Wikipedia:Reference desk/Archives/Science/2013 April 14

= April 14 =

What is this engine part?
Shown is a picture of the engine of a 2004 Ford Escape. The silver cylindrical part in the red oval has a cable socket coming in on the left. I just repaired the cable and got the vehicle to work again, the problem being that it would start up fine but die within a second, unless I gave it gas, in which case it would keep running, until I took my foot off the gas, at which point it died. So whatever this part is seems to be related to the idling circuit. Like I said, the car works now. I'm just curious what the part is. Peter Michner (talk) 04:29, 14 April 2013 (UTC)


 * I'm pretty sure that's the oxygen sensor. But I'm not a mechanic.  -- Jayron  32  04:46, 14 April 2013 (UTC)
 * Scanning some other stuff, it could also be part of the Exhaust gas recirculation (EGR) system. There's a bit called the "DPFE sensor" or "Differential Pressure Feedback (EGR) sensor" which looks like it is in about this location.  I think this diagram is from a 2001 Ford Escape, and the DPFE sensor looks to be in about the location it is in your picture.  But I'm just guessing here.  -- Jayron  32  04:56, 14 April 2013 (UTC)


 * Thanks, looks like it's definitely called the idle air control valve Peter Michner (talk) 06:35, 14 April 2013 (UTC)

4D strorage device
How would one encode information onto a 4D crystal such as the example recently created? Plasmic Physics (talk) 07:20, 14 April 2013 (UTC)

Would there be any advantage over a conventional 2D storage device such as a USB stick? Plasmic Physics (talk) 10:04, 14 April 2013 (UTC)


 * I think you probably mean 3D, not 4D? If that's the case, see 3D optical data storage and Holographic data storage.  Red Act (talk) 12:56, 14 April 2013 (UTC)


 * I think the question refers to this weird press release. As near as I can make it out they made a simple quantum system that has angular momentum in its ground state and for some reason called it a "4D crystal". Since it's in the ground state, you can't encode any information into it. -- BenRG 15:52, 14 April 2013 (UTC)
 * If anyone cares, here's the paper and here's the theoretical treatment it cites. The theoretical preprint, which is by Frank Wilczek, starts with a point particle confined to a circle through which there's a magnetic flux. He shows that the ground state has nonzero (orbital) angular momentum and seems to think that's surprising, having apparently forgotten that the ground states of a lot of atoms have that property. He discusses how this counterintuitive result can possibly be true. The answer, of course, is that the particle is uniformly smeared around the circle; it's a "clock" whose hand is in a uniform superposition of all directions at all times. It's rotating, but it doesn't tell time. He then introduces more particles to the loop and a mutually attractive force and shows that they clump together, and seems to argue that this clumping will counteract the smearing out. I don't know how a guy who won a Nobel prize for explaining the structure of hadrons could make that mistake, but as far as I can tell he did. In reality switching from a point particle to a clump changes nothing because the clump is a composite particle (like a hadron) whose position can be characterized by a single angular parameter, and the wave function in terms of that parameter is the same as before. It has to be because a ground state is a state of definite energy, and in a state of definite energy the probability density is time-invariant. He even mentions that fact at the start of the paper, but seems to believe he can circumvent it. Really bizarre. The experimenters have the same misconception about the state they created, but they're experimentalists so it's easier to understand. Wilczek's preprint is apparently unpublished, and maybe PRL accepted the experimental paper because of something interesting on the experimental side. They 2should have made them drop the crystal-power nonsense, though. -- BenRG 20:03, 14 April 2013 (UTC)
 * The thought occurs to me that Frank Wilczek may have been making an elaborate joke. He also speculates about iGlasses and iQuasicrystals (the "i" meaning "imaginary", possibly also a play on words).  — Quondum 20:56, 14 April 2013 (UTC)
 * I think if it was a joke he would have said so by now. Imaginary time is an actual thing. Respectable physicists have written weirder preprints, like the ones coauthored by Holger Bech Nielsen claiming that the LHC exploded because of a Higgs-discovery-prevention mechanism in the laws of physics. -- BenRG 18:18, 15 April 2013 (UTC)


 * That is exactly what I'm talking about. So what did the experiment actually achieve? Plasmic Physics (talk) 13:10, 15 April 2013 (UTC)
 * I didn't read most of the paper, but they confined a number of charged ions to a circular path at very low temperature, so that they ended up in a ground state (effectively absolute zero). They threaded a magnetic field through the circle, which shifts the ground state into one where the ions have a fixed nonzero angular momentum. It's not a clock, though, because if you measure the position of the "hand" you'll get a random value that's uncorrelated with the time of the measurement. (One way of seeing that is the uncertainty principle: the angular momentum is exact so the angular position is totally indeterminate.) And it seems quite ridiculous to call it a crystal, much less a 4D crystal. I doubt this configuration of ions is useful for anything. Maybe it was an impressive experimental achievement to create it—I don't know.
 * By the way, I just now noticed that there's a Space-time crystal article. I can't critique Wilczek's paper in it, of course, because that would be original research. -- BenRG 18:18, 15 April 2013 (UTC)


 * If there truely existed such a thing as a codeable 4D crystal then it would circumvent the problem noted below by StuRat. All data is at the surface, just not all the time, so it should be possible to write as well as read. Plasmic Physics (talk) 22:42, 15 April 2013 (UTC)
 * Now that I've thought more about it, it still wouldn't be 4D - it would only be 3D (2DL1DT, not 3DL), since the data is still only encoded onto a quantum surface. Plasmic Physics (talk) 08:09, 16 April 2013 (UTC)


 * However, 3D storage may make sense to replace 2D. Or, a convoluted surface like in the brain, designed to increase surface area.  This would get by the problem of how to access and change data deep inside a 3D object (something like a CAT scan could conceivable read data inside a 3D object, but changing it is a bit more of a challenge).  So, maybe 3D storage for read-only memory, with convoluted 2D storage for read/write memory. StuRat (talk) 18:08, 14 April 2013 (UTC)

If you have a "4D crystal" with a charged carrier moving in a circle (for sake of argument let's say that it's a 1-foot superconducting ring with a single electron going around and around) wouldn't it still emit some kind of electromagnetic energy into space over time until it comes to a stop or some kind of homogeneity? Wnt (talk) 21:51, 16 April 2013 (UTC)


 * In theory, no, because it supposed to be in its ground state, so it has no energy to lose, it can perform no work. Motion does not automatically imply energy. The only energy that it can lose would be potential energy, by physically decaying. Plasmic Physics (talk) 13:37, 17 April 2013 (UTC)
 * But is an electron moving in a ring in its ground state, before it is perfectly degenerate at all positions around the ring with no observable position? Wnt (talk) 15:07, 17 April 2013 (UTC)


 * Care to rephrase? Plasmic Physics (talk) 22:48, 17 April 2013 (UTC)

Compromised title
When searching for "Thin Layer Extraction" one is only redirected to the article "Liquid-Liquid Extraction" that refers to "Thin Layer Extraction" through a dead link. There exists apparently no article by the name "Thin Layer Extraction" to be edited. I have prepared an extended article on "Thin Layer Extraction" and I am unable to create it under this name. How else can one assign a title to a new article? RogerLie (talk) 14:23, 14 April 2013 (UTC)
 * Questions like this are better asked at the Help desk, but I'll answer anyway. The trick for bypassing a redirect is, after clicking on Thin Layer Extraction and being taken to the Liquid–liquid extraction page, note at the top a line saying Redirected from Thin Layer Extraction.  If you click on the link in that sentence, you are taken to the redirect page.  You can then edit it to turn the redirect into an article, or you can look at the Page History, which, to save effort, is here.


 * I note when I look at the page history that you already created a version of that article, back in 2009. It was turned into a redirect a few months ago because an editor felt that the article did not establish that the topic is sufficiently notable.  In other words, it is not clear that the term is used in the literature to a significant degree.  If you think you can resolve that issue, then you can either edit the redirect page to turn it back into an article, or else revert back to your earlier version and make improvements to it.


 * If you have further questions about how to edit articles, please ask them at WP:HELPDESK. Regards, Looie496 (talk) 15:09, 14 April 2013 (UTC)

RAST
Is RAST test an example of RAS syndrome?? My textbooks all say that "RAST" stands for "radioallergosorbent" (presumably the T is the final t in that word, which would make it more correctly RASt) and google doesn't show anyone referring to it as a RAS Test. 2.98.248.78 (talk) 15:35, 14 April 2013 (UTC)


 * The Department of Redundancy Department is definitely interested in this question. Looie496 (talk) 15:56, 14 April 2013 (UTC)


 * Yes. Affirmative. StuRat (talk) 18:12, 14 April 2013 (UTC)

Power-to-weight ratio: electric and combustion motors
What of both have a better power-to-weight ratio? Even not considering the storage (battery/tank), can an electric motor ever have a better power-to-weight ratio? OsmanRF34 (talk) 19:28, 14 April 2013 (UTC)
 * See Power-to-weight ratio. The Hi-Pa Drive electric motor has a (theoretical) power/weight ratio of 2.92 hp/lb, better than the Wankel engine at about 1.0 hp/lb, and much better than a conventional Otto engine.  The advantage of IC is not so much the weight of the engine, but the weight of the fuel compared to the equivalent battery.  Tevildo (talk) 22:10, 14 April 2013 (UTC)
 * Much lower percentages of waste heat can't hurt. Sagittarian Milky Way (talk) 03:33, 15 April 2013 (UTC)
 * But, what is the most common scenario when it comes to real life motors, like those found in cars? I have the impression that electric cars have smaller motors for the same HP, however, I thought it should be the opposite: an Otto or Diesel motor should be smaller by same HP. OsmanRF34 (talk) 00:20, 17 April 2013 (UTC)

Shouldn't this graph be periodic?
Why is the current/voltage diagram in Franck-Hertz experiment not actually periodic? Why is there an overall upward trend? Wouldn't you expect the function to be truly periodic according to the theory presented in the article?

150.203.115.98 (talk) 22:43, 14 April 2013 (UTC)


 * No. As voltage increases, electrons are drawn more quickly from the cathode and through the mesh, so current increases.  This isn't surprising--if you increase the voltage across a resistor, current increases, and for similar reasons.  --140.180.243.134 (talk) 23:27, 14 April 2013 (UTC)
 * A resistor isn't really the best comparison in this case, although the basic principle is correct. The null hypothesis for the experiment is that it should behave like a vacuum diode, so the curve would follow Child's law, I ∝ V^(3/2), if there were no interaction between the electrons and the gas.  Tevildo (talk) 23:29, 14 April 2013 (UTC)
 * That certainly explains why the current increases between the peaks, but shouldn't the current drop down to zero at each multiple of 4.9 Volts, and start again? 130.56.234.8 (talk) 01:49, 15 April 2013 (UTC)
 * But it does drop down almost to 0 at each multiple of 4.9 volts. It doesn't get to 0 completely because some of the electrons don't encounter an atom before hitting the anode, and some of the electrons that encounter 1 atom don't encounter another, etc.  --140.180.243.134 (talk) 05:34, 15 April 2013 (UTC)
 * Right, but that's not what the diagram shows; the diagram shows a long-run increase, an overall increase, as well.
 * 150.203.115.98 (talk) 05:40, 15 April 2013 (UTC)
 * Are you perhaps confused by the fact the diagram is not current v time, but current v voltage? With higher voltages, electrons are more likely to be excited (or whatever the correct term is) even when the voltage is a multiple of 4.9v. The potential difference would be an average, but there would be fluctuations at the "particle" level so that some small portion of the electrons experience a potential difference not precisely a multiple of 4.9v. The higer the voltage, the larger the portion of electrons not precisely in that 4.9v region ergo the higher the current. Vespine (talk) 07:00, 15 April 2013 (UTC)
 * I don't think that per-particle KE variation is the principal reason for these effects. We never expect for the current to be 0: the only place we could have that is at na V (for a first excitation of a eV), but in that case the region (near the accelerating grid) in which the electrons can experience inelastic collisions is vanishingly small.  The increase in the minimum for each "period" is then easily explained by the increased total flow of electrons.  --Tardis (talk) 13:12, 15 April 2013 (UTC)
 * Yes I think I had it kind of backwards sorry, it's the absorbtion of electrons that reduces the current, so the fact there is a small current is explained by the fact that not all electrons are absorbed, even if they have the required energy to do so.. Vespine (talk)