ComPhys @comphys@qoto.org

New post: electrostatic problems with charge densities in FEniCS. A domain is specified within the mesh to have a uniform charge density, the fields both inside and outside the region are then solved. The finite element solution is then compared with the analytical result. All materials available as a repo. https://wp.me/p8Kvfs-cX #physics #electromagnetism #python #opensource #rf

@freemo get yourself a red pitaya and a directional coupler off eBay and you'll have everything to make a one-port VNA for €300.

After a couple of months without a new post I've started writing about simulating charge distributions, rather than just boundary value problems. I'll explain how #FEniCS can calculate the electrostatic fields of arbitrarily shaped charge densities, which are specified with mesh subdomains. These will have hard edges for now but I want to look into having more general charge distributions.

I've also run 3D simulations for calculating capacitances between arbitrarily shaped conductors and 2D linear dielectrics. I need to do some more testing & comparison with other FEA tools/ analytical methods before I publish any posts. Seems to be going well though!

@arkedos @mycroft@mastodon.social My first gen moto g is 6 years old and shows no imminent signs of stopping. LineageOS has kept it usable from a software perspective :)

@arteteco I think it was episode 7.

@arteteco Blue Planet II, in general its an incredible nature documentary, but one of the episodes focused on plastic pollution if that's what you're looking for.

I was reading the help files of a well-known commercial microwave FEA package and it suggested calculating characteristic impedance from the power and voltage rather than finding the current directly.

This way doesn't require surface normals or line integrals which my previous methods did, so it's probably better (easier to do anyway). I've added this into my TEM mode post - https://comphysblog.wordpress.com/2018/09/06/tem-mode-analysis-with-fenics/

Just made a bow tie, surprisingly easy. Actually putting it on is another matter.

@gka @pkok @peanutbutter144 keepass doesn't come with a sync feature built in, you'd have to use something like syncthing. As for the different versions (keepassxc etc) they are supposed to all work in the same way; you just choose the one you like the most. On Linux I find keepassxc to have the nicest ui, and on windows I use keepass. To my knowledge you should be able to switch between them without a problem.

@gka @pkok @peanutbutter144 online password managers are convenient but some people prefer to keep their passwords local. Some would also prefer an open source password manager. I think its also worth mentioning that Lastpass recently had a bug where a dodgy regular expression would allow somebody to access any password in your lastpass account: https://labs.detectify.com/2016/07/27/how-i-made-lastpass-give-me-all-your-passwords/

@aparrish always happy to try and help with maths :)

@4of92000 the battery of my laptop has a single connector which is pretty easy to connect/ disconnect and it's easy to get to. I'd recommend having a look for a disassembly video to check how accessible the battery is and going from there.

Small update to the TEM mode analysis with #FEniCS example.

I've added in a calculation for the mutual capacitance and self-inductance per unit length of the transmission line.

https://comphysblog.wordpress.com/2018/09/06/tem-mode-analysis-with-fenics/

#opensource #physics #python #ham

@QuantumHemp I don't personally use it, but I recently installed Ubuntu on somebody's laptop and was pretty impressed with gnome. The thing that I liked the most was how easy it was to customise the UI via little toggle switches on a website. Within a few minutes we'd installed a traditional start menu & taskbar and a weather indicator.

@freemo oh yeah =] nice, could actually convince me to use emojis.

The full code from the example, results etc are all on gitlab too https://gitlab.com/comphysblog/coax_tem the notebook has all of the steps and plots etc.

I've just finished my new post: TEM mode analysis with #FEniCS an #opensource finite element differential equation solver. https://comphysblog.wordpress.com/2018/09/06/tem-mode-analysis-with-fenics/

In this post I calculate the electric and magnetic fields on a coaxial cable, characteristic impedance of the line, the Poynting vector, the conductor and dielectric loss, an estimated loss coefficient, Q-factor and s-parameter for a given length of cable.

Coax has been a useful example for comparisons with analytical results but the methods are very general. TEM modes of systems with different geometries can also be analysed with the exact same techniques!

Very happy to hear any comments, corrections or suggestions.

#physics #ham #python

@Miredly@mastodon.technology @rey some of these concepts might be useful for you, for example in answering questions of whether gold coated cables are actually worth it etc.

@freemo I think it would be better if there was some kind of reference to mastodon generally as well as the unique personality of the instance? Perhaps a mastodon with a mortarboard, or a lightbulb over its head? Anybody that recognised the mastodon logo would be able to guess what the instance was about.