The Wikipedia page of this article is basically a masterclass why Wikipedia is useless for learning technical subjects. They are not even able to teach such a simple subject properly there!
Bibliography:
- www.maths.cam.ac.uk/postgrad/part-iii/files/misc/index-notation.pdf gives a definition that does not consider upper and lower indexes, it only counts how many times the indices appearTheir definition of the Laplacian is a bit wrong as only one appears in it, they likely meant to have written instead of , related:
Miele C2 Complete PowerLine vacuum cleaner by 
Ciro Santilli 35 Updated 2025-03-28 +Created 1970-01-01
Ciro Santilli 35 Updated 2025-03-28 +Created 1970-01-01Similar to: www.miele.co.uk/e/cylinder-vacuum-cleaner-compact-c2-powerline-sdrf4-10931670-p but slightly different from image. Indistinguishable from: www.currys.co.uk/gbuk/home-appliances/floorcare/vacuum-cleaners/miele-complete-c2-pure-power-powerline-cylinder-vacuum-cleaner-graphite-grey-10208570-pdt.html
Power symbol meanings: images-eu.ssl-images-amazon.com/images/I/A14OZ5TuwGS.pdf
2020-12: buying Miele SF AP 50 AirClean Plus filter www.miele.co.uk/e/airclean-plus-filter-sf-ap-50-10107860-p. Once it arrived, changed the filter, which fit comes with plastic casing and accordion shaped filter. Also changed bag. But the bag full meter still goes to red on carpet even with everything new while vacuuming. Is it supposed to be checked while not vacuuming?
A tiny idealized magnet! It is a very good model if you have a small strong magnet interacting with objects that are far away, notably other magnetic dipoles or a constant magnetic field.
The cool thing about this model is that we have simple explicit formulas for the magnetic field it produces, and for how this little magnet is affected by a magnetic field or by another magnetic dipole.
This is the perfect model for electron spin, but it can also be representative of macroscopic systems in the right circumstances.
The intuition for the name is likely that "dipole" means "both poles are on the same spot".
Different macroscopic magnets can be approximated by a magnetic dipole when shrunk seen from far away
. Source. What it adds on top of reverse debugging: not only can you go back in time, but you can do it instantaneously.
Or in other words, you can access variables from any point in execution.
TODO implementation? Apparently Pernosco is an attempt at it, though proprietary.
Wikipedia mentions that it is completely analogous to Planck's law.
What makes lasers so special: Lasers vs other light sources.
How Lasers Work by Scientized (2017)
Source. An extremely good overview of how lasers work. Clearly explains the electron/photon exchange processes involved, notably spontaneous emission.
Talks about the importance of the metastable state to achieve population inversion.
Also briefly explains the imperfections that lead to the slightly imperfect non punctual spectrum seen in a real laser.
- youtu.be/_JOchLyNO_w?t=188 says LED is "also monochromatic", but that is not strictly true, it has way way larger frequency band than a laser. Only narrower compared to other sources such as incandescent light bulbs.
- youtu.be/_JOchLyNO_w?t=517 stimulated emission. This is the key to laser formation as it produces coherent photons.
- youtu.be/_JOchLyNO_w?t=581 spontaneous emission happens too fast (100 ns), which is not enough time for stimulated emission to happen. Metastable electrons to the rescue.
- youtu.be/_JOchLyNO_w?t=832 the parallel mirrors select perpendicular photons preferentially
Laser Fundamentals I by Shaoul Ezekiel
. Source. 2008, MIT. Many more great videos in this series.Bought around: 2017-09.
TEFAL Multicook 8in1 RK302E15 MultiCooker - 4 Portions / 5L.
Likely bought from: www.johnlewis.com/tefal-rk302e15-8-in-1-multi-cooker/p231378165
Markings say: "SERIE R13-B REF: RK302E15 / 79 A - 1017"
How to open videos: can't find any, but the hard part (remove top lid) was the same as the video for joyoung rice cooker (2014), can be done by inserting a thin metal and going around it.
Bottom opens by taking off a single screw on the bottom and pulling it out (not obvious, a little bit of force).
2021-01: while making congee it overflowed without us noticing it, and next time we were going to cook something, it started to burn bits of congee that stuck to the heat plate. Opened it up and tried to clean everything.
2020-03: E01 error, looked up on manual and it is a top wire broken, opened up and confirmed one of the three wires going up broken, exactly like the previous one joyoung rice cooker (2014). Managed to fix easily with heat gun and Solder Seal Heat Shrink, no soldering iron, that thing is amazing: www.amazon.co.uk/dp/B085415G8N Let's see how long it lasts.
GDB Nirvana?
Similar to: www.amazon.co.uk/dp/B013AV45IS
2019: broke with sign number 6. Ciro Santilli opened it up a bit destructively.
How to open: www.youtube.com/watch?v=8Lf68mAB0Vk
System of linear ordinary differential equations by Ciro Santilli 35 Updated 2025-03-28 +Created 1970-01-01
Ciro Santilli 35 Updated 2025-03-28 +Created 1970-01-012022-02: Kiea Barlast floor lamp: www.ikea.com/gb/en/p/barlast-floor-lamp-black-white-50437810 Bulb: LED bulb E27 globe opal white.
Analytical method to solve a partial differential equation by Ciro Santilli 35 Updated 2025-03-28 +Created 1970-01-01
Ciro Santilli 35 Updated 2025-03-28 +Created 1970-01-01Obviously coupled with measures to prevent capital flight. This would be a required step to achieve Ciro Santilli's dream of unconditional basic income.
Why don't the poor vote in mass for it is incomprehensible considering e.g. the wealth inequality in the United States as of 2020!
Perhaps the election of Donald Trump in 2016 woke up the democrats at last, that they were just making empty promises without actually benefiting the poor? www.vox.com/2019/3/19/18240377/estate-tax-wealth-tax-70-percent-warren-sanders-aoc. Or is just another facade?
Bibliography:
- www.npr.org/sections/money/2019/02/26/698057356/if-a-wealth-tax-is-such-a-good-idea-why-did-europe-kill-theirs If a Wealth Tax is Such a Good Idea, Why Did Europe Kill Theirs?
- www.youtube.com/watch?v=XzonR81vVzM The Mayfair Set, Episode 2 - Entrepreneur Spelt S.P.I.V. (1999) by Adam Curtis explains nicely how in the 60's, Jim Slater bought stock of inefficient companies, and sold off inefficient assets to make a profit.He managed to do that because previously people had regarded those companies as family companies, and never looked into the fact that they families weren't actually majority shareholders anymore.While this increased efficiency, it also fired many people, and the government didn't manage to change legislation fast enough to tax those profits to increase welfare.
Pinned article: ourbigbook/introduction-to-the-ourbigbook-project
Welcome to the OurBigBook Project! Our goal is to create the perfect publishing platform for STEM subjects, and get university-level students to write the best free STEM tutorials ever.
Everyone is welcome to create an account and play with the site: ourbigbook.com/go/register. We belive that students themselves can write amazing tutorials, but teachers are welcome too. You can write about anything you want, it doesn't have to be STEM or even educational. Silly test content is very welcome and you won't be penalized in any way. Just keep it legal!
We have two killer features:
- topics: topics group articles by different users with the same title, e.g. here is the topic for the "Fundamental Theorem of Calculus" ourbigbook.com/go/topic/fundamental-theorem-of-calculusArticles of different users are sorted by upvote within each article page. This feature is a bit like:
- a Wikipedia where each user can have their own version of each article
- a Q&A website like Stack Overflow, where multiple people can give their views on a given topic, and the best ones are sorted by upvote. Except you don't need to wait for someone to ask first, and any topic goes, no matter how narrow or broad
This feature makes it possible for readers to find better explanations of any topic created by other writers. And it allows writers to create an explanation in a place that readers might actually find it.
Figure 1. Screenshot of the "Derivative" topic page. View it live at: ourbigbook.com/go/topic/derivative - local editing: you can store all your personal knowledge base content locally in a plaintext markup format that can be edited locally and published either:This way you can be sure that even if OurBigBook.com were to go down one day (which we have no plans to do as it is quite cheap to host!), your content will still be perfectly readable as a static site.
- to OurBigBook.com to get awesome multi-user features like topics and likes
- as HTML files to a static website, which you can host yourself for free on many external providers like GitHub Pages, and remain in full control
Figure 2. You can publish local OurBigBook lightweight markup files to either OurBigBook.com or as a static website.
Figure 3. Visual Studio Code extension installation.
Figure 4. Visual Studio Code extension tree navigation.
Figure 5. . You can also edit articles on the Web editor without installing anything locally. Video 3. Edit locally and publish demo. Source. This shows editing OurBigBook Markup and publishing it using the Visual Studio Code extension.Video 4. OurBigBook Visual Studio Code extension editing and navigation demo. Source. - Internal cross file references done right:
- Infinitely deep tables of contents:
Figure 6. Dynamic article tree with infinitely deep table of contents.Live URL: ourbigbook.com/cirosantilli/chordateDescendant pages can also show up as toplevel e.g.: ourbigbook.com/cirosantilli/chordate-subclade
All our software is open source and hosted at: github.com/ourbigbook/ourbigbook
Further documentation can be found at: docs.ourbigbook.com
Feel free to reach our to us for any help or suggestions: docs.ourbigbook.com/#contact