# Past Junior Applied Mathematics Seminar

3 December 2013
13:15
Lloyd Chapman
Abstract
It is often difficult to include sufficient biological detail when modelling cell population growth to make models with real predictive power. Continuum models often fail to capture physical and chemical processes happening at the level of individual cells and discrete cell-based models are often very computationally expensive to solve. In the first part of this talk, I will describe a phenomenological continuum model of cell aggregate growth in a specific perfusion bioreactor cell culture system, and the results of numerical simulations of the model to determine the effects of the bioreactor operating conditions and cell seeding on the growth. In the second part of the talk, I will introduce a modelling approach used to derive continuum models for cell population growth from discrete cell-based models, and consider possible extensions to this framework.
• Junior Applied Mathematics Seminar
19 November 2013
13:15
James Herterich and Ingrid von Glehn
Abstract
JH: Water filtration systems typically involve flow along a channel with permeable walls and suction applied across the wall. In this cross-flow'' arrangement, clean water leaves the channel while impurities remain within it. A limiting factor for the operation of cross-flow devices is the build-up of a high concentration of particles near the wall due to the induced flow. Termed concentration polarization (CP), this effect ultimately leads to the blocking of pores within the permeable wall and the deposition of a cake'' on the wall surface. Here we show that, through strategic choices in the spatial variations of the channel-wall permeability, we may reduce the effects of CP by allowing diffusion to smear out any build up of particles that may occur. We demonstrate that, for certain classes of variable permeability, there exist optimal choices that maximize the flux of clean water out of a device. \\ IvG: TBC
• Junior Applied Mathematics Seminar
5 November 2013
13:15
Partick Raanes
Abstract
Data assimilation is a particular form of state estimation. That's partly the "what". We'll also look at the how's, the why's, some who's and some where's.
• Junior Applied Mathematics Seminar
22 October 2013
13:00
Stuart Thomson
Abstract
In the first JAM seminar of 2013/2014, I will discuss the topic of singular perturbed hyperbolic systems of PDE arising in physical phenomena, particularly the St Venant equations of shallow water theory. Using a mixture of analytical and numerical techniques, I will demonstrate the dangers of approximating the dynamics of a system by the equations obtained upon taking a singular limit $\epsilon\rightarrow 0$ and furthermore how the dynamics of the system change when the parameter $\epsilon$ is taken to be small but finite. Problems of this type are ubiquitous in the physical sciences, and I intend to motivate another example arising in elastoplasticity, the subject of my DPhil study. \\ \\ Note: This seminar is not intended for faculty members, and is available only to current undergraduate and graduate students.
• Junior Applied Mathematics Seminar
28 May 2013
13:00
Marta Sarzynska
Abstract
<p>We detect communities on time-dependent correlation networks to study the geographical spread of disease. Using data on country-wide dengue fever, rubella, and H1N1 influenza occurrences spanning several years, we create multilayer similarity networks, with the provinces of a country as nodes and the correlations between the time series of case numbers giving weights to the edges.</p> <p>We perform community detection on these temporal networks of disease outbreaks, looking for groups of provinces in which disease patterns change in similar ways. Optimizing multilayer modularity with a Newman-Girvan null model over a wide parameter range, we observe several partitions that corresponding roughly to relevant historical time points, such as large epidemics and introduction of new disease strains, as well as many strongly spatial partitions.</p> <p>We develop a novel null model for community detection that takes into account spatial information, thereby allows to uncover additional structure that might otherwise be obscured by spatial proximity. The null model is based on a radiation model that was proposed recently for modelling human mobility, and we believe that it might be better at capturing disease spread than existing spatial null models based on gravity models for interaction between nodes.</p> <p>The radiation null model performs better than the Newman-Girvan null model and similarly to the gravity model on benchmark spatial networks with distance-dependent links and a known community structure (both static and multislice networks), and it strongly outperforms both on flux-based benchmarks. When applied to the disease networks, the radiation null model uncovers novel, clear temporal partitions, that might shed light on disease patterns, the introduction of new strains, and provide epidemic warning signals.</p>
• Junior Applied Mathematics Seminar
27 November 2012
13:15
Stephen O'Keeffe
Abstract

Multi-layered cylinders, or 'multitubes', are ubiquitous throughout the biological world, from microscopic axons to plant stems. Whilst these structures share an underlying common geometry, each one fulfils a different key role in its relevant environment. For example plant stems provide a transport network for nutrients within the organism, whilst the tongue of a chameleon is used for prey capture. This talk will be concerned with the mechanical stability of multitubes. How do the material properties, applied tractions and geometry of elastic rods and tubes influence their critical buckling pressure and mode of buckling? We will discuss the phenomenon of differential growth, an important factor in the mechanical behaviour of such systems and introduce a mathematical framework, which can be used to model differential growth in soft tissues and predict the onset of buckling. We will also present a small number of applications for this research.

• Junior Applied Mathematics Seminar
13 November 2012
13:15
Arnaud Lionnet
Abstract

I will present the basics of mathematical finance, and what probabilists do there. More specifically, I will present the basic concepts of replication of a derivative contract by trading, market completeness, arbitrage, and the link with Backward Stochastic Differential Equations (BSDEs).

• Junior Applied Mathematics Seminar
30 October 2012
13:15
Abstract

High-pressure freezing processes are a novel emerging technology in food processing,
offering signiﬁcant improvements to the quality of frozen foods. To be able to simulate
plateau times and thermal history under different conditions, a generalized enthalpy
model of the high-pressure shift freezing process is presented. The model includes
the effects of pressure on conservation of enthalpy and incorporates the freezing point
depression of non-dilute food samples. In addition, the signiﬁcant heat-transfer effects of
convection in the pressurizing medium are accounted for by solving the two-dimensional
Navier–Stokes equations.
The next question is: is high-pressure shift freezing good also in the long run?
A growth and coarsening model for ice crystals in a very simple food system will be discussed.

• Junior Applied Mathematics Seminar
16 October 2012
13:15
Matt Hennessy
Abstract
<p><span>When ice is raised to a temperature above its usual melting temperature</span><br /><span>of 273 K, small cylindrical discs of water form within the bulk of the</span><br /><span>ice. Subsequent internal melting of the ice causes these liquid discs to</span><br /><span>grow radially outwards. However, many experimentalists have observed</span><br /><span>that the circular interface of these discs is unstable and eventually</span><br /><span>the liquid discs turn into beautiful shapes that resemble flowers or</span><br /><span>snowflakes. As a result of their shape, these liquid figures are often</span><br /><span>called liquid snowflakes. In this talk I'll discuss a simple</span><br /><span>mathematical model of liquid snowflake formation and I'll show how a</span><br /><span>combination of analytical and numerical methods can yield much insight</span><br /><span>into the dynamics which govern their growth.</span></p>
• Junior Applied Mathematics Seminar
12 June 2012
13:15
Joseph Parker
Abstract

Nuclear fusion offers the prospect of abundant clean energy production, but the physical and engineering challenges are very great. In nuclear fusion reactors, the fuel is in the form of a plasma (charged gas) which is confined at high temperature and density using a toroidal magnetic field. This configuration is susceptible to turbulence, which transports heat out of the plasma and prevents fusion. It is believed that rotating the plasma suppresses turbulence, but experiments are expensive and even modest numerical simulation requires hundreds of thousands of CPU hours. We present a numerical technique for one of the five phase-space dimensions that both improves the accuracy of the calculation and greatly reduces the resolution required.

• Junior Applied Mathematics Seminar