaros (UCLA) -

When: Thu, March 30, 2017 - 3:30pm
Where: Kirwan Hall 3206

### View Abstract

Abstract:
Abstract: In this talk the main question that I will consider is the regularity of solutions of certain variational problems in optimal transport. In particular I will be interested in the Wasserstein projection of a measure with BV density on the set of measures with densities bounded by a given BV function f. I will show that the projected measure is of bounded variation as well with a precise estimate of its BV norm. Of particular interest is the case f = 1, corresponding to a projection onto a set of densities with an $L^\infty$ bound, where one can prove that the total variation decreases by the projection. This estimate and, in particular, its iterations have a natural application to some evolutionary PDEs as, for example, the ones describing a crowd motion. In fact, as an application of our results, one can obtain BV estimates for solutions of some non-linear parabolic PDEs by means of optimal transport techniques. The talk is based on a joint work with G. De Philippis (SISSA, Italy), F. Santambrogio (Orsay, France) and B. Velichkov (Grenoble, France).
• #### Speaker: Alpar Meszaros (UCLA) -

When: Thu, March 30, 2017 - 3:30pm
Where: Kirwan Hall 3206

### View Abstract

Abstract: In this talk the main question that I will consider is the regularity of solutions of certain variational problems in optimal transport. In particular I will be interested in the Wasserstein projection of a measure with BV density on the set of measures with densities bounded by a given BV function f. I will show that the projected measure is of bounded variation as well with a precise estimate of its BV norm. Of particular interest is the case f = 1, corresponding to a projection onto a set of densities with an $L^\infty$ bound, where one can prove that the total variation decreases by the projection. This estimate and, in particular, its iterations have a natural application to some evolutionary PDEs as, for example, the ones describing a crowd motion. In fact, as an application of our results, one can obtain BV estimates for solutions of some non-linear parabolic PDEs by means of optimal transport techniques. The talk is based on a joint work with G. De Philippis (SISSA, Italy), F. Santambrogio (Orsay, France) and B. Velichkov (Grenoble, France).
• #### Speaker: Richard Wentworth (UMCP) -

When: Thu, March 30, 2017 - 3:30pm
Where: PHYS 1117

### View Abstract

Abstract: We will go back to Ch. 3 of "Dirichlet Branes and Mirror Symmetry, that gets into the heart of the subject.

• #### Speaker: Dmitry Jakobson (McGill University ) - http://www.math.mcgill.ca/jakobson/

When: Fri, March 31, 2017 - 3:15pm
Where: Kirwan Hall 3206

### View Abstract

Abstract: After giving an overview of Quantum Ergodicity results on
compact Riemannian manifolds with ergodic geodesic flow (due to
Shnirelman, Zelditch, Colin de Verdiere and others), we discuss joint
work with Yury Safarov and Alex Strohmaier, which concerns the
semiclassical limit of spectral theory on manifolds whose metrics have
jump-like discontinuities. Such systems are quite different from
manifolds with smooth Riemannian metrics because the semiclassical
limit does not relate to a classical flow but rather to branching
(ray-splitting) billiard dynamics. In order to describe this system we
introduce a dynamical system on the space of functions on phase space.
We prove a quantum ergodicity theorem for discontinuous systems. In
order to do this we introduce a new notion of ergodicity for the
ray-splitting dynamics. If time permits, we outline an example
(provided by Y. Colin de Verdiere) of a system where the ergodicity
assumption holds for the discontinuous system.
We end with a list of open problems.