Monthly Archives: February 2022

Dissertation: Lattice Boltzmann methods for microswimmers in complex environments

My dissertation has been published by the university:

Lattice Boltzmann methods for microswimmers in complex environments
Michael Kuron
PhD thesis, Universität Stuttgart
DOI: 10.18419/opus-11926

Printed copies are available at the university library and at the national library in Frankfurt and Leipzig. I also have a few spare ones, so if you think you really need one, let me know. The SHA1 hash of the PDF file I submitted to the library is 45f8b26dc10c04a5221d79fa3a2c42478a2b89b6, which matches the file available online as of today.

Abstract

This dissertation introduces, validates, and applies various models for the study of microswimmers, predominantly focusing on the development of lattice algorithms. The models are applicable to biological swimmers like bacteria, but also to artificial ones propelled via chemical reactions. The unifying theme is a complex fluidic environment, ranging from Newtonian single-component fluids, to electrolyte solutions, to viscoelastic media flowing through arbitrary geometries. A particular focus is placed on resolving each swimmer’s surface since the propulsion, or phoresis, originates from a small layer of fluid around it. Resolving the propulsion mechanism is necessary to accurately study hydrodynamic interactions with obstacles and other swimmers. It is also a prerequisite for the study of taxis, that is, alignment with an external field such as a nutrient gradient. Similarly, phoretic interactions can be investigated, like when a swimmer senses and avoids the trail where another swimmer has already depleted the fuel.

Update January 2024

Here is an updated PDF with all the preprint citations replaced with the published versions. This should make it easier to find all references via the DOI system.

Dell WD19TBS review

Four years ago, I reviewed the Dell WD15 USB-C docking station for use with a MacBook Pro. It worked reasonably well, but not all of the USB ports worked and high resolutions didn’t work over DisplayPort. Also, over time it has become a bit unstable for me, requiring the USB-C cable to occasionally be unplugged and replugged, or even requiring the dock to be power-cycled. The latter is also necessary when switching between a Dell and a MacBook, which can be a bit annoying. I also noticed that the WD15’s firmware cannot be upgraded unless you use a Dell laptop from around 2017 — newer ones will try and fail, while non-Dell laptops won’t even run the updater.

Dell’s current docking solution is the WD19. It is available in three variants: the WD19S connects via USB-C, the WD19TBS connects via Thunderbolt or USB-C, and the WD19DCS connects to certain high-end Dell laptops via two USB-C cables. Conveniently, the WD19TBS is certified for use with Macs too. The WD19/WD19TB/WD19DC (without the “S” at the end) are identical, but do not have an audio output.

This review is going to be really short. The WD19 eliminates all the WD15’s flaws that I complained about. Dell provides good documentation that tells you what works via USB-C and what requires Thunderbolt, which resolutions you can get on how many video outputs, etc., so I am not going to repeat that here (the executive summary is that there are no surprises here).

The WD19 has one downside though: it has a fan. Mine turns on and spins up to relatively loud levels every couple hours for a few minutes, which I find quite annoying. Another WD19 I have used never spins up. I don’t really think the fan is even needed for regular usage unless you have a laptop that draws more than 80W of power. So if you’re feeling adventurous and want to void the warranty, open up the WD19 and disconnect the fan. Dell laptops will occasionally display a BIOS warning about a failed fan, but other than that it works fine and completely silent.

Firmware updates no longer require Windows or even a Dell laptop. You can apply them via fwupd on Linux too.