{c}

= XRD
{c}
{synonym}
{title2}

Often used as a synonym for <X-ray crystallography>, or to refer more specifically to the diffraction part of the experiment (exluding therefore sample preparation and data processing).


X-ray diffraction

{c}
{wiki}

https://askubuntu.com/questions/220802/no-sound-zynaddsubfx-and-jack-wont-run/1297988\#1297988

Contains a large database of instruments, and allows you to edit them. This is a fun toy.

Instruments are edited on a <GUI>. It is a multi-window program, and you open new windows from new windows from new windows, all filled with hundreds of virtual knobs that you drag with your keyboard, and which would be better done from textual software like <Csound>. It is a thing of beauty.

It does not seem possible to program arbitrary <modular synthesizer> circuits therefore. But if you understand <additive synthesis> and <subtractive synthesis> well, you can make some funky sounds with it.

It is basically a superset of all popular <hardware synthesizers> ever made.

Has its own built-in MIDI keyboard which is nice.

On Ubuntu 20.04 Version: 3.0.5:
``
sudo apt install zynaddsubfx
zynaddsubfx -O alsa
``
as per https://askubuntu.com/questions/220802/no-sound-zynaddsubfx-and-jack-wont-run/1297988\#1297988
To do anything of interest, switch to the Advanced UI:
* Misc
* Switch Interface Mode

The UI is completely different form what is shown on the website as of 2020: https://zynaddsubfx.sourceforge.io/[], it looks instead like: https://www.youtube.com/watch?v=iVPr6iUuO3g[] Maybe on the website it is the new zyn-fusion UI... https://www.reddit.com/r/linuxaudio/comments/bxn3ur/some_help_for_installing_zynfusion_zynaddsubfx/ so confusing.

And they have some crappy policy of asking for 45 USD for binary downloads.

Compiling from source:
``
git clone https://github.com/zynaddsubfx/zynaddsubfx
cd zynaddsubfx
git checkout a789866de4d45a784c1f4d95fcf5a1938347baef
sudo apt build-dep zynaddsubfx
mkdir build
cd build
cmake ..
make -j`nproc`
``
fails with:
``
Traceback (most recent call last):
  File "/usr/bin/cxxtestgen", line 7, in <module>
    import cxxtest.cxxtestgen
  File "/usr/share/cxxtest/cxxtest/__init__.py", line 33, in <module>
    from cxxtest.cxxtestgen import *
  File "/usr/share/cxxtest/cxxtest/cxxtestgen.py", line 18, in <module>
    import __release__
ModuleNotFoundError: No module named '__release__'
``
Ciro gives up for now.


ZynAddSubFX

{c}
{wiki=Yang–Mills_existence_and_mass_gap}

* https://www.youtube.com/watch?v=-_qNKbwM_eE Unsolved: Yang-Mills existence and mass gap by J Knudsen (2019). Gives 10 key points, but the truly hard ones are too quick. He knows the thing though.

\Video[https://www.youtube.com/watch?v=j3fsPHnrgLg]
{title=Yang-Mills 1 by David Metzler (2011)}
{description=
Playlist: https://www.youtube.com/watch?v=j3fsPHnrgLg&list=PL613A31A706529585&index=13

A bit disappointing, too high level, with very few nuggests that are not Googleable withing 5 minutes.

Breakdown:
* 1 https://www.youtube.com/watch?v=j3fsPHnrgLg[]: too basic
* 2 https://www.youtube.com/watch?v=br6OxCLyqAI?t=569[]: mentions <groups of Lie type> in the context of <classification of finite simple groups>. Each group has a little diagram.
* 3 https://youtu.be/1baiIxKKQlQ?list=PL613A31A706529585&t=728 the original example of a <local symmetry> was <general relativity>, and that in that context it can be clearly seen that the local symmetry is what causes "forces" to appear
  * https://youtu.be/1baiIxKKQlQ?list=PL613A31A706529585&t=933 <local symmetry> gives a conserved current. In the case of <electromagnetism>, this is electrical current. This was the only worthwhile thing he sad to 2021 Ciro. Summarized at: <local symmetries of the Lagrangian imply conserved currents>.
* 4 https://youtu.be/5ljKcWm7hoU?list=PL613A31A706529585&t=427 <electromagnetism> has both a global symmetry (<special relativity>) but also <local symmetry>, which leads to the conservation of charge current and forces.

  <quantum field theory lecture by tobias osborne 2017/lecture 3> properly defines a <local symmetry> in terms of the context of the <lagrangian density>, and explains that the conservation of currents there is basically the statement of <Noether's theorem> in that context.
}
\Video[https://www.youtube.com/watch?v=vMiY7zlBOFI]
{title=Millennium Prize Problem: Yang Mills Theory by David Gross (2018)}
{description=2 hour talk at the <Kavli Institute for Theoretical Physics>. Too mathematical, 2021 Ciro can't make much out of it.}

\Video[https://www.youtube.com/watch?v=pCQ9GIqpGBI]
{title=Lorenzo Sadun on the "Yang-Mills and Mass Gap" <Millennium Prize Problems>[Millennium problem]}
{description=Unknown year. He almost gets there, he's good. Just needed to be a little bit deeper.}


Yang-Mills existence and mass gap

{title2=C}
{title2=MPhys}

= Oxford MPhys
{c}
{synonym}

= Oxford physics MSc
{c}
{synonym}
{title2}

= Oxford physics masters
{c}
{synonym}
{title2}

Students choose only one of the Cx courses.

Then there are PhDs corresponding to each of them: https://www.ox.ac.uk/admissions/graduate/courses/mpls/physics


Year 4 of the physics course of the University of Oxford

* https://www.youtube.com/channel/UCDyR_C_QVjZR24ze0fl5S_Q Goat-on-a-Stick channel

\Video[https://www.youtube.com/watch?v=g-sgw9bPV4A]
{title=Kazoo Kid - Trap Remix by Mike Diva (2016)}

\Video[https://www.youtube.com/watch?v=3Q12xOukVAI]
{title=Ravioli Remix: Black and Yellow by Wiz Krablifa by TheDoubleAgent (2015)}

\Video[https://www.youtube.com/watch?v=Fc1P-AEaEp8&list=PLcZOZrP1P_V6uAU4QhldipGBW86qJFvLk&index=13]
{title=Afraid of Technology by adarkenedroom (2008)}
{description=TODO source show, appears "Brass Eye", TODO episode https://www.reddit.com/r/videos/comments/jpyfi/technology_scares_the_crap_out_of_me/}


YouTube poop

{c}
{wiki}

Split in the <spectral line> when a <magnetic field> is applied.

Non-anomalous: number of splits matches predictions of the <Schrödinger equation> about the number of possible states with a given angular momentum. TODO does it make numerical predictions?

<anomalous Zeeman effect>[Anomalous]: evidence of <spin (physics)>.

http://www.pas.rochester.edu/~blackman/ast104/zeeman-split.html contains the hello world that everyone should know: 2p splits into 3 energy levels, so you see 3 spectral lines from 1s to 2p rather than just one.

p splits into 3, d into 5, f into 7 and so on, i.e. one for each possible <azimuthal quantum number>.

It also mentions that polarization effects become visible from this: each line is polarized in a different way. TODO more details as in an experiment to observe this.

Well explained at: <video Quantum Mechanics 7a - Angular Momentum I by ViaScience (2013)>.

\Video[https://www.youtube.com/watch?v=ZmObNFAqkBE]
{title=Experimental physics - IV: 22 - Zeeman effect by Lehrportal Uni Gottingen (2020)}
{description=
This one is decent. Uses a <cadmium> lamp and an <etalon> on an <optical table>. They see a more or less clear 3-split in a circular <interference pattern>,

They filter out all but the transition of interest.

* https://youtu.be/ZmObNFAqkBE?t=165 passes the lines through a <polarizer>, which shows how orbital angular momentum is carried by <photon polarization>
* https://youtu.be/ZmObNFAqkBE?t=370 says they are looking at 1D2 to 1P1 changes.
}

\Video[https://www.youtube.com/watch?v=OzkcB1lkgGU]
{title=Zeeman Effect - Control light with magnetic fields by <Applied Science (YouTube channel)> (2018)}
{description=Does not appear to achieve a crystal clear split unfortunately.}


Zeeman effect

{wiki}

= 粽子
{synonym}
{title2}

Eaten during <Dragon Boat Festival>, but can be bought year round.

Buy frozen. Pick the ones with meat and eggs!!! Boil.

Cost about 4 dollars for 2.

You can't eat them every day because too heavy, but they are so amazingly tasty!!!

\Image[https://upload.wikimedia.org/wikipedia/commons/thumb/4/42/Zongzi.jpg/800px-Zongzi.jpg]


Zongzi

{wiki}

Currently an informal name for the <Standard Model>

Chronological outline of the key theories:
* <Maxwell's equations>
* <Schrödinger equation>
  * Date: 1926
  * Numerical predictions:
    * <hydrogen spectral line>, excluding finer structure such as 2p up and down split: https://en.wikipedia.org/wiki/Fine-structure_constant
* <Dirac equation>
  * Date: 1928
  * Numerical predictions:
    * <hydrogen spectral line> including 2p split, but excluding even finer structure such as <Lamb shift>
  * Qualitative predictions:
    * Antimatter
    * Spin as part of the equation
* <quantum electrodynamics>
  * Date: 1947 onwards
  * Numerical predictions:
    * <Lamb shift>
  * Qualitative predictions:
    * Antimatter
    * <spin (physics)> as part of the equation


Particle physics

{wiki}

As https://en.wikipedia.org/w/index.php?title=ZX-calculus&oldid=1071329204\#Diagram_rewriting tries to explain <ourbigbook com/Wikipedia>[but fails to deliver as usual] consider the <GHZ state> represented as a quantum circuit.

How can we easily prove that that quantum circuit equals the state:
$$
\frac{|000> + |111>}{\sqrt{2}}
$$
?

The naive way would be to just do the matrix multiplication as explained at <quantum computing is just matrix multiplication>{full}.

However, ZX-calculus provides a simpler way.

And even more importantly, sometimes it is the only way, because in a real circuit, we would not be able to do the matrix multiplication 

What we do in ZX-calculus is we first transform the original quantum circuit into a ZX graph.

This is always possible, because we can describe how to do the conversion simply for any of the <Clifford plus T> gates, which is a set of <universal quantum gates>.

Then, after we do this transformation, we can start applying further transformations that simplify the circuit.

It has already been proven that there is no efficient algorithm for this (TODO source, someone said P-sharp complete best case)

But it has been proven in 2017 that any possible equivalence between quantum circuits can be reached by modifying ZX-calculus circuits.

There are only 7 transformation rules that we need, and all others can be derived from those, universality.

So, we can apply those rules to do https://en.wikipedia.org/w/index.php?title=ZX-calculus&oldid=1071329204\#Diagram_rewriting[the transformation shown in Wikipedia]:

\Image[https://upload.wikimedia.org/wikipedia/commons/0/05/GHZ_circuit_as_ZX-diagram.svg]
{height=500}
{title=GHZ circuit as ZX-diagram}

and one of those rules finally tells us that that last graph means our desired state:
$$
\frac{|000> + |111>}{\sqrt{2}}
$$
because it is a Z spider with $m = 3$ and $n = 1$.

\Video[https://www.youtube.com/watch?v=JafI_LZts2g]
{title=Working with <PyZX> by Aleks Kissinger (2019)}
{description=
This video appears to give amazing motivation on why you should care about <ZX-calculus>, it mentions
* <quantum compilation>
* <quantum computer simulation>
}

Bibliography:
* https://quantumcomputing.stackexchange.com/questions/9774/what-are-some-applications-of-the-zx-calculus


ZX-calculus

{c}
{wiki}

https://en.wikipedia.org/wiki/Paulo_Freire[]:
\Q[During his childhood and adolescence, Freire ended up four grades behind, and his social life revolved around playing pick-up football with other poor children, from whom he claims to have learned a great deal. These experiences would shape his concerns for the poor and would help to construct his particular educational viewpoint. Freire stated that poverty and hunger severely affected his ability to learn. These experiences influenced his decision to dedicate his life to improving the lives of the poor: "I didn't understand anything because of my hunger. I wasn't dumb. It wasn't lack of interest. My social condition didn't allow me to have an education. Experience showed me once again the relationship between social class and knowledge"]
OMG so nice.


Paulo Freire

{wiki}

* the American stock market gives 10% / year, which is about 2x over 10 years. It has been the sure-fire best investment on a 10 year horizon for many decades, and should serve as your benchmark.
* risky diversified investments (e.g. ETFs that track a market index) are basically the best investment if you can keep your money in them in the long term (10 years)
* risky investments can gown down for a while, and you cannot take your money out then. This effectively means risk is a form of <illiquidity>
* investment funds have taxes, which eat into your profit. The best investments are dumb index tracking investments (like an ETF that tracks the stock market) that are simply brainless to manage, and therefore have lowest taxes. No fund has managed to beat the market long term essentially.
* when you are young, ideally you should invest everything into riskier higher yielding assets like stock. And as you get older, you should move part of it to less risky (and therefore more <liquid (asset)>, but lower yielding) assets like bonds

  The desire to buy a house however complicates this for many people.


Title	Created	Updated
X-ray diffraction	1970-01-01	1970-01-01
ZynAddSubFX	1970-01-01	1970-01-01
Yang-Mills existence and mass gap	1970-01-01	1970-01-01
Year 4 of the physics course of the University of Oxford	1970-01-01	1970-01-01
YouTube poop	1970-01-01	1970-01-01
Zeeman effect	1970-01-01	1970-01-01
Zongzi	1970-01-01	1970-01-01
Particle physics	1970-01-01	1970-01-01
ZX-calculus	1970-01-01	1970-01-01
Paulo Freire	1970-01-01	1970-01-01
Personal finance	1970-01-01	1970-01-01

Ciro Santilli (@cirosantilli, 32)