Today I Learned

[jack action]

 

[mfb]

TIL about Roman dodecahedrons. They have been found in many places, so they were clearly a thing - but no one knows why.

 

[fresh_42]

TIL about Roman dodecahedrons. They have been found in many places, so they were clearly a thing - but no one knows why.

That is completely clear to me. It is a "Knochen". Sorry, I have no idea how to find the English word for it.

 

[Tom.G]

That is completely clear to me. It is a "Knochen". Sorry, I have no idea how to find the English word for it.

View attachment 281411

In the U.S. it is a "Dog Bone Wrench."

 

[mfb]

That is completely clear to me. It is a "Knochen". Sorry, I have no idea how to find the English word for it.

With round holes with inconsistent diameter?

Knochen=Bone

 

[fresh_42]

With round holes with inconsistent diameter?

Knochen=Bone

The Romans were around in many places. They've found the artifact only in Celtic areas. Ergo: universal beer bottle opener!

 

[Frabjous]

TIL about Roman dodecahedrons. They have been found in many places, so they were clearly a thing - but no one knows why.

I always like when we find mysterious ancient tech. It keeps us humble.

I also like the line from the wiki
”A Roman icosahedron has also come to light after having long been misclassified as a dodecahedron.”

 

[jack action]

TIL about Roman dodecahedrons. They have been found in many places, so they were clearly a thing - but no one knows why.

I knew what to do with those when I was 2 years old:

 

[Keith_McClary]

They've found the artifact only in Celtic areas. Ergo: universal beer bottle opener!

Hmm. So much for my spagghetometer theory.

 

[hmmm27]

They've found the artifact only in Celtic areas. Ergo: universal beer bottle opener!

Snake trap, invented by an ex-Roman slave.

 

[berkeman]

TIL that when you see a Fire Engine with big black pipes on top (instead of the usual wooden ladders), those are used for siphoning water from standing water sources (ponds, pools, rivers, etc.) when fighting fires.

I saw such an apparatus on my commute home recently here in Silicon Valley, and had never seen one like it before. I posted on Facebook about it, and luckily a Fremont Fire Captain (that I have worked with in the past) responded with a great and detailed explanation. Makes sense now!

Pipes? Are you looking at the black hoses in this picture? Most of the hose on the engine is soft and requires positive water pressure to operate. The black hoses are rigid and are used for drafting water from a static water source. (More about drafting below...)

The ladders are probably in an internal compartment accessed from the rear of the apparatus. The old model had ladders on the exterior of the passenger side at about shoulder level. That greatly limited the amount of storage available on the engine. The first solution was to add a hydraulic rack to store the ladders up high. The ladders would rotate from a horizontal position above the hose bed to a vertical position beside the engine. This system also worked adequately, but it did require maintenance on the hydraulic system which moved the ladders and the pneumatic system which locked them into place. The increased the storage space, but required extra clearance beside the engine, limited access to the cabinets when the ladders were lowered and left the ladders exposed to the elements.

Back to drafting... The main pump on a fire engine is normally a centrifugal pump. Such a pump is used because it can add pressure to a pressurized water source like a hydrant. It cannot pump air.

The engine also has a small "primer pump" which is a positive displacement pump. A positive displacement pump CAN pump air, but it cannot add pressure to a pressurized source. We use the primer pump to remove air from the pump so the pump is fully filled

We also use the primer pump for drafting. To draft, we position the engine near a static water source like a pond or swimming pool. (It could be a river or large stream, but we're looking for a large volume of water.) We place a strainer on the end of the hard suction hose (black hose in picture). That hose is relatively rigid, so it will not collapse if negative pressure is applied. So, the primer pump is operated with starts pulling air from the hard suction. This creates a lower pressure in the hose. Atmospheric pressure forces the water from the water source into the hard suction to try to equalize the internal and external pressures. If things go right, you fill the hose and main pump and hose with water. At that point, you can operate the main pump. As long as you keep water circulating and don't end up with any air leaks into the system, you can keep pumping as long as the water source has water.

I have never had to use the large hard suction on a real incident. I have used smaller hoses for drafting during wildland fires - both directly to the engine and with a small portable pump.
If I'm completely wrong and you weren't looking at the black hard suction hose and there were really pipes somewhere on that engine, let me know and I'll call down there and ask them why they're driving around with pipes on their engine. That would be a new one for me.

>The black hoses are rigid and are used for drafting water from a static water source.

Thanks Cap!

That's very helpful and answers my question. I'd just never seen rigid drafting hoses that big on a fire apparatus before. Great info, as usual

 

[etotheipi]

So-called "toughened glass" isn't always tougher; windscreen manufacturers deliberately quench the surface with jets of air to impart residual compressive stresses to the glass, so that upon fracture the greater strain energy release rate causes the glass to shatter into many more, smaller and less-dangerous shards (whose formation exposes are greater amount of new surface area $\leftrightarrow$ greater surface energy cost). In other words, it's desirable to promote crack propagation!

 

[pinball1970]

Today I learned your name is the Euler identity.
I thought it was some mythical thing like Yggdrasil all this time.
@etotheipi

 

[fresh_42]

Today I learned your name is the Euler identity.
I thought it was some mythical thing like Yggdrasil all this time.
@etotheipi

It is a war cry! "Eeeeee! To the pie!"

 

[Twigg]

How did I not catch that before... Here I've been wondering what kind of epithet "the ipee" was

 

[Borg]

I always read it too quickly and it registers as a country to me.

 

[pinball1970]

How did I not catch that before... Here I've been wondering what kind of epithet "the ipee" was

It looks Egyptian to me, the mummy's name in the film the mummy was Imhotep,

Imhotep,
etotheipi

 

[jack action]

I always read it too quickly and it registers as a country to me.

The same with me! In French, the country's name is Éthiopie, which is one T short of @etotheipi . I always felt dyslexic reading that name! But - since we are in this thread - TIL I was actually experiencing typoglycemia.

 

[pinball1970]

How did I not catch that before... Here I've been wondering what kind of epithet "the ipee" was

The same with me! In French, the country's name is Éthiopie, which is one T short of @etotheipi . I always felt dyslexic reading that name! But - since we are in this thread - TIL I was actually experiencing typoglycemia.

Its not like I worked it out, either it was a maths thread on pf about Euler formula having irrational numbers or something and Etotheipi, responded “I am not irrational!”
I wondered what he talking about then it hit me!

Ethiopie is very close – you win.Re typoglycemia

Sounds like extreme tiredness and low blood sugar resulting from a marathon lap top session.

 

[pinball1970]

TIL I know nothing about mathematics and i mean zero (I don't know about zero either)
Using maths for stuff is one thing, learning about what it actually is, the real structure, is another.
I always kind of knew this but I still always thought I could get by. When I have learned QM I am taking on Mathematics next.

 

[Janus]

TIL how to simulate a chain-mail animation without crashing Blender.
While Blender does have a pretty good physics simulator, and it is theoretically possible to do it with rigid body physics, doing so would take up vast amounts of computer resources to get any degree of accuracy (even doing swinging chain takes some work in order get it right.)
The following example has almost 1300 individual interlocked rings. Even if my computer didn't hang, it would take an extremely long time to work things out using rigid body physics.

However, I learned a better way.

Blender also has a cloth simulator, And while you can't apply it directly to the chain mail ( well you could, but the results would not behave right, as each individual ring would act like it was made of cloth.), what you can do is make a subdivided plane, give it the Cloth modifier, and then give the chain mail a Surface Deform modifier using the plane as the target. What this does is cause the chain mail model follows the movement of the plane.
You place the plane so it cuts through the chain mail like this:

The chain mail is bound to the plane with the modifier, When the animation is run, the plane drops onto the cylinder and drapes over it like cloth would, and the surface deform modifier causes the chain mail to follow it shape.
The plane is set not to render, so it isn't visible in the final product.

The end result is this:

 

[Tom.G]

TIL that there are things worse than snow. i.e. Invasion of Rome -- by Birds

 

[jack action]

TIL that there are things worse than snow.

What's wrong with snow? My best memories involve snow.

 

[BillTre]

TIL that OSU (Oregon State University), where my daughter goes to school, has little robot mini-car-things that drive around campus to deliver food service food:

They are pretty autonomous. Stop at corners, wait for cars.
Apparently one got hit by a train (tracks go through campus).

 

[DaveC426913]

TIL that OSU (Oregon State University), where my daughter goes to school, has little robot mini-car-things that drive around campus to deliver food service food:

View attachment 282357

Forgive, me ... your daughter is ... a beaver??
I mean, that is what it says...

 

[berkeman]

Forgive, me ... your daughter is ... a beaver??
I mean, that is what it says...

No, a beaver supporter. Beavers need all the support they can get (damn dams!).

 

[Tom.G]

a beaver??
Well, I tried very hard (obviously unsuccessfully) not to mention that word is sometimes used to refer to an anatomical region.

Oh well, delete if you must.

 

[pinball1970]

a beaver??
Well, I tried very hard (obviously unsuccessfully) not to mention that word is sometimes used to refer to an anatomical region.

Reminds me of naked gun

 

[epenguin]

TIL that there are things worse than snow. i.e. Invasion of Rome -- by Birds

I have often seen them. You can see them well from the Campidoglio and centre which they seem to prefer, typical tourists, and all roost in the trees along the Tiber, the Lungotevere, to judge from the daily state of cars parked there.

Giorgio Parisi, a leading luminary of Science in Rome, whose Physics is so advanced I don't even know what branch it's called, has made a study of the flocking dynamics: https://www.pnas.org/content/107/26/11865/tab-figures-data
(The paper also contains some film of the flocking - far from the biggest in the one I could see (the last one)).

 

[BigDon]

Do the Oregon State Beavers football team still wear Black and Negligee Orange?

(They had a phrase, "It takes a brave man to wear negligee orange!)

 

[Borg]

For some reason, it reminds me of the phrase at my college - Where men are men and women are too.

 

[BigDon]

So is it all right to place "recently learned" as opposed to today I learned?

Because I've been delving hard into myrmecology lately and have learned a lot we thought knew about ants was wrong, and even entomologists are passing along misinformation now. For instance:

One cannot conflate the functions of the majors of different genuses. Turns out the majors of leaf cutter ants are *not* a soldier class as in the army and driver ants but a class of heavy equipment operators. Atta cephaloides soldiers are their minors! (Not minums) The minors respond first, longest and most aggressively to nest invaders, including pursuing them several meters out of the nest.

Two other amusing facts about leaf cutters.

One is all workers have the same "information" but have one of four body shapes due to epigenetic factors relating to diet. So when a large major sees a particular job that needs doing but is incapable because of her size she will go and pick up a smaller worker, carry her over to the job site, and point her at it. 80 percent of the time the "recruited" ant will adopt the task.

In the presence of phorid flies, (parasitoids AND predators of worker ants) carnivorous members of the fruit fly clade, Atta colonies will send out majors with minums riding on their backs to act as a defensive force!

That's a little more clever than one would expect out of an insect.

(Phorids attack large ants from above and behind to lay their eggs on their necks. The young phorids use the ant's head capsule as a food source and as a chrysalis to metamorphize in.)

A counterintuitive discovery about the South American army ant species Eciton burchelli, the most studied species, is that while a group of them are more than capable of killing smaller vertebrates, they have one problem with doing so.

They can't eat them!

E. burchelli will readily kill small vertebrates but lack a shearing surface on their mandibles so they can't process them! (Other species in the genus can and do eat vertebrates, it's the burchelli that are the "weirdos".)

I never saw that one coming.

And then we get into the differences between old world and new world army ants and you see different prey adaptations. In the new world some insects can avoid predation simply by holding still. This never works with old world army ants.

Why?

None of them have eyes! So motion isn't important in prey detection. They can clear a much higher percentage of the local arthropods in a given area than the new world varieties, sometimes up to 85%.

 

[epenguin]

These flocks #3,761 #3,768 have been seen in Rome and in Naples to my recollection for decades, maybe the numbers have increased. Other changes in the bird population I believe fairly widespread in Europe are increases in the numbers and also the boldness and invasivity of seagulls (who never confined themselves exclusively to the sea) explainable by increased scavenging opportunities.

Another but really new coloniser of the last ten years or less now not rare to see and hear in London and in Rome and no doubt many other places is green parrots! There are lots in trees in streets near us and in a garden opposite. Day before yesterday for first time seen perching over our terrace!

 

[fresh_42]

Another but really new coloniser of the last ten years or less now not rare to see and hear in London and in Rome and no doubt many other places is green parrots! There are lots in trees in streets near us and in a garden opposite. Day before yesterday for first time seen perching over our terrace!

The last 50 years is closer to the truth:

In Germany, the first rose-ringed parakeets appeared in Cologne in 1969; in 2014 an estimated 3,000 specimens lived there. Other independent occurrences are along the Rhine, especially in Düsseldorf, Wiesbaden (together with Mainz 2011: approx. 1500 animals sleeping in summer), Worms, Mannheim, Ludwigshafen am Rhein (Ludwigshafen sleeping area - presumably with parakeets from Worms, Frankenthal and the few animals from the Rhine-Neckar area in summer 2011: 1640 animals) and Heidelberg. Based on these, new populations formed in Bonn, Mainz, Speyer and Zweibrücken. The settlement of the Rhine-Neckar area began in 1973. The first sightings in Frankfurt am Main date back to 2012. In Germany in 2006 the population was 6000–7000 individuals and 650–880 breeding pairs. For 2011 the population size for Germany was given as 7500 animals and around 1500 breeding pairs, the Federal Agency for Nature Conservation assumes a population of 1700–2500 breeding pairs for the years 2011–2016 on the basis of the DDA data.

 

[BillTre]

There are peacocks in the Eugene, Oregon area.
The LA area has peacocks and lots of parrots (at least 5 species).

They are noisy and often like to go in groups.
I had shared a house with a guy once who have 3 or 4 parrots. They make good alarm clocks.
A group of parrots is called a pandemonium of parrots.

 

[BigDon]

Coit Tower in San Francisco has green conures. But whenever they try to expand to new locations the local Cooper's hawks make short work of them.

 

[pinball1970]

There are peacocks in the Eugene, Oregon area.
The LA area has peacocks and lots of parrots (at least 5 species).

They are noisy and often like to go in groups.
I had shared a house with a guy once who have 3 or 4 parrots. They make good alarm clocks.
A group of parrots is called a pandemonium of parrots.

Some good collective names for bird species

Murder of crows
Parliament of Rooks...

 

[BillTre]

There are lots of murders where I live.
Have not heard of the rooks (thought they were a chess piece).
Guessing they hang out in groups and appear to be talking about something?

 

[strangerep]

Some good collective names for bird species

Murder of crows
Parliament of Rooks...

I'd always thought it was a "parliament of owls", but it seems that particular collective is used for multiple species.

Here's few more which I found amusing:

• A wake of buzzards
• A confusion of chiffchaffs
• A chattering of choughs
• A commotion of coots
• A murder of crows
• An asylum of cuckoos
• A curfew of curlews
• A trembling of finches
• A swatting of flycatchers
• A prayer of godwits
• A crown of kingfishers
• A parcel of linnets
• A cast of merlins
• A conspiracy of ravens
• A worm of robins
• A parliament of rooks
• An exultation of skylarks
• A murmuration of starlings
• A hermitage of thrushes
• A volery of wagtails
• A museum of waxwings
• A chime of wrens
• An orchestra of avocets
• A mural of buntings
• A water dance of grebes
• A booby of nuthatches
• A quilt of eiders
• A mischief of magpies
• An Aerie of eagles
• A wisdom of owls
• A quarrel of sparrows

I suppose the list could go on indefinitely. E.g., a septic tank of internet vultures...

 

[HAYAO]

Today I learned quitting smoking isn't so hard.

I wrote this about 4 years ago. I still haven't smoked since. Not so hard, but you have to firmly make that decision.

 

[Borg]

I suppose the list could go on indefinitely. E.g., a septic tank of internet vultures...

A cesspool of politicians?

 

[Frabjous]

I'd always thought it was a "parliament of owls", but it seems that particular collective is used for multiple species.

Here's few more which I found amusing:I suppose the list could go on indefinitely. E.g., a septic tank of internet vultures...

I disagree. Septic tanks have some utility.

 

[pinball1970]

I'd always thought it was a "parliament of owls", but it seems that particular collective is used for multiple species.

Here's few more which I found amusing:I suppose the list could go on indefinitely. E.g., a septic tank of internet vultures...

Some funny ones here

https://www.countrylife.co.uk/country-life/collective-nouns-for-people-and-professions-84184
I think terms for shepherds is a bit harsh
Nothing for physicists or Chemists
Mathematicians is a bit predictable , they could have been more inventive than “set” I think.

 

[etotheipi]

 

[mfb]

A collection of biologists
A (periodic) table of chemists?
An aggregate of solid state physicists

 

[jedishrfu]

A plethora of PFers.

 

[strangerep]

Some funny ones here

https://www.countrylife.co.uk/country-life/collective-nouns-for-people-and-professions-84184

I found most of those amusing, but,... er,...
"A smear of gynaecologists"...

I think terms for shepherds is a bit harsh

It could be worse: "A bestiality of shepherds"?
[Reference: ancient Dave Allen joke about a ventriloquist.]

 

[pinball1970]

I found most of those amusing, but,... er,...
"A smear of gynaecologists"... It could be worse: "A bestiality of shepherds"?
[Reference: ancient Dave Allen joke about a ventriloquist.]

Yeah the Gynaecologists seems rather unpleasant, mind you considering the area of expertise I suppose options for something less distasteful are limited.

A collection of biologists
A (periodic) table of chemists?
An aggregate of solid state physicists

One could have fun with this
A quantum (I also like entanglement) of physicists
A mole of chemists
An infinity of mathematicians – I would like @fresh_42 view on that
A byte of technologists
A megabyte of programmers
A plasma of particle physicists
A cluster of cosmologists
A manifold of geometers
Engineers?
From experience a Beer of Engineers would be a fit and it also has a ring to it.

 

[Janus]

TIL what the original Apollo mission design concept from North American Aviation looked like:
https://apollopreliminarydrawings.com/

 

[Ibix]

Today I learned that the Mission: Impossible theme is in 5/4 time, so the first two notes are a beat and a half long and the second two are a beat long and it kind of sounds like 4/4 with a speed change every second beat.

Apparently the inspiration for the rhythm was that two long beats and two short beats (dah dah dit dit) is Morse for MI.