8 ms·
Water compresses under a high gradient electric field
- ahelwer 8y ago"This is an unexpected phenomenon, contrary to what we thought we knew about nanopore transport. It took three years to work out what it was the simulations were showing us. After exploring many potential solutions, the breakthrough came when we realized that we should not assume water is incompressible. Now that we understand what's happening in the computer simulations, we are able to reproduce this phenomenon in theoretical calculations." Pretty interesting that the rules of the simulation were such that it took three years to explain an emergent phenomenon. I probably would have written it off as floating point shenanigans.
- slimsag 8y ago> I probably would have written it off as floating point shenanigans. Pretty sure anyone in actual scientific computing stays far, far away from floating point numbers and sticks to arbitrary precision ones instead.
- philipkglass 8y agoDouble precision floating point numbers are the most common in scientific computing. Sometimes software will mix in single precision for more speed. The molecular dynamics package GROMACS can use mixed single/double precision, for example: http://manual.gromacs.org/documentation/2016/install-guide/index.html http://manual.gromacs.org/documentation/2016/install-guide/i...
- wtallis 8y agoI'm quite curious what niche of scientific computing you've dealt with that gave you that impression.
- geoalchimista 8y agoError analysis can tell you whether the roundoff error would grow exponentially with time steps for the algorithm you use. If you avoid this kind of conditions in scientific computing, then double precision floating point number would work perfectly fine. And by the way, scientific computing is a diverse discipline, or a federation of disciplines. Say, there may be little overlap between the algorithms, tools, and environments that a physicist uses for scientific computing and those used by a bioinformatician. So I don't think it is universally true in scientific computing that arbitrary precision is preferable to double precision.
- leovailati 8y agoI found it counterintuitive that it was predicted in simulation and then confirmed with experiments, rather than the other way around.
- felipemnoa 8y agoThis is how lots of new science is discovered. One example is the Theory of Relativity. Sure it was not a software simulation per se but it was still simulated on paper. It was not confirmed by experiment until several years latter.
- wallace_f 8y agoIf I'm not mistaken I think what OP is referring to is an apparent emergent phenomena that contradicted theory, whereas I believe GR was discovered through theory (ie Einstein's "happiest thought" was in an elevator shaft).
- waiquoo 8y agoWith nanopore experiments, it's not unusual to see unusual behavior that could possibly be explained by macromolecule interactions, contamination, or electrical interference. There are often more unknowns than knowns due to the scale of the system, novel materials, measurement precision, unique physics, etc etc... What usually happens is the undesired measurement gets filed away for 'later study'. Unless you have some theoretical framework or model that explains it, you may never go back. So probably the experimental part was previously dismissed as an error or contamination, but now it is interesting because there is an explanation
- ahartmetz 8y agoThat is how it's supposed to work. You build a theory based on known phenomena, then you look for any new phenoma it predicts and test them in experiments. Without the new phenomena, your theory is more likely to be just "overfitting" the data. A famous example of overfitting the data - adding more cruft to account for unexplained aspects - is this: https://en.wikipedia.org/wiki/Deferent_and_epicycle https://en.wikipedia.org/wiki/Deferent_and_epicycle
- 8y ago
- inetknght 8y agoThis page, or something it loads, is causing Firefox to use 100% CPU. Cryptocurrency malware, perhaps?
- AngryData 8y agoSame here, it was lagging out my browser and I just updated it the other day too.
- Arbalest 8y agoEven with ublock origin+umatrix, so not many scripts were run. I was wondering whether that causes a script to fail and loop infinitely. IDK what conditions you guys were running your browser as.
- ChuckMcM 8y agoThat is a really neat effect. Basically if you can put a water molecule inside a flat field it lines itself up with that field and can be compressed. I would bet this has an impact on Graphene based desalination efforts as well.
- stephengillie 8y agoThis sounds akin to electrons forming Cooper pairs in atoms. https://en.wikipedia.org/wiki/Cooper_pair https://en.wikipedia.org/wiki/Cooper_pair
- Retra 8y agoHow so?
- mjevans 8y agoThat type of filtering was also something that I had in mind. It would additionally be interesting if the water would react to EM fields and confined spaces in a way that allowed for a 'micro' pump. Such a system might be able to operate in zero-g and thus be useful on extended space missions.
- ChuckMcM 8y agoThat is a really good observation. Microgravity environments have an issue with the lack of sediment settling, and while the current centrifuge system are effective, it would be really interesting if you could separate the precipitates without spinning everything.
- fooker 8y agoDoes this also mean compressing/decompressing water can generate an electric field?
- stephengillie 8y agoProbably, but it would take a lot of mechanical force. From the article: > The compression is only 3 percent, but that pressurizes the water—it's equivalent to 100 atmospheres Although, that's not uncommon for ice giants, so it might be causing part of Ouranos (aka Uranus) magnetic field. > The troposphere is thought to have a highly complex cloud structure; water clouds are hypothesised to lie in the pressure range of 50 to 100 bar[1] [1] https://en.wikipedia.org/wiki/Uranus https://en.wikipedia.org/wiki/Uranus
- rdlecler1 8y agoImplication: Depending on the energy input, couldn’t you create an engine from this? Sounds like a perpetual motion machine.
- stephengillie 8y agoThis effect does convert energy from mechanical to electrical, and so could be used in a type of engine. But AFAIK there would still be inefficiencies causing this conversion to be less than 100%, and so sadly not a perpetual motion machine.
- CamperBob2 8y agoCoincidentally, I just watched a great video by Ben Krasnow yesterday that suggests that the answer to fooker's question is indeed "Yes." There are other well-known principles along these lines, ranging from piezoelectricity to the Seebeck and Peltier effects, and it's almost more of a rule than an exception for such effects to behave symmetrically. Glowing plasma created by a high speed jet of water: https://www.youtube.com/watch?v=_vTq8oGpqwM&list=LLaIdy5TkkQclZa0K4LaCJEw&index=2&t=0s https://www.youtube.com/watch?v=_vTq8oGpqwM&list=LLaIdy5TkkQ... He definitely has the "whole lot of mechanical force" thing going for him, considering that he's about 2 psi away from fragging himself with a hydraulic cylinder.
- stephengillie 8y ago> Aksimentiev adds, "All of this only works because the membrane is so thin, and the electric field is focused where the membrane is, compressing the water molecule from both sides. It's not _pushing_ the molecules together, rather _pulling_ them together. This happens because the electric field is smaller than the water molecule, and pulls from inside.
- Someone 8y ago”Wilson found that a high electric field applied to a tiny hole in a graphene membrane would compress the water molecules travelling through the pore by 3 percent” So, it changes the distances between the atoms of a water molecule? If so, would that mean this can affect chemical reactions involving dipoles, too?
- mrfusion 8y agoCould this be used for a new kind of pump with no moving parts? Maybe a worm drive for submarines?
- geoalchimista 8y ago> "Physics Professor Aleksei Aksimentiev and his post doctoral researcher James Wilson found that a high electric field applied to a tiny hole in a graphene membrane would compress the water molecules travelling through the pore by 3 percent." Ahh, "3 percent" means that from a fluid dynamics point of view, the incompressibility assumption is still a good assumption valid for most macroscopic applications. :) Still very impressive to achieve that under ambient pressure with an electric field gradient.
- A_Person 8y agoIt's always surprised me how many people do not know that water is incompressible! For example, when someone is filling a scuba tank, it's common to put the tank in a large, often metal-sided container of water. When asked why, the shop staff member will typically say: "In the unlikely event of the tank blowing up, the water will absorb the force of the explosion." But in fact, water being incompressible, it will absorb approximately 0% of that force - which is then transmitted undiminished to the metal walls - which then explode like a giant hand grenade, promptly maiming or killing everyone standing nearby! The purpose of the water is instead, to absorb the heat from adiabatic compression, and keep the tank cool.
- politician 8y ago> "...the breakthrough came when we realized that we should not assume water is incompressible..." The shop staff was right, water is not incompressible (under important conditions that don't apply to their scenario!).
- andromeduck 8y agoThat's just wrong. The the blast from the tank would have to displace water before of the energy of the blast can exit the side or top of the container. That spreads out the energy from the blast and the container would redirect much of that energy upwards both of which reduces the effective radius of the blast.
- zamalek 8y agoThe shopkeeper is still somewhat wrong though: it's redirecting the energy, not absorbing it. Regardless, Mark Rober and The Backyard Scientist have a pretty great video demonstrating exactly what is going on here: https://youtu.be/W4DnuQOtA8E https://youtu.be/W4DnuQOtA8E
- A_Person 8y agoI'm no scientist and you may well be right. But I'm skeptical of your statement that "much" of the blast would be directed upwards. If you look at the pictures of tank explosions, they often show the entire room flattened right to floor level - not a big hole in the roof and minor damage everywhere else.
- yosito 8y agoWhat would happen if you compress water using this method and then seal the container it's in and turn off the electricity? Anything interesting? Does the water stay compressed? Does the container explode? Does it depend on the strength of the container?
- craftyguy 8y agoIntuition says that the water would then exert more pressure on the container. Like if you emptied and sealed a plastic bottle while at sea level, and then ascended to a high altitude in an airplane (or climb a mountain). The bottle would be bloated. Whether or not it would explode depends entirely on the properties of the container..
- hoppa_liza 8y agoWould not the bottle be squished now that it is under more pressure?
- craftyguy 8y agoYea, you're absolutely right, I swizzled the analogy. I fixed my previous comment. Thanks :)
- sandworm101 8y agoWho said water does not compress? It doesnt compress much, but at the depths of the ocean it is a tiny bit denser than at the surface. I was suprised to see phys.org so cassually state that it doesnt.
- JakeTyo 8y agoI wonder if this mechanism can be used as a molecular solenoid. I'm endlessly fascinated by the concept of molecular-scale machines.