# Today I learned

#### pinball1970

Gold Member
The best way to learn something is to teach it. But I learned that a long time ago. While teaching.
If you can't explain it to someone else then you don't understand it. Feynman?
Edit, No it was Einstein and it was, 'If you can't explain it simply...'

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#### Stavros Kiri

TIL that Switzerland has a real good law: What once is forest, has to stay forest!
In Oregon, its more like:
what was once forest, if now it is made not forest,
replant it to make it forest again (for a while).
I've also seen the logic 'burn forests to expand cities!' ... Too bad, I tell you that.

#### Klystron

Gold Member
Today I learned more about salt water pools and water quality.

Our Fair City, famous in song and story for scams and corruption that would cause a Vampire to blush, has issued new health regulations on allowable levels of cyanuric acid (CYA) in swimming pools forcing pool owners to change the water ~once a week. In the desert.

CYA is added as a component of the "approved" chlorine tablets added to ensure water quality, delaying UV effects on free chlorine in swimming pools. The only information on the new regulations I can find so far is written by swimming pool maintenance companies who profit greatly from the new regulations. The City health regulations remain impenetrable.

I am trying to educate local home owners on the benefits of salt water pools with a simple ionizer to dissociate the sodium and chlorine from table salt disolved in the water. The chlorine and salt are almost unnoticeable while the sodium "softens" the water and feels silky smooth.

#### Tom.G

That cyanuric acid limit seems to apply to public pools (including HOA maintained ones), not private pools. See:

#### Tom.G

I am baffled why the HOA pool maintenance contractor uses so much CYA?
Because he can earn more profit that way? It's easier than testing for the acid?

I know only what I read in the references I supplied, but apparently the acid accumulates in the water and even clings to the pool walls upon emptying. Don't know if it stays active re the Chlorine but might be worth investigating.

BTW my references were found with:

Cheers,
Tom

p.s. the 'CYA' abbreviation works in context but was initially interpreted as 'Cover Your A**'!

#### A M

It is based on trophy points, the increasing levels are in increasing mass and size (until it goes into the speculative region).
Yes, the increasing PF levels are in increasing both mass and size.
But there are some exceptions; e.g. Quarks are -at least 4 times- more massive than Electrons. In this case, only their size is notable. (Electrons are larger than Quarks; so 0≤Quark<10<Electron)
I noticed that I am a pf molecule the other day and I thought it was very sweet
I've just found a relation between trophy levels: (numbers are trophy points)

0Quark<10<Electron<30<Atom<50<Molecule<100<Cell<150<Organism<200<Mountain
200<Mountain<300<Ocean<400<Asteroid<500<Moon<600<Planet<700<Star<800<Galaxy
800<Galaxy<900<SuperCluster<1000<Universe<1100<Multiverse<1200<Singularity<1300

(The only member that has reached singularity is fresh_42, so the next level is Unknown at present.)
By my relation, you can find out the correct order of these levels and calculate how many trophies you need to reach next achievements.
Hope that it will be helpful for members not so familiar with PF.
A M

#### mfb

Mentor
Mountain and galaxy are there twice.

Both quarks and electrons are expected to be point-like, but the wave function of quarks is typically confined to a smaller space than electrons.

#### A M

Mountain and galaxy are there twice.
I think that would make it easier to analyze. (To avoid little confusion due to multiple lines.)
but the wave function of quarks is typically confined to a smaller space than electrons.
And that's why: 0≤Quark<10<Electron

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#### epenguin

Homework Helper
Gold Member
I am trying to educate local home owners on the benefits of salt water pools with a simple ionizer to dissociate the sodium and chlorine from table salt disolved in the water. The chlorine and salt are almost unnoticeable while the sodium "softens" the water and feels silky smooth.
Sounds relaxing, your worries dissolve, Then so do you?

#### epenguin

Homework Helper
Gold Member
Today I learnt that nearly all the bananas in the world are practically a clone, that reproduces asexually, so cannot easily adapt nor do breeders have a great resources to combat a new menace of a fungal infection which after having devastated in Asia and Africa is turning up also in Columbia.

I didn't wish to know that.

#### phinds

Gold Member
Today I learnt that nearly all the bananas in the world are practically a clone, that reproduces asexually, so cannot easily adapt nor do breeders have a great resources to combat a new menace of a fungal infection which after having devastated in Asia and Africa is turning up also in Columbia.

I didn't wish to know that.
I read an article some time back that said all the bananas we eat today are an inferior species that was all that could be recovered and re-populated from a massive banana blight in the (I think it was) early part of the 1900's and that if another such blight occurs it will likely again totally wipe out the current banana species.

Where I've said "species" it's possible I should have said "hybrid". Not sure.

#### fresh_42

Mentor
2018 Award
Here's a list of a few of our breeds compared to wild ones - and corn is missing, which also looks tremendously different now and then:

#### Klystron

Gold Member
Today I learnt that nearly all the bananas in the world are practically a clone, that reproduces asexually, so cannot easily adapt nor do breeders have a great resources to combat a new menace of a fungal infection which after having devastated in Asia and Africa is turning up also in Columbia.

I didn't wish to know that.
As a child in the 1960's I remember eating bananas or plantains from a private garden planted circa 1868 in Santa Barbara CA. Do not remember colors but they were shorter wider flatter than Dole store-bought, bittersweet with small soft seeds. The plants were tall enough to shade upper floors; like bamboo with yummy fruit.

They were gone a few years later when I lived at the college. "Attracted rats." said Brother Caretaker.

[Edit: Brother Simon, a man of few words, actually said "Ratten" in German. The other kids thought he said "rotten" as in spoiled fruit. We spent that afternoon clearing overgrown prickly pear cactus. I learned a new word glochid.]

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#### pinball1970

Gold Member
As a child in the 1960's I remember eating bananas or plantains from a private garden planted circa 1868 in Santa Barbara CA. Do not remember colors but they were shorter wider flatter than Dole store-bought, bitter and had small soft seeds. The plants were tall enough to shade upper floors; like bamboo with yummy fruit.

They were gone a few years later when I lived at the college. "Attracted rats." said Brother Caretaker.
I hope these wild types are all in botany labs around the world. We never know when we may need to reintroduce them.

#### Lewis Goudy

Today I learned that the bond formed by red oak and Titebond III is over twice as strong as that formed by any other domestic (US) wood and any other glue tested: a traditional yellow glue (PVA), a Type I waterproof PVA [Titebond III], a liquid hide glue, a hot hide glue, a slow-set epoxy, and a polyurethane. (Case Western Reserve 2007).

#### diogenesNY

Maybe not today... but a few days ago I learned:

A library that I frequent has an (online) institutional subscription to the journal _Nature_.

Not only does this solve a paywall problem, but I now have an all new time-sync.

diogenesNY

#### Drakkith

Staff Emeritus
2018 Award
Not only does this solve a paywall problem, but I now have an all new time-sync.
Did you mean a 'time-sink', or are you syncing your reference frames?

#### diogenesNY

My dear Mr. Lexicop.... while I was almost inclined to plead fully and totally guilty to the former....... I think I will just claim the latter on the basis of: "well, if _Nature_ isn't a sufficiently authoritative source, well, then to the devil with all of it!" and why the hell not? :)

diogenesNY

#### Drakkith

Staff Emeritus
2018 Award
TIL that pink Himalayan salt, when escaping from an open container that your girlfriend's daughter just tossed into the air while dancing in the kitchen, looks oddly similar to what happens when two galaxies interact with each other. A beautiful arc of pink color, like the arc of gas, dust, and stars following the interaction.

#### Stavros Kiri

TIL that pink Himalayan salt, when escaping from an open container that your girlfriend's daughter just tossed into the air while dancing in the kitchen, looks oddly similar to what happens when two galaxies interact with each other. A beautiful arc of pink color, like the arc of gas, dust, and stars following the interaction.
Drakkith! ..., I thought you knew!?! ...

Staff Emeritus
2018 Award

#### Klystron

Gold Member
TIL... or realized that what seems like an advantage in one physics application can be a disadvantage to another. Specifically, I like the narrow bandwidth inherent in klystron designs centered around a particular wavelength, given the tendency of individual tubes to vary.

What I learned or realized: many physics labs require large bandwidth RF sources. Makes sense. Now I understand some of the frustration experienced by tube manufacturers such as Varian Associates. Radar and communication types demand tight bandwidths with minimal frequency drift while laboratories want a single (expensive) device to produce as much spectrum as possible to power a large variety of experiments.

"Today I learned"

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