# Past OCCAM Wednesday Morning Event

13 March 2013
14:00
Konstantinos Papafitsoros
Abstract

********** PLEASE NOTE THE SPECIAL TIME **********

Total generalised variation (TGV) was introduced by Bredies et al. as a high quality regulariser for variational problems arising in mathematical image processing like denoising and deblurring. The main advantage over the classical total variation regularisation is the elimination of the undesirable stairscasing effect. In this talk we will give a small introduction to TGV and provide some properties of the exact solutions to the L^{2}-TGV model in the one dimensional case.

• OCCAM Wednesday Morning Event
6 March 2013
10:15
Prof. Michael Mackey
Abstract
In this talk aimed at a general audience I will discuss the ways in which we have used mathematical models of the regulation of haematopoiesis (blood cell production) to understand haematological diseases, and suggest successful treatment strategies for these diseases. At the end I will talk about our current work on tailoring chemotherapy so that it has less damaging effects on the haematopoietic system and, consequently, improve the quality of life for patients being treated for a variety of tumours.
• OCCAM Wednesday Morning Event
5 March 2013
10:15
Dr Wolfgang Erb
Abstract

******************** PLEASE NOTE THIS SEMINAR WILL TAKE PLACE ON TUESDAY ********************

Well-known iterative schemes for the solution of ill-posed linear equations are the Landweber iteration, the cg-iteration and semi-iterative algorithms like the $\nu$-methods. After introducing these methods, we show that for ill-posed problems a slight modification of the underlying three-term recurrence relation of the $\nu$-methods provides accelerated Landweber algorithms with better performance properties than the $\nu$-methods. The new semi-iterative methods are based on the family of co-dilated ultraspherical polynomials. Compared to the standard $\nu$-methods, the residual polynomials of the modified methods have a faster decay at the origin. This results in an earlier termination of the iteration if the spectrum of the involved operator is clustered around the origin. The convergence order of the modified methods turns out to be the same as for the original $\nu$-methods. The new algorithms are tested numerically and a simple adaptive scheme is developed in which an optimal dilation parameter is determined. At the end, the new semi-iterative methods are used to solve a parameter identification problem obtained from a model in elastography.

• OCCAM Wednesday Morning Event
27 February 2013
10:15
Abstract
<p><span>Cell polarity in the rod-shaped bacterium Myxococcus xanthus is crucial&nbsp;</span><span>for the direction of movement of individual cells. Polarity is governed by&nbsp;</span><span>a regulatory system characterized by a dynamic spatiotemporal oscillation&nbsp;</span><span>of proteins between the opposite cell poles. A mathematical framework for&nbsp;</span><span>a minimal macroscopic model is presented which produces self-sustained&nbsp;</span><span>regular oscillations of the protein concentrations. The mathematical model&nbsp;</span><span>is based on a reaction-diffusion PDE system and is independent of external&nbsp;</span><span>triggers. Necessary conditions on the reaction terms leading to&nbsp;</span><span>oscillating solutions are derived theoretically. Possible scenarios for&nbsp;</span><span>protein interaction are numerically tested for robustness against&nbsp;</span><span>parameter variation. Finally, possible extensions of the model will be&nbsp;</span><span>addressed.</span></p>
• OCCAM Wednesday Morning Event
20 February 2013
10:15
Yang Cao
Abstract

Complex systems emerging from many biochemical applications often exhibit multiscale and multiphysics (MSMP) features: The systems incorporate a variety of physical processes or subsystems across a broad range of scales. A typical MSMP system may come across scales with macroscopic, mesoscopic and microscopic kinetics,
deterministic and stochastic dynamics, continuous and discrete state space, fastscale and slow-scale reactions, and species of both large and small populations. These complex features present great challenges in the modeling and simulation practice. The goal of our research is to develop innovative computational methods and rigorous fundamental theories to answer these challenges. In this talk we will start with introduction of basic stochastic simulation algorithms for biochemical systems and multiscale
features in the stochastic cell cycle model of budding yeast. With detailed analysis of these multiscale features, we will introduce recent progress on simulation algorithms and computational theories for multiscale stochastic systems, including tau-leaping methods, slow-scale SSA, and the hybrid method.

• OCCAM Wednesday Morning Event
19 February 2013
10:15
Thomas Hillen
Abstract

***** PLEASE NOTE THIS SEMINAR WILL TAKE PLACE ON TUESDAY 19TH FEBRUARY *****

With "fully anisotropic" I describe diffusion models of the form u_t=\nabla \nabla (D(x) u), where the diffusion tensor appears inside both derivatives. This model arises naturally in the modeling of brain tumor spread and wolf movement and other applications. Since this model does not satisfy a maximum principle, it can lead to interesting spatial pattern formation, even in the linear case. I will present a detailed derivation of this model and discuss its application to brain tumors and wolf movement. Furthermore, I will present an example where, in the linear case, the solution blows-up in infinite time; a quite surprising result for a linear parabolic equation (joint work with K.J. Painter and M. Winkler).

• OCCAM Wednesday Morning Event
13 February 2013
10:15
David Holcman
Abstract
<p>I propose to present modeling and experimental data about the organization of telomeres (ends of the chromosomes): the 32 telomeres in Yeast form few local aggregates. We built a model of diffusion-aggregation-dissociation for a finite number of particles to estimate the number of cluster and the number of telomere/cluster and other quantities. We will further present based on eingenvalue expansion for the Fokker-Planck operator, asymptotic estimation for the mean time a piece of a polymer (DNA) finds a small target in the nucleus.</p>
• OCCAM Wednesday Morning Event
6 February 2013
10:15
Jacco Snoeijer
Abstract
<p>When two drops come into contact they will rapidly merge and form a single drop. Here we address the coalescence of drops on a substrate, focussing on the initial dynamics just after contact. For very viscous drops we present similarity solutions for the bridge that connects the two drops, the size of which grows linearly with time. Both the dynamics and the self-similar bridge profiles are verified quantitatively by experiments. We then consider the coalescence of water drops, for which viscosity can be neglected and liquid inertia takes over. Once again, we find that experiments display a self-similar dynamics, but now the bridge size grows with a power-law $t^{2/3}$. We provide a scaling theory for this behavior, based on geometric arguments. The main result for both viscous and inertial drops is that the contact angle is important as it determines the geometry of coalescence -- yet, the contact line dynamics appears irrelevant for the early stages of coalescence.</p>
• OCCAM Wednesday Morning Event