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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)[reply]

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)[reply]

Plane parachute works. Also, our article on Cirrus Aircraft points to Cirrus Airframe Parachute System. Dolphin (t) 09:30, 10 May 2014 (UTC)[reply]

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

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)[reply]

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)[reply]

Schizophrenia

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

94.67.95.188 (talk) 08:47, 10 May 2014 (UTC)[reply]

Causes of schizophrenia. 84.209.89.214 (talk) 12:00, 10 May 2014 (UTC)[reply]

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)[reply]

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)[reply]

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

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)[reply]

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

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

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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

Resolved

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)[reply]

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)[reply]

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)[reply]

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

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)[reply]

Can someone identify this plant please?

Unsure what it is, some kind of Rhododendron? --S.G.^(GH) _ping! 14:13, 10 May 2014 (UTC)[reply]

File:UnknownflowerSGGH.jpg

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)[reply]

Today, Haldon Forest in Devon. S.G.^(GH) _ping! 15:23, 10 May 2014 (UTC)[reply]

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. Dbfirs 16:22, 10 May 2014 (UTC)[reply]

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)[reply]

That will do nicely, many wondrous thankyous! S.G.^(GH) _ping! 16:45, 11 May 2014 (UTC)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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, May 11, 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)[reply]

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, May 11, 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)[reply]

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, May 12, 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)[reply]

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

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, May 15, 2014 (UTC)

Ah...polymerization. InedibleHulk (talk) 04:30, May 12, 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)[reply]

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)[reply]

Ditto. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:10, 10 May 2014 (UTC)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

Yes, but who sells make-up is purely a cosmetic difference. :-) StuRat (talk) 14:00, 11 May 2014 (UTC) [reply]

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) [reply]

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)[reply]

An example of a similar latching mechanism is in every retractable Ballpoint pen. 84.209.89.214 (talk) 23:51, 10 May 2014 (UTC)[reply]

...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)[reply]

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, May 11, 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)[reply]

May 11

Rings and moons

Since planetary rings consist of small rocks and recently discovered moons don't have large diameters, I'm wondering when is the chunk of rock considered a moon? I don't know the exact definitions, but isn't then every piece from a ring theoretically a moon? --2.246.58.160 (talk) 16:12, 11 May 2014 (UTC)[reply]

A moon would need to be separate and distinct. The rings of Saturn, for example, look like solid objects, although we know they're not. The Voyagers and other exploratory vehicles didn't see individual particles of the rings (as far as I know) even from relatively close range. Saturn's moons, in contrast, are large enough to be visible on their own. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:18, 11 May 2014 (UTC)[reply]

According to the section §The definition of a moon in our article Natural satellite, the definition is vague, but the implication is that objects that are "too small" are not normally labelled as moons. —Quondum 16:23, 11 May 2014 (UTC)[reply]

The implication is "large enough to be seen". The article indicates that the individual particles of the rings have not been directly observed. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:28, 11 May 2014 (UTC)[reply]

I don't see where you get that. It leads to a nonsensical dependence on factors such as where the observation is being made from relative to the body under consideration, resolving power of the optical system being used, ambient lighting (e.g. distance from the Sun), and albedo. Do you have a reference? While there may be roots in what could be observed by specific people at a certain point in history, to use such an interpretation without more context in modern times is worse than vague. —Quondum 19:22, 11 May 2014 (UTC)[reply]

Feel free to give us your interpretation of what the article says. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:29, 11 May 2014 (UTC)[reply]

The section that I linked to, when discussing a lower limit, says "Every natural celestial body with an identified orbit around a planet of the Solar System, some as small as a kilometer across, has been identified as a moon, though objects a tenth that size within Saturn's rings, which have not been directly observed, have been called moonlets." This would suggest a criterion of size might be considered since no other criterion is mentioned, but what is clearest is the lack a formal definition of what a "moon" or "natural satellite" is defined to be in this sense. The clause "which ..." does not relate to a definition as stated, as it simply adds information. —Quondum 22:31, 11 May 2014 (UTC)[reply]

This question is purely a matter of definition. What do we mean when we use the word "moon" ? Who has authority to define that word? We could pull out a reputable dictionary, like the Oxford English Dictionary or Wiktionary: wikt:moon. The OED cites four hundred years of English usage in which "moon" refers to an object other than Earth's primary natural satellite ...including this barely-passable snippet in which moon appears to refer to an extrasolar planet. I would nitpick the definition, but many language-scholars attest that John Milton's writings define the English language we speak today).

Alternately, we could defer to an astronomy subject matter expert, or to an authoritative organization, like NASA or the International Astronomical Union, or the American Geophysical Union; or even, lest we stray into fringe territory, we might even ask the Planetary Society. Were we to publish a peer-reviewed paper, we could defer to the editorial board of our journal for a definition; if we violated that definition without good cause, we probably couldn't get published. But, alas. there is not a lot of active debate on the definition of "moon", because new discoveries of moon-like entities are somewhat rare. The recent kerfuffle about the definition of "planet" - culminating in the formal IAU definition of planet - was important, because we have new technology that is allowing us to discover new extrasolar planets. Scientists needed to formalize and standardize their terminology so that they could efficiently communicate new knowledge at the cutting edge of our observational capabilities. Reputable organizations, like IAU and NASA weighed in on the issue.

But moons are not presently an area of active research. If you go back just a few decades - say, to 1954 - you'd find voluminous writings by reputable scientific authorities about moon terminology. Is lunar sand "dust" or "dirt"? Neither! It's regolith. And when we study the interior of the moon, are we conducting geology or geophysics? Neither! It's selenology. Can a terrain feature be called a deep valley or canyon, even if it wasn't eroded? No, those are rills, and moons have rilles. And a flat plain-like area ... that would be a mare. The point in an orbit that makes its closest approach to a moon a perigee? No, it's a perilune. And so on. An entire specialized vocabulary was created, 'because lots of educated people were talking about moon things.

Today, lunar research is nearly dead. The Lunar Science Institute aggregates legacy research publications, but doesn't sponsor new scientific inquiry. You'd be hard-pressed to find a "moon expert" on the payroll of any physics or astronomy department at most universities. The IAU does not publicize definitions for lunar terminology these days. So, we ought to defer on the definition to whatever the dictionary says; that definition will be vague and suitable for general purpose" usage. For the details, we can point you to articles in Wikipedia or elsewhere that summarize everything we know about moons - Earth's moon and elsewhere among the cosmos. I can recommend several great books:

Planetary Sciences, (de Pater & Lissauer), co-authored by one of the NASA scientists who defined the Kepler mission to search for extrasolar planets. This text has an entire chapter on moons and moon formation, and is up-to-date with everything that we have learned about moons from 21st century space-travel and science.
Strange World of the Moon: an excellent book written before the Apollo missions. This book presents an incredibly robust theoretical overview of the moon and its ~~geology~~ selenology. It also provides great context for the non-Earth-moon enthusiast, because you can read for yourself how accurately we were able to remotely ascertain lunar properties before we visited our Moon; and compare to our present-day descriptions of moons around other planets.

Between those two, you'll probably get as robust and formal a definition of "moon" as any scientist can provide.

But it's unlikely that we can find any recent formalized defintion from IAU or anywhere else that explicitly lays out what a "moon" is, in the general sense.

Nimur (talk) 02:12, 12 May 2014 (UTC)[reply]

Thanks, that is about as thorough a treatment of the topic as one could ask for. For a simple, accessible web page on the topic, I thought I'd add this: What is a moon?. —Quondum 03:17, 12 May 2014 (UTC)[reply]

This one is most definitely not a moon. - ¡Ouch! (^{hurt me} / _{more pain}) 07:29, 13 May 2014 (UTC)[reply]

<samll>One of the more consistent criteria is that man-made/artificial objects do not qualify. I wonder what'll happen with natural objects with man-made trajectories. —Quondum 13:33, 13 May 2014 (UTC)[reply]

"samll"? LLO.

Same here. The criteria of "destroying the Earth" are satisfied if the planetary mass is redistributed into two spherical bodies. By that definition, Earth has been "destroyed" more than once. First, the collision with Theia (planet), and if you count this as the moment of its creation, you still have the launch of Sputnik and man after that. The only catch is that the spherical bodies aren't even remotely similar in mass.

If only natural bodies can be moons, that's OK so far. Then, it is probably OK to call objects moons only if they are unique in a sense like the small moons within Saturn's rings (there are at least 4 or 5 bodies that stand out, the smallest is about a mile in diameter) but not the millions of pebbles that actually are the rings.

However, this is still a bit arbitrary; in what one counts as "unique." - ¡Ouch! (^{hurt me} / _{more pain}) 14:46, 13 May 2014 (UTC)[reply]

And to further complicate matters the Earth is sometimes orbited by minimoons Richerman (talk) 07:40, 12 May 2014 (UTC)[reply]

The correct meaning of a Kepleren orbit is an elliptical path to which the orbiting body is bound by the gravitational force of the central attractor; it is periodic and reversible in space-time. The transient interactions of asteroids with Earth's gravity are examples of gravitational slingshot events. I disagree with calling such minimoon one-off trajectories "orbits". 84.209.89.214 (talk) 12:26, 12 May 2014 (UTC)[reply]

Moons are still being discovered and the edges of the meaning still debated. See the new moon Peggy, for instance.[1] 75.41.109.190 (talk) 14:46, 12 May 2014 (UTC)[reply]

Dove Offspring?

My doves just had babies and according to a calculator, both babies will be orange mutation But neither of them have the color,

The mother is Orange Pearled, The father is a Wild Blond

The calculator displays the father as dwBdwB

The calculator also displays the mother as TaTa dwB- Mm+

Please assist me if you can :>

FYI: The calculator can be found Here

--208.107.179.233 (talk) 19:55, 11 May 2014 (UTC)[reply]

Do the feathers of mature doves have the same color as when they first hatch out? ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:30, 11 May 2014 (UTC)[reply]

I don't understand the notation of the calculator, but if orange is the dominant trait, the percentage being orange is high. It doesn't automatically result in orange because both parents could have hidden traits you couldn't have considered in your calculation unless you had detailed information about the DNA. --2.246.58.160 (talk) 21:41, 11 May 2014 (UTC)[reply]

@Baseball bugs No. Its all down before they shed it and start growing pin feathers — Preceding unsigned comment added by 208.107.179.233 (talk) 23:34, 11 May 2014 (UTC)[reply]

I thought so. But are the downy feathers fairly close to the color the feathers will be for an adult, or is there no correlation? ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:26, 12 May 2014 (UTC)[reply]

@Baseball No. It barely resembles the adult plumage, if any. — Preceding unsigned comment added by 208.107.179.233 (talk) 03:24, 12 May 2014 (UTC)[reply]

Wouldn't that explain why they don't have the color (yet), then? Evan ^{(talk|contribs)} 03:47, 12 May 2014 (UTC)[reply]

I agree - I would bet that the color would emerge only as the adult plumage comes in. In many species of animal, the juveniles need really good camoflage to avoid the attention of predators - which changes into more showy colors in adulthood...I wouldn't be at all surprised if the same effect was at work here. SteveBaker (talk) 14:45, 12 May 2014 (UTC)[reply]

For those of you who don't know, Here's what a squab/baby dove looks like --208.107.179.233 (talk) 21:05, 12 May 2014 (UTC)[reply]

May 12

I keep cracking my joints

It's not a medical issue! 2 doctors told me "It's nothing" and they crack their joints before me and told me "See? It's normal". Oh yea? than way only at the last two years I started having that? (Before that I never had Cracking-Joints). this phenomenon is annoying... how do I lower it's frequency? thanks! — Preceding unsigned comment added by Ben-Natan (talk • contribs) 00:35, 12 May 2014 (UTC)[reply]

If you're asking how to lower the frequency of annoying bodily phenomena, it's a medical issue. If two medically trained professionals tell you it's nothing to worry about, they're the qualified ones. Take it or leave it. Generally speaking, things get older with time. Every year brings new wear and tear. You're not whatever age you used to be. InedibleHulk (talk) 00:41, May 12, 2014 (UTC)

I agree that one should listen to one's doctor, but have we no article on the subject iteslf? One of my nephews started cracking his knuckles at 3. THe older one still can't 7 years later. μηδείς (talk) 00:48, 12 May 2014 (UTC)[reply]

Cracking joints is somewhat relevant. I suggest drinking a bottle of synovial fluid for increased vigor and vitality. Seriously though, don't listen to me. InedibleHulk (talk) 00:49, May 12, 2014 (UTC)

Smoking joints fights joint pain. You didn't say if they hurt or not yet, so this isn't advice. Right? InedibleHulk (talk) 00:59, May 12, 2014 (UTC)

I've been cracking many of my joints (not just all of my knuckles, but also both wrists, right shoulder, at least 3 cervical vertebrae, both knees, both ankles and all my toes) since I was 9 years old, and have never experienced any pain or discomfort from that. One thing I noticed is that my joints usually crack after being left immobile for a few hours -- so if cracking joints bothers you, a good way to reduce occurrence of this would be to keep your joints moving periodically. 24.5.122.13 (talk) 06:55, 12 May 2014 (UTC)[reply]

After 20 years or so of the same, I noticed the wait time between cracking and stiff enough again has drastically dropped. Only takes a few minutes to "recharge" now, and where I used to have to try, now it's just automatic. Still in my thirties, so just a very dull soreness, but the stiffness is sort of making me regret it. Both get worse in the cold.

Sort of like an addiction, it just doesn't feel as rewarding, either. Especially with my back, it used to be almost thrilling. Now, meh. But gotta keep on chasing that dragon, on account of the stiffness. Also, my hands look like owls should be perching on them in a cemetery. In my case, it actually fits nicely with my tall frame, pale skin, sunken eyes and wizard beard. But it's something you may want to avoid. InedibleHulk (talk) 04:19, May 14, 2014 (UTC)

Lifting legs and blood pressure

Hello, I am doing a project to see the how laying down and lifting one's legs higher than their heart affects blood pressure. However, I have tried researching the following, and could not get an answer. Which of the two is likelier to raise blood pressure higher: the height at which the legs are lifted, or the length of time for which the legs are lifted? We are only able to choose one of those two variables to change, and we have a "subject" with a fairly low blood pressure and we wanted to see which one is better to try. Any help would be great. Thanks. 70.54.113.147 (talk) 02:09, 12 May 2014 (UTC)[reply]

The basic intent of the system is to maintain the blood pressure in the brain/head at optimum. The sensor for blood pressure is in the neck arteries, and the brain has a built-in algorithm to compensate for sensor lag and non-optimum position. In a young healthy person, the head pressure remains constant regardless of body and limb position, but the blood pressure in the limbs will vary in order to keep the head presure constant even though the effects of gravity vary depending on how much lower than the head the body and limbs are.

In very old people, the system tends to deteriorate, due to cholesterol clogging up the neck arteries and preventing the pressure sensing from working fully.

If you are laying down, and decide to get up, there is a brain reflex that automatically raises blood pressure to compensate for gravity now being able to pull blood to the extremities. The presure sensing in the neck functions so as to fine tune the reflex and keep pressure stable over time.

The heart and circulatory system also automatically raises pressure, as well as pulse rate, as your physical activity level goes up.

You can see from all this, that what blood presure reading you get depends on how you measure it. If you measure it in the forearm in the usual way, it will not change much with changes in leg position. If you have the person hold their arm slightly up from horizontal, so that you are measuring at the same height as the neck, it should not change at all, regardless of what the legs are doing - held up as high as posible, or dangling down. If you measure blood pressure in a leg, it varies considerably with leg position. Leg presure is greatest when upright and running - as usefull side effect to having the sensor in the neck.

In young healthy persons, time has little or no effect on pressure. However, in very old people, people with certain types of brain deterioration, and people with low blood pressure, there may be a propitious drop in head blood presure when they stand up upon getting out of bed, or when getting up from a chair - for a few heartbeats anyway. This is due to the reflex I mentioned above not able to work properly. Excessive cholesterol can also cause a slow response in the neck artery sensor. It's why stenting a neck artery should not be done unless really necessary, and then only on one side. Stenting both sides, or the wrong side, will cause very unstable blood pressure with very adverse consequences as the stent prevents the sensing from working.

120.145.72.212 (talk) 02:35, 12 May 2014 (UTC)[reply]

How can a drop in head blood pressure, likely experienced as dizziness or nausea be called propitious? 84.209.89.214 (talk) 11:57, 12 May 2014 (UTC)[reply]

Perhaps 120.145.72.212 meant precipitous. AndrewWTaylor (talk) 12:13, 12 May 2014 (UTC)[reply]

No, I meant propitious. This is a cultural thing - the dictionary meaning is about things that are positive, but in my part of the World, many people use the word to indicate any change that will initiate something, be it positive or just very interesting consequences. The usual effect of a drop in head blood presure is not nausea but blacking out and perhaps falling back into the chair or bed. If severe enough, you'll faint. 121.215.85.7 (talk) 13:40, 12 May 2014 (UTC)[reply]

The Latin root of propitious is propitius "favorable, kind, gracious, well-disposed". English language Wikipedia has no good reason to promote so-called "cultural" malaproprisms arising in isolated areas when to do so both contradicts reliable English dictionaries and will mislead an OP who by IPs appears to be as distant from your part of the World as Canada is from Australia. 84.209.89.214 (talk) 19:20, 12 May 2014 (UTC)[reply]

Note the condition being referenced above is orthostatic hypotension. Wnt (talk) 20:33, 12 May 2014 (UTC)[reply]

Work done

I always thought that work done is the force x distance moved by force. (I.e. Axial work done =Fd or Torsion=T*theta etc so why is it that when equating to strain energy it becomes Fd/2? The result is Fd/2=F^2L/AE. Clover345 (talk) 13:55, 12 May 2014 (UTC)[reply]

Because the general formula for the work done by a force is the integral of the force over the distance moved (in the direction of the force) i.e. the integral of F.dr in vector terms. This simplifies to force times distance if the force is constant. In the case of strain energy, the force is not constant, but is assumed to be proportional to d (i.e. Hooke's law is assumed to hold). Hence you get Fd/2 where F is the final force at distance d. Gandalf61 (talk) 14:23, 12 May 2014 (UTC)[reply]

thanks for the answer. Is another way to look at this dU/dF? I find calculating dU/dF also gives me Fd/2 but I'm not sure if this is a coincidence? Clover345 (talk) 14:51, 12 May 2014 (UTC)[reply]

When we write physics using a slightly more general formulation, we define force as the gradient of the potential energy field. So,

-\nabla U={\vec {F}}

. If you play with the partials, you'll find that your algebraic "coincidence" works only for certain forms of energy field. Nimur (talk) 16:00, 12 May 2014 (UTC)[reply]

Resting eyes by closing

If the [human] eyes are closed, does the lens change focus to infinity ("resting" the eyes)? --129.215.47.59 (talk) 14:36, 12 May 2014 (UTC)[reply]

Answered recently. 84.209.89.214 (talk) 18:44, 12 May 2014 (UTC)[reply]

The previous answers were not entirely intelligible. The focus of the eyes due to accommodation in the absence of anything to focus on (such as in total darkness), is believed to be typically closer than infinity (see e.g. [2]. A closely related question is that of dark vergence. --catslash (talk) 20:23, 12 May 2014 (UTC)[reply]

What is the current scientific position on the issue of race supported by American anthropologist and biologists?

I've come across different websites saying that most biologist and anthropologist in the U.S. are convinced that race is not a biological or genetic concept. However, based on my Google searches, there are also a number of notable scientists who oppose the idea that there are no different human races.119.95.198.47 (talk) 16:46, 12 May 2014 (UTC)[reply]

Here's a recent Nature paper on the issue from the genetics perspective, titled 'Genetic variation, classification and race' [3]. It's freely accessible, and a short read.

“

there is no scientific support for the concept that human populations are discrete, nonoverlapping entities.

”

- is one of their final conclusions. The key is "nonoverlapping" -- most humans who are familiar with people of different recent ancestry (e.g. Sub-Saharn Africans, Northern Europeans, South-east Asians, etc.) will recognize that there seem to be some differences. However, what the science shows, is that there is just as much genetic variation within these groups as between these groups. The conclusion is that, from a purely genetic perspective, distinct human "races" like "white" or "black" are not well supported by evidence. See also our articles Race_and_society, Race_(human_classification)#Modern_debate, and Race_(human_classification)#Social_constructions. Anecdote: my friend grew up in Brazil, and was considered "white". He was very shocked when he moved to Idaho, and was considered "black". Genetics aside, there is definitely as strong cultural component to how we use race in everyday language and social interactions. SemanticMantis (talk) 17:18, 12 May 2014 (UTC)[reply]

This sounds like an argument of semantics. Different pedigrees of dog can breed and different strains of bacteria can exchange genetic material yet no-one would suggest that dog breeds and bacterial strains are "not well supported by evidence". I've never used the word race to mean "non-overlapping" populations and I think pretending differences don't exist instead of accepting or embracing difference is about as ridiculous an undertaking as accepting that 2+2=5 or that the chocolate ration went up to 20 grams. 129.215.47.59 (talk) 17:27, 12 May 2014 (UTC)[reply]

The problem is that race and genetics do not easily correspond. For example, two neighboring ethnic groups in Africa may have greater genetic differences between them than, say, someone from the Maya and the Chinese would, and yet the understood "racial" classification system would consider the two Africans to be of the "same" race, and the Mayan and Chinese to be of different races. Ultimately, racial groups are largely based on a superficial classification system which is fluid and based on who is doing the classifying. --Jayron32 17:33, 12 May 2014 (UTC)[reply]

Right. Nobody is claiming that there is no such thing as e.g. black people. What is being claimed is that our current understanding of genetics indicates that "the race of black people" is not a grouping supported by genetics. SemanticMantis (talk) 17:43, 12 May 2014 (UTC)[reply]

But that's because the things that define races (even if they are nebulous) are superficial anatomical ones and nothing to do with the functions of the plethora of enzymes and structural proteins in the brain, heart, skeletal muscle, liver, kidneys, gut etc etc. I think if you looked at the genes that governed those superficial characteristics, you'd find that genetics does support the existence of races. 129.215.47.59 (talk) 18:00, 12 May 2014 (UTC)[reply]

With all due respect, we don't care much for opinions here, our goal is to provide references that can be of use in answering questions. Please refrain from speculating on the reference desk, in accordance with our guidelines [4]. Consider also that your opinion is not consistent with the findings of the paper I linked above, and that has been published in one of science's most prestigious and competitive journals. Finally, note that if we search for "scientific" evidence to support our prior notions, and ignore scientific evidence that contradicts our prior notions, we are no longer truly following the path of scientific inquiry. SemanticMantis (talk) 19:33, 12 May 2014 (UTC)[reply]

The article you linked to seems to say the opposite of what you're suggesting. When they look at most genes, yes there is as much variation within a race as between races but there are still many genes 10-15% for which there is a distinction. Thus, as per figure 2, when comparing a sufficiently large number of alleles there are in-fact clear distinctions between races. Importantly, they aren't saying that there is more variation within a group than between groups. They're saying that there are more genes for which there is as much (not more) variation within groups as between groups. 78.148.106.196 (talk) 22:26, 12 May 2014 (UTC)[reply]

I agree entirely with your final two sentences. I'm pretty confused about the first. I did say "just as much genetic variation", not "more variation" above. Anyway, I encourage readers to read the paper for themselves. There are far more subtleties there than I can address here. SemanticMantis (talk) 16:51, 13 May 2014 (UTC)[reply]

See, this is where the better concept to work with is ethnicity and memetics rather than race and genetics. Race is based on superficial characteristics, such as skin tone. If you really want to learn about people's cultural connections and treat cultural groups as distinct cohesive populations, race and genes are a lousy way to do it. Memetics, a non-biological idea, which acts as a sort of "stand in" for genes when looking at how cultures develop, evolve, and become distinct from each other in humanity, is a pretty decent construct to work in. Then one can speak of cultural groups and memes rather than races and genes, which do not correspond in useful ways. --Jayron32 19:28, 12 May 2014 (UTC)[reply]

In the old south, allegedly, some of the "white only" signs had the footnote "no albinos". Race tagging is about more than skin tone. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:50, 12 May 2014 (UTC)[reply]

In the language known as English, the phrase "such as" means "one example, but not the only possible example" and does not mean "an exact synonym" or "the only example possible". --Jayron32 20:56, 12 May 2014 (UTC)[reply]

True. I just think back to MLK's famous statement about wanting to be judged by the content of one's character rather than the color of one's skin. And he was oversimplifying. Race prejudice is about a lot more than just skin color. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:27, 12 May 2014 (UTC)[reply]

Agreed. But many of the other markers - such as accent - are not genetic at all. AlexTiefling (talk) 23:29, 12 May 2014 (UTC)[reply]

Yes. But keep in mind that accents evoke all manner of stereotypes and prejudices that are by no means confined to race. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:39, 12 May 2014 (UTC)[reply]

I'm sure you're right, but I'm not sure how I'd recognise something that was 'confined to race', since part of the point is that the concepts of race, culture and ethnicity overlap to a significant extent. AlexTiefling (talk) 23:41, 12 May 2014 (UTC)[reply]

Accent is often thought of, rightly or wrongly, as an indicator of economic class and education level than anything else. If you didn't know Obama was black, and heard him only on the radio, you wouldn't necessarily think he's black. The lack of a stereotypical black accent hasn't stopped the right wing from railing against him with less-than-subtle race-oriented remarks. Whereas if you heard someone talking with an obvious southern white accent, you might automatically think "redneck", despite the fact that many with southern twangs are well-educated and unprejudiced. Accent can be part of the prejudice package, but it's not a requirement. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:52, 12 May 2014 (UTC)[reply]

The term is vague, ambiguous, and emotionally charged. For these reasons it is of little use to geneticists and other biologists, but important to sociologists. Anthropologists use it in some parts of their work, and avoid it in others. Jim.henderson (talk) 17:21, 13 May 2014 (UTC)[reply]

Google Maps, the Red River and the Texas/Oklahoma border

Google Maps and Google Earth show the Texas/Oklahoma border as deviating from the Red River by several hundred meters, usually to the north, where the state line nominally follows the south bank. Is this because the river's course has changed since it was surveyed, or is it because of an error in Google Maps? (It is known, for example, that Maps distorts the WGS84 ellipsoid into a sphere, and that some of its satellite photos are off-register compared to the elevation data. But the latter wouldn't explain why there's no southward bend in the state line where Groesbeck Creek joins the Red River at 34°22′08″N 99°36′47″W / 34.368805°N 99.613165°W / 34.368805; -99.613165.) Neon Merlin 17:58, 12 May 2014 (UTC)[reply]

Likely it has. Border irregularities of the United States does not specifically list those examples, but notes many other examples where a river has changed course and left land from one state on the "wrong side" of the river. See, for example, Kaskaskia, Illinois. This is especially true in the midwestern and great plains regions of the U.S., where the rivers run over wide flood plains and tend to meander and change course rather dramatically in relatively short periods of time (decades or centuries). By legal convention, land can lost to a river changing course through the gradual change of the course of the river, but if the river suddenly abandons its old channel and takes a new one some distance away (as in a rincon or oxbow lake), the land it "jumped" around stays with its former owner. This process is known as Avulsion (legal term), and can explain why some state boundaries don't exactly follow the modern borders of rivers they are supposed to. --Jayron32 19:17, 12 May 2014 (UTC)[reply]

Note that the satellite view and the Maps view differ — I looked upstream and downstream for several miles from the Groesbeck Creek confluence, and in most spots, the line was within the watered area. Looks like a Maps error, at least in part. But yes, rivers often move a bunch, and on both banks too; Grand Tower Island isn't that far below Kaskaskia, and it's on the other "wrong" side of the Mississippi. See our article on the 1820 US Supreme Court case of Handly's Lessee v. Anthony, although a 1980 decision by the Court has substantially weakened Handley's Lessee. You may find this article from the Southeast Missourian rather relevant to your interests. Nyttend (talk) 04:03, 13 May 2014 (UTC)[reply]

On the USGS topo map, your marker is on the "indefinite boundary" – and the main channel of the Red River is shown some distance north, near where Google and Mapnik have the boundary. The river must have meandered considerably in recent decades. —Tamfang (talk) 00:10, 15 May 2014 (UTC)[reply]

A/C efficiency

It seems to me that A/C would be more efficient if it cycled on and of, giving the coils time to cool off to close to the ambient temperature in between cycles. Is this correct ? Does any A/C unit try to take advantage of this ? Obviously there are times when the A/C needs to run full-out to provide sufficient cooling, but if you only need a bit of cooling, this approach might work, say by kicking on when the temp is 1 degree above the temperature setting, and back off when it reaches the setting. I also understand that restarting too soon after it stops is bad for A/C units, but a timer could prevent that.

I'd also expect A/C to be more efficient while it's raining, with all that free cool water to cool the coils, but the logistics of only running the A/C when it rains would require some type of chilled water system to implement. StuRat (talk) 18:07, 12 May 2014 (UTC)[reply]

Is it conceivable that an air conditioner manufacturer somewhere has not heard of the invention called a Thermostat ? 84.209.89.214 (talk) 19:37, 12 May 2014 (UTC)[reply]

(EC) I'm confused. Does not a thermostat do what you describe? It's 85F where I live today. My home thermostat is set for 78. The air conditioner runs until indoor temp is 78, then rests until indoor temp reaches ~79. The cycle seems to be on for ~15 minutes, off for ~25 minutes today, but of course the details will depend on insulation, size of house, temperature differentials, etc. Note that there are many types of thermostats, and some models allow for more control over the duty cycle. The Nest Labs thermostat has been attracting attention recently, in that it claims to achieve very high efficiency through artificial intelligence and machine learning. SemanticMantis (talk) 19:42, 12 May 2014 (UTC)[reply]

The only situation I can think of where a thermostat won't stay pretty close to the optimal (in terms of power use) control assuming that the hysteresis band is tuned reasonably is for initial start up or a step change in demand, which are both essentially the same. A thermostat will kick on full blast to cool the area down to the setpoint, where technically you may be able to get better efficiency by running it at a lower duty cycle over a longer time period if you don't mind the slower temperature change, for example cooling off while you're out of the house and reaching the setpoint right as you get home. It's hard to say just how much of a difference it would make, if any. Katie R (talk) 20:04, 12 May 2014 (UTC)[reply]

Good point. That idea slowly cooling until the set point is reached about when you get home is what the Nest is supposed to do by "learning" your habits (I swear I don't work for them, nor do I even own one. But I'm pretty intrigued by the possibility of saving money/energy with better algorithms!) SemanticMantis (talk) 20:26, 12 May 2014 (UTC)[reply]

I guess what I'm asking about is the "swing setting" (how far above the set point the thermostat has to be to kick the A/C on, and how far below it has to be to turn it off). Central air units often have an option to adjust that swing range on the thermostat, but I haven't seen it on portable window units. So, what is the swing on those units ? Is it small, to take advantage of ambient cooling of the coils ? StuRat (talk) 22:43, 12 May 2014 (UTC)[reply]

The whole point of all the coils and fins is to take advantage of ambient cooling, and your scheme wouldn't do much good when one most want cooling. If you think there is a problem I'd have thought you'd be better off just making sure the radiator is in the shade, has good air circulation and is cleaned of any dust and lint. If it has a big slow moving fan I don't think you're going to get anything much better except with a bigger system. Dmcq (talk) 11:51, 13 May 2014 (UTC)[reply]

If we're only considering window AC units, I agree that their control schemes leave a lot to be desired. I suspect a clever hobbyist could rig up an arduino or similar such controller to program all sorts of more interesting and efficient behavior. Though "proving" the efficiency increase would be tough outside of a laboratory context. SemanticMantis (talk) 16:48, 13 May 2014 (UTC)[reply]

The band on the window units is hard-set to a value chosen by the engineers that designed it to match the size of area it is rated for. They test the designs in environmental testing chambers, allowing the unit to cool a chamber that is either sized to match the rated area or programmed to simulate it by running it's own temperature and humidity controls, while other half of the unit sits in another chamber that is programmed to simulate various outdoors temperature and humidity conditions. The engineers hook up instrumentation to measure whatever aspects of the unit they want to test, and work out controls that optimize the performance. Obviously, there are situations where tweaking the factory-set values could improve things, but for the most part they are already very well tuned for the setup they are sold for. That's why it's important to buy a unit that is sized and rated for the area you want. Going smaller or larger will result in suboptimal control of your room's environment, and presumably worse efficiency. The same thing goes for central A/C units, but like you've noted they tend to be more tweakable. Sorry I don't have a reference for this - the company I work for builds environmental testing chambers, and has sold custom units to air conditioning manufacturers, so I know the sort of testing that at least some of them are doing. Katie R (talk) 11:54, 14 May 2014 (UTC)[reply]

Do window A/C units have any "intelligence" to them ? I've seen some with an "economy" setting, but I'm not quite sure what that includes. Would it detect when the temp is near the set point and run shorter A/C cycles at those times ? StuRat (talk) 19:14, 14 May 2014 (UTC)[reply]

Question about Penis Transplantation

Is it possible after a certain number of years, can a doctor/surgeon still be able to transplant a penis. I'm asking this because it is not stated in the article: Penis Transplant.

Penis transplantation is indeed an article! I am mystified what sort of "psychological trauma" would demand removal though ... should look into that, something sounds fishy. In general my impression is that motor and sensory nerves to severed parts remain functional as far as they go [5] though I don't really understand how this works at the cellular level. Also, apparently people can actually have a "phantom erection" like a phantom limb! [6] None of this actually answers the OP's question because this is biology and you really never know until you try. Wnt (talk) 20:29, 12 May 2014 (UTC)[reply]

Don't try. Evan ^{(talk|contribs)} 21:10, 12 May 2014 (UTC)[reply]

Can the regulars here who are finding this such fun please tell me why this isn't a medical advice question? The Rambling Man (talk) 21:12, 12 May 2014 (UTC)[reply]

Because we're not telling anybody whether (s)he in particular needs a penis transplant (though I imagine it doesn't take much of a doctor to make that diagnosis!) Wnt (talk) 21:30, 12 May 2014 (UTC)[reply]

Agreed, and as long as it's not medical advice, we should attempt to answer both member and non-member questions. StuRat (talk) 00:06, 13 May 2014 (UTC)[reply]

Unless I dismember, I think such member-raised questions are covered by the policy of Kainaw's criteria. Why the latter was castrated without any discussion here where it is used stumps me. μηδείς (talk) 21:24, 13 May 2014 (UTC)[reply]

@Evanh2008: why do you say "Don't try"? I saw some yammering about 'ethics' in the article too, and I'm afraid I don't grasp it. Is there some sort of religious-ish attitude that the borrowed penis would be adulterous...? Wnt (talk) 18:12, 13 May 2014 (UTC)[reply]

First moment of area calculations

I've asked this question before but I'm still not sure which area to use when calculating things like first moment of area, shear flow etc. My understanding is that it should be the area above the neutral axis (or below as they should be equal) but when I actually do the calculations, this doesn't seem to be the case. Clover345 (talk) 21:21, 12 May 2014 (UTC)[reply]

The answer completely depends on why you are calculating this term. The moment is a purely mathematical tool; it's just a special type of weight function. You may calculate the area pre-multiplied by anything - but the application dictates whether that calculation is useful. Once you reach problems of a certain complexity, you'll probably replace the "area" with an integral, whose boundaries are defined according to a boundary function (or its approximation). Again, the problem will dictate what those boundaries are - and therefore, which area you are calculating.

For example, if I were solving equations related to fluid flow, I would want to construct the generalized fluid flow equations. Some people describe those equations as a superposition of several moment integrals, where each term represents a linearly-independent physical property. We integrate over a volume, or apply Stoke's theorem to integrate over an area.

You might have a dramatically different formula; your class or textbook or professor might prefer a different form of equations; you might have a different application altogether. Nimur (talk) 00:46, 13 May 2014 (UTC)[reply]

May 13

light dependent and light independent reactions in photosynthesis

are both light dependent and light independent reactions in photosynthesis so important and are both the reactions/phases performed in a single plant in a photosynthesis? Also, what is the importance of light independent reactions? Also,what is the difference between the two ? — Preceding unsigned comment added by Sumukhmlohit (talk • contribs) 06:05, 13 May 2014 (UTC)[reply]

Wikipedia has an article titled photosynthesis that covers all of your questions, and probably a lot more. --Jayron32 11:43, 13 May 2014 (UTC)[reply]

For the mathematically inclined, this classic paper gives a brief overview of the most important biochemistry, then stitches it together into a fairly simple differential equation model [7]. There have been updates since 1980, but most of the current generation of simulation schemes (that care at all about photosynthesis) still use this Farquar model at the core. SemanticMantis (talk) 15:45, 13 May 2014 (UTC)[reply]

phoebe fledging

How long does it take for eastern phoebes to leave the nest?2601:6:6800:25C:FD70:9B92:89E:8A06 (talk) 15:14, 13 May 2014 (UTC)[reply]

Eastern Phoebe doesn't answer your question, but it does say that they typically have two broods per year, so that at least puts an upper bound on it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:22, 13 May 2014 (UTC)[reply]

According to [8] under the section How do they reproduce, " Though the chicks are able to fly by day 15, they usually do not fledge until day 16 or 18. Both males and females feed the young. The young are capable of breeding in their first year." Bielle (talk) 16:26, 13 May 2014 (UTC)[reply]

Building an ice-dam.

Various news reports yesterday are talking about a really seriously bad discovery about the Thwaites Glacier and how it's the lynch-pin holding back many other large chunks of ice in the antarctic:

  http://www.washington.edu/news/2014/05/12/west-antarctic-ice-sheet-collapse-is-under-way/

Seems like preventing it from slipping any further would save multiple very large and expensive cities - so it would be worth considering what it would take to hold it back rather than spending the money on sea defenses and so forth.

I was wondering what scale of engineering project it would take to build an "ice dam" to hold back the glacier. Just how big an engineering effort would it take compared to things like the Three Gorges dam? The reports seem to suggest that a 700meter tall ridge was what was holding it back...can we possibly build something strong enough and of similar size to do the same job? Three Gorges is only 150 meters tall...would something that big help at all? How wide would it have to be?

SteveBaker (talk) 15:36, 13 May 2014 (UTC)[reply]

What would stop the ice dam from melting too? ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:22, 13 May 2014 (UTC)[reply]

I think Steve means "a dam to hold back ice", not "a dam made of ice". Though using the extant ice might help. SemanticMantis (talk) 16:42, 13 May 2014 (UTC)[reply]

Yes, exactly. Contrasting a (wet) water dam with a frozen water dam...either being made of whatever materials seem appropriate. Most of what's in a dam is weight - so you could probably make a watertight casing and fill it with ice - and you might not care if it melted...but I don't know whether liquid filled dams holding back solid ice would really work...I think you need something denser than ice to make the dam out of. The "existing" dam is made of sea water... SteveBaker (talk) 18:47, 13 May 2014 (UTC)[reply]

I don't think this is something we can asses on the "back of the envelope". There's no replacement for doing the actual force loading calculations and engineering. I'm certain such a thing is theoretically possible, but I have no idea if it is practically feasible. One thought I had was to perhaps reinforce the ice, e.g. with nylon or rebar. The idea is pure concrete shatters easily, but reinforced concrete has much more strength. Also e.g. ripstop nylon has very different properties than "regular" nylon. Of course, this would still weaken as the ice melts, but it might be a cheaper way to stave off disaster for a few decades, perhaps centuies (the "fast" scenario is still ~200 years away...) Imagining that our governments are willing to think and plan and spend money on time scales of centuries it itself rather optimistic :-/ SemanticMantis (talk) 16:45, 13 May 2014 (UTC)[reply]

The only vaguely possible way I can think of stopping a glacier would be to drain water from the bottom of it. That would slow down the total amount of water reaching the sea. It would still be a huge undertaking. Dmcq (talk) 17:40, 13 May 2014 (UTC)[reply]

Yeah - I was wondering about that too. The effect of meltwater from the surface cutting channels into the ice, then getting underneath it and lubricating the interface with the rock below is one of the factors that accelerate the flow of the glacier. SteveBaker (talk) 18:47, 13 May 2014 (UTC)[reply]

I have absolutely no idea if this makes engineering sense, but the "obvious" idea that strikes me is that the plug's integrity should depend on its weight, and the key to keeping it in place might be to put more weight on it. I'd think that that could be accomplished as easily as setting up some pumps and hoses and those awful noisy goddamned snow guns from the ski resorts to spray the meltwater leaving under the glacier into the air over the plug during the colder months, when it should freeze solid. The problem being... a foul up in planning here would be a Real Big Oops. (In other news, how hard would it be for North Korea to threaten to nuke the thing wide open today?) Wnt (talk) 18:09, 13 May 2014 (UTC)[reply]

It would be easy for them to threaten it. They have lots of practice making threats. Katie R (talk) 12:01, 14 May 2014 (UTC)[reply]

Pykrete is a reinforced form of ice that is stronger, thermally insulates and melts slower. Pykrete walls or dams might bolster the underside of a glacier. There is time to investigate whether pykrete can be formed efficiently by exploiting the Antarctic seasonal thaw-freeze cycle, while “All of our simulations show [the ice] will retreat at less than a millimeter of sea level rise per year for a couple of hundred years..." (Joughin). 84.209.89.214 (talk) 18:39, 13 May 2014 (UTC)[reply]

Interesting idea! SteveBaker (talk) 18:47, 13 May 2014 (UTC)[reply]

I meant to mention Pykrete, but forgot, so thanks :) It does seem conceptually very similar to reinforced concrete, and if the wood/fiber component were harvested from the right places, it would also be a form of carbon sequestration. One risk would be altering the albedo so much that the pykrete actually absorbs more heat than ice, which could accelerate melting. SemanticMantis (talk) 19:05, 13 May 2014 (UTC)[reply]

Yes, the pykrete will almost certainly be darker than natural snow. That is why I speculate use on the glacier's underside only. 84.209.89.214 (talk) 23:15, 13 May 2014 (UTC)[reply]

The explanation I saw on TV recently is that what's happening is that warmer water is coming up under the ice shelf and eroding it away from the underside. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:14, 13 May 2014 (UTC)[reply]

Yes, it says that under the high-resolution map in the article linked above: "Warm circumpolar deep water is melting the underside of this floating shelf, leading to an ongoing speedup of Thwaites Glacier". Richerman (talk) 16:48, 14 May 2014 (UTC)[reply]

Why doesn't Huntington's disease burn itself out?

Since Huntington's disease exhibits anticipation due to the Huntingtin gene becoming longer and longer faster and faster with each generation, why does Huntington's disease run in families long-term, instead of appearing in one generation, running in the family for a few generations with symptoms appearing earlier and earlier each generation, and then, after a few generations, causing symptoms so early as to kill the carriers before they reach reproductive age, thus burning Huntington's out of the family line after a certain number of generations? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 20:13, 13 May 2014 (UTC)[reply]

Well, Huntington's_disease#Epidemiology says it "does not usually affect reproduction." So, even if your proposed mechanism makes sense, it may well just not work that way, and increased depth of vertical transmission might just not have an effect on onset of syptoms. Also, though this disease is not pathogenic, keep in mind optimal virulence, which describes how agents that are too virulent in their methods of reproduction will indeed tend to go away. Also consider the possibility that it will go away eventually, just not yet. That's the sort of ecological take on it, I can't help with the details of mechanisms of genetic control. SemanticMantis (talk) 21:22, 13 May 2014 (UTC)[reply]

evilution means maximum discomfort for all living things as long as it doesn't keep one from procreating. hence back pains, bad teeth, common cold and everything. only the most fatal stuff, the ebolas among mutations, gets weeded out fast. blatant OR Asmrulz (talk) 21:37, 13 May 2014 (UTC)[reply]

I'd say Huntington's disease does burn itself out, in that 7 out of 100,000 is only a little bit more common than rarer syndromes caused by simple point mutations, and in that the "anticipation" demonstrates that it is not genetically stable over time. In order to have new mild alleles coming in all the time, the worst ones must be being removed. Wnt (talk) 21:43, 13 May 2014 (UTC)[reply]

Point of order: the claims of anticipation are unsourced in both OP's first two wikilinks. If there is indeed solid evidence of progressively earlier onset, we still have to firmly establish a negative impact on fecundity, which is a common proxy for Fitness_(biology) (this does seem reasonable, but very tough to show). If both those features are true, then we would indeed expect that disease to eventually go extinct, along with a certain lineage. However, it's not clear to me that the disease cannot also be the result of spontaneous mutation. If that's the case, a sufficient influx of first-generation carriers could keep the disease persisting in the human population indefinitely. SemanticMantis (talk) 22:25, 13 May 2014 (UTC)[reply]

If we can prove that onset's getting earlier by generation, do we have to study whether it affects fecundity? Unless it simultaneously causes puberty to happen sooner and breaks down societal impediments to children becoming parents, it's got to reduce fecundity. Oops, I misread things and didn't realise how slowly the disease acted. Nyttend (talk) 00:53, 14 May 2014 (UTC)[reply]

Actually, we know that Huntington's can arise spontaneously through a random mutation. Depending on how you crunch the numbers, spontaneous mutations causing expansion of the 'normal' huntingtin protein's polyglutamine repeats is responsible for anywhere between 0.1 and about 3% ([9], [10]) of new Huntington's cases. TenOfAllTrades(talk) 02:05, 14 May 2014 (UTC)[reply]

Huntington's doesn't burn itself out after a few generations because in Huntington's, "propensity to anticipation is heritable for a number of generations through the male line, [but] it originates at the time of differentiation of the germ line of a male who acquires the Huntington allele from his mother".[11] Red Act (talk) 23:20, 13 May 2014 (UTC)[reply]

Thanks for digging out that paper - it shows among other things that anticipation in maternally derived cases is 1.35 years and in paternally derived 6.73 years; and that there are indeed juvenile (age of onset <20 years) and even infantile (age of onset < 10 years) cases. The 0.1-3% figure above is sort of irrelevant in that they are looking at what proportion of sufferers had a truly new mutation; but if a mutation were to have no apparent effect (small expansion) then it wouldn't count as a sporadic mutation; rather it would be an expansion in the offspring. Still, that paper points out that the Haldane approach I was thinking to use doesn't really give accurate results in a rapidly changing society/environment. What we can be sure of though is that yes, there is at least 0.1% of new mutation, and at least 0.5% lethality (that's roughly the rate of onset < 20 years in the first table) so there ought to be something around 0.5% "churn" through the pool of sufferers, genuinely new mutant alleles added and genuinely lethal mutant alleles removed from the population. Wnt (talk) 05:34, 14 May 2014 (UTC)[reply]

There's also a little evidence that Huntington's confers some sort of health benefit when people are younger [12]. So it may be a bit like sickle cell anemia where there is a tradeoff. There's probably a lot of this sort of stuff with various mental diseases where humans haven't been around long enough to just get the benefits without any of the down sides [13]. Dmcq (talk) 12:11, 14 May 2014 (UTC)[reply]

Reliable biography of Nikola Tesla

I have seen all sorts of nonsense about Nikola Tesla, pro- and con-. Can anyone recommend a sympathetic but not credulous biography? Thanks. μηδείς (talk) 21:14, 13 May 2014 (UTC)[reply]

Where do you draw the line between sympathetic and credulous? InedibleHulk (talk) 06:04, May 15, 2014 (UTC)

Well, one that doesn't embrace crackpot conspiracy theories, but which gives reliable, objective information on projects he's believed to have worked on--basically one that takes neither a pro- nor a debunking stance as a whole. I only ever learned enough electricity to pass Physics for Science Majors 201 & 202 over the summer, then promptly forgot it. So I know there are depictions of him by David Bowie and suggestions he was the basis for Ayn Rand's John Galt, but that's not very helpful or reliable. μηδείς (talk) 17:47, 15 May 2014 (UTC)[reply]

Typhoid Mary

How can typhoid fever live for years and years in the same person without ever producing symptoms and without dying off, yet still remain capable of infecting other people? The asymptomatic carrier article mentions how HIV can run for years before causing symptoms, but that's normal for an HIV carrier (get it, and nobody will expect AIDS to start right away), but Mary had the infection for years and years while people around her got it within days of exposure. Her article mentions that Stanford scholars believe that the bacteria hid in macrophages, but it wouldn't seem to me that something that's hiding in another cell would be able to get out easily and start infecting people within a few days. Nyttend (talk) 21:45, 13 May 2014 (UTC)[reply]

From [14] it sounds like it was hiding on gallstones. [15] repeats this but suggests other sites also exist, and says the carriers are the entire reservoir of the disease. Wnt (talk) 05:40, 14 May 2014 (UTC)[reply]

Chronic Salmonella Typhi infection of gallbladder is a well known phenomenon and one of the strong risk factor of Gallbladder cancer. Ruslik_Zero 14:07, 14 May 2014 (UTC)[reply]

See Typhoid Mary. Also, an infectious disease might not be entirely dormant, but only produce a rather low level infection, which is either not taken as a sign of disease at all or is taken to be something less serious, like a minor allergy. StuRat (talk) 14:19, 14 May 2014 (UTC)[reply]

This isn't exactly on topic (so remove this if you'd like), but HSV is an example of something that can become entirely asymptomatic, yet still contagious. (again, if this is useless to your question, just delete this - wasn't sure).Phoenixia1177 (talk) 04:38, 16 May 2014 (UTC)[reply]

May 14

HCV

If the Hepatitis C virus can survive on dry surfaces for prolonged periods, why is it so rare in developed countries? — Preceding unsigned comment added by 82.40.46.182 (talk) 02:35, 14 May 2014 (UTC)[reply]

Even if the virus remains viable, it still needs to get into the bloodstream (probably) to cause an infection. (See Hepatitis C#Transmission.) Even if there is viable Hep C on a surface, and you poke it with your finger, it's not going to do anything (probably, and this isn't intended as medical advice or a guarantee of safety) unless you happen to have an open wound. The principle routes of infection are through blood transfusions (in the developing world) and intravenous drug use (shared needles) in the developed world. TenOfAllTrades(talk) 02:44, 14 May 2014 (UTC)[reply]

I posted a comment about environmental degradation earlier: I've removed it, because I've just looked up the appropriate reference ([16]) and been quite shocked by just how slowly -- if at all -- the viruses degrade over time. I wonder how long they can stay viable at room temperature? -- The Anome (talk) 13:08, 15 May 2014 (UTC)[reply]

Biochem question

How do (some) living organisms produce primary halides? I'm pretty sure that haloperoxidases can't halogenate anything in the primary position, because they follow Markovnikov's rule. The way I see it, such a primary halide would have to be produced by phosphorylation of a primary hydroxyl group, followed by an Sn1 reaction -- is my understanding correct? 24.5.122.13 (talk) 04:57, 14 May 2014 (UTC)[reply]

Anyone? 24.5.122.13 (talk) 06:36, 15 May 2014 (UTC)[reply]

Cannabis and lung cancer

It says over here, 1,

"Cannabis also has been shown to have a synergistic cytotoxic effect on lung cancer cell cultures in vitro with the food additive butylated hydroxyanisole (BHA) and possibly the related compound butylated hydroxytoluene (BHT). The study concluded, "Exposure to marijuana smoke in conjunction with BHA, a common food additive, may promote deleterious health effects in the lung." BHA & BHT are human-made fat preservatives, and are found in many packaged foods including: plastics in boxed cereal, Jello, Slim Jims, and more."

The paragraph seems to be contradicting itself. First it says that it has a synergistic cytotoxic effect on lung cancer cells with the food additive BHA, but then it says that marijuana smoke in conjunction with BHA maybe promote deleterious health effects in the lung, so which is it? ScienceApe (talk) 15:45, 14 May 2014 (UTC)[reply]

The presumption is that lung cancer cell lines are derived from cells which are present in (normal) lung tissue, and that toxicity in these lung-derived cell lines may suggest a likelihood of toxicity in lung tissue. That is, the idea is that the A549 cells used in the study recapitulate many of the properties of 'normal' lung cells, and so can be used as a model for how lung cells might respond to toxins.

Of course, it's a 12-year-old, primary, in vitro only study that found a modest effect in a non-primary cell line and doesn't seem to have been followed up on...so I'm probably going to go ahead and remove that paragraph from our article as giving undue weight to a source that doesn't meet the requirements of WP:MEDRS. TenOfAllTrades(talk) 16:02, 14 May 2014 (UTC)[reply]

Um, there is no "which is it". You've just quoted two synonymous passages. "Synergistic" means "work together". "Cytotoxic" means "bad for cells". So, in the first sentence, it says "Marijuana smokes works together with BHA to have a bad effect on the cells of your lungs" and then in the second sentence it says "Marijuana smokes works together with BHA to have a bad effect on the cells of your lungs." So the two statements are somewhat redundant. They say the same thing. ---Jayron32 02:02, 15 May 2014 (UTC)[reply]

I guess my answer wasn't as clear as I had hoped. I think ScienceApe noticed that the first part of the passage dealt with cytotoxic effects on lung cancer cells, whereas the second part suggested a negative effect on (presumably) non-cancerous lung tissue—leading to the question, why would a chemical combination that kills lung cancer be seen as bad for healthy lung? Our text wasn't explicit in noting that the lung cancer cell line was being used as a model to draw conclusions about the (possible) response of healthy cells in an intact lung. Without that crucial bit of context – the inconvenient fact that many of the things that kill cancer cells also are quite good at killing normal cells – it would be easy to see a cytotoxic effect on lung cancer cells as a good and desirable thing. TenOfAllTrades(talk) 03:04, 15 May 2014 (UTC)[reply]

The two statements are not synonymous, but how are they (as the OP says) not compatible? —Tamfang (talk) 21:26, 15 May 2014 (UTC)[reply]

This study has a really unimpressive abstract. We're talking about 0.2 mM BHA * 180 g/mol = 36 mg/l, and 10 mg/l THC ... these are pretty large amounts. I'm a little unclear on [17] but it sounds like food items never contain that much BHA, and the body hopefully isn't preserved like a product on the store shelf. Tested in one cell line that isn't actually a lung - doesn't have the sort of barrier function you expect a lung to have. It's not a study that proves anything, even at a primary level, about actual smoking. Wnt (talk) 05:42, 15 May 2014 (UTC)[reply]

Common sense would indicate that inhaling concentrated quantities of smoke, from whatever source, can't be good for you. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:51, 15 May 2014 (UTC)[reply]

Common sense has its uses, but its weight in peer-reviewed research is limited. —Tamfang (talk) 21:24, 15 May 2014 (UTC)[reply]

Oddly enough, some doctors used to promote cigarette smoking. As for the above, it's always comforting to learn that the research bears out the obvious. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:23, 16 May 2014 (UTC)[reply]

Not to quibble, but wouldn't it be more apt to say "A lot of what seems obvious is what has been borne out by overwhelming evidence"? I find that it's a 50/50 over if new research is obvious - and when it is, it's more in a "Looking at it now, yes that was obvious" sense than a "Of course, I said that ten years ago" sense. It's easy to forget how informed we are by a background of research already. (yes, this is terribly off topic, I apologize).Phoenixia1177 (talk) 05:21, 16 May 2014 (UTC)[reply]

A lot of us were certain that cigarette smoking was bad for you, long before science dared to report their findings. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:28, 16 May 2014 (UTC)[reply]

Perhaps, in that specific case, I have no idea what you believed, nor why - however, as a general principle, research and obvious does not seem to go hand in hand, at first. Usually, after a set number of years, what is obvious, is the common understanding of what was researched. If this weren't true, then the billions of folks that didn't believe what we believe would have to have been exceptionally stupid if it was, indeed, obvious - that they, many times, believed the opposite would seem to indicate much of what we know is not, actually, obvious at all. (Since I am derailing the thread here, I'm going to stop at this post - :-) )Phoenixia1177 (talk) 05:38, 16 May 2014 (UTC)[reply]

How do portable (not window) A/C units work ?

1) Do they have a hot air discharge hose that blows out a window ? That's the only way I can picture them working. I saw one had an absurdly inefficient option to heat the condensate to get it to evaporate back into the air (hopefully that's the discharge air, not going back into the room).

2) This type of unit seems like it would be a lot easier to use, if I don't have to remove and replace window screens to place it in spring and remove it in autumn. I'm guessing they are less efficient than window A/C units, and you would also need to drain the condensate, if it can't drip out the window and you don't use the heater option to evaporate it. So, how does the efficiency compare with window A/C units ?

3) Do any just pump the condensate water out another hose, going to a sink or also out the window ? StuRat (talk) 19:19, 14 May 2014 (UTC)[reply]

Looks like this page: http://homeenergypros.lbl.gov/profiles/blogs/warnings-about-portable-air-conditioners and this page: http://www.sylvane.com/portable-ac-faq.html - answers most of your questions. Justin15w (talk) 19:28, 14 May 2014 (UTC)[reply]

Thanks, good info, although they seem to disagree on the value of a second (fresh air intake) hose. The first source says this increases efficiency by not sucking cool air out of the room, which is then replaced by hot, moist air being sucked into the house, while the second source points out that the need for an extra fan and the lower efficiency of cooling the coils with hot, moist air may negate that advantage. The first source seemed to have numbers to back up their claim that 2 hoses are better, so I tend to trust them.

Interestingly, the unit I looked at at the store made absolutely no mention of hoses, condensate, etc., and the pic didn't show them, either. So, that probably means a single hose, and no window install kit is included, and you have to empty the condensate bucket regularly or get a puddle on the floor. I won't be buying that unit, and probably will stick with window A/C. My window screens are apparently not removable, so I had to cut a hole in them to install my window A/C, which means I can never open the windows again when the A/C unit is out, or be deluged with bugs. StuRat (talk) 21:49, 14 May 2014 (UTC)[reply]

You can cut holes through your wall instead, hire a good drill to put holes through a concrete wall. Standard warning be careful there aren't any wires or pipes there. Site the unit outside in the shade and off the ground a bit. The installation instructions should hopefully tell you also to insulate the pipes going through the wall. Dmcq (talk) 12:06, 15 May 2014 (UTC)[reply]

In fact here [18] is a nice step by step intro showing the sort of thing required and the various tools needed. Dmcq (talk) 12:19, 15 May 2014 (UTC)[reply]

LOL, I'm trying to minimize to amount of work required and damage to the house, not maximize it. StuRat (talk) 12:40, 15 May 2014 (UTC)[reply]

Well of course one can always get the manufacturers to do it but it should cost you less than $400 in hire and extra equipment and it would look much better than a great hulking thing on the window. I'm sure you gain on the worth of the house. Dmcq (talk) 13:29, 15 May 2014 (UTC)[reply]

The laws of thermodynamics demand that the energy that these things consume as electricity plus the energy they remove from the air as they cool it MUST GO SOMEWHERE...and the "somewhere" clearly shouldn't be "back into the room again"! So there has to be some kind of external hose or something. Using this waste heat to evaporate the condensate seems like a reasonable thing to do - so that may not be that inefficient. After all, some people use swamp coolers to cool their homes - and evaporating water is a great way to get rid of waste heat if the air in the room isn't too humid to start with. SteveBaker (talk) 20:25, 14 May 2014 (UTC)[reply]

That's the problem. Unless you live in a desert, hot air comes with high humidity, and dehumidifying is as important of a function for an A/C unit as actual cooling. Also, I find my A/C units dehumidify first, with very little cooling until they get the room humidity down to a reasonable level. StuRat (talk) 21:13, 14 May 2014 (UTC)[reply]

Same deal though - if it pulls the water out of the air while dehumidifying it - then evaporates the resulting liquid - then it just humidified the air again! So even if it pulls some kind of stunt to get rid of the water, it still has to vent someplace outside. Those darned conservation laws tell you that if you want to go from air with too much energy and too much water to air with less energy and less water - then there is going to be energy and water left over that has to go somewhere. Doesn't matter how the machine does it - what matters is were the resulting matter and energy winds up. In a household situation - out of the window or down some drain are really the only sensible options. SteveBaker (talk) 15:05, 15 May 2014 (UTC)[reply]

I wonder if you could use the temp diff from the coils to the outside air to generate a bit of electricity, to increase overall efficiency a bit. StuRat (talk) 16:23, 15 May 2014 (UTC)[reply]

You'd be decreasing their efficiency. If you had a really large radiator where the temperature differential was lower the efficiency could be improved. Dmcq (talk) 11:32, 16 May 2014 (UTC)[reply]

You want to maximize the rate of heat flow between the coils and the outside air. Anything that reduces this rate (such as a thermoelectric converter) reduces the overall efficiency of the cooling system. --Carnildo (talk) 00:18, 17 May 2014 (UTC)[reply]

Static discharge - where is the charge held and how does it get conducted?

Through what route does static discharge from my person to, say, a tap (faucet)? My skin isn't a very good conductor of electricity right? Where about my person is the static charge being built up when the cause is certain items of clothing? Where are these electrons coming from and wouldn't it end up with an increasingly positive charge? --78.148.110.113 (talk) 22:31, 14 May 2014 (UTC)[reply]

You're right that skin isn't a very good conductor, and neither is air, which allows a charge to build up until large enough to overcome that resistance. If you were holding onto a good conductor, say a grounded steel bar, then the charge wouldn't build up. For an example of a person holding a large charge, think of the case where a person's hair stands on end, because of the charge: [19]. StuRat (talk) 22:45, 14 May 2014 (UTC)[reply]

See Static electricity. According to http://www.sciencemadesimple.com/static.html electrons are lost from your body to the the material (e.g. wool) and so your body becomes positively charged (click on 'Read more' under 'Where Do the Electrons Go?' and then look at 'Triboelectric series'). When you touch a conductor such as a piece of metal and ground yourself then presumably electrons will then move from the ground to your body to replace those that have been lost and neutralise the positive charge. However, I'm sure someone will correct me if I got that bit wrong :) Richerman (talk) 23:32, 14 May 2014 (UTC)[reply]

No, that's pretty much it. --Jayron32 01:59, 15 May 2014 (UTC)[reply]

There's a slight subtlety that the conductor you touch must be connected to the ground for you to discharge. My office has doors with a metal handle in an otherwise completely glass door. You can build up a fairly significant static charge over the day, which you don't notice until you press the button for the lift on the way home. MChesterMC (talk) 08:28, 15 May 2014 (UTC)[reply]

In that case, if you have more of a charge than the handle, a slight amount of the charge will go into the handle, but since it has nowhere to go from there, once the charge is equalized, the flow will stop. StuRat (talk) 12:42, 15 May 2014 (UTC)[reply]

May 15

old steel bike frame compromised due to cold temperatures?

So I live in Minneapolis and I ride an old heavy steel framed Fuji road bike, probably from the 70's or 80's, kind of like this. I left it outside all through the winter, though under an awning so it wasn't covered in snow. It was one of our coldest winters ever, with windchills hitting -20F or worse for weeks. We'd have days when the high temp, not even the windchill, was like -7F. One of my extreme bike enthusiast friends told me that the frame is compromised simply from being that cold regardless of if it was actually exposed to snow/moisture. Is this true? NIRVANA2764 (talk) 13:50, 15 May 2014 (UTC)[reply]

Windchill doesn't matter. That's just a measure of how weather conditions "feel" to people. But either way, cold temperatures shouldn't have made a difference. Even if it was cooled below the ductile–brittle transition temperature, that's not a permanent change. Permanent changes in metals generally require high temperatures, not low ones. So as long as there was no load on it, it should be fine. Moisture could cause rust, but cold temperatures would slow rusting, and as long as the paint is intact, that should prevent rust as well. Mr.Z-man 14:36, 15 May 2014 (UTC)[reply]

Our article steel doesn't seem to mention it, but steel gets more brittle at low temperatures. See e.g. here [20] for a description. I agree with Z-man that there is no lasting degradation to the frame after being stored at cold temps. But it is possible that e.g. an accident that leaves the frame intact at 70F could crack the frame if it happened at a low enough temperature. SemanticMantis (talk) 14:44, 15 May 2014 (UTC)[reply]

So that impact would only damage it if it happened while the frame was very cold? We have sunny warm spring weather here now, but I'm worried about the frame being permanently delicate now that it simply has been very cold for months on end at one point. My friend told me that bumps which used to be fine could now buckle the frame. NIRVANA2764 (talk) 14:59, 15 May 2014 (UTC)[reply]

I'm sure it would not be difficult to subject the bike to a few test bumps or torsion without you actually riding it. I have no doubt your bike will be fine. Richard Avery (talk) 15:23, 15 May 2014 (UTC)[reply]

The main issue is that steel shrinks significantly when it gets cold, and if different parts of the bike shrink by different amounts, you could get warping, and conceivably a cracked weld somewhere. But I don't think the risk is very high, given how robust steel bikes are, especially those heavy old Fujis (I rode one for years). If the wheels don't wobble when you spin them, and there is no feeling of vibration when you ride, and no visible damage, I wouldn't worry about it. Looie496 (talk) 16:02, 15 May 2014 (UTC)[reply]

Agreed. I'd inspect all the welds for cracks. If you don't see any, it's probably fine. StuRat (talk) 16:20, 15 May 2014 (UTC)[reply]

The great and terrible thing about failure analysis is that on any individual unit, you only get one shot. I think your friend is 100% correct: the bicycle is compromised. That is a very specific word-choice: your friend does not say the bicycle is damaged - only that it is compromised. Statistically, there is a greater chance that it will become damaged. We don't know whether your specific bicycle is actually going to break due to brittle failure until it breaks! If (or when) it does break, we can't know whether it would have broken later - or if it would have withstood the same force - had it never been exposed to the cold.

What we can know is that in laboratory experiments, if we subject steel to cold (or any thermal cycle), then that steel is statistically more likely to yield or fracture. To what extent does this make your bicycle unsafe? Well, that's a very hard question. We'd need to have boatloads of statistics about the design and materials of the bike frame; we'd need data about the temperatures it had been exposed to; and so forth.

So what we can say - at the risk of using a weasel word - is that your bicycle is compromised. We suspect that it has been exposed to a condition that can adversely affect the structural integrity. We don't know how much it's affected. Presumably, we can't find any actual damage, and we won't go so far as to call the bicycle unsafe.

Entire factories are full of specialists who study this problem as it applies to mass production. These people include material science and engineering experts; reliability engineers, operations and supply chain experts, and so on. Not to discredit Richard Avery - but his approach is not really applying the scientific method. You can thump around the bike frame all you like, and you might still find that it is undamaged. But have you actually tested the null hypothesis? Of course not!

If you want to know whether the cold has compromised the bicycle, you must conduct a proper controlled experiment. You need a statistically-valid population (say, many dozens or many thousands of bicycles). You need a test group and a control group. You need sterile laboratory conditions to isolate variables from the independent variable - the thermal cycle; and you need to conduct enough tests to determine time until failure on many bicycle frames (damage the bicycle until they break!) And then you need a statistician to tell you whether we can confidently say that the dependent variable ("damage") correlates to the thermal cycle.

And that's failure-analysis for a steel bicycle frame - a couple pieces of welded steel! Steel is a material whose properties are well-known; the common alloys haven't changed in decades and their thermal characteristics have entire ASME and ASTM handbooks encyclopedically detailing how and when they break.

My bicycle owner's manual, which I've of course read cover-to-cover, has an entire chapter on thermal properties of bicycles with complex parts including carbon fiber. Actually, high temperatures are the worse condition for my bike! If stored above 66.5°C, I'm afraid my bicycle falls "out of specification." I suspect exfoliation of the carbon-fiber from the aluminum becomes problematic. Long before we hit that temperature, the synthetic polymer "rubberized" grips also start to become irreparably melted. Around here, my bicycle rarely gets exposed to freezing conditions.

Now imagine if you mass-produce computers. Suppose, hypothetically, that your computer were mostly made out of metal and glass, but with lots of weird alloys - especially new, "non-hazardous metal" - plus silicon and plastic and fibers and flex circuits - and you want to know whether thermal cycles cause them to fracture. (Hey, people leave their metal-and-glass computers outside in the cold all the time - does that "compromise" the device?) Just imagine for a moment the complexity and the cost of building fully-functional computers, thermal-cycling some of them in hot ovens and ice-boxes for many weeks, and then dropping them on concrete by the thousands, just to see if they break. Only then can you safely assert that you know whether the mechanical parts are "compromised;" and you can confidently advertise an environmental requirement for operating- and non-operating temperatures.

Nimur (talk) 16:29, 15 May 2014 (UTC)[reply]

What an elaborate response! What my friend meant is, in layman's terms: it's trashed; don't ride it; permanently beyond repair now that it has at one point been so cold. But others have said that even if it got cold enough that it crossed the ductile–brittle transition temperature it would not be permanent change since there was no weight on it and it's warm now. So, Nimur... would you ride it? :) NIRVANA2764 (talk) 16:43, 15 May 2014 (UTC)[reply]

Sure, I'd ride it... but I wouldn't ramp it. Nimur (talk) 21:07, 15 May 2014 (UTC)[reply]

Indeed, what a lot of woffle from Nimur. But he is right in saying metalugy of the steels etc that bicylcles are made of is well understood. No permanent change in brittleness will occur. There is another aspect: Steel bicycle frames are made with brazed joints (similar to soldering). Any join involving dissimilar metals is subject to eventual failure if subjected to thermal cycling. The basic mathematical approach to predicting failure is called the Coffin-Manson relationship, after the names of two pioneering researchers. Coffin-Manson mathematics has been used to explain effectively "fatigue" failute in things ranging from aircraft airframes to power transistors. At the root of it is uneven thermal expansion. But if you do the calculation on a typical brazed jointed steel bicycle frame, you'd need 1000's of years of extreme weather to induce Coffin-Manson failure. 121.215.85.7 (talk) 16:56, 15 May 2014 (UTC)[reply]

As Nimur suggests, nobody here can assure you that the bike is just as safe to ride now as it was two years ago (or 10, or 20, etc). But consider: how old is the bike, and how many cold winters has it seen? What is the marginal change from just one cold winter? Personally, I'd ride it around town without a second thought. But maybe I wouldn't race it, or take a multi-day solo tour. For a point of comparison, I ride a ~1975 steel-frame Chicago Schwinn. It's seen plenty of temps that low over the past ~4 decades, and it still feels indestructible to me :) SemanticMantis (talk) 19:15, 15 May 2014 (UTC)[reply]

I live in a place where we get cold temperatures for months on end. Every winter people put their bikes into cold storage and bring them out again in the spring (around this time of year) and they have no problems. CBWeather, Talk, Seal meat for supper? 00:24, 16 May 2014 (UTC)[reply]

Just out of curiosity -- if people worry this much about bikes, why is it seemingly universal practice for states to leave bulldozers, road rollers, and such-like heavy duty equipment lying around in state parks, and even when they care enough to stockpile it in a secure lot they leave it out exposed to the elements? I mean, they don't even keep the snow and rain off them let alone anything else. I'd think if I had a $100k+ machine I'd garage it. Wnt (talk) 16:09, 16 May 2014 (UTC)[reply]

I think because of the expense of moving such things on the road. You need to rent special flat bed tow trucks that can lift them onto their bed, etc., and that's pricey. If you've been using it in that park until winter hit, and expect to use it again there next spring, it's cheaper to leave it on the job site. Presumably they are also built to withstand such weather. As far as theft goes, it would be rather difficult to hide and then sell such a stolen big rig. StuRat (talk) 16:30, 16 May 2014 (UTC)[reply]

Any bulldozer, grader, loader or any other heavy equipment that is going to be used during the winter will usually be kept inside. On the other hand things like dump trucks that are only used in the summer will be stored outside. For personal vehicles if you want to use it all winter and you don't have the space to build a shelter or you can't afford to heat one then it gets parked and plugged in on a daily basis. If you don't plan on using it till spring then it gets left outside. CBWeather, Talk, Seal meat for supper? 22:40, 16 May 2014 (UTC)[reply]

Bipedalism

Why back in dinosaurian times bipedalism in animals was more common and more widespread than now, when there are relatively few bipedal species (especially since small upper limbs of bipedal dinosaurs were of little use)? Brandmeister^talk

This is not true when you consider birds to be bipedal. They are modern dinosaurs. The reason that they are smaller is:

1) To allow them to fly (except for flightless birds, of course).

2) Because oxygen content in the air is less now, making breathing more difficult for huge land animals. (Whales get past this restriction because swimming is far more efficient than walking.) StuRat (talk) 16:15, 15 May 2014 (UTC)[reply]

Citing birds they way StruRat did is a nonsense. Birds are a later adaption, and their wings are adapted front legs/arms.

I note that most of the larger lizards around today are partially bipedal. When they want to go fast, the raise up their fronts so that the front legs are hanging free, raise their tails up for balance, and run on their back legs only. The back legs are bigger than the front legs, though the difference is nowhere as extreme as it was for certain types of dinasaur. A leg is not mechanically 100% efficient, having a certain level of energy loss mainly dependent on length and to a lesser extent on mass. So running on two legs is more energy efficient that running on four. Efficiency is not critical for mammals as their pressurised blood system, with 4-chambered hearts, allowing the presure to the limbs much higher than the pressure to the lungs, facilitates vastly better oxygen delivery to the muscles. Lizards can run pretty fast, but they tire extremely quickly due to low body temperature and a simplified low pressure blood system. Some large lizards can run as fast or faster than a man, but at max speed conk out after only 10 meters or so.

Running balanced on two legs also confers a significant manouverability advantage when negotiating complex terrain, as in dodging and going around rocks and plants. I've seen a dog chasing chickens that had had their wing feathers removed (so they could not escape over fences). They could not take off, but they could turn so fast the dog could not catch one, uselessly doing 4-paw slides and colliding with trees. But on open ground with no obstacles, those chickens would have been goners, as the dog has greater stamina.

I doubt that the very small front limbs of certain dinasours were completely useless. These dinosaurs persisted for millions of years, so evolution should have got rid completely of anything useless. When you look at some apparently useless feature on an animal, it's usually for sexual attraction or for courtship rituals/"dances".

121.215.85.7 (talk) 16:35, 15 May 2014 (UTC)[reply]

While the question of why the bipedalism was ostensibly more common in animals in Mesozoic era than at present may not be answered in the strict sense, I believe the following factors should be considered. (1). Evolution does not produce perfect species, just "good enough" species capable of occupying an available ecological niche. It so happened, due to the mass extinction, that at the beginning of Paleogene many ecological niches became available; and the surviving land vertebrates were mostly small and nocturnal. A nocturnal biped is a rarity: there is no evolutionary benefit in tripping and falling. The available niches were therefore taken by quadrupeds. The quadrupeds diversified, became active at various time of day, and some of them (kangaroos, humans) did become bipedal. Flightless birds also occupied some of the available niches (see e.g. Cassowary, Ostrich, Moa, Aepyornis for extant or recently extinct examples). (2) Vegetation was quite diffferent in the Mesozoic than it is at present. It is possible that whatever suits velociraptor well wouldn't have suited a jaguar nearly as well, and vice-versa. (3) Bipedalism is not unique to birds, humans, and Mesozoic theropods. Even cockroaches are capable of bipedal locomotion when running fast to escape a threat. (4) The perception of the more common bipedalism in the Mesozoic may be rooted in human culture rather than in real fact. We are best acquainted with the largest terrestrial vertebrates. Indeed, they preserve the best, and draw the biggest crowds to museums and movie theaters. Vast majority of terrestrial species, however, are arthropods, molluscs, and small vertebrates. There are not too many bipeds among those, either then or now. A lot of the smaller Mesozoic animals haven't even left any fossils to work with. Hope this helps. Dr Dima (talk) 17:45, 15 May 2014 (UTC) NB. Velociraptor is actually a bad example: there wasn't too much vegetation where it used to live :) Dr Dima (talk) 18:06, 15 May 2014 (UTC)[reply]

I question the premise of the OP. Per plurium interrogationum the OPs question posits a presumption we have not yet established as true. Do we know for certain that bipedalism was more common in the mesozoic era than at other times? I've seen no evidence that is even true. It may be, I am not saying that it is or isn't true, just that until we've established it as true, it makes no sense to say why it is true. --Jayron32 18:09, 15 May 2014 (UTC)[reply]
- I may be actually wrong, it's just my impression. However, in terms of habitual, constant bipedalism it looks like back in the Mesozoic there were more terrestrial animals with such locomotion, than in modern times. My speculation after 121.215.85.7's reply is that at least partially bipedal manouverability proved to be superior to quadrupedal speed, such as in cheetahs. Brandmeister^talk 18:31, 15 May 2014 (UTC)[reply]
  - See, that's the problem. People have all kinds of impressions. Has there been any systematic quantification of the prevalence of terrestrial bipedalism across the eons? If not, then what are we basing this on? The fact that we've seen a lot of pictures of bipedal dinosaurs? Couldn't that just mean that the T-Rex is a popular dinosaur? Could it mean that our museums and artists tend to favor familiar forms, and that they tend to put more bipedal dinosaurs on display than others, merely because they generate more interest, being that humans are bipedal and thus tend to be more interested or attracted to bipedal dinosaurs? There's many ways to interpret your impression, and until we've established your impression as reliably enough confirmed, there's really no point in telling you why it is true; if in fact its truthfulness is an open question. It may be true, I haven't said it isn't. Just that it isn't worthwhile to develop a theory to explain why it is true, if it may turn out later to not be true. --Jayron32 00:54, 16 May 2014 (UTC)[reply]
    - Indeed. Given that in any ecosystem, herbivores necessarily outweigh carnivores (after all, carnivores need to eat something), and that triceratops, apatosaurus and stegosaurus species were all quadrupeds, this may simply be a wrong impression caused by the popularity of representations. --Stephan Schulz (talk) 05:55, 16 May 2014 (UTC)[reply]
      - What you say is common sense, but it is not always true that herbivores outweigh carnivores at a certain locale. See e.g. this (freely-accessible) paper [21], search for "pyramid". There is a whole section on 'inverted biomass pyramids', discussing how in some cases top predator biomass far exceeds herbivore biomass. When I heard Sandin present this work he had great photos of these shark-dominated waters. SemanticMantis (talk) 14:24, 16 May 2014 (UTC)[reply]
      - The relatively high prevalence of bipedalism among terrestrial vertebrates (except mammals) is probably because they can not run efficiently using all four limbs. This is related to the structure of their spines, which could only bend in the horizontal and not in the sagittal plane—good for swimming but not for running. So, the only option if you want to run fast was to use only one pair of limbs. On the other hand mammals acquired a number of adaptations that allowed them to effectively use all four limbs for running. This includes spines that bend in the sagittal plane. Ruslik_Zero 12:43, 16 May 2014 (UTC)[reply]

Ruslik obviously has never seen a lizard. When on all fours, their sideways swinging gate is generally quite pronounced. 121.221.156.103 (talk) 02:08, 17 May 2014 (UTC)[reply]

an illustration for the standard model of particle physics

Hi!

Could you please check this diagram for errors?

I double checked it, but i'm not a specialist in particle physics and i fear i got something wrong.

Mass:

more than 80 GeV/c^2

1-5 GeV/c^2

90-110 MeV/c^2

less than 16 MeV/c^2

Massless

Spin (small blue circles in the middle):
empty circle: 0
full circle: 1
half-circle: 1/2

Charge (external circles):

positive

negative

full circle: 1 or -1 respectively
2/3 circle: 2/3 or -2/3 respectively
1/3 circle: 1/3 or -1/3 respectively

Participation in interactions:

Weak force

Electromagnetic force

Strong force

Thanks!

P.S. I don't want to replace the standard diagram, this diagram is just an additional illustration.

Zhitelew (talk) 17:12, 15 May 2014 (UTC)[reply]

It's a really neat diagram, but it sure isn't the standard diagram. Did you create this diagram yourself or are you following a model from a reliable source?

Reputable publications all seem to use the same diagram - in other words, the standard diagram - to illustrate the standard model. I've never seen your new circular lay-out before - and I've read a lot of physics books - so I wonder if it really belongs in an encyclopedia article.

For example, you might find the diagrams in CERN's eduation resource website FermiLab's education resources page look awfully similar to the present diagrams we use in Wikipedia. It's probably best to stick to the schematic representation that real physicists are actually familiar with. Nimur (talk) 21:36, 15 May 2014 (UTC)[reply]

Hi, Nimur. Thanks for the answer!

I made this diagram myself, but there is nothing original in it. I just bended the "standard" table into a circle and replaced numbers with colors. The design of the diagram can be new, but all the science and data are from the same "standard" table. --Zhitelew (talk) 21:59, 15 May 2014 (UTC)[reply]

...Right, but what does it mean? Let me clarify: I know about the Standard Model, but let's imagine momentarily that I know nothing, and I'm learning it all from your chart. And, I apologize for nitpicking here... you've made a really nice picture and I can see that it took effort. It's quite artistic and very skillful. But, we're making an encyclopedia, not a graphics showcase... and I think there are important and problematic issues with your diagram as a physics-education tool.

See, I look at this chart, and I wonder why you've apparently plotted it in polar coordinates. I see that particles at larger radius have a larger area on the diagram. What does this represent? Are those particles larger? Are they more abundant? What does "area" represent in this chart? What does radial-distance from the origin represent? Are particles at the center of the diagram "inside", while particles at the outer rim or the diagram "outside" of composite particles?

The chart is circular. It "wraps around." What is the physical meaning of this? I'm going to start making inferences - physically incorrect ones! - "photons are close to tau mesons on the chart, so are they related?" ... And now, on account of a confusing diagram, I've embedded incorrect physics into my understanding of things.

So, you see, there is a reason why all the standard diagrams look the same. Consider, for example, the Periodic Table of the elements. It can be re-drawn in many ways;if you read into it, you'll see that many alternate diagrams do exist. But, except for a small number of special-purpose variants that are made for expert users, most of those charts just serve to confuse science-students.

You might enjoy reading the Junk Charts blog. The authors tear apart a variety of infographics that they find on the internet. Artistic creators can draw lots of neat-looking charts - and nowadays, it's very popular to design an exciting-looking infographic diagram - but what do the axes mean? Does the diagram convey information in a straightforward, accurate way that is easy to interpret? Does your diagram? Or, quoting Mr. Fung more directly:

What practical question are you trying to answer?
What does the scientific data say?
What does your chart say?

So: how are the particles of the standard model related? Does your chart answer this question?

These are tough questions, but if you want an honest and very brief answer, "no." (It is my opinion that) your chart is not the best way to represent the standard model in an encyclopedia article. The standard diagram - as boring as it may seem - has been around for a while, and it's best to stick to that layout, unless you find a reliable physics education source that makes a convincing case otherwise. Nimur (talk) 04:10, 16 May 2014 (UTC)[reply]

OP isn't suggesting replacement of extant figures. I take your points, but I think this figure is quite nice. Of course I would personally never think the areas represent anything, but that can be explained in the legend to head off confusion. I actually think the colors and pie chart insets for spin and charge make those pieces of info much more easy to grasp at a glance. That is something that this new chart "says" much more clearly than the ones you linked. So, provided there are no factual errors (which I assume you'd have mentioned), I see no reason why this can't be used to supplement other, more standard graphics in our articles. I also don't think this is WP:OR, insofar as nothing is original except for layout. We aren't publishing a paper book, (WP:Notpaper), and there is no limitation on how many figures can be used to express concepts. I don't share your fear of the graph leading to non-physical notions, but again, a good legend will go a long way in preventing that. SemanticMantis (talk) 15:22, 16 May 2014 (UTC)[reply]

I have to agree with Nimur. What is this trying to show? For example reading this graph in the top column you have the Higgs with the Z⁰followed by the neutinos (why no anti neutrinos, they haven't been confirmed as Majorana particle yet) working away from the centre of the circle. Okay they all only weak force and are neutral but they are fundamentally different particles. The neutrinos are seperated from the other leptons, why? From this graph it doesn't look as if the charged leptons and the neutrinos are part of the same family but the neutrinos are asociated with the Higgs. There is nothing fundamentally wrong with graph (besides saying for sure the neutrino is not a Dirac particle like all the fermions) but it can lead people to make the wrong connections.Dja1979 (talk) 19:53, 16 May 2014 (UTC)[reply]

Thanks for the critics! I didn't add antineutrinos because (as far as i know) the existence of antineutrinos is not confirmed yet.

Agree. The diagram should better display borders between particles with different spin. This should help against possible wrong connections and accentuate the right ones.

I probably should mark the empty slots with other color. These white spaces only indicate the absence of the particles with corresponding properties, not borders between groups of particles.

By the way, aren't neutrinos fundamentally different from other leptons? Yes, they have the same spin as other leptons, but they have all these unique wired properties like oscillations, extremely low mass, only week interacting etc. Shouldn't we indicate this somehow? --Zhitelew (talk) 20:48, 16 May 2014 (UTC)[reply]

This might also be a good question for the Mathematics desk since what you have here is a rectangle transformed into a cylinder looked at from a polar prjection (I may have the terms slightly off.) This works fine if the opposite edges joined to form a cirle actually can be so joined--you can do this with a periodic table with some jiggering. You can't do it with a normal chessboard howver, since pieces aren't allowed to move diagonally acrost the right and left edges in the standard game. μηδείς (talk) 20:07, 16 May 2014 (UTC)[reply]

Engineering disciplines

Is there a huge difference between different engineering disciplines other than what they're engineering? For example civil engineers engineer civil infrastructure and aerospace engineers engineer aircraft but do they use the same principles? 82.40.46.182 (talk) 22:38, 15 May 2014 (UTC)[reply]

No, there isn't a huge difference in disciplines. At my university the big divide was between civil and all the rest, and in the second year the electricals started to specialise away from the rest. Civil is a bit odd as they often design to code, whereas most disciplines design for function. As such I would expect a mechanical engineer to happily work in aerospace, I think that might be more of a stretch for a civil engineer. If you see a mechie in a civil firm he is likely to be working either on the mechanical systems (lifts, HVAC,plumbing) or as a structural engineer, as frankly the civil guys seem a bit flaky on structural analysis. FWIW I was more or less in the mechanical stream, yet my career includes fairly big lumps of electrical and signal processing. University is NOT about teaching you to do a job, it is about giving you the basic tools and the confidence to be able to teach yourself. As such, if you haven't covered the design of power amps during uni, you know at least enough to find the right book and learn from it (to pick an example that came up for me). For that matter I've worked with engineers who did maths or physics at uni, they taught themselves what they hadn't picked up at uni. Greglocock (talk) 23:40, 15 May 2014 (UTC)[reply]

On a day-to-day basis engineers usually work with approximations and simplifications that apply in their field or sub-field, even though these approximations and simplifications are not true in general. An example for electrical engineers would be Kirchhoff's circuit laws. Jc3s5h (talk) 23:53, 15 May 2014 (UTC)[reply]

Kirchoff's circuit laws are conservation laws which when properly applied to lumped components are exact, not approximate. 84.209.89.214 (talk) 01:55, 16 May 2014 (UTC)[reply]

But the real world is not made up of lumped components. Jc3s5h (talk) 02:18, 16 May 2014 (UTC)[reply]

On the contrary, I find that, other than some superficial similarities, the practices and workings of various engineering fields to be quite different. I'm not sure that the training and/or job requirements of a civil engineer, a chemical engineer, and a biomedical engineer are all that similar, excepting that they all are engineering fields; more like each other than they would be to other jobs like say a school teacher, a chef, or an economist; but otherwise I'm not sure many job skills from one of those fields would transfer well to the other. Someone designing a prosthesis would have a hard time working out the fluid dynamics and heat transfer problems a chemical engineer needs to face, and neither would necessarily be able to do the work necessary to design an automobile from first principles, without being fully retrained for the others job. Certain broad concepts, such as the mathematics background and basic physics principles, may cross over, but I'm not sure much more than that. --Jayron32 00:39, 16 May 2014 (UTC)[reply]

Curious. Are you an engineer? Greglocock (talk) 01:54, 16 May 2014 (UTC)[reply]

Civil engineering tends to be more about managing people and less on the technical side than say electronics engineering, but there is always a large component of working with other people. All also have to work safely within set constraints, be a bit practical, and be conscientious about keeping to schedule and documenting things. And it seems all have to at least occasionally work long hard and unsocial hours. It is a career for people who want to make something useful in the world. Dmcq (talk) 11:19, 16 May 2014 (UTC)[reply]

A military perspective. Mechanical engineers build weapons. Civil engineers build targets. HiLo48 (talk) 01:52, 17 May 2014 (UTC)[reply]

May 16

Patterns That Change When Tilted

Hello. I do not know how to best word my question but here is a start. I would like to know the field that is concerned with designing patterns that change drastically in appearance when the paper on which it is printed is tilted so slightly. I am not looking for a specific change in appearance; this is be open-ended. Thanks in advance. --Mayfare (talk) 00:37, 16 May 2014 (UTC)[reply]

It sounds like you're asking about lenticular printing. Red Act (talk) 01:13, 16 May 2014 (UTC)[reply]

Iridescence also is affected by viewing angle, and diffraction gratings can be used to produce angle-dependent effects. —Quondum 04:45, 16 May 2014 (UTC)[reply]

There's also holograms of course. It might help if you could link to an example.--Shantavira|^{feed me} 08:53, 16 May 2014 (UTC)[reply]

Is there a method that does not change the properties of the paper? --Mayfare (talk) 11:04, 16 May 2014 (UTC)[reply]

Anamorphosis is a sort of optical illusion involving an image that appears distorted from one angle, but is intelligible from another angle. The Ambassadors (Holbein) famously uses this technique. ZMBrak (talk) 13:49, 16 May 2014 (UTC)[reply]

Doing this on normal paper sounds difficult - paper is a very bumpy material at microscopic scales - so the orientation of the surface to the eye changes across every fraction of a millimeter across the surface. Hence any straightforward "ink" approach isn't going to work because the orientation of your eye to the surface is uncontrollable. If you're prepared to go with very smooth plastic films and such - then it gets easier. There are printable holographic approaches - and of course metal films like the ones on many credit cards. Simplest of all is to use a lenticular film over a printed image - which is a technology that's been around for 80 years or more. I think we need to understand more about the application for this. SteveBaker (talk) 18:21, 16 May 2014 (UTC)[reply]

I'll suggest moire pattern since that ended up being the answer to a similar question I asked. μηδείς (talk) 18:24, 16 May 2014 (UTC)[reply]

In theory paper should be compatible with a diffraction grating - in a really quick search I get [22] which points me at Optically variable inks, Optically variable pigment (whatever the difference is), multi-diffraction grating, pixelgram as (perhaps, I'm not sure) methods of printing diffraction gratings on currency to make copying harder. I don't know how much modification they involve from regular paper though... would be interesting to see more. Wnt (talk) 20:33, 16 May 2014 (UTC)[reply]

radical surgery on antarctic ice using lasers

Would a high powered laser be able to amputate the part of the sliding ice, if any, that overhangs into the ocean? I was thinking that would slow the slide of the remaining ice into the ocean, giving us more time to deal with it. I know the ice is very thick and hard to cut with a laser, but the overhanging ice would tend to open up any laser cut further, like when a leaning tree is cut on the upper side with an axe. The power level of such a laser would be immense, im sure, but what would an estimate for that power level be? (So that if 50 or so years from now, such a very powerful laser became feasible.)--(If not much of the ice is currently already over the ocean, the report is that it will be in a few years.) Thanks.Rich (talk) 04:31, 16 May 2014 (UTC)[reply]

Methinks high explosives (as used, e.g., for avalanche control) would be much more cost-effective. 24.5.122.13 (talk) 04:52, 16 May 2014 (UTC)[reply]

It could depend on location. An orbital laser would have an enormous initial cost but could use natural nuclear power, which is close to free, and once in orbit, there wouldn't be any travel overhead, no matter if it's an antarctic glacier, or closer to populated areas.

A pulsed laser to which ice is opaque would probably be the optimal tool for the job. At high power, it would crack, rather than melt, the ice without much heat transfer.

OTOH, wouldn't it be more useful to cut through cultures of this or that, with a laser that big? Preferably while they're being harvested, for added evulz? - ¡Ouch! (^{hurt me} / _{more pain}) 09:22, 16 May 2014 (UTC)[reply]

Hmmm...what kind of orbit is this laser in? If it's a polar orbit, then you won't have much time to do your work in each orbit...if it's in a low equatorial orbit, then it wouldn't even see the poles - and if you put it all the way out in a geosynchronous orbit, the accuracy and focussing issues would be amazingly difficult. Plus, I'm not sure how other countries would feel about a laser out there in space with the capacity to slice through half a kilometer of ice at a positional accuracy down to a fraction of an inch...that would make a really good death-ray! SteveBaker (talk) 18:05, 16 May 2014 (UTC)[reply]

Why should we even bother to ask them, when we have the means and the ability to do it unilaterally? But I agree that it won't work for cutting ice (although it CAN work against Iranian nuclear missiles). 24.5.122.13 (talk) 22:42, 16 May 2014 (UTC)[reply]

Are you sure of your assumption that overhanding glaciers pull the rest down with them ? Aren't they supported by seawater ? I believe the floating ice shelves act more as a cork, stopping the rest from sliding off the land. StuRat (talk) 06:13, 16 May 2014 (UTC)[reply]

I'm puzzled as to why you would want to "deal with it", but anyway a laser would be completely ineffective as the hole it creates would continually fill with water which would block the beam.--Shantavira|^{feed me} 08:45, 16 May 2014 (UTC)[reply]

That's why Rich made it "high powered". The water would be blocked out by a bubble (or possibly a jet) of water vapor. Not sure how much power you'd need. Also, this. - ¡Ouch! (^{hurt me} / _{more pain}) 09:22, 16 May 2014 (UTC)[reply]

The notion of a destructive laser orbiting the globe would likely be met with very vigorous opposition, and in fact might already be banned by existing treaties. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:28, 16 May 2014 (UTC)[reply]

You'd need a powerful laser. If you can't grok the orders of magnitude involved in this problem, then perhaps a more visual demonstration will help build intuition: go grab the most powerful laser you can find, and try to melt a block of ice with it. (Unless you're SteveBaker, who owns a personal CO2 laser cutter - but he knows enough to be careful). Everyone else: good luck. Your ice will melt from ambient room temperature long before you etch away anything. Between the immense heat-capacity of water ice, and the high reflectivity of ice to wavelengths of visible light, and the other inefficiencies related to making laser light, this whole exercise becomes very impractical when you scale it up to iceberg-sized objects. Even if you put the laser and ice-cube in the freezer - so the ice doesn't heat up from the room - and let the laser shine on for days - every time it melts a little bore-hole, the water will re-freeze and seal it up pretty quickly.

For anyone interested in real-world ice boring, you might want to read about the IceCube Neutrino Observatory. Conventional technology that we use for drilling into materials like solid rock does not work on Antarctic ice. (The ice flows into the bore-hole, moving as a fluid; and on contact, the pressure re-liquifies and re-freezes!) So the ice just seals up the holes you've cut. The AMANDA and IceCube projects avoided "drilling" and "cutting" and instead relied on "melting" using a steady stream of hot water - and a very wasteful fossil-fuel plant to generate that water! And here's an awesome review from Schlumberger - the oilfield service company - on "Drilling Through Ice". Nimur (talk) 15:33, 16 May 2014 (UTC)[reply]

There are two or three significant problems with doing this. So let's talk a bit about my laser cutter...and then we'll see how this idea extends to cutting a glacier.

My laser puts out about 100 watts of energy - no more than an incandescent light bulb. That surprises most people when they see it slicing through a half inch of plywood like it wasn't there! But take all of the heat from a 1000 watt bulb and put it into a beam the diameter of a pencil - and the result will set fire to wood and paper...but it won't cut it. To get it to put enough energy into the material to cut it, you have to focus that pencil-thick beam into something about three hundredths of a millimeter across. When you do that, it'll make most organic materials and many plastics simply "go away"! A light bulb has about 100 square centimeters of area to radiate those 100 watts. But that same amount of energy emitted as a one-square-centimeter beam is 100 times more energy per square centimeter than a lightbulb - but focus it down to 0.03mm and you get about 10 million times as many watts per square centimeter as that light bulb...and that's enough to zap just about anything that absorbs it.
However, my laser can't cut metal...even a thin sheet of kitchen foil is utterly impenetrable. That's because the metal reflects almost all of the energy away. Because it's an infra-red laser, it also can't cut anything that's transparent to IR light because the beam goes right through it without the energy being absorbed. There are lasers that can cut metal - but they have to be around 3000 watts and they aren't usually
The laser cutter has big fans to extract the smoke and hot gasses produced by the cutting process - and a high pressure air jet that squirts into the slot that the laser is cutting. These are there to remove smoke and debris from the path of the laser beam. Anything like that that get in the way attenuates the beam so badly that it won't cut.

The trouble with slicing through a glacier is that you can't focus the beam thin enough once you're more than a few centimeters down into the ice. So you need VASTLY higher wattages. If I wanted to cut wood with an unfocussed beam, I'd need a 100,000 watt laser rather than a 100 watt device! Those kinds of laser exist...but they are massive, difficult, dangerous, fragile and horrendously expensive! I suppose you could consider dynamically focussing the beam, increasing the depth of the focus into the ice as the beam cut deeper - but focussing is problematic. My lasers focussing lens is made of Zinc selenide with a gold coating that's just 2 atoms thick! That 1" lens costs $300 and is about as hard as candle-wax, so it scratches if you so much as look at it. You can't use just ordinary lenses because if they aren't super-transparent, they get hot enough to melt in very short order! Worse still, if you cut with a focussed beam, the "kerf" (the width of the slot) is about the same width as the diameter of the focal point of the beam...but that's not wide enough to fit the unfocussed beam as it enters at the top of the material. For that reason, I can't cut wood that's more than a half inch thick without getting a much longer focal length lens.

Then the light frequency is a problem. Ice is both transparent and incredibly shiny at optical wavelengths...so you'd need to choose a frequency that the ice would strongly absorb and not be either transparent or reflective.

Finally, as you hit the ice, it's probably going to flash into steam...and you get a LOT of steam from a very small chunk of ice. Where that steam goes is a problem...if it simply drifts up the slot that you're cutting, then it'll absorb laser light and attenuate the beam...or it may condense back onto the sides of the slot...causing liquid water to fill the slot and have to be boiled away again. You'd need to extract the steam as you cut if you wanted to make any progress. Worse still, the steam will drift sideways back along the slot you've been cutting...it'll first condense and then re-freeze...so in all probability, your nicely lasered slot would just fill up with new ice again.

So I don't think a laser is the best way to do this. We know that ice is drilled using hot water jets...and that's probably what you want here. SteveBaker (talk) 17:59, 16 May 2014 (UTC)[reply]

I have a hard time believing this could have any chance. I don't think of glacial ice having much tensile strength - after all, deep crevasses are all over the place. Wnt (talk) 15:40, 16 May 2014 (UTC)[reply]

And if all the reasons already given don't convince you, also consider that glaciers are constantly moving, and different layers move at different rates, so the hole would move and skew as you are trying to cut it. Therefore, you'd need to be able to cut the whole thing off quickly, so the movement wouldn't be significant. StuRat (talk) 18:06, 16 May 2014 (UTC)[reply]

Staged fire alarms

Why don't many public buildings use staged fire alarms? Some shopping malls and airports do but many places still seem to use the "if alarm goes off, evacuate building" method. In the staged alarm, there is a first stage where the occupants of the building are made aware that an emergency has been reported in the building and that people should prepare to evacuate, if necessary. During this first stage, building staff normally investigate the situation and make a decision as to whether evacuation is necessary. Normally this is a very quick process so doesn't delay evacuation significantly, in case it is necessary whilst also avoiding mass evacuatiation and system shut downs, if it is false alarms. The staged alarm can also be used for partial evacuation. So why don't many buildings opt for this staged alarm to minimise disruption in the case of false alarms? 82.40.46.182 (talk) 19:36, 16 May 2014 (UTC)[reply]

Why aren't magnets used to make pushing colenoids?

To make a pulling colenoid, you just need an iron core that is pulled by a coil. To make a pushing colenoid, you need plastic attached to the core, more length, and a spring to go back to the original situation. It seems much simpler to make the coil push the core by using a permanent magnet as core, where the coil makes a magnetic field in the opposite direction. Nobody seems to use that option, so my question is: why? I rewrote this a few times but I really can't explain it better than this. Sorry for that. Joepnl (talk) 22:11, 16 May 2014 (UTC)[reply]

I've never heard of "colenoid" - do you mean solenoid? I suspect that the article relay might answer, but I'm not sure. --ColinFine (talk) 23:05, 16 May 2014 (UTC)[reply]

The reason is strength. If you apply a weak magnetic field (as from a coil) to a soft ferromagnetic material (eg iron), yoy get a weak pull. If you increase the strength of the field, the pull gets roughly proportionally stronger until the iron saturates (it is fully magnetised). Increasing the field even more does not increase the strength of the pull, but it does not decrease it either. Solenoids are generally designed to just saturate the iron - this reliably furnishes maximum strength, even if the current is not a precise amount, without wasting too much electrical energy.

To repell a magnet, the solenoid field has to be less than the permanent magnet field. If the current is a bit stronger than needed for balance, the "push" is cancelled out and the coil will pull the magnet in anyway, as the magnet field is simply overwhelmed. Engineers always strive to make things non critical.

Further, there is a choice of materials to make magnets out of. If a metal alloy, such as alnico (a common permanent magnet material), its going to be a lot more costly than a soft iron and a spring, and the coil field will reverse its magnetisation so that it pulls anyway. The other choice is a ferrite. The strength of magnetisation of ferrites is way below that of metal alloys.

121.221.156.103 (talk) 02:25, 17 May 2014 (UTC)[reply]

wage slavery around the world

hello, are there stats as to what percentage of (fit) people in a given country derive their livelihood from hired labor (as opposed to self-employment (such as keeping a shop), civil service, subsistence farming etc)? I presume it's roughly two thirds pretty much everywhere, but still? also, what makes the difference between the average worker and the "big" CEO's etc, who are but employed workers like everyone else (a fact of which they as a class always seem to make a big point), yet are hardly wage slaves. I only want to know just how prevalent this model, which afaik is pretty recent (300 years?), has become. thanks Asmrulz (talk) 23:58, 16 May 2014 (UTC)[reply]

I think the whole idea that "employee" = "slave" is just completely wrong. There are many highly compensated employees, such as the CEOs you mentioned, sports and movie stars, etc. There are also many dirt poor self-employed people, like subsistence farmers, especially in poor nations. The protest that began the Arab Spring was even started by a self-employed man (Mohamed Bouazizi) who was systematically abused by the government. StuRat (talk) 00:37, 17 May 2014 (UTC)[reply]