Science Squabbling

[quote=XKCD]Since drag increases with the square of the speed, this limit would be pretty hard to push any further. Biking at 200 m/s would require at least 25 times the power output needed to go 40 m/s.
[/QUOTE]

This is wrong. Drag force is proportional to v², but as power = force × speed, the power needed to overcome drag is proportional to v³. Therefore, going 200m/s need 5³=125 time more power than going 40m/s

Damn, so it's even more impossible now :(

just spend the winter on the rollers you'll be ok

If the question is about cycling fast enough to heat the air next to the skin, using a fully-faired recumbent in the answer is a bit silly.

You can heat the air next to your skin quite effectively if you wear clothing with a low U value.

Which doesn't answer the question either.

is the world running out of helium ?

http://www.zerohedge.com/news/2013-08-27/looming-federal-helium-reserve-cliff-no-really

is the world running out of helium?

Probably not, as new Helium is being made all the time in the long alpha decay chains from heavy elements in rocks. It might become expensive, but that's not the same as running out. It's possible that high temperature superconductors might allow Nitrogen cooling in application currently using Helium, which will have a strongly adverse effect on your position, should you be thinking of investing in Helium futures :-)

I blame Baumgartner.

Recycling Heluim will also become financially viable/necessary. In our department the companies state a 95% plus recovery rate with their most expensive options. The cost will increase a lot though.

is the world running out of helium ?

http://www.zerohedge.com/news/2013-08-27/looming-federal-helium-reserve-cliff-no-really

Not so much as running out as wasted. If usage isn't curbed, it'll start getting very very expensive. There are still plenty of Gas wells that could, statistically, last us another 100+ years, but who's gonna foot the bill for that infrastructure. Dig, purify, extract, transport, store etc etc

Helium is fucking badass. supercooled it turns into a superfluid which is the mammoths nuts! Fusion makes plenty of Helium3, but...we kinda need it as fuel to begin with (cleaner fuel).

TO THE MOON WE GO!

I blame Baumgartner.

There was only 180,000 cubic feet of Helium in his balloon, compared with global annual extraction of about 6 billion cu.ft.

Using 0.003% of the annual production of something for just one year doesn't really count as market manipulation

It's possible that high temperature superconductors might allow Nitrogen cooling in application currently using Helium,

Aside from its superior cooling properties, is efficiency the only reason its used more often than Nitrogen? I'd imagine it varies, but how does Helium favour against Nitrogen in Superconductivity. Also, is this your field of expertise?

There was only 180,000 cubic feet of Helium in his balloon, compared with global annual extraction of about 6 billion cu.ft.

Using 0.003% of the annual production of something for just one year doesn't really count as market manipulation

I can do maffs, me!

Copycats use 89.8864% of the Earth's yearly extraction flying from sheds worldwide.

No, it's not my field.

Currently, the only superconductors which can be made into high field electromagnets need to be cooled way below the boiling point of Nitrogen to even be superconductors at all, which is why Helium is used as the refrigerant. The high price of Helium (compared with Nitrogen) is already one of the drivers of research into high temperature superconductors. "High Temperature" in this context means above the boiling point of Nitrogen, still pretty nippy at 77K but in absolute temperature terms that's toasty next to the 4K boiling point of Helium

Aside from its superior cooling properties, is efficiency the only reason its used more often than Nitrogen? I'd imagine it varies, but how does Helium favour against Nitrogen in Superconductivity. Also, is this your field of expertise?

At risk of repeating mdcc_tester: Efficiency of cooling is not defined by the coolant (it's either cold enough as a liquid or not), but by the engineering of it's environment. The boiling point of He is 4K so if He is kept as a liquid then it will provide an environment of 4K. How well you insulate the He defines how long you can use a unit volume of it to cool. Nitrogen is commonly used in a secondary cryostat to slow the evapouration of He.

There are other methods of cooling which use less He than a conventional heat sink, such as magnetic refrigeration. This uses magnetism to manipulate the entropy of a paramagnetic heat sink in cycles with contact to an external He heat sink, but it's limited in scale. It is viable for MRI though

No, it's not my field.

Currently, the only superconductors which can be made into high field electromagnets need to be cooled way below the boiling point of Nitrogen to even be superconductors at all, which is why Helium is used as the refrigerant. The high price of Helium (compared with Nitrogen) is already one of the drivers of research into high temperature superconductors. "High Temperature" in this context means above the boiling point of Nitrogen, still pretty nippy at 77K but in absolute temperature terms that's toasty next to the 4K boiling point of Helium

ok lads we've found his weakness target your arrows upon his lack of knowledge of blokes in sheds

Researcher controls colleague’s motions in 1st human brain-to-brain interface

http://www.washington.edu/news/2013/08/27/researcher-controls-colleagues-motions-in-1st-human-brain-to-brain-interface/

At risk of repeating mdcc_tester: Efficiency of cooling is not defined by the coolant (it's either cold enough as a liquid or not), but by the engineering of it's environment. The boiling point of He is 4K so if He is kept as a liquid then it will provide an environment of 4K. How well you insulate the He defines how long you can use a unit volume of it to cool. Nitrogen is commonly used in a secondary cryostat to slow the evapouration of He.

There are other methods of cooling which use less He than a conventional heat sink, such as magnetic refrigeration. This uses magnetism to manipulate the entropy of a paramagnetic heat sink in cycles with contact to an external He heat sink, but it's limited in scale. It is viable for MRI though

Ahh, so its not a case of how cold you can get things, rather how consistent your cooling is around its environment? So while Nitrogen can be used used as a primary coolant, it's boiling point occurs with any body that's warmer than itself, while helium in liquid form doesn't? or rather, evaporates at a slower rate? Am I getting this or completely off the ball?

As for Magnetic Refrigeration. FUCK YOU! My head already hurts. Actually had to dig a little further back and released how Vapor-Compression refrigeration works. It's not so much as cooling as un-heating! Urgh...my brain...

Just keep connecting Fonzies, in series.

Ahh, so its not a case of how cold you can get things, rather how consistent your cooling is around its environment? So while Nitrogen can be used used as a primary coolant, it's boiling point occurs with any body that's warmer than itself, while helium in liquid form doesn't? or rather, evaporates at a slower rate? Am I getting this or completely off the ball?

No, it is a case of how cold you can go, He is valuable simply because it boils at 4K, N boils at 77K. If you have bath cryostat filled with liquid He it will provide an almost 4K environment to anything it's in thermal contact with. How long you can keep it at 4K is determined solely by how long you can keep the He as a liquid. He will boil off like any other liquid if it receives enough energy to convert it all to a vapour. This is inevitable in a room temperature, 300K, environment, it's just a question of how long.

A more specific description would be in terms of latent heat, the energy required to change the phase of a system. In an ideal constant pressure and temperature environment, all the energy given to a liquid at its boiling temperature is used in its conversion to a vapour. At its boiling point the bulk liquid cannot gain any energy without vapourising, therefore it remains at a constant temperature until it's all boiled off.

Ahh, so its not a case of how cold you can get things, rather how consistent your cooling is around its environment?

It's both. A cryogenic liquid at atmospheric pressure provides very convenient and even cooling to its boiling point.

So while Nitrogen can be used used as a primary coolant, it's boiling point occurs with any body that's warmer than itself, while helium in liquid form doesn't? or rather, evaporates at a slower rate? Am I getting this or completely off the ball?

A bit off. At atmospheric pressure, liquid nitrogen in contact with any body hotter than 77K will boil, and its latent heat of vaporisation will carry heat away from the body until it is at 77K or all the liquid nitrogen is gone. Liquid helium will do the same, except at 4K, and it's latent heat is much smaller so you have to boil a lot more helium to carry away the same amount of heat. Re-liquefying such refrigerants isn't trivial, but it's still a very convenient way of cooling things. Even below 4K, helium is useful for carrying heat around because it's the only substance not solid at those temperatures.

As for Magnetic Refrigeration. FUCK YOU! My head already hurts. Actually had to dig a little further back and realised how Vapor-Compression refrigeration works. It's not so much as cooling as un-heating! Urgh...my brain...

Thermodynamic cycles are fun. There are also dilution refrigerators which use a varying mixture of helium 3 and 4 to reach temperatures below 4K.

edit: oops got distracted with thermodynamic cycles, so neu was faster.

Even below 4K, helium is useful for carrying heat around because it's the only substance not solid at those temperatures.

And coolant pump power requirement should be trivial, what with it being a superfluid. Or should we not explode Chak's brain by getting into superfluidity as he is already struggling with superconductivity?

err, yeah, that too.

Researcher controls colleague’s emotions in 1st human brain-to-brain interface

http://www.washington.edu/news/2013/08/27/researcher-controls-colleagues-motions-in-1st-human-brain-to-brain-interface/

I control my GFs through my passive aggressive behavior

Researcher controls colleague’s motions in 1st human brain-to-brain interface

Oops misread that. For controlling her motions I use string theory