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Twenty Four posted:/roll 20 You successfully make your disbelieve check! Magic is real, you're a wizard, Harry (your name is now Harry, sorry...) https://i.imgur.com/QKTkerO.mp4 |
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Jun 8, 2017 14:01
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| # ? Apr 26, 2024 21:16 |
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Serious question, DirtyBear- how hard is it to resist the urge to freeze the h*ck out of everything and see what it looks like when it melts/you shatter it with a hammer?
https://i.imgur.com/QKTkerO.mp4 |
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Jun 8, 2017 14:55
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in my experience everyone who works with cryo liquids went thru "that phase" in grad school and got it out if their system |
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Jun 8, 2017 15:01
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Splatmaster posted:Serious question, DirtyBear- how hard is it to resist the urge to freeze the h*ck out of everything and see what it looks like when it melts/you shatter it with a hammer? As al says I have already frozen most of the things on my bucket list, but that's not to say I don't still play with with the cryogens. Marshmallows in liquid nitrogen is funny and timeless (see YouTube, has a dragon breath effect), playing with liquid nitrogen compatible superconductors is neat, can just levitate small magnets, and whenever I have extra liquid nitrogen I like to throw it in the floor. The leidenfrost effect makes it all bead up and move weirdly across the floor and any dirt and dust gets flash frozen and I just call that cleaning the floor i guess |
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Jun 8, 2017 15:13
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On a hot day a good blast of liquid nitrogen boil off is a quick way to cool off |
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Jun 8, 2017 15:14
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I had a friend who worked in the Lox/Nitro shop on the flightline, it doesn't take long at all to quick-cool a case of warm beer to frosty on a hot summer day
https://i.imgur.com/QKTkerO.mp4 |
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Jun 8, 2017 15:30
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We don't have liquid oxygen since its not really useful as a cryogen for us. Oxygen is highly reactive so can alter sample properties, and it also interacts with magnetic fields and then we'd have to try to take that into account for measurements. That being said, condensing liquid oxygen has been something ive wanted to do for a while, just for fun. I've seen ways of doing it and it seems to be criminally easy to do. I think I would try to do the burning iron wool in oxygen experiment that periodic videos did (https://www.youtube.com/watch?v=6NNt0Pup6jU) and I'm sure i would do the classic pour liquid oxygen past a magnet to visibly show oxygen's paramagnetism. i guess if im wishlisting i'd pour some liquid oxygen into a basin inside of a bonfire too. |
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Jun 8, 2017 15:57
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  This is a dilution refrigerator cryostat, the tall thing on the crane gets inserted into the middle of the blue dewar on the ground- "wait you already showed so many cryostats why do you need all these don't they do the same thing?" Well sort of, they all get things cold. For background ill quickly describe the way previous cryostats worked. The optical cryostat is simple- pass liquid helium through the cryostat, liquid helium boils at 4.2 Kelvin, so the liquid is 4.2K in atmospheric pressure. But there is an easy way to get lower temperatures from liquids: blow on them. its literally just like a hot bowl of soup with steam above it. Liquids like to have vapor at the surface of the liquid (this is related to vapor pressure) so when you blow away the vapor above soup, molecules from the liquid soup transition to become a vapor, but this transition isn't free and in fact costs quite a bit of energy to change from liquid->vapor, and this energy comes in the form of heat. Every molecule that moves from liquid to vapor state takes with it some heat, so we use this to cool liquid helium even further. When people speak of "liquid helium", they are almost always talking about liquid He4, which is the most common isotope of Helium. By pumping away the vapor above He4, its possible to reach temperatures of more like 1.8K. In exactly the same way, there is another Helium isotope, He3, which boils at 3.3K but by pumping the vapor away its possible to reach temperatures of 0.3 Kelvin. At the lowest temperatures, the vapor pressure of the liquid is so low that no more atoms transition from liquid to gas. This crysostat uses both of these Helium isotopes together in a mixture. Inside this cryostat, there is a mixture of He4 and He3 which is formed into two sections: a part of the mixture that is rich in He3 and a part that is poor in He3. Now naturally two liquids in contact with each other may exchange atoms, and in this case He3 atoms will move from the rich zone to the poor zone through dilution. Again, this dilution is not free and the energy comes in the form of heat. Crucially, this dilution process is allowed to keep going to... I guess probably 0 Kelvin, but practically it is possible to use this dilution refrigerator to reach temperatures of 0.02 Kelvin, 200 times colder than liquid helium 4. The dilution refrigerator is mostly used to look at the low temperature behavior of samples. Yes we can learn a lot from a measurement taken at a certain temperature, but there is well understood theory about how to relate the low temperature behavior of superconductors to the underlying physics of how superconductivity works, which there is still not good comprehensive answers to. For example, if a property of a superconductor increases from zero linearly with temperature, that means something very different about the physics if that property rises exponentially, and to compare these things you need very very low temperature data. |
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Jun 8, 2017 18:16
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i got to see the graphite reactor where they made the bomb once, it was cool |
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Jun 14, 2017 07:52
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pogi posted:i got to see the graphite reactor where they made the bomb once, it was cool The Cp-1 in Chicago? Im not sure which of those old reactors are still around but that one is particularly historical and interests me a lot |
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Jun 14, 2017 15:59
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| # ? Apr 26, 2024 21:16 |
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DirtyBear posted:The Cp-1 in Chicago? Im not sure which of those old reactors are still around but that one is particularly historical and interests me a lot nope, the x-10 in oak ridge. There's a national lab around the old facility now, but you can still tour the reactor. Also got to see the neutron collider they had on site, which was neat! |
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Jun 14, 2017 17:21
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