Astronomy Updated +Created
Ciro Santilli likes to learn astronomy a bit like he learns geography: go down some lists of "stuff that seems most relevant in some criteria to us!", possibly at different size scales e.g.:
Carleson's theorem Updated +Created
The Fourier series of an function (i.e. the function generated from the infinite sum of weighted sines) converges to the function pointwise almost everywhere.
The theorem also seems to hold (maybe trivially given the transform result) for the Fourier series (TODO if trivially, why trivially).
Only proved in 1966, and known to be a hard result without any known simple proof.
This theorem of course implies that Fourier basis is complete for , as it explicitly constructs a decomposition into the Fourier basis for every single function.
TODO vs Riesz-Fischer theorem. Is this just a stronger pointwise result, while Riesz-Fischer is about norms only?
Carl Jung Updated +Created
Caroline Ellison Updated +Created
Some analysts seem to suggest that the things she said were bad.
But they're not.
They're a rare example of someone with some power saying cool honest stuff that comes across their mind.
Unlike the endless mandatory corporate bullshit we usually get otherwise.
Carrier wave Updated +Created
Early transmitters such as the spark-gap transmitter could only send noises to send Morse code.
To send voice and music, amplitude modulation had to be developed. And a key ingredient of this is the carrier wave.
The problem is, the carrier wave needs to have somewhat high frequencies, in the hundreds of kHz TODO why. But as you might imagine, that is hard to achieve by mechanical means such as a hand cranck like Hippolyte Pixiis alternator!
Interestingly, some of the first carrier wave generators were actually mechanical, e.g. the Alexanderson alternator.
But clearly such mechanical machines were not very scalable, and soon more electronic devices were introduced, notably the vacuum tube.
Cartesius (1974) Updated +Created
Electronic money Updated +Created
Our minimal definition of "electronic money" is the following.
Instead of creating legal tender such as Dollars as banknotes or transactions in some complex obscure banking system, the government offers an official simple centralized API that represents it instead.
Each citizen or legal entity has an account there, and transfers between registered users are just simple API calls.
So for example you would e able to put all your money in the government account instead of using useless banks. And then you would invest it as you want with the investment company of your choice, without tying the "my money is here" with "this is the best investment" aspects of banks.
Eli Benderski Updated +Created
Amazing systems programming tutorials. Whenever you Google a hard topic, his blog comes up.
Also has many great contributions on Stack Overflow: stackoverflow.com/users/8206/eli-bendersky
As of 2016, Eli worked at Google (reference). TODO before that, I had found his earlier info previously but lost it.
Eli focuses mostly on compiler toolchains.
Cascading Style Sheets Updated +Created
Cat 5e Updated +Created
This is the most common home "ethernet cable" as of 2024. It is essentially ubiquitous. According to the existing Ethernet physical layer, the maximum speed supported is 2.5 Gbit/s.
Video 1.
Cat 5e cable stripped
. Source.
Cataclysm DDA build from source on Ubuntu 21.10 Updated +Created
sudo apt build-dep cataclysm-dda-curses cataclysm-dda-data cataclysm-dda-data
git clone https://github.com/CleverRaven/Cataclysm-DDA
cd Cataclysm-DDA
git checkout cdda-experimental-2022-01-27-0622
mkdir build
cd build
cmake -DCMAKE_BUILD_TYPE=Release -DTILES=ON -DSOUND=ON -DLOCALIZE=OFF ..
make -j`nproc`
fails with:
:part_index_’ may be used uninitialized [-Werror=maybe-uninitialized]
   55 |             return part_index_;
as reported at: github.com/CleverRaven/Cataclysm-DDA/issues/52657 now open for 3 months. Basically every commit I tried fails with a different -Werror check, they don't test GCC new enough regularly.
Cataclysm DDA multiplayer Updated +Created
This would be a dream, but it is also impossible: how can you reconcile automated tasks that are simulated quickly like batch crafting 20 muffings in 30 in-game minutes, with someone who is at the same time fighting a hoard of zombies and taking one action every 2 in-game seconds? Alas.
Cataclysm DDA save scum Updated +Created
Tested as of Cataclysm: Dark Days Ahead 0.E-3-1, seems possible built-in:
  • Disable autosave on settings
  • Quisave (Esc + 9)
  • To restore the save, just close the game window directly before clicking Yes or No on the "Watch the last moments of your life" dialog.
A less risky save scum can be achieved with rsync:
rsync -av ~/.local/share/cataclysm-dda/save/ ~/.local/share/cataclysm-dda/save.bak/
and after you die:
rsync -av ~/.local/share/cataclysm-dda/save.bak/ ~/.local/share/cataclysm-dda/save/
Cavendish Laboratory Updated +Created
Cavity magnetron Updated +Created
Apparently, DC current comes in, and microwaves come out.
TODO: sample power efficiently of this conversion and output spectrum of this conversion on some cheap device we can buy today.
Video 1.
Magnetron, How does it work? by Lesics (2020)
Source.
Video 2.
Device that Won WW2 by Curious Droid
. Source.
Cayley-Dickson construction Updated +Created
Constructs the quaternions from complex numbers, octonions from quaternions, and keeps doubling like this indefinitely.
Change of basis matrix Updated +Created
The change of basis matrix is the matrix that allows us to express the new basis in an old basis:
Mnemonic is as follows: consider we have an initial basis . Now, we define the new basis in terms of the old basis, e.g.:
which can be written in matrix form as:
and so if we set:
we have:
The usual question then is: given a vector in the new basis, how do we represent it in the old basis?
The answer is that we simply have to calculate the matrix inverse of :
That is the matrix inverse.
Charge conservation Updated +Created
Charitable organization Updated +Created

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