AMRC Seminar Series

The AMRC hosts a series of seminars on subjects in statistical physics and fluid dynamics.

Julia Yeomans (Oxford University, UK)

Stirring by Microswimmers
Wednesday April 24, 2013, 15:00 h, DH Seminar room

Because of their size bacteria and fabricated micro-swimmers swim at low Reynolds number, a regime where the effect of hydrodynamics can be counterintuitive. Moreover micro-swimmers provide experimentally accessible examples of active systems that create their own energy and operate out of thermodynamic equilibrium.

The mechanisms by which bacteria interact with particles in their environment are relevant to their feeding strategies and may contribute to oceanic mixing. We discuss how ?tracer particles are advected by swimmers, and use our results to link the swimming strokes of the bacteria to their effectiveness as ?stirrers.

Steve Simon (Oxford University, UK)

Topological Matter and Why You Should Be Interested
Wednesday April 10, 2013, 16:00 h, DH Seminar room

In two dimensional topological phases of matter, processes depend on gross topology rather than detailed geometry. Thinking in 2+1 dimensions, particle world lines can be interpreted as knots or links, and the amplitude for certain processes becomes a topological invariant of that link. While sounding rather exotic, we believe that such phases of matter not only exist, but have actually been observed in quantum Hall experiments, and could provide a uniquely practical route to building a quantum computer.   Possibilities have also been proposed for creating similar physics in systems ranging from superfluid helium to strontium ruthenate to semiconductor-superconductor junctions to quantum wires to spin systems to cold atoms.

Tobias Preis (University of Warwick, Coventry, UK)

Quantifying Economic Behavior Using Big Data
Wednesday March 20, 2013, 15:30 h, DH Seminar room

In this talk, I will outline some recent highlights of our research, addressing two questions. Firstly, can big data resources provide insights into crises in financial markets which affect humans worldwide? By analysing Google query volumes for search terms related to finance, we find patterns which may be interpreted as early warning signs of stock market moves. Secondly, can we provide insight into international differences in economic wellbeing by comparing patterns of interaction with the Internet? To answer this question, we introduce a future-orientation index to quantify the degree to which Internet users seek more information about years in the future than years in the past. We analyse Google logs and find a striking correlation between the country's GDP and the predisposition of its inhabitants to look forward. Our results illustrate the potential that combining extensive behavioural data sets offers for a better understanding of large scale human economic behaviour.

Stefan Grosskinsky (University of Warwick, Coventry, UK)

Scale-invariant growth processes in expanding space
Wednesday February 13, 2013, 15:00 h, DH Seminar room

Many growth processes lead to intriguing stochastic patterns and complex fractal structures which exhibit local scale invariance properties. Such structures can often be described effectively by space-time trajectories of interacting particles, and their large scale behavior depends on the overall growth geometry. We establish an exact relation between statistical properties of structures in uniformly expanding and fixed geometries, which preserves the local scale invariance and is independent of other properties such as the dimensionality. This relation generalizes standard conformal transformations as the natural symmetry of self-affine growth processes. 

We illustrate our main result numerically for various structures of coalescing L┬┤evy flights and fractional Brownian motions, including also branching and finite particle sizes. One of the main benefits of this approach is a full, explicit description of the asymptotic statistics in expanding domains, which are often nontrivial and random due to amplification of initial fluctuations.