ComPhys @comphys@qoto.org

Half way through the magnetostatics post I promised a year ago. I've finished an introductory coax example and now I'm writing the intro theory for a cos(phi) magnet. I think it'll be ready in a week :) After that I see two options to progress: eigenmodes or time dependence.

If I go with the eigenmode, I can write an example for how the finite difference method works and talk about linear algebra methods. I haven't tried any time dependent problems in FEniCS yet, so that'll be a whole new area to learn.

Surprisingly, the blog is apparently getting a citation of some kind.

Is there a good way to identify low Q resonances over long cables with a VNA reflection measurement? The long cables can mean the phase doesn't cross zero, the low phase gradient of the resonant termination means there isn't a jump in phase and the BW of the amplitude makes it hard to identify a peak/ trough...

"Everybody believes in the law of errors [the final result of many small, independent, random errors is normally distributed], the experimenters because they think it is a mathematical theorem, the mathematicians because they think it is an experimental fact" - Poincare, Calcul des Probabilites

I've just compared my formula for the characteristic impedance of an eccentric coax with results from a series of finite element simulations with FEniCS. They look excellent. I've added them to my post https://comphysblog.wordpress.com/2020/06/28/conformal-mapping-1/

@revistazunai As somebody that has never touched a philosophy book, where would you suggest that I start?

New post - Conformal Mapping Example, the Eccentric Coax

https://comphysblog.wordpress.com/2020/06/28/conformal-mapping-1/

This post is different from all my others. Rather than stepping through solving a problem with FEniCS, I step through solving a problem with the mathematical method of conformal mapping.

I introduce the method by solving the far easier problem of a pair of slanted parallel plates with a potential difference.

After that I get to the main point of the post: finding the characteristic impedance of a coaxial cable where the centre conductor isn't in the middle; where the cylinders are eccentric. Although the process has quite a lot of algebra, the final solution is simple and very usable.

I've really enjoyed doing this example, because I think it's a great demonstration of using analytical methods to solve a problem with strange boundaries. These days we'd probably just solve this kind of thing numerically, but the analytical solution gives insight and a formula that can be used over-and-over.

I'll add a numerical comparison in the coming days.

#RF #HAM #physics #maths #mathematics

@coldwave It's a bit old now so, some things might have changed, but this tutorial is excellent https://python-packaging.readthedocs.io/en/latest/

@Lwasserman I used to do voluntary tech support for Firefox on the forums. 95% of the time this happened it was because of extensions or weird setting mods rather than Firefox itself. I recommend you run the FF profile manager, make a clean profile, don't install any extensions and see whether the problem persists.

I haven't written a blog post for a long time. Although I'm aware that I never posted the magnetostatic solutions, my next post is going to be a bit different to all my previous ones. I'm going to introduce conformal mapping with a very simple example, then demonstrate finding the characteristic impedance of a coaxial cable where the inner and outer conductors aren't concentric. I've done the maths and written about half of it :)

What is everybody's view of the FCC project?

The opinions on YC seemed pretty critical in general. While I see some validity to the point that it's a shot in the dark, I also think that shots in the dark might be the best way to go. We know there are problems with our current model of the universe and aren't sure how to resolve them, maybe it'll give us some direction. The final price tag €21B sounds like a lot, but that is spread over a number of years and across multiple governments. Finally, if we don't fund a large project now, then 50 years into the future when we need a big collider for something specific we won't have the skills or expertise to build one. To me, that seems like reason enough to build something.

@freemo No flex, I'm not really into calligraphy although I certainly wish I had beautiful handwriting. With that said, I love my pen. It's so smooth, I don't have to apply even a touch of pressure. Works well for maths, which in was originally concerned about. Being able to try different inks has made writing a bit more interesting & I've enjoyed it. I've also got a few J. Herbin rollerball pens. They take standard cartridges and are cheap enough to have a few for different colours.

@freemo I use a Faber Castell e-motion fountain pen and my wife has a pen from Beaufort which is also very nice. Currently using pelikan brilliant black ink, which I'm very happy with. Originally I bought it so that I could stop throwing away plastic bics every month, but now I love it and would never go back.

@design_RG Casio, ZR1000, the docs just say "USB AV"... I've found some eBay items which say the same thing as you .

@design_RG afraid not, I've had the whole cable drawer out!

@freemo apparently it is a non-standard port by Casio. But it seems you can get them https://www.ebay.co.uk/itm/CASIO-EXILIM-EX-ZR1000-DIGITAL-CAMERA-USB-CABLE-BATTERY-CHARGER-/254591417490

@marwe Ah, it's my wife's and I've never bought a camera so i had no idea the ports wouldn't be standard :') Thanks for the info.

Does anybody know the name of this type of usb connector? (Not the HDMI)

@freemo @lupyuen I'm in a funny situation. In my work we use classical EM to make detectors/pickups and kicker magnets etc, but these can be at very low frequencies. For example a couple of years ago, I found an unwanted resonance on a kicker magnet at 6MHz. The PCB I mentioned to you was for phase matching signals from a bunched particle beam at 200 MHz. At very low frequencies (~100 kHz) fields leak through conductors, which can also a potential concern for me. It feels a world away from typical modern RF/electrical engineering, but clearly there is overlap. I'm always interested to read your EE posts :)

@freemo thanks, I'll check it out. Ultimately I'm going to put this into a grounded box with sma connectors on the front, so I'm inevitably going to have them connected somewhere.