For the casual observer it is fascinating to watch the orderly and seemingly choreographed motion of hundreds or even thousands of fish, birds or insects. However, the formation and the manifold motion patterns of such flocks raise numerous questions fundamental to the understanding of complex systems.
A team of physicists from Technische Universitaet Muenchen (TUM) and LMU Muenchen has developed a versatile biophysical model system that opens the door to studying these phenomena and their underlying principles. Using a combination of an experimental platform and theoretical models, more complex systems can now be described and their properties investigated. The Munich researchers report on their findings in the current issue of the renowned journal Nature.
"Everything flows and nothing abides," is a saying ascribed to the Greek philosopher Heraclitus. Large groups of individuals may show collective behavior where the individuals' actions appear to be coordinated or even subordinated to the common good: Flocks of birds move through the air without a conductor, as if they were choreographed, and shoals of fish change their direction instantaneously when a shark appears. Yet science is still puzzled: Do all these systems obey the same universal laws? Does complex group behavior emerge from simple interactions between individuals intrinsically and inevitably? A team of researchers headed by Professor Andreas Bausch, Chair of Biophysics at TUM and Professor Erwin Frey, Chair of Statistical and Biological Physics at LMU, are unraveling the mystery.
The Munich researchers have developed a biophysical model system that makes it possible to carry out targeted high-precision experiments under controlled conditions. To this end, Volker Schaller from the TUM Chair of Biophysics, first author of the study, fixed biological motor proteins to a microscope coverslip in such a way that they could drive filaments of the muscle protein actin, suspended loosely over them, in any direction. The filaments measure about seven nanometers across, i.e. seven millionths of a meter, and are about ten micrometers long, i.e. a ten thousandth of a millimeter. The movement of the filaments is visualized using high-resolution microscopy.
In the experiments described in Nature, the actin filaments began to move as soon as ATP – the fuel for the motor proteins – was added. With low concentrations of actin filaments, the motion remained completely chaotic. Once the density crossed a threshold of five actin filaments per square micrometer, the filaments began to move collectively in larger clusters – with an astonishing resemblance to flocks of birds or shoals of fish. "We can set and observe all relevant parameters in this system," says Schaller. "Using this approach, we can experimentally test the propositions of different theories on self-organization – and that on the tiny scale of 'nanomachines'."
Structures like waves, swirls or ordered clusters seem to appear spontaneously during the experiments. Some of these structures grow to a size of almost one millimeter and remain stable for up to 45 minutes before they dissolve again. Based on these observations, Frey, together with his PhD student Christoph Weber, developed theoretical models to describe the experimental results. With the combination of extensible theoretical models and a precisely controllable experiment, the physicists have set out to tackle more difficult problems and unravel their underlying principles.
"Self-organization phenomena surround us on all levels of our lives," says Bausch. "It begins with traffic jams and the movement of human crowds or the swarming of animals and extends all the way to the organization of biological processes. Important examples are the formation of the cellular cytoskeleton or protein transport facilitated by motor proteins in cells." The underlying principles, though – whether in economic, biological or physical systems – are still among the great open questions of theoretical physics. "For our understanding of nature, as well, there are many fundamental principles yet to be discovered," emphasizes Frey. "However, forecasts should not be applied to the dynamics of human crowds over-hastily – thus far, their complexity is much too great to be captured in simple theoretical models."
The research is funded by the Deutsche Forschungsgemeinschaft (DFG, SFB 863), the cluster of excellence Nanosystems Initiative Munich (NIM), the TUM Institute for Advanced Study at the Technische Universitaet Muenchen, and the Elite Network of Bavaria (CompInt, NanoBioTechnology).
Volker Schaller, Christoph Weber, Christine Semmrich, Erwin Frey und Andreas R. Bausch: Polar patterns of driven filaments. Nature, 2 September 2010, pp 73-77 - doi:10.1038/nature09312Picture and video credits:
Andreas Battenberg | EurekAlert!
Smooth propagation of spin waves using gold
26.06.2017 | Toyohashi University of Technology
A 100-year-old physics problem has been solved at EPFL
23.06.2017 | Ecole Polytechnique Fédérale de Lausanne
An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.
Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...
Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.
Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...
Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.
As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...
Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.
With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...
Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine
Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...
19.06.2017 | Event News
13.06.2017 | Event News
13.06.2017 | Event News
26.06.2017 | Life Sciences
26.06.2017 | Physics and Astronomy
26.06.2017 | Information Technology