Today I Learned

[Ibix]

Today I learned that King George III donated his large private library to the nation and it became the British Library.

It's actually on display around the cafe on the first floor (in huge glass-fronted cases - you can't read one of his books while you munch on a croissant). When CV-19 has gone away, if you are around Kings Cross/St Pancras and fancy an over priced coffee, pop in for a look.

 

[Astronuc]

TIL that ZZ Top grew out of a group called Moving Sidewalks, which was influenced by 13th Floor Elevators. Gibbons was the guitarist for Moving Sidewalks. After two members of Moving Sidewalks were drafted, the band ceased and Gibbons form ZZ Top with bassist/organist Lanier Greig and percussionist Dan Mitchell. Greig was susequently replaced by bassist Billy Ethridge, a bandmate of Stevie Ray Vaughn, and Mitchell was replaced by Frank Beard of America Blues. Ethridge quit the band and Dusty Hill replaced him.

The name of the band was Gibbons's idea. The band had a little apartment covered with concert posters and he noticed that many performers' names used initials. Gibbons particularly noticed B.B. King and Z.Z. Hill among the posters and thought of combining the two into "ZZ King", but considered it too similar to the original name. He then figured that "king is going at the top" which brought him to "ZZ Top."
https://en.wikipedia.org/wiki/ZZ_Top#Early_years_(1969–1972)

NETFLIX has a documentary on ZZ Top and Billy Gibbons verified the story about the name of ZZ Top.

 

[mfb]

Two mathematical results that look wrong, but they are actually right:

log(1+2+3)=log(1)+log(2)+log(3)

If A and B are matrices and AB = A + B, then BA = B + A

 

[strangerep]

Two mathematical results that look wrong, but they are actually right:

log(1+2+3)=log(1)+log(2)+log(3)

Cool -- since log(2)+log(3) = log(2x3) = log(6).

 

[berkeman]

TIL that some USB cables are for charging only, and do not have the data twisted pair connected inside them.

https://www.androidrecovery.com/blog/fix-android-usb-device-not-recognized-but-charging.html

My Android phone stopped offering me the option of File Transfer when I connected it to my home laptop. I use that feature a lot, especially at work where I take a lot of documentation pictures with my phone. But all of a sudden connecting my phone did nothing other than to start charging it, and I could not find the USB connection from my phone or from my laptop. I also tried it on my work laptop which I have temporarily here at home during the shelter-in-place order, and still nothing.

But a quick Google search led me to the website above, and the very first suggestion turned out the be the problem. I had no idea that some innocent-looking USB cables did not have the data pair in them. Lordy!

Bad, bad USB cable in the middle. Good USB cable on the outside...

 

[BillTre]

Wow, there should be some designation of their lack of capability on them, instead of them being disguised.

 

[Keith_McClary]

Wow, there should be some designation of their lack of capability on them, instead of them being disguised.

According to this Answer a "charging-only" cable should not have the USB logo.

If the bad cable has it, you should complain to your reputable supplier.

 

[berkeman]

It did have it; I checked right after I saw Bill's reply. At least they could delete that center part of the trident to indicate power but no data. Sheesh!

 

[Keith_McClary]

It did have it

Is it from a reputable supplier?

 

[berkeman]

No clue. It was in a tangle of cables in our home computer supplies cabinet. In fairness, it may have once been attached to a wall-wart USB charger, but you would think that if it were not captured to the charger, that it would be a regular USB cable.

At least I now know what to check right away if my phone is not connecting to a computer when I plug in the USB cable. Now that I know that this is an issue, I know what to check right away (use a known-good cable).

 

[jtbell]

TIL that the US has a huge surplus of chicken wings, thanks to the cancellation of March Madness (the NCAA basketball tournament) and other sports events because of the coronavirus.

https://www.washingtonpost.com/business/2020/04/08/chicken-wings-coronavirus-march-madness/

 

[Jonathan Scott]

Today I learned, after many years, exactly what bird here (in the UK) goes "Tweep" at regular intervals - a common chaffinch, which I spotted in a nearby tree. I know the song of a chaffinch, but I didn't realize it also made that call.

I know quite a few birds by sight and sound, and with the beautiful spring weather here at the moment there seem to be a lot around. Yesterday from my back garden (in lockdown) I saw a red kite (which have now become more common than buzzards around here) and house martins (first day I've seen them back after migration), and a wren came to have a bath in our bird bath while I was sitting only a few feet away. A cheerful robin tried to get under my rake when I was collecting up old leaves so I stepped back to let it forage for a few minutes. A blackbird sang tunefully but loudly and incessantly from about 5.30am (when I shut the bedroom window) to dusk. It also came and called my attention with an alarm call to magpies grouping on a nearby roof (they attack blackbird nests) but went back to singing after I clapped a couple of times to frighten them off. A starling joined in the dusk chorus with all sorts of weird sound effects. Many other common birds appeared during the day. I sometimes can't resist teasing the collared doves or wood pigeons by imitating their calls (hooting by whistling using cupped hands) - they seem to have a very good sense of direction of sound, as they then fly over me making a mewing call (so far without bombing me).

 

[Borg]

Today I learned how bicycles can stay upright on their own.

 

[Ibix]

Today I learned that, although a bad workman may blame his tools, good tools make an enormous difference. My normal skill with a saw is good to ##\pm##1mm (or so...) each end and right angles are a rarity. Using a jig I inherited from my dad, I've just cut four planks to have right-angled ends and the same length to the point where I can only just feel a difference with my fingertips. And it was easy.

 

[berkeman]

Did you measure twice?

 

[Ibix]

Did you measure twice?

To the extent that putting two pieces back to back and aligning them with my fingers is measuring, yes. Several times, in fact. The degree of accuracy was... unexpected.

 

[BillTre]

Jigs are like applied geometry.
They can be very useful.

 

[BillTre]

A man accidentally ejected himself from a jet over France.
It was a surprise joy ride organized by coworkers.
He hit the eject button by accident.
CNN story here.

 

[mfb]

Fortunately, the man avoided seriously injury after tumbling to Earth in a field near the German border.

Oh no! The French are coming!

 

[strangerep]

Today I learned that, although a bad workman may blame his tools, [...]

I've come to really hate that cliche, ever since an idiot former boss once (tried to) use it against me when I insisted on using vi over emacs (even though all the other programmers in the group were emacs users). In fact, I was vastly more productive than all those other programmers, in terms of features implemented, and I was 2 orders of magnitude(!) better than them in terms of number of bugs per lines of code.

A good workman chooses good tools that give him/her the best results. An idiot boss prevents the good workman from doing so. <End rant>

Using a jig [...]

This is my current "jig".

It's one of the best things I've ever bought.

Hmm. Maybe I should start a new thread: "The Best Things You've Ever Bought" ?

 

[BillTre]

NASA’s ICESat-2 satellite (made to measure ice coverage with a green light laser) can unexpectedly map ocean depths to 40 meters.
Now that harbors are not so obscured by sediments stirred up by ships (due to Coronavirus changes in activity), it can measure channel and canal depths in some areas.
Science news article here.

 

[fresh_42]

TIL that 73 is the only Sheldon prime.
https://math.dartmouth.edu/~carlp/sheldon02132019.pdf

 

[Buzz Bloom]

TIL that 73 is the only Sheldon prime.
https://math.dartmouth.edu/~carlp/sheldon02132019.pdf

Hi fresh:

I could no acces the PDF youcited. I found the description at

https://en.wikipedia.org/wiki/73_(number)​

Here is a quote:

has the product property[3] (i.e., the product of its base-10 digits is precisely its index in the sequence of primes: 7 × 3 = 21 and 73 is the 21st prime number). It also has the mirror property[3] (i.e., its permutable prime 37 is the 12th prime number, which is, again, the reverse of 21). Because of these two properties, it is the sole Sheldon prime[4], an homage to Sheldon Cooper, the fictional theoretical physicist on the television show The Big Bang Theory who claimed that 73 is the best number.​

Regards,
Buzz

 

[Hsopitalist]

TIL that 73 is the only Sheldon prime.
https://math.dartmouth.edu/~carlp/sheldon02132019.pdf

Aaahhh. I can finally graduate from using 42. Thanks for this.

 

[fresh_42]

Aaahhh. I can finally graduate from using 42. Thanks for this.

Yes, but the emphasize lays on "graduate". We still have ##7\cdot 3 \cdot 2 = 42, 7-3=4 \text{ vs. } -4=3-7,## again a symmetry, which is why we have to multiply ##7\cdot 3## by another ##2##. And ##7\cdot 3 + 3\cdot 7 =42##.

The problem is, that ##73## is a lucky number. And Marvin doesn't like lucky numbers.

DYK that ##73!+1## and ##37!+1## are also prime?

 

[mfb]

We define a Super-Sheldon prime p as Sheldon prime with the additional condition that p!+1 and rev(p)!+1 must be prime as well.

Theorem: 73 is the only Super-Sheldon prime.
Proof: 73 is the only Sheldon prime, as shown in [1], and 73!+1 and 37!+1 are prime.

 

[fresh_42]

Yes, but "as shown in" is equally nasty. I haven't read the paper, only what was said about it elsewhere.
The authors had a nasty way to prove it. They showed that there is no Sheldon prime greater than ##10^{45}##. So there were only finitely many possibilities left, which they left to the reader to check.

I like these kind of proofs.

 

[fresh_42]

Aaahhh. I can finally graduate from using 42. Thanks for this.

Another interesting property: ##37## is fortunate and ##73## less fortunate.

 

[mfb]

TIL: "Can composite numbers be fortunate" is an actual unsolved question in mathematics.

(Fortunate number - unlike happy, lucky, ... numbers Fortunate numbers are named after a person)

 

[fresh_42]

TIL: "Can composite numbers be fortunate" is an actual unsolved question in mathematics.

(Fortunate number - unlike happy, lucky, ... numbers Fortunate numbers are named after a person)

Another example are Münchhausen numbers: ##n=a_na_{n-1}\ldots a_0=\sum_{k=0}^na_k^{a_k}##, which are named after a person.

 

[BillTre]

Billfish are not named after a person!

 

[mfb]

Salmonella has nothing to do with salmon, it was named after Daniel Salmon. By Joseph Lignières, after Theobald Smith discovered it.

 

[Adesh]

Today I learned that not all little brats fear this insect

I must devise some new ways for controlling those naughty little demons.

 

[Jonathan Scott]

Today I learned to be more careful when taking powers of matrices. I had used the following:
$$\begin{bmatrix}
a & 0 \\
0 & 0
\end{bmatrix} ^ n
=
\begin{bmatrix}
a^n & 0 \\
0 & 0
\end{bmatrix}
$$
... but I got an unexpected result for a case which included ##n = 0##, because any matrix to the power zero should be the identity matrix. My daughter kindly pointed out a more generally correct identity as follows:
$$\begin{bmatrix}
a & 0 \\
0 & 0
\end{bmatrix} ^ n
=
\begin{bmatrix}
a^n & 0 \\
0 & 0^n
\end{bmatrix}
$$
The term ##0^n## then correctly gives the identity matrix when ##n=0##, assuming ##0^0 = 1##, and gives the same overall result as I had expected using my usual (Clifford Algebra) method of calculation.

 

[Klystron]

Today I learned that not all little brats fear this insect View attachment 260888

I must devise some new ways for controlling those naughty little demons.

Teach it to smoke a tiny hookah while sitting on a mushroom. You can discuss the nature of reality.

Reference: "Alice's Adventures in Wonderland" by Lewis Carroll.