# gst: how to create a helix from a straight rod, “twist” or “bend” approaches.

<< There are two independent ways of creating a helix from a straight rod: curl the rod into a circle and then twist the rod all along its length to convert the ring into a helix (“twist” method), or deform the rod into a sine wave and then bend it with a sinusoidal distortion that curls at right angles to the first sine wave (“bend” method). Both procedures produce the same shape, but they generate different internal stresses within the rod, and their implementations require different amounts of energy. >>️

AA << say that their experiments could serve as a model for many physical systems that undergo handedness transitions, including the tendrils of plants, the flagella of microorganisms, and the strands of DNA molecules.  >>

️

David Ehrenstein. Two Experimental Observations of Helix Reversals. Physics 16, s158. Oct 24, 2023.  

https://link.aps.org/doi/10.1103/Physics.16.s158

Paul M. Ryan, Joshua W. Shaevitz,  Charles W. Wolgemuth. Bend or Twist? What Plectonemes Reveal about the Mysterious Motility of Spiroplasma. Phys. Rev. Lett. 131, 178401. Oct 24, 2023. 

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.131.178401

Emilien Dilly, Sebastien Neukirch, Julien Derr, Drazen Zanchi. Traveling Perversion as Constant Torque Actuator. Phys. Rev. Lett. 131, 177201. Oct 24, 2023. 

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.131.177201

Also: elastic, swim, in https://www.inkgmr.net/kwrds.html

Keywords: gst, elastic, elastic deformation, swimming

# gst: behavior of microswimmers in a vortex with translational and rotational noise

AA << propose a theoretical model to investigate the dynamics of elongated microswimmers in elementary vortices, namely active particles in two- and three-dimensional rotlets. A deterministic model first reveals the existence of bounded orbits near the centre of the vortex and unbounded orbits elsewhere. (AA) further discover a conserved quantity of motion that allows (..) to map the phase space according to the type of the orbit (bounded vs unbounded). (They) next introduce translational and rotational noise into the system. Using a Fokker--Planck formalism, (AA) quantify the quality of trapping near the centre of the vortex by examining the probability of escape and the mean time of escape from the region of deterministically bounded orbits. (AA) finally show how to use these findings to formulate a prediction for the radius of the depletion zone, which compares favourably with the experiments of Sokolov and Aranson (2016). >>

Ivan Tanasijevic, Eric Lauga. Microswimmers in vortices: Dynamics and trapping. arXiv: 2211.05866v1 [physics.bio-ph].  Nov 10, 2022. 

https://arxiv.org/abs/2211.05866

Also

'microswimmers' in FonT 

https://flashontrack.blogspot.com/search?q=microswimmers

Keywords: gst, behav, translation,  rotation, trapping, noise, swimmer, swimming,  microswimmers, fluid dynamics, vortex, vortices, vortexes, vorticity

# gst: self-buckling and self-writhing of semi-flexible Entities (among P. mirabilis)

<< Multi-flagellated microorganisms can buckle and writhe under their own activity as they swim through a viscous fluid. New equilibrium configurations and steady-state dynamics then emerge which depend on the organism's mechanical properties and on the oriented distribution of flagella along its surface. Modeling the cell body as a semi-flexible Kirchhoff rod and coupling the mechanics to a dynamically evolving flagellar orientation field, (AA) derive the Euler-Poincaré equations governing dynamics of the system, and rationalize experimental observations of buckling and writhing of elongated swarmer P. mirabilis cells. >>

<< A sequence of bifurcations is identified as the body is made more compliant, due to both buckling and torsional instabilities. The results suggest that swarmer cells invest no more resources in maintaining membrane integrity than is necessary to prevent self-buckling. >>

️

Wilson Lough, Douglas B. Weibel, et al. Self-buckling and self-writhing of semi-flexible microorganisms. arXiv: 2211.04381v1 [cond-mat.soft]. Nov 8, 2022. 

https://arxiv.org/abs/2211.04381

Also 

keyword 'swimming' in FonT

https://flashontrack.blogspot.com/search?q=swimming

Keywords: gst, motility, swarm, swarming, swarmer, swim, swimming, swimmer, buckling, writhing.