Fe-C Updated 2025-07-16
Ferromagnetism Updated 2025-07-16
The wiki comments: en.wikipedia.org/w/index.php?title=Ferromagnetism&oldid=965600553#Explanation
The Bohr-van Leeuwen theorem, discovered in the 1910s, showed that classical physics theories are unable to account for any form of magnetism, including ferromagnetism. Magnetism is now regarded as a purely quantum mechanical effect. Ferromagnetism arises due to two effects from quantum mechanics: spin and the Pauli exclusion principle.
Feynman diagram Updated 2025-07-16
I think they are a tool to calculate the probability of different types of particle decays and particle collision outcomes. TODO Minimal example of that.
And they can be derived from a more complete quantum electrodynamics formulation via perturbation theory.
At Richard Feynman Quantum Electrodynamics Lecture at University of Auckland (1979), an intuitive explanation of them in termes of sum of products of propagators is given.
- www.youtube.com/watch?v=fG52mXN-uWI The Secrets of Feynman Diagrams | Space Time by PBS Space Time (2017)
Feynman was a huge womanizer during a certain period of his life Updated 2025-07-16
Feynman became a terrible womanizer after his first wife Arline Greenbaum died, involving himself with several married women, and leading to at least two abortions according to Genius: Richard Feynman and Modern Physics by James Gleick (1994).
Ciro Santilli likes to think that he is quite liberal and not a strict follower of Christian morals, but this one shocked him slightly even. Feynman could be a God, but he could also be a dick sometimes.
One particular case that stuck to Ciro Santilli's mind, partly because he is Brazilian, is when Feynman was in Brazil, he had a girlfriend called Clotilde that called him "Ricardinho", which means "Little Richard"; -inho is a diminutive suffix in Portuguese, and also indicates affection. At some point he even promised to take her back to the United States, but didn't in the end, and instead came back and married his second wife in marriage that soon failed.
Richard's third and final wife, Gweneth Howarth, seemed a good match for him though. When they started courting, she made it very clear that Feynman should decide if he wanted her or not soon, because she had other options available and being actively tested. Fight fire with fire.
Fick's laws of diffusion Updated 2025-07-16
Field-effect transistor Updated 2025-07-16
Field (mathematics) Updated 2025-07-16
A field can be seen as an Abelian group that has two group operations defined on it: addition and multiplication.
And then, besides each of the two operations obeying the group axioms individually, and they are compatible between themselves according to the distributive property.
Examples:
Fifth Solvay Conference (1927) Updated 2025-07-16
Fighting game Updated 2025-07-16
Omics Updated 2025-07-16
Each of the omics studies a subset of molecular biology with a data intensive and broad point of view that tries to understand global function or organisms, trying to understand what every biologically relevant molecule does as part of the hole metabolism.
The main omics are:
Omics might be stamp collecting, but maybe it is a bit more like Trading card game/Magic: The Gathering collecting, in which the cards that you are collecting actually have specific uses and interactions, especially considering that most metabolic pathways are analogous across many species.
Hierarchical diagram of the major omics
. Once upon a time in the west (1968) Updated 2025-07-16
graphviz/node.dot Updated 2025-07-16
graphviz/quotes.dot Updated 2025-07-16
js/matterjs/hello.html Updated 2025-07-16
Hello world adapted from: github.com/liabru/matter-js/wiki/Getting-started/1d138998f05766dc4de0e44ae2e35d03121bb7f2
Also asked at: stackoverflow.com/questions/28079138/how-to-make-minimal-example-of-matter-js-work/76203103#76203103
Renderer questions:
- follow object on viewport: codepen.io/csims314/pen/goZQvG
- draw text: github.com/liabru/matter-js/issues/321
File manager Updated 2025-07-16
Ciro Santilli used to use file managers in the past.
But he finally converted to a shell
cd aliases that auto-ls: github.com/cirosantilli/dotfiles/blob/a51bcc324f0cff0eddd4c3bb8654ec223a0adb7b/home/.bashrc#L1058 Open boundary condition Updated 2025-07-16
In the context of wave-like equations, an open-boundary condition is one that "lets the wave go through without reflection".
This condition is very useful when we want to simulate infinite domains with a numerical method. Ciro Santilli wants to do this all the time when trying to come up with demos for his physics writings.
Here are some resources that cover such boundary conditions:
- www.asc.tuwien.ac.at/~arnold/pdf/graz/graz.pdf lots of slides
- hplgit.github.io/wavebc/doc/pub/._wavebc_cyborg002.html mentions them and gives a 1D formula. It mentions that things get complicated in 2D and 3D TODO why.The other page: hplgit.github.io/wavebc/doc/pub/._wavebc_cyborg003.html shows solution demos.
OpenShot Updated 2025-07-16
Ubuntu 20.10 crash...:
exceptions:ERROR Unhandled Exception
Traceback (most recent call last):
File "/usr/bin/openshot-qt", line 11, in <module>
load_entry_point('openshot-qt==2.5.1', 'gui_scripts', 'openshot-qt')()
File "/usr/lib/python3/dist-packages/openshot_qt/launch.py", line 97, in main
app = OpenShotApp(argv)
File "/usr/lib/python3/dist-packages/openshot_qt/classes/app.py", line 218, in __init__
from windows.main_window import MainWindow
File "/usr/lib/python3/dist-packages/openshot_qt/windows/main_window.py", line 45, in <module>
from windows.views.timeline_webview import TimelineWebView
File "/usr/lib/python3/dist-packages/openshot_qt/windows/views/timeline_webview.py", line 42, in <module>
from PyQt5.QtWebKitWidgets import QWebView
ImportError: /usr/lib/x86_64-linux-gnu/libQt5Quick.so.5: undefined symbol: _ZN4QRhi10newSamplerEN11QRhiSampler6FilterES1_S1_NS0_11AddressModeES2_, version Qt_5_PRIVATE_API nodejs/sequelize/parallel_select_and_update.js Updated 2025-07-16
This example is the same as nodejs/sequelize/raw/parallel_select_and_update.js, but going through Sequelize rather than with Sequelize raw queries.
NONE is not supported for now to not have a transaction at all because lazy.The examples illustrates: stackoverflow.com/questions/55452441/for-share-and-for-update-statements-in-sequelize
Sample invocation:where:
node --unhandled-rejections=strict ./parallel_select_and_update.js p 10 100 READ_COMMITTED UPDATEREAD_COMMITTED: one of the keys documented at: sequelize.org/master/class/lib/transaction.js~Transaction.html which correspond to the standard sQL isolation levels. It not given, don't set one, defaulting to the database's/sequelize's default level.UPDATE: one of the keys documented at: sequelize.org/master/class/lib/transaction.js~Transaction.html#static-get-LOCK. Update generates aSELECT FOR UPDATEin PostgreSQL for example. If not given, don't use anyFOR xxxexplicit locking.
Other examples:
node --unhandled-rejections=strict ./parallel_select_and_update.js p 10 100 READ_COMMITTED UPDATE
Then, the outcome is exactly as described at: nodejs/sequelize/raw/parallel_select_and_update.js:
READ_COMMITTED: failsREAD_COMMITTED UPDATE: works- This case also illustrates Sequelize transaction retries, since in this transaction isolation level transactions may fail:
nodejs/sequelize/raw/parallel_select_and_update_deterministic.js Updated 2025-07-16
This example contains a deterministic demo of when postgreSQL serialization failures may happen.
Tested on PostgreSQL 13.5.
nodejs/sequelize/raw/parallel_select_and_update.js Updated 2025-07-16
This example is similar to nodejs/sequelize/raw/parallel_update_async.js, but now we are doing a separate SELECT, later followed by an update:
Although this specific example is useless in itself, as we could just use
UPDATE "MyInt" SET i = i + 1 as in nodejs/sequelize/raw/parallel_update_async.js, which automatically solves any concurrency issue, this kind of code could be required for example if the update was a complex function not suitably implemented in SQL, or if the update depends on some external data source.Sample execution:which does:
node --unhandled-rejections=strict ./parallel_select_and_update.js p 2 10 'READ COMMITTED'- PostgreSQL, see other databases options at SQL example
- 2 threads
- 10 increments on each thread
Another one:this will run SELECT FOR UPDATE rather than just SELECT
node --unhandled-rejections=strict ./parallel_select_and_update.js p 2 10 'READ COMMITTED' 'FOR UPDATE'Observed behaviour under different SQL transaction isolation levels:
READ COMMITTED: fails. Nothing in this case prevents:REPEATABLE READ: works. the manual mentions that if multiple concurrent updates would happen, only the first commit succeeds, and the following ones fail and rollback and retry, therefore preventing the loss of an update.READ COMMITTED+SELECT FOR UPDATE: works. And does not do rollbacks, which probably makes it faster. Withp 10 100,REPEATABLE READwas about 4.2s andREAD COMMITTED+SELECT FOR UPDATE3.2s on Lenovo ThinkPad P51 (2017).SELECT FOR UPDATEshould be enough as mentioned at: www.postgresql.org/docs/13/explicit-locking.html#LOCKING-ROWSFOR UPDATE causes the rows retrieved by the SELECT statement to be locked as though for update. This prevents them from being locked, modified or deleted by other transactions until the current transaction ends. That is, other transactions that attempt UPDATE, DELETE, SELECT FOR UPDATE, SELECT FOR NO KEY UPDATE, SELECT FOR SHARE or SELECT FOR KEY SHARE of these rows will be blocked until the current transaction ends; conversely, SELECT FOR UPDATE will wait for a concurrent transaction that has run any of those commands on the same row, and will then lock and return the updated row (or no row, if the row was deleted). Within a REPEATABLE READ or SERIALIZABLE transaction, however, an error will be thrown if a row to be locked has changed since the transaction started. For further discussion see Section 13.4.
A non-raw version of this example can be seen at: nodejs/sequelize/parallel_select_and_update.js.
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