Ciro Santilli @cirosantilli 35

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P1 by

Ciro Santilli 35  Updated 2025-04-05  +Created 2024-07-12

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Q2 by

Ciro Santilli 35  Updated 2025-04-05  +Created 2024-07-12

Section "Greatest common divisor".
Section "Farey sequence".
- Section "Number of elements in a Farey sequence"
- Farey sunburst, e.g. $F_{5}$ :

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Q1 by

Ciro Santilli 35  Updated 2025-04-05  +Created 2024-07-12

Section "Greatest common divisor".

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@cirosantilli/_file/gmp/gmp/antihydra.c by

Ciro Santilli 35  Updated 2025-04-05  +Created 2024-07-12

Also posted at:

wiki.bbchallenge.org/w/index.php?title=Antihydra&oldid=958 But obviously it got deleted, not even a tiny shitpage maintained by 5 people is immune to it.
cstheory.stackexchange.com/questions/20978/what-is-the-smallest-turing-machine-where-it-is-unknown-if-it-halts-or-not/53326#53326
cs.stackexchange.com/questions/59344/what-are-very-short-programs-with-unknown-halting-status/162108#162108

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Antihydra GMP implementation by

Ciro Santilli 35  Updated 2025-04-05  +Created 2024-07-12

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PROMYS Europe application problem set answers by

Ciro Santilli 35  Updated 2025-04-05  +Created 2024-07-12

www.reddit.com/r/math/comments/17y9zj3/how_do_i_tackle_problems_from_the_promysross/

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Set 2 by

Ciro Santilli 35  Updated 2025-04-05  +Created 2024-07-12

Ciro Santilli got his hands on this one. But he was unable to obtain the others. Solving them here would also pose a serious DMCA risk, so perhaps it's just not worth it.

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Ciro Santilli 35  Updated 2025-04-05  +Created 2024-07-12

wiki.bbchallenge.org/wiki/Antihydra

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Ciro Santilli 35  Updated 2025-04-05  +Created 2024-07-12

Figure 1.
Toshiba D-088 dental X-ray tube
. Source.

William Coolidge explains medical imaging and X-rays (1940).

Source. Video sponsored by General Electric. A cool insight of this video is that a hot cathode is a more reliable electron source. Previous systems, and presumably including the discovery of X-rays, leftover gas in the tube was used. But this makes things more difficult to control, as we also want to remove as much gas as possible from the vacuum, otherwise electrons collide with the gas and lose energy before hitting the anode.

How Does X ray Tube Works by BiomedEngg

. Source. Describes in particular the rotating cathode method. Interesting observation that this is especially important since the cathode cannot cool quickly due to the vacuum.

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PROMYS Europe 2024 problem set by

Ciro Santilli 35  Updated 2025-04-05  +Created 2024-07-12

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PROMYS Europe application problem set by

Ciro Santilli 35  Updated 2025-04-05  +Created 2024-07-12

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PROMYS Europe problem set answers by

Ciro Santilli 35  Updated 2025-04-05  +Created 2024-07-12

TODO.

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Oxford physics past exam paper by

Ciro Santilli 35  Updated 2025-04-05  +Created 2024-07-12

2010-2016: www.whatdotheyknow.com/request/physics_past_papers_2
2014-2021: www.whatdotheyknow.com/request/oxford_physics_past_papers_2

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Oxford mathematics past exam paper by

Ciro Santilli 35  Updated 2025-04-05  +Created 2024-07-12

www.whatdotheyknow.com/request/maths_papers asked but didn't upload...
www.whatdotheyknow.com/request/oxford_mathematics_prelims_past from 2021 asked for prelims only but no upload

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@cirosantilli/_file/gmp/gmp/hello.c by

Ciro Santilli 35  Updated 2025-04-05  +Created 2024-07-12

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Erbium-doped fiber amplifier by

Ciro Santilli 35  Updated 2025-04-05  +Created 2024-07-12

This one was a huge advance it seems.

Erbium-doped fiber amplifier by Millennium Technology Prize

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X-ray source by

Ciro Santilli 35  Updated 2025-04-05  +Created 2024-07-12

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PROMYS Europe 2024 by

Ciro Santilli 35  Updated 2025-04-05  +Created 2024-07-12

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PROMYS Europe problem set by

Ciro Santilli 35  Updated 2025-04-05  +Created 2024-07-12

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Fiber optical amplifier by

Ciro Santilli 35  Updated 2025-04-05  +Created 2024-07-12

These are pretty cool, they are basically a laser

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