Journal ArticleDOI
Analysis of the Swimming of Microscopic Organisms
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TLDR
In this article, it was shown that if the waves down neighbouring tails are in phase, very much less energy is dissipated in the fluid between them than when the waves are in opposite phase.Abstract:
Large objects which propel themselves in air or water make use of inertia in the surrounding fluid. The propulsive organ pushes the fluid backwards, while the resistance of the body gives the fluid a forward momentum. The forward and backward momenta exactly balance, but the propulsive organ and the resistance can be thought about as acting separately. This conception cannot be transferred to problems of propulsion in microscopic bodies for which the stresses due to viscosity may be many thousands of times as great as those due to inertia. No case of self-propulsion in a viscous fluid due to purely viscous forces seems to have been discussed. The motion of a fluid near a sheet down which waves of lateral displacement are propagated is described. It is found that the sheet moves forwards at a rate 2π 2 b 2 /λ 2 times the velocity of propagation of the waves. Here b is the amplitude and λ the wave-length. This analysis seems to explain how a propulsive tail can move a body through a viscous fluid without relying on reaction due to inertia. The energy dissipation and stress in the tail are also calculated. The work is extended to explore the reaction between the tails of two neighbouring small organisms with propulsive tails. It is found that if the waves down neighbouring tails are in phase very much less energy is dissipated in the fluid between them than when the waves are in opposite phase. It is also found that when the phase of the wave in one tail lags behind that in the other there is a strong reaction, due to the viscous stress in the fluid between them, which tends to force the two wave trains into phase. It is in fact observed that the tails of spermatozoa wave in unison when they are close to one another and pointing the same way.read more
Citations
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Journal ArticleDOI
Bacteria Swim by Rotating their Flagellar Filaments
TL;DR: It is shown here that existing evidence favours a model in which each filament rotates, which is commonly believed that each filament propagates a helical wave3.
Journal ArticleDOI
A spherical envelope approach to ciliary propulsion
TL;DR: In this paper, an attempt has been made to model the dynamics of ciliary propulsion through the concept of an "envelope" covering the ends of the numerous cilia of the microscopic organism.
Journal ArticleDOI
Structured light enables biomimetic swimming and versatile locomotion of photoresponsive soft microrobots
Stefano Palagi,Andrew G. Mark,Shang Yik Reigh,Kai Melde,Tian Qiu,Tian Qiu,Hao Zeng,Camilla Parmeggiani,Daniele Martella,Alberto Sanchez-Castillo,Nadia Kapernaum,Frank Giesselmann,Diederik S. Wiersma,Eric Lauga,Peer Fischer,Peer Fischer +15 more
TL;DR: Soft microrobots consisting of photoactive liquid-crystal elastomers can be driven by structured monochromatic light to perform sophisticated biomimetic motions and multiple gaits, mimicking either symplectic or antiplectic metachrony of ciliate protozoa are confirmed.
Journal ArticleDOI
Simple swimmer at low Reynolds number: Three linked spheres
Ali Najafi,Ramin Golestanian +1 more
TL;DR: A very simple one-dimensional swimmer consisting of three spheres that are linked by rigid rods whose lengths can change between two values can be used in constructing molecular-sized machines.
Journal ArticleDOI
A Self-Organized Vortex Array of Hydrodynamically Entrained Sperm Cells
TL;DR: A spatiotemporal pattern mediated by hydrodynamic interactions at planar surfaces is reported, showing that large-scale coordination of cells can be regulated hydrodynamically, and chemical signals are not required.
References
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Journal ArticleDOI
Sea-urchin spermatozoa.
TL;DR: The head of the sea‐urchin spermatozoon is pear‐shaped and axially symmetrical, and the tail, which terminates in an axial fibre, probably contains spiral or coiled structures, as in mammalian spermatozoa.