Wikipedia:Reference desk/Archives/Science/2014 May 10

= May 10 =

A parachute for a plane
This news item describes a small plane "crashing" gently after it deployed a parachute. I hadn't heard of this feature before. Are parachutes for small planes becoming a common feature these days? HiLo48 (talk)


 * We have an article on Ballistic Recovery Systems - a manufacturer of such systems. AndyTheGrump (talk) 07:31, 10 May 2014 (UTC)


 * Thanks Andy. That's great, except for one thing. The name. I did a full Google search for parachute and plane, and found nothing but parachutes for people. Ballistic Recovery Systems may be the technically correct name, but no non-specialist is ever going to search for that. (How did you find it?) I wonder if there's some simple redirect we could come up with to help non-aficionados like me? HiLo48 (talk) 07:53, 10 May 2014 (UTC)
 * Plane parachute works. Also, our article on Cirrus Aircraft points to Cirrus Airframe Parachute System. Dolphin  ( t ) 09:30, 10 May 2014 (UTC)


 * Also Drogue parachute. Alansplodge (talk) 02:55, 11 May 2014 (UTC)


 * Don't know which strange version of Google HiLo48 is using, a simple search for "parachutes for planes" brings up numerous sites, including manufacturers and forums with information on these devices 203.13.128.104 (talk) 01:40, 12 May 2014 (UTC)
 * Could be a censored Google (terrorism paranoia again?)
 * My google (searching for plane parachute, from central Europe) returns both images and useful links, but we had Google concentrate on "hot" WP topics before. Maybe it's because I'm late to the topic again... - ¡Ouch! (hurt me / more pain) 08:21, 16 May 2014 (UTC)

Schizophrenia
How does a Health people get sick by Schizophrenia???...

94.67.95.188 (talk) 08:47, 10 May 2014 (UTC)
 * Causes of schizophrenia. 84.209.89.214 (talk) 12:00, 10 May 2014 (UTC)

Balloon in Virginia
A balloon burned and crashed after hitting electrical wires, and three people are presumed dead. Why would the gondola have ignited though? Clarityfiend (talk) 09:36, 10 May 2014 (UTC)
 * Balloon baskets are typically made of wicker. I imagine if a wicker basket were exposed to high voltage it would readily ignite. Even though the wicker basket is very old technology it is still favored for hot-air balloons because of its flexibility (important when a balloon "lands") and because the porous nature of wicker structures is ideal in allowing any flammable gas to escape and not pool in the bottom of the basket. Dolphin  ( t ) 09:50, 10 May 2014 (UTC)


 * Why wasn't it like birds perching on the wire with no ill effect? Clarityfiend (talk) 10:09, 10 May 2014 (UTC)


 * Birds touch only one wire at a time, and the ballon probably touched more than one wire at the same time. There's a voltage difference between the wires which makes a current flow through any conductive material that connects them. Sjö (talk) 10:17, 10 May 2014 (UTC)


 * Ah. I assumed the wires were at the same voltage. Clarityfiend (talk) 10:45, 10 May 2014 (UTC)


 * Same in voltage magnitude, but different in sign, I believe (one positive and one negative). StuRat (talk) 13:17, 10 May 2014 (UTC)


 * Actually, high-voltage lines normally carry three-phase current (except for HVDC lines, which do carry equal voltages of opposite sign). 24.5.122.13 (talk) 21:25, 10 May 2014 (UTC)


 * See also this story from last year: http://abcnews.go.com/blogs/headlines/2013/10/two-men-severely-burned-as-hot-air-balloon-crashes-into-power-lines-during-flight-festival/ Ssscienccce  (talk) 11:24, 10 May 2014 (UTC)


 * It would actually depend on the voltage of th power lines hit by the gondola. Very high voltage (400kV or 132kV in the UK) is delivered by quad or paired conductors with the same voltage and phase on them: in principle you could touch them simultaneously with no harm.  There are then typically six of these "bundles" per route and they will deliver power in 3 difference phases, 120 degrees apart.  There is therefore a very high voltage between each, but they are widely separated and touching them simultaneously with a gondola would be impossible, I would expect.  However, lower voltage lines (e.g. aakV in the UK) typically have 3 conductors, again each is one phase of a 3 phase supply.  Touching 2 of these would likely be possible, and expose the item touching them to over 11kV in potential difference.  I assume that would cause gongola material to burn.--Phil Holmes (talk) 14:15, 10 May 2014 (UTC)


 * Also, with a typical 6-wire electricity pylon (used on power lines carrying as much as 400 kV here in the USA, and even on part of one 500-kV power line), it's very much possible for a balloon to touch 1 wire with the gondola and a second wire with the envelope -- which would send as much as 300 kV across the whole balloon, incinerating it at once. 24.5.122.13 (talk) 21:38, 10 May 2014 (UTC)

The spacing between conductors increases with voltage level. A balloon or its basket would be less likely to touch 2 conductors simultaneously at 345 kv, say than at 12kv. But balloons are really big and it would be very easy for one pushed by the wind to drape the envelope across 2 conductors or to hit one with the basket and one with the envelope. If I were buying a balloon, I would certainly try to get one with nonconduuctive fabric, just as i would prefer a fiberglass ladder to a wooden or metal one if I were working near a 12kv conductor. That said, if the fabric or basket were covered with dust and the air was damp, it would become all too conductive. If it came near one transmission conductor (138kv, say) then there could be an impressive arc from the conductor to any conductive part due to capacitance, perhaps enough to ignite it. Again, if buying a balloon, I would prefer one which was flame-suppressing. It might just develop a hole from such an arc rather than burning up like the Hindenberg or having such a hot sustained flame that it shot up into the air like this one. Edison (talk) 00:19, 11 May 2014 (UTC)

I don't know the specifics of the recent accident, but I'll point out that in general a short need not involve two separate conductors. It could also be between a single conductor and anything grounded, which for some high-voltage lines includes the metal pylons as well as one or more lightning conductors above the main conductors. Also note that the impact will move the conductors around. It might push things close enough together to arc when they normally never would; and the impact with a single conductor might also break it, in which case there will certainly be an arc between the broken ends until they fall far enough apart to stop it. (That last hazard is not too big a deal with something soft like a balloon, but it is a possibility.) --50.100.193.30 (talk) 22:57, 11 May 2014 (UTC)

Lactulose and cavities
From our article's side effects section: "Although lactulose has less potential to cause dental caries than sucrose, there is a minimal potential because it is a sugar. This should be taken into consideration when taken by people with a high susceptibility to this condition."

I don't understand. It's not digestible by humans, but is it by bacteria ? Or does it cause cavities by other means, like plugging a cavity during formation and preventing oxygen from getting in to kill anaerobic bacteria already present ? StuRat (talk) 13:22, 10 May 2014 (UTC)


 * From this pdf: http://onlinelibrary.wiley.com/doi/10.1046/j.1472-765X.1998.00403.x/pdf:
 * Most bacteria tested were able to metabolize lactulose with the exception of strains of Streptococcus salivarius, Lactobacillus acidophilus and Lact. fermentum. Streptococcus mutans produced most acid overnight but the initial rate of acid production from lactulose by uninduced cultures was very low. Plaque pH was monitored in 12 volunteers following rinsing the mouth with lactulose, sucrose or sorbitol or Lactulose BP.
 * These studies in vivo showed both lactulose and Lactulose BP to exhibit low acidogenic potential. Thus, although plaque bacteria are capable of fermenting lactulose, the results suggest that lactulose is likely to pose a small acidogenic challenge to teeth under normal conditions of use.
 * Best sweetener for your teeth is Xylitol, I believe Ssscienccce  (talk) 15:18, 10 May 2014 (UTC)


 * Excellent answer ! I will mark this Q resolved. StuRat (talk) 21:03, 10 May 2014 (UTC)

Are their any substances which do the inverse of Transitions lenses?
(Not necessarily at the same brightness values. Heck, not even from the same frequencies, anything electromagnetic) Sagittarian Milky Way (talk) 13:29, 10 May 2014 (UTC)
 * From New organic photochromic materials and selected applications:
 * Solid photochromic spiropyrans or solutions (in ethanol, toluene, ether, ketones, esters, etc.) are colorless or weakly colored. Upon UV irradiation, they become colored. The colored solutions fade thermally to their original state; in many cases, they can also be decolorized (bleached) by visible light. A few spiropyrans display negative photochromism. They are colored in the dark and bleached by UV light.  Ssscienccce  (talk) 15:53, 10 May 2014 (UTC)
 * Unfortunately, the Photochromism article doesn't list negative photochromic materials, but you can find others besides the above-mentioned spiropyrans by googling the phrase "negative photochromic". Red Act (talk) 00:21, 11 May 2014 (UTC)


 * Not quite the opposite, but you may want a saturable absorber.--Srleffler (talk) 17:04, 14 May 2014 (UTC)

What's the slickest solid to bubbles?
They tend to stick. Teflon? Something that takes advantage of polarity or surface tension? Sagittarian Milky Way (talk) 13:35, 10 May 2014 (UTC)

Can someone identify this plant please?
Unsure what it is, some kind of Rhododendron? --S.G.(GH) ping! 14:13, 10 May 2014 (UTC)


 * Yes it's a Rhododendron, but if as our page says there are 28,000 cultivars registered with the Royal Horticultural Society, we're going to need a lot more information to nail it down! So if you can give us location and date taken that'll give us a start. --TammyMoet (talk) 14:37, 10 May 2014 (UTC)
 * Today, Haldon Forest in Devon. S.G.(GH) ping! 15:23, 10 May 2014 (UTC)


 * It looks like a rather battered example of Rhododendron ponticum (the one that the Victorians imported in vast quantities, and that I call "wild rhododendron"), but I'm not an expert, so perhaps someone else can look more carefully.   D b f i r s   16:22, 10 May 2014 (UTC)
 * Yes I agree, especially if it's in a forest setting - such rhodies are usually naturalised. I learnt a lot about these plants when I took part in a rhododendron pull in a woodland in South Yorkshire - by heck there were a lot of them and they were choking the native woodland species out, and were also unsuitable for wildlife being poisonous to many species. --TammyMoet (talk) 18:17, 10 May 2014 (UTC)

That will do nicely, many wondrous thankyous! S.G.(GH) ping! 16:45, 11 May 2014 (UTC)

Suitable insulating material for end of hair curling iron
I have an electric hair iron which I have modified to curl my moustache. Nine millimetres is the smallest diameter commercially available so I replaced the stainless steel tube with one of a 5 mm diameter. Of course I can't reuse the piece of plastic the original tube used so I'll need to terminate it with something else. I need a material that is hard or will become hard, easily shaped and of course heat-resistant and insulating. I have a tap and die set if that helps. --78.148.106.196 (talk) 15:35, 10 May 2014 (UTC)
 * Epoxy seems the obvious choice (to me as a layman), there's a wide range of epoxy resins available (2-component), many for high temperature applications, used for electronics, muffler repair etc.  Ssscienccce  (talk) 16:13, 10 May 2014 (UTC)


 * While many expoxies are quite suitable, beware of epoxies intended for general purpose adhesives, potting, and filling. These generally have fillers (wood flour, synthetic substances) that will not take high temperatures.  You could consider cutting and filing down as required the handle of an old saucepan - the type with black thermoset handles. 120.145.72.212 (talk) 16:31, 10 May 2014 (UTC)


 * A ceramic wire nut might work, perhaps with the epoxy used to attach it. (I see our article only has pictures of the plastic ones, which I don't recommend.) StuRat (talk) 20:57, 10 May 2014 (UTC)


 * PEEK is machinable and good to 340°C. You can buy a rod of it from any industrial supply company (including Amazon). Teflon (PTFE) is good to even higher temperatures, but is softer. It comes in rods, too.--Srleffler (talk) 17:02, 14 May 2014 (UTC)

Thermal resistance of tungsten-molybdenum alloy
Where can I find data on the thermal resistance of alloys of tungsten and molybdenum, particularly for 50% Mo+50% W? — Preceding unsigned comment added by 120.145.72.212 (talk) 16:23, 10 May 2014 (UTC)
 * Tungsten and molybdenum are both Refractory metals with similar high melting points and thermal resistances. As a start, this Chinese source gives Thermal conductivity (i.e. the reciprocal of thermal resistance) of pure W and Mo, and their e-mail address may be able to comment on the alloy. 84.209.89.214 (talk) 19:19, 10 May 2014 (UTC)

Astronomy help request
Hello astronomers, there's a short discussion taking place at Talk:Horsehead Nebula. Some of the descriptive prose in the article is a little confusing and we were hoping someone familiar with astronomy could help clarify the existing prose. I doubt it would take more than a few minutes to clarify what we are seeing. Thank you! Cyphoidbomb (talk) 18:49, 10 May 2014 (UTC)

A question to sink your teeth into
Are dentures ever made with a single "megatooth" for the entire upper or lower, as opposed to separate teeth ? This would seem to be more practical, as it would eliminate the possibility of food being stuck between the teeth, and would make cleaning far easier. Are separate teeth better for any reason other than aesthetics ? I imagine black lines at the proper spacing would somewhat simulate the look of separate teeth, although probably not up close. StuRat (talk) 20:50, 10 May 2014 (UTC)
 * Human teeth differ in shape and strength, and are used for different purposes such as cutting, crushing or grinding food (and exceptionally for holding or aggression). Tooth fusion ocasionally occurs as an abnormality with zero evolutionary benefit. Deliberately fusing together all the teeth in a denture jaw set would likely impair speech, drinking and saliva circulation, and create a single unwieldy oversized rigid structure liable to fracture. 84.209.89.214 (talk) 00:24, 11 May 2014 (UTC)


 * Have you ever tried to cut wood with a straight blade? Not so fun. Saw blades allow for more cuts, from more angles. Teeth aren't exactly the same (you've probably noticed), but every gap makes two more edges and the slicers more effective, just like the ridges make the crushers. If your jaw moved like scissors and you mostly ate plants, two very sharp blades might do. But more likely, they'd be attached to the jaw, like an iguana. Like the IP says, one long flat jaw-shaped tooth would be just asking to break. InedibleHulk (talk) 00:48, 11 May 2014 (UTC)


 * If you imagine biting into (say) an apple. If the row of teeth was one single, smooth curved 'blade' then your jaw would have to apply enough pressure to break through a couple of inches of apple all in one go.  By having smaller points, you can break just one small section at a time - so that MUCH less pressure is required.  That's why animals that have to bite through food have sharp, pointy, jagged rows of teeth where animals that grind up their food have flatter teeth. SteveBaker (talk) 03:53, 11 May 2014 (UTC)


 * And why animals with radulae have to settle for the crud they do. Speaking of which, ghost slug is worth a read, if you're into horror. InedibleHulk (talk) 07:54, 11 May 2014 (UTC)

The single megatooth could still have points. Think of a serrated knife blade. It could also have molar-like sections, incisor-like sections, etc.  StuRat (talk) 03:54, 12 May 2014 (UTC)
 * Sure. But the bits of food in between your teeth went there for a reason. Without that space to slide into and apart in, chewing should feel much more like squeezing. If you've eaten a tough enough steak, you know that after sufficient inefficient bites, the corners of your jaw hurt. People (especially old ones) don't need that grief for mere tough waffles.


 * And when it does break, you'd have to buy a whole new one, rather than a part. It'd get pricey, especially if granny tried the steak. After thinking about drinking a bit more, the IP's also right about that. Do you always put the lip of your drink over your teeth? You'd have to learn. InedibleHulk (talk) 04:12, 12 May 2014 (UTC)


 * I wasn't aware that you could replace a single "tooth" within a denture plate. StuRat (talk) 04:16, 12 May 2014 (UTC)


 * Me neither, I just assumed. Are they made of the same stuff the gums are? InedibleHulk (talk) 04:27, 12 May 2014 (UTC)


 * I would assume not, since the teeth need to be hard, while the gums need to be somewhat soft. StuRat (talk) 12:47, 15 May 2014 (UTC)
 * That's how I remember them from the '80s. Haven't felt them since. Figured the teeth were attached by some sort of superglue, which some acid could dissolve. But nope. Just throw the whole thing out when you bite a peach pit, I guess, onto the pile. Though according to Ron, teeth do come out, and they can be repaired. InedibleHulk (talk) 13:06, 15 May 2014 (UTC)
 * Ah...polymerization. InedibleHulk (talk) 04:30, 12 May 2014 (UTC)

Commercialisation of Engineering
Why is Engineering such a commercialised profession compared to other professions such as medicine, law, accounting etc. Engineering in modern times is very profit driven. Why? 82.40.46.182 (talk) 21:58, 10 May 2014 (UTC)
 * What makes you think that medicine and law are not commercialized or profit-driven? 24.5.122.13 (talk) 22:09, 10 May 2014 (UTC)
 * Ditto. ←Baseball Bugs What's up, Doc? carrots→ 22:10, 10 May 2014 (UTC)
 * So is everything profit driven in the modern world? Why?  People say even some charities are these days.   82.40.46.182 (talk) 22:54, 10 May 2014 (UTC)
 * Where I live, not everything is profit driven, but a lot more of it is now than when I was young. The exceptions would be government services, plus some (but certainly not all) charities and voluntary organisations. In answer to "Why?" it seems to be that the masses choose to elect politicians who have that ideology, because they can claim it's a system that allows lower taxation. Not everyone sees it that simply. HiLo48 (talk) 23:14, 10 May 2014 (UTC)
 * How profit-driven various fields are depends a lot on what country is being talked about. The OP is from the UK, which has provided universal health care to its residents through its National Health Service since 1948.  24.5.122.13 and Baseball Bugs are from the US, which doesn't have government-provided health care, so they are going to have a considerably different perspective of how profit-driven medicine is.  Red Act (talk) 01:04, 11 May 2014 (UTC)
 * I agree more or less with the premise, that Engineering is relatively commercialised. I have often wondered at this myself, not so much how it came to be, but how it manages to sustain itself. When a doctor says that erythromycin is not so good anymore, he is quoting publicly funded research. When an engineer says we should build the bridge here, he seems to be making a commercial decision. Yet the market somehow sustains itself, and does quite well at building big, heavy stuff. Your question about "why" this is so, is difficult to answer, but it probably has something to do with the scale of the thing. An engineer doesn't do much on his own; he needs a big company behind him before any of his decisions have any meaning. Building bridges is a large scale enterprise, so the decision of where to build has no meaning without a company to do the building. A doctor can act more or less alone, and his decisions will still be meaningful. However, a pharmaceutical company cannot. So "big medicine" is commercialised, and in much the same way as engineering. The difference is that, after all the drug research by the company, there are still a bunch of researchers and doctors debating whether a particular drug is right for a particular infection. So the brakes can still be applied somewhere. IBE (talk) 01:51, 11 May 2014 (UTC)


 * At least in England, while companies engage in a lot of propriatory work and research, they also invest in links with university departments that carry out training and research that can be made more widely available. A lot of this can be traced back to decisions made by groups of industrialists in the 19th and early 20th century, who wanted to ensure a supply of trained workers. See UMIST, for example. 86.146.28.229 (talk) 11:42, 11 May 2014 (UTC)


 * Who ever heard of accountants not focused on the profit? That's their whole reason for existing.  I'm a consulting engineer myself, get to attend lots of project/client meetings with laywers and accountants.  We engineers have a lot of the same business concepts as lawyers - e.g., billable hours.  But lawyers are far more rapacious.  If I make a photcopy for a client, I don't charge for it.  If I write to a client, I don't charge for it.  Phone calls to answer client's questions and help him understand what he's getting are part of the service - they aren't chargeable. I only charge for the documented original intellectual property I deliver up.  A lawer won't just make a photocopy - he'll have a clerk initial each page, certify it a "true copy" (why would anyone want a non-true copy??) and charge you for it.  If a laywer writes a letter, he charges for it.  If he makes a phone call, that's billable hours too.
 * How profit driven things are, and how rapacious the charging is, tends to be linked to the competition regime. A simple way to undertsand it is to see that the cost of some product or service can be approximated by the formula
 * Cost = A + Bx
 * where A is a fixed cost that does not vary with the quantity of product/serve delovered, B is a cost that varies in proportion to the quantity delivered, and x is the quanity delivered. A railway line is an example of a business with a very large A and a very small B.  It costs a fortune to install all the tracks and buy the locomotives and wagons.  But once you have it all, it costs very little per item to shift the freight - just a bit of fuel and the salary of the train crew, who can run a train amounting to thousands of tonnes.  So railways with their large A and very small B tend to be monopolies and not be very profit driven  (you might say wasteful).
 * Same with power companies - it costs vast amounts of money to set up power stations and transmission lines, but once its there, there's not much additional cost per kilowatt hours.
 * Note that I am talking about the true cost, not what you get on your bill. For political reasons, sooner or later, governments always get involved and regulate the prices of natural monopolies. For example, where I live, the govt mandates an artificially low service charge and a higher than natural per kilowat-hour rate, so that pensioners can have the lights on.
 * The power generation business thus tends toward monopolies. In many countries railways and power companies tend to be governement owned.  Only very large countries such as the USA can provide such things via private industry.  In fact, where I live, we had a rail company that did not pay a single dividend to shareholders for over 100 years, and then was taken over by the only other rail company - the Government.  Retailing makeup to females is a business with a very small A and a large B.  There's practically zero infrastructure to set up, but each sales girl spends a lot of time in girl talk with each and every customer on nearly every sale.  Such games tend to be vast numbers of very small businesses, and each operates with an enormous markup, very profit diven and the proprieter is very focused on eliminating waste.  Only in the Soviet Union was the selling of makeup products a government business.
 * 120.145.72.212 (talk) 01:52, 11 May 2014 (UTC)


 * Yes, but who sells make-up is purely a cosmetic difference. :-) StuRat (talk) 14:00, 11 May 2014 (UTC)
 * WP:OR: Of all the socialist republics that I would like to visit, I have only spent a significant amount of time in one.  Everything was nationalized: the clothing stores, the up-scale restaurants; the shopping mall; the ice-cream parlor, the hotels; the universities; even the cheap plastic toys that you find in boxes of candy.  The plastic injection molding factories were 100% nationalized!  Utility stores sold small motors built in-country; hand-held transistor radios were built in-country (from whence came the transistors, I can only assume "a crate the Russians left behind in 1966").  The automobiles: they were all pre-war Mercedes.  The most mind-blowing detail was that I couldn't find a single item imported from China!  Not the plastic wrap, not the cotton, not the electronics!  Even the cotton in the clothing was nationalized.  (Imported goods can be problematic).  The engineer in me was amazed at the pragmatism; and the theorist in me marveled at the concept of an economy with no net flux through the walls of the gaussian pillbox!  But I specifically remember seeing that the cosmetics - all the "girly" products like perfumes and make-ups that my aunts bought - all of those were the primo stuff, smuggled from France and Italy.  Nimur (talk) 03:11, 12 May 2014 (UTC)

How a switch button works?
How a button manages to stay "down" when pressed and go "up" by pressing it again? 201.216.12.182 (talk) 23:20, 10 May 2014 (UTC)
 * An example of a similar latching mechanism is in every retractable Ballpoint pen. 84.209.89.214 (talk) 23:51, 10 May 2014 (UTC)
 * ...which doesn't really help to explain it - it's quite a subtle mechanism - hard to deduce how it works even if you dismantle it. The latching push button switches that I've dismantled don't seem to use the same rotary mechanism that a typical ballpoint pen uses.  It's hard to explain it in words - I've yet to see a good diagram or animation. SteveBaker (talk) 03:47, 11 May 2014 (UTC)


 * Here's the patent application for the pen thingy. A little too detailed. The same guy invented this lighter design. I still see those. And people suffer the extra digits on gas pumps. InedibleHulk (talk) 03:52, 11 May 2014 (UTC)


 * There's an upsides-down arrow-head shaped slot, with a bar that engages with it, sprung to remain in the centre. When you press the button the first time, the bar moves around to the far side, and holds the button down. Pressing the button again will force the bar to move around to the near side. Hopefully that explains it… CS Miller (talk) 09:10, 11 May 2014 (UTC)