Condensed Matter Theory

Abstract:

The green alga {\it Chlamydomonas} swims with synchronized beating of its two flagella, and is experimentally observed to exhibit run-and-tumble behaviour similar to bacteria. Recently we studied a simple hydrodynamic three-sphere model of {\it Chlamydomonas} with a phase dependent driving force which can produce run-and-tumble behaviour when intrinsic noise is added, due to the non-linear mechanics of the system. Here, we consider the noiseless case and explore numerically the parameter space in the driving force profiles, which determine whether or not the synchronized state evolves from a given initial condition, as well as the stability of the synchronized state. We find that phase dependent forcing, or a beat pattern, is necessary for stable synchronization in the geometry we work with.

Abstract:

DNA has enormous potential as a programmable material for creating artificial nanoscale structures and devices. For more complex systems, however, rational design and optimization can become difficult. We have recently proposed a coarse-grained model of DNA that captures the basic thermodynamic, structural, and mechanical changes associated with the fundamental process in much of DNA nanotechnology, the formation of duplexes from single strands. In this article, we demonstrate that the model can provide powerful insight into the operation of complex nanotechnological systems through a detailed investigation of a two-footed DNA walker that is designed to step along a reusable track, thereby offering the possibility of optimizing the design of such systems. We find that applying moderate tension to the track can have a large influence on the operation of the walker, providing a bias for stepping forward and helping the walker to recover from undesirable overstepped states. Further, we show that the process by which spent fuel detaches from the walker can have a significant impact on the rebinding of the walker to the track, strongly influencing walker efficiency and speed. Finally, using the results of the simulations, we propose a number of modifications to the walker to improve its operation.