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[TheBiggerFish]

Shouldn't. Two semi-permeable membranes to stop the solute entering the pure water.

But if it has to flow down to...

[smirk]

As the water is re-filtered at the upper membrane on the way down to the generator, glucose would build up on the membrane, removing it from the main chamber below. Eventually there would be too much glucose jammed at that filter and not enough left down below to sufficiently raise the water level. Equilibrium reached.

I have no chemistry or maths training, so that's an educated guess. No idea how long it'd take.

[scrdest]

Let's see what would happen if there weren't a second membrane: the water goes up, flows through to the generator, then raises the amount of sugar in the pre-membrane side until it equalizes. Basic stuff.

So, what happens when we block it with a second membrane? You're trying to reverse-osmosis the water through that membrane using gravitation. That is impossible. Osmotic pressure is pressure, so it's not gravity you're looking for, it's pressure - and you need a gradient of it.

How much depends on the composition of the solution, but it's far more than you could reasonably generate by a water column of any reasonable height on Earth.

The solution simply wouldn't pass through the upper filter.

[Cryxis, Prince of Doom]

(Not actually adding anything to the conversation)

How much depends on the composition of the solution, but it's far more than you could reasonably generate by a water column of any reasonable height on Earth.

The solution simply wouldn't pass through the upper filter.

What do you consider reasonable?

[LARD]

I figured it must be something like that.  If we had a simple vertical tube with a membrane half way down and poured glucose solution into the top, it wouldn't go through?

[A Thing]

Can you restart polls after it expires? More specifically, once it goes over the date you set it to expire on.

Edit: Problem has been solved, ignore this.

[Yoink]

I don't believe so, that's a known issue.
The only real workaround is to set the poll to never end at first, then you can just count the results yourself and re-use the poll when you want to.

[My Name is Immaterial]

Or use a third-party site like Strawpoll.me.

[scrdest]

(Not actually adding anything to the conversation)

How much depends on the composition of the solution, but it's far more than you could reasonably generate by a water column of any reasonable height on Earth.

The solution simply wouldn't pass through the upper filter.

What do you consider reasonable?

The amount of pressure depends on the concentration of the solution. Fresh water requires a minimum of 2 atm going by Wikipedia, requiring roughly a 10m (~33 feet) high column at least.

For solutions with higher osmotic pressure, like seawater, it's an order of magnitude larger and then some, and the column height scales accordingly - even if it was pretty low, to simplify calculations, it would require a 100m high column.

Now, don't forget, we're trying to get that column going by water's own osmotic pressure, that's where the logical fault lies. No matter how big it were, the pressure differential you're trying to get on the upper membrane cannot exceed the pressure you've gotten on the lower one.

The free energy you're apparently getting from the generator at a glance is in fact the energy you'd need to use to overcome the osmotic pressure at the upper membrane. If you artificially applied additional pressure on the water on the upper membrance, you WOULD get that kind of motion and generate power on the generator - except what you generate would inevitably be less than you used to power the piston.

[Aklyon]

Can you restart polls after it expires? More specifically, once it goes over the date you set it to expire on.

The answer is no, you shouldn't set an expiration date for polls. Just lock it and count manually, and unlock it the next time you need a poll in the thread.

[Arx]

So I have a set of data, each with a different uncertainty. To propagate the uncertainty to the average of those data is



(sorry about the LaTeX image weirdness), where A is the average of my values, u(a_i) is the uncertainty of the value a_i, and n is the number of data in the set, yes?

The A seems wrong to me, but I'm not sure.

E: never mind, my brother just confessed to accidentally giving me faulty information. I should just be able to average the uncertainties.

[Cryxis, Prince of Doom]

Would it be inappropriate to use the letter Thorne (like a B but with only one bump in the middle, used for the th sound/the letters th themselves as a pair) when writing in english?

[Frumple]

... usually, yes. There's very rare occasions when it's appropriate, but it should pretty much never be used in anything even resembling normal writing.

The vast, vast majority of english readers will have no idea what that is, or that a "letter Thorne" even exists. E: Tellingly, autocorrect set it to "Throne" and doesn't even recognize it as a word.

Though checking google shows that's because you misspelled thorn, heh. Still, no, it should pretty much never be used in modern english.

[Cryxis, Prince of Doom]

I ask because it's really convenient to me, it just seems like a very useful letter and should be reused. (Yeah I know me of all people wants to correct something in the English language)

[Frumple]

... well, you're welcome to try, but don't expect anyone to know what it is, and expect to be marked points off for spelling if you use it in anything graded :V