Dynamics Today

By Matthew J. Hoffman
The New Year kicked off with the XXXIV Dynamics Days U.S. 2015 conference January 9-11 in Houston, TX, hosted by the Center for Theoretical Biological Physics at Rice University. The conference contained a heavy dose of low Reynolds number dynamics of microorganisms, but included a range of other systems including—but not limited to—bird flapping, natural gas production, cardiac dynamics, and climate sensitivity. What follows is my attempt at summarizing some of the discussion, with the caveat that I cannot possibly touch on everything that happened.

The conference kicked off on Friday with a talk from Michael Shelley (New York University) on how swimming or flapping organisms interact with each other through their interactions with the fluid. He discussed examples both at the microscopic level (of proteins swimming within a cell) and at the macroscopic level (of birds in flight). Michael Graham (University of Wisconsin) then spoke about movement of uniflagellar bacteria and dynamic processes that lead to flagella bundling. He described how such organisms can take helical trajectories due to a buckling instability. In other talks, Sibani Bismal (Rice University) discussed engineering microscale swimmers by using non-attached magnetically coupled “arms” to cause motion. She demonstrated how these swimmers can increase efficiency by reconfiguring themselves. Also, Suhas Rao (Baylor School of Medicine) gave a nice overview of the study of genome folding and described how recent experiments have shed light on the loop folding structure of DNA strands in the intermediate scales between the helix structure and the full chromosome.

On Saturday Gemunu Gunaratne (University of Houston) addressed network analysis for applications such as how to determine genes to change in order to battle cancer when the true gene networks are partially known, thus preventing the use of many common methods. Instead, a collection of system responses to perturbations were used to determine a means to alter a small subset of the system to drive it towards the desired state. Later, Daniel Rothman (Massachusetts Institute of Technology) discussed analyzing the stability of the biosphere-geosphere system with the goal of answering the question of why some significant environmental change events in the Earth’s history have led to mass extinctions while others have not. By looking of rates of change in the carbon cycle and rates of change in evolution, a stability plot was constructed, and he showed that while the system was marginally stable, similar instability mechanisms could account for the great extinctions of the past. Juan Restrepo (University of Colorado) then showed how an application of the mean field approximation to a network of phase oscillators allowed the macroscopic behavior of the system to be approximately modeled by a set of ordinary differential equations. Saturday also featured a poster session and reception in the evening where about 30 posters were on display

The last day had a couple of talks related to cardiac dynamics. Emilia Entcheva (Stony Brook University) described a method for optically stimulating cardiac tissue which allows for unprecedented control of the initialization of experimental cardiac wave propagation. She also showed video of the apparatus initializing spiral waves and then changing the propagation direction using coordinated bursts of light. Alain Karma (Northeastern University) followed with a discussion of modeling abnormal cardiac action potential behavior with respect to long QT syndrome. He demonstrated how his advanced mathematical models can reproduce bursting events when the system-wide response to prolonged QT is considered, but not when considering only the effect of single ion channel defects. The talk emphasized the importance of considering dynamics in a system-wide manner. On a different topic, Michael Ghil (University of California, Los Angeles) gave an engaging talk on efforts to quantify sensitivity of climate models. He spoke about the importance of trying to get a handle on sensitivity in simple climate models, since many climate models are overly complex, and he discussed efforts to measure sensitivity using random dynamical systems principles.

The conference included many more wonderful dynamics-related talks than I can summarize in this short review, but I had a wonderful time at Dynamics Days and I would encourage anyone reading this to check out the conference next year.

Matthew J. Hoffman


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