Nebraska-Iowa Iowa-Nebraska Functional Analysis Seminar
General Format
This is a one-day mathematics conference held once or twice a year, usually in
April in Omaha, Nebraska and in October in Des Moines, Iowa.
The format consists of four hour-long talks, with a one-and-a-half or two hour lunch.
between the 2nd and 3rd talk.
The first talk typically starts at 11:00 am and the last talk finishes about 5:00 pm.
In Des Moines, we usually meet at
The University of Iowa John and Mary Pappajohn Education Center, located at
1200 Grand Ave., Des Moines, IA 50309.
Here is a map.
(For many years, we met on the campus of Drake University,
and we are grateful for their support.)
In Omaha, we usually meet on the campus of
Creighton University.
The conference first met in March of 1994; the April 2014 meeting represented the
twentieth year and the twenty-seventh meeting. (There have not been two meetings every year.)
It is jointly organized by the Mathematics Departments of
Creighton University,
Iowa State University,
The University of Iowa, and
The University of Nebraska-Lincoln.
Faculty and students from a number of other nearby universities also attend.
All are welcome. There is no registration fee.
If you have any questions, please contact one of the organizers.
Organizers
- Randall Crist of Creighton
- Raul Curto of Iowa
- Yiu T Poon of Iowa State
- Allan Donsig of Nebraska-Lincoln
Next Meeting: April 2020
When the meeting is scheduled and as speakers scheduled, they will be posted here.
Speakers and Titles from Previous Meetings
- November 2, 2019
- Yiu Tung Poon (of Iowa State University)
- Title: Preservation of the joint essential matricial range
(slides)
- Chris Schafhauser (of University of Nebraska---Lincoln)
- Title: On the classification of simple nuclear C^{*}-algebras
- Abstract:
A conjecture of George Elliott dating back to the early 1990's asks if separable, simple, nuclear C^{*}-algebras are
determined up to isomorphism by their K-theoretic and tracial data. Restricting to purely infinite algebras, this is the famous
Kirchberg-Phillips Theorem. The stably finite setting proved to be much more subtle and has been a driving force in research in
C^{*}-algebras over the last 30 years. A series of breakthroughs were made in 2015 through the classification results of
Elliott, Gong, Lin, and Niu and the quasidiagonality theorem of Tikuisis, White, and Winter. Today, the classification conjecture
is now a theorem under two additional regularity assumptions: Z-stability and the UCT. I will discuss recent joint work with
Jose ́ Carrio ́n, Jamie Gabe, Aaron Tikuisis, and Stuart White which provides a much shorter and more conceptual proof of the
classification theorem in the stably finite setting.
- Lawrence Fialkow (of SUNY at New Paltz)
- Title: The core variety and open questions in the multivariable moment problem
(slides)
- Abstract:
We discuss three equivalent ``solutions'' to the Truncated Moment Problem (TMP), based on: 1) flat extensions of moment matrices,
2) positive extensions of Riesz functionals, and 3) the core variety of a multisequence.
In work with G. Blekherman [J. Operator Theory, to appear] we proved that a real n-dimensional multisequence of degree
m has a representing measure if and only if the core variety is nonempty, in which case the core variety is
the union of supports of all finitely atomic representing measures.
We discuss open questions concerning difficulties in applying of any of the above solutions to TMP in special cases
or in numerical examples.
- Steven Nathan Harding (of Iowa State University)
(slides)
- Title: A generalized Walsh system for arbitrary matrices
- Abstract:
Inspired by ``Orthonormal bases generated by Cuntz algebras'' by Dutkay and others, we introduce the construction of a collection of functions from filters that arise from a rectangular matrix, generalizing the Walsh basis. We show that properties of the matrix elicit certain desirable features of the generalized Walsh system. In particular, we find a rich source of Parseval frames that are not orthonormal bases. We then conclude an application of the associated generalized Walsh transform to digital image processing.
- November 3, 2018
Ruy Exel is visiting the University of Nebraska--Lincoln during the 2018-19 academic
year.
As part of his visit, he gave the
2018 Rowlee Lecture
on Friday, November 2nd. On the following day, there was a one day
research conference.
For convenience, we post speakers, titles and slides here.
- Ionut Chifan (the University of Iowa)
- Title: Rigidity in group von Neumann algebras
(slides)
- Valentin Deaconu (the University of Nevada, Reno)
- Title: Symmetries of Cuntz-Pimsner algebras
(slides)
- Ken Dykema (Texas A&M University)
- Title: Schur-type upper triangular forms and decomposability in finite von Neumann algebras
- Ruy Exel (University of Nebraska-Lincoln and Universidade Federal de Santa Catarina)
- Title: Quasi-invariant measures for generalized approximately proper equivalence relations
(slides)
- Elizabeth Gillaspy (University of Montana)
(slides)
- Title: Generalized gauge actions, KMS states, and Hausdorff dimension for higher-rank graphs
- Isaac Goldbring (University of California, Irvine)
- Title: Embedding problems, games, and square roots
(slides)
- Jesse Peterson (Vanderbilt University)
- Title: Properly proximal groups and their von Neumann algebras
- April 7, 2018
- Sayan Das (University of Iowa)
- Title: A remark on the ultrapower algebra of the hyperfinite factor
- Zhuang Niu (University of Wyoming)
- Title: The Classification of simple separable nuclear C^{*}-algebras
- Sarah Reznikoff (of Kansas State University)
- Title: Further analysis of the Cartan abelian core
(slides)
- Eric Weber (of Iowa State University)
- Title: The Paley-Wiener theorem for singular measures
(slides)
- November 11, 2017
- Raul Curto (of the University of Iowa)
- Title: Toral and spherical Aluthge transforms
(slides)
- Friedrich Littmann (of the North Dakota State University)
- Title: Perfect band-limited reconstruction
(slides)
- Palle Jorgensen (of the University of Iowa)
- Title: Representations of the Cuntz-algebras, some of their uses, and why they are important.
- Lara Ismert (of the University of Nebraska-Lincoln)
- Title: A weakly-defined derivation and stability of its kernels
- Derek DeSantis (of the University of Nebraska-Lincoln)
- Title: Operator algebras generated by a left invertible
- April 8, 2017
- Roger Smith (of Texas A&M University)
- Title: A Galois Correspondence for Crossed Products
- Abstract:
If a discrete group G acts on an operator algebra A (C^{*} or von Neumann) the question arises of
whether the algebras between A and its crossed product by G can be characterized by subgroups of
G. When A is a simple C^{*}-algebra and G acts by outer automorphisms, a positive answer has been
given by Landstad-Olesen-Pedersen when G is abelian, by Choda (with some rather restrictive
extra hypotheses) and by Izumi when G is finite. In this talk I will give a positive solution for all
discrete groups G and discuss some consequences. This is joint work with Jan Cameron.
- Daniel Freeman (of St. Louis University)
- Title: The Discretization Problem for Continuous Frames
- Abstract:
Functions on L^{2}([0, 1]) can be analyzed continuously through the Fourier transform, or discretely
through Fourier series and sampling the Fourier transform only at the integers. The discretization
problem essentially asks what other continuous representations can be sampled to obtain
discrete representations. We solve this problem by giving a complete characterization of when
a continuous frame for a Hilbert space may be sampled to obtain a discrete frame. In particular,
every bounded continuous frame may be sampled to obtain a discrete frame. This is joint work
with Darrin Speegle.
- Gabriel Nagy (of Kansas State University)
- Title: Essential inclusions revisited - preliminary report
- Abstract:
Call a C^{*}-algebra inclusion A ⊂ B essential, if there is no non-trivial closed two sided ideal
J ⊂ B, such that J ∩ A is empty. Over the past five years or so (joint works with Brown, Reznikoff,
Sims and Williams), most examples of such inclusions were produced by investigating the space
of states on A that extend uniquely to states on B. I will try to explain why conceptually (but not
literally!), this is the only technique that works, if it is suitably adapted to the case when the above
mentioned state space is rather small (or even empty!). As an application, we provide a simplicity
criterion for reduced C^{*}-algebras of etale groupoids. (Joint work with Danny Crytser)
- Lance Nielsen (of Creighton University)
- Title: Feynman's Operational Calculus: Introduction and Essential Properties
- Abstract:
After some background and history related to Feynman’s development of his operational calculus,
the Jefferies-Johnson approach to the operational calculus will be introduced. We will then
survey some important results and applications of the operational calculus, including a look at
stability properties as well as evolution/generalized integral equations satisfied by the operational
calculus.
- November 5, 2016
- Gordon Aiello (of University of Iowa)
- Title: Euclidean Scattering and the Problem of Moments
(slides)
- Calvin Hotchkiss (of Iowa State University)
- Title: Fourier Bases on the "Skewed Sierpinski Gasket"
(slides)
- Paul Muhly (of University of Iowa)
- Title: Operator Algebras as Algebras of Functions
(slides)
- Abstract:
Suppose R and S are two unital rings and let X be the space of all unital homomorphisms of R to S.
Of course, X may be empty, but under favorable conditions, X can be rich and then R can be represented as a ring of S-valued functions on X: r -> r , where r (p) := p(r), p in X.
One can then turn her attention to studying the functions and investigating information they reveal about R.
This may sound familiar - perhaps as some sort of generalized Gelfand theory. In a sense, it is. However, the first thing I want to do is to show that Gelfand was nearly 60 years late to the party. This point of view arose long before Gelfand. I then want to show how the perspective plays an important role in the noncommutative function theory that arises in free analysis and in Baruch Solel's and my work on tensor operator algebras. The operator algebras involved may be represented as algebras of bonafide operator-valued, analytic functions with remarkable properties. That is, the operator algebras are repreented as noncommutative function algebras.
These, in turn, prove to be a fertile environment in which to apply Arveson's theory of subalgebras of C^{*}-algebras.
- David Pitts (of University of Nebraska-Lincoln)
- Title: Unique Pseudo-Expectations, Dynamics, and Minimal Norms
(slides)
- Yiu Tung Poon (of Iowa State University)
- Title: Compression, Matrix Range and Completely Positive Map
(slides)
April 30, 2016
- Sergei Bezuglyi (of University of Iowa)
- Title: Harmonic functions on Bratteli diagrams
(slides)
- Jon Brown (of University of Dayton)
- Title: A ``Weyl type'' groupoid for Leavitt path algebas
- Abstract: Given a Cartan subalgebra A of C^{*}-algebra B, Renault (2008) constructed a topologically principal groupoid whose reduced groupoid C^{*}-algebra is isomorphic to B and where the isomorphism restricts to an isomorphism of the canonical Cartan subalgebra of C_r^{*}(G) to A. However there are many interesting examples abelian subalgebras of a given C^{*}-algebra that are not Cartan; for example given a directed graph E that doesn't satisfy condition L, the subalgebra D(E) generated by the range and source projections of paths in a graph algebra C^{*}(E). Recently, Brownlowe, Carlsen and Whittaker constructed a ``Weyl type'' groupoid for this inclusion: importantly their construction relies only on the algebra and not the graph itself. They showed that this Weyl groupoid is isomorphic to the graph groupoid and thus an isomorphism from C^{*}(E) to C^{*}(F) that is ``diagonal preserving'' in the sense that it restricts to an isomorphism of D(E) to D(F) gives an isomorphism of the graph groupoids. In this talk, I present joint work with Clark and an Huef, which follows Brownlowe et al to construct a Weyl groupoid for Leavitt path algebra. We use this construction to prove that for ``diagonal preserving'' *-ring isomorphisms of Leavitt path algebras, the resulting C^{*}-algebras must also be isomorphic: proving a special cases of the Abrams-Tomforde isomorphism conjecture.
- Rolando de Santiago (of University of Iowa)
- Title: Product rigidity for the von Neumann algebras of hyperbolic groups
(slides)
- Rachel Norton (of University of Iowa)
- Title: Comparing Two Generalized Nevanlinna-Pick Theorems
(slides)
- Eric Weber (of Iowa State University)
- Title: Fourier and Harmonic Analysis of Measures
(slides)
March 28, 2015 (the first meeting at Creighton University in Omaha)
- Danny Cryster (of Kansas State University)
- Title: The abelian core and the trace space of a graph algebra
(slides)
- Abstract: The abelian core of a graph algebra is a MASA which has nice state-extension properties. The spectrum of the abelian core encodes information about the pure states of the graph algebra. We describe the trace space of a graph algebra as the set of measures on this spectrum which satisfy a certain natural covariance condition. Joint work with Gabriel Nagy.
- Jennifer Good (of University of Iowa)
- Title: Toward a complete Pick Property in a W^{*}-Setting
(slides)
- Sarah Reznikoff (of Kansas State University)
- Title: Graph, k-Graph, and Groupoid C*-algebras (cancelled)
(slides)
- Jason Ekstrand (of Iowa State University)
- Title: Positivity in Function Algebras
(slides)
- Travis Russell (of University of Nebraska---Lincoln)
- Title: Order Bounded Maps and Operator Spaces
(slides)
October 19, 2014 .
- John Haussermann (of University of Central Florida)
- Title: On Spectra of a Cantor Measure
(slides)
- Adam Fuller (of University of Nebraska---Lincoln)
- Title: Von Neumann Algebras and Extensions of Inverse Semigroups
(slides)
- Abstract: In the 1970s, Feldman and Moore classified separably acting von Neumann algebras contain ing Cartan MASAs using measured equivalence relations and 2-cocycles on such equivalence relations. In this paper, we give a new classification in terms of extensions of inverse semigroups. By avoiding most measure theory, our approach is simpler, and allows for the classification of all Cartan pairs, even those which do not act separably. Our approach is more algebraic in character and less point-based than that of Feldman-Moore.
- Chris Schafhauser (of University of Nebraska---Lincoln)
- Title: AF-Embeddings of Graph Algebra
(slides)
- Abstract: In the late 1990's, Blackadar and Kirchberg asked if every separable, nuclear, stably finite C*-algebra can be embedded into an AF-algebra. We will discuss this conjecture for the class of graph C*-algebras and Cuntz-Pimsner algebras. In particular, if either that E is a discrete graph or that E is a compact topological graph with no sinks and C*(E) is finite, then C*(E) is AF-embeddable. Also if E is a totally disconnected topological quiver and C*(E) is stable finite, then C*(E) is AF-Embeddable.
- Baruch Solel (of Technion, Israel)
- Title: Matricial Families and Weighted Shifts
(slides)
April 19, 2014 .
- Robert Pluta (of University of Iowa)
- Title: Corners of C*-algebras
(slides)
- Philip Gipson (of University of Nebraska)
- Title: The Invariant Basis Number Property for C*-Algebras
(slides)
- Jon Brown (of Kansas State University)
- Title: Purely infinite simple C*-algebras associated to etale groupoids
(slides)
- Abstract: Let G be a Hausdorff, etale groupoid that is minimal and topologically principal.
In this talk, we reduce the problem of checking if C^{*}_{r}(G) is purely infinite
to checking that elements of C_{0}(G^{(0)}) are infinite
in C^{*}_{r}(G).
In particular, we show that C^{*}_{r}(G) is purely infinite simple
if and only if all the nonzero
positive elements of C_{0}(G^{(0)}) are infinite in C^{*}_{r}(G).
If G is also ample, then we show that C^{*}_{r}(G) is purely infinite simple
if and only if every nonzero projection in C_{0}(G^{(0)})
is infinite in C^{*}_{r}(G).
We then show how this result applies to k-graph C*-algebras.
This work is joint with Lisa Clark and Adam Sierakowski.
- Dima Kaliuzhnyi-Verbovetskyi (of Drexel University)
- Title: Free Noncommutative Functions: An Introduction
(slides)
- Abstract: This talk is intended to be a brief introduction to noncommutative function theory
that derives from the free algebra in the same sense that ordinary analytic functions may be derived from the
polynomial algebra. The fundamental difference is that in the theory of polynomials and ordinary
analytic functions, a polynomial determines a single function of one or more variables, depending
on where one starts. However, in the theory I will be discussing, an element in the free algebra
determines a whole sequence of functions, each one of which is matrix-valued. The problem is
to understand how all these sequences fit together and to base a general theory upon them. This
idea originated in the work of Joe Taylor in the early 1970s. It lay fallow for some years, and
only recently has exploded into a full-fledged theory. This talk is intended to give an introduction
to the theory, which is exposed in detail in my soon-to-be published book with Victor Vinnikov,
Foundations of Noncommutative Function Theory.
November 9, 2013.
- Sergli Berzuglyi (of University of Iowa)
- Title: Full groups of transformations in measurable, Borel, and Cantor dynamics
- Michael Hartglass (of University of Iowa)
- Title: Planar Algebras and thier graded structure
- Matthew Kennedy (of Carleton University)
- Title: The Choquet boundary of an Operator System
(slides)
- Abstract: In this talk, I will discuss the recent solution (with Ken Davidson) of Arveson's conjecture on the existence of the noncommutative Choquet boundary of an operator system. This is an intrinsic invariant of an operator system that plays a fundamental role in Arveson's approach to the study of non-commutative dilation theory and non-self-adjoint operator algebras. I will also mention some recent work (with Orr Shalit) connecting these ideas to the essential normality of a commuting tuple.
- Gabriel Picioroaga (of University of South Dakota)
- Title: Cuntz algebras, generalized Walsh bases, and applications
(slides)
Spring 2013.
There was a very nice AMS special session at the AMS regional meeting at Iowa State.
November 3, 2012.