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Science

Superconducting DNA 70

Posted by michael from the short-circuit dept.
Mr_Dyqik writes "Alik Kasumov of the Laboratoire de Physique des Solides in France and co-workers have shown that DNA molecules act as ohmic conductors above 1K and that below this temperature they can superconduct. This could allow the creation of self assembling superconducting circuits. (A Y Kasumov et al 2001 Science 291 280). The story is on PhysicsWeb."
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Superconducting DNA

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  • background information (Score:1)

    by Anonymous Coward
    The fact that something conducts has nothing to do with it becoming a superconductur. Gold never becomes superconducting while lead does. There are simply not that many superconducting systems. Now what is it going to do that DNA superconducts at 1K. Probably not much for practical purpose, because you need liquid helium to cool down your system to that temperature and it's not too practical. The dna based superconducting circuits that are mentioned are just the kind of science fiction that real scientists need to come up with if they want to get some kind of recognition. I know that 'caus I'm a scientist and I used to work in Orsay (where they've done this experiment).

  • Nanotechnology (Score:1)

    by Anonymous Coward
    A picture of DNA from a LEEPS (Low Energy Electron Point Source) microscope can be found here [pawlitzek.com].

  • Re:FP (Score:1)

    by vik ( 17857 )
    Just download any DNA PDB file and use pdb2pov on it. Vik :v)
  • Yes it was the liquid nitrogen required stuff that caused the excitement. I forget how cold liquid nitrogen (173K seems to pop to mind) is but its damn toasty compared to liquid helium @ 4K which was required for other superconductors.
  • At a molecular scale you can reproduce the functionality of the human brain in a few cc's - if you can keep it cold.

    I wasn't aware that the complete workings of the human brain had been cracked as yet. As far as I know, whether the human brain is a quantum device is undecided as yet, and if it is, I bet it will take a lot more than a few CC's.

  • You're right, I think. Most of the new high-Tc superconductors are type-2. Even conventional type-2 superconductors tend to have higher critical temperatures (and critical fields, and critical currents) than type-1's.

    By the way, PHYS 317 was a great course (I was a physics major myself). Is LePage still teaching it?
  • Sorry, couldn't help myself. One minor correction. The type of superconductors which were discovered in the 1980's (1984, by Bednorz and Muller at IBM-Zurich, I think) are known as "high-temperature" superconductors. They appear to be fundamentally different than previous superconductors (conventional, or low-temperature). High-temperature superconductors superconduct at roughly liquid nitrogen temperatures (77K).

    Most low-temperature superconductors are pure metals, alloys, or oxides (like Nb, NbTi, or NbO2). Most high-temperature superconductors are, as Maurice said, cuprates. For example, YBCO (Yttrium Barium Copper Oxide). It appears that the actual "supercurrents" flow in the 2-dimensional copper-oxide sheets.

    Now for the actual correction (to eliminate a bit of confusion). There are type-1 and type-2 superconductors, although those terms refer exclusively to classes of LOW-temperature superconductors. The difference lies in how their conductivity is affected by a magnetic field. Basically, type-1 superconductors have a sharp transition between superconductivity at low magnetic fields, and normal conductivity above a critical field (at constant temperature). Type-2's have a much more gradual transition. Of course, that's only a functional definition, and it isn't the whole story.

    Basically, HIGH-temperature superconductors were what was discovered in the 1980's, and type-1 and type-2 refer to types of conventional superconductors.

  • You don't need a band gap above the critical temperature. Although many really good metals aren't superconductors (e.g. Au and Ag), many other metals (which have no band gap, of course) are, like Nb. The normal-superconducting transition opens up a gap between the paired states at the Fermi surface and the next-lowest ("broken pair") states, but it's not necessary for there to be a gap in the normal state. That would imply that ONLY insulators and semiconductors could be superconductors.

  • I predict this technology won't really take off until we develop Compassionate 64-bit Superconducting DNA Extreme.

  • Normally, for smaller molecules and proteins, yeah... but DNA can be kilobases long. Just the process of forming ice crystals can break longer strands of DNA.

    In fact, one of the methods in the laboratory used to split long segments of dna into more managable parts is to stir it. (Basically, getting to 0K without breakage isn't the real problem, it's geting past 273K without having freezing going on...[dehydration may be a possibility])

    Don Armstrong -".naidnE elttiL etah I"
  • wouldn't that be more attributable to the 70% of your body that's salty water?
  • How about a beowulf cluster of me!
  • I would imagine that they would have the DNA assemble at ~290K, and only cool it during use. Once it is assembled, its DNA properties are not important.
  • Well, there was another post referring to a Niven story, but that pretty much describes the state of Terran society over a certain temporal period about which many Niven stories were written. "Patchwork Woman" was a good one, but the whole Flatlander (adventures of Gil "The Arm" Hamilton) collection talks about things like organleggers.

    Also excellent (and entirely irrelevant to the discussion) is the set of assorted short stories by Niven that, as a whole, chronicle the devleopment of an instantaneous transport technology (transfer booths). The man's good, real good.

    -J
  • No, I had Dugan and I think it's Teukolsky in Spring. We use some of LePage's software though for the compuer labs. (BTW I'm not a physics major, just a minor, otherwise I'm CS, just graduated actually)

  • It just happened that this is my usual sig, and it's a joke. In this case somewhat relevant.

  • I thought that all of the new hot superconductors are Type II, partially explaining the high critical temperature. I guess my physics prof didn't explain it well enough or (most probably) I didn't study enough. (I see you are at Cornell, FYI I wrote all that from memory from PHYS 317 which I took last semester).

  • "Self-assembling"! "Superconducting"! "DNA"! Now all it needs is to be "overclocked", run "Java", and use "XML."
    * mild mannered physics grad student by day *
  • This all seems a little tenuous, I mean 1K for god's sake. Is there really any true distance gained by this?
  • Don't forget muti-threaded, peer to peer, code morphing , 3D , distributed, and 'e'
  • Funny idea, but fortunately you don't need nuclei to replicate DNA... Thats what PCR (Polymerase Chain Reaction) is for. Yeah, I take jokes too seriously.

    Skreech
  • See this experiment [gamespy.com] and this information from the same source [gamespy.com].

    --Sam L-L

  • One of my moderator points!

    --

  • that's not the point. The point is that these circuits could be made self-assembling. Anyway, once you've got somethig to that temperature, it's quite easy to keep it there, especially since superconductors don't give off a lot of heat. This would allow much more complicated superconducting circuits, which no analogues in normal electronics, and also givves very low noise devices (thermal noise way down at these temps)
  • Some Japanese companies were working on this, but I think they're still building the prototype (it takes a long time to build a ship and a long time to modify what's inside it).
  • And you'd ready have the leetest oc cooling system in place, liquid helium cooling.
  • Quite a few, but not all of them have the other properties that DNA has. Basically there has to be a small band gap at the Fermi surface of the crystal, and a strong electron phonon interaction.
  • Below 1K, it would certainly be cool.

    --
  • Oh, I missed one part of the question:

    being able to suspend bits of metal in the air over some stove burner looking thingy

    The things they were suspending were actually magnets. If you drop a magnet on top of a superconductor, it won't get any closer than a certain distance due to the fact that if you move a conductor through a magnetic field (or move a magnetic field "through" a conductor) it generates electricity. Since there is no resistance to electricity - and thus, no way for the superconductor to eliminate the potential energy, the magnet will essentially float above the superconductor.

    The stove burner was really some sort of cooler with a superconducting wafer on top.

  • (almost?) Every MRI machine in the country uses superconductors to produce the magnetic field. Basically, they charge up the superconducting wire and then connect the ends together.

    One of my acquantances up here services the things. It's really fun when he tries to sell a zero volt 1000 amp power supply to someone else and they say that it is impossible to have current without voltage. But since you can have current in a conductor with no resistance, you can also have lots of current and no voltage.

    There are some other real applications for this stuff. The revolution was being able to do this at a much higher temperature than say the 1 degree above absolute zero discussed above.

  • Evidence for electrical conductivity in DNA molecules has been inconclusive until now.
    Inconclusive? Ever since I stuck my hand in a light socket, I KNEW my DNA was conducting a HELL of a lot of electricity!
  • Nobody would listen when I did this [gamespy.com]. You all thought that I had gone off the overclocking deep end. But who's laughing now [gamespy.com]?
  • Why not? Obviously you can't assemble much of anything at 1K, but you can assemble the structure at room temperature (or thereabouts), then cool it down quickly below freezing to avoid ice-crystals, then freeze-dry it or whatever. It won't fall apart at 1K if you can get it below freezing and get rid of the water. Its at high temperatures that the DNA strands denature (fall apart).
  • <drunk>
    IANAB (I am not a biologist), but wouldn't DNA stop acting like DNA usually does at 1K?
    I though the whole point was it had to be in the 290K kind of range (around room temp/blood temp) to do much at all.
    But hey, I just encourage .1 - .75 ton mammals to replicate their DNA just so we can eat them. So maybe I'm wrong...
    </drunk>
  • Seems reasonable. That would also stop the William Gibson "runaway AI cancer-polycarbon-neuro-implant" horror stories that the tabloid press would love.
    I think I found something self-replicating in a coffee cup under my bed. I bet it superconducts...
  • From the article: "...these rolled up sheets of graphite atoms...". Graphite not generally considered to be an atom, one really needs to consider the source.

    -Mike-

  • Other posters pointed out that Niven wrote about this problem more than once; the longest treatment is the novel "A Gift From Earth". The planet in the novel has a very repressive police state which is tolerated by its citizens mainly because executions lead to organs available for transplant

    Niven felt strongly that our fate w.r.t. replacement organs rested on which technology matured first: artifical organs or transplantation from humans. If the latter, he thought it was pretty inevitable that, um, our correctional institutions and our medical institutions would begin to collaborate.

    --Timboy

  • Having something superconduct at, near, 0 Kelvin isn't all that difficult as everything superconducts at that temperature. Now having a superconductor at "normal" temp's, that would be a huge boost to science.

    And trust me, cooling stuff with icecubes won't get the temperature down to 1 Kelvin. you'll have to think a tad harder for that Nobel prize :o)

  • ...it was a short story, not more than ten pages long if I remember properly. I'll have to try to get the book back to look...

    "Titanic was 3hr and 17min long. They could have lost 3hr and 17min from that."
  • Nah....

    Just slap some molecular-sized heat transfer goop on a heat sink, combine it with a thermal transfer plate, (don't remember the name of the things..) and it'll work... Or my name isn't Bill Clinton.

    (which it isn't.)
  • I think their idea of 'room temperature' may be a lot lower than mine.... ;)

  • As far as I can tell, there are two things hyped up as the next generation's CPU circuitry: fiber optics and superconductors.



    I'll venture a guess that fiber optics will take home base, but here are som pros and cons that I've thought of:



    • Fiber Optics:
      • Pros:
      • Embeddable in other materials.
      • Works well at room temperature and above.
      • Theoretically infinite data throughput, via varying wavelengths and the lack of a size for quanta.
      • No RF generation
    • Cons:
      • Requires quanta source. However, there's the option of includnig the quanta source inside or outside the CPU.

    Superconductors

    • Pros
      • No electrical resistance, so no heat generation. (Cooling becomes an entirely different prospect.)
      • Molecular-sized superconductors can be shrunk to molecular-scale space.
    • Cons
      • Massive (though changing for the better) cooling requirements.
      • RF generation. (Not sure on this one)
      • Embedding in materials introduces complications to cooling. (IIRC)

    (srry about the length of the list...Couldn't figure out how to clear out any more whitespace...)

  • Probably "The Jigsaw Man", by Larry Niven, 1967.

    What do I win?
  • Yet there are people whose job it is to do so...

    How do you get this job? Morally upstanding, my ass...

    Y'know... what's really great about filtering software is that it attempts to filter 'The Internet' for naughtiness and subversiveness, yet rarely filters anything other than HTTP. I mean... anyone who knows *anything* about porn, warez, mp3's, texts, etc... realizes that the best place to find them without having to look is Usenet and IRC.
  • Oh, so you could make a superconductor out of common household items, eh? ;-)
  • I remember that superconductors were this big thing back in the 80's, some sort of revolution that meant more than being able to suspend bits of metal in the air over some stove burner looking thingy. Superconductors had been around longer than that, but there was some kind of renaissance at that time that made it cheaper and easier.

    Anyway, it's two decades later, and I still don't have any damn superconductors. Who *does* have them, what are they doing with them, and when can I get my own superconductive nonferrous magnets?
  • It is quite likely that the "genetic" content of DNA used in this manner is garbage in the genetic context.

    Actually, no, as it turns out the experiementers tried garbage DNA first, and many other sequences, without success. It turns out that the only DNA that would superconduct was Hitler's.

  • For a commercial vendor, try American Superconductor. Their web page is at http://www.amsuper.com [amsuper.com]. They sell many devices based on superconductors, and some raw materials as well (under "Products & Solutions", "Electric Power Applications").
  • Umm.. Seems to me that almost anything that acts as a conductor would superconduct at that temperature. Problem is, it takes so much energy to get to that temperature, it's not worth it.
  • The exact workings haven't, and don't need to be for the purposes of this rough calculation. We know what a neuron does, and we know how many there are in the brain. We know how hard it is to make an artificial neuron, so we can provide a good guess at how big a molecular scale computing device with the same capabilities could be.

    We don't need to worry about specialist areas like quantum computing - I'm only setting an upper limit on size here, based on the AI section in Drexler's "Engines of Creation"

    Vik :v)

  • Argh! I must check The Vault! How did they gain access to mein secret Hitler DNA sample? :-P


    Vik :v)

  • Read the article [sciencemag.org] if you want.

    This could allow the creation of self assembling superconducting circuits.
    As far as self assembling superconducting circuits, DNA is probably not the right way to go. Currently the rules of DNA superhelix assembly are way to complex to easily predict. Plus, at super conducting temperatures, there is no way that the DNA is going to be capable of self assembly. (the experiment was conducted with DNA molecules of length 2-3, 10sh and 20-30 bases.)

    Furthermore, just the process of supercooling DNA will probably denature molecules of any interesting length and structure. Finally, once all this is done, how in the world do you compute with just a string of DNA at that cold of a tempurature? I wouldn't think that it would be any more interesting in ability to compute than a bucky tube.

    Don Armstrong -".naidnE elttiL etah I"
  • I don't disagree with you. I mean what kind of dummy would think of looking for pornography on the web?

    But you're posting to the wrong article bud.

    You meant to post to the article about the worst jobs on the net and this about cooling your body to within 1 degree of absolute zero to create a self assembling super computer. In fact you and some linuxchix could get together and create a beowulf cluster out of yourselves.

    Science is great huh?

  • ...when cooled below 1K become superconducting?

  • Congratulations!!! It's a binary adder!

    *passes out cigars*
  • Why not make your own? If you have acess to a chemistry lab you almost certainly have the chemicals to do so.

    First measure out the proper stoichiometric amounts of chemicals to satisfy the final Y BA2 Cu3 O7-X formula. Your amounts could be: Yttrium Oxide, Y2O3 11.29 grams, Barium Carbonate, BaCO3 39.47 grams, and Cupric Oxide, CuO 23.86 grams for one example.

    Then grind together and heat the mix to 950 degrees Celsius for about a day. After you let it cool grind it again and heat back up to about 1000C if you can, pass pure oxygen over the sample and now cool it very slowly at no more than 100C/hour. If you like press the final powder into a pellet.

    Voila, your very own superconductor. I did it over a weekend once it's really easy and kinda fun once you get it to work. Get some liquid nitrogen from your local welding shop and nab one of the superstrong samarium cobalt magnets from an old pair of headphones to do the meissener demo. :o]

  • Most superconductors work between temperatures of 1mK and 4K, and it's not difficult to work at this temperature. Obviously it's not a lot of use for building MagLev trains or those sorts of uses for superconductivity, but it is very useful for building superconducting electronics, which have very different properties to semiconducter electronics. Self asssembly is one of the major goals of nanoelectronics and engineering, because it's far too hard to use lithography techniques at these scales (you have to use x-ray lithography, and that doesn't exist yet). So the idea is you mix up these enzymes, DNA strands etc. and give them the right heat treatments, and out pops your circuit. At the moment nanoelectronics uses electron microscopes and atomic force microsopes to make circuits, which is very slow.
  • This doesn't require laser cooling in anyway, as Liquied He cryostats can get to 30mK, Laser cooling isn't required unless you want to hit 1nK, and only really works on a few atoms at a time.

    The actual advance is that it could become easier to create superconducting circuits that can do a job that normal silicon can't. e.g superconducting circuits can operate quite easily in the 100 GHz region, where all silicon circuits have to laid out as waveguides etc.

    Most of the useful effects in superconducting circuits come from the presence of Shapiro steps and other microwave resonances in Josephson junctions and their ilk.
  • Man, you thought names like "Athlon" and "Duron" were wierd...just wait until they start naming them after all of your friends after they find our how nice their DNA is...

  • So, if they like go and slam a CPU into my arm, some RAM into my stomach, and a few expansion slots into my spine, I can be a super computer with no electrical resistance? ALRIGHT!

    No more laptops and dead batteries! (Just don't forget to eat...)

    My karma's bigger than yours!

  • While interesting in an academic sense, such a discovery is rather trivial in a practical sense. Superconductivity itself has a number of astonishing uses that can sometimes look like magic, but they're only useful when we can get them to occur at useful temperatures. Unfortunately, cooling something to 1K will require something along the lines of laser cooling in order to achieve, and this turns out to not be very practical. Superconductors with a very low critical temperature cannot conduct much current before they exceed their critical energy level and "go normal".

    Laser cooling only works for gases. 1K is usually achieved by first cooling using liquid Helium, then using various tricks to go a few degrees lower. Releasing pressure, or realignment of magnetic fields can all cause temperature drops sufficient to reach 1K, or even lower. Laser cooling is used to reach temperatures far lower than 1K.

    Useful superconductors are more in the line of HTC's, high temperature superconductors. The simplest of these are the superconductors that work when cooled to the order of 70 degrees Kelvin (-200C) by liquid nitrogen (which is cheaper than beer). If I recall correctly, the highest published HTC was around 175K, which is only 100 degrees below freezing. I've heard rumors of higher temperature superconductors, but haven't seen any referreed publications of results yet. Keep your eyes peeled, we'll see room-temperature superconductors within the lifetimes of most slashdotters.

    That might not be possible. Many physicists now question if RTSCs are possible, because the thermal energy of the lattice might break apart the delicate electron-electron pairing. Certainly, there is a lot of territory to cover, like strained crystal lattices, doped bucky tubes and the like, but don't get your hopes up. Also, most HTSCs are brittle, difficult to manufacture, very expensive, and often toxic.

    To be fair to lower temperature superconductors, I believe the maglev train in Japan uses a lower temperature superconductor cooled by liquid helium, which is somewhere down on the order of 10K.

    Most modern experiments involve liquid Nitrogen temperatures, or no superconductors at all. It's just cheaper. Liquid Helium is expensive, and requires complex insulation systems.

    Superconductors aren't too useful for their property of not conducting current, since they have a critical maximum current level anyway. They are mostly used for their diamagnetic properties (they repel magnetic flux lines). This is the basis for how an MRI works, or for how super-fast magnetic trains work.

    Their maximum current capacity is huge, but unlike copper, if you stay under the maximum, superconductors can transfer the current with zero loss, even at lower voltages. They are already in use at several powerplants for short-haul, high-current lines, etc... I've heard of at least one powerplant that uses a superconducting ring (inductor) to smooth out demand surges.

  • It'll be like in that science fiction story (sorry, I cannot remember the author of the story, but it was in book one of an anthology that was published by Polaris, a division of White Wolf Publishing) where people convicted to die were required to donate their organs to health officials... they started changing stuff like parking tickets to get a death sentence!

    They'll do that to DNA now! they're going to need our nuclei to copy their DNA strands, and they'll make it so if we breathe wrong, badmouth someone, or use Macintoshes we'll be convicted and they'll take our nuclei!

    Join the "Save the Nuclei" movement now, before it's too late for humanity!!!



    "Titanic was 3hr and 17min long. They could have lost 3hr and 17min from that."
  • Edmund Scientific sells kits including the magnet and type II superconducting wafer which will let you demonstrate the Meisner Effect with cheap liquid nitrogen as the coolant. They don't sell the liquid nitrogen, you have to scare that up yourself.

  • not simultaneously (Score:3)

    by Goonie ( 8651 ) <robert.merkel@b[ ... g ['ena' in gap]> on Saturday January 13, 2001 @04:14PM (#509017) Homepage
    While your friendly DNA might self-assemble, and might indeed superconduct if you get it cool enough (and 1K is pretty damn cool), it's not going to do both at the same time, which if you were going to ever use this in a practical sense might be something you'd like to get it do do (to build a molecular-level write-once memory system, for instance). In addition, getting things this cold is quite hard to do, IIRC.

    While this is fascinating stuff, it'd be even cooler (if you'll excuse the pun)if we could make variant DNA that superconducts at higher temperatures :-)

    Anyway, one slightly offtopic question about superconductivity and the high-temperature superconductors that caused all the fuss back in the 1980's: what happened? Did we reach another temperature plateau? Was it still at liquid-nitrogen-required temperatures?

  • DNA does not mean genetic - Read before ranting (Score:3)

    by vik ( 17857 ) on Saturday January 13, 2001 @03:34PM (#509018) Homepage Journal
    Before people go off on a tangent thinking that DNA here is used as a genetic material, be advised that it is not.

    The concept of using DNA for structural purposes is about as different from genetics as using mortar is to building seashells.

    The DNA is only sequenced to stick to itself, not to create or emulate any gene. It is quite likely that the "genetic" content of DNA used in this manner is garbage in the genetic context. The prime requirement in fact is that the DNA used for structural purposes will not interact with anything other than the target it is to join to.

    Vik :v)

  • Re:Below 1K - but in a small area (Score:3)

    by vik ( 17857 ) on Saturday January 13, 2001 @03:41PM (#509019) Homepage Journal
    Rememebr that we're talking a very, very small device here. To cool a Pentium chip of several square centimetres area to 1K would take a reasonable amount of machinery, say about 6 filing cabinet drawers worth.

    But to do the same to a volume less than 1 cubic millimetre? That could be done inside a desktop case. 1 cubic mm of DNA is a hell of a lot of circuitry. At a molecular scale you can reproduce the functionality of the human brain in a few cc's - if you can keep it cold.

    Vik :v)

  • Re:OK, someone brief me on this (Score:3)

    by Maurice ( 114520 ) on Saturday January 13, 2001 @03:40PM (#509020)
    Superconductors were discovered in the early 1900s by Onnes (in mercury). In the 80s they discovered the so called type 2 superconductors which have much higher critical temperature, i.e. they are superconducting at higher temperatures, making it possible to use cheap liquid nitrogen for cooling instead of liquid helium. Type 2 superconductors are not metals (or have impurities) and are usually some kind of copper oxide. They have much different properties than Type 1 (which are usually pure metals).

  • Re:Below 1K (Score:3)

    by Maurice ( 114520 ) on Saturday January 13, 2001 @03:42PM (#509021)
    Nope. Some things don't superconduct. Like gold or silver for example, even though they are the best ohmic conductors.

  • OC !! (Score:3)

    by slashdoter ( 151641 ) on Saturday January 13, 2001 @03:06PM (#509022) Homepage
    So if Superconductors can be made out of DNA then could I make an IC out of myself? and if I could make an IC out of my own cells, then could I make a CPU out of them? and if I could make a CPU could I Overclock myself? Opps to much, time to stop smoking this shit


    ________

  • Superconductors in a nutshell. (Score:5)

    by zCyl ( 14362 ) on Saturday January 13, 2001 @06:12PM (#509023)
    While interesting in an academic sense, such a discovery is rather trivial in a practical sense. Superconductivity itself has a number of astonishing uses that can sometimes look like magic, but they're only useful when we can get them to occur at useful temperatures. Unfortunately, cooling something to 1K will require something along the lines of laser cooling in order to achieve, and this turns out to not be very practical. Superconductors with a very low critical temperature cannot conduct much current before they exceed their critical energy level and "go normal".

    Useful superconductors are more in the line of HTC's, high temperature superconductors. The simplest of these are the superconductors that work when cooled to the order of 70 degrees Kelvin (-200C) by liquid nitrogen (which is cheaper than beer). If I recall correctly, the highest published HTC was around 175K, which is only 100 degrees below freezing. I've heard rumors of higher temperature superconductors, but haven't seen any referreed publications of results yet. Keep your eyes peeled, we'll see room-temperature superconductors within the lifetimes of most slashdotters.

    To be fair to lower temperature superconductors, I believe the maglev train in Japan uses a lower temperature superconductor cooled by liquid helium, which is somewhere down on the order of 10K.

    Superconductors aren't too useful for their property of not conducting current, since they have a critical maximum current level anyway. They are mostly used for their diamagnetic properties (they repel magnetic flux lines). This is the basis for how an MRI works, or for how super-fast magnetic trains work.

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