Today I Learned

[hutchphd]

We have both lots of old people and lots of the "less important" people. Actually the vaccination program here has been surprisingly good (I got my second Moderna two weeks ago at the Kroger three blocks from my door...I am 69) so I am not personally very worried. Good thing I am computer literate (and white) of course.

 

[Jarvis323]

Whoaa! Life on Mars! They've found it!

NASA Announces Life on Mars

 

[Frigus]

Whoaa! Life on Mars! They've found it!

NASA Announces Life on Mars

I was about run on street shouting "nasa found life on Mars"

 

[Borg]

Whoaa! Life on Mars! They've found it!

NASA Announces Life on Mars

People should mark this day on their calendar.

 

[jack action]

 

[Frabjous]

Only during the undergraduate study. It turns out to be 22/7 in the master classes.

I like to think of myself as a 355/113 guy.

(355/113 - Pi ~ 2.7e-7)

 

[mfb]

I was about run on street shouting "nasa found life on Mars"

Life found NASA on Mars!

 

[Klystron]

Pi, shmi. I like e the base of the natural logarithms. And its first digit is to too, two to, tutu, 2 also.

 

[gmax137]

Pi, shmi. I like e the base of the natural logarithms. And its first digit is to too, two to, tutu, 2 also.

Here, let me help: "And its first digit is Desmond."

 

[Klystron]

Pi, shmi. I like e the base of the natural logarithms. And its first digit is to too, two to, tutu, 2 also.

Here, let me help: "And its first digit is Desmond."

Think... think... Desdemona?... Desiderius?... "click!"... "Desmond Tutu!" lol.

 

[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...