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The people who work on this will go straight to heaven, no questions asked.

Magnetic resonance imaging by

Ciro Santilli 40 Updated 2025-07-16

MRI is using NMR to image inside peoples bodies!

Video 1.

How does an MRI machine work? by Science Museum (2019)

Source. The best one can do in 3 minutes perhaps.

Video 2.

How MRI Works Part 1 by thePIRL (2018)

Source.

youtu.be/TQegSF4ZiIQ?t=326 the magnet is normally always on for the entire lifetime of the equipment!
youtu.be/TQegSF4ZiIQ?t=465 usage of non-ionizing radiation (only radio frequencies) means that it is very safe to use. The only dangerous part is the magnetic field interacting with metallic objects.

Video 3.

What happens behind the scenes of an MRI scan? by Strange Parts (2023)

. Source.

Video 4.

Dr Mansfield's MRI MEDICAL MARVEL by BBC

. Source. Broadcast in 1978. Description:

Tomorrow's World gave audiences a true world first as Dr Peter Mansfield of the University of Nottingham demonstrated the first full body prototype device for Magnetic resonance imaging (MRI), allowing us to see inside the human body without the use of X-rays.

Featuring the yet-to-be 2003 Nobel Prize in Physiology and Medicine Dr. Mansfield.

nodejs/sequelize/raw/parallel_create_delete_empty_tag.js by

Ciro Santilli 40 Updated 2025-07-16

In this example, posts have tags. When a post is deleted, we check to see if there are now any empty tags, and now we want to delete any empty tags that the post deletion may have created.

If we are creating and deleting posts concurrently, a naive implementation might wrongly delete the tags of a newly created post.

This could be due to a concurrency issue of the following types.

Failure case 1:

thread 2: delete old post
thread 2: find all tags with 0 posts. Finds tag0 from the deleted old post which is now empty.
thread 1: create new post, which we want to have tag tag0
thread 1: try to create a new tag tag0, but don't because it already exists, this is done using SQLite's INSERT OR IGNORE INTO or PostgreSQL's INSERT ... ON CONFLICT DO NOTHING
thread 1: assign tag0 to the new post by adding an entry to the join table
thread 2: delete all tags with 0 posts. It still sees from its previous search that tag0 is empty, and deletes it, which then cascades into the join table

which would result in the new post incorrectly not having the tag0.

Failure case 2:

thread 2: delete old post
thread 2: find all tags with 0 posts
thread 1: create new post
thread 1: try to create a new tag tag0, but don't because it already exists
thread 2: delete all tags with 0 posts. It still sees from its previous search that tag0 is empty, and deletes it
thread 1: assign tag0 to the new post

which leads to a foreign key failure, because the tag does not exist anymore when the assignment happens.

Failure case 3:

thread 2: delete old post
thread 1: create new post, which we want to have tag tag0
thread 1: try to create a new tag tag0, and succeed because it wasn't present
thread 2: find all tags with 0 posts, finds the tag that was just created
thread 2: delete all tags with 0 posts, deleting the new tag
thread 1: assign tag0 to the new post

which leads to a foreign key failure, because the tag does not exist anymore when the assignment happens.

Sample executions:

node --unhandled-rejections=strict ./parallel_create_delete_empty_tag.js p 9 1000 'READ COMMITTED': PostgreSQL, 9 tags, DELETE/CREATE the tag0 test tag 1000 times, use READ COMMITTED
Execution often fails, although not always. The failure is always:
```
error: insert or update on table "PostTag" violates foreign key constraint "PostTag_tagId_fkey"
```
because the:
```
INSERT INTO "PostTag"
```
tries to insert a tag that was deleted in the other thread, as it didn't have any corresponding posts, so this is the foreign key failure.
TODO: we've never managed to observe the failure case in which tag0 is deleted. Is it truly possible? And if not, by which guarantee?
node --unhandled-rejections=strict ./parallel_create_delete_empty_tag.js p 9 1000 'READ COMMITTED' 'FOR UPDATE': do a SELECT ... FOR UPDATE before trying to INSERT.
This is likely correct and the fastest correct method according to our quick benchmarking, about 20% faster than REPEATABLE READ.
We are just now 100% sure it is corret becase we can't find out if the SELECT in the DELETE subquery could first select some rows, which are then locked by the tag creator, and only then locked by DELETE after selection. Or does it re-evaludate the SELECT even though it is in a subquery?
node --unhandled-rejections=strict ./parallel_create_delete_empty_tag.js p 9 1000 'REPEATABLE READ': repeatable read
We've never observed any failures with this level. This should likely fix the foreign key issue according to the PostgreSQL docs, since:
- the DELETE "Post" commit cannot start to be seen only in the middle of the thread 1 transaction
- and then if DELETE happened, the thread 1 transaction will detect it, ROLLBACK, and re-run. TODO how does it detect the need rollback? Is it because of the foreign key? It is very hard to be sure about this kind of thing, just can't find the information. Related: postgreSQL serialization failure.
node --unhandled-rejections=strict ./parallel_create_delete_empty_tag.js p 9 1000 'SERIALIZABLE': serializable
node --unhandled-rejections=strict ./parallel_create_delete_empty_tag.js p 9 1000 'NONE': magic value, don't use any transaction. Can blow up of course, since even less restrictions than READ COMMITTED

All executions use 2 threads.

Some theoretical notes:

Failure case 3 is averted by a READ COMMITTED transaction, because thread 2 won't see the uncommitted tag that thread 1 created, and therefore won't be able to delete it

stackoverflow.com/questions/10935850/when-to-use-select-for-update from SELECT FOR UPDATE also talks about a similar example, and has relevant answers.

Open source LLM by

Ciro Santilli 40 Updated 2025-07-19

A Three-Dimensional Model of the Myoglobin Molecule Obtained by X-Ray Analysis (1958) by

Ciro Santilli 40 Updated 2025-07-16

www.nature.com/articles/181662a0 on Nature. Paywalled as of 2022.

Non-coding DNA by

Ciro Santilli 40 Updated 2025-07-16

Metabolism by

Ciro Santilli 40 Updated 2025-07-16

Urine by

Ciro Santilli 40 Updated 2025-07-16

nodejs/sequelize/raw/parallel_select_and_update.js by

Ciro Santilli 40 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:

SELECT FROM to get i
update on Js code newI = i + 1
UPDATE SET the newI

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:

node --unhandled-rejections=strict ./parallel_select_and_update.js p 2 10 'READ COMMITTED'

which does:

PostgreSQL, see other databases options at SQL example
2 threads
10 increments on each thread

Another one:

node --unhandled-rejections=strict ./parallel_select_and_update.js p 2 10 'READ COMMITTED' 'FOR UPDATE'

this will run SELECT FOR UPDATE rather than just SELECT

Observed behaviour under different SQL transaction isolation levels:

READ COMMITTED: fails. Nothing in this case prevents:
- thread 1: SELECT, obtains i = 0
- thread 2: SELECT, obtains i = 0
- thread 2: newI = 1
- thread 2: UPDATE i = 1
- thread 1: newI = 1
- thread 1: UPDATE i = 1
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. With p 10 100, REPEATABLE READ was about 4.2s and READ COMMITTED + SELECT FOR UPDATE 3.2s on Lenovo ThinkPad P51 (2017).
SELECT FOR UPDATE should be enough as mentioned at: www.postgresql.org/docs/13/explicit-locking.html#LOCKING-ROWS
FOR 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.

Metabolic pathway by

Ciro Santilli 40 Updated 2025-07-16

Some notable examples:

citric acid cycle

Richard Feynman's drug use by

Ciro Santilli 40 Updated 2025-07-16

From Surely You're Joking, Mr. Feynman chapter O Americano, Outra Vez!:

The people from the airlines were somewhat bored with their lives, strangely enough, and at night they would often go to bars to drink. I liked them all, and in order to be sociable, I would go with them to the bar to have a few drinks, several nights a week.
One day, about 3:30 in the afternoon, I was walking along the sidewalk opposite the beach at Copacabana past a bar. I suddenly got this treMENdous, strong feeling: "That's just what I want; that'll fit just right. I'd just love to have a drink right now!"
I started to walk into the bar, and I suddenly thought to myself, "Wait a minute! It's the middle of the afternoon. There's nobody here, There's no social reason to drink. Why do you have such a terribly strong feeling that you have to have a drink?" - and I got scared.
I never drank ever again, since then. I suppose I really wasn't in any danger, because I found it very easy to stop. But that strong feeling that I didn't understand frightened me. You see, I get such fun out of thinking that I don't want to destroy this most pleasant machine that makes life such a big kick. It's the same reason that, later on, I was reluctant to try experiments with LSD in spite of my curiosity about hallucinations.

One notable drug early teens Ciro consumed was Magic: The Gathering, see also: Section "Magic: The Gathering is addictive".

Amnion by

Ciro Santilli 40 Updated 2025-07-16

AI research entity by

Ciro Santilli 40 Updated 2025-07-16

Population inversion by

Ciro Santilli 40 Updated 2025-07-16

Pentane interference by

Pentane interference typically refers to the impact that pentane, a straight-chain hydrocarbon with five carbon atoms, can have on various chemical analyses, particularly in chromatographic methods. In the context of gas chromatography or mass spectrometry, pentane can co-elute with other compounds, potentially leading to inaccurate results or difficulties in identifying and quantifying other analytes.

Suspension (film) by

"Suspension" is a film that was released in 2015. It is a psychological horror film directed by Dave R. Sheppard, featuring a storyline that revolves around a group of friends who find themselves trapped in a series of bizarre and suspenseful situations. The narrative often intertwines elements of fear and the supernatural, typical of the horror genre. The film delves into themes of isolation and psychological strain, often keeping viewers on edge through its suspenseful atmosphere and twists in the storyline.

Suvini Zerboni by

As of my last update in October 2023, there is no widely recognized entity or subject known as "Suvini Zerboni." It’s possible that it could refer to a person, a brand, or a concept that emerged after that date, or it might be a relatively niche or obscure reference.

Per Carlqvist by

Per Carlqvist is a name that could refer to different individuals or contexts, but it's not widely recognized in popular culture, politics, or science as of my last knowledge update in October 2023.

Swedish nuclear physicists by

"Swedish nuclear physicists" refers to scientists from Sweden who specialize in the field of nuclear physics, which is the study of atomic nuclei, their constituents, and interactions. This field encompasses a variety of topics, including nuclear decay, nuclear reactions, and the properties of nuclear matter. Sweden has contributed significantly to nuclear physics research and development, particularly through institutions like the Uppsala University, Lund University, and the Swedish National Space Agency.

Symposium on Theoretical Aspects of Computer Science by

The Symposium on Theoretical Aspects of Computer Science (STACS) is a renowned academic conference that focuses on theoretical computer science. It serves as a venue for researchers to present their work, exchange ideas, and discuss various aspects of theoretical foundations related to computer science. The topics covered in STACS typically include areas such as algorithms, complexity theory, automata theory, formal languages, logic in computer science, and computational models.