Countless tiny hairs (cilia) are found on the outer wall of some cells, for example in our lungs or in our brain. When these micrometre-sized hairs coordinate their movement and produce wave-like movements together, they can cause currents on a microscale and thus pump fluid from one place to another. Until now, this could only be studied in large computer simulations. However, more than a few thousand hairs cannot be simulated in this way. Now a continuum theory of micro-hairs has been developed — a powerful and completely new approach.
They are only very simple structures, but without them we could not survive: Countless tiny hairs (cilia) are found on the outer wall of some cells, for example in our lungs or in our brain. When these micrometre-sized hairs coordinate their movement and produce wave-like movements together, they can cause currents on a microscale and thus pump fluid from one place to another. Paramecia — unicellular organisms with numerous cilia — also use such effects to move around.
How the synchronisation of such micro-hairs comes about and what effects it has — such questions have so far only been studied in large computer simulations. However, more than a few thousand hairs cannot be simulated in this way. Sebastian Fürthauer from TU Wien has now taken a completely different approach: Together with research teams from the USA, he has developed a continuum theory of micro-hairs. This makes it possible to investigate questions that were previously completely out of reach. The theory has now been published in the scientific journal PNAS.
Micro-world and macro-world
“The complicated connection between the micro-world and the macro-world plays an important role in many areas of physics,” says Sebastian Fürthauer. Every air flow, every flow in a liquid can be understood as the movement of small particles — of atoms and molecules. It is possible to study the forces that act between the individual particles, how they collide and move together.
But it is also possible to disregard this view on the level of individual particles completely and look at things differently — using concepts like pressure, density and mean flow velocity. “In fluid mechanics, that’s exactly what you do,” says Sebastian Fürthauer. “You don’t care about the fact that every flow consists of individual particles, instead you look for mathematical equations that use terms like pressure or density to describe the entire flow in a continuous way.”
Collective waves instead of individual hairs
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