ComPhys @comphys@qoto.org

What do you think of this article on the education of physics?

https://physicsworld.com/a/building-a-physics-degree-for-the-future-five-key-questions-we-need-to-answer/

Something which often concerns me about opinion pieces like this, is that employability, which was until recently a side effect of having a physics degree, seems to have become the primary goal. The first example in the article says
"[...] during which they apply their learning to solve research or technical problems based on global challenges, possibly posed by businesses." However notably, physics challenges aren't mentioned.

Encouraging children to learn from online resources, rather than textbooks is also (currently) a mistake; as they are in my experience very often inferior. Whilst a mix of resources is probably the best, I have encountered students who genuinely believed that watching a 3blue1brown video was in some way equivalent to doing exercises themselves. Students starting university need to be told what the best resources are, we shouldn't be simply accept their potentially inferior preferences. Find me a single online resource better suited to teaching Fourier Transforms than Robert Bracewell's textbook, and I'll reevaluate my opinions.

I actually agree that exam grades can be misleading and maybe there is a better way to assess. Everybody I know who got good grades, myself included, crammed before exams, and I'm not convinced if that really represents a mastery of the subject; although it does demonstrate work ethic, dedication, ability to learn etc.

The suggestion to reduce time in the lab is just downright wrong. We need to be improving our students practical abilities by expanding lab work and making it far more integral to the learning process and maybe even the assessment process. I've seen high-grade, covid generation students confused why their circuits didn't work with only one end of a battery connected. In my opinion, that was brought about by a lack of opportunity to turn their theoretical knowledge into real world knowledge. Students like that are leaving university without the skills to contribute to making technology for physics or addressing global challenges.

In my opinion, physics degrees should adapt to meet physics needs, and we should accept employability for whatever it is after that. If physics graduates become less employable then so be it; it's natural that desirable skills change with time (although physics skills are definitely important at the moment). Fundamentally, physics degrees should never be allowed to become generic workplace training courses.

@freemo I don't think it's controversial to say that you've appealed at an extreme by suggesting workers might expect infinite money. If anything close to that were true then companies would regularly fail after negotiating with unions. Anecdotally, that doesn't seem to happen very often, and this article in time[1] quotes a study[2] of nearly 30,000 US companies that “**Unions likely do not affect businesses by making them more susceptible to failure or re-location, despite the fears of many employers and employees.**” In reality, it seems unions negotiate with the knowledge that demanding too much would not be in anybody's interest.

I think where we will differ is your suggestion that a workers pay is directly correlated to their value, or perhaps what that really means. If a workers value is how much money they generate and this were true, then we would see pay rise with profits. I suppose that vested interests on both sides will make finding reliable evidence difficult, but this paper[3] suggests that large companies with high profits do not necessarily pay workers more. This also seems to agree with my own experiences; especially for low-pay jobs (although there will always be exceptions.) It could then be argued, that some employers are paying their employees less than they are really worth.

I found this point in that time article very interesting: "The only time that the bottom tenth of the population and the top tenth of the population have come closer together has been during those years, when unions were operating in the largest corporations in this country,” If unionisation reduces income inequality on average, then it seems reasonable to conclude that it will also drive improvement in the metrics I mentioned earlier. Certainly, the effects of extreme income inequality are well documented [4].

[1] https://time.com/6168898/why-companies-fight-unions/
[2] https://www.princeton.edu/~davidlee/wp/unionbf.pdf
[3] http://dx.doi.org/10.5465/AMBPP.2008.33660403
[4] https://www.imf.org/en/Publications/Staff-Discussion-Notes/Issues/2016/12/31/Causes-and-Consequences-of-Income-Inequality-A-Global-Perspective-42986

@freemo I think you can look at this from many angles. In my opinion, our institutions should be regulated in a way that optimises for things like improved living standards for the average citizen, average life expectancy, average level of happiness etc.

When companies engage in price fixing, the result will almost invariably be higher prices for the majority of society. This is bad, because it will limit access to goods for the average person.

When individuals collectively agree not to work for less than some amount (you said "price fixing", which I suppose is accurate), the result will hopefully be higher pay for the individuals. This is good, because it improves access to goods for the average person. You might say the price of goods will increase, but prices in a competitive market can't be raised arbitrarily.

Morally if not legally, companies are not people. They don't starve if they can't earn a living, they don't suffer when their kids are hungry etc. There are good reasons for companies to be restricted in ways that individuals are not. I see unions as a mechanism for individuals to collaborate.

A short post on evaluating the Fourier integral numerically. https://comphysblog.wordpress.com/2023/07/06/computing-fourier-integrals/

When I tried to look up how to do this, I almost exclusively found information on the FFT. This gave inadequate results, which I now know is expected. Numerical recipes says:

"It is a sobering exercise to implement equation (13.9.6)[DFT] for an integral that can be done
analytically, and to see just how bad it is."

This week I came across zenodo.org. It issues doi's for datasets (or other things) that you upload, and it's apparently hosted on CERN infrastructure. I wish I had found this earlier.

@rvlobato while I'm a Firefox advocate, I also don't really see an issue with this. Chromium is open source, but that doesnt mean any associated services like Sync have to be made freely available. Google are looking out for google, and having complete control of the browser market would be a huge advantage for them. If you don't think they would be suitable custodians of a browser monoculture, then don't use their browser (chrome or chromium) while that is still an option; also give Mozilla some money.

@freemo I was confused earlier on by a minicircuits spec sheet for a 180 degree hybrid [1]. They only seem to sell three port varieties, I assume they fourth port is internally terminated or it isn't included somehow. Now the thing which confused me was that they referred to one of the ports as the SUM port. Hybrid couplers are often shown as 4 port devices with Sigma, Delta 1 and 2 ports. I would have thought the "SUM" port would be the sigma port, but then the output of the splitter would be two in-phase signals and it wouldn't really be much of a "180" degree" hybrid. Their SUM port must correspond to the Delta port, that is, the signal out of the "sum" port would be large if the inputs at ports 1 and 2 were entirely out of phase, I.e. the difference. It does behave this way, I tried it today, but my question is: why would they call it a "sum" port when if anything it's subtracting?! Am I alone in finding that confusing?

[1] - https://www.minicircuits.com/WebStore/dashboard.html?model=ZFSCJ-2-1

@AmpBenzScientist I need the passband to be at 202 MHz, with a few MHz of bandwidth. I'm no expert on filter technology, but this frequency seems a bit high for quartz and their passbands apparently tend to be very narrow. It is unfortunate for me, because they'd be ideal otherwise.

I need to maintain the phase between two signals and to filter at least one of them. At the moment I've just made a simple LC ladder and put an identical filter on both signals, so that hopefully when they drift, they drift together. The temperature stability of this approach doesn't seem terrible actually.

Does anybody have any experience with designing thermally stable HF filters (100's of MHz)? Any references appreciated :)

@freemo ah fair enough, I was looking out for a single resistor. Yes that works.

@freemo I can see you've got one on the reflected_SIG, but I can't see one on forward_SIG.

@freemo the dev board of the ad8302 has a 50 ohm shunt resistor at the inputs (R1 & R2). Is there a reason you haven't included these?

@freemo I used the AD8302 recently as part of an analogue phase detection system for a linear accelerator. I hadn't thought about how they could be used in a VNA.

Finally made my 2D magnet post. In this example I do a simple demonstration of finding a magnetic field from a coax, and verify the result with an analytical solution. I then use the same method to find the field inside a dipole magnet of the type used at the LHC; a cos(phi) magnet. https://comphysblog.wordpress.com/2020/08/19/2d-magnetostatics-cos%cf%86-dipole-magnet/

#fenics #physics #finite_element_analysis

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