# Analysis Seminars 2017/18

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**Speaker:**

**Date: **

**Time: ** 3pm

**Location: ** **2nd Seminar**

**Title:** TBC

**Speaker:** TBC

**Date: **

**Time: ** 4.15pm

**Location:**

**Title: ** The continuity of betweenness**Speaker:** Richard Smith (UCD)**Date: ** Tuesday, 3rd October 2017**Time: ** 4pm**Location: ** UCD, 125 Science North (JK Lab)**Abstract:**

Given a set $X$, we can use a suitable ternary relation $[\cdot,\cdot,\cdot] \subseteq X^3$ to express the notion of `betweenness' on $X$: $x$ is between $a$ and $b$ if and only if $[a,x,b]$ holds. We assume that this relation is "basic": $[a,a,b]$ and $[a,b,b]$ always hold, $[a,x,b]$ implies $[b,x,a]$, and $[a,x,a]$ implies $x=a$. Many natural examples of betweenness arise when $X$ is endowed with some additional order-theoretic or topological structure. Given $a,b \in X$, we can define the "interval" $[a,b] = \lbrace x \in X\,:\,[a,x,b]\rbrace\;(= [b,a])$. If $X$ has additional topological structure, it is reasonable to ask whether the assignment $\lbrace a,b\rbrace \mapsto [a,b]$ has good continuity properties, given a suitable hyperspace topology. We examine this question in the context of "Menger betweenness" on metric spaces $(X,d)$ ($[a,x,b]$ holds if and only if $d(a,b)=d(a,x)+d(x,b)$), and the "K-interpretation of betweenness" on topological continua ($[a,x,b]$ holds if and only if $x$ is an element of every subcontinuum that includes $a$ and $b$). This is joint work with Paul Bankston (Marquette University, WI) nd Aisling McCluskey (NUI Galway).

**Please note there will be two talks; one at 3pm and a 2nd at 4.15pm****There will be coffee during the interval in Room G26A****Title: ** Non-commutative graph parameters and quantum chanel capacities

**Speaker: ** Rupert Levene - (UCD)**Date: ** Tuesday, 10th October 2017**Time: ** 3pm**Location:** Room 1.25 Science Centre North**Abstract:**

We generalise some graph parameters to non-commutative graphs

(a.k.a. operator systems of matrices) and quantum channels. In particular,

we introduce the quantum complexity of a non-commutative graph,

generalising the minimum semidefinite rank. These parameters give upper

bounds on the Shannon zero-error capacity of a quantum channel which can

beat the best general upper bound in the literature, namely the quantum

Lovász theta number.

This is joint work with Vern Paulsen (Waterloo) and Ivan Todorov (Belfast).

Please note there will be two talks; one at 3pm and a 2nd at 4.15pm

There will be coffee during the interval in Room G26A**Title: ** Fractal substitution tilings and applications to noncommutative Geometry**Speaker:** Michael Whittaker (Glasgow)

**Date: ** Tuesday, 10th October 2017**Time: ** 4.15pm**Location: ** Room 1.25 Science Centre North**Abstract:**

Starting with a substitution tiling, such as the Penrose tiling, we demonstrate a method for constructing infinitely many new substitution tilings. Each of these new tilings is derived from a graph iterated function system and the tiles typically have fractal boundary. As an application of fractal tilings, we construct an odd spectral triple on a

C*-algebra associated with an aperiodic substitution tiling. Even though spectral triples on substitution tilings have been extremely well studied in the last 25 years, our construction produces the first truly noncommutative spectral triple associated with a tiling. My work on fractal substitution tilings is joint with Natalie Frank and Sam Webster, and mywork on spectral triples is joint with Michael Mampusti.

This is joint work with Paul Bankston (Marquette University, WI)

and Aisling McCluskey (NUI Galway).

**Title: **Nearby Birkhoff averages

**Speaker:** Neil Dobbs (UCD) Date: Tuesday, 17th October 2017

**Time:** 4pm

**Location:** Room 1.25, O’Brien Centre for Science

**Abstract:**

Birkhoff averages (of an observable along orbits) are objects of interest when investigating statistical behaviour of a dynamical system. If there is a unique physical measure, the Birkhoff averages will converge, for almost every orbit, to the space average (i.e. the integral) of the observable, so the physical measure captures important statistical properties of the dynamical system. However, in the quadratic family, for example, physical measures don't always exist, and even when they do, they don't necessarily depend continuously on the parameter. In joint work with Alexey Korepanov, we examine what happens for finite time Birkhoff averages for nearby parameters.

Coffee will be served in Room G0.26A, Ground floor, Science North at 3.45pm.

**Title: ** TROs and Morita equivalence

**Speaker: ** Richard Timoney (TCD)

**Date: ** Tuesday, 24th October 2017**Time: ** 4pm**Location: ** Room 1.25, O’Brien Centre for Science (North)**Abstract:**

It is possible to recast the theory of Morita equivalence in terms of the elementary theory of Ternary Rings of Operators (TROs). In particular the Morita correspondence between primitive ideals follows by extending irreducible representations from the right C*-algebra to the linking

C*-algebra. The celebrated Brown-Green-Reiffel theorem characterising Morita equivalence as stable isomorphism in

the separable case follows by using a Lemma of Brown to show that separable stable TROs are TRO isomorphic to C*-algebras.

Coffee will be served in Room G0.26A, Ground floor, Science North at 3.45pm.

**Title: ** Real Extreme points of Spaces of Complex Polynomials

**Speaker:** Christopher Boyd (UCD)

**Date: ** Tuesday, 7th November 2017

**Time: ** 4pm**Location: ** Room 1.25, O’Brien Centre for Science (North)**Abstract:**

Given a Banach space $E$ and a positive integer $n$ we let $\mathcal P_I(^nE)$ denote the space of all $n$-omogeneous integral polynomials on $E$. This space generalise the trace class operators and plays an important role in the duality theory of spaces of homogeneous polynomials. When $E$ is a real Banach space and $n\ge 2$ it is known that the set of extreme points of the unit ball of $\mathcal P_I(^nE)$ is equal to the set $\{ \pm\varphi^n : \|\varphi\|=1 \}$.

When $E$ is a complex Banach space a characterisation of the set of extreme points of the unit ball of $\mathcal P_I (^nE)$ is not so easy to establish. In this talk, I will look at what can be said for low values of $n$ and small linear combinations of extreme points. This is joint work with Anthony Brown.

Coffee will be served in Room G0.26A, Ground floor, Science North at 3.45pm.

**Title: ** Isoperimetric inequalities for Bergman analytic content I

**Speaker: ** Stephen Gardiner (UCD)

**Date: ** Tuesday, 14th November 2017

**Time:** 3pm (1st talk)

**Location: ** Room 1.25, O’Brien Centre for Science (North)

**Abstract:**

The analytic content of a plane domain measures the distance between $\bar z$ and a given space of holomorphic functions on the domain. It has a natural analogue in all dimensions which is formulated in terms of harmonic vector fields. This talk will review known results about analytic content, and then focus on the Bergman space of $L^p$ integrable holomorphic functions. It will describe isoperimetric-type inequalities for Bergman p-analytic content in terms of the St Venant functional for torsional rigidity, and address the cases of equality with the upper and lower bounds. (This is joint work with Marius Ghergu and Tomas Sjödin.)

Coffee will be served in Room G0.26A, Ground floor, Science North at 3.45pm.

**Title: ** The differential equation of second order for the cross product of Bessel functions

Speaker: Herman Render (UCD)

**Date: ** Tuesday, 14th November 2017

**Time: ** 4.15pm (2nd talk)

**Location: ** Room 1.25, O’Brien Centre for Science (North)

**Abstract:**

Bessel functions play an important role for problems with cylindrical symmetry. The cross product of Bessel functions is used for solving boundary value problems of an annular cylinder. In this talk we shall present the construction of a second order differential equation for the cross product. The method applies in a more general

setting and various examples will be given. For the case of half-integers the potential of the cross product can be explicitly computed and examples show that the potential seems to have a special form, having a unique maximum at one point $x_0$ and it is increasing for $x < x_0$ and decreasing for $x > x_0$.

**Title: ** The Denjoy-Wolff theorem for Hilbert geometries

**Speaker: ** Bas Lemmens (University of Kent)

**Date: ** Tuesday, 21st November 2017

**Time: ** 3pm (1st talk)

**Location: ** Room 1.25, O’Brien Centre for Science (North)

**Abstract:**

The classical Denjoy-Wolff theorem asserts that all orbits of a fixed point free holomorphic self-mapping of the open unit disc in the complex plane, converge to a unique point in the boundary of the disc. Since the inception of the theorem by Denjoy and Wolff in the nineteen-twenties a variety of extensions have been obtained. In this talk I will discuss some extensions of the Denjoy-Wolff theorem to certain real metric spaces, namely Hilbert geometries. Hilbert geometries are a natural generalisation of Klein's model of the real hyperbolic space, and play in important role in the analysis of linear, and nonlinear, operators on cones.

**Coffee will be served in Room G0.26A, Ground floor, Science North at 4pm prior to second seminar.**

*Coffee will be served in Room G0.26A, Ground floor, Science North at 4pm.***2nd Seminar****Title: ** Isoperimetric Inequalities for Bergman Analytic Content II

**Speaker: ** Stephen Gardiner (UCD)

**Date: ** Tuesday, 21st November 2017

**Time: ** 4.15pm (2nd talk)

**Location:** Room 1.25, O’Brien Centre for Science (North)

**Title:** Nonlocal Pertubations of Fractional Choquard

**Speaker: ** Gurpreet Singh (UCD)

**Date: ** Tuesday, 28th November 2017

**Time: ** 3pm (1st talk)

**Location: ** Room 1.25, O’Brien Centre for Science (North)

**Abstract:**

We study the Nonlocal Fractional Choquard equation. These kind of problems (involving fractional Laplace and nonlocal operators) arise in various applications, such as continuum mechanics, phase transitions, population dynamics, optimization, finance and many others. First, the existence of a groundstate solutions using minimization method on the associated Nehari manifold is obtained. Next, the existence of least energy sign-changing solutions is investigated by considering the Nehari nodal set.

Coffee will be served in Room G0.26A, Ground floor, Science North at 4pm.

**Title: ** Exact behaviour of positive solutions near isolated singularity in a logarithmic setting

**Speaker: ** Marius Ghergu (UCD)

**Date: ** Tuesday, 28th November 2017

**Time: ** 4.15pm (2nd talk)

**Location: ** Room 1.25, O’Brien Centre for Science (North)

**Abstract:**

We study the exact behaviour around the isolated singularity at the origin for $C^2$-positive solutions of $-\Delta u=u^\alpha |\log u|^\beta$ in a punctured neighbourhood of the origin of $R^n$, $n\ge 3$. This talk discusses first the power case $\beta =0$ then underlines the difficulties in dealing with logarithmic terms and presents further directions of investigation. This is based on a joint work with Henrik Shahgholian (KTH, Stockholm) and Sunghan Kim (National University of Seoul, Korea).

**Title: ** Overconvergence properties of harmonic homogeneous polynomial expansions with gaps

**Speaker:** Mayya Golitsyna (UCD)

**Date: ** Tuesday, 5th December 2017

**Time: ** 3pm (1st talk)

**Location: ** Room 1.25, O’Brien Centre for Science (North)

**Abstract:**

The series expansions of holomorphic functions with gaps have been studied since the beginning of the twentieth century and found applications in the recent study of universal Taylor series. In this talk I will discuss analogous theory for harmonic functions and its application to show non-existence of universal harmonic homogeneneous expansions on certain type of domains in $R^N$.

Coffee will be served in Room G0.26A, Ground floor, Science North at 4pm.

2nd Seminar**Title: ** Inner iteration of holomorphic functions on hyperbolic domains

**Speaker: ** Michael Mackey (UCD)

**Date:** Tuesday, 5th December 2017

**Time:** 4.15pm (2nd talk)

**Location: ** Room 1.25, O’Brien Centre for Science (North)

**Abstract:**

If $(f_n)$ is a sequence of holomorphic self-maps of a domain then the associated inner iterated function system is $(F_n)$ where $F_n=f_1\circ\cdots\circ f_n$. We survey results of Gill, Lorentzen, Beardon et al., Keen and Lakic, and Bracci concerning the convergence of such systems, focusing (in the sprit of the Denjoy-Wolff theorem) on conditions which guarantee that limit points are constant.

**Title: ** Approximation of norms in Banach spaces

**Speaker: ** Richard Smith (UCD)

**Date:** Tuesday, 6th February 2018

**Time:** 4.00pm

**Location: ** Room 1.25, O’Brien Centre for Science (North)

**Title: ** Positive maps in quantum information theory

**Speaker: ** Alexander Müller-Hermes (Copenhagen)

**Date: ** Tuesday, 13th February 2018

**Time: ** 4pm

**Location: ** Room 1.25, O’Brien Centre for Science (North)**Abstract:**

Many problems in quantum information theory are connected to properties of positive linear maps between matrix algebras. After a brief introduction to some basic concepts of quantum information theory I want to focus on the problem of entanglement distillation. I will explain how this problem is connected to the existence problem of positive linear maps that stay positive under taking tensor powers and that are neither completely positive nor completely co-positive. If time permits I will outline some constructions of interesting positive maps and how non-decomposability arises naturally from tensorisation.

**Title: **“1973 and all that”

**Speaker: **Dr Robin Harte (TCD)

**Date: **Tuesday, 20th February 2018

**Time: **4pm

**Location: ** Room 1.25, O’Brien Centre for Science (North)

**Title: ** On the least doubling constant of a metric space

**Speaker: ** Pedro Tradacete (Madrid Carlos III)

**Date: ** Tuesday, 27th February 2018

**Time: ** 4pm

**Location: ** Room 1.25, O’Brien Centre for Science (North)**Abstract:**

We will explore the question of determining the least doubling constant

among all doubling measures defined on a metric space. We will show that in many natural instances this constant is at least 2. This is based on work in progress with J. Soria (Barcelona).

**Title: ** Diaz Saa Inequality for $p(x)$-laplacian and applications

**Speaker:** Jacques Giacomoni (Pau, France)

**Date: ** Tuesday, 6th March 2018

**Time: ** 3.00 pm

**Location:** Room 1.25, O’Brien Centre for Science (North)

**Abstract:**

In this talk, I will present a recent work with P. Takac. It concerns a new extension of the well-known inequality by Diaz-Saa which in our case, involves an anisotropic operator, such as p(x)-Laplacian. Our present extension of this inequality enables us to establish several new results on the uniqueness of solutions, comparison principles and stabilization for some anisotropic quasilinear elliptic and parabolic equations.

**Title: ** Universal Fourier and Taylor series**Speaker: ** Stephen Gardiner (UCD)**Date: ** Tuesday, 13th March 2018**Time: ** 3.00 pm **Location: ** Room 1.25, O’Brien Centre for Science (North)**Abstract:**

It has long been known that there exist trigonometric series, the partial sums of which possess universal approximation properties on the unit circle. It turns out that, for most smooth functions on the unit circle, the partial sums of the associated Fourier series, when extended to the plane, have universal approximation properties off the circle. There are also related results for pairs of Taylor and Laurent series arising from functions that are holomorphic off a Jordan curve. (This is joint work with Vassili Nestoridis and Christos Papadimitropoulos).

**Title: ** Holomorphic dynamics on bounded symmetric domains

**Speaker: ** Pauline Mellon (UCD)

**Date: ** Tuesday, 20th March 2018

**Time: ** 4.00 pm

**Location: ** Room 1.25, O’Brien Centre for Science (North)

**Abstract:**

The open unit ball, $B$, of a Banach space is homogeneous if given any two points $z,w$ in $B$, there is a biholomorphic map sending $z$ to $w$. Such balls classify the bounded symmetric domains, include many classical spaces and ensure a Jordan structure on the underlying space. Let $f:B\mapsto B$ be a holomorphic fixed-point free map. The behaviour of the sequence of iterates, $f^n=f\circ f^{n-1}$, of $f$ is the subject of much study since the Wolff Denjoy results for the complex disc $\Delta $ in 1926. Generally, in infinite dimensions, $(f^n)$ does not converge, even in the Hilbert

space case. Our work therefore seeks to establish the 'location' of accumulations points of $(f^n)$, with respect to the topology of local uniform convergence on $B$.

This seminar will present results in this direction, using a recentlyproved Wolff type theorem for infinite dimensional bounded symmetric domains.

**Title: ** Isolated singularities for semilinear elliptic systems with power-law nonlinearity

**Speaker: ** Marius Ghergu (UCD)

**Date: ** Tuesday, 27th March 2018

**Time: ** 3.00 pm

**Location: ** Room 1.25, O’Brien Centre for Science (North)

**Abstract:**

We discuss the behaviour around isolated singularity for nonnegative solutions of semilinear elliptic systems. Unlike the standard methods available in the literature which rely on moving plane methods, we apply several tools that pertain to free boundary problems in order to pursue our investigation.

This talk is based on a joint work with Sunghan Kim (National University Seoul, South Korea) and Henrik Shahgholian (KTH Stockholm).

**Title: ** Integral and Nuclear Polynomials on tree spaces

**Speaker:** Christopher Boyd (UCD)

**Time: ** 4.15 pm

**Abstract:**

We examine the Radon-Nikodym Property and Asplundness, in particular their connection to integral and nuclear mappings and polynomials. We show that the structure given to us by tree spaces provides the ideal setting to uncover the intricacies of the relationship between integral and nuclear polynomials.

(This is joint work with C. Poulios and M. Venkova.)

**Title: ** Generalized Bernstein operators

**Speaker: ** Hermann Render (UCD)

**Date: ** Tuesday, 10th April 2018

**Time: ** 4.00 pm

**Location: ** Room 1.25, O’Brien Centre for Science (North)**Abstract:**

In this talk we discuss the existence and properties of generalized Bernstein operators in the context of extended Chebyshev spaces. Special analysis is given to Bernstein operators in the polynomial setting which fix the constant function 1 and the function $x^3$ with respect to an interval $[a,b]$ containing 0.

This talk is based on a joint work with J.M. Aldaz (Universidad Autonoma de Madrid)

**Title: ** Overconvergent properties of Dirichlet series

**Speaker: ** Mayya Golitsyna (UCD)

**Date: ** Tuesday, 24th April 2018

**Time: ** 4.00 pm

**Location:** Room 1.25, O’Brien Centre for Science (North)**Abstract:**

In this talk I will describe overconvergent properties of Dirichlet series with regard to the behavior of their partial sums near infinity. The results are inspired by corresponding phenomena for Taylor series, which were recently discovered using the notion of thinness. This talk is based on a joint work with J.M. Aldaz (Universidad Autonoma de Madrid)

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