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August 19

Why cant you hear the jet engine anymore before the jet takes off?

Everytime i watch a jet take of before the take of the engine spools up but then you cant hear it anymore the jet takes off and only what you hear is the noise of air but the actual sound of the engine is gone. Saludacymbals (talk) 15:37, 19 August 2018 (UTC)

Do you mean while observing from the ground, or while riding in the airplane? ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:41, 19 August 2018 (UTC)

See Aircraft_noise#Noise_mitigation_programs. Ruslik_Zero 17:45, 19 August 2018 (UTC)

Speed of electrons

How is the speed of an electron calculated? —Eli355 (talk | contribs) 16:11, 19 August 2018 (UTC)

Do our articles on Speed of electricity, Drift velocity, and Electron mobility answer your question? --Guy Macon (talk) 16:49, 19 August 2018 (UTC)

Of course the universe is more confusing than that...

"What if you point to some particular electron and ask how fast it is moving? Unfortunately, that’s a question we can’t answer, because in quantum mechanics, individual electrons in the metal really don’t have well-defined velocities. Rather, there is a probability distribution of many different possible velocities that they can possess. Since the uncertainty principle tells us it’s impossible to measure a particle’s position and velocity at the same time, successfully pinning down an electron’s velocity also means that you lose information about its position. Thus, you can’t tell which electron you are looking at." Source: [1]

--Guy Macon (talk) 16:55, 19 August 2018 (UTC)

With laboratory electric experiment setups combined with an Interferometer. --Kharon (talk) 04:04, 20 August 2018 (UTC)

Answer to the original query: Very carefully! Sorry, I couldn't resist. Anyway, that's discussing electrons in a metal, but the questioner didn't specify any particular medium. In experiments in particle accelerators where electrons or other particles are accelerated, discussing particle velocities is common. For instance our own Large Hadron Collider article states: …the protons have a Lorentz factor of about 6,930 and move at about 0.999999990 c… Now I'm not sure how that figure is arrived at. Is it data from the particle collisions, or from just calculating the amount of energy injected and subtracting losses? I took a gander at a few of the article references but they didn't seem to answer this. Also, this is measuring groups of particles and, I presume, giving their average velocity. From my layperson's understanding, I know about the issues with the uncertainty principle. But, and the source seems to agree, I think you can give an average velocity if you have a decent number of particles that you measure. --47.146.63.87 (talk) 05:10, 20 August 2018 (UTC)

The speed of an electron can be extrapolated from its momentum. By the Heisenberg uncertainty principle, an electron's momentum can be well defined so long as its position isn't; and if we know the mass of that electron (which we do), velocity is just momentum divided by mass. Of course, that's treating an electron as a particle in orbit around an atom; which isn't really all that right. But you can still make the calculation. --Jayron32 14:35, 20 August 2018 (UTC)

A bit more here is the formula for calculating electron orbital velocity for a specific energy level in a hydrogen atom per the Bohr model of the atom; how much this calculation applies to an actual electron in actual motion is debatable, but for a simple one-electron atom according to the Bohr model, it's a calculable thing. --Jayron32 17:57, 20 August 2018 (UTC)

Helpful Parasites?

Are there any parasites or worms that can be beneficial to a human host? Makuta Makaveli (talk) 22:37, 19 August 2018 (UTC)

Gastrointestinal tract has some information about bacteria used as part of digestion. —PaleoNeonate – 23:45, 19 August 2018 (UTC)

Adding: Commensalism may also be of interest, but I don't remember of particular ectosymbiosis cases in humans. —PaleoNeonate – 23:50, 19 August 2018 (UTC)

More: There is Maggot therapy (potentially repulsive image warning), but myiasis is generally not considered beneficial. —PaleoNeonate – 23:55, 19 August 2018 (UTC)

The distinction is maggots used for maggot therapy are species that preferentially eat dead tissue, whereas harmful myiasis usually involves species that eat dead and live tissue indiscriminately. --47.146.63.87 (talk) 04:16, 20 August 2018 (UTC)

You have to be careful with terminology. Parasitism is defined as being a situation where one organism survives at the expense of another. Of course, nature is rarely clean-cut. Some related topics: hygiene hypothesis, effects of parasitic worms on the immune system, and helminthic therapy. Matt Deres (talk) 01:34, 20 August 2018 (UTC)

Thank you for the link to effects of parasitic worms on the immune system, I was looking for something similar when I wrote the above but couldn't find it (I looked in the nematode article as I remembered that some were voluntarily swallowed). —PaleoNeonate – 01:56, 20 August 2018 (UTC)

Yes, to be pedantic, parasitism means a situation where one organism (the parasite) benefits in a way that reduces another organism's (the host's) fitness, but without killing the host, at least immediately. This is only one type of symbiosis; see that article for others. Our gut and skin flora are commensalistic or mutualistic, as long as they stay where they "belong". An interesting case that isn't exactly what was asked about, but kind of similar: malarial therapy. Before antibiotics, intentionally infecting people with malaria was sometimes used successfully to cure syphilis. The fever produced by the malaria infection killed the syphilis bacteria, which are temperature-sensitive. But the malaria pathogen did not directly affect the syphilis; it just happened to induce an immune response that harmed the syphilis bacteria. Another interesting example along this same line: innate resistance to HIV. A mutation in the CCR5 receptor that appears to have been selected for because it confers resistance to smallpox also happens to "accidentally" confer resistance to HIV. --47.146.63.87 (talk) 04:16, 20 August 2018 (UTC)

We're also seeing cancer treatment testing, which involves infecting a tumor with the polio virus, which then tricks the immune system into attacking the polio virus and also the tumor. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:50, 20 August 2018 (UTC)

Well it's not really a "trick" since the immune system should be attacking both the virus and the tumor. The immune system normally attacks cancerous cells; cancers can only develop when they are able to evade the immune system. --47.146.63.87 (talk) 03:58, 21 August 2018 (UTC)

August 20

Ni-MH batteries

I use rechargeable Ni-MH batteries in my GPS unit. I am aware that these slowly lose their charge when not in use. For this reason I charge a few the night before I need them. They are all getting rather old, and I know that after a few years they die completely, but when I take them out of the charger they all give a reading of about 1.2 volts on my multimeter. However when I put them in my Garmin GPS (Oregon 450) the battery level indicator shows some of them fully charged but others as empty or part charged. What is the battery level indicator measuring that the voltmeter is not?--Shantavira|^{feed me} 09:11, 20 August 2018 (UTC)

A voltmeter is not a good way to show either charge state or cell health in NiMH cells. I'm curious though as to what the GPS is doing to judge the batteries like this. It has two AAs and I've not seen a consumer device like this which showed individual cell health before. Also, to do that, it usually requires a long-term relation to that particular identifiable cell, specfically by watching its behaviour during charging.

To charge my 18650 LiPo cells (a useless format, best avoided) I use a VC4 charger. This is a useful charger and does NiMH too. I like it because it has a seemingly accurate per-cell charge meter. I also have a discharge tester (cheap thing, based on an Arduino and a big load resistor). The ratios of the charge capacity vs. rated capacity, and the charge capacity vs discharge capacity are a pretty good guide to cell health and aging. Much better, albeit more awkward, than any instantaneous measure with a voltmeter. Andy Dingley (talk) 09:47, 20 August 2018 (UTC)

My Garmin Etrex GPS unit takes two AA cells. I never intended to use anything but rechargeable Ni-Mh, but found that the unit shut down due to low battery after a disappointingly short time. The conclusion I came to was that it was meant to be used with 1.5V cells such as carbon (full charge 1.6V, a total of 3.2V), and my two Ni-Mh cells at 2.4V fully charged were already way down the discharge curve at switch-on, so the flat battery shutdown occurred far too soon. Akld guy (talk) 10:37, 20 August 2018 (UTC)

I have a few bits of kit like that (although not GPS). I've refitted them with simple DC-DC converter modules to raise the battery voltage. These are now in the couple-of-bucks range direct from China. Andy Dingley (talk) 10:41, 20 August 2018 (UTC)

Thank you both. The unit has a settings option: System > battery type > rechargeable Ni-MH, but as you say even the "fully charged" ones don't last long and I have to take at least a few spares with me when I go out.--Shantavira|^{feed me} 14:41, 20 August 2018 (UTC)

One option would be some new, high quality, NiMH. I only buy the good ones now (any lesser uses can use up my old ones) and those have a reliable 2,000 mAh capacity, and negligible storage losses. This is also why I don't waste effort on 18650s. Apart from the utter junk and counterfeits, that's the same capacity / volume as any 18650 I can afford, and without all the drawbacks. Andy Dingley (talk) 15:32, 20 August 2018 (UTC)

I've had the same problem with older NiMH cells, especially in recent GPSr models and in cameras. I find that new 2900 mAh NiMH cells last most of the day, even in newer models, and last more than a day in old eTrex models. As Andy says above, perhaps it is time to buy new? Your battery level indicator is measuring voltage under load conditions, probably with a significant startup current drain. Dbfirs 18:41, 20 August 2018 (UTC)

Characteristics of common wasps and bees

This list states that yellow jackets and paper wasps (among honey bees and bumblebees) supposedly are not attracted by light at night (except this appears near their nests). However, as I can clearly testify – not only from my very personal painful (in both senses) experience –, this is simply wrong! Wasps, yellow jackets, hornets etc are indeed attracted by light, and I guess at least some of you can agree and tell a thing or two about that phenomenon… Also, the sting pain intensity is rated with 2.0, equally for a honey and a bumblebee sting, but with "2.x" for yellow jackets and European hornets, which I find hard to believe, as bee venom is said to be far stronger than wasp and even more so than hornet venom. Finally, the article calls wasps' (in the broader sense) nests "hives", which I consider incorrect, too, as in my view, the term hive is only to be applied when speaking of bees. But, as I am probably not sufficiently competent in this field, what would the experts say?--Neufund (talk) 22:59, 20 August 2018 (UTC)

But how do you know they were attracted by the light, rather than something else which just happened to be in the same place? Andy Dingley (talk) 23:21, 20 August 2018 (UTC)

The sting indices in the article were unreferenced, and "The Sting of the Wild" by Justin O. Schmidt lists yellow jackets at 2, the same as honey bees and bumble bees, but does not mention European hornets as far as I can see. The article has now been corrected in regards to yellow jackets.--Wikimedes (talk) 04:53, 21 August 2018 (UTC)

You're quite right as regards photophilia--some social wasps are attracted to light in a darkened environment. While most such species are diurnal by nature, they are efficacious workers, and in the peak of summer will sometimes push the limits of nightfall during forays for food and other nest resources, making the ability to navigate after dark a valuable if infrequently used ability--some species of hornet and yellow jacket also regularly hunt at night, though there may not be any such species native to where you live, depending where you are, as such species are an exception to the general rules governing social wasp activity levels (more broadly, nocturnal behaviour is quite common amongst the larger array of wasp species).

For almost all species of insect which display an attraction to artificial light sources, the individual in question is not actually "drawn to" the object in question as a matter of "wanting" to be near it--rather, the behaviour is a consequence of their normal means of navigation being thwarted by the light source. Nocturnal animals which rely upon light as their primary modality for navigation use the stars and moon to orient themselves. These celestial objects are so far away as to be functional fixed as regards the insect's movements in any given moment, but this is not so with a light that is mere feet away, so the hapless creature ends up flying in circles or in other no-productive paths around that object, confused by its actual vs. apparent position as a navigational point. Note that in some cases, the insect may utilizing polarized light, though either variation can result in the short-circuit of the evolved navigational strategy.

As to "hives", you're correct that this is less common than "nests" as the go-to label in most areas, but you'll hear both with frequency, and neither is a formal, set clinical term. Most researchers doing entomological research of eusocial Hymenoptera species will refer to the collective as the "colony", and may do so when referring to the actual structure of the nest itself or the kin-group/superorganism. Snow ^{let's rap} 15:31, 21 August 2018 (UTC)

August 21

Fat pads on palm at the base of fingers

Is there a medical term for the fat pads located on the palm just below the base of the fingers? (I know there are terms in palmistry, but I’m looking for the medical terms.) Also, is there any significance to having only three fat pads instead of four? --24.76.103.169 (talk) 02:57, 21 August 2018 (UTC)

Reviewing Hand, I'm not seeing where they come out and name those pad-like structures. However, notice that they are between the digits, like the webbing is. Hence there are only three of them. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:40, 21 August 2018 (UTC)

Callosity seems the term for natural occurrences. The connected term Callus seems to be restricted to diseased conditions of the same. --Kharon (talk) 03:57, 21 August 2018 (UTC)

Looking a Gray's Anatomy image there are no sub-dermal fat pads noted at the base of each finger but there is a continuous strip of fascia crossing the palm at the base of the fingers. This strip overlays the fascia running from the wrist up and into each finger. The crossing of these two strips of fascia may add to the impression of a pad at the base of each digit. But I tend to agree with Kharon that callosity of the skin probably has more to do with pad formation than underlying structure. Richard Avery (talk) 09:06, 21 August 2018 (UTC)

Only the thumb's "pad" has an established medical term. It is the thenar eminence. But, that refers more to the group of muscles than the skin overlaying the muscles. Just as there is no medical term for the skin on the elbow (regardless of what the Internet claims), there is no medical term for the skin areas around the palm of the hand. 209.149.113.5 (talk) 12:41, 21 August 2018 (UTC)

Not forgetting the hypothenar eminence on the other side of the palm from the thenar eminence.Klbrain (talk) 22:54, 21 August 2018 (UTC)

Having trouble finding normal and shear forces

I got the other answers. [2] I'm reviewing Statics ahead of the next semester, since I've forgotten a lot over the summer. Thank you. 161.185.160.175 (talk) 21:00, 21 August 2018 (UTC)

Winkler-Bach formula would be the place to look. As we don't (yet!) have an article on it, you're going to have to Google it. Andy Dingley (talk) 22:43, 21 August 2018 (UTC)

Maybe try german wikipedia article de:Rittersches_Schnittverfahren together with google translate for a start. But i would highly advice otherwise because things like formula letters are often chosen differently in different countries, schools, from different professors, so you may end up very irritated by learning the same formulas with different letters.

If you are a student, you should ask/know what books are used or recommended by your professor or lecturer for statistics. They also often have some university-webpage about themselves and/or their courses where these recommended books are listed up. Go try to be one of the first at your local library or buy used ones from other students. --Kharon (talk) 21:47, 25 August 2018 (UTC)

August 22

Maxwell's demon

If you explained Maxwell's proposal and told me to suggest a solution, I would imagine that it was the necessity of the demon adding energy to the system by opening and closing the door. However, I see that the actual answer is different, e.g. the necessity of expending energy to learn which molecules were which, or the necessity of erasing one's memory of past molecular movements. So where do I go wrong in suggesting that the energy of moving the door is a possible answer? And has anyone published a WP:RS addressing door-energy requirements and explaining why they don't work? Nyttend (talk) 02:19, 22 August 2018 (UTC)

• It's not about energy, it's about entropy.

Maxwell's demon uses entropy to produce energy. It works within the same simplified world of "light inextensible string" and "frictionless doors" as much conceptual physics. The assumption is that "filtering the entropy" would allow energy to be produced (this is uncontentious) and also that the demon can do this without consuming energy itself (that's a conceptual simplification, but it's valid because if the demon can't do it with this simplification, it certainly can't achieve it without.)

However, even with these advantages over reality, Maxwell's claim is that the demon can't function. Not for lack of energy, but for lack of entropy. Although this didn't really get a theoretical basis until the 1960s. Andy Dingley (talk) 09:48, 22 August 2018 (UTC)

The assumption is ... that the demon can do this without consuming energy itself (that's a conceptual simplification, but it's valid because if the demon can't do it with this simplification, it certainly can't achieve it without.) Doesn't that just show how meaningless the thought-experiment is? You might as well say "If I use a perpetual-motion machine to operate the door, I can generate free energy!". Iapetus (talk) 09:54, 22 August 2018 (UTC)

But the demon doesn't say that. It says, "even if I did have a perpetual motion machine, I couldnt generate free energy; so I certainly can't do it without." Andy Dingley (talk) 10:15, 22 August 2018 (UTC)

• Sort-of repeating what AD said: the idea is that Maxwell's demon paradox's standard solution does not involve door-opening costs. It might well be that, if you try to build a Maxwell demon in the lab, the door-opening costs would be prohibitive even with a door in unobtanium; it might even be that matter properties at small scales forbid entirely whatever design you have in mind. However, the crux of the Maxwell demon paradox is in the information/decision part, not in the door design whose refutation will depend on the specifics (for another example of extract-work-from-single-temperature-source design, see Brownian ratchet). Tigraan^{Click here to contact me} 14:27, 22 August 2018 (UTC)

• So in other words, I went wrong because my answer didn't answer the question that Maxwell posed :-) Thanks for the correction. Nyttend backup (talk) 16:20, 22 August 2018 (UTC)

Just to clarify, the solution to the problem posed by Maxwell's demon is that it is, as originally presented, supposed to violate the second law of thermodynamics by allowing the entropy of the closed system to decrease without itself increasing the entropy of the universe. This was solved by Information Theory's contribution to the idea of entropy, which is that the storage of information always creates entropy. In order to decide when to open and close the door, the demon has to store information in his "mind" (whatever that is) to allow him to decide when to open the door; every new particle creates a new memory location, which creates more entropy. Thus, the second law is still saved. This video, starting at about 7:00 minutes, explains exactly how this works. --Jayron32 16:33, 22 August 2018 (UTC)

Why is the letter 'G' used to represent Conductivity ?

This came up on the Sieman's Talk page {1} and it got me curious, so I tried to research it myself briefly to no avail, and thought I would bring it here:
Why was the letter 'G' chosen to represent electrical conductance, the reciprocal of resistivity.
Any insight is appreciated. Cheers! --Elfabet (talk) 14:07, 22 August 2018 (UTC)

In German one may suggest G stands for Geleitfähigkeit because "Das Formelzeichen des elektrischen Leitwerts ist G (und) seine Maßeinheit Siemens" [3]. Both Georg Ohm and Werner von Siemens were Germans. DroneB (talk) 15:12, 22 August 2018 (UTC)

(edit conflict) It might not mean anything. There are a limited number of letters one can use, and the obvious letter (C) already is used for electric charge (coulomb charge), so other letters needed to be chosen for other variables; I for current and G for conductance. "G" doesn't have to mean anything per se, it just needed to be an unused letter one could press into service. Notably, G isn't always the symbol used. Sometimes, an inverted omega sign is used, (called the "mho") since the Siemens is an inverse of the Ohm. --Jayron32 15:14, 22 August 2018 (UTC)

@DroneB: that technically works, but doesn’t feel natural. I don’t think the term Geleitfähigkeit was ever used (the google results I found are generally typos for Gleitfähigkeit). However, Greek γ is occasionally used for Electrical conductivity, and I could imagine G could be derived from that. Cheers ✦ _hugarheimur 17:02, 22 August 2018 (UTC)

I lack a reliable relevant source for Geleitfähigkeit ("conduct capacity") because an expression such as "Die Sekretion der Bartholin-Drüsen regt die Geleitfähigkeit des Penis zusätzlich an."[4] gives a wrong (but interesting and useful to know) idea, and is probably a typo of Gleitfähigkeit. So in our fruitless search of the source of G, Geleitfähigkeit fails Wikipedia's WP:SYN and the mho character $\mho$ is the unit, not the symbol of conductivity. DroneB (talk) 19:47, 22 August 2018 (UTC)

It's worse than that: C isn't even the symbol for electric charge. C was already taken for electric capacitance, so the symbol for electric charge is Q and thus conductivity had to settle for G. 97.115.66.87 (talk) 23:43, 22 August 2018 (UTC)

Really? I thought it was because C already stood for coulomb, and writing C = 0.05 C might be a little bit confusing. 78.0.242.89 (talk) 23:43, 24 August 2018 (UTC)

There is often no connection with a deeper background or higher meaning. Engineers are traditionally painfully pragmatic in such cases - they pick then "next best" letter and carry on engineering. So the letters "A-F" where already in use and thus they picked "G". --Kharon (talk) 21:24, 25 August 2018 (UTC)

What's the best estimate for Mauna Kea's all-time high height? How far in the future or past is this?

I'd be interested in any height (from base, from sea level (current or at the time), average pressure altitude..) Sagittarian Milky Way (talk) 19:31, 22 August 2018 (UTC)

Mauna Kea is towards the end of its growth, although it remains active. It is unlikely to have been higher than it is now and is likely never to get substantially higher. Mikenorton (talk) 05:52, 23 August 2018 (UTC)

Sapphire

According to sapphire, it's an aluminium oxide Al₂O₃. Does it mean that if I properly oxidize a common alumunium, I can obtain an inexpensive sapphire? 212.180.235.46 (talk) 20:18, 22 August 2018 (UTC)

Synthetic sapphires are made using the Verneuil process, the Czochralski process, or just by hot isostatic pressing, as explained later in the article. Perhaps someone else can explain how easy or how difficult this is. Dbfirs 20:23, 22 August 2018 (UTC)

• You have three problems to solve:

1. Grow some corundum. This is fused aluminium oxide. It has been commercially manufactured as an abrasive for about 120 years. It's mostly done by the Verneuil process, which is a fairly simple process using an oxy-hydrogen flame. You now have the sort of thing that looks like a geological sample - chemically it's right, but the structure is amorphous and opaque. If you can see through it at all, that's luck.
2. Refine the material to make it a single crystal, thus transparent. This might use the Czochralski process. Again, this is much easier than it used to be - induction heater modules are on eBay these days, and they don't catch fire all that quickly.
3. Change the colour. This is a matter of adding dopants to the aluminium (yes, just like semiconductor manufacturing). Usually chromium. This is very tricky to get the colour right. One of my favourite sapphires are padparadscha sapphires, which have a red colour, somewhere from a salmon pink to an orangey red. If you see one of these for sale today, chances are they're synthetic, grown in Myanmar or Thailand - especially if they're orangey. You can also deepen an existing colour, just by heating them in a controlled manner.

So, not easy. But if you have a glassworking workshop, or even a ceramics workshop, you're halfway there. Or you can grow them directly as crystals, using epitaxial growth. But CVD processes, let alone MO-CVD, tend to involve horribly toxic chemistry. Andy Dingley (talk) 20:51, 22 August 2018 (UTC)

We have Sapphire § Padparadscha. Might want to make a redirect. --47.146.63.87 (talk) 06:45, 23 August 2018 (UTC)

 Done Tigraan^{Click here to contact me} 07:57, 23 August 2018 (UTC)

This video may be of interest: https://www.youtube.com/watch?v=a0N4JYN9lFI --Guy Macon (talk) 21:02, 22 August 2018 (UTC)

Or just buy a synthetic one outright, which will be cheaper than the equipment necessary to make it (as detailed above), unless you're already in the jewelry business. Synthetic gemstones are cheap because gemstones are rocks. They don't involve rare materials. "Natural" gems are only expensive because of a combination of factors that are an object lesson in behavioral economics: the gem mining industry is an oligopoly, and said industry heavily promotes "natural" gems as somehow fundamentally different from "fake" synthetic ones and the only suitable material for demonstrating your love for someone, or from showing off how rich you are, which justifies their exorbitant cost. At least in the Western world the public largely goes along with this because propaganda works. Industrial and scientific use of gemstones is almost universally synthetic stones because in those contexts the people using them aren't trying to impress others; they know the stones are cheaper and just as good. (Sometimes better, because the properties of the stone can be carefully controlled, which is important for some applications.) --47.146.63.87 (talk) 06:35, 23 August 2018 (UTC)

Nitpick: Synthetic gemstones are cheap because gemstones are rocks. They don't involve rare materials. - Partly true. Ruby and sapphire are waaay cheaper to manufacture (in a marginal cost sense once you have all the equipment) than the natural thing, but synthetic diamonds cost almost as much as natural ones even though it is pure carbon. It depends on the temperatures etc. needed in the production process. Tigraan^{Click here to contact me} 08:03, 23 August 2018 (UTC)

Are you sure? I thought gem-quality diamonds could be made pretty cheaply (but for the reasons discussed previously people prefer expensive natural ones). The linked article doesn't say anything about the cost to manufacture, just the selling price. Iapetus (talk) 08:14, 23 August 2018 (UTC)

Hmm, I did base this on the article sentence synthetic diamonds sold as jewelry were typically selling for 15–20% less than natural equivalents, and my knowledge that synthetic rubies are cheap enough that a crazy friend of mine bought some to forge his own proposal ring (here's a retailer at $40 for 200 pieces). However our article also says De Beers started selling synthetic diamonds to the general public at a couple of hundred dollars each, so the manufacturing cost cannot be super high either. Tigraan^{Click here to contact me} 11:03, 24 August 2018 (UTC)

I've a few 3/4" diameter rubies. One or two I've used, set into sword pommels. I've no real use for 3/4" rubies, but when you see them listed and they're so cheap, it's hard to resist. Much silversmithing I've done has involved padparadscha sapphires, just because I like the colour.

This isn't to say that synthetic means cheap though. Laser rods, or the three foot discs in some of the big lasers, can cost as much as Liz Taylor's diamonds. I've a small piece of a three footer, which one day "just broke". Most of the bigger pieces were worth so much as scrap they were re-ground as rods or discs for smaller lasers. Andy Dingley (talk) 12:03, 24 August 2018 (UTC)

• Even for diamonds, it's cheap to make bulk polycrystalline diamonds, and these have been part of the industrial abrasives trade for decades. It's when you need monocrystalline (i.e. transparent) diamonds in large sizes that it gets expensive. Andy Dingley (talk) 08:20, 23 August 2018 (UTC)

Cheap is relative. The cheapest industrial abrasive is Sand. Compared to Sand, industrial diamonds are still very expensive. The question of worth is nicely pointed out in the article Opal. (cite) The internal structure of precious opal causes it to diffract light, resulting in play-of-color. (citeend) Ofcourse that includes how common these colors are. Thus like the rare pink and blue diamonds are traded highest it seems blue and orange-pink are the most expensive sapphires. Else they become industrial parts like in case of sapphires as bearings in watches or as part of cutting tools in glass works. --Kharon (talk) 21:14, 25 August 2018 (UTC)

Rice foamed after being soaked for a couple of days, probably less

I put the rice in the rice cooker but never got to cooking it. It's summer, and after more than a day, the water had quite some foam on the top with a hint of fermentation. Is the rice still safe for cooking? 104.162.197.70 (talk) 21:44, 22 August 2018 (UTC)

• see Rice wine which is what is forming. Rice is quite cheap, chuck out, wash it out and start again. Graeme Bartlett (talk) 21:58, 22 August 2018 (UTC)
• Going by this NHS page, I'd strongly suggest not eating it. As Graeme says, even if it is actually safe, why risk it? › Mortee _talk 22:36, 22 August 2018 (UTC)
  • Could be Bacillus cereus which can survive boiling and is a known pathogen of cooked rice. Heaviside glow (talk) 22:40, 22 August 2018 (UTC)
    • Yes but the OP isn't referring to cooked rice. There are significant differences between cooked rice and uncooked rice, especially regarding nutrient availability. Germinated brown rice is a common thing, and while it's generally suggested to change the water after a while, there doesn't seem to be great concern over food illnesses from Bacillus cereus. Of course nutrient availability is likely to be reduced further with brown rice although interestingly this [5] mentions that brown rice has higher Bacillus cereus load in the first place. Germinated brown rice seems to end up with an overall load of a bit over 1 order of magnitude higher load although they didn't test enterotoxin levels. Nil Einne (talk) 01:21, 23 August 2018 (UTC)
      • All true, and I'm interested in the white vs brown rice distinction you raised. Still, given that the bugs are there and inclined to grow in a damp environment at room temperature, unless OP fancies experimenting on themselves, it's probably best that they just get some new rice. Per our article, germinated brown rice is left for 4–20 hours, not "a couple of days". At a guess, brown rice is also more resilient to soaking because its husk is intact, so I'd expect B. cereus to get started rather faster with white rice, regardless of the initial load (not that we know what colour OP's rice is). I don't have any expertise here at all, but I'm still very much inclined towards caution. › Mortee _talk 01:35, 23 August 2018 (UTC)

        • No that's for 30-40 degrees C water. The OP appears to come from New York, and while a lot of the northern hemisphere is having hot summers, i find it unlikely that water sitting there. Most sources including our article recommend longer for lower temperatures although I can't find good sources discussing recommended times for more reasonable temperate country room temperatures (say 20 degrees C). Although this source mentions one commercial processor using 72 hours at 30 degrees C [6]. Various sources e.g. [7] [8] mention GABA or other levels peak at 48 hours, so they seemingly didn't think these such dangerous levels to be not worth testing. This isn't exactly surprising since as the sources also mentioned, soaking grains and other seeds for such periods isn't exactly uncommon. This source actually suggests up to 72 hours may be best [9]. (As an aside it also hints at as do other sources another thing namely that you probably also get better results at higher temperatures (well the 30-40 degrees) than you do at lower temperatures.)

          I'm not suggesting there is no risk or the OP does it, but we also have to be realistic here that there's very limited evidence either way. The risks with cooked rice have very little relation to the risks with cooked rice.

          BTW an an interesting point, some sources recommend soaking rice overnight to reduce arsenic levels and I'm pretty sure this includes white rice which I assume is what the OP is referring to. Unfortunately the best source I could find is some BBC show [10]. (Since it's just a summary from the show, it doesn't say if this soaking was at room temperature or in the fridge or what.) This source which is discussing the results of the show includes a quote from an epidemiologist endorsing soaking [11]. While it's impossible to know if she gave some dire warnings the source neglected to mention, none are mentioned there.

          Weirdly this group carried out fancy percolator tests for cooking but didn't seem to test such a basic step. However I don't believe this is likely to be due to health concerns from soaking rice overnight. More likely that percolator makes for a more popular paper than simple soaking and also as fancy as it sounds, it's probably a more cost effective method for industrial and commercial kitchen usage. Of course 48 hours is quite a bit longer than overnight, however I don't think sources are going to recommend leaving cooked rice out overnight or even for 4 hours. (This is of course a common problem. Simple solutions which have the potential to work well in lesser developing countries where the problems may be significant are not well considered.)

          Nil Einne (talk) 04:25, 23 August 2018 (UTC)

          • P.S. I initially gave Bangladesh as an example in my last sentence but removed it as in retrospect it may be a poor one give the frequently high arsenic levels in their water levels meaning that you could perhaps make the problem worse or at least get a lot less improvement than may be observed in countries with better water supplies. Nil Einne (talk) 04:33, 23 August 2018 (UTC)
          • Interesting, I'd never heard the arsenic advice. › Mortee _talk 09:30, 23 August 2018 (UTC)
            • Personally, I think there's far too much personal speculation going on here, and I wish this matter had been left at the initial advice of Graeme and Mortee. This is an inquiry that is close enough to a request for medical advice (it is, afterall, an inquiry about the safety and health implications of a course of action) that the editors here should have refused to answer this question outright, and if any answer were put forth, it should be the one which clearly endorses precaution and safety. A protracted discussion about whether or not food poisoning is actually likely to occur only creates the possibility that the OP may decide to consume something at least potentially dangerous on the basis of opinions (or a sense of doubt among them) here. That is exactly the kind of outcome our no medical advice rule was established to guard against. Frankly, some of the laissez-faire opinions above display a marked lack of understanding of the topic and a pretty free-wheeling willingness to discount the risk of contamination. For starters, one doesn't just have to consider common pathogens associated with under-prepared foodstock of this sort; so long as there is standing water involved, the question of what was in that water initially, what was on the surface of the cooker, and in the immediate environment (in the addition to heat and other factors) all create risk of bacterial and/or fungal growth after that period of time, with potential toxicological consequences. Indeed, the fact that the OP mentioned the heat and apparent fermentation are additional signs of why it is imprudent to say anything tot he OP which might induce them to have doubt as to whether to pursue the more cautious course (in the present case or in the future). And even if I were not familiar with these basics microbial concerns, I'd still be saying as a matter of policy that opining on this topic is not appropriate use of the desk. The OP should be advised to seek their health and safety advice from appropriate sources, and this discussion should be closed. Props to Mortee, however, for maintaining a consistent tone of discouragement to the notion of reheating already fermenting food. Snow ^{let's rap} 06:18, 24 August 2018 (UTC)

Some medical advice ("don't risk it. Throw it out and thoroughly clean the cooker") is OK, and is vastly preferable to "ask your doctor if eating rotten food is OK", Other medical advice ("go ahead and eat rotten food") is definitely not OK.

There are some who believe that Wikipedia has a policy against giving medical, legal, and business advice, but no such policy or guideline exists. (If you are about to cite the reference desk guidelines, please read WP:LOCALCON and then show me where the Wikipedia community approved them).

Here is some medical advice: Don't do crystal meth. It will screw up your health. Don't bother asking a doctor if crystal meth is good for you. It isn't. Here is some legal advice: Don't do crystal meth. It is likely to get you arrested. Don't bother asking a lawyer if crystal meth is illegal. It is. Here is some professional advice: Don't do crystal meth. It will use up all of your money and is likely to get you fired. Don't bother asking a certified financial planner if becoming a meth addict is good for your finances. It isn't. (general disclaimer, medical disclaimer. legal disclaimer, risk disclaimer.)

There. I just provided medical, legal, and professional advice, and while I did make a point, I did so without being disruptive.

Feel free to report my behavior at WP:ANI if you believe that I have violated any Wikipedia policy or guideline.

BTW, here is some more free advice: In my opinion both terminal cancer and AIDS are even more effective methods of weight loss than food poisoning or crystal meth, so if you really want to shed those pounds why not try all four at the same time? More advice: don't get your medical advice from an electronics engineer. --Guy Macon (talk) 07:38, 24 August 2018 (UTC)

_{Re. the above, see WP:SOAPBOX. The Wikipedia article about Methamphetamine gives referenced information about the illicit use of methamphetamine hydrochloride as a recreational drug and its less common legally controlled medical prescription as a second-line treatment for attention deficit hyperactivity disorder and obesity. DroneB (talk) 13:03, 24 August 2018 (UTC)}

In order to properly evaluate your assertion, would you be so kind as to tell us which of the five numbered entries on the WP:SOAPBOX page you believe forbids the above? --Guy Macon (talk) 13:57, 24 August 2018 (UTC)

_{No. DroneB (talk) 23:52, 24 August 2018 (UTC)}

I'm not sure what to make of your post, because you seem to frame it as if in counterpoint to my own, and yet much of your perspective seems similar to my own assertions. However, a few important caveats:

• No, it's is not really appropriate (let alone "vastly preferable") to answer even simple questions where they have potential medical or legal consequences. The best course of action there is -always- to point the individual in question to a qualified professional, no matter how obvious the answer may seem, because the devil is very much in the detail when it comes to risks in this area. I agree with you insofar as there is a world of difference between the inappropriateness of telling someone not to take a risk and the inappropriateness of encouraging them to do so; the latter is clearly much more unacceptable. But neither form of speculation should be engaged with by amateurs. The irony is, some of us certainly are qualified to provide medical or legal advice, but it is exactly those individuals who would never do so in this highly problematic forum (for both professional and ethical reasons). Which means by definition the people providing advice of that sort here are those who are not qualified to be doing so. Shutting down inquiries that can lead to poor advice that may affect another's well-being is such a substantial way is manifestly the appropriate thing to do in such situations; engaging with such questions just so one can scratch the itch of playing expert is irresponsible in the extreme.

And as to your closing comment there, I presume that the electrical engineer in question is yourself, in a quasi-self-effacing jib. Here's the problem with that: the person requesting that information probably doesn't know your background (I didn't, and we've been editing alongside eachother in multiple spaces for years) and they may be foolish enough to assume anyone answering a question knows their stuff, which is...not likely, to put it mildly, when it comes to the RefDesks. Meaning no disrespect to the present OP, but many of the people who will come here seeking guidance on a question with medical implications may not be exactly flush with good common sense, or they probably would not be making such an inquiry here to begin with. We have a moral obligation not to facilitate their reliance on advice about such issues, by closing down such conversations. With certainty, nobody should be spitballing answers to such questions here. We should especially never be telling them "don't bother to check with a professional, just trust me."

• I think you may want to review WP:LOCALCONSENSUS yourself, because you've nearly completely inverted the policy with your presentation of it there. Here's the very first sentence from that section of WP:CONSENSUS: "Consensus among a limited group of editors, at one place and time, cannot override community consensus on a wider scale." (emphasis added). Nothing in that subsection remotely implies that local groups of editors cannot come to their own conclusions about the best way forward on an issue, be it content or process. And indeed, obviously this is so, because the entirety of that policy is about how one goes about doing exactly that. LOCALCON only tells us that broader approaches already adopted cannot be put aside by local editors.

And dearth of guidelines or not, this is a topic the community (here at the RefDesks and elsewhere) have grappled with, and shown a great deal of concern about. I guarantee you that anyone making a habit of providing medical or legal advice (even if the answers seem entirely straightforward in every instances) would eventually be removed from this space. Indeed, I'm not sure how heavily involved you have been here recently, but in the event you missed the actions, we have recently topic banned an editor (and warned others) who have a habit of offering fly-by responses, and most of their offenses didn't even rise to the level of importance of medical or legal advice. Partly this was done out of a concern with the quality of our responses, but also because acting with impunity in this regard has been increasingly bringing the broader community's scrutiny upon this corner of the project (for entirely legitimate reasons, in my opinion). There was even a VPP discussion six months ago that sought to close the desks altogether because of the problems wrought by our most free-wheeling "contributors"--and potentially dangerous advice was one of the issues raised there. I guarantee the regular and semi-regular contributors to this space are not going to allow the people who think they are a qualified expert on everything get the RefDesks (a valuable part of our educational exercise) shutdown over such nonsense.

Beyond that, you've been around long enough that you surely know that there are higher authorities on this project than even community consensus. For example, the WMF, which (in the strict legal sense anyway) owns this project and its assets. The WMF imposes many rules that put limitations upon what our policies can or cannot say, and provide guidance that is in effect regardless of whether or not the community has yet arrived at the same conclusions. Shall we ping WMF legal here and ask them if we are allowed to provide medical or legal advice in direct response to explicit inquiries? Because I feel I can tell you with some certainty that the standard they will require of us will not map very well to the one you're suggesting. And indeed, they have very compelling reason for requiring that we err on the side of caution; as the entity hosting this space, they have substantial vicarious liability for any ill-advised (read: dumbarse) medical or legal (or otherwise dangerous) advice provided here. Such considerations being in addition to any previously mentioned moral restraints that we ought to be applying in such cases.

Sorry, but all said, I strongly disagree with you. Would I call an editor out for telling someone to do the cautious thing with regard to consuming something potentially toxic? No--in fact, the above discussion demonstrates as much, so it would be foolish for me to claim otherwise. But do I think that is the ideal solution? No, I do not, because to encourage such an approach is to open up the door to someone pressing the matter too far on an issue they feel is "obvious", and potentially causing real harm as a consequence. The appropriate response is to close down all such threads on sight and encourage the individual to seek the professional advice they need. Not the random best guesswork of the Reference Desk regulars--no matter the fact that we are a generally knowledgeable group whom I am happy to count myself amongst. Snow ^{let's rap} 04:57, 25 August 2018 (UTC)

August 23

Varicoceles

Would a varicocele show up on a conventional (black and white) ultrasound, or would it only show using Doppler ultrasonography? I'm reading conflicting information. Thanks Uhooep (talk) 13:18, 23 August 2018 (UTC)

Ultrasound with color Doppler is diagnostic in nearly all cases of varicocele and is the imaging technique of choice. The linked article shows images with and without Doppler. DroneB (talk) 16:00, 23 August 2018 (UTC)

August 24

Fertility question

If one gets one's entire epididymis (on both sides) surgically removed and one's vas deferens grows and attaches itself to the the spot on the testicles to which the epididymis was previously connected, would you once again begin ejaculating sperm--but with the sperm being undeveloped this time around (since it won't have an epididymis to go through)--thus ensuring that you'd remain infertile? 68.96.95.13 (talk) 21:58, 24 August 2018 (UTC)

Just use spermicide condoms and the calendar method. Sagittarian Milky Way (talk) 23:00, 24 August 2018 (UTC)

That doesn't answer my question here, though. 68.96.95.13 (talk) 02:18, 25 August 2018 (UTC)

Who was it that asked this question a few months ago? ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:34, 24 August 2018 (UTC)

I did--though I don't think that it was quite the same question. Futurist110 (talk) 19:09, 25 August 2018 (UTC)

Thanks for giving us your IP address. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:37, 25 August 2018 (UTC)

What use would it give you? Futurist110 (talk) 20:50, 25 August 2018 (UTC)

So that we'll know not to block the IP for trolling. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:03, 25 August 2018 (UTC):::

"07:04, 25 August 2018 Mz7 blocked 68.96.95.13 with an expiration time of 36 hours (anon. only, account creation blocked) (ref desk trolling)" --Guy Macon (talk) 21:12, 25 August 2018 (UTC)

Who is Mz7, though? Futurist110 (talk) 21:56, 25 August 2018 (UTC)

That would be the admin that blocked the IP after I reported it to AIV. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:09, 25 August 2018 (UTC)

Oh. Futurist110 (talk) 22:26, 25 August 2018 (UTC)

Also, for the record, my question here was actually meant to be completely serious. Futurist110 (talk) 21:56, 25 August 2018 (UTC)

Especially the joke about my mother, eh? That's what led me to assume it was just a troll. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:09, 25 August 2018 (UTC)

Yeah, I'm sorry about that. I went too far with that comment of mine. However, you weren't answering my question and thus I got a bit sassy. Futurist110 (talk) 22:26, 25 August 2018 (UTC)

I thought the IP was mocking the original questioner from some months back (you), and the personal attack on me cemented it. Henceforth, either log in or explain, and you shouldn't get blocked. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:51, 25 August 2018 (UTC)

Yeah, the reason that I asked this question anonymously is that I was hoping not to get future employers of mine to notice this question. I don't know if this is a good idea, but I want to describe my work on Wikipedia on my resume (along with my work verifying supercentenarian cases) since I don't have much else to brag about. I mean, I've recently (two months ago) got a bachelor's degree from a good university, but I don't have much else to write about on my resume. Futurist110 (talk) 00:23, 26 August 2018 (UTC)

Also, I really do hope that someone here is actually going to answer this question. Futurist110 (talk) 00:25, 26 August 2018 (UTC)

August 25

Source of a basemap

Greetings, does someone have an idea where the underlying information of File:Peru physical map.svg might come from? Jo-Jo Eumerus (talk, contributions) 07:30, 25 August 2018 (UTC)

Range of Likely Rise in GMST

The second paragraph of the global warming article reports "Climate model projections summarized in the report indicated that during the 21st century, the global surface temperature is likely to rise a further 0.3 to 1.7 °C to 2.6 to 4.8 °C depending on the rate of greenhouse gas emissions." What is the significance of four temperatures in defining this range? Shouldn't a range be defined by two temperatures and a confidence level? Also, where do theese numbers come from in the source? --Tag (talk) 15:35, 25 August 2018 (UTC)

It has to be 4 because how much of the 2001 carbon humans decide to burn by 2101 and how front-loaded or back-loaded and how much they slash-and-burn, desertify and plant trees and stuff is hard to pin down. Sagittarian Milky Way (talk) 17:32, 25 August 2018 (UTC)

I don't think this answers my question. Can you elaborate specifically on what each of the four numbers means and where I can find them in the source? --Tag (talk) 18:01, 25 August 2018 (UTC)

The first number is fast emissions cutting timeline, low estimate; second is fast emissions cutting timeline, high estimate; third is humans treat the Earth like crap timeline, low estimate; fourth is humans treat the Earth like crap timeline, high estimate. Probably. This is useful because it provides more information than just 2 numbers, it shows what's scientific uncertainty and what's "we don't know what humans will do in the future". Sagittarian Milky Way (talk) 20:00, 25 August 2018 (UTC)

The source is likely to be IPCC5. I'm not going to bother to look through it to find out. As SMW says, the 4 numbers encapsulate different CO2 emissions rates, and different estimates of the sensitivity of GMST to CO2 concentration. Specifically the higher numbers are based on RCP 8.5 which the frauds called 'business as usual'. Among other assumptions is that the population of Nigeria will grow to 1.5 billion (one eighth of the then predicted population) , giving the same population density for the entire country as the Vatican City is at the moment https://link.springer.com/article/10.1007%2Fs10584-011-0148-z. Really? Here's an article with a graph that agrees with the numbers in question. Overplotting the actual data would be an interesting exercise. https://medium.com/@davidfurphy/what-on-earth-is-an-rcp-bbb206ddee26 Greglocock (talk) 21:16, 25 August 2018 (UTC)

August 26

Feynman Lectures. Exercises. Exercise 27-8 PNG

...

27-8. Two thin lenses L and L', of focal lengths f and f', are separated by a distance D. Find the equivalent focal length F of the combination, and the distances Δ, Δ' of the principal planes from the respective lenses L and L'.

—  R. B. Leighton , Feynman Lectures on Physics. Exercises

The Solutions give next explanation:

...

27.8. From the definition of the main planes of the optical system follows their important property: if the point is in the main plane at a distance y from the optical axis, then its image is obtained in the other principal plane at the same distance from the optical axis. We use this property of the principal planes to solve the problem. The image of the point located in the main plane is shown in the figure. The following relations are obvious:

$y=f\tan(\varphi )=F\tan(\Phi )$
$y'=(D-f)\tan(\varphi )=(f'+x')\tan(\Phi )$.

It follows from the lens equation for $L'$ also

$f'^{2}=x'(D-f-f')$.

Eliminating from this the angles $\varphi$ and $\Phi$, as well as the distance $x'$, we obtain

$F={\tfrac {ff'}{D-f-f'}}$
$\Delta '=f'+x'+F={\tfrac {f'D}{D-f-f'}}$ .

From a similar consideration for the lens $L$:

$\Delta ={\tfrac {fD}{D-f-f'}}$ .

—  MEPhI , Solutions (Google Translate)

But I don't understand why does MEPhI use both -- principal planes and lenses -- simultaneously . The principal planes are only for replacing the lens system, not for using simultaneously . Username160611000000 (talk) 06:02, 26 August 2018 (UTC)

If we draw the rays correctly PNG, we see that the ray will go through the path BNE'S' if the principal planes are used , or the path BEE'S' if the lenses are used. From this correct image I found :
Consider light path BEE'S'.
for lens L':
${\tfrac {1}{s'}}+{\tfrac {1}{s''}}={\tfrac {1}{f'}}$
${\tfrac {1}{s'}}+{\tfrac {1}{\infty }}={\tfrac {1}{f'}}$
${\tfrac {1}{s'}}={\tfrac {1}{f'}}$
for lens L :
${\tfrac {1}{F-\Delta }}+{\tfrac {1}{s'}}={\tfrac {1}{f}}$
${\tfrac {1}{F-\Delta }}+{\tfrac {1}{f'}}={\tfrac {1}{f}}$
By analogy consider the light path B'G'GS:
${\tfrac {1}{F-\Delta '}}+{\tfrac {1}{f}}={\tfrac {1}{f'}}$.
Now we see
${\tfrac {1}{F-\Delta '}}=-{\tfrac {1}{F-\Delta }}$
$2F=\Delta +\Delta '$, which absolutely doesn't coincide with The Exercises answer and The Solution answer. Where is my mistake???
Username160611000000 (talk) 07:00, 26 August 2018 (UTC)