Nav: Home

Surprising results found in the swimming mechanism of microorganism-related model

January 24, 2017

WASHINGTON, D.C., Tuesday, January 24, 2017 -- For years, B. Ubbo Felderhof, a professor at the Institute for Theoretical Physics at Germany's RWTH Aachen University, has explored the mechanisms that fish and microorganisms rely on to propel themselves. Flying birds and insects face similar challenges propelling themselves, but without the luxury of buoyancy these creatures also contend with overcoming gravity to stay aloft.

Over 20 years ago, Felderhof, who was working with Bob Jones, now an emeritus reader in theoretical physics at Queen Mary University of London, was studying the theory behind the "swimming" of microorganisms, described by the friction interactions between the microbodies and their surrounding fluid. Because of the small size of many such microorganisms like bacteria, such inertial forces could be neglected in the description. For slightly larger organisms, however, this was not the case.

Felderhof has since created mechanical models to more fully develop the theory, consisting of linear chains of spheres connected by springs and immersed in fluid. Here he took into account that the interaction with the fluid involves both friction and inertia, since the effect of mass can't be neglected for these larger structures.

As Felderhof now reports in Physics of Fluids, from AIP Publishing, he's just pushed this work even further by addressing what happens in the case of adding one sphere to the chain that's much larger than the other spheres.

Felderhof studies structures of spheres because the effect of friction and fluid inertia on the motion of a single sphere is fairly well known. With multiple spheres, however, the picture is more complex and has to take into account positions and orientations. "For several spheres, there is the complication of hydrodynamic interactions due to interference of flow patterns," he said. "These hydrodynamic interactions depend on the relative positions of sphere centers."

If the relative positions of the spheres are varied periodically by applying an oscillating force on each of them, with the constraint that the total net force vanishes at any time, the system still sees movement. "In spite of the latter constraint, the set of spheres in general performs a net motion, which is called 'swimming,'" Felderhof said.

A mathematical formulation allows finding the optimum stroke -- the combined applied forces -- that yields the maximum average speed for a given power.

For this new work, Felderhof explored a linear chain of spheres with one big, passive sphere, meaning the applied force on that sphere vanishes. "The big sphere is called the 'cargo,'" he said. "Think of it as a large body with small moving appendages, or of a boat being pushed or pulled by a small propeller."

His work provides an important conceptual clarification of flow theory. "In popular explanations of swimming and flying, we're told that speed is achieved by a balance of thrust and drag," Felderhof said. "My model calculations, however, show that the mean thrust and drag both vanish when averaged over a period. The effect is more subtle. Interactions of body and fluid are such that periodic shape deformations of the body lead to a net motion relative to the fluid, even though the net thrust vanishes."

Much of the previous work on swimming has concentrated on either the friction-dominated limit, valid for microorganisms, or on the inertia-dominated limit, valid for large animals. "In my model, both friction and inertia play a role so that swimming can be studied in the intermediate regime, where both effects are important," he said.

In terms of applications, the swimming linear chain model is particularly useful because of its slender structure and ability to travel through narrow tubes, such human veins.

"Biologists have already considered the possibility of drug transport via such means," Felderhof said. "And now we've developed a mathematical model that allows optimization of deformations of the body, which leads to maximum speed for given power. This method isn't limited to linear chains, so we can envision applying it to more complicated structures in future work."

First, Felderhof points out that it is important to validate the model by comparison with computer simulations and subsequent experiments, which is beyond his focus, so he hopes other researchers will pursue it.

"Friction and inertia aren't the only effects that can lead to swimming," Felderhof said. "Flapping leads to vortex shedding and possibly a 'street' of vortices. This effect is absent from my model, but may be essential for the swimming of some fish and for flying birds. It will be of value to establish the relative importance of friction, inertia, and vortex shedding, but at present I don't see how this can be accomplished in analytical theory. Again, computer simulation would be helpful."
-end-
The article, "Swimming of a linear chain with a cargo in an incompressible viscous fluid with inertia," is authored by B.U. Felderhof. The article will appear in Physics of Fluids Jan. 24, 2017 (DOI: 10.1063/1.4973711). After that date, it can be accessed at: http://aip.scitation.org/doi/full/10.1063/1.4973711.

ABOUT THE JOURNAL

Physics of Fluids is devoted to the publication of original theoretical, computational, and experimental contributions to the dynamics of gases, liquids, and complex or multiphase fluids. See http://pof.aip.org.

American Institute of Physics

Related Microorganisms Articles:

Lost in translation: Organic matter cuts plant-microbe links
Soil scientists from Cornell and Rice Universities have dug around and found that although adding carbon organic matter to agricultural fields is usually advantageous, it may muddle the beneficial underground communication between legume plants and microorganisms.
Montana State researcher harnesses microorganisms to make living building materials
Chelsea Heveran, assistant professor in the Department of Mechanical and Industrial Engineering, is the lead author of a new study showing that certain bacteria can be used to create an easily recyclable, concrete-like substance.
Crop residues are a potential source of beneficial microorganisms and biocontrol agents
While studies of the microbiomes (which comprises all the microorganisms, mainly bacteria and fungi) of the phyllosphere and the rhizosphere of plants are important, scientists at INRA believe more attention should be given to the microbiomes of crop residues.
Soil scientist researches nature versus nurture in microorganisms
Ember Morrissey, assistant professor of environmental microbiology at West Virginia University, uncovered that nature significantly affects how the tiny organisms under our feet respond to their current surroundings.
Microorganisms reduce methane release from the ocean
Bacteria in the Pacific Ocean remove large amounts of the greenhouse gas methane.
Microorganisms build the best fuel efficient hydrogen cells
With billions of years of practice, nature has created the most energy efficient machines.
How microorganisms protect themselves against free radicals
There are numerous different scenarios in which microorganisms are exposed to highly reactive molecules known as free radicals.
Scientists' warning to humanity: Microbiology and climate change
When it comes to climate change, ignoring the role of microorganisms could have dire consequences, according to a new statement issued by an international team of microbiologists.
Climate change could affect symbiotic relationships between microorganisms and trees
An international research consortium mapped the global distribution of tree-root symbioses with fungi and bacteria that are vital to forest ecosystems.
Microorganisms on microplastics
A recent study shows that that the potentially toxin-producing plankton species Pfiesteria piscicida prefers to colonize plastic particles, where they are found in 50 times higher densities than in the surrounding water of the Baltic Sea and densities about two to three times higher than on comparable wood particles floating in the water.
More Microorganisms News and Microorganisms Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: Reinvention
Change is hard, but it's also an opportunity to discover and reimagine what you thought you knew. From our economy, to music, to even ourselves–this hour TED speakers explore the power of reinvention. Guests include OK Go lead singer Damian Kulash Jr., former college gymnastics coach Valorie Kondos Field, Stockton Mayor Michael Tubbs, and entrepreneur Nick Hanauer.
Now Playing: Science for the People

#562 Superbug to Bedside
By now we're all good and scared about antibiotic resistance, one of the many things coming to get us all. But there's good news, sort of. News antibiotics are coming out! How do they get tested? What does that kind of a trial look like and how does it happen? Host Bethany Brookeshire talks with Matt McCarthy, author of "Superbugs: The Race to Stop an Epidemic", about the ins and outs of testing a new antibiotic in the hospital.
Now Playing: Radiolab

Dispatch 6: Strange Times
Covid has disrupted the most basic routines of our days and nights. But in the middle of a conversation about how to fight the virus, we find a place impervious to the stalled plans and frenetic demands of the outside world. It's a very different kind of front line, where urgent work means moving slow, and time is marked out in tiny pre-planned steps. Then, on a walk through the woods, we consider how the tempo of our lives affects our minds and discover how the beats of biology shape our bodies. This episode was produced with help from Molly Webster and Tracie Hunte. Support Radiolab today at Radiolab.org/donate.