Today I Learned

[mathwonk]

I have my own issues with Wikipedia. I often find useful information there about things I am ignorant of, but do not post on things I feel knowledgable about, after one experience, when I tried to post an answer to a question about the Riemann-Roch theorem.

My elementary and concrete version was quickly altered and eventually erased, in favor of a generic abstract modern account, written by someone possibly less conversant with, or less appreciative of, classical sources.

So to me the problem with Wikipedia is that everyone has license to edit work of others, leading to a sort of generic second or third hand homogenization of readily available treatments. Thus I often prefer individual signed explanations such as one can find here, and on mathoverflow, and tend to restrict my contributions to such sites.

 

[Swamp Thing]

I have often wondered what could have led Fourier to consider expressing the initial temperature profile in a rod in terms of many "wavy things" added up together, when there is no waviness at all in the problem itself.

But today I learned that he started out with a simpler problem -- the diffusion of heat along an "anchor ring", a metal ring used to attach a chain to an anchor. Of course, the temperature profile on the ring is periodic in the sense that it repeats as you move along the ring over and over; and this gave him the germ of the idea of expressing any temperature profile on the ring in terms of many waves that "close" exactly over the ring.

https://www.yalescientific.org/2010/12/fourier-transform-natures-way-of-analyzing-data/#:~:text=The question itself was complicated,sinusoidal waves around the ring.

https://iopscience.iop.org/article/10.1088/1361-6404/acdf2e/pdf

There are also accounts that claim he went "eureka" when he happened to see an actual anchor ring, but this seems to be historically uncertain.

 

[jack action]

Today I learned that Canada has its own "Grand Canyon" called The Gully but ... it's underwater! It's a protected area, home to many marine species.

​

The Gully is located approximately 200 kilometres off Nova Scotia to the east of Sable Island on the edge of the Scotian Shelf. Over 65 kilometres long and 15 kilometres wide, the Gully is the largest underwater canyon in the western North Atlantic. The movement of glaciers and meltwater erosion formed the canyon approximately 150,000 to 450,000 years ago, when much of the continental shelf was above the current sea level.

The Gully ecosystem encompasses shallow sandy banks, a deep-water canyon environment, and portions of the continental slope and abyssal plain, providing habitat for a wide diversity of species. The Gully’s size, shape, and location have an effect on currents and local circulation patterns, concentrating nutrients and small organisms within the canyon.

The Gully is home to the endangered Scotian Shelf population of Northern bottlenose whales and is an important habitat for 15 other species of whales and dolphins. Tiny plankton, a variety of fish such as sharks, tunas and swordfish, and seabirds inhabit surface waters, while halibut, skates, cusk and lanternfish can be found as deep as one kilometre. The ocean floor supports crabs, sea pens, anemones, brittle stars, and approximately 30 species of cold-water corals.

 

[docnet]

Should have posted how I found out about it - a recent deployment:

The video is a minute and a half and mostly air traffic control communications, but there's some mobile phone footage at the end of the thing coming down.

Wow, that's wild. I wonder if the airplane has to be scrapped afterwards because of safety concerns.

 

[Ibix]

Wow, that's wild. I wonder if the airplane has to be scrapped afterwards because of safety concerns.

According to the Wiki link in the post above the one you quoted, "The goal of employing this system is the survival of the crew and passengers and not necessarily the prevention of damage to the airframe". So you definitely need to take it to the shop before taking off again...

 

[DaveE]

I wonder if the airplane has to be scrapped afterwards because of safety concerns.

The vertical speed is about 17 knots (1700 fpm). Then there's the question of what you hit at that speed. So the expectation is that the airframe will be scrapped. But, IDK, maybe if your lucky and spend a bunch of money... I wouldn't buy that airplane.

 

[Astronuc]

YIL,

(Reuters) -Telecom company AT&T said on Saturday that it is investigating a data set released on the "dark web" about two weeks ago, and said that its preliminary analysis shows it has impacted approximately 7.6 million current account holders and 65.4 million former account holders.

The company said the data set appears to be from 2019 or earlier. AT&T said it does not have evidence of unauthorized access to its systems resulting from the incident.

https://finance.yahoo.com/news/t-says-leaked-data-set-142120306.html

 

[Astronuc]

TIL about Lincombian-Ranisian-Jerzmanowician complex.
https://en.wikipedia.org/wiki/Lincombian-Ranisian-Jerzmanowician

The technocomplex is named after findings in Kents Cavern, Lincombe Hill, Torquay (Devon, England), the cave of Ilsenhöhle in Ranis (Thuringia, Germany), and the Jerzmanowicien cave in Ojców (Kraków County, Poland).

https://www.msn.com/en-us/news/tech...timeline-of-ancient-human-history/ar-BB1iaEuR

https://www.cnn.com/2024/02/01/europe/ancient-tools-humans-neanderthals-europe-scn/index.html

Nature - Homo sapiens reached the higher latitudes of Europe by 45,000 years ago
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10849966/

 

[F X]

OK now I just learned about that as well. Thanks

 

[gmax137]

He just grinned and shook my hand. "No", was all he said!

So, I went to the webz to read the entire lyrics of "The Weight," and found this:
"Take a load off Fanny..."
I had always heard "Annie" not "Fanny." That's after listening to Big Pink for 50 years.

 

[DaveE]

So, I went to the webz to read the entire lyrics of "The Weight," and found this:
"Take a load off Fanny..."
I had always heard "Annie" not "Fanny." That's after listening to Big Pink for 50 years.

TIL "Fanny" was a Jewish bookseller in NYC.
https://forward.com/culture/music/3...and-roll-songs-of-all-time-was-inspired-by-a/

 

[Astronuc]

So, I went to the webz to read the entire lyrics of "The Weight," and found this:
"Take a load off Fanny..."
I had always heard "Annie" not "Fanny." That's after listening to Big Pink for 50 years.

I thought it was Manny.


My favorite song by The Band is Chest Fever. I do not get the lyrics, but I like the organ and piano. I never did get poetry, although there are some poems I like and do understand.





Lyrics

I know she's a tracker
Any style that would back her
They say she's a chooser
But I just can't refuse her
She was just there, but then she can't be here no more
And as my mind unweaves
I feel the freeze down in my knees
But just before she leaves, she receives
She's been down in the dunes
And she's dealt with the goons
Now she drinks from a bitter cup
I'm trying to get her to give it up
She was just here, I fear she can't be there no more
And as my mind unweaves
I feel the freeze down in my knees
But just before she leaves, she receives
It's long, long when she's gone
I get weary holding on
Now I'm coldly fading fast
I don't think I'm gonna last very much longer
"She's stoned, " said the Swede
And the moon calf agreed
But I'm like a viper in shock
With my eyes in the clock
She was just there somewhere and here I am again
And as my mind unweaves
I feel the freeze down in my knees
But just before she leaves, she receives

 

[Tom.G]

Those lyrics read like a drug hallucination!

 

[Hornbein]

Those lyrics read like a drug hallucination!

It was the 60's. They got their big break as Bob Dylan's band. He was/is highly respected for this kind of thing.

I don't care about sense in lyrics. If it sounds good, it is good. Lyrics are also at the bottom of my musical priority list. My focus goes elsewhere.

 

[BillTre]

TIL that Lucy the fossil (named for the Beatle's song "Lucy in the Sky with Diamonds") is 50 years old (time above the ground).
Closer to 3 million in total age.

 

[BillTre]

TIL there are RNAs in mouse neurons that have exist in cells 2 years (a significant part of the mouse's lifespan). Very unusual.
They are thought to have something to do with maintaining chromatin (chromatin vs. heterochromatin) structure in particular neurons.

 

[Swamp Thing]

Today I learned that in one of his Lectures, Feynman estimated that the age of the stuff at the center of the earth is about a day older than stuff at the surface, a la General Relativity. This idea then remained embedded in the conventional wisdom canon for decades. Only in 2016 did someone fact-check Feynan on this ... https://iopscience.iop.org/article/10.1088/0143-0807/37/3/035602 ... Turns out, GR says the core is around 2.5 years older than the surface.

Edit: Core younger. Thanks, collinsmark.

 

[collinsmark]

Today I learned that in one of his Lectures, Feynman estimated that the age of the stuff at the center of the earth is about a day older than stuff at the surface, a la General Relativity. This idea then remained embedded in the conventional wisdom canon for decades. Only in 2016 did someone fact-check Feynan on this ... https://iopscience.iop.org/article/10.1088/0143-0807/37/3/035602 ... Turns out, GR says the core is around 2.5 years older than the surface.

I think you mean "younger." But whatever the case, interesting.

 

[Orodruin]

Turns out, GR says the core is around 2.5 years older than the surface.

Younger. The article says so as well.

 

[pinball1970]

T.I.L. Voyager 1 problem has been identified

https://blogs.nasa.gov/voyager/2024...e-of-voyager-1-issue-are-working-on-solution/

 

[Swamp Thing]

TIL that magnetic compasses are made slightly unbalanced so that they won't scrape against the glass or the lower plate due to magnetic dip, and you don't need to tilt the case to keep the pointer free. The compasses' imbalance is tailored for the intended latitude.

And then there are "global" compasses that use a little trick to solve this problem...

 

[Hornbein]

TIL that magnetic compasses are made slightly unbalanced so that they won't scrape against the glass or the lower plate due to magnetic dip, and you don't need to tilt the case to keep the pointer free. The compasses' imbalance is tailored for the intended latitude.

And then there are universal compasses that use a little trick to solve this problem...

Is the imbalance in an angled plane of magnetization?

 

[Swamp Thing]

Yes, they add a bit of weight that opposes the effect of dip (inclination).

 

[pinball1970]

T.I.L An eclipse and supernova visible in the same year?

EDIT: Nova not supernova

https://blogs.nasa.gov/Watch_the_Skies/2024/02/27/view-nova-explosion-new-star-in-northern-crown/

 

[Orodruin]

T.I.L An eclipse and supernova visible in the same year?

https://blogs.nasa.gov/Watch_the_Skies/2024/02/27/view-nova-explosion-new-star-in-northern-crown/

Nova, not supernova.

A star that goes supernova will not do so again.

 

[Orodruin]

For some reason this brought me to look up apparent magnitudes of different objects in the sky. Found this on Wikipedia:

Apparently Betelgeuse is expected to be almost as bright as a full Moon when it goes boom. Easily visible during the day (assuming it is on the right side).

Just imagine all we would learn from the neutrino signal alone! Some precision neutrino astronomy right there, waiting to be made.

 

[Hornbein]

Nova, not supernova.

A star that goes supernova will not do so again.

Neutron stars near an ordinary star may suck off hydrogen until the intense gravity and heat triggers a star-wide thermonuclear explosion. They can do that over and over. I don't know what the catchword is.

 

[jack action]

After witnessing the eclipse, I tried to imagine how terrifying it would appear to people not knowing what was happening. TIL it actually may have stopped a war:

The Battle of the Eclipse (or Battle of Halys) was fought in the early 6th century BC in Anatolia (present-day Turkey) between the Medes and the Lydians. According to ancient Greek historian Herodotus, the battle was interrupted by "day turning into night" – presumably a solar eclipse – and the result was a draw which led to both parties negotiating a peace treaty and ending a six-year war.

 

[BillTre]

TIL about ancient technology:

 

[jtbell]

TIL that the San Francisco Municipal Transportation Agency still uses 5.25 inch floppy disks to boot up its Automatic Train Control System that runs light-rail trains in the Market Street subway.

https://arstechnica.com/gadgets/202...-to-help-run-san-francisco-trains-until-2030/