Building better diffusion models for active systems

November 19, 2020

In normal circumstances, particles will follow well-established random motions as they diffuse through liquids and gases. Yet in some types of system, this behaviour can be disrupted - meaning the diffusion motions of particles are no longer influenced by the outcomes of chains of previous events. Through research published in EPJ E, Bernhard Mitterwallner, a Ph.D. student in the team of Roland Netz at the Free University of Berlin, Germany, has developed new theories detailing how these unusual dynamics can be reproduced in generalised mathematical models.

The team's approach could enable researchers to learn more about behaviours including the transport of biological cells, and the motions of 'active' materials - whose particles harvest energy in their surrounding environments to propel themselves forwards. Typically, these diffusion characteristics only appear briefly as systems transition between stable states - but under the right conditions, they can persist over far longer timescales. Researchers can study this effect by introducing a 'memory term' into their calculations, which can account for the influences of past events on different timescales. Several studies have now used this principle to explore how this 'transient persistent motion' can be captured in models of viscoelastic media - which can resist deformation when stress is applied.

The authors took a more general approach in their study; basing their calculations around an equation of motion which offered a useful framework for describing unconventional diffusion behaviours. When adding a memory term into the equation, their models give rise to transient persistent motion in a range of different systems, which had not been explored in previous studies. The team's results could now enable researchers to accurately model diffusion behaviours in a broader range of situations - and could be particularly useful for studies of advanced materials which respond to their surrounding environments.
-end-
Reference
B. G. Mitterwallner, L. Lavacchi, R. R. Netz (2020), Negative friction memory induces persistent motion, Eur. Phys. J. E 43:67.
https://doi.org/10.1140/epje/i2020-11992-5

Springer

Related Particles Articles from Brightsurf:

Comparing face coverings in controlling expired particles
Laboratory tests of surgical and N95 masks by researchers at UC Davis show that they do cut down the amount of aerosolized particles emitted during breathing, talking and coughing.

Big answers from tiny particles
A team of physicists led by Kanazawa University demonstrate a theoretical mechanism that would explain the tiny value for the mass of neutrinos and point out that key operators of the mechanism can be probed by current and future experiments.

How small particles could reshape Bennu and other asteroids
NASA's OSIRIS-REx spacecraft observed tiny bits of material jumping off the surface of the asteroid Bennu.

Probing the properties of magnetic quasi-particles
Researchers have for the first time measured a fundamental property of magnets called magnon polarisation -- and in the process, are making progress towards building low-energy devices.

TU Darmstadt: Pause button for light particles
Researchers at TU Darmstadt halt individual photons and can release them at the push of a button.

Chamber measurement standards established for fine particles
What effects do global warming and the formation of fine particles have on each other?

Distortion isn't a drag on fluid-straddling particles
New research published by EPJ E shows that the drag force experienced by fluid-straddling particles is less affected by interface distortion than previously believed.

Tiny 'bridges' help particles stick together
Understanding how particles bind together has implications for everything from the likelihood a riverbank will erode to the mechanism by which a drug works in the body.

Micromotors push around single cells and particles
A new type of micromotor -- powered by ultrasound and steered by magnets -- can move around individual cells and microscopic particles in crowded environments without damaging them.

Tiny particles lead to brighter clouds in the tropics
When clouds loft tropical air masses higher in the atmosphere, that air can carry up gases that form into tiny particles, starting a process that may end up brightening lower-level clouds, according to a CIRES-led study published today in Nature.

Read More: Particles News and Particles Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.