## Past Seminars

To subscribe or unsubscribe to the Department of Mathematics and Statistics seminar mailing list, please send an email message to the organisers below:

Lyndon Koens, for Colloquium series

Thomas Fung, for Research seminar series

Justin Tzou, for Lunchtime seminar series

Vladimir Gaitsgory, for Applied Analysis Seminar

### Past Colloquia

#### 2018 series...

**Date:** Friday, 09 November 2018**Speaker: **Prof Michael Small (University of Western Australia)

**Venue: **E7B 146 ACE room

**Title: **Transportation on complex networks

**Abstract: **

Over the last couple of decades, complex networks have attracted the interest of physicists largely because they are described by simple generative processes and exhibit a host of unexpected emergent properties. Applications have been more sporadic - the friendship paradox (that your Facebook friends have more friends than you do) has been proposed as an improved method for distribution of limited vaccines, and my own work has helped to understand dynamical systems, measured from time series, via the topology of an associated graph. One interesting class of problems is those related to transport on complex networks and in this talk I will review two specific examples which we have looked at - on-field interaction among players of an (AFL) football team (the object of transport here is the ball), and water distribution networks. In both cases we are interested in failure of transport - either because the ball is intercepted, or the water network fails. We show that properties of the network are informative and helpful in understanding the underlying dynamics of these systems and even have practical implications. If time permits, I will also briefly mention a separate class of problems currently percolating through the physics literature - where one is searching on a complex network for a moving target.

**Date:** Friday, 02 November 2018**Speaker: **Dr Jennifer Flegg (University of Melbourne)

**Venue: **E7B 146 ACE room

**Title: **Mathematical modelling of the emergence and spread of antimalarial drug resistance

**Abstract:**

Malaria parasites have repeatedly evolved resistance to antimalarial drugs, thwarting efforts to eliminate the disease and contributing to an increase in mortality. In this talk, I will introduce several statistical and mathematical models for monitoring the emergence and spread of antimalarial drug resistance. For example, results will be presented from Bayesian geostatistical models that have quantified the space-time trends in drug resistance in Africa and Southeast Asia. I will discuss how the results of these models have been used to update public health policy.

**Date:** Friday, 26 October 2018**Speaker: **Dr Edward Green (University of Adelaide)

**Venue: **E7B 146 ACE room

**Title: **Quantification and modelling of biological patterns

**Abstract: **

Tissue growth requires cells of various types to organise themselves into the appropriate patterns and structures to produce viable, functional tissue. Similar processes occur in tissue repair (e.g. wound healing) or in biofilms (communities of bacteria or yeast cells). Understanding how this organisation is coordinated is therefore an important basic problem in biology, and mathematicians have made important contributions, such as Alan Turing's seminal work on 'The chemical basis of morphogenesis'.

I will present a brief overview of continuum and individual-cell based approaches to modelling pattern formation in biological systems, and discuss how we have applied them in recent work on pattern formation in biofilms, and in interacting cell populations. A particular focus of our work has been on using image processing methods and spatial statistics (such as pair-correlation functions) to quantify experimental data, to allow more precise comparisons with our model results

**Date:** Friday, 19 October 2018**Speaker: **Prof Matthew Simpson (Queensland University of Technology)

**Venue: **E7B 146 ACE room

**Title: **Challenges in parameterising mathematical models of cell migration and cell proliferation

**Abstract:**

In this presentation, I will give an overview of some of the challenges we face when attempting to quantitatively calibrate mathematical models of cell migration and cell proliferation to match experimental data. Two different experimental scenarios will be considered. First, we will deal with very simple observations of cell migration and cell proliferation on a two-dimensional substrate, called a cell proliferation assay. I will present an off lattice model of cell migration, cell proliferation and crowding effects, and explore how to parameterise the computational model using approximate Bayesian computation. Second, we will deal with a much more complicated experimental situation where we observe three-dimensional spreading and invasion of malignant melanoma cells within human tissues, called a human melanoma skin equivalent assay. I will present a typical continuum model of cell invasion and explain how to use a Bayesian learning approach, with an exact likelihood, to calibrate the model. In both example problems there are no accepted protocols for connecting mathematical models with experimental data. Therefore, both approaches I present are novel, and I hope that the presentation will stimulate discussion about how these methods can be improved and adapted to other situations.

**Date:** Friday, 12 October 2018**Speaker: **Prof Billy Todd (Swinburne University of Technology)

**Venue: **E7B 146 ACE room

**Title: **Towards an extended Navier-Stokes hydrodynamics at the nanoscale

**Abstract:**

In this presentation, both theoretical and simulation studies are highlighted that clearly demonstrate the importance of several non-classical phenomena fundamental to the extension of Navier-Stokes hydrodynamics for highly confined fluids. These are: (1) the prevalence of slip, (2) the strong coupling of molecular spin to linear translational momentum, and (3) the non-locality of viscous transport at the nanoscale. In the first of these, we utilize a newly developed equilibrium based model to accurately predict the slip velocity and slip lengths of systems such as water or methane flowing in graphene nanochannels and carbon nanotubes. We demonstrate that traditional molecular dynamics simulations of such systems are far less efficient and accurate than the easily implemented model we propose. Next, we show that ignoring the coupling of spin angular momentum to linear translational motion of a highly confined fluid can lead to significant over-estimation of the predicted flow rates using conventional Navier-Stokes treatments. By including spin-coupling into the extended Navier-Stokes equations, hydrodynamic prediction is seen to be very accurate down to length scales of a few atomic diameters. We also demonstrate how this knowledge, coupled with our knowledge of slip, can be used to pump molecular fluids such as water via non-intrusive application of a rotating electric field. Finally, we show that a complete generalisation of Navier-Stokes hydrodynamics comes about in the realisation that at the nanoscale viscous transport is fundamentally non-local in nature. We explore this theme for homogeneous systems and discuss the ramifications and problems yet to overcome for nanofluidic applications.

**Date:** Friday, 05 October 2018**Speaker: **Dr David Harvey (University of New South Wales)

**Venue: **E7B 146 ACE room

**Title: **Integer multiplication and the truncated product problem

**Abstract:**

It is now over a decade since the appearance of Fürer's breakthrough result on the asymptotic complexity of integer multiplication. Over the past few years, several authors, building on Fürer's ideas, have proposed improved and simplified algorithms for this problem. I will give an overview of the current status of research in this area. I will also discuss recent progress on the problem of computing a truncated integer product, i.e., computing only the top half (or bottom half) of the product of two integers.

**Date:** Friday, 14 September 2018**Speaker: **Prof Mason Porter (University of California Los Angeles, USA)

**Venue: **E7B 146 ACE room

**Title: **Multilayer networks

**Abstract:**

Networks arise pervasively in biology, physics, technology, social science, and myriad other areas. Traditionally, a network is modelled as a graph and consists of a time-independent collection of entities (the nodes) that interact with each other via a single type of edge. However, most networks include multiple types of connections (which could represent, for example, different modes of transportation), multiple subsystems, and nodes and/or edges that change in time. The study of "multilayer networks", which is one of the most popular areas of network science, allows one to investigate networks with such complexities. In this talk, I'll give an introduction to multilayer networks and their applications.

**Date:** Friday, 07 September 2018**Speaker: **A/Prof Linda Stals (Australian National University)

**Venue: **E7B 146 ACE room

**Title: **Multigrid methods applied to the thin-plate spline saddle point problem

**Abstract: **

Data fitting is an integral part of a number of applications including data mining, 3D reconstruction of geometric models, image warping and medical image analysis. A commonly used method for fitting functions to data is the thin-plate spline method. This method is popular because it is not sensitive to noise in the data. We have developed a discrete thin-plate spline approximation technique that uses local basis functions. With this approach the system of equations is sparse and its size depends only on the number of points in the discrete grid, not the number of data points. Nevertheless the resulting system is a saddle point problem that can be ill-conditioned for certain choices of parameters. In this talk I will present a multigrid based preconditioner that works with a wide choice of parameters.

**Date:** Friday, 31 August 2018**Speaker: **Dr Geoffrey Vasil (University of Sydney)

**Venue: **E7B 146 ACE room

**Title: **Flexible, accurate, efficient, and automatic numerical computations

**Abstract: **

In this talk I will discuss the latest developments from the Dedalus project. This will describe an effort to create genuinely flexible and automatic solvers for a wide range of applied partial differential equations. Creating software that operates with minimal human intervention requires mastering some pretty interesting abstract mathematics. I will discus some of the latest results in this regard. I will also give an overview of several application areas that we can now better model. These include example from geophysical and astrophysical fluid dynamics, fluid-solid interactions, actively driven bio-fluids, quantum graph networks, and pattern formation.

**Date:** Friday, 24 August 2018**Speaker: **A/Prof Jessica Purcell (Monash University)

**Venue: **E7B 146 ACE room

**Title: **Cusp shape and tunnel number

**Abstract:**

Throughout their history, 3-manifolds have been studied by investigating surfaces embedded within them. In the last 50 years, the geometry of manifolds and surfaces have played an increasingly important role. However, there are still many open questions concerning which surfaces with which geometries embed isometrically in geometric 3-manifolds. In this talk, I will discuss one such question. Associated to a cusped hyperbolic 3-manifold, such as a knot complement, is a cusp shape, which is a Euclidean structure on the torus and therefore determines a point in Teichmuller space. It is natural to ask which points arise. In the 1990s, Nimmersheim showed that the cusp shapes of finite volume hyperbolic 3-manifolds, which form a countable set, are dense in Teichmuller space. However, the 3-manifolds constructed in that theorem are very complicated topologically. Restrict instead to simpler manifolds. For example, every 3-manifold has a Heegaard splitting. If we restrict to simple Heegaard splittings, of bounded genus g, which cusp shapes arise? In this talk, we will give background on hyperbolic geometry and Heegaard splittings, and show that for fixed genus g, cusp shapes of finite volume 3-manifolds of genus g are still dense in Teichmuller space.

**Date:** Friday, 17 August 2018**Speaker: **Prof Troy Farrell (Queensland University of Technology)

**Venue: **E7B 146 ACE room

**Title: **From bagasse to biofuel: the modelling of a cellulosic biomaterial

**Abstract: **

Sugar cane is harvested in Australia over a six month period (generally June to December). Bagasse is the fibrous residue produced in sugar mills in large quantities when the cane is crushed. The energy balance in raw sugar factories has traditionally been configured such that little surplus bagasse remains at the end of the crushing season. However, over the past decade a number of factories have reduced their energy consumption in order to produce surplus bagasse for conversion to bioenergy products.

Support for such conversion processes requires significant bagasse storage capability so that surplus bagasse produced is available to maintain the utilisation of bioenergy conversion processes beyond the milling season. This surplus bagasse is stored in large stockpiles, typically of the order of 8m high, 20m wide, 100m long, however, a wide variety of local conditions and requirements means that in practice the sizes and shapes of bagasse stockpiles vary between locations. Some are covered with tarpaulins and others are uncovered, allowing infiltration of water during rainfall, and the degree of compaction can vary significantly between stockpiles. The bagasse that is stockpiled has a water content of up to 55% by weight and an initial temperature of approximately 50 degrees Celsius. The oxidation processes that occur within stockpiles can, under certain conditions, lead to spontaneous combustion and a potential total loss of feedstock. In the first part of this talk we will present a comprehensive, one-dimensional mathematical model for the heat and mass transfer within large-scale bagasse stockpiles with the aim of understanding the transport dynamics that take place within large stockpiles and analysing some of the important parameters that govern the predicted stockpile dynamics.

Bagasse is also a promising feedstock for the production of bioethanol, whereby the cellulosic material within bagasse is hydrolysed by enzymes to produce glucose, which is subsequently fermented to produce bioethanol. Hemicellulose within the bagasse fibres forms a monolayer coating around cellulose that inhibits the enzymatic saccharification process. Acid pre-treatment is a method of removing the hemicellulose, which allows enzymes greater access to the cellulose. Ensuring the efficiency of acid pre-treatment improves the overall cost-effectiveness of bioethanol production. In the second part of this talk, I will present a fibre-scale model that marries the chain length dependency of population balance equations with “hard-to-hydrolyse” kinetics. The model also accounts for the diffusion of species from within the fibre into the surrounding hydrolysate and allows for the material to vary temporally and spatially. The model predictions will be compared with experimentally obtained oligomer yield profiles.

**Date:** Friday, 10 August 2018**Speaker: **Dr Anja Slim (Monash University)

**Venue: **E7B 146 ACE room

**Title: **Gravity currents and similarity solutions of the shallow-water equations

**Abstract:**

Gravity currents occur whenever fluid of one density flows predominantly horizontally into fluid of a different density. A common example is the sea breeze, where cooler, denser air above the ocean displaces hotter, less dense air above land. Such flows can be accurately modeled by the shallow-water equations with a particular frontal boundary condition. At long times, solutions of this model are typically self-similar. Transforming to the appropriate similarity variable, the governing pdes become a pair of autonomous odes on the surface of a torus. Finding similarity solutions then corresponds to finding the integral curve connecting the phase-plane point representing the frontal boundary condition and a phase-plane equilibrium particular to the problem geometry. I will present several example solutions, illustrating the connection with characteristic solutions of Riemann problems, showing that anticipated similarity variables are not always correct, and finding a similarity solution of the second kind, where the similarity exponent is obtained from an eigenvalue problem.

**Date:** Friday, 03 August 2018**Speaker: **Dr Joanne Hall (Royal Melbourne Institute of Technology)

**Venue: **E7B 146 ACE room

**Title: **Skolem circles

**Abstract:**

A Skolem sequence on m symbols is a sequence of 2m symbols from the symbol set {1,2,...,m} with each symbol appearing twice, such that the distance between any pair of that same symbol is that symbols value in integers. For example, 41134232 is a Skolem sequence on 4 symbols. We investigate wrapping a Skolem sequence around a circle. A Skolem circle is a circular configuration of 2m cells which can be filled with the symbol set {1,2,...,m} with each symbol appearing twice, such that the distance between any pair of that same symbol is that symbols value in integers. There are some Skolem circles which cannot be unwrapped into a Skolem sequence. Joint work with James Bubear, QUT.

**Date:** Friday, 27 July 2018**Speaker: **Dr Ross Moore (Macquarie University)

**Venue: **E7B 146 ACE room

**Title: **Authoring accessible tagged PDF documents using LaTeX

**Abstract:**

Several ISO standards have emerged for what should be contained in PDF documents, to support applications such as 'archivability' (PDF/A) and 'accessibility' (PDF/UA). These involve the concept of 'tagging', both of content and structure, so that smart reader/browser-like software can adjust the view presented to a human reader, perhaps afflicted with some physical disability. In this talk we will look at a range of documents which are fully conformant with these modern standards, mostly containing at least some mathematical content, created directly in LaTeX. The examples are available on my website (http://web.science.mq.edu.au/~ross/TaggedPDF/).

The desirability – both morally and legally – of producing documents this way will discussed, along with aspects of how much extra work is required of the author.

Also on the above website is a 'five-year plan' proposal how to modify the production of LaTeX-based scientific publications to adopt such methods. This will involve cooperation between academic publishers and a TeX Users Group (TUG) working group. The proposal PDF document (http://web.science.mq.edu.au/~ross/TaggedPDF/PDF-standards-v2.pdf) is itself produced to be fully accessible, complying with both PDF/UA-1 and PDF/A-2a standards.

###### Session 1, Week 13 - 08 June

**Date:** Friday, 08 June 2018**Speaker: **Dr Petrus van Heijster (Queensland University of Technology)

**Venue: **E7B 146 ACE room

**Title: **Pulse dynamics in reaction-diffusion equations with strong spatially localised impurities

**Abstract:**

In this talk, I will discuss a general geometric singular perturbation framework to study the impact of strong, spatially localised, nonlinear impurities on the existence, stability and bifurcations of localised structures in systems of linear reaction–diffusion equations. By taking advantage of the multiple-scale nature of the problem, I derive algebraic conditions determining the existence and stability of pinned single- and multi-pulse solutions. Our methods enable us to explicitly control the spectrum associated with a (multi-)pulse solution. In the scalar case, I show how eigenvalues may move in and out of the essential spectrum and that Hopf bifurcations cannot occur. By contrast, even a pinned 1-pulse solution can undergo a Hopf bifurcation in a two-component system of linear reaction–diffusion equations with (only) one impurity. This is joint work with A. Doelman from Leiden University and J. Shen from Fujian Normal University.

###### Session 1, Week 12 - 01 June

**Date:** Friday, 01 June 2018**Speaker: **Dr Bronwyn Hajek (University of South Australia)

**Venue: **E7B 146 ACE room

**Title: **Reaction-diffusion in various geometries: symmetry techniques for analytic solutions

**Abstract:**

Nonlinear reaction-diffusion equations are used to describe many different processes in biology and chemistry, for example, population dynamics, cell proliferation, and chemical reactions. In this talk, I'll show how the nonclassical symmetry method can be used to find analytic solutions to nonlinear reaction-diffusion equations. Provided the nonlinear reaction and nonlinear diffusion terms are related in a certain way, there exists a nonclassical symmetry that gives rise to a transformation that will linearise and separate (in time and space) the reaction-diffusion equation, so that analytic solutions may be constructed. The transformation is valid in different coordinate systems (e.g. Cartesian, polar, spherical) and so may be applied in many situations. In this talk, I will give examples from heat conduction, population dynamics and biology.

###### Session 1, Week 11 - 25 May

**Date:** Friday, 25 May 2018**Speaker: **Dr Marcy Robertson (University of Melbourne)

**Venue: **E7B 146 ACE room

**Title: **How can topologists think like computers?

**Abstract:**

The main purpose of this talk will be to introduce the Grothendieck-Teichmuller group -- a large, profinite group defined by Drinfeld in his study of quantized deformations which is closely related to (and conjecturally equal to) the absolute Galois group. The idea was based on Grothendieck's suggestion that one should study algebraic number theory and topology as two sides of the same coin. In this talk, we will introduce this large and complicated object by appealing to a notion of iterated, nested processes similar to how hierarchical networks are built in computing. This notion is that of an (\infty)-operad. This talk will be aimed at a general audience and will not assume any previous knowledge of the Grothendieck-Teichmuller group or operads. This talk will survey results joint with Pedro Boavida de Brito, Philip Hackney, Geoffroy Horel and Donald Yau.

###### Session 1, Week 10 - 18 May

**Date:** Friday, 18 May 2018**Speaker: **Dr Emma Carberry (University of Sydney)

**Venue: **E7B 146 ACE room

**Title: **Bubble, bubble, toil and trouble: soap bubbles, integrable systems and deformations

**Abstract:**

In this talk I shall focus on the simple example of constant mean curvature surfaces, or soap bubbles. Much of what I have to say applies also to other interesting classes of surfaces such as minimal, Willmore or pseudospherical surfaces or indeed to harmonic maps into symmetric spaces. In all these cases, the realisation that they could be viewed as an integrable system brought significant progress. More recently this viewpoint has been combined with Whitham deformation techniques to yield a number of interesting geometric conjectures and information on the moduli space of all solutions. I will give an overview of this story and some of its consequences for constant mean curvature tori.

###### Session 1, Week 9 - 11 May

**Date:** Friday, 11 May 2018**Speaker: **A/Prof Adelle Coster (University of New South Wales)

**Venue: **E7B 146 ACE room

**Title: **Mathematical modelling of biological systems – identifying structure and mechanisms

**Abstract:**

Biological systems are notorious for having multiple and complex interacting pathways. A case in point is the translocation of proteins in cells in response to external biochemical signals. This system can be considered as a black box where key biochemical players in the networks are known, but the structure and interactions between them are not. The aim of this mathematical modelling is to determine where the different effectors and perturbations impinge on the signalling network, giving valuable biological insight into the operation of the system. The modelling also allows the exploration of a variety of “what-if” scenarios that are difficult or impossible to implement experimentally.

However, as with much of science, there are usually multiple hypotheses and multiple models that fit the observations. Multiple observations of the system under different conditions can be advantageous – they constrain the models. However, increases in the number of different conditions and perturbations increase the number of parameters and possible model variations. This raises the questions: how do we determine which model is a valid representation of the dynamics and how do we quantify which model is the “better” or “correct” description of the system?

I will present some methods that I have been developing to create mean-field coupled ODE models of the translocation of glucose transporter proteins in response to insulin with a view to exploring these questions. In this framework, we can use parameter optimisation and residual analysis to rank and assess the different model hypotheses. The assessment becomes more problematic, however, at different biophysical and temporal scales especially when stochasticity is taken into account.

###### Session 1, Week 8 - 04 May

**Date:** Friday, 04 May 2018**Speaker: **Prof Anthony Henderson (University of Sydney)

**Venue: **E7B 146 ACE room

**Title: **Enhancing the Jordan canonical form

**Abstract:**

In undergraduate linear algebra, the Jordan canonical form theorem tells us that each similarity class of n x n complex matrices is similar to one in a very simple block-diagonal form. From the Lie-theoretic viewpoint, this theorem is about classifying the orbits of the general linear group in its adjoint representation. This suggests natural follow-up questions about the closures of the orbits, and raises the hope of finding analogous orbit classifications for other representations of algebraic groups. After explaining some of this general context, I will focus on a case which, despite its close proximity to the Jordan canonical form theorem, was worked out only ten years ago by Pramod Achar (Louisiana State University) and myself.

###### Session 1, Week 7 - 13 April

**Date:** Friday, 13 April 2018**Speaker: **Dr Bishnu Lamichhane (University of Newcastle)

**Venue: **E7B 146 ACE room

**Title: **Computing and visualising the solutions of partial differential equations

**Abstract:**

The finite element method has become the most powerful approach in solving partial differential equations arising in modern engineering and physical applications. We present computation and visualisation of the solutions of some applied partial differential equations using the finite element method for most of our examples. Our examples come from solid and fluid mechanics, heat conduction in sliding meshes and image processing.

###### Session 1, Week 7 - 12 April

**Date:** Thursday, 12 April 2018**Speaker: **Prof Christopher Howls (University of Southampton, UK)

**Venue: **E7B 146 ACE room

**Title: **Complex rays, cones of silence and catastrophes, or when to turn an asymptotic blind eye

**Abstract:**

We develop a complex-ray approach to the calculation of high-frequency flow-interaction effects for 3D jet engine noise in a moving media obeying the Lilley equation. The method copes with caustics, complex rays and the multiplicity of ray solutions. Excellent agreement with modal and numerical solutions is achieved. For off-axis point sources, the solution field is rich in the canonical, but easily calculable, caustic structures of catastrophe theory. This reveals not only previously unknown additional upstream beaming of engine noise, but also some novel, vanishing caustic behaviour. The result is not only new engineering but also a striking novel phenomenon of direct relevance to asymptotic beyond all orders.

###### Session 1, Week 6 - 06 April

**Date:** Friday, 06 April 2018**Speaker: **Prof Dmitry Pelinovsky (McMaster University Canada)

**Venue: **E7B 146 ACE room

**Title: **Reversing interfaces in the slow diffusion equation with strong absorption

**Abstract:**

Bifurcations of self-similar solutions for reversing interfaces are studied in the slow diffusion equation with strong absorption. We show that such bifurcations occur at points where the confluent hypergeometric functions satisfying Kummer's differential equation are truncated to finite polynomials. A two-scale asymptotic method is employed to obtain the local dependencies of the self-similar reversing interfaces near the bifurcation points. Numerical shooting techniques are developed to confirm the asymptotic results.

###### Session 1, Week 4 - 23 March

**Date:** Friday, 23 March 2018**Speaker: **Prof Norman Dancer (University of Sydney)

**Venue: **E7B 146 ACE room

**Title: **The Fucik spectrum

**Abstract:**

We discuss the Fucik spectrum, which is {(α,β) ∈R² : −∆u = αu^{+}+βu‾ in Ω,u = 0 on ∂Ω,has a non-trivial solution}.

Here Ω is a ﬁxed bounded open set in R². We discuss positive results, counterexamples, and conjectures and connections with more classical problems. The proofs of results tend to involve linear and nonlinear analysis.

###### Session 1, Week 3 - 16 March

**Date:** Friday, 16 March 2018**Speaker: **Prof Holger Dullin (University of Sydney)

**Venue: **E7B 146 ACE room

**Title: **Quantum monodromy in the Kepler problem

**Abstract:**

The motion of the Earth around the Sun is well described by Kepler’s problem, which is a beautiful example of a super-integrable system. Its full (sometimes called “hidden”) symmetry group is SO(4), which makes every orbit periodic. The quantum analogue of the Kepler problem is the Hydrogen atom, which can be separated in spherical coordinates and leads to the well known spherical harmonics. We found that when the system is separated in spheroidal coordinates instead, the lattice of the joint spectrum of the corresponding commuting operators lacks global basis. This phenomenon is called quantum monodromy, and I will trace its origin back to the classical dynamics of the Kepler problem and show that it can be found generally in spheroidal harmonics.

###### Session 1, Week 2 - 09 March

**Date:** Friday, 09 March 2018**Speaker: **Dr Kevin Coulembier (University of Sydney)

**Venue: **E7B 146 ACE room

**Title: **Ideals in monoidal categories

**Abstract:**

I will discuss some topics in the study of “tensor ideals” in monoidal categories (categories equipped with a tensor product). One version of such ideals are studied in tensor triangulated geometry, where the Balmer spectrum of a tensor triangulated category mimics the notion of a scheme from algebraic geometry. After reviewing some generalities and surprising connections, I will mainly focus on a different version of tensor ideals, which I recently classified in Deligne’s universal monoidal categories. This led to some new applications in the representation theory of Lie supergroups.

###### Session 1, Week 2 - 08 March

**Date:** Thursday, 08 March 2018**Speaker: **Professor John Sader (University of Melbourne)

**Venue: **E7B 146 ACE room

**Title: **Why does an inverted-flag flap in a uniform steady flow?

**Abstract:**

The dynamics of a cantilevered elastic sheet, with a uniform steady flow impinging on its clamped-end, have been studied widely and provide insight into the stability of flags and biological phenomena. Recent measurements show that reversing the sheet's orientation, with the flow impinging on its free-edge, dramatically alters its dynamics. In contrast to the conventional flag, which exhibits (small-amplitude) flutter above a critical flow speed, the inverted-flag displays large-amplitude flapping over a finite band of flow speeds. In this talk, a combination of mathematical theory, scaling analysis and measurement is used to investigate the origin of this large-amplitude flapping motion. Flapping is found to be a vortex-induced vibration and is periodic predominantly, with a transition to chaos as flow speed increases. These findings have implications to leaf motion and other biological processes, such as the dynamics of hairs, because they also can present an inverted-flag configuration.

###### Session 1, Week 1 - 02 March

**Date:** Friday, 02 March 2018**Speaker: **Professor Nalini Joshi (University of Sydney)

**Venue: **E7B 146 ACE room

**Title:** Symmetry through geometry

**Abstract:** Symmetry is an essential part of our description of the world. The quality of being made up of exactly similar parts facing each other is all around us: one day reflects another and the days fill out the year in the same way that similar hexagonal compartments fill out a honeycomb. The mathematical description of symmetries is built from only two operations: reflections and translations. In two dimensions, these give rise to triangular, hexagonal and square tilings of the plane. But in higher dimensions, many more tiling patterns are available. One of the many questions that arise is how to go from higher dimensional tilings to two-dimensional ones. I will show how to use these ideas to link two major theories that arise in mathematical physics.

###### 09 February

**Date:** Friday 09 February, 2018**Speaker:** Professor Herbert Huppert (University of Cambridge, UK)**Venue: **E7B 146 ACE room

**Title:** How to frack into and out of trouble

**Abstract:** After a short introduction to the mechanism and politics of fracking, the talk will concentrate on the fluid mechanics and elastodynamics of driving fluid into cracks and the quite different response when the pressure is released and the fluid flows back out. Development of the governing equations will be presented along with their numerical solution and asymptotic analysis in certain useful limits. Videos of laboratory experiments will be shown and the results compared with the theoretical predictions.

#### 2017 series...

###### Session 1 - Week 1 - 03 Mar 2017

**Date:** Friday 3 March 2017 **Speaker:** Emeritus Professor Ross Street (Macquarie)**Venue: **TBA**Title:** The Natural Transformation in Mathematics**Abstract:** The goal is to give some idea of what category theory is about: some history, some examples, some concepts, and an application to physics. The subject officially began in 1945 with papers focussing on examples and applications to

group theory. The authors were prepared to look at the collection of all groups as a mathematical object; this was quite controversial at the time. By now category theory has become a vital language for expressing much of mathematics and has

found many significant applications. A feature of the subject is the use of diagrams made of arrows. The arrows are an abstraction of functions f from one set A to another set B. More recently, a dual viewpoint, where f is depicted as a node with

input string A and output string B, has led to deep connections with knot theory, invariants for low dimensional manifolds, and the branch of theoretical physics called quantum field theory. The talk should be accessible to senior mathematics majors.

###### Week 2 - 10 Mar 2017 - Cancelled

###### Week 3 - 17 Mar 2017

**Date:** Friday 17 March 2017 **Speaker:** Dr Cecilia González Tokman (University of Queensland)**Venue: **E6B 149**Title:** Non-autonomous dynamical systems and multiplicative ergodic theorems**Abstract:** Non-autonomous dynamical systems yield very flexible models for the study of time-dependent systems, with driving mechanisms allowed to range from deterministic forcing to stationary noise. Multiplicative ergodic theorems (METs) encompass fundamental information for the study of transport phenomena in such systems, including Lyapunov exponents, invariant measures and coherent structures.

In this talk we will discuss recent developments on METs, motivated by applications in the geophysical sciences. We will then address related stability questions, which arise naturally in the context of non-autonomous systems from the use of numerical approximation schemes, as well as from the presence of modelling errors and noise. (This talk is based on joint work with Gary Froyland and Anthony Quas)

###### Week 4 - 24 Mar 2017

**Date:** Friday 24 March 2017 **Speaker:** Dr Pierre Portal (ANU)**Venue: **TBA**Title:** Harmonic Analysis in Rough Contexts**Abstract:** In recent years, perspectives on what constitutes the ``natural" framework within which to conduct various forms of mathematical analysis have shifted substantially. The common theme of these shifts can be described as a move towards roughness, i.e. the elimination of smoothness assumptions that had previously been considered fundamental. Examples include partial differential equations on domains with a boundary that is merely Lipschitz continuous, geometric analysis on metric measure spaces that do not have a smooth structure, and stochastic analysis of dynamical systems that have nowhere differentiable trajectories.

In this talk, aimed at a general mathematical audience, I describe some of these shifts towards roughness, placing an emphasis on harmonic analysis, and on my own contributions. This includes the development of heat kernel methods in situations where such a kernel is merely a distribution, and applications to deterministic and stochastic partial differential equations.

###### Week 5 - 31 Mar 2017

**Date:** Friday 31 March 2017 **Speaker:** Dr. Emily Riehl (Johns Hopkins University)**Venue: **E7A 801-803**Title:** Functoriality in algebra and topology**Abstract:** This talk will survey mathematical innovations involving functoriality. In the first examples - drawn from algebraic topology, algebraic geometry, and topological data analysis - the functors in question are “large” objects, bridging two large categories. In the second half of the talk, we will turn to “small” examples, functors indexed by small categories, and illustrate how such diagrams provide efficient combinatorial models of algebraic or topological data. This connects to recent work in progress, developed in conversation with John Bourke, Richard Garner, and Dominic Verity, to develop a unified framework for inductive arguments for those functors indexed by a certain family of categories.

###### Week 6 - 7 Apr 2017

**Date:** Friday 7 Apr 2017 **Speaker:** Dr Norman Do (Monash University)**Venue: **E7A 801-803**Title:** Counting surfaces: A mixed bag of combinatorics, geometry, and physics**Abstract:** Given some polygons, how many ways can you glue their edges together to create a particular surface? This enumeration is governed by two simple objects - a "spectral curve" and a "quantum curve" - that are related by a mysterious process called "quantisation". We will discuss exactly what this means and why it is mysterious, before observing the same structure in seemingly unrelated problems that involve permutations, knots and more. The talk will be G-rated, in the sense that almost no prerequisites are required!

###### Week 7 - 14 April 2017 - No talk due to Good Friday Public Holiday

###### Week 8 - 5 May 2017

**Date:** Friday 5 May 2017 **Speaker:** Dr Robert Marangell (Sydney University)**Venue: **E7A 801 (12 Wally's Walk roof top)**Title:** Travelling Wave Dynamics in Mathematical Biology**Abstract:** In their independent seminal works in 1937, Fisher, and Kolmogorov, Pescunov and Petrovskii (F-KPP) were among the first apply the analysis of travelling waves to a problem in mathematical biology. Subsequently, travelling waves have appeared in a host of mathematical biological problems, including chemototaxis, nerve impluse propagaion, intestinal crypt dynamics, tumour growth, wound healing, and population migrations, to name just a few. The first part of my talk will focus on some examples: specifically, a (classic) chemotactic model, and a Wolbachia infection model. The second half of my talk will discuss how a dynamical systems approach can shed light on the evolution of travelling waves. Using the F-KPP equation as a motivating example, I will show how much of the dynamic behaviour of a travelling wave is encoded in the spectrum of an associated linear equation.

###### Week 9 - 12 May 2017

**Date:** Friday 12 May 2017 **Speaker:** Dr Joshua Ross (University of Adelaide)**Venue: **E7A 801 (12 Wally's Walk roof top)**Title:** Mathematical problems in pandemic influenza response.**Abstract:** The emergence of a novel strain of influenza poses an ever-present threat to our health and well-being. Whilst a vaccine is available that typically provides protection against seasonal influenza, the development and production of a vaccine for a novel strain will take at least five months. Furthermore, the characteristics of the strain, pertinent to its threat and method of control, are obviously largely unknown. Mathematics and statistics are key to tackling this problem. I will present some of the contributions I have made to this topic and some insights they have provided.

###### Week 10 - 19 May 2017

**Date:** Friday 19 May 2017 **Speaker:** Dr Tanya Evans (Auckland, New Zealand)**Venue: **E7A 801 (12 Wally's Walk roof top)**Title:** An intra-departmental professional development model which is fun. . .but actually works**Abstract:** In this presentation we will give an overview of a model of professional development and highlight my personal experience in this project which led to a remarkable transformation of my lecturing practice. We will also talk more generally about transferable mechanisms for examining and improving our overall teaching practices. The model of professional development grew out of an inter-departmental initiative at the University of Auckland in which a group of lecturers meets regularly during the year as part of an ongoing professional development programme. The group is very diverse in the nature of the courses they teach and their mathematical research interests, including algebra, analysis, applied mathematics and mathematics education. At these meetings, we view a short excerpt from a video-recording of one of the lecturers from the group, which might be at either the undergraduate or graduate level. We then discuss aspects of the excerpt, with the discussions guided by the ROG (Resources, Orientations & Goals) framework formulated by Schoenfeld (2010).

References: Paterson, J., & Evans. T. (2013). Audience insights: Feed forward in professional development. In D. King, B. Loch & L. Rylands (Eds.), Proceedings of Lighthouse Delta, the 9th Delta conference of teaching and learning of undergraduate mathematics and statistics Through the Fog (pp.132-140). Kiama, Australia: Delta. Leong, Y. H., Ho, W. K. & Evans, T. (2016). Videos in teacher professional development, Discussion Group, Proceedings of the 13th International Congress on Mathematical Education (ICME), Hamburg, 24-31 July 2016: ICME. Barton, B., Oates, G., Paterson, P., & Thomas, M. O. J. (2015). A marriage of continuance: professional development for mathematics lecturers. Mathematics Education Research Journal, 27(2), 147-164. Schoenfeld, A. H. (2010). How we think. A theory of goal-oriented decision making and its educational applications. Routledge: New York.

###### Week 11 - 26 May 2017

**Date:** Friday 26 May 2017 **Speaker:** Dr Christopher Lustri (Macquarie University)**Venue: **E7A 801 (12 Wally's Walk roof top)**Title:** Applications of Exponential Asymptotic Methods**Abstract:** The utility of asymptotic series expansions has been long-established within applied mathematics for providing approximations to exact solutions in some asymptotic limit. However, these methods are typically unable to capture behaviour that is exponentially-small in the limit, irrespective of how many terms of the series one chooses to take. Behaviour on this scale is described as lying "beyond-all-orders".

This talk will be divided into two parts. In the first part, I will discuss how exponential asymptotic methods may be used to obtain information about behaviour that occurs on an exponentially-small scale, and in particular, how such methods uncover behaviour known as the Stokes Phenomenon. In the second part of the talk, I will discuss applications of these methods to problems arising in fluid dynamics and particle lattices.

###### Week 12 - 2 June 2017

**Date:** Friday 2 June 2017 **Speaker:** A/Prof. Zihua Guo (Monash University)**Venue: **E7A 801 (12 Wally's Walk roof top)**Title:** Recent development on the long time behaviour to some quadratic dispersive systems**Abstract:** In this talk I will survey some recent results on the study of the long time behaviour to some quadratic dispersive systems such as Zakharov system and Gross-Pitaevskii equation. These equations have quadratic nonlinear terms which usually cause considerable difficulties to study the long-time behaviour in low dimensions.

###### Week 13 - 9 June 2017

**Date:** Friday 2 June 2017 **Speaker:** Prof. Martin Weschelberger (University of Sydney)**Venue: **E7A 801 (12 Wally's Walk roof top)**Title:** Stellar Winds: The Force Awakens Through Ducks**Abstract:** Looking at the gas dynamics of stars under the assumption of spherical symmetry, I will show that transonic events in such systems are canard phenomena — peculiar solution structures identified in geometric singular perturbation problems. Consequently, stellar winds are carried by `supersonic ducks', and canard theory provides a mathematical framework for this astrophysical phenomenon. This is collaborative work with Paul Carter (University of Arizona) and Edgar Knobloch (UC Berkeley) published in Nonlinearity 30 (2017), 1006-1033.

###### Session 2 - Week 1 - 04 August 2017

**Date:** Friday 4 August 2017 **Speaker:** Professor Stuart Anderson (Adelaide)**Venue: **E7B 146 ACE**Title:** Mathematical problems arising in HF radar investigations of the geophysical environment**Abstract:** It is a common feature among remote sensing technologies that very considerable progress can be made with relatively simple physical and mathematical models. This is often fortuitous as, without getting `runs on the board' at an early stage, support for further development may evaporate and consign a technology to the graveyard of good-in-principle ideas. But, having survived to puberty, it is equally common for progress to slow or even stall because the detail and fidelity of measurements fail to meet the rising expectations of the users. At this point there is no option but to identify the factors that are limiting performance and to develop techniques to mitigate them. Typically the research problems which arise at this point demand a marriage, or even a menage-a-trois, between the disciplines of physics, engineering and mathematics. In the case of HF radar in its diverse roles, several topics within the realm of applied mathematics are of special interest at present, and it so happens that these are strongly represented in the research activities of the Department of Mathematics at Macquarie University, specifically in the areas of (i) fluid dynamics, oceanic and atmospheric sciences, (ii) nonlinear phenomena, (iii) inverse problems, (iv) optimisation, and (v) computational mathematics. In this talk I shall illustrate the application of these branches of mathematics to the problems currently of concern to the HF radar community.

###### Week 2 - 11 August 2017

**Date:** Friday 11 August 2017 **Speaker:** Dr Alessandro Ottazzi (UNSW)**Venue: **E7B 146 ACE**Title:** An introduction to sub-Riemannian geometry and its applications**Abstract:** Sub-Riemannian geometry is a flourishing subject of research that appears in many different areas of pure and applied mathematics. It is a generalisation of Riemannian geometry that provides models in robotics, aerospace engineering, medical imaging, and neurobiology. Applications in pure mathematics include metric geometry, PDEs, harmonic analysis, and geometric control theory. In this presentation I will give an introduction "by examples" to sub-Riemannian geometry and I will briefly describe a couple of models: a special car and the primary visual cortex. If there is some time left, I will also discuss in one example how simple calculus notions differ from the Euclidean case.

The talk is tailored for a general audience.

###### Week 3 - 18 August 2017

**Date:** Friday 18 August 2017 **Speaker:** Prof Gary Froyland (UNSW)**Venue: **E7B 146 ACE**Title:** Dynamics, Mixing and Coherence**Abstract:** Coherent structures in geophysical flows play fundamental roles by organising fluid flow and obstructing transport. For example, in the ocean, coherence manifests itself at global scales down to scales of at least tens of kilometres, and strongly influences the transportation of heat, salt, nutrients, phytoplankton, pollution, and garbage. I will describe some recent mathematical constructions, ranging across dynamical systems, probability, and geometry, which enable the accurate identication and tracking of such structures, and the quantication of associated mixing and transport properties. I will present case studies from a variety of geophysical settings.

###### Week 4 - 23 August 2017

**Date:** Friday 23 August 2017 **Speaker:** Dr Yoni Nazarathy (UQ)**Venue: **E7B 146 ACE**Title:** Reward Observing Restless Multi Armed Bandits**Abstract:** Much of operations research has to do with constraints. You want to do your best, but need to operate within certain bounds. A key question in the field is: what choice to make so as to maximise reward? You often try to answer this question in a dynamic manner over time, occasionally dealing with uncertainty and randomness. One such class of problems is the case where you have D assets that evolve in some random manner over time. An asset can be in "good" state or \bad" state. You can only choose K out of D such assets at every time slot. Which do you choose? Clearly giving priority to those in "good" state makes sense. But perhaps you don't have full information about the state of the assets. What do you do then? In this talk we'll show different approaches and variants of this problem and discuss some solution and performance analysis methods. Some concepts to be encountered are Markov Chains, Partially Observable Markov Decision Processes and Restless Bandits.

###### Week 5 - 1 September 2017

**Date:** Friday 01 September 2017 **Speaker:** A/Prof Ngamta (Natalie) Thamwattana (UoW)**Venue: **E7B 146 ACE**Title: **Modelling carbon nanostructures: mathematics, mechanics and molecular dynamics**Abstract: ** The talk will consist of three parts. First I will look at modelling mathematically the interaction between carbon nanostructures, including graphene, nanotubes and fullerenes. Two particular problems will be considered: interactions between graphene oxide and water and the spiral motion of molecules inside nanotubes. Molecular dynamics simulations for these problems will also be presented. Secondly I will show how to use calculus of variations to predict shapes of carbon nanostructures, such as graphene folds and wrinkles. Finally, I will touch on a recent result on modelling electromaterials in dye-sensitized solar cells.

###### Week 6 - 8 September 2017

**Date:** Friday 08 September 2017 **Speaker:** Dr Shane Keating (UNSW)**Venue: **E7B 146 ACE**Title:** Estimating turbulent mixing using stochastic filtering and superresolution of satellite imagery**Abstract: **The era of earth-observing satellites has revolutionised our understanding of our planet and the dynamical processes that shape it. In many real-world geophysical systems, however, estimates of turbulent mixing and transport are limited by the resolution of available observations. In this talk, I will describe a suite of stochastic filtering strategies for estimating mixing in turbulent geophysical flows from "superresolved" satellite imagery obtained by combining coarse observations with an efficient stochastic parameterization for the unresolved scales.

The method enhances the effective resolution of satellite observations by exploiting the effect of spatial aliasing and generates an optimal estimate of small scales using standard Bayesian inference. The technique is tested in quasigeostrophic simulations driven by realistic climatological shear and stratication profiles. Two applications are considered: calculating poleward ocean eddy heat flux from satellite altimetry, and estimating the three-dimensional upper ocean velocity field from superresolved sea-surface temperature imagery. In each case, the superresolved satellite observations result in a considerable improvement in estimates of turbulent fluxes compared with the raw observations.

###### Week 7 - 15 September 2017 - No talk this week

###### Week 8 - 6 October 2017

**Date:** Friday 6 October 2017 **Speaker: **Prof Scott McCue **Venue: ** E7B 146 (ACE room)**Title:** Linear and nonlinear ship waves: wake angles and time-frequency analysis**Abstract:** It is commonly believed that the half-angle which encloses a Kelvin ship wave pattern is simply arcsin(1/3) (roughly 19.5 degrees), provided the fluid is deep and the disturbance is small. However, observations and calculations for sufficiently fast-moving ships suggest that the apparent wake angle decreases with ship speed. We explore this phenomenon with a toy model, considering linear and nonlinear versions, in both infinite depth and finite depth. It turns out that the apparent wake angle also decreases for sufficiently slow-moving ship, which provides another interesting mathematical limit that involves exponential asymptotics and novel wave patterns. Finally, if time permits, the final topic of this walk will concern time-frequency analysis of ship wakes. Here, we analyse wave signals with short-time Fourier transforms and spectrograms, and describe some attempts to match our models with experimental data.

###### Week 9 - 13 October 2017

**Date:** Friday 13 October 2017 **Speaker: **Dr Justin Tzou (Macquarie) **Venue: ** E7B 146 (ACE room) **Title:** Mean first passage time problems and localised pattern formation - analysis, results, and surprising connections**Abstract: **Mean first passage time (MFPT) problems, a classic example of which is the gambler's ruin problem, generally ask the question - how long on average does it take for a random walker to first encounter a set of targets? Analysis of these problems in the past has been restricted to the scenario where targets are stationary. In this talk, we discuss how to derive and analyse the boundary-value problem associated with moving targets, and report some counterintuitive results. For localised spot patterns in reaction-diffusion systems, we will demonstrate a hybrid asymptotic-numerical method for obtaining key analytic results for their stability and dynamics. Finally, we draw some surprising links between these two seemingly very different problems.

###### Week 10 - 20 October 2017

**Date:** Friday 20 October 2017 **Speaker: **Prof. Michael Cowling (UNSW) **Venue: **E7B 146 (ACE room)**Title: ** The Brascamp-Lieb inequalities**Abstract:** About 20 years ago, the mathematical physicists Herm Brascamp and Eliott Lieb discovered a family of

inequalities, which now bear their names. These inequalities generalise several of the classical inequalities of analysis,

including Hölder's inequality, Young's convolution inequality, and the Loomis-Whitney inequality. The Brascamp-Lieb inequalities depend on linear maps *Lj* with a common domain *V* and different ranges *Vj* and a family of indices *θj* in [0,1]. The inequalities hold for some but not all of the possible indices. For applications in partial differential equations it is important to understand for which *Lj* and *θj* the inequalities hold, and whether the constants that appear in the inequalities depend continuously on the parameters. In this talk, I review the inequalities, and discuss some recent progress on these questions.

###### Week 11 - 27 October 2017

**Date:** Friday 27 October 2017 **Speaker:** Daniel Hauer (USyd) **Venue: ** E7B 146 (ACE room)**Title:** Non-concavity of Robin eigenfunctions

###### Week 12 - 3 November 2017

**Date:** Friday 3 November 2017 **Speaker: **Dr. Philipp Braun from University of Newcastle **Venue: **E7B 146 (ACE room)**Title: **Lyapunov and Control Lyapunov Functions: Stability of and Feedback design for Nonlinear Systems**Abstract: **Lyapunov’s second method is one of the most successful tools for analyzing stability properties of dynamical systems. To illustrate the idea behind Lyapunov’s second method we review existing results on Lyapunov functions and (nonsmooth) control Lyapunov functions in the context of stability and stabilization of nonlinear dynamical systems. Moreover, we highlight open problems and results on the ongoing research topic of control Lyapunov functions for destabilization of nonlinear systems. The talk concludes with ideas combining the concepts of stabilizing and destabilizing controllers based on the knowledge of appropriate control Lyapunov functions. The results presented in the talk are illustrated and motivated on the examples of an inverted pendulum, a nonholonomic integrator and Artstein’s circles.

###### Week 13 - 10 November 2017

**Date:** Friday 10 November 2017 **Speaker: **Dr Jiakun Liu from University of Wollongong **Venue: **E7B 146 (ACE room)**Title: **Optimal transportation on the hemisphere**Abstract: **In this talk, we first give a brief introduction to the optimal transportation problem. Then we study the optimal transportation on the hemisphere with the cost function $c(x,y)=d^2(x,y)/2$, where $d$ is the Riemannian distance of the round sphere. The potential function satisfies a Monge-Ampere type equation with a natural boundary condition. In this critical case, the hemisphere does not satisfy the $c$-convexity assumption. We obtain the a priori oblique derivative estimate, and in the special case of dimension two, we obtain the boundary $C^2$ estimate. Our proof does not require the smoothness of densities. This is a joint work with S.-Y. Alice Chang and Paul Yang.

#### 2016 series...

**Date:** 11 November 2016**Speaker:** Dr Richard Garner (Macquarie University)**Venue:** AHH Lecture Theatre 1.200**Title: ***Homotopy type theory***Abstract: ** Homotopy type theory is a new area of mathematics which, over the past ten or so years, has successfully combined aspects of the highly constructive disciplines of type theory and functional programming, and the highly non-constructive disciplines of algebraic topology and homotopy theory. The sheer unlikeliness of the pairing has been the source of both fascination and suspicion among workers in both fields. We attempt to give an introduction to the area comprehensible to a general mathematical audience.

**Date:** 4 November 2016**Speaker:** Associate Professor Catherine Greenhill (University of New South Wales)**Venue:** C5C Collaborative Forum**Title: ***Colouring random graphs and hypergraphs***Abstract:** A colouring of a graph (or hypergraph) is a map which assigns a colour to each vertex such that no edge is monochromatic. If there are k available colours then this map is called a k-colouring, and the minimum value of k such that a k-colouring exists is called the chromatic number of the graph. Graph colourings are fundamental objects of study, with applications in many areas including statistical physics and radio frequency assignment. The chromatic number of random graphs has been studied since the pioneering work of Erdős and Renyi (1960). We will take a tour through some of the major results in this area, and the methods used to prove them, including the probabilistic method and martingale arguments. I will also discuss some results on the chromatic number of hypergraphs with a linear number of edges (joint work with Colin Cooper and Martin Dyer and, subsequently, Peter Ayre and Amin Coja-Oghlan.) This work uses a more analytic approach, inspired by ideas from statistical mechanics.

**Date:** 28 October 2016**Speaker:** Professor Andrew Francis (University of Western Sydney)**Venue:** C5C Collaborative Forum**Title: ***Bacterial genome rearrangements and phylogeny in the Cayley graph***Abstract: **Modelling bacterial genome rearrangement operations as group actions on the space of all possible genomes provides a one-to-one correspondence between genome space and the group that acts. This means that a subset of genomes defines a set of points on the Cayley graph of the group, and a phylogeny on those genomes is represented by a Steiner tree on those points. In this talk I will describe this viewpoint and several related results. First, I will show how group theory can be used to calculate the "minimal distance" between genomes. Then I will describe a more nuanced view of the distance between genomes through a maximum likelihood estimate, and finally, I will describe some algorithmic results relating to the median problem for three genomes on the Cayley graph.

**Date: **21 October 2016**Speaker:** Dr Melissa Tacy (Australian National University)**Venue:** AHH Lecture Theatre 1.200**Title:**** **Semiclassical analysis in PDE**Abstract: **Semiclassical analysis arose as a set of techniques for studying the high energy (or semiclassical) limit of quantum mechanics. These techniques however can be used for a wide range of problems in PDE that feature a large (or small) parameter. In this talk I will discuss some of the applications of semiclassical analysis and the intuitions that drive this theory.

**Date: **14 October 2016**Speaker: **Professor Mary Myerscough (University of Sydney)**Venue:** AHH Lecture Theatre 1.200**Title: ***Why do hives die? Using mathematics to solve the problem of honey bee colony collapse.***Abstract: **Honey bees are vital to the production of many foods which need to be pollinated by insects. Yet in many parts of the world honey bee colonies are in decline. A crucial contributor to hive well-being is the health, productivity and longevity of its foragers. When forager numbers are depleted due to stressors in the colony (such as disease or malnutrition) or in the environment (such as pesticides) there are significant effects. These include a reduction in the amount of food (nectar and pollen) that can be collected and a reduction of the colony's capacity to raise brood (eggs, larvae and pupae) to produce new adult bees to replace lost or old bees.

We use a set of differential equation models to explore the effect on the hive of high forager death rates. We track the population of brood, hive bees (who work inside the hive) and foragers (who bring back food to the hive) and we track stored food. Using data from experimental research we devised functions that described the effect of the age that bees first become foragers on their success and lifespan as foragers. In particular we examine what happens when bees become foragers at a comparatively young age and how this can lead to a sudden rapid decline of adult bees and the death of the colony.

**Date:** 7 October 2016**Speaker: **Dr Julie Clutterbuck (Monash University)**Venue: **AHH Lecture Theatre 1.200**Title: ***Extreme eigenvalues***Abstract: **Each bounded domain has a sequence of eigenvalues associated to it. These are *determined* by the geometry of the domain, but do not* completely encode* the geometry. A natural question is to ask: which domains optimise the eigenvalues? For example, which domains have the smallest or largest first eigenvalue, or have the largest gap between eigenvalues? This is a rather old problem, with connections to the isoperimetric problem. I will describe some old and new results.

**Date:** 16 September 2016**Speaker:** Associate Professor Lesley Ward (University of South Australia)**Venue:** AHH Lecture Theatre 1.200**Title:** *Harmonic Analysis on Spaces of Homogeneous Type***Abstract: **The Calder\'on-Zygmund theory in harmonic analysis deals with singular integral operators and the function spaces on which they act. Early impetus came from problems in partial differential equations and Fourier theory. Much effort has been devoted to generalising the Calder\'on-Zygmund theory in several directions. Here we focus on the generalisation from functions defined on Euclidean spaces to functions defined on spaces of homogeneous type. The underlying space $\mathbb R^n$, equipped with the Euclidean metric and Lebesgue measure, is replaced by a general set X equipped only with a metric or quasi-metric and a doubling measure. In particular, the group structure and the Fourier transform are missing. Varied examples of spaces of homogeneous type arise in Riemannian geometry, several complex variables, and Lie theory. The goal is to build on this widely applicable foundation a Calder\'on-Zygmund theory which is as complete as it can be, recovering the classical results where possible and finding appropriate replacements or analogues where needed. I will survey some current progress towards this goal.

**Date:** 9 September 2016**Speaker:** Dr Georgy Sofronov (Department of Statistics, Macquarie University)**Venue**: AHH Lecture Theatre 1.200**Title:** *The theory of multiple optimal stopping rules and its applications***Abstract: **We observe a sequence of random variables and have to decide when we must stop, given that there is no recall allowed, that is, a random variable once rejected cannot be chosen later on. Our decision to stop depends on the observations already made, but does not depend on the future which is not yet known. The objective is to nd an optimal procedure that maximizes an expected gain. We consider problems when at least two stops are required, for example, a sequential problem of selling several identical assets over a nite time horizon.

**Date: **2 September 2016**Speaker:** Dr Luke Bennetts (University of Adelaide)**Venue:** AHH Lecture Theatre 1.200**Title: ***Water wave interactions with line arrays of vertical cylinders***Abstract: **In a highly cited paper, Maniar & Newman (J Fluid Mech, 1997) considered the impact of surface water waves on supports for bridges or other oshore structures, modelled by line arrays of vertical cylinders. They showed that the cylinders experience extreme resonant loads (i.e. hydrodynamic forces) at certain wave frequencies. Over the following decade, a sequence of papers by Evans, Porter, Linton and others, showed that the resonances are caused by excitation of so-called Rayleigh-Bloch waves "trapped" modes propagating along the array and decaying away from it. I'll summarise this previous work, then show how random perturbations in cylinder locations damp the resonances, and connect this with the phenomenon of Anderson localisation.

**Date:** 26 August 2016**Speaker:** Dr Peter Kim (University of Sydney)**Venue:** AHH Lecture Theatre 1.200**Title: ***Modelling evolution of post-menopausal human longevity: The Grandmother Hypothesis***Abstract: **Human post-menopausal longevity makes us unique among primates, but how did it evolve? One explanation, the Grandmother Hypothesis, proposes that as grasslands spread in ancient Africa displacing foods ancestral youngsters could eectively exploit, older females whose fertility was declining left more descendants by subsidizing grandchildren and allowing mothers to have new ospring sooner. As more robust elders could help more descendants, selection favoured increased longevity while maintaining the ancestral end of female fertility. We develop a probabilistic agent-based model that incorporates two sexes and mat- ing, fertility-longevity tradeos, and the possibility of grandmother help. Using this model, we show how the grandmother eect could have driven the evolution of human longevity. Simulations reveal two stable life-histories, one human-like and the other like our nearest cousins, the great apes. The probabilistic formulation shows how stochastic eects can slow down and prevent escape from the ancestral condition, and it allows us to investigate the eect of mutation rates on the trajectory of evolution.

**Date: **19 August 2016**Speaker:** Dr John Power (University of Bath)**Venue:** AHH Lecture Theatre 1.200**Title**:*Category theoretic semantics for theorem proving in logic programming: embracing the laxness***Abstract: **I shall first outline the central ideas of logic programming, in particular the concept of SLD-resolution. I shall then discuss category theoretic semantics: first of propositional logic programs, then of more general ones. The central mathematical concept is that of a coalgebra, and the central construct is that of the cofree comonad on an endofunctor; in order to extend from propositional logic programs to more general ones, one needs to consider lax transformations between coalgebras if one is to model theorem proving. There is a natural category-theoretic alternative in terms of "saturated semantics", and if time permits, I shall discuss that too.

**Date:** 12 August 2016**Speaker:** Professor Moshe Haviv (Jerusalem University)**Venue:** AHH Lecture Theatre 1.200**Title:** *A rate balance principle and its application to queueing models***Abstract:** We introduce a rate balance principle for general (not necessarily Markovian) stochastic processes. Special attention is given to processes with birth and death like transitions, for which it is shown that for any state i, the rate of two consecutive transitions from i-1 to i+1, coincides with the corresponding rate from i+1 to i-1. This observation appears to be useful in deriving well-known, as well as new, results for the Mn/Gn/1 and G/Mn/1 queueing systems, such as a recursion on the conditional distributions of the residual service times (in the former model) and of the residual inter-arrival times (in the latter one), given the queue length. The talk is based on Oz, Adan and Haviv (2016) http://arxiv.org/pdf/1510.02779v1.pdf

**Date:** 5 August 2016**Speaker:** Dr Brett Wick (Washington University)**Venue:** AHH Lecture Theatre 1.200**Title: **Commutators, Factorization and Function Spaces**Abstract: **In this talk we will discuss the connection between function theory and operator theory by showing that certain operator theory concepts have natural analogues in function theory. This will be motivated by examples in spaces of analytic functions, results from harmonic analysis and partial dierential equations. In particular, we will discuss how to characterize certain function spaces related to second order dierential operators in terms of cancellation conditions.

### Past Research Seminar Series

#### 2018 series...

Date and Venue | Speaker | Title and link to Abstract |
---|---|---|

20th November, Tuesday | Prof Pierre Del Moral, Research Director INRIA, Bordeaux Research Center, University of Bordeaux | Uniform estimates for particle filters |

31st October, Wednesday 2pm-3pm Room 801, 12 Wally's Walk | Mahler Public Lecture by Prof Ivan Corwin, Columbia University, New York USA | Beyond the Gaussian universality class Find abstract, details of public lecture and registration here. |

24th October, Wednesday 2pm-3pm Room 803, 12 Wally's Walk | Dr Rachel Wang, University of Sydney | Metropolis-Hastings MCMC with dual mini-batches |

25th September, Tuesday 1pm-2pm Room 264, 14SCO Avenue | A/Prof Shelton Peiris, University of Sydney | On Theory and Applications of Generalized Fractional Processes: Applications to Univariate and Multivariate Gegenbauer Processes with Long Memory |

4th September, Tuesday 1pm-2pm Room 264, 14SCO Avenue | Professor Ken Siu, Department of Actuarial Studies and Business Analytics, Macquarie University | Option Pricing with Market Frictions and Regime Switching |

Specialist Lecture 24th August, Friday | Professor Susan Murphy, Harvard University Professor of Statistics, Professor of Computer Science at the Harvard John A. Paulson School of Engineering and Applied Sciences and Radcliffe Alumnae Professor at the Radcliffe Institute at Harvard University | Assessing time-varying causal interactions and treatment effects with applications to mobile health. |

31st July, Tuesday 1pm-2pm Room 264, 14SCO Avenue | Professor Irène Gijbels, Department of Mathematics and Leuven Statistics Research Center, KU Leuven, Belgium | Copula-based dependence modeling and applications: what, why and how? |

20th June, Tuesday 2pm-3pm Room 149, 7 Wally's Walk | Professor Kim-Anh Do, Department of Biostatistics, The University of Texas MD Anderson Cancer Center, Houston, USA | DINGO: Differential Network analysis in GenOmics |

5th June, Tuesday 1pm-2pm Room 264, 14SCO Avenue | Dr Dana Pascovici, Australian Proteome Analysis Facility, Macquarie University | Recent Trends in Proteomics Experiments |

29th May, Tuesday 1pm-2pm Room 264, 14SCO Avenue | Dr Libo Li, School of Mathematics and Statistics, University of New South Wales | On a positivity preserving numerical scheme for jump-extended CIR process: the alpha-stable case |

22nd May, Tuesday 1pm-2pm Room 264, 14SCO Avenue | Professor Barry Quinn, Department of Statistics, Macquarie University | Estimation of Fundamental Frequency |

1st May, Tuesday 1pm-2pm Room 264, 14SCO Avenue | Professor Richard Gerlach, Discipline of Business Analytics, Business School, The University of Sydney | Inversion copulas for GARCH models and tail risk forecasting |

27th March, Tuesday 1pm-2pm Room 264, 14SCO Avenue | Dr Ian Renner, School of Mathematical and Physical Sciences, The University of Newcastle | Species distribution models with point process models (and extensions!) |

6th March, Tuesday 1pm-2pm Room 264, 14SCO Avenue | Professor Margo Barr, The University of New South Wales Australia | 45 and up study: A tool for local population health service planning (Abstract) |

#### 2017 series...

Date and Venue | Speaker | Title and link to Abstract |
---|---|---|

7th November, Tuesday 1pm Room 264 E7B | Dr Zdravko Botev, University of New South Wales Australia | Regenerative Sampling via Monte Carlo Splitting (Abstract) |

31st October, Tuesday 3pm Room 130 E5A | Dr Jakub Stoklosa, University of New South Wales Australia | A Generalized Estimating Equation approach to Multivariate Adaptive Regression Spline (Abstract) |

24th October, Tuesday 1pm Room 264 E7B | Prof. Gillian Heller, Department of Statistics, Macquarie University | Parameter orthogonality and the GAMLSS family of distributions |

18th October, Wednesday 1pm Room 108 E6A | Assoc. Prof. Armando Teixeira-Pinto, School of Public Health, The University of Sydney | Causal inference from observational data – the Mendelian randomisation design (Abstract) |

12th September, Tuesday 1pm Room 264 E7B | Assoc. Prof. Peter Radchenko, The University of Sydney Business School , The University of Sydney | High-dimensional regression with L_0 regularization (Abstract) |

29th August, Tuesday 1pm Room 264 E7B | Peter Mere, SMARTS Innovation Lab, NASDAQ | Modern financial markets: a user's guide from the inside (Abstract) |

8th August, Tuesday, 1pm Room 264 E7B | Dr Feng Chen, School of Mathematics and Statistics, University of New South Wales Australia | Direct Likelihood Evaluation for the Renewal Hawkes Process (Abstract) |

#### 2016 Series...

Date and Venue | Speaker | Title and link to Abstract |
---|---|---|

4th October, Tuesday, 1pm 1.200 Lecture Theatre AHH | Dr Emi Tanaka, Centre of Bioinformatics and Biometrics, University of Wollongong | How statistics feeds us – applied statistics in agriculture (Abstract) |

6th September, Tuesday, 1pm 1.200 Lecture Theatre AHH | Dr Jennifer Chan, School of Mathematics and Statistics, University of Sydney | Volatility estimation and forecast using quantile range-based measures and parametric quantile regression (Abstract) |

30th August, Tuesday, 1pm 1.200 Lecture Theatre AHH | Dr Peter Straka, School of Mathematics and Statistics, University of New South Wales | Max-sum stable distributions and Extremes of Intermittent Events (Abstract) |

23rd August, Tuesday, 1pm 1.200 Lecture Theatre AHH | Dr Ningbo Jiang, Office of Environment and Heritage (NSW) | Interested in applying your statistical power to real world data? (Abstract) |

16th August, Tuesday, 1pm 1.200 Lecture Theatre AHH | Dr Robert Borotkanics, Faculty of Medicine and Health Sciences, Macquarie University | ROC analyses in the classification of chemicals that result in hepatocarcinogenesis (Abstract) |

31st May, Tuesday, 1pm 1.200 Lecture Theatre AHH | Dr Jennifer Hallinan, Department of Biological Sciences, Macquarie University | Engineering Bacterial Populations for Pattern Formation (Abstract) |

3rd May, Tuesday, 1pm 1.200 Lecture Theatre AHH | Dr Yanan Fan, School of Mathematics and Statistics, University of New South Wales | Bayesian inference for quantile regression (Abstract) |

29th April, Tuesday, 1pm 1.200 Lecture Theatre AHH | Prof Matt Wand, School of Mathematical and Physical Sciences, University of Technology Sydney | Fast Approximate Inference for Arbitrarily Large Statistical Models via Message Passing (Abstract) |

5th April, Tuesday, 1pm 1.200 Lecture Theatre AHH | Prof Vladimir Gaitsgory, Department of Mathematics, Macquarie University | Linear Programming Relaxations of Nonlinear Optimal Control Problems (Abstract) |

15th March, Tuesday, 1pm 1.200 Lecture Theatre AHH | Prof Pavel V. Shevchenko, CSIRO Australia | Valuation of Variable Annuities with Guarantees via Stochastic Control Optimization (Abstract) |

#### 2015 series...

Date and Venue | Speaker | Title and link to Abstract |
---|---|---|

27th October, Tuesday, 2pm 1.200 Lecture Theatre AHH | Matthew Ames, Department of Statistical Science, University College London | Violations of Uncovered Interest Rate Parity and International Exchange Rate Dependence (Abstract) |

Tuesday 29 September 2015, Time 2pm 1.200 Lecture Theatre AHH | Dr Garth Tarr, School of Mathematical and Physical Sciences, University of Newcastle | Visualising model selection stability (Abstract) |

8th September, Tuesday, 2pm 1.200 Lecture Theatre AHH | Dr Craig Anderson, School of Mathematical and Physical Sciences, University of Technology Sydney | Identifying Growth Faltering in Young Children (Abstract) |

11th August, Tuesday, 2pm 1.200 Lecture Theatre AHH | Prof John McAneney, Risk Frontiers, Macquarie University | Natural Disasters, Property Losses and Climate Change Attribution (Abstract) |

2nd June, Tuesday, 2pm E4A, Room 523 (level 5 seminar room) | Prof Barry Quinn, Department of Statistics, Macquarie University | Estimating the parameters of an exponentially damped sinusoid (Abstract) |

12th May, Tuesday, 2pm E4A, Room 523 (level 5 seminar room) | Dr Ivor Cribben, Department of Finance and Statistical Analysis, University of Alberta | Two novel methods for estimating connectivity change-point models for brain imaging data (Abstract) |

5th May, Time 2pm E4A, Room 523 (level 5 seminar room) | Dr Artem Prokhorov, Discipline of Business Analytics, Business School, the University of Sydney | New aspects of nonparametric copula density estimation (Abstract) |

28th April, Tuesday, 2pm E4A, Room 523 (level 5 seminar room) | A/Prof Xinyuan Song, Department of Statistics, Chinese University of Hong Kong | Statistics analysis of a generalized hidden Markov model (Abstract) |

24th March, Tuesday, 2pm E4A, Room 523 (level 5 seminar room) | Dr David Nipperess, Department of Biological Sciences, Macquarie University | The PD-calculus: integrating evolutionary relationships into biodiversity measurement and conservation (Abstract) |

10th March, Tuesday, 2pm E4A, Room 523 (level 5 seminar room) | Dr Bob Carpenter, Department of Statistics, Columbia University | Stan: A probabilistic programming language for Bayesian inference (Abstract) |

**Past Lunchtime Seminar Series**

#### 2018 series...

**Session 2, 2018**

###### Tuesday 16 October: Dr Richard Garner, "Mathematics for Deleuzers"

In this talk I will give an idiosyncratic introduction to the philosophy of mathematics. One of the great dichotomies that has riven the philosophy of maths is between "realist" and "anti-realist" perspectives. That is, do mathematical objects really exist in some Platonic realm, and we merely discover them, or is mathematics just shuffling symbols around on a page, and so invented by us? I propose the answer "no" to this question. Having laid this thorny problem to rest, I will go on to address the much more profound question: why are assignments hard?

###### Tuesday 04 September: Dr Paul Bryan, "Cantor tried to solve the heat equation and accidentally invented set theory"

In the early 19th century, Fourier solved the heat equation, describing the flow of heat in a body by using infinite series of trigonometric functions. The question of whether expressing the solution in terms of such "Fourier series" was unique occupied a number of mathematicians throughout the 19th century. While attempting to solve this problem, Cantor discovered the need for a rigorous notion of sets of real numbers and indeed for real numbers themselves. In this talk, we will see how the uniqueness of Fourier series question lead Cantor to define ordinal numbers and a remarkable theorem of Cantor showing uniqueness of Fourier series for sets with "infinities upon infinities" of discontinuities!

###### Tuesday 21 August: Dr Joshua Peate, "Finding the square root of a derivative, and why this is useful"

When learning mathematics, an early concept is that of the square root. The square root of two, for example, is defined as the number that if multiplied by itself gives back 2. Originally, you are told, you cannot square root a negative number, but then in university mathematics you are told you can, and in fact all of the imaginary numbers are defined through the square root of -1. But can we take this further and apply the concept of a square root to just anything? For example, can I find an operator, that if applied to a function twice, would result in the same as differentiating?

This talk will look at some specific examples of square roots and other parts of functional calculus, and how this type of thinking allows us to represent difficult mathematical problems in new ways. The talk will conclude with some comments on current research.

**Session 1, 2018**

###### Tuesday 01 May: Mr Ali Shariati, "Statistical Inference Using Empirical Likelihood for Survival Data under Length-bias and Right-censorship"

A frequent problem statisticians face is the analysis of survival data. Survival data, known as time-to-event data, arises in various disciplines, such as reliability, engineering, economics, demography, biology, epidemiology and public health.

To study the natural history of a disease, survival data collected in a cohort of prevalent cases may be used to make statistical inference on survival functions. In such studies, we only observe subjects who have already been diagnosed with a condition or disease (e.g. HIV, cancer or dementia) but are yet to experience the failure event (e.g. AIDS, or death). Statistical procedures and methodology for assessment of interventions or treatments based on such data often involve different bias, the most important of which are right-censorship and length-bias.

In this talk, I will introduce some basic parameters to characterize the survival data. I will discuss the problem of making inference on survival parameters based on right-censored and length-biased data. I will propose an empirical likelihood procedure for analyzing such data. A simulation study is conducted to reveal the performance of the proposed methods. Several real examples are presented for better illustration. I will also demonstrate the usage of the methods proposed for engineering and reliability through some examples.

###### Tuesday 10 April: Prof. Ross Street, "Trees, Permutations, Trigonometry, and Ploughing"

There are two kinds of “research”: one is finding out what was done, the other is discovering new facts for yourself. This talk involves a bit of both. Some years back, a colleague spoke of his interest in certain kinds of mathematical trees that he needed for some application of category theory to physics. He wanted to count the number of these trees with a given number of nodes. After our people used the internet to find that these numbers existed in the literature, I set two Vacation Scholars on further research of this first kind. The talk will outline their lovely results, including research of the second kind.

**Tuesday 13 March: Justin Tzou, " Diffusion is not always a-smoothin' "**

When a drop of ink spreads through a glass of water, when the smell of a perfume sprayed in one corner of a room makes its way to all corners, or when a disease that begins in a few isolated pockets overtakes entire regions, the underlying process at work is the ubiquitous phenomenon of diffusion. A result of random motion, diffusion acts to transport material (whether it be actual material such as atoms and molecules, or abstract material such as the prevalence of a disease) from regions with high concentration of material to those with low concentration. As such, one might assume that diffusion always drives a system toward a state in which concentrations of material are the same everywhere. If this was the case, why do bacteria colonies form in clumps, how can vegetation patterns persist, and, as was famously put by the math biologist Prof. J.D. Murray, how did the leopard get its spots? In this seminar, we take a brief journey through the mathematical underpinnings of diffusion-driven pattern formation, highlighted by the pioneering work of Alan Turing in 1952. Because of its prevalence in nature, the study of pattern formation is still currently an area of intense research in applied mathematics.

#### 2017 series...

**Session 2, 2017**

Talks take place in C5A 310, 1pm-2pm

**Tuesday 15 August: Eugenia Cheng, "Character vs gender in mathematics"**

This will be an informal discussion of my experience of being a female mathematician and teaching mathematics at all levels from elementary school to grad school. The question of why women are under-represented in mathematics is complex and there are no simple answers, only many many contributing factors. I will focus on character traits and argue that if we focus on this rather than gender we can have a more productive and less divisive conversation. To try and focus on characters rather than genders I will introduce gender-neutral character adjectives "ingressive" and "congressive" to replace masculine and feminine. I will share my experience of teaching congressive abstract mathematics to art students, in a congressive way, and the possible effects this could have for everyone in mathematics, not just women.

**Tuesday 12 September: Gerry Myerson, "How to cover the integers"**

Every integer n satisfies at least one of the following:

n is a multiple of 2;

n is a multiple of 3;

n+1 is a multiple of 4;

n+1 is a multiple of 6;

n+11 is a multiple of 12.

This is known as a system of covering congruences. These were introduced by Erdos in his proof that there are odd numbers – indeed, infinitely many odd numbers – that can't be written as the sum of a prime and a power of two. We'll look at some solved and unsolved problems concerning covering congruences and, time permitting, some related concepts.

**Tuesday 17 October: Chris Green, "The basics of conformal mapping in the complex plane"**

During a first course in complex analysis, we learn about what it means for a complex function to be analytic in a region of the complex plane and why this is special. If we think of an analytic function as a mapping of a particular region of the complex plane to another, it is interesting to ask what the target region will look like under the action of this mapping. In this talk, I will explain what it means for an analytic function to be conformal, introduce a couple of well-known conformal maps and what they do, and discuss why they are important in applications.

**Session 1, 2017**

Talks take place in C5A 310, 1pm-2pm

**Tuesday 23 May: Christopher Cooper, "Several Slices of Pi"**

RECIPE FOR PI

Take one of each odd natural number.

Square each of them and take their reciprocals.

Mix together and bake in an infinite sum.

Garnish by multiplying by 8 and taking the square root.

This will make one delicious pi.

The geometric definition of pi is the ratio of the circumference of a circle to its diameter. This is fine unless you happen to be a disembodied angel, an intelligent being with no concept of the spatial world ("what is a circle?"). The definition in terms of an infinite series would be more satisfactory in that case.

We'll also discuss some other definitions of pi: the biblical definition in 1 Kings 7:23, the statistician's definition in terms of throwing sticks on the floorboards, and finally the astronomer's definition based on the brightness of the moon.

Finally, we'll ask whether we should reject pi and become Tauists instead.

**Tuesday 9 May: Steve Lack, "Counting and Measurement"**

The traditional approach to counting is to use whole numbers, and the traditional approach to measurement is to use real numbers. I’ll argue that counting sometimes leads to negative numbers and that measurement should often be done with polynomials. To do this requires a tiny modification to the rulers we use, as I shall also explain.

**Tuesday 11 April: Emily Riehl, "A solution to the stable marriage problem"**

Consider what might be called the “matchmaker’s dilemma”: A matchmaker wishes to arrange (opposite-sex) marriages in a dating pool of single men and single women in such a way that no unmatched couple would prefer to elope together rather than remain with their assigned partners. (There is a mathematical reason that this theory requires a heteronormative framework that will be discussed). Is it always possible, given any numbers of men and women, each with their own personal preferences, to arrange marriages that are stable in this way?

We’ll discuss this problem, an algorithmic solution, its sexist implications, and a real-world application that demonstrates that the theorems proven here aren’t simply another case of “mathematical make-believe.”

**Tuesday 28th March: Richard Garner, "Cataloguing the Alhambra"**

Islamic art provides a cornucopia of intricate and beautiful geometric patterns; particularly interesting to mathematicians are those made by sticking polygons together in a repeating pattern which tiles the plane. For a long time, people have sought ways of cataloguing these patterns, but it was not until the 1980's that the definitive way of doing so was found by Delaney and Dress. In this talk, I will give an interactive introduction to these "Delaney-Dress symbols" and to the rich world of patterns that they can encode.

#### 2016 series...

**Session 2, 2016**

Talks take place in C5A 315, 1pm-2pm

- Tuesday 30th August: Chris Cooper, "The many faces of a cube"
- Tuesday 13th September: Richard Garner, "On dithering, uncertainty and loping basslines"
- Tuesday 4th October: Jim Denier, "Fluid Mechanics: what’s Maths got to do with it?"
- Tuesday 18th October: Steve Lack, "Games"
- Tuesday 1st November: William Chen, "There is no integer between 0 and 1, and Schmidt chocolate cake theorem"