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January 7

Walking from the Earth to the Sun

If one built a long enough and strong enough ladder, would it be possible to walk from the Earth to the Sun? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 03:10, 7 January 2012 (UTC)

The distance between the moon and the Earth varies from around 356,400 km to 406,700 km. How fast do you walk? 5km/h? How would you transport the supplies needed for such a long trip? Von Restorff (talk) 03:18, 7 January 2012 (UTC)

(edit conflict) Walking the distance that would be between the earth and sun? Not possible in a lifetime, given that the earth is 150,000,000 kilometers from the sun, and a person can walk, what, 8 minutes per kilometer? That's a speed of like 7.5 kilometers per hour, so it would take someone 20,000,000 hours to walk there. The human lifespan is about a century at the outside, if we're generous, and at 24*365 = 8,760 hours in a year, that means you could get as far as 87,600 hours in a lifetime. 87,600*7.5 = 650,250 kilometers. You'd not even make it to Venus, assuming you did nothing but walk (no stopping to sleep, eat, shit, etc) for 100 years, and that's at a pretty decent clip. --Jayron32 03:20, 7 January 2012 (UTC)

You lost an order of magnitude when you computed the number of hours in a 100 year lifetime (and then you transposed the 7 and the 6 before multiplying against the speed), but it hardly makes a difference as even at 6.5 million km a century, the trip takes over two millennia. -- ToE 13:01, 7 January 2012 (UTC)

150,000,000??? Was the moonlanding a hoax? Von Restorff (talk) 03:23, 7 January 2012 (UTC)

What does the moon have to do with the OPs question? --Jayron32 03:32, 7 January 2012 (UTC)

Oops, meth is a hell of a drug. Von Restorff (talk) 03:35, 7 January 2012 (UTC)

"And for that, by the gods, if I say the moon be the sun then to you, good wife, it shall be so" -- ToE 03:51, 7 January 2012 (UTC)

"Good wife I am in name only, good husband, and thus it is the moon and 'tis the moon no matter what thee says!" Von Restorff (talk) 04:12, 7 January 2012 (UTC)

<snipped>

(edit conflict) Slower than that with the proper attire. Clarityfiend (talk) 03:22, 7 January 2012 (UTC)

I am guessing climbing a ladder is slower than walking on a flat surface. But there is a bit less friction in space so that would improve the speed a bit. Von Restorff (talk) 03:26, 7 January 2012 (UTC)

Yes. The ladder would also need to be elastic, given that the Earth's orbit is elliptical - you'd also need to anchor it at both one of the Earth's poles, and one of the Sun's, on some sort of bearing to allow for their rotation. Assuming you had a spacesuit that could support you indefinitely, and ignoring the fact that it would take rather a long time at a walking pace, you'd initially be 'climbing' the ladder to escape Earth's gravity, only to find yourself under increasing gravitational pull towards the Sun as you approached. I'll leave it for someone else to speculate how close you could get before losing your grip - and then there is the problem of increasing heat etc... I think that anyone with the sort of technology to approach that close to the Sun would use something more sophisticated than a ladder. AndyTheGrump (talk) 03:24, 7 January 2012 (UTC)

I agree. A space elevator is a bit more sophisticated than a ladder. Von Restorff (talk) 03:30, 7 January 2012 (UTC)

I meant theoretically if you could "walk" for as long as it took to get from the Earth to the Sun. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 03:36, 7 January 2012 (UTC)

Well Jayron answers that pretty well. I guess, yes, theoretically if you could "walk" for as long as it took without dying you could do it, but it would take many normal lifetimes to do so. Additionally in all that time, and as others have pointed out, you'd need a massive amount of supplies of food, drink, and oxygen, and some sort of surface to "walk" on. Then somehow you've to counter the varying gravity, from escaping the Earth, to essentially zero out in space, to massively high as you approach the sun. And frankly it would be a sod of a boring walk, there wouldn't be that much variation in what you were seeing for periods of 50yrs or more, so somehow you've got to deal with that. And then as you approach the sun you've somehow got to figure out how to deal with the heat (reminds me of an old Goon Show skit where they wanted to fly to the sun in a wooden rocket, when asked how they were going to prevent the rocket from burning up as they got near the sun they said they were going to go at night). So the answer is probably theoretically "yes" in the sense that almost anything is theoretically possible, but in any sense of reality, then "no". --jjron (talk) 04:18, 7 January 2012 (UTC)

Everyone is ignoring the fact that it is not possible to walk in a weightless environment, period. Walking depends intimately on gravity pulling the body down towards a surface. Without that, only floating is possible, not walking. --99.237.252.228 (talk) 06:58, 7 January 2012 (UTC)

I guess that if you have a ladder you could probably "walk" on it by pushing your heels against the rungs. Maybe a bit of velcro makes it even more comfortable. Von Restorff (talk) 07:05, 7 January 2012 (UTC)

You could also do it if the walking path were iron-based and you were wearing magnetic shoes. ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:06, 7 January 2012 (UTC)

Maybe even something like an inverted jetpack is an option. Von Restorff (talk) 07:09, 7 January 2012 (UTC)

I was expecting some type of elastic based attachment to the walking path. But since we're just making all this up anyway, I also thought that you may just use some type of artificial gravity device. --jjron (talk) 08:01, 7 January 2012 (UTC)

I think we're getting into the realms of fantasy now. Caesar's Daddy (talk) 08:49, 7 January 2012 (UTC)

All we can usefully say is if you had the technology to continuously travel for as long as you liked at a constant speed equal to a walking pace of 7.5 km/hr it would take you about 20 million hours or about 2,300 years to travel a distance equivalent to the distance from the Earth to the Sun. Gandalf61 (talk) 13:10, 7 January 2012 (UTC)

Several people have mentioned gravity, but you need to account for it together with the fact that the Earth is orbiting the Sun. Once you've climbed out of the Earth's gravitational field, you will be pretty much weightless because you are in free-fall (you, the ladder and the Earth are all going around the sun at orbital velocity). As you get closer, your orbital period stays constant meaning you are now orbiting too slowly and are not in free-fall any more. The net effect of all the various forces and your rotation is quite difficult to work out and can be very counter-intuitive, but I expect you would end up having more difficulty holding onto the ladder against the sideways forces caused by you trying to orbit at orbital velocity and the ladder orbiting much slower (these same forces would rip the ladder apart, but let's ignore that) than you would holding on against the Sun's gravity (some of the sun's gravity is, loosely speaking, cancelled out by centrifugal force, which ought to help, although I'm not sure how far you could get because not enough is being cancelled out and you get pulled off the ladder). Can someone that is better are celestial mechanics than me work out exactly what would happen? --Tango (talk) 16:38, 7 January 2012 (UTC)

The ladder would be going around the Sun at Earth's orbital period, so the Sun's gravity would soon be felt. The point of zero G would be at the L1 Lagrange point. Wnt (talk) 18:02, 7 January 2012 (UTC)

Once you were far enough from the Earth you could just slide down the ladder like it was a fireman's pole. With that technique you could probably make the journey in a single lifetime. APL (talk) 06:12, 9 January 2012 (UTC)

This reminds me of the science fiction short story (maybe "The Long Way Home" by Fred Saberhagen?) about the disabled spaceship being laboriously dragged slowwwly back to Earth by its crew's descendants by rope (attached to a "space anchor"). Clarityfiend (talk) 03:02, 8 January 2012 (UTC)

Yes, that's Saberhagen's The Long Way Home, which is collected in his Of Berserkers, Swords and Vampires anthology. It just happens that that short story is one of the free sample chapters visible at Baen Ebooks, linked from the table of contents here. -- ToE 08:39, 8 January 2012 (UTC)

Several compound names

There are about vitamin B12 total synthesis, I am not sure about their meanings:

1. α-corrnorsterone(corr = corrin ?)
2. thiodextrolin(dextro- = dextrorotation ? lin = ?)
3. cyanocorrigenolide(corrigen = oleandrin ?)

Bold parts of these words is most confusing. I have linked them to some pages, and I want to confirm if they are right. --Makecat_Talk 05:30, 7 January 2012 (UTC)

Thiodextolin doesn't seem to exist outside of this article. Oddly, Google Scholar finds zero cites for that term: [1] which is a red flag. The only places a regular google search finds it is in the Wikipedia article you cite and mirrors thereof. I'm working on the other two... --Jayron32 05:38, 7 January 2012 (UTC)

The article made a spelling mistake...--Makecat_Talk 05:56, 7 January 2012 (UTC)

I dug this up: [2] Skip the Wikipedia article and work from there instead. --Jayron32 05:40, 7 January 2012 (UTC)

Thanks. And I want to understand the meaning of the prefix corr- and dextrolin. Could explain them?--Makecat_Talk 05:56, 7 January 2012 (UTC)

this was all I can find using Google Scholar on "dextrolin". It isn't much. --Jayron32 06:01, 7 January 2012 (UTC)

My best guess is that corr is from corrin, given the presence of the corrin structure in B-12. You may also be interested in norsteroid. --Jayron32 06:06, 7 January 2012 (UTC)

And my guess is that "corrigen" is "corrin" and "-gen-" as meaning "forming" like in oxygen, if you look at structure 57, it is clearly about to form the corrin ring structure. --Jayron32 06:24, 7 January 2012 (UTC)

I got lucky with Google (Hmmm, that makes it sound like a porno search...) and found [3], which says "It has been a loose but fairly consistent practice of the Zürich group to refer to the B/C moiety of the vitamin B₁₂ molecule as the 'eastern' half, and the A/D area as the 'western' part. By contrast, Cambridge custom has tended to utilize the terms 'right' and 'left'. In such trivial affairs consistency is hardly a matter of moment, and we need not cavil at the action of the Zürich group in adopting the name 'dextrolin' for a B/C building block which they first succeeded in constructing..." The same source describes [4] "the compound LIII, which we have more or less jocularly dubbed 'α-corrnorsterone'. The 'corr' in this appellation represents our hope that the substance is destined one day to be transformed into a corrin; the 'norsterone' devolves from the fact that LIII is a ketone whose skeleton is that of a norsteroid if the nitrogens be ignored; and finally, if the name be pronounced in Slurvian, it becomes 'cornerstone'!" The Zürich group is introduced at the beginning of the section [5] as the laboratory of Albert Eschenmoser. Wnt (talk) 18:20, 7 January 2012 (UTC)

porno search...Does it mean that "dextrolin" is just a symbol without any special meaning? --Makecat_Talk 05:55, 8 January 2012 (UTC)

Well, he doesn't analyze their motives, but at least the "dextro" part just means "right". Besides being on the right hand as (arbitrarily) drawn on a chalkboard, it has nothing in common with dextran sulfate or dextrose or dextrorphan or manual dexterity. (Wow. We don't have an article for dextran sulfate yet...?) Wnt (talk) 15:34, 8 January 2012 (UTC)

Accidents/Injuries jumping into sea from a height

How deep a person will go if he jumps into the sea from a height of 12 meters/14 meters? — Preceding unsigned comment added by 175.100.188.30 (talk) 05:33, 7 January 2012 (UTC)

Ourdiving article states that Olympic divers use a 10m high board, and the pool is at least 5m deep for safety. I think it would be reasonable to extrapolate that another few metres of drop would likewise require a little more - but there is more to it than this. From a greater height, the instantaneous deceleration as one hits the water will have more effect, and one may be more at risk from this than with possible impact with the bottom of the pool. There is an increasing risk from getting the initial entry wrong - a belly flop from a few metres may result in little more than immediate pain, whereas a misjudged dive from higher might have severe consequences: to quote from our article "hitting the water flat from 10m brings the diver to rest in about 1 ft. The extreme deceleration causes severe bruising both internal and external, strains to connective tissue securing the organs and possible minor hemorrhage to lungs and other tissue. This is very painful and distressing, but not life-threatening". AndyTheGrump (talk) 05:58, 7 January 2012 (UTC)

That suggests another question or two: What is the greatest height anyone has fallen into (sufficiently deep) water and survived? And how deeply into the water did they go? And is it better to go in feet-first or head-first? All of these questions assuming you hit the water vertically. ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:02, 7 January 2012 (UTC)

Read this and look at this chart. Windresistance is a factor, and the weight because of the momentum. You do not even need water to survive falling from a great height: Vesna Vulović, Ivan Chisov, Nicholas Alkemade, Alan Magee. Von Restorff (talk) 07:15, 7 January 2012 (UTC)

See also shallow diving. Oh, and @Bugs, just in case anyone is reading this post and considering testing this out I'll put out a safety warning as a disclaimer. The Lifesaving Society guidelines for entering water are to only jump into water of known (and safe) depth. If it's unknown you should walk in, or use some type of 'slide entry' if you can't walk. And if you have to jump in, then you always go feet first (better to break your leg than break your neck). There is a technique, the which name eludes me, where you can jump into deep water feet first from a reasonable height without your head going under water - you have to be able to do this to get even a basic lifesaving qualification such as the pool Bronze Medallion (which, for the record, I have). --jjron (talk) 07:51, 7 January 2012 (UTC)

Actually, the evidence seems to suggest that when falling from a great height, your chances of survival (small as they are) are less than when falling on land, where you have a slight chance of coming down through trees, into snowdrifts etc. Water is water, and impact is likely to be predictable - over land, you have at least a theoretical chance of landing on a duvet factory's surplus output repository, or the like... AndyTheGrump (talk) 07:59, 7 January 2012 (UTC)

If you want to break the Guinness book of records world record you need to defeat Harry Froboess who fell 361 feet (110 m) into Lake Constance from the airship Graf Zeppelin on June 22, 1936; that sounds easier than doing what Vesna Vulović did (if the story is true and not just propaganda). Von Restorff (talk) 08:02, 7 January 2012 (UTC)

If which story is true and not just propaganda? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 15:11, 7 January 2012 (UTC)

The story about Vesna Vulović. According to the section called "2009 report", there is a possibility the story about her surviving the highest fall without a parachute ever: 10,160 metres (33,330 ft) is made up to cover up a serious mistake made by the Czechoslovak Air Force. Von Restorff (talk) 15:25, 7 January 2012 (UTC)

All those people would have reached terminal velocity. Once you're at terminal velocity it makes no difference how far you've fallen from, only how you hit the ground. Rckrone (talk) 20:11, 7 January 2012 (UTC)

That's not necessarily true. If you've only only just reached terminal velocity (after about 15 seconds), you're probably still breathing, conscious and reasonably warm. If you fell from 10 km, you might be hypoxic, unconscious and half-frozen, because the air is quite thin and cold for the first part of your fall. This could affect you chances of surviving the "landing". Mitch Ames (talk) 23:58, 7 January 2012 (UTC)

Being unconscious might increase your chances of surviving the landing. It would mean your body was completely relaxed. Compare landing feet first with your legs held out straight and landing with them relaxed. The latter is much less painful. --Tango (talk) 14:10, 8 January 2012 (UTC)

Yes, which means that less of the energy of impact is absorbed by your legs and feet, and more is transmitted through the torso and the vital organs, thus, ironically, increasing the probability of death. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 02:44, 9 January 2012 (UTC)

Imaging of potato growth

I'm trying to find a method which would allow me to visualise potato tubers as they grow in a field, but aren't sure what the best technology to use would be. X-ray tomography can be used to visualise plant roots [6], but all the studies I can find grow plants in pots, rather than the field e.g. [7]. Is there a reason that it can't be used in the field? X-ray tomography may not be necessary anyway, since the resolution is extremely high (μm) whereas potato tubers are obviously a lot larger. Ground-penetrating radar seems like another option, but the only relevant thing I could find is this thesis and the resolution isn't great. Could 3D ultrasound be used or does anyone have any other ideas? SmartSE (talk) 15:09, 7 January 2012 (UTC)

Typically scientist don't go quite so high tech, for cost reasons, among others. A rhizotron can be dug relatively cheaply, though mini and micro rhizotron rigs can get more costly, see paper here: [8]. SemanticMantis (talk) 15:39, 7 January 2012 (UTC)

That might work, but it sounds as if you can only see structures that grow around a tube placed in the soil, meaning that you wouldn't be able to see all the tubers on a plant without seriously disturbing the soil around it. SmartSE (talk) 16:12, 8 January 2012 (UTC)

From a strictly mechanical standpoint, x-ray tomography requires the x-ray source and detector to be on directly opposite sides of the volume being scanned. To get an accurate and unbiased three-dimensional reconstruction, you need to be able to rotate source and detector a full 180 degrees. If you've seen clinical CT scanners, you know that they're doughnut shaped, and that you slide the patient through the doughnut hole to collect sequential image slices. That's easy to do with a plant in a pot; that's very difficult to do with a field full of soil. TenOfAllTrades(talk) 19:19, 7 January 2012 (UTC)

Ah that explains why I can only find papers using pots or soil columns. Thanks for that. SmartSE (talk) 16:12, 8 January 2012 (UTC)

Transparent soil? {The poster formerly known as 87.81.230.195} 90.197.66.116 (talk) 09:00, 8 January 2012 (UTC)

Concur. I don't really know the name of this stuff, but at least over here you can get a transparent soil substitute (in the form of crystals or somesuch) which apparently works fairly well (haven't tried it myself though). --Ouro (blah blah) 13:45, 8 January 2012 (UTC)

You mean products like that sold here: [9]? These would be very expensive to fill a field with, and I think would be too wet for potatoes. Also, it seem the OP might be interested in 'natural conditions', which these 'crystals' would not replicate. 'Hydroponic potato' does yield some google hits, but those seem to be mostly pots filled with perlite, with small amounts of nutrients dripped through. SemanticMantis (talk) 14:34, 8 January 2012 (UTC)

That's an intriguing idea, but SM is right that I'm interested in natural conditions. Even growing plants in pots causes enough problems, so artificial media aren't much use. Also, if you used that with potatoes, you'd end up with green tubers. SmartSE (talk) 16:12, 8 January 2012 (UTC)

Exactly, that's something like that. I know it's not natural but it would satisfy the criterion of you being able to inspect the underground development easily. Sidenote, I for one have always been a fan of planting plants in weird things, so I used all manners of disused teapots and even cut enormous glass jars in half (had them cut, okay, I didn't do it myself) to plant cacti in. --Ouro (blah blah) 20:10, 8 January 2012 (UTC)

Shooting down a falling bomb

Is it possible to destroy a falling bomb or artillery shell in midair? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 16:06, 7 January 2012 (UTC)

Possible, yes. Easy, no. But see close-in weapon system. --Stephan Schulz (talk) 16:17, 7 January 2012 (UTC)

In the 1982 Falklands War, the Argentine garrison defending Stanley airfield claimed a number of "kills" with the Roland missile system, which did not relate to lost British aircraft. Our article on the missile says: " This system fired 8 out of the 10 missiles it was deployed with and is credited with shooting down one Harrier Jump Jet and two 454kg (1,000lb) bombs." Alansplodge (talk) 17:24, 7 January 2012 (UTC)

The Iron Dome system aims to intercept artillery shells. In the short term at least, such a system is useful only in the unusual environment of Israel, or perhaps in defending small vital areas. As a general defence against artillery, it's much too expensive - artillery rounds and pieces are cheap and readily available, whereas these interceptors and their related launch and control infrastructure are super expensive. -- Finlay McWalterჷTalk 17:37, 7 January 2012 (UTC)

To make this more entertaining - is it possible for a skilled military sniper, seeing the bomb falling down toward his position on a flat plain, to use his rifle to detonate or deactivate the bomb in mid-air and thus somehow survive? Wnt (talk) 17:53, 7 January 2012 (UTC)

Theoretically possible, but practically impossible. — Lomn 18:01, 7 January 2012 (UTC)

Shrapnel shell gives the terminal velocity of a WW-1 era 3" artillery shell (presumably modern, longer range round like NATO 155mm, which travel much further, have much higher terminal velocities). That gives a very conservative speed of 400 ft/sec, which is about 120 m/s. So even if the sniper knew exactly where the projectile was, and could see it (and it's essentially impossible to see a 3" black circle at a range of a km or more, against the bright daytime sky) and given 10 seconds to aim and fire (in practice snipers need much longer than that, for long distance shots) he'd be shooting a 3" target 1.2km up, which is the about the limit of accuracy of a conventional sniper bullet. This all discounts the practical impossibility of knowing where to point his gun to begin aiming, of seeing the shell, of needing much more time to properly aim, of shooting upward with a heavy rifle, and the unpredictable layers of high-speed winds above him - as Lomn said, in practice it's impossible for a person. Gravity bombs have a terminal velocity of around 300m/s (reportedly; I can't find a very reliable source) and missiles and high-performance bombs like Tallboy get to over 1000m/s. Things like Goalkeeper only have a chance of working because they have very accurate long-range radar, fully automated operation, and spam the sky with bullets. -- Finlay McWalterჷTalk 18:30, 7 January 2012 (UTC)

It is extremely likely that incidents of fratricide amongst munitions have happened many times in war, especially in 20th and 21st century war. If you drop a stick of bombs, or salvos of artillery, fused to detonate at a given height above ground, the fragments could hit other munitions and detonate them. This would not be much of a boon to the targets below. A bomb or shell detonating when it struck a hard target might throw back fragments which detonated a bomb or shell which had not yet reached the target, which would be an advantage to the target. Could a shell be detonated by a piece of shrapnel or a bullet? There have been numerous news reports of people setting off "war souvenir" shells by firing small calibre bullets at them, but there is little chance of intentionally shooting a bullet which hits a falling bomb or shell. Fratricide is probably more likely than someone on the ground firing flak or bullets and detonating a bomb or shell. While a bomb is still in the airplane, a fragment from an antiaircraft shell might hit and detonate a bomb. If the bomb is falling with its descent slowed by a parachute, like the atom bombs dropped on Japan in 1945, hitting it with fragments from high velocity antiaircraft shells would be easier. Edison (talk) 21:19, 7 January 2012 (UTC)

It certainly is. I am aware that in early (maybe 30 years ago) trials of the Seawolf missile, it destroyed an incoming 4inch shell (Although I dont think I can provide a ref for that)--92.25.100.174 (talk) 11:16, 8 January 2012 (UTC)

Just found it in Sea Wolf (missile) in History section.--92.25.100.174 (talk) 11:22, 8 January 2012 (UTC)

I want a Goalkeeper CIWS for my birthday. Von Restorff (talk) 14:53, 8 January 2012 (UTC)

This page on the British Ordnance Collectors Network forum says that special "radar enhanced" 4.5 inch shells were produced and used in the Sea Wolf trials. Shooting down a normal shell might be more difficult. Alansplodge (talk) 18:37, 8 January 2012 (UTC)

How do you radar enhance a shiny metal cylinder?--92.25.99.162 (talk) 20:12, 8 January 2012 (UTC)

It is an experimental 4.5" Mk8 radar enhanced round; the top half is made of opaque fibre with an aluminium cross section insert which acts in the same way as a radar cone on a boat ie it reflects and so can be seen by the radar. Click the link. Von Restorff (talk) 20:34, 8 January 2012 (UTC)

They're made for missiles and aircraft, but a Close-in weapon system could theoretically also hit bombs or shells. 68.156.149.62 (talk) 23:18, 9 January 2012 (UTC)

There's also SDI: Strategic_Defense_Initiative. --Sean 20:22, 10 January 2012 (UTC)

Thick, dripping liquids

When thick liquids like saliva or semen drip from a surface, why do they form a column of liquid with a rounded drop at the tip, which can be pulled back up into the air in its entirety? Wouldn't such a structure be unstable and break apart into separate drops very quickly? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 16:13, 7 January 2012 (UTC)

Gravity and fluid mechanics. Yes. Von Restorff (talk) 16:29, 7 January 2012 (UTC)

Surface tension may be important too. Breaking into drops increases the surface area, which surface tension acts against. If the surface tension is high enough, then it will overcome gravity and cause the liquid to form a single, spherical shape. --Tango (talk) 16:44, 7 January 2012 (UTC)

Surface tension works to change liquid into spherical drops. It takes less energy to change a narrow stream of liquid into many small drops than into one large drop. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 18:19, 7 January 2012 (UTC)

Many small drops have a larger surface area than few large drops or a single column. Surface tension acts to minimise surface area. You are wrong if you think it encourages water to break up into drops; rather, it encourages liquid to stay in a single mass. --Colapeninsula (talk) 19:19, 7 January 2012 (UTC)

In any case, wouldn't a long, thin column of liquid with a round drop at the tip be at or near a maximum-energy state? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 21:25, 7 January 2012 (UTC)

Perhaps those thick fluids aren't just liquids, but gels. In particular, they may start out as liquids, but, as the water evaporates, the reminder forms a gel. The proteins, in particular, seem to play a role in gel formation. StuRat (talk) 21:24, 7 January 2012 (UTC)

Both saliva and semen exhibit this behavior even without significant water evaporation, and neither one starts out as a gel. You try dripping those liquids from an object - you will end up with exactly the same behavior that I described. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 21:29, 7 January 2012 (UTC)

Note that evaporation occurs very quickly from a strand of saliva, etc., presumably at body temperature to start, due to the extreme surface area to volume ratio. StuRat (talk) 22:08, 7 January 2012 (UTC)

Do these liquids contain proteins that might affect their characteristics as a liquid? Richard Avery (talk) 22:30, 7 January 2012 (UTC)

They definitely contain proteins. Whether those particular proteins tend to form the weak cross-linking characteristic of a gel, I cannot say. StuRat (talk) 22:48, 7 January 2012 (UTC)

What does the weak field do?

I think I understand some of what the other fields do:

• Gravity field: attracts (or repels?) mass, bends space-time.
• Electric field: attracts or repels charged particles.
• Magnetic field: attracts or repels other magnetic fields and by extension causes moving electrical charges to circle around. (Interchanges with the electric field in other ways, including light polarization.)
• Strong field: attracts or repels quarks and other particles with color charge.

I can visualize all of these.

Now suppose I had a device of some sort that generated a weak field. What exactly would it act on? What sort of particles would it attract, repel or make travel in circles? Hcobb (talk) 20:43, 7 January 2012 (UTC)

The strong force holds neutrons together with protons in the atomic nucleus and also holds quarks together. The weak force is responsible for beta decay. StuRat (talk) 20:58, 7 January 2012 (UTC)

The weak force does the flavor changing, but what if you had a device that generated a dipole (or tripole?, monopole?) in the weak force. What would that do? Hcobb (talk) 23:50, 7 January 2012 (UTC)

It could deflect all weakly-interacting particles (which is basically all particles except gluons and right-handed fermions, I think?), albeit very weakly and the "device" would be necessarily be extremely short-ranged. (Unlike gravity and the electromagnetic field, which are long-ranged because their force carriers are massless, weak field has an effective range that is determined by the mass of its carrier bosons and it is smaller than the typical size of a nucleus.)--Itinerant1 (talk) 22:33, 8 January 2012 (UTC)

January 8

Hot peppers

I know why peppers hurt going in, but why do they hurt coming out? Mingmingla (talk) 04:29, 8 January 2012 (UTC)

Same reason. The capsaicin is still there and active. It doesn't hurt in between as much due to the mucus lining of the digestive tract. StuRat (talk) 04:39, 8 January 2012 (UTC)

(after ec) Agreed, capsaicin is a physical irritant. From the article Trinidad Scorpion Butch T pepper: "The Trinidad Scorpion Butch T pepper is so strong that those who handle it must wear protective gloves." That should give you the general idea. If this is correct, I found it out just by reading a couple of articles, although I admit the article Chili pepper doesn't seem to make the skin irritant factor explicit. IBE (talk) 04:45, 8 January 2012 (UTC)

Hence the saying Ring of fire--92.25.100.174 (talk) 11:30, 8 January 2012 (UTC)

Shortest life-span

Which animal has the shortest life-span? --Amoeba159 (talk) 05:30, 8 January 2012 (UTC)

The mayfly has brief adult life, but can live a year as a nymph. StuRat (talk) 05:33, 8 January 2012 (UTC)

A fruit fly lives around a month. StuRat (talk) 05:38, 8 January 2012 (UTC)

Thanks, and which bird and mammal has shortest life-span? --Amoeba159 (talk) 05:43, 8 January 2012 (UTC)

According to this article by WonderQuest, the gastrotrich has the shortest lifespan, at 3 days. --184.218.118.2 (talk) 07:21, 8 January 2012 (UTC)

Does an amoeba live for long? (Just noticed the OP's username, and couldn't find the answer in the article.) HiLo48 (talk) 07:26, 8 January 2012 (UTC)

Amoebas are protists. DRosenbach ^{(Talk | Contribs)} 02:48, 11 January 2012 (UTC)

The average life span of an amoeba is little more than two days. Because they reproduce by dividing they are more or less immortal. Clones of amoebae are normally immortal". The normally immortal Amoeba proteus could be switched into a state of limited lifespan by restricting their food intake for several weeks. Von Restorff (talk) 07:44, 8 January 2012 (UTC)

Since amoebas reproduce by cell division, it's hard to define "life span" for a single individual. Is it the longest branch starting from a given cell? The shortest? The average? However, since in the big picture, the number of amoebas has to remain more-or-less constant, the average life time has to be the same as the average time between reproductions. --Stephan Schulz (talk) 10:47, 8 January 2012 (UTC)

Why would the number of amoebas have to remain more-or-less constant? Von Restorff (talk) 13:55, 8 January 2012 (UTC)

If the number is declining then they will eventually all die out. Since they haven't, we know that isn't happening (or is happening too slowly to be of interest). If the number is increasing, then they'll eventually run out of resources and then they'll have to stop increasing. It doesn't take long for amoeba introduced to a new environment to reach maximum numbers, since they reproduce so often and show exponential growth. --Tango (talk) 14:16, 8 January 2012 (UTC)

Even if the total number has to remain constant that does not necessarily mean that the average life time has to be the same as the average time between reproductions; for instance if we imagine that the 50% of the current population that was cloned before the other 50% has a huge advantage. Von Restorff (talk) 15:27, 8 January 2012 (UTC) p.s. A long time ago the amoeba population must've been smaller than it is now. Except if you assume there was a god who created the earth and created the same number of amoebas that are alive now; but that obviously never happened.

Do the math. If the average lifetime is longer than the time between reproductive cycles, then there will be some amoebas left over after each cycle. This results in exponential growth. Unchecked exponential growth drowns the planet in grey goo very quickly. If the older generation has a huge advantage, then the young generation has to die immediately to avoid population increase. Of course there are some simplifications in the model (the number of amoebas will go up and down, and only be approximately constant in the long run and an eco-system in equilibrium). But that does not change the basic result - as long as the number of amoebas stays roughly the same, the same number of amoebas that is born needs to die, and hence the average lifetime is the time between two successive cell divisions. --Stephan Schulz (talk) 22:31, 8 January 2012 (UTC)

Imagine 10% of the first generation is still alive. Then do the math. Von Restorff (talk) 15:23, 12 January 2012 (UTC)

How do the total number of Amoebas in a specific ecosystem remain constant? --Amoeba159 (talk) 15:16, 8 January 2012 (UTC)

Statements from old sources about the "immortality" of unicellular organisms should be interpreted carefully. See [10]. Even E. coli experiences aging, despite its superficially symmetric replication, because one cell, which ages, retains the old cell pole, and the daughter cell creates a new cell pole. In some cases, as with budding yeast, you can see which is the daughter cell; sometimes you can't. Saying that a culture of amoebas is immortal because some still survive is like saying that the human race, or a branch thereof, is immortal because it hasn't been wiped out to the last man woman. Wnt (talk) 15:27, 8 January 2012 (UTC)

Of course they are not really immortal, I just liked the quotes, but on Wikipedia we would probably consider all three sources reliable enough for someone to use them as a source without being reverted within a couple of minutes. Von Restorff (talk) 15:46, 8 January 2012 (UTC)

combustion - volume of products

An experiment demostrated in most schools: You invert a beaker over a trough of water with a candle burning in it. The water moves up the beaker ‘proving’ that air contains 20% oxygen. My question: oxygen has been used up but carbon dioxide and water vapour have been produced – therefore there are MORE atoms now in the air around the candle – so the water should move down. Why does it move up? — Preceding unsigned comment added by YakovKorer (talk • contribs) 12:55, 8 January 2012 (UTC)

The "explanation" neglects the more important factor of temperature. The candle heats the air which expands. When the flame is extinguished, the remaining gas cools and contracts, allowing normal air pressure to force water into the beaker. Dbfirs 13:00, 8 January 2012 (UTC)

Using the ideal gas law approximation (PV = NkT), N, the number of particles in the gas, is a count of gas molecules, not atoms, but you are exactly right YakovKorer, for every O₂ molecule consumed, you would expect two CO₂ or H₂O molecules produced (with about twice as many of the latter than the former, depending on the composition of the fuel (oops, see below) -- (CH₂)_nH₂ with 20 ≤ n ≤ 40 for paraffin wax). Depending on the humidity, some of the water vapor may condense, complicating matters a bit, but, as Dbfirs says, T is the driving force. If elementary science texts explain this via the consumption of oxygen, then it is an example of a lie told to children gone wrong, as the behavior is the opposite of what you would expect when taking the combustion gases into account. It would be like using a radiometer to demonstrate radiation pressure. -- ToE 15:40, 8 January 2012 (UTC)

Oop - careful, ToE, your molecule count is off. Combustion of one one atom of carbon to form one molecule of CO₂ consumes one molecule of O₂, not two. (All other things being equal, the net volume change would be zero if the experiment involved complete combustion of pure carbon.) Given a paraffin wax made from saturated long-chain hydrocarbons – molecular formula (CH₂)_nH₂ – combustion will involve:

(CH₂)_nH₂ + (1.5n + 0.5)O₂ → nCO₂ + (n+1)H₂O

For long chains (larger n), that means that about 1.5 moles of oxygen gas will be consumed to produce one mole each of carbon dioxide and water vapor—leading to a presumed volume increase, because the number of molecules in the gas phase has increased. However, we're not quite done. The experiment will be mostly at room temperature; the water below the gas and the beaker around it are all big heat sinks sitting at room temperature. At that temperature, the vapour pressure of water is about 0.02 atmospheres. Once the gas phase gets above 2% water vapor, water will start to condense out—so the combustion reaction really converts 1.5 moles of oxygen into 1 mole of gaseous carbon dioxide and 1 mole of liquid water (with effectively negligible volume compared to the gases). This will mean that the volume of gas in the beaker really is reduced — though not by the full, advertised 20%.

Incomplete combustion, incidentally, will also skew this distribution. Candle soot is almost pure elemental carbon ([11]); to make it, the reaction is stripping most of the hydrogen from the hydrocarbon and forming much more water than carbon dioxide. All that said, I am inclined to agree with the other posters here that volume contraction caused by the cooling of trapped hot gas is a contributing factor to the observed effect in most such demonstrations. It is possible to design the demo in such a way that this problem is avoided (or at least minimized), but I doubt that most demonstrators will go to the trouble. TenOfAllTrades(talk) 16:39, 8 January 2012 (UTC)

Thanks for catching my faulty stoichiometry. I picture your refined experiment involving an unlit water-surrounded candle covered with a beaker with the water levels equalized (perhaps by temporarily slipping a small tube up into the inverted beaker to equalize pressures). The candle is then remotely lit (probably using an electric resistive heater) and the water level is observed during and after combustion. If the water level initially drops low enough for air to bubble out, then it wasn't deep enough to begin with. If we can imagine it, shouldn't there already be a YouTube video if it? -- ToE 17:15, 8 January 2012 (UTC)

Athlete's foot fungi

How long can the fungus that causes athlete's foot live outside the human body? How can you kill the athlete's foot fungi on carpeting?11virginia (talk) 15:45, 8 January 2012 (UTC)

The Wikipedia articles Trichophyton rubrum and Athlete's foot don't contain any information on that. However, if you use Google or Google scholar, and search for Trichophyton rubrum, you may find the information you seek. --Jayron32 18:30, 8 January 2012 (UTC)

Achhhh, that's not an answer! We want to get the data up and front so we can discuss and evaluate it, and leave it in an archive for some day when we get our act together and have all these answers ready on cue if you ask an artificial semi-intelligence a question. Now looking I do quickly find [12], a 1979 study that found that Trichophyton mentagrophytes remain viable on guinea pig scales for 182 days at 4-30 C but not 37 C. (Working up this study further sounds like an excellent high school class experiment, which might even be publishable) According to [13] (speaking very generally of many species), "Dermatophyte spores are susceptible to common disinfectants such as benzalkonium chloride, dilute (1:10) chlorine bleach, or strong detergents. Chlorhexidine is no longer considered to be a good environmental decontaminant for these fungi. The mechanical removal of any material containing keratin, such as shed skin and hairs, facilitates disinfection. Vacuuming is considered to be the best method in many cases." Wnt (talk) 23:00, 8 January 2012 (UTC)

The real secret, is avoid keeping ones feet in an environment that encourages the fungi that causes athlete's foot to take hold – the fungi itself, is unavoidable as it is every where. I discovered by accident, when I was a student (before man landed on the moon and all that), that the reason it is called athletes foot, is that whilst sock got washed frequent (well almost) my running shoes/ plimsolls etc. didn't. Being constructed differently from regular (leather) foot wear, some sports-ware was obviously harboured the this fungi because the problem magically disappeared, when thy too got a regular trip in through the washer. Therefore, I suggest that using medications/carpet treatments to mitigate this problem is not the right approach.--Aspro (talk) 23:28, 8 January 2012 (UTC)

Also, I might add, that the skin has a pretty good defense again fungi, bacteria and viruses, providing it is not over whelmed by numbers. In other words, the natural contact with the odd fungi spore here and there is no going to bother it. Just vacuuming the carpet should be enough to keep the natural fungal population benign.--Aspro (talk) 23:46, 8 January 2012 (UTC)

My feeling is that susceptibility to fungal infections varies wildly. I don't have that exceptional an immune system where bacteria are concerned, but my idea of treating athlete's foot has been to absent-mindedly scratch away the dead skin between two toes and (correctly) expect not to see it again. Whereas other people have constant trouble with it, onychomycosis, even strange diseases like blastomycosis. An example of a susceptibility factor is a gene CARD9.^[14]

what is the typical expected ultimate recovery (EUR) of traditional gas wells?

Google searches keep reporting breakeven prices and initial production rates, but I am interested in ultimate recovery. I know for example, that according to Chesapeake Energy, a 7.5 million horizontal fracturing shale gas well (that will typically replace 24-32 vertical wells) will have an average EUR of 3.75 mmcf (or MMBTU). What is the typical EUR of a vertical well, and what is the typical EUR of a conventional gas well? Can someone help me find some figures? I realise they are different whether they are onshore, shallow offshore, or deep offshore. Thanks. elle _{vécut heureuse} ^{à jamais} (be free) 17:41, 8 January 2012 (UTC)

Maybe you want to read UK Gas Reserves and Estimated Ultimate Recovery 2011. Von Restorff (talk) 23:40, 8 January 2012 (UTC)

Those don't cite per-well statistics =( elle _{vécut heureuse} ^{à jamais} (be free) 01:23, 9 January 2012 (UTC)

Sorry I am unable to find the data you want. I would recommend contacting a company that owns a gas well. Von Restorff (talk) 13:40, 9 January 2012 (UTC)

IC Engine braking

When changing down gears to slow down in a car with an IC engine, some of the kinetic energy loss of the car must go into speeding up the engine, and the rest into heating up the clutch. How do I calclulate the distribution of this energy? Also, assuming my gear change was instantaneous, does the speed of the engine also change instantaneously? BTW not homework, just wondering.--92.25.99.162 (talk) 20:09, 8 January 2012 (UTC)

I don't think there would be a way to easily calculate the distribution, it would depend on too many other factors: The efficiency of the clutch, the weight of the engine and drive train components, the speed difference. You'd probably have to measure it. For the second bit, the engine could only change speed instantaneously if the clutch didn't dissipate any energy at all, so if you assume the clutch is doing some of the work, the engine won't change speed instantaneously. Vespine (talk) 21:22, 8 January 2012 (UTC)

What's an IC engine? HiLo48 (talk) 22:05, 8 January 2012 (UTC)

internal combustion Von Restorff (talk) 22:11, 8 January 2012 (UTC)

You are also absorbing energy by compressing the gas in the cylinders before the valves open again - that is what is meant by engine braking!.... Sorry, got that back to font. Expanding the gases in the cylinder.--Aspro (talk) 22:19, 8 January 2012 (UTC)

Our article engine braking does a good job describing this, though it is in dear need of references (and so tagged since June 2008). -- ToE 00:44, 9 January 2012 (UTC)

January 9

Neutrinos vs Neutron decay

How often on average does a Neutrino pass within one radii of a free Neutron and how does this compare with the halflife to beta decay of a free Neutron? Hcobb (talk) 00:32, 9 January 2012 (UTC)

Total neutrino flux through any area in the vicinity of the Earth is on the order of 10^15 neutrinos per m^2 per second. "Radius of a free neutron" is not a well-defined concept, but, as long as we're doing order-of-magnitude estimates, let's say 10^-15 m, which makes the answer to your question "once every hundred million years".--Itinerant1 (talk) 00:58, 9 January 2012 (UTC)

To answer the other part, Neutron#Stability_and_beta_decay says the half-life of a free neutron is about 611 seconds. Which is quite different. --Colapeninsula (talk) 10:34, 9 January 2012 (UTC)

One more thing. What's the point of that question? Dauto (talk) 15:50, 9 January 2012 (UTC)

It's to consider the possibility that the Neutron is a stable particle in isolation. If we include the Cosmic neutrino background we "gain" six orders of magnitude, but that's still not enough, unless we switch from the Neutron radius to the Neutrino Compton wavelength, which is of course huge (mass around 0.04 eV, therefore around a few 10^-5 meters), when it isn't zipping around at almost the speed of light. (Like say as part of the CNB.) So every free Neutron is touched by a background neutrino before it goes. Hcobb (talk) 20:53, 9 January 2012 (UTC)

Neutron is not a stable particle in isolation simply because the mass of neutron is greater than masses of proton and electron, combined. That is sufficient to result in decay. Also, my flux estimate already included cosmic neutrino background. --Itinerant1 (talk) 21:14, 10 January 2012 (UTC)

Ellipsoidal Dyson shell

Would it not be possible to build a megastructure, essentially an ellipsoidal Dyson shell, with the Sun at one focus and a solar-energy collection device at the other, to collect the Sun's entire output of light? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 02:54, 9 January 2012 (UTC)

Would it be possible for whom? TenOfAllTrades(talk) 03:00, 9 January 2012 (UTC)

The idea being that it would be a giant reflector ? StuRat (talk) 03:00, 9 January 2012 (UTC)

Yes. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 03:05, 9 January 2012 (UTC)

Would it be theoretically possible, I don't see why not. Would it be feasible or practical? Almost certainly not. Vespine (talk) 03:03, 9 January 2012 (UTC)

One problem is that a Dyson shell would require far more mass than all the planets and other items in our solar system, outside the Sun, with current technology. StuRat (talk) 03:07, 9 January 2012 (UTC)

The article you just linked says that if we somehow disassembled the rocky inner planets in the solar system we could make a spherical shell of 42kg/m², more than enough for a mylar envelope, if we could get it to stay open. APL (talk) 09:05, 9 January 2012 (UTC)

Gravity might pull the sun away from the focus. With a spherical shell, there is no net gravitational force on the sun due to the shell. I'm not sure that this is true for an ellipsoidal shell.--Srleffler (talk) 17:49, 9 January 2012 (UTC)

Shouldn't a helicopter be able to fly even without a tail rotor?

Since the mass of the helicopter itself is much greater than that of the main rotor, shouldn't the main rotor spin much faster than the helicopter, thus allowing the helicopter to fly even with no tail rotor at all? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 03:34, 9 January 2012 (UTC)

Yes, the rotor turns much faster, but the helicopter spins in the opposite direction too fast to handle, and who wants a constantly spinning chopper, anyway ? Note that dual top rotor systems can eliminate the need for a tail rotor. StuRat (talk) 03:38, 9 January 2012 (UTC)

Define "Fly". If you mean "Be in the air for some time" then yeah, sure. If you mean "and be controlable well enough not to dash itself into the ground and kill everyone", then probably not. Helicopter#Antitorque_configurations explains the problem: The spinning rotor generates a torque, and because of Newton's third law, this torque results in the body of the helicopter torquing in the opposite direction. Some means of control must be used to counteract this torque. You can use any number of methods, including multiple horizontal rotors (which can be installed coaxially or on seperate axles), or having a perpendicular rotor which deflects the reaction torque. But a single rotor would cause the helicoptor to corkscrew through its flight, making it impossible to control. --Jayron32 03:42, 9 January 2012 (UTC)

Addendum: there is a helicopter stabilization system known as NOTAR, which does not have an exposed tail rotor, but still uses a powered internal "fan" to direct a stream of air countract the main rotor torque. It still provides an active force to solve the torque problem, but does so through a means different from a tail rotor. --Jayron32 03:47, 9 January 2012 (UTC)

Slower than the rotor is still too fast. One way to deal with tail rotor failure is to maintain significant forward speed and allow the tail to aerodynamically stabilize the helicopter. This is more easily said than done, particularly when you have to set it down; a runway comes in handy at that point. Tail rotor failure in a hover or at slow speed results in a hard landing at least, and usually something much worse. Acroterion (talk) 03:45, 9 January 2012 (UTC)

It might be an interesting exercise to make a single rotor helicopter. If you put wheels on it, so it could rotate as it takes off and lands, had a single occupant at the center of gravity so the spinning wouldn't kill him, and used an electronic display that compensated for the spinning to provide views in every direction, you just might be able to get it to work. It would be good for a laugh, if nothing else. An unmanned surveillance helicopter with a single rotor might be of some use, in that the cameras would rotate to view 360°. StuRat (talk) 03:47, 9 January 2012 (UTC)

Even if the center of rotation was inside of the pilot, that point is still just a point, and his arms, legs, and head would still be outside of it, and still be experiencing rather profound forces which would make operation of such a vehicle difficult to the point of imposibility; unless you could encase him in a pod of somesort which was stable; such as a pod which rotated exactly counter to the spinning helicopter. Which would require a motor of some sort, which could just be used to power a tail rotor instead of some complex stable pod within a rotating helicopter body. There are any number of rather inelegant ways to design a stable helicopter; however not many of them are necessarily better than current designs. Designing a working, but more cumbersome, means of solving a problem which has already been solved doesn't seem like a good use of engineering. --Jayron32 04:00, 9 January 2012 (UTC)

Well, there's the Spruce Goose, which was also a rather impractical method of solving a problem which had already been solved, by using materials better than wood to build airplanes. Also, the Red Bull Flugtag is full of silly flying machines, and people enjoy that. StuRat (talk) 04:11, 9 January 2012 (UTC)

Except the Spuce Goose was made with wood specifically because they were looking for alternate materials other than metals to build a plane out of. There were not yet reasonable plastics or composite materials to build a plane out of, and if metals could be freed up for other purposes than building planes, why not use wood, given the stresses put on the U.S. during World War II. The Spruce Goose was wood for a reason, not just "lets see if we can do it". Oh, and guys getting drunk, dressing like birds, and throwing themselves into a lake is hardly a major engineering effort. Designing a working production helicopter as described would be. --Jayron32 04:36, 9 January 2012 (UTC)

The pilot could in theory (if not in practice) sit in a seat with controls and gauges in front of it which was rotated by a motor so that it remained stable with respect to the ground while the rest of the ship was allowed to rotate in a direction contrary to the spinning blade. Maybe it would look like a flying saucer. The landing gear could also rotate so as to be stationary with respect to the ground. Not saying this design would be practical or efficient, just cool. Edison (talk) 04:05, 9 January 2012 (UTC)

The helicopter could also use a cylindrical crew compartment which is completely inertially isolated from the rest of the helicopter, using roller bearings maybe, so that much of the helicopter rotates but the crew compartment doesn't. You could also drive it through a reduction gear train from the main rotor mast ;-) Whoop whoop pull up ^{Bitching Betty | Averted crashes} 11:43, 9 January 2012 (UTC)

In the event of a helicopter tail rotor failure, the safest procedure is likely to be to disengage the engine (!). This isn't as nuts as it sounds, as it can then (assuming it has enough height and/or forward speed) autorotate to a safe landing. AndyTheGrump (talk) 04:23, 9 January 2012 (UTC)

Autorotation is something extensively practiced by helicopter pilots, but would work best if the tail rotor failure is gradual. Sudden tail rotor failure can whip the helicopter around faster than the pilot can kill the throttle, although with enough height there is a chance to regain control. See [15] for a discussion of autorotation and running landings with a failed tail rotor. See also loss of tail-rotor effectiveness which happen more often than actual failure. Acroterion (talk) 04:31, 9 January 2012 (UTC)

It doesn't matter where the centre of rotation is, the results is the same. The craft has a much higher moment of inertia than the main rotor, and for every action there is an equal and opposite reaction; the the craft and rotor will turn in opposite directions, but the angular acceleration of the craft will be low, and will take some time to reach a terminal angular velocity. Even initially, the craft will experience a torque and will begin to slowly turn. Plasmic Physics (talk) 05:29, 9 January 2012 (UTC)

Because the angular momentum is distributed over both craft and rotor, the magnitude of lift generated is allot less than with a tail rotor. For this reason, I'd be surprised if the craft could stay airborne once it has attained terminal angular velocity. Plasmic Physics (talk) 06:30, 9 January 2012 (UTC)

Of course, some helicopters don't need tail rotors.--Shantavira|^{feed me} 08:33, 9 January 2012 (UTC)

Of course they don't, but the question was concerned with single rotor craft. Plasmic Physics (talk) 09:08, 9 January 2012 (UTC)

Seriously though, would it be possible to develop an emergency software autopilot that would keep a helicopter with a non-working tail rotor relatively stable in the air and allow it to make a gradual though awkward descent? Wnt (talk) 14:31, 11 January 2012 (UTC)

Not really. The forces involved in the torque pretty much make "control" a moot point. Cutting the throttle (or at least reducing it substantially) is the only way to keep it controllable. I suppose you could set up a sensor that automatically cuts the throttle back when a tail rotor failure is detected... but then you're taking control away from the pilot. Kind of a Catch-22 in that situation, where neither solution is really viable. — The Hand That Feeds You:^Bite 18:18, 11 January 2012 (UTC)

Human chloroplasts

What would happen if someone implanted both chloroplasts and the genes coding for their internal constituents into a human zygote and then placed the newly modified zygote into a woman's body and allowed it to grow? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 03:41, 9 January 2012 (UTC)

If the idea is to have the humans be able to photosynthesize their own energy while in the sunlight, note that the surface area of our skin is way too small to provide for all of our energy needs. StuRat (talk) 03:54, 9 January 2012 (UTC)

Yeah, but it could at least provide for some small fraction of them... Whoop whoop pull up ^{Bitching Betty | Averted crashes} 19:43, 9 January 2012 (UTC)

The reverse would be interisting. To be able to convert fat reserves into light during the daytime. Plasmic Physics (talk) 06:33, 9 January 2012 (UTC)

-The sendentary art of doing nothing, and still losing weight, perfected. Plasmic Physics (talk) 09:11, 9 January 2012 (UTC)

I would totally sign up for calorie-burning flashlight skin. APL (talk) 09:19, 9 January 2012 (UTC)

I imagine that the baby wouldn't be born green, without light, only etioplasts will develop which in turn develop into chloroplasts. Once the baby was exposed to light they would presumably turn green, but as StuRat points out this wouldn't be much use to them. As this has come up though, I have to mention Elysia chlorotica - the sea slug that does photosynthesise. SmartSE (talk) 10:41, 9 January 2012 (UTC)

Nothing. Some zygotes would die from the implantation but most would still be viable. What you mean, what would happen if the genes for chloroplast were genetically engineered into the zygote?
Sleigh (talk) 12:07, 9 January 2012 (UTC)

Has someone been reading "by light alone"?Equisetum (talk | contributions) 12:38, 9 January 2012 (UTC)

Well, if you look up Elysia, you'll see it actually has taken a gene by horizontal gene transfer to help maintain the chloroplast. Even so, it is still dependent on the algae to make them in the first place. Transferring the genetic program for a complete morphological structure into a radically different type of cell is no easy task. I won't say it couldn't be done, though. Wnt (talk) 14:26, 11 January 2012 (UTC)

Trying to recall some chemistry

I remember seeing a graph which showed the amount of energy required to remove an atom's electrons one by one i.e. the first point showed the amount of energy required to remove the first electron, the second point showed the amount of energy required to remove the second electron etc. Can someone remind what it is which dictates the amount of energy required to remove each particular electron? Widener (talk) 09:35, 9 January 2012 (UTC)

Do you mean this graph? I found it here. Maybe this article is useful. Von Restorff (talk) 09:47, 9 January 2012 (UTC)

Galvanic metals

This link gives "galvanic metals" as a name for the group 12 elements. Has anyone heard of this term? Double sharp (talk) 11:33, 9 January 2012 (UTC)

I have also posted this at Wikipedia talk:WikiProject Elements. Double sharp (talk) 11:33, 9 January 2012 (UTC)

1200 results on Google (125 in Google Books) so I think the answer is yes. Von Restorff (talk) 11:36, 9 January 2012 (UTC)

Careful with that search; it shows that the phrase "galvanic metals" is used, but the search doesn't confirm that it is used in the same way as in the reference Double sharp asks about. From the context of the first few hits, it looks like the phrase mostly shows up in descriptions of galvanism, Galvanic corrosion, galvanic cells, or the galvanic series. I haven't yet come across another instance where it is used as a synonym for Group 12 elements, but I may not have come across the right reference yet—and it's rather difficult to prove a negative. TenOfAllTrades(talk) 15:09, 9 January 2012 (UTC)

Well, I did a bit of Googling and I agree. Many people have heard of the term "galvanic metals", but I was unable to find a source that said it was using this definition. Some of the sources I saw did include non-group 12 elements. Von Restorff (talk) 15:59, 9 January 2012 (UTC)

Breathing air requirement?

How much air does a slim adult doing reading etc.. require on average, a ballpark figure?, ie m³/h. It ought to be the basis for ventilation, room volume etc. Electron9 (talk) 12:34, 9 January 2012 (UTC)

The average adult at rest inhales and exhales something like 7 or 8 liters (about one-fourth of a cubic foot) of air per minute. But for safety reasons you want to provide much more, in case someone is exercising and smoking and burning incense etc. The amount of air breathed by an average adult varies from 6 Litre/minute (when at rest) to 50 Litre/minute after hard exercise. But you should read this, and think about oxygen too, not just air. Von Restorff (talk) 13:08, 9 January 2012 (UTC)

Our article on the per minute inhalation/exhalation rate is respiratory minute volume. -- ToE 13:22, 9 January 2012 (UTC)

The "respiratory minute volume" article only defines various parameters. No practical data. The "how much oxygen" page is way more on to real life characteristics. I know it's about oxygen. But in most situation thats 21% unless special equipment is used. How much CO₂ buildup that is acceptable is however unclear. The lowest life sustainable percent is 17.5% according to psu.edu, but at what level does it become "unpleasant" low oxygen? Electron9 (talk) 13:51, 9 January 2012 (UTC)

If life cannot be sustained at less than 0.175 atm partial pressure of O₂, we had best lower the population figures in our Mexico City article. -- ToE 14:45, 9 January 2012 (UTC)

The articles partial pressure and breathing gas says the same thing: the minimum safe partial pressure of oxygen in a breathing gas is commonly held to be 16 kPa (0.16 bar). Von Restorff (talk) 16:08, 9 January 2012 (UTC)

Lack of oxygen starts interfering with your normal levels of physical performance below 75% of normal (which is 0.16 kPa). Survival below 75% is possible because your body acclimatizes to low oxygen by producing extra blood cells. It takes time to acclimate, though. 50% of normal is the lowest level where people are known to live for extended periods of time. 35% of normal is the lowest level that your body can tolerate for more than a couple of days with acclimatization.

But it is the maximum tolerable level of CO2 that is more pertinent to this question. I seem to recall that the air exhaled by a human contains 5% of CO2. Our article on CO2 reports that levels of 1% will cause discomfort, levels of 4% are "dangerous", and levels of 8% will cause loss of consciousness within minutes. So, if my recollection is correct, we can say that the human can breathe 1/5'th of the volume of his enclosed space before he starts experiencing discomfort.--Itinerant1 (talk) 20:15, 9 January 2012 (UTC)

Your recollection is corroborated by the (unreferenced) section Breathing#Components: "The permanent gases in gas we exhale are roughly 4% to 5% more carbon dioxide and 4% to 5% less oxygen than was inhaled.". -- ToE 08:19, 10 January 2012 (UTC)

The time frame I wonder about is minutes, not days. Thus no acclimatisation ;) Electron9 (talk) 00:11, 10 January 2012 (UTC)

OK, leave Mexico City (7,350 ft, 2,240 m, 772 mbar, 15.9% atm pO₂) aside and consider the cabin pressurization of a flight departing a coastal airport, thus allowing no acclimatisation. The FAA restricts cabin pressurization to an equivalent altitude of below 8,000 ft. The "Need for cabin pressurization" section addresses hypoxia concerns, saying that "symptoms may begin as low as 5,000 feet (1,500 m) [846 mbar, 17.4% atm pO₂], although most passengers can tolerate altitudes of 8,000 feet (2,400 m) [756 mbar, 15.6% atm pO₂] without ill effect. At this altitude, there is about 25% less oxygen than there is at sea level." (mbar and pO₂ mine.) I'm not saying that I want you to fill my SCBA with O₂ deficient air, but only that I take exception to the "lowest life sustainable percent is 17.5%", and agree that Itinerant1 is addressing the more important concern. Ventilate your enclosure well enough to keep the pCO₂ well down, and pO₂ won't be a problem. -- ToE 02:24, 10 January 2012 (UTC)

I made a typo above: it should have been 16 kPa, not 0.16 kPa. Personally, I've been on several camping trips where I'd leave the sea level and drive directly to a campground at the altitude of 10,000 feet (pO₂ at 70% of normal), it is noticeably harder to move around and you quickly run out of breath when you get there, but you get used to it after 12-24 hours.

It is also interesting to note that, based on numbers above, a single human adult sleeping inside a car (let's even say a minivan) will reach uncomfortable levels of CO2 in about two hours if the car is sealed tightly enough. Most cars will not be sufficiently airtight for this to happen, but, just in case, if you decide to sleep in a car, crack a window or, better yet, leave some kind of a leak near the floor (CO2 is heavier than the air).--Itinerant1 (talk) 09:15, 10 January 2012 (UTC)

Why Ritalin against ADHD?

Why do we treat ADHD, which is a form of hyperactivity, with Ritalin, which is a stimulant? Shouldn't we go the other way round, and try to treat ADHD sufferers with some sedative drug? (if we treat them at all with pills) — Preceding unsigned comment added by 80.39.202.227 (talk) 13:35, 9 January 2012 (UTC)

It does not have the same effect on people with ADHD. It has the opposite effect. Von Restorff (talk) 13:41, 9 January 2012 (UTC)

That's the question, Restorff. Why does it work like that? — Preceding unsigned comment added by 80.39.202.227 (talk) 13:44, 9 January 2012 (UTC)

It stimulates certain areas of the brain that help the person to contain impulsive behavior. You can compare this to being drunk. If you drink alcohol, the sedative effect will actually make you behave in a more uncontrolled, impulsive way. I'm not an expert in this area, but I tend to think of this as follows. A very complex system like the brain can be faced with having to cut back on its activity for many reasons. A natural reason could be that the person is exhausted and has a lack of energy. But in Nature, you would still need a working brain to survive, so the brain will tend to cut down on certain higher level sophisticated control mechanisms, rather than on lower level functions. And, that will lead to the person becoming more aggrssive, more impulsive, not less, because that will help you to survive. Count Iblis (talk) 13:46, 9 January 2012 (UTC)

"Stimulants" are named that way because they are used to stimulate certain parts of the brain that are not acting at normal levels; not because they make you more active. The brains of children with ADHD have too little dopamine because the children's brains have too many molecules that suck up dopamine before it does its thing. Ritalin exerts its attention-increasing effects by increasing the amount of dopamine in brain cell synapses, the space between cells. It does this by blocking dopamine transporters, proteins that normally transport dopamine from the synapse back into dopamine cells, recycling it for future use. More dopamine in the synapse yields a stronger reward signal, and more enjoyment of and motivation to perform certain tasks. When a person concentrates on a task, the part of the brain that is working becomes highly active. But other parts of the brain are active, too. This "white noise" helps a person without ADHD make new, creative associations. But for someone with ADHD, the white noise drowns out the main signal. (Von Restorff (talk) 13:56, 9 January 2012 (UTC)

(edit conflict)An ADHD brain need more stimulus than other people in order to feel "normal", according to the low arousal theory of ADHD. ADHDers fidget, talk and walk around, etc., because there isn't enough stimulation coming in from the environment. Stimulant medications work on ADHD because they reduce the need for the person to seek stimulation from the environment, thus helping them focus and sit still when necessary. :From the low arousal theory article:

"The low arousal theory is a psychological theory explaining that people with attention-deficit hyperactivity disorder (ADHD) seek self-stimulation or excessive activity in order to transcend their state of abnormally low arousal. The theory states that one with ADHD cannot self-moderate, and his or her attention can only be sustained by means of sustained external/environmental stimuli. This results in an inability to sustain attention on any task of waning stimulation or novelty, as well as explaining compulsive hyperactive behavior."

A sedative might also calm the hyperactive behaviours of ADHDers, but not in such a way that would help the ADHDer to focus and get things done.

I have ADHD myself, and for me and my doctor, the low arousal theory best explains the symptoms and the reason that stimulants work, but please note that there are other theories of ADHD. They can be found at the main ADHD article. Feel free to ask if you have any questions; I don't mind talking about my ADHD. Cheers, Dawn Bard (talk) 14:09, 9 January 2012 (UTC)

As an aside, I believe that sedatives are sometime also prescribed, to counter-act the effects of the stimulant. I think this is only done with patients that need unusually large dosages that disrupt the patient's sleep schedule. APL (talk) 19:59, 9 January 2012 (UTC)

E.T.

What are the probabilities of discovering an alien species, capable of replying to a message, in the near future? If we did so what message would we send them? Kittybrewster ☎ 16:08, 9 January 2012 (UTC)

Us discovering them, in the near future? 0% chance. Von Restorff (talk) 16:21, 9 January 2012 (UTC)

The SETI article would be a good place to start reading, with lots of links off to other relevant places. The Drake equation is a commonly used (and commonly criticised) equation to estimate the number of likely intelligent alien civilisations. The Pioneer plaque and Voyager Golden Record are two messages we chose to dispatch with spacecraft in the 70s, so may indicate what we would send now. (Realistically though they'll probably pick up signals of Two and a Half Men first and decide that we're all total morons and simply come and destroy us before we know anything about them). --jjron (talk) 16:31, 9 January 2012 (UTC)

Also, between the pioneer plaque and the voyager record, we sent the Arecibo message. SemanticMantis (talk) 16:47, 9 January 2012 (UTC)

It can't really be said that there's precisely 0% chance of that happening, but the outlook for that happening certainly doesn't appear too promising. At the very least, any communication with aliens would be extremely slow. Round-trip radio or light communication with the closest known star with a planet around it, Epsilon Eridani, would take about 21 years. And the failure so far of SETI to find any sign of intelligent life within the Milky Way would suggest that if intelligent life ever is discovered, the closest such life would be much further away than Epsilon Eridani. A round-trip radio or light communication to a typical star within the Milky Way would take tens of thousands of years. Red Act (talk) 17:26, 9 January 2012 (UTC)

That is just the rate of two-way communication. We could send the entire works of Shakespeare before we found out that that they didn't like Hamlet. Of course we might want to withhold broadcasting the military articles of Wikipedia until we found out if they were non-hostile. Rmhermen (talk) 17:40, 9 January 2012 (UTC)

More likely they wouldn't understand Hamlet. Of course we don't censor Wikipedia from known hostiles on earth. Kittybrewster ☎ 17:57, 9 January 2012 (UTC)

Yes, the OP said "...capable of replying to a message...", so I was addressing the time it would take to send a message and receive a reply. When I said "slow", I was just referring to communication latency, not bandwidth. Red Act (talk) 18:01, 9 January 2012 (UTC)

Maybe an alien species is broadcasting a signal to space, like us BTW, which could reach the earth tomorrow. That falls within your definition of "capable of replying.", but I don't know any way of calculating a probability of something that didn't happen at least a few times. 88.9.214.197 (talk) 17:34, 9 January 2012 (UTC)

Completely unknown. This could be computed with the Drake Equation, except that virtually every number you need to plug into that equation is also unknown. APL (talk) 19:54, 9 January 2012 (UTC)

Semantically I would disagree with "completely unknown". That suggests you have no opinion either way; we clearly have quite a lot to suggest the chances are far less then 100%. I don't know if I'd bet my life on it, but I'd probably bet my house that we won't be communicating with intelligent space aliens in the near future, I doubt many scientists in the field would think that was a frivolous wager because the odds are "completely unknown". Vespine (talk) 21:32, 9 January 2012 (UTC)

All fair points, of course. However, if we're nitpicking semantics, I'd like to point out that "communicating" is not the same as "discovering". If you made that wager and even if the discovering happened right now, odds are that your house would be safe for many years to come. APL (talk) 22:33, 9 January 2012 (UTC)

All of the responses above assume that communicating with aliens means communicating with their home planet. There's no reason why the first human detection of an alien can't be of a sentient Bracewell probe in our own solar system, in which case two-way communication could be nearly instantaneous. Alternatively, the alien planet could send an alien ambassador upon receiving Earth's radio signals, and there's no reason why this ambassador can't arrive tomorrow. --140.180.15.97 (talk) 04:37, 10 January 2012 (UTC)

If we assume they can't send their ambassador faster than the speed of light, then they would have to be quite close to have gotten our radio transmissions and sent him/her/it already. StuRat (talk) 21:34, 10 January 2012 (UTC)

Vacuum metastability event warning?

Could a Gravitational lens give us a few scant million years warning of our inevitable doom from a False vacuum collapse? Hcobb (talk) 20:38, 9 January 2012 (UTC)

It depends how fast the lower vacuum bubble was expanding, and where in space it nucleated. The farther away, and the slower it expands, the more warning we would get. Goodbye Galaxy (talk) 21:46, 9 January 2012 (UTC)

I'm assuming a speed of light spread, because otherwise the boundary conditions get really odd. But that is of course speed of light through space and space is bent. Hcobb (talk) 01:12, 10 January 2012 (UTC)

If it expands at the speed of light then there isn't any warning. If it expands slower then there is some kind of warning (if nothing else, the stars disappear!). Gravitational lensing doesn't make a difference either way. Gravity affects everything equally, even vacuum decay. -- BenRG (talk) 19:55, 10 January 2012 (UTC)

Health adjusted life table

Is there, in the actuarial science a health-adjusted life table? (note: this is not a disability-adjusted life years or healthy Life Years or quality-adjusted life year). I mean, if you are x years old and healthy, you probably will live longer than the average.88.9.214.197 (talk) 23:19, 9 January 2012 (UTC)

The problem with that approach is most people don't actually know if they're healthy. Do you know how much plaque has accumulated in your arteries ? Do you know if a small tumor is currently growing inside you ? So, they typically ask questions like your BMI, whether you smoke, how stressful your job is, etc., and use those to determine how healthy you are likely to be. StuRat (talk) 21:28, 10 January 2012 (UTC)

January 10

Water-fueled car - Where are they?

We are getting starved of oil, with the Strait of Hormuz soon to be choked off.

Snopes claims that oil companies do not buy up patents to vehicles that save or even go off of oil-based fuels entirely. (Perhaps Snopes succumbed to a conspiracy of being paid to lie.)

The vid says "...in the very near future." 3 1/2 years would be stretching it.

Why don't we see them out on the streets everywhere today? If it's in the best interest for many governments worldwide to wean off of oil, why wouldn't they pump funding into this car's development?

Japanese Company Invents Water Fueled Car

--70.179.174.101 (talk) 00:24, 10 January 2012 (UTC)

Water powered cars, according to the article you linked to, is a sort of a scam, with no real chances of working ever. Besides that, not all governments want to leave the oil economy behind. Just think about Kuwait, Saudi Arabia and such. — Preceding unsigned comment added by 88.9.214.197 (talk) 00:30, 10 January 2012 (UTC)

I said many governments. Many ≠ all. --70.179.174.101 (talk) 01:25, 10 January 2012 (UTC)

See water-fuelled car. You'd be hard put to find any sort of bullshit that we don't have an article about. Looie496 (talk) 00:32, 10 January 2012 (UTC)

Where are they? They're nowhere. They're impossible. — Preceding unsigned comment added by [[User:{{{1}}}|{{{1}}}]] ([[User talk:{{{1}}}#top|talk]] • [[Special:Contributions/{{{1}}}|contribs]])

What did you think you saw on the video? --70.179.174.101 (talk) 01:25, 10 January 2012 (UTC)

The process of invention involves finding the materials you need. In this case, inventors of the car knew they needed a fuel source with a lot of potential chemical energy, and they tried some substances like that until they found one that worked well. (They tried things like Coal, wood, gunpowder, etc.)

You can't work that process backwards. You can't say "We've got a lot of water. Let's use that!"

Imagine you ran a pizza parlor and the price of pepperoni was getting too high. You could start looking for other toppings that were equally delicious, but you couldn't just say "Hey, rocks are basically free. I'm going to figure out how to bake a delicious rock pizza." APL (talk) 01:05, 10 January 2012 (UTC)

(editing convlict) Did you watch the video? Here it is again! --70.179.174.101 (talk) 01:25, 10 January 2012 (UTC)

I watched the video. It's a con. It's a fake. It doesn't work. My guess would be that the video would have been followed soon after by an opportunity for people to pay money as an investment. Sorry. Scam. HiLo48 (talk) 01:57, 10 January 2012 (UTC)

Yes I watched it. Very amusing. The TV news loves these things. They crop up about every six months. They're always either cons, or sadly self-delusional "inventors", but they're great fun.

It's like in the olden days when everyone would get excited because some crackpot and/or swindling alchemist said he could turn lead into gold. It was never true, it couldn't possibly have been true. But every time a few suckers would go for it and everyone else would have a good laugh.

That particular one is Genepax. They mysteriously ran out of money and closed in 2009. They never actually proved that their car worked the way they claimed. Probably they had built a primitive metal-hydride cell. Or maybe they just had batteries hidden under the seats. Who knows?

I strongly suspect that they got a bunch of Venture Capitalists to fork over some cash before they suddenly shut down, but I can't find any evidence of that.

They never proved that their car was running on water, apparently expecting us to take their word for it. Many people suspected that it was running on a home-made metal hydride battery, (which do have water in them, but it's not the water that gets "used up".) APL (talk) 06:09, 10 January 2012 (UTC)

This looks like yet another conspiracy: Maybe Big Oil bought up their property and/or assets or paid off the owners to sell out their company. Perhaps the company ran out of money because the new owners made it that way, while the old owners enjoyed the windfall of new wealth. --70.179.174.101 (talk) 07:00, 10 January 2012 (UTC)

Yea, I'm sure that's exactly it. These people claimed they could do something completely impossible. When it turns out they can't it must be because they're being oppressed, not because it was impossible all along.

Seriously, free-energy con artists are a dime a dozen. (Many of them even get on TV, because the TV news stations love this junk even more than they love crackpot scientists who say something harmless is actually super dangerous, or vice-versa. TV News is mostly just entertainment. Don't take any of it too seriously.)

P.S., Please don't edit my post. That's not how the ref-desk works. APL (talk) 09:37, 10 January 2012 (UTC)

Of course you CAN make a pizza out of rock, it's called transmutation. However it costs a lot of energy ;-) So I guess this points out an obvious hard issue, you need to get a positive energy gain from your fuel. And it has to be economically viable. And of course oil companies will continue as long as the money flow, even if that means death to everyone else. Electron9 (talk) 01:21, 10 January 2012 (UTC)

Hey, why bother with a water-fueled car? I found a metric ton of YouTube videos about dilithium fusion, which is apparently much more efficient. --Mr.98 (talk) 03:06, 10 January 2012 (UTC)

Patents are listed in the public domain. They cannot be made to disappear. Even if an oil company did buy the patent to this wondrous process, the identity of the patent and its purpose would still be available to the public. Why have we never been told the identity of the patent(s) purchased by the oil company? Dolphin (t) 06:31, 10 January 2012 (UTC)

Presumably the evil oil conspirators (Since they're apparently uninterested in making a king's ransom selling unlimited zero-cost energy, and driving their competitors out of business.) would keep the water-engine as a trade secret. That's pretty ridiculous as well, though. Apple can't even keep their latest phones a secret, you're telling me nobody would leak plans or theoretical background to the water-engine? Not one Big Oil employee would publish the secret plans under their own name and win a Nobel prize? All those Genepax employees are all bought off so well that a billion dollar invention doesn't tempt them? The Pentagon couldn't keep a secret that big!

All nonsense. We all know how corporate America works. Big Oil Corp would buy the patents, and sell the free energy devices for an unimaginable fortune. All their CEOs, and top executives would give themselves gigantic bonuses. If that cut into long-term profits they wouldn't give a crap! They'd write themselves a giant bonus check, cash out their shares, and give their investors the shaft! That's how corporations work nowadays. APL (talk) 09:51, 10 January 2012 (UTC)

To summarize the water-fueled car article, a water-fueled car that turns water into hydrogen and oxygen (which is what the video claims) can't work because water has a lower potential energy than the corresponding quantity of free hydrogen + free oxygen. Burning hydrogen in an oxygen atmosphere releases energy, so it makes sense that to convert water to hydrogen and oxygen, energy must be added.

It is possible, however, to make a car that runs on hydrogen by converting hydrogen and oxygen into water. However, producing hydrogen also takes energy, so in the end it might not be worth the necessary investment. This might change if extraction of hydrogen from Jupiter or another gas giant becomes feasible, but so far that's a long way off. --140.180.15.97 (talk) 21:04, 10 January 2012 (UTC)

Krakatoa explosion – must it happen again?

When Krakatoa exploded in 1883, it killed 40,000 people. From a recent TV doco, I learnt that the island is growing again very quickly (in geological terms) and will soon have the same volcanic form that caused the prior explosion. Next time, it will destroy probably 10 times the number of people that it did in 1883. This is confirmed in the WP article. There seems to be a: "It is as Allah wills" sort of fatalism here. Why do we have to wait for an "inevitable" catastrophe? Drop the big one, I say! Nuke the mother, and KEEP ON nuking it every time it raises its ugly head from beneath the waves! Why do we have all these nukes? Let's do something useful with them. That's my three pence worth anyway. What say you? Myles325a (talk) 01:43, 10 January 2012 (UTC)

Two points. Firstly, I doubt that we know enough about volcanoes to know how to usefully bomb it, even it's possible. Secondly, Nuking has side effects. See Chernobyl. HiLo48 (talk) 02:02, 10 January 2012 (UTC)

Two other points: Both a future eruption and Chernobyl would have far worse effects than nuking Krakatoa. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 02:13, 10 January 2012 (UTC)

APL (talk) 09:55, 10 January 2012 (UTC)

Op Myles325a back. How is it that Chernobyl "would have far worse effects than nuking Krakatoa. Chernobyl did not kill 40 000 people. Or is that because they are natives and thus not worth Russian lives.

The Krakatoa eruption that destroyed the island involved an energy equivalent to about 200 megatons of TNT. That's four times larger than the largest nuclear bomb ever detonated, and about 170 times the energy of the largest nuclear bomb actively maintained in the current US arsenal. Even if we wanted to blow up the island up with nuclear bombs, it could take a lot of them. At the same time, if you do it poorly, there is a significant risk of triggering a large eruption. We don't really know how to blow up a volcano safely. Beyond that, people tend to take a very dim view of polluting the environment with radioactive fallout, which is likely if you used nuclear weapons to destroy a volcano. Maybe there is a way to vent the volcano before a catastrophic eruption, but I doubt anyone would seriously use nuclear weapons for this purpose. Dragons flight (talk) 02:15, 10 January 2012 (UTC)

I ADVISE that very thing. If the use of them cannot be rationalised for this task, then it cannot be rationalised for ANY task, including military ones.

We have to destroy the village volcano in order to save it. Clarityfiend (talk) 03:01, 10 January 2012 (UTC)

Prediction is very difficult for geologists. Extrapolation from the recent past (and within the last 10,000 years is considered "very recent" in deep time) doesn't tell you what will happen in the near future. The error bars are huge, and the understanding of the science itself is dynamic and changing. (Remember that plate tectonics, on which all current seismological theories are based, only became scientific consensus in the 1970s. This isn't to denigrate the current understanding, just to point out that the most recent paradigm shift is pretty recent indeed.) "Very quickly" in geological terms could be tens of thousands of years, so it's not clear that this is something that really needs much more than fatalism, unless you're deciding whether to live there, and even then, your chances of dying from some other cause greatly outstrip the chances of dying from Krakatoa. I'm not sure if anyone's done any really rigorous studies as to what would happen if a large nuclear explosion was detonated in a volcano, but I see no reason to assume a priori that it would be a positive thing. --Mr.98 (talk) 03:02, 10 January 2012 (UTC)

Some references. Fehér Klára, A földrengések szigete (novel, 1968, Móra, Budapest) has something like this as the main plot point: the heros are digging a hole in a volcano to avoid eruption. This is played in an optimistic future, when volcanos are the last natural force to be ruled, in particular, weather is already controlled by humans. Jules Verne, The Mysterious Island has as a plot point a volcano eruption predicted successfully, though there's no consideration of averting the eruption. Antoine de Saint-Exupérym The Little Prince says that the volcanos on the Prince's asteroid burn with a steady flame and never erupt because the Prince sweeps them every day, but notes that this technique could not work on Earth because our volcanos are two large. What? This is not the Humanties desk you say? – b_jonas 05:59, 10 January 2012 (UTC)

Well, at least that darn volcano didn't go off today...

I have personally experienced volcanic ashfall on three separate occaisions.It's not fun. Neither is the distinct possibility of a volcano-generated tsunami, a pyroclastic flow burning your house down or a lahar burying the whole town in mud. When a nearby (as in, within like 150 miles since they can kill you from that far away) volcano is active, it tends to fill your thoughts at every idle moment. But it sure beats the hell out of being covered in keloids or feeling your teeth melt while they are still in your mouth, or watching your neighbor turn into a pillar of fire, or even having every single device that is dependent on any type of computer technology fail simultaneously. But sure, nuke the volcano, two disasters for the price of one! Beeblebrox (talk) 07:23, 10 January 2012 (UTC)

This would be the Lex Luthor scheme from Superman: The Movie, and we know how well that turned out. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:21, 10 January 2012 (UTC)

I'm puzzled by the OP's "will soon have the same volcanic form that caused the prior explosion". Does this actually mean anything geologically? --ColinFine (talk) 13:02, 10 January 2012 (UTC)

A reasonable guess is that he means the volcano will gradually build up to the kind of geologically volatile structure that resulted in the earlier eruption. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:59, 10 January 2012 (UTC)

Krakatoa was 813 m high when it blew; Anak Krakatau is currently about 324 m and growing at 2 to 7 meters a year. So we have about a hundred years left. Rmhermen (talk) 15:25, 10 January 2012 (UTC)

But is the shape or size of the surface feature actually of any great consequence? Surely it is what is going on deep below the surface that will govern when an eruption occurs? --ColinFine (talk) 00:38, 11 January 2012 (UTC)

It sounds like your goal is use small nukes to periodically blow the plug off the volcano, so it can have many small eruptions, like in Hawaii, instead of occasional huge explosions. There's the issue of us not knowing what we're doing, and the pressure has likely already grown to where we could trigger a dangerous eruption. The radiation danger was mentioned, too. Perhaps by the time it does erupt on it's own, our prediction methods will be better and we can fully evacuate. Combining all these factors makes it better to wait. StuRat (talk) 21:07, 10 January 2012 (UTC)

The problem is that we call what happens in Hawaii a "volcano" just as we call what happened at Krakatoa a "volcano", but the mechanism and type of event is so vastly different that it doesn't serve us well to think of them as all that similar. Hawaii is a shield volcano and Krakatoa is a stratovolcano. Catagorizing them together is like categorizing a Hurricane and a Tornado as the same thing because they both called storms and they both spin. --Jayron32 01:04, 11 January 2012 (UTC)

Asteroid impacts can also be used. By changing the orbit of an asteroid, it can be made to impact at any point on Earth. By aiming for Yellowstone National Park, the next eruption of the supervolcano can be triggered. An asteroid of about 1 km diameter is needed to penetrate the magma chamber. Count Iblis (talk) 22:44, 10 January 2012 (UTC)

I think we need to call in Xenu for technical assistance with those H-bombs. ;) The mechanics of volcanic eruption perplex me - I don't understand how releasing pressure increases pressure (if it does). Still, I am intrigued by the notion that someone could drill a fairly small hole into a volcano, surrounded by a heated casing (some kind of liquid metal circulated through the magma chamber to keep it warm?) and slowly draw off the magma in a controlled way, at the same rate that it enters the chamber, to avoid instability. I'd think the amount of electric power and steam for heating generated by such a plant would be enormous, and if it delays or stops the eruption, so much the better... Wnt (talk) 22:50, 10 January 2012 (UTC)

ATP--used by all/most organisms?

Long time user, first time questioner on the ref desk. Today, I was checking out Adenosine triphosphate as a reader rather than as an editor...and I cannot for the life of me figure out if ATP is used by all biological organisms, most, or just a limited number. It may well be that the info is in the article somewhere, but I'm just not seeing it. I'm not looking for any sort of exact breakdown, more a general feel: is ATP universal, or is it one of a number of options? I imagine that once upon a time, many years ago, I learned this in college bio...but I'm getting too old to recall such things without electronic aid. Appreciate the help in advance. Qwyrxian (talk) 02:57, 10 January 2012 (UTC)

Yes, ATP is used by all (known) living organisms. From Microbiology: An Introduction (Tortora et al., 1995, p. 129):

"In aerobic respiration and anaerobic respiration, a series of electron carriers called an electron transport chain releases energy that is used . . . to synthesize ATP. Regardless of their energy sources, all organisms use similar oxidation-reduction reactions to transfer electrons and similar mechanisms to use the energy released to produce ATP." [16]

Though ATP is used by all living organisms, it's not the only energy currency. GTP is another nucleoside triphosphate that fills the same type of role as ATP does in a number of biochemical pathways. (That's not to say that they are interchangeable—some reactions employ ATP, some GTP. TenOfAllTrades(talk) 03:26, 10 January 2012 (UTC)

Thanks, that is exactly the info I was looking for. Qwyrxian (talk) 03:33, 10 January 2012 (UTC)

So far as I know, all known life uses related proteins, specifically RNA polymerases, to create the mRNA transcripts which are used to direct the production of those polymerases and other proteins. And all those polymerases work by the same principle, of using NTPs, including ATP and GTP, to provide the energy for this polymerization reaction. Thus, without exception, ATP and GTP are used as energy storage methods by every organism with a genetic code, even viruses (though in that case they co-opt this energy from another organism). However, ribozymes can mediate the same reaction (at a slow rate) without the need for a protein, and, I think, in theory a different ribozyme could indeed mediate such a reaction without using an NTP for its energy source but some other nucleotide derivative instead. Such ribozymes are of interest to researchers as an analog for early living organisms; thus it is possible that some uncharacterized living organism is out there with this, or some other biochemistry. But this is about as close to a rule without exception as can be found in biology. Wnt (talk) 23:05, 10 January 2012 (UTC)

amaloydosis

My Mom passed away in 1988 from Amaloydosis. Do I have a chance of getting this disease? I am a female of 56 years. E-mail [redacted email] — Preceding unsigned comment added by 198.228.199.175 (talk) 18:59, 10 January 2012 (UTC)

There are many types of amyloidosis. Your risk of developing it will depend on what type your mother had, in addition to many other factors. This is something best asked of your doctor. 148.177.1.210 (talk) 19:03, 10 January 2012 (UTC)

This is exactly the kind of medical advice Wikipedia can't give. If you want to ask which kinds of amyloidosis have a genetic basis, or how strong that is, we should try to answer, but we certainly can't give accurate information about her kind, whatever that might be, or your case in particular. Wnt (talk) 23:10, 10 January 2012 (UTC)

The article says it's possible to inherit it or to acquire it. The simple (and largely useless) answer to the question, "Do I have a chance of getting this disease?", is YES. Just like you have a chance of getting most any disease (with the possible exception of prostate). And as noted above, "Talk to a doctor." ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:39, 10 January 2012 (UTC)

To what extent are atoms understandable?

often when they teach us quantum mechanics, we are told not to try to visualize atoms, because they are unimaginable.Well, to what extent?When we study chemistry, for example, which discusses interactions that occur in a scale not much bigger than the atomic scale, or biochemistry, for example how DNA codes proteins, we see explanations that are... well very imaginable and sort of mechanical.And also, new methods of microscopy seem to give us images that at least show how atoms are arranged in space.So I wanna know, how unimaginable are atoms, and when some models fit very well experiments, is it safe to visualize atoms according to that models?--Irrational number (talk) 19:12, 10 January 2012 (UTC)

Atoms are not unimaginable. But they are different than what students usually imagine them to be and that's why teachers often tell them to stop wasting time trying to imagine them. It's part of the "shut up and calculate" philosophy of teaching physics. Dauto (talk) 20:33, 10 January 2012 (UTC)

I think that approach is a mistake. Most people think visually, so giving them a way to visualize things helps a lot. Just like a globe is a useful, but not entirely accurate, model of the Earth, so are atomic models. We just need to keep in mind where the model is off, like the Earth not having a metal rod thru the center. StuRat (talk) 20:47, 10 January 2012 (UTC)

A globe is a much better representation of the Earth than any possible imagery is for an atom. A better example would be trying to imagine distances on the Earth if you're only allowed to view a Mercator projection map. There's a precise mathematical relationship between distances on the map and distances on the Earth, but it's hard to make that relationship intuitive if you've never seen a sphere in your life.

The explanations in chemistry and biochemistry seem mechanical partly because they're highly simplified and wishy-washy. No analytical quantum mechanical solution is possible for anything more complex than hydrogen, so these simplifications are needed to get anything done. Also, biochemical molecules, especially proteins and DNA, are enormous by the standards of quantum mechanics. Many proteins are tens of kilodaltons, almost macroscopic compared to the one dalton hydrogen atom that quantum mechanics can describe. --140.180.15.97 (talk) 21:16, 10 January 2012 (UTC)

well, my point is that they work, and they work pretty well in a lot of occasions, so why not think as if they really represent the "image" of atoms?--Irrational number (talk) 21:47, 10 January 2012 (UTC)

The problem is that the models have a tendency to reinforce misconceptions that the teacher is trying to dispel, so naturally the teacher tells the students to stop thinking about those visual models. Dauto (talk) 22:55, 10 January 2012 (UTC)

I agree with Irrational. All models, visual or otherwise, are an imperfect representation of the thing they model. They're still better than nothing. All models can lead to misconceptions, even precise mathematical models. Overemphasis of the canonical formalism in undergraduate QM seems to have left a lot of people with the impression that quantum mechanics is all about collapsing wave functions, for example.

I think teachers emphasize the mathematics not for the benefit of the students, but because it's the only part they themselves understand. Most of them, anyway. I think Feynman would agree with the statement that atoms are little fuzzy balls. -- BenRG (talk) 03:37, 11 January 2012 (UTC)

I want to mention instrumentalism, although I'm not sure whether to accuse you of veering towards it by saying "they work", or applaud you for resisting it by trying to imagine something.  Card Zero  (talk) 14:47, 11 January 2012 (UTC)

by "they work" I mean that they explain natural world very well.--Irrational number (talk) 16:13, 11 January 2012 (UTC)

Enrichment percent of Pu-239 ?

Regarding the latest international crisis, How high enrichment does Pu-239 need to have before becomes a weapons usable material?, guess Pu-241 falls into a similar category. Electron9 (talk) 19:25, 10 January 2012 (UTC)

The article you linked to states that "weapons-grade" plutonium is at least 93% Pu-239 and has no more than 7% Pu-240. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 19:47, 10 January 2012 (UTC)

Is that separated from atoms with different proton number or from differen isotopes of Plutonium? Electron9 (talk) 19:51, 10 January 2012 (UTC)

Those are isotopes. (Pu-239 tends to capture neutrons in a reactor and become isotope Pu-240 which is unsuitable for weapons.) RJFJR (talk) 20:53, 10 January 2012 (UTC)

There are degrees of unsuitability. It's true that a government weapons program wants <7% Pu240, but more than that doesn't mean the bomb would be a dud. As the Pu article says, over exposure in a reactor makes too much Pu240, so military reactors (used to make weapons-grade Pu) fish their fuel out relatively early, while civilian power reactors keep it in and so cook up more Pu240. In John McPhee's The Curve of Binding Energy, Ted Taylor talks about how someone might steal civilian post-reactor fuel elements, do some challenging but not impossible chemical and metallurgical steps to separate the Plutonium from the bulk of the uranium-oxide and make either a plutonium oxide or plutonium metal pit from that. As he's not talking about isotopic separation of the Pu, that would have a relatively high proportion of Pu240 (too high to be called "weapons grade", but not, Taylor argues, for it to make a weapon unviable). As Pu240 has too high a spontaneous fission, any bomb someone might make would dismantle itself as it was being explosively assembled, and so would be very inefficient and dirty - but it would, Taylor claims, explode never the less. Taylor's thesis is that if someone can steal some post-reactor fuel, they can probably (perhaps over a period of time) steal quite a lot, thus making up somewhat for the inefficiency of their device. It's an old book (and perseverates on the security of civilian nuclear installations one hopes have long been improved) but it's scary nonetheless. -- Finlay McWalterჷTalk 21:26, 10 January 2012 (UTC)

I don't think Taylor talks about stealing heavily irradiated spent fuel in that book; spent fuel is going to be too radioactive for your average terrorist or amateur. My recollection is he's talking about converting liquid plutonium oxide (I think), which is not suitable for a bomb,into a metallic form that would be useful for a weapon. This was in reference to the fact that many people at the time (early 1970s) thought that plutonium oxide was not a huge terrorist problem on account of it being difficult to work with, and were shipping it around rather cavalierly. (I think you're confusing the two things.) He was especially worried about the amount of plutonium you'd create through nuclear reprocessing. Reprocessing itself (removal of plutonium from spent fuel) is not something you can do in your basement; it requires pretty specialized facilities (hot cells) to do so without killing yourself immediately. --Mr.98 (talk) 21:42, 10 January 2012 (UTC)

It's worth noting you don't enrich plutonium the way you do uranium. You just use different reactor cycles to make sure that the plutonium you make isn't too contaminated — you run a weapons reactor differently than a power reactor. (You could, in theory, enrich plutonium the same way you do uranium, but it would be very difficult, in part because of plutoniums increased radioactivity and toxicity, and it would be a stupid way to do things. If you can enrich uranium, you should enrich uranium.) But as Finlay says, it's worth noting that there is evidence that reactor grade plutonium — relatively high levels of Pu240 — can be used in a bomb. In 1962, the Atomic Energy Commission did test a bomb fueled with "reactor-grade plutonium" and "it successfully produced a nuclear yield."[17] It's not an ideal material and it won't get your maximum bang for your buck, but if you're worried about terrorists (or even just large numbers of deaths from inefficient weapons!), it's still worth being concerned about. (Remember that even a fizzle of half a kiloton is still many, many times the size of the Oklahoma City bombing or 9/11 in its effects.) It is considered more proliferation-resistant than weapons-grade plutonium, and given the option, no nuclear weapons state would use it in their weapons if they could use weapons-grade Pu or HEU, but it's still weaponizable. --Mr.98 (talk) 21:42, 10 January 2012 (UTC)

I was under the impression that a fizzle bomb is no more explosive than the high explosives used to implode the device? the only exception would be some fusion boosting, but then you got to get that reaction started too. Electron9 (talk) 00:16, 11 January 2012 (UTC)

Fizzle (nuclear test): "... a nuclear bomb fails to meet its expected yield. ... For practical purposes, a fizzle can still have considerable explosive yield when compared to conventional weapons." -- ToE 04:17, 11 January 2012 (UTC)

Fizzle can also mean that only a fraction of the potential energy is released. --Mr.98 (talk) 12:42, 11 January 2012 (UTC)

January 11

Mercator projection of Earth for a different rotation axis position

I put a climatology experiment on the shelf a while back because I searched all over and could not find a way to convert my globe or any map of the Earth to the new Lat./Long. alignment I created. As it is globes and maps of the Earth converted into the Merctor projection spread out what are the current 90° North/South axis points, the North Pole and the South Pole. I repunched my globe so that it rotates from the point on the current system at 30 degrees North by 173 degrees East, The new South Pole rotation axis at 30 degrees South by 7 degrees West.
This has nothing to do with any predictions of any future Earth, the reason I chose the middle of the North Pacific was because if frees up the most amount of land from being covered by snow and ice, obversely making the largest amount of land available as naturally habitable.
My curiosity is about the climates that would exist with such things as the Himalayas nearer the Equator, all of North America below the Arctic Circle (Alert, Nunavut like Miami, Florida), the Equator passing below Australia instead of above it with Antarctica instead like Australia, the change of orthographic rain patterns, new ocean currents, etc.
So I am asking if anyone can create a Mercator Projection for a globe that has the North pole at 30°N/173°E and the South pole at 30°S/7°W, or if anyone knows of a program, or anyway other way I can visualize and work with it other than actually painting my globe because I would like to have it all figured out before I take the step of painting my globe. 24.79.40.48 (talk) 02:14, 11 January 2012 (UTC)

Searching on "Oblique Mercator projection" might be useful. We also have an article on Transverse Mercator projection, which is the version that goes through the poles. As far as programs, you could try some Geographic information system software. It sounds like you just need some program that can make oblique Mercator map projections with user-defined parameters. Pfly (talk) 02:24, 11 January 2012 (UTC)

Oh and by the way, it's not clear to me why you need a Mercator projection. There are many map projections, and if you are mostly interested in visualizing an alternate axis there are probably better choices than Mercator. Pfly (talk) 02:29, 11 January 2012 (UTC)

If someone here can't help, you might try asking at Wikipedia:WikiProject Maps or Wikipedia:Graphic Lab/Map workshop. --Jayron32 02:30, 11 January 2012 (UTC)

The reason I chose Mercator is that I can roughly transfer ocean temperatures from other Mercator projections of the current poles that have been made to show the ocean temperatures at the current latitudes, and that in turn will affect the land temperatures. Also it is the most common projection of the Earth, as far as I know, and I want to make the comparison. I'm an algebra person, trig is the worst for me, imagining the mathematical coversions seems like a nightmare to me. 24.79.40.48 (talk) 02:48, 11 January 2012 (UTC)

I can write a program to do it. Can you give me a reference map to transform? Ideally it shouldn't have any labels, because they'll obviously get severely distorted. --140.180.15.97 (talk) 02:56, 11 January 2012 (UTC)

If I had a "map" I wouldn't need a conversion, I literally drilled new holes in my globe at 30°N/173°E and the South pole at 30°S/7°W,
I don't know what else I can give you. Any basic mercator projection would do if that's what you mean, even ones like these
http://courses.moodleshare.com/file.php/156/Week_2_Resources/mercator_map.jpg
http://en.wikipedia.org/wiki/File:Peirce_quincuncial_projection_SW.jpg
http://en.wikipedia.org/wiki/File:Mercator_projection_SW.jpg
There was one like that last one that looked like a photograph there before.
http://upload.wikimedia.org/wikipedia/commons/7/74/Mercator-projection.jpg
It would also be helpful to be able to have a completely blank copy
http://www.freeusandworldmaps.com/images/WorldPrintable/WorldMercator6LinesPrint.jpg
If you could swap in various maps, and it would draw the new longitudinal and latitudinal lines after that it would be awesome!
24.79.40.48 (talk) 03:42, 11 January 2012 (UTC)

I couldn't access the first map, but here are transformed versions of the other three:

• http://i1234.photobucket.com/albums/ff408/ideasrule/mercator.png
• http://i1234.photobucket.com/albums/ff408/ideasrule/photolike.png
• http://i1234.photobucket.com/albums/ff408/ideasrule/blank.png

I also dumped the code as a comment, at the end of this section. --140.180.15.97 (talk) 22:42, 11 January 2012 (UTC)

Generic Mapping Tools can do stuff like this.

 ( GMT pscoast -K -R-180/180/-67/67 -Jo-7/60/173/-60/1:256000000 \
                                             -G200 -N1/0.25p -Dc ;
   GMT psbasemap -O -B30g10/30g10 -R-180/180/-67/67 -Jo0/0/180/0/1:256000000
 ) > tiltedmap.ps

The above command produces one very weird-looking map. 68.60.252.82 (talk) 05:59, 11 January 2012 (UTC)

Incremental cost per nuclear bomb

What is the rough incremental cost of building a nuclear bomb given that you are a nation state with the capability to refine the material and already have designs and tools to manufacture the bomb? I assume it varies considerably by bomb type, but I'm only looking for rough estimates, so I don't care too much about the details. I'm sure the research and development is very expensive, but if you ignore that part is it still very expensive? Dragons flight (talk) 02:38, 11 January 2012 (UTC)

The Brookings Institution's U.S Nuclear Weapons Cost Study Project has all kinds of interesting stuff. Their book "Atomic audit" (from page 93 onward) considers the question, "What do nuclear bombs cost?" (Google Books preview.)

The answer, in the U.S., has always been basically a secret, but there is some data out there. In 1973, in a congressional hearing, it was stated that the (later cancelled) W74 and W75 nuclear artillery shells would cost about $400,000 each, or a couple of million in today's dollars. In 1981, it was revealed that the W84 warhead was projected to cost $1.1 million apiece, or about $3 million today. And in 1990, the U.S. GAO accidentally let slip that the W80 had a unit cost of $720,000, or about $1.2 million today.

The book also notes that unit costs have been going up because of increasing complexity, and the later designs have often significantly overrun their budgets.

So the answer would seem to be from about a million dollars up.--Rallette (talk) 07:27, 11 January 2012 (UTC)

Also, the correct term is "marginal cost", so the google search string <marginal cost nuclear weapons> gives some results confirming the above answer, although they seem to be about fission bombs eg. [18] . IBE (talk) 09:48, 11 January 2012 (UTC)

Note that this makes it expensive from an average consumer point of view but on par with other big weapons. Each nuke is about 2X the price of a Tomahawk, 1/6th the price of an M1 Abrams, 1/20th of an F16, 1/1000th of a B-2. But you can't ignore the fact that the total prices are high. You're including R&D as the expensive part, and it's certainly expensive, but the biggest costs, by far, are from developing delivery vehicles (rockets and planes and etc.) and maintaining them in alert status and all that. The Brookings Institution page (and book) makes that pretty clear. The price doesn't stop once you have the nuke in hand, it only goes up. --Mr.98 (talk) 12:22, 11 January 2012 (UTC)

Research and development would be cheap because you don't need to reinvent the wheel. A basic nuclear pile (using uranium-238 with graphite moderator) can be used to produce plutonium cheaply. A plutonium processing plant can be built cheaply to produce plutonium. Hydorgen bombs using plutonium-239 can be built from the plutonium cheaply (as long as plutonium-240 is less than 7% of the plutonium). However, plutonium can be detected from space with satellites. If you don't want your nuclear bombs to be detected from space, then you need to build hydrogen bombs from uranium-235. U-235 processing from U-238 is prohibitively expensive even if you import the processing equipment. You need a lot of spare electricity either from a nuclear power plant or a hydro-electric power station. Also, U-235 processing takes a long time so you will have very few hydrogen bombs.
Sleigh (talk) 12:32, 11 January 2012 (UTC)

Detected from space? Yeah, let's see some evidence of that before we blindly claim it to be true. An engineer working 10 m from a plutonium warhead is receiving ~2 billion times the radiation that a satellite 500 km overhead receives. Either the engineer can't work there for more than about 30 seconds or the satellite can't actually detect anything above background noise. Now, granted, there are other ways that space-based reconnaissance can detect nuclear warheads, but none of them are particular to plutonium vs uranium designs. — Lomn 14:24, 11 January 2012 (UTC)

Alright, I'll bite. I've long suspected that plutonium could be detected from space (ever since they caught some fellow driving across then still East Germany with a pound of it rolling around in the back of his car) but can you point us to a source saying they definitely do it, and more importantly how? Plutonium doesn't say anything about satellites or spacecraft, at least, and we ought to add it. ;) Wnt (talk) 14:19, 11 January 2012 (UTC)

You can't detect quantities of plutonium from space. If it is unshielded there are ways to detect it terrestrially (looking for specific radiation) but it's not hard to shield. The odds are your specific East German incident is either related to regular old radiation detectors, or from human (not technical) intelligence. Plutonium-producing reactors give off characteristic emissions that can be detected by plane (maybe by satellite, I don't know). Plutonium facilities are generally pretty large and look pretty distinctive, so plain old satellite photography is used in many instances. If you could detect raw plutonium metal from space, it would vastly simplify the problem of keeping all of it under control... I wish we could! --Mr.98 (talk) 16:21, 11 January 2012 (UTC)

You're confused on a few points here. R&D is still not cheap — you don't have to reinvent the wheel, but if you don't already have means of making nuclear reactors, extracting plutonium from spent waste, and fabricating the explosives and etc. in the right shapes, that still costs. If you don't already have a nuclear complex, then it's not cheap. (And if you already have one, then you've already spent the cash on R&D.) This isn't to say you have to make a Manhattan Project's worth of effort, but it's still not cheap. Probably a billion or so USD at the minimum.

Nuclear reactors of sufficient size to produce sufficient amounts of plutonium for weapons purposes are not cheap to produce. If you already have lots of civilian power reactors, then you just need reprocessing facilities. Still not straightforward.

You can't "detect plutonium from space." You can detect the signatures of various nuclear facilities from space. But not plutonium itself. Production reactors and reprocessing facilities are fairly detectable, though. But so are uranium enrichment facilities, on the whole.

Why you would jump from U-235 to hydrogen bombs, I don't know. You can have perfectly good U-235 bombs without trying to make hydrogen bombs. Hydrogen bombs are much harder to manufacture than fission bombs, and the general consensus is that you won't be able to produce them without doing nuclear testing first. Which probably excludes the possibility of making them covertly. You seem confused about what hydrogen bombs are. --Mr.98 (talk) 16:16, 11 January 2012 (UTC)

Molecular form of carbon gas

If pure carbon is heated above the sublimation temperature in a closed vessel, what molecular form will the gas be? C1 (monatomic), C2 (diatomic), or C3 (tricarbon), or a mixture? I would have thought that it would be a mixture with a temperature-dependent proportions as with other gasses like dissociated oxygen or hydrogen, but references indicate that C2 and C3 are rare transient forms. I cannot find any arrhenius data for C3 + x > product reactions, not any relative enthalpy data, which would allow calculation of the proportions. Does such data exist? Does anyone know a good reference? 121.221.232.241 (talk) 02:53, 11 January 2012 (UTC)

Buckminsterfullerene C₆₀ sublimes as C₆₀ gas and is interesting in that there is no liquid phase, whatever the pressure or temperature. (triple point above critical point). Wikipedia articles are at dicarbon and tricarbon but they do not answer your question. Graeme Bartlett (talk) 03:12, 11 January 2012 (UTC)

[19] talks about creation of carbon gas using a laser pulse, and all three of your carbon forms are produced. C₂ must be pretty stable as it is detected in carbon stars. [20] has some data for C2 if you can understand it. Graeme Bartlett (talk) 04:24, 11 January 2012 (UTC)

Thanks Graeme. I can understand it with difficulty. More help from somebody would be nice. AKH121.215.152.114 (talk) 05:32, 11 January 2012 (UTC)

Suicide bombing

Do suicide bombers feel pain at the time of explosion? If yes, how long? --Amoeba159 (talk) 07:18, 11 January 2012 (UTC)

Yes, for the rest of their lives.--Shantavira|^{feed me} 08:35, 11 January 2012 (UTC)

Have any of them ever survived long enough to describe the pain of having their legs and arms ripped off in a split second, or their entire stomach blown up, or to express any remorse for what they did to innocent others? -- Jack of Oz ^{[your turn]} 08:51, 11 January 2012 (UTC)

Plenty. These guys tend not to be the brightest buttons in the box and a lot of them mess up.--Shantavira|^{feed me} 08:57, 11 January 2012 (UTC)

Jeff Dunham#Achmed the Dead Terrorist. No, they do not. Plasmic Physics (talk) 09:36, 11 January 2012 (UTC)

A simple search finds [21], I'm sure there are others. Note that in this case it doesn't appear he had planned to be a suicide bomber, rather he was (probably intentionally) caught in the blast of a remotely trigerred device. Nil Einne (talk) 13:59, 11 January 2012 (UTC)

There are various stories of people being caught in explosions (e.g. IEDs and mines), and looking down to see body parts missing without having felt anything. Also similar stories about people being shot without realising. So it's possible they wouldn't feel it. But some have survived explosions so there should be accounts somewhere (albeit surviving would be far more painful). --Colapeninsula (talk) 10:11, 11 January 2012 (UTC)

In such an explosion, you are ripped apart faster than what your central nervous system can communicate a sense of pain. Shock isn't even an issue. Plasmic Physics (talk) 10:23, 11 January 2012 (UTC)

I recall a figure of 120 m/s for nerve communication. A simple test is to let a friend squeeze your to and measure the time from squeeze to detection ;) Electron9 (talk) 13:57, 11 January 2012 (UTC)

Black lung

Are there any plans of research for future treatment options of black lung disease, or plans of research for a cure to completely rid the disease in a person? 71.146.10.10 (talk) 11:32, 11 January 2012 (UTC)

The only things I can find as a possible treatment for Coalworker's pneumoconiosis are lung transplants: [22] and [23], breathing exercises and lung lavage: [24] SmartSE (talk) 13:02, 11 January 2012 (UTC)

Interesting lead. See also PMID 8794962, which says lavage gets out about a gram of dust in a treatment. What I find interesting about this treatment is that macrophages should be able to be directed to move. In concept, I would think that the right migration factors added to the lavage fluid or inhaled beforehand ought to increase the yield of dust-laden macrophages considerably, whether the dust is coal or silica. Wnt (talk) 14:56, 11 January 2012 (UTC)

"Black lung" isn't a disease in the conventional sense. It's the damage & scarring of the lungs due to inhaling coal dust. Either the dust itself damages the tissue, or macrophages surround the dust but can't remove it from the body. The aveoli are very sensitive, so you can't just scrape the dust or macrophage clusters out without causing more damage to the tissue. — The Hand That Feeds You:^Bite 18:59, 11 January 2012 (UTC)

A possibility might be cell cultivation to build new lungs. But there are problems with cancer and structural support and associated nutrition support system ie blood supply. When these problems will be solved is any ones guess. Another option might be some kind of fluid or gas that would react with foreign objects in such way that they can be removed or dissolved. But both options requires plenty of research to be of any use! Electron9 (talk) 20:37, 11 January 2012 (UTC)

Electron in a magnetic field

Recently in a physics test, a question was this: "An electron with a constant speed enters a uniform magnetic field in a direction perpendicular to the magnetic field. What is the shape of the path that the electron would follow?

• Parabolic
• Circular
• Elliptical
• A line parallel to the magnetic field"

The answer is circular, but however I try to think about it, I do not understand why it is not parabolic. Can anyone please explain? Chaosandwalls (talk) 16:42, 11 January 2012 (UTC)

is it not Helical? Basically, the force is always(?)(F = v x B) perpendicular to the velocity. circularity is probably provable from this rule. The centripetal force in uniform circular motion is also perpendicular to the velocity if you recall. Cplusplusboy (talk) 17:10, 11 January 2012 (UTC)

It would be helical, if not for the stipulation about the direction being perpendicular to the field. --Trovatore (talk) 18:53, 11 January 2012 (UTC)

It can be viewed as a matter of symmetry.

There are no changes in potential energy involved here, so the electron can't change speed, because a change in speed would change the electron's kinetic energy, which would mean that the total energy was violating the conservation of energy. There's nothing preventing the electron from changing velocity, but only the direction of the velocity can change, not the magnitude.

Furthermore, the electron starts off with a zero component of velocity parallel to the magnetic field, and a zero component of force parallel to the magnetic field, which means that there's a zero component of acceleration parallel to the magnetic field, so the electron remains with a zero component of velocity parallel to the magnetic field.

If you put the above two together, at any time t₁, the electron's properties and environment must be the same as at the initial time t₀, in that the electron is still travelling at its initial speed, perpendicular to a uniform magnetic field of the same magnitude. If the electron's properties and environment are the same at the two times, except for a change in coordinates used to measure those properties consisting of at most a translation and a rotation, then the shape of the electron's path at the two times must be the same. A circular path has the property that the shape of the path (specifically, the curvature) is the same at all points along the path. A parabolic or elliptical path would not have that property. So the right answer must be the circular path. Red Act (talk) 18:44, 11 January 2012 (UTC)

I have a hunch as to why you thought the path would be parabolic. The path would indeed be parabolic, if the force on the electron were constant. But although the magnitude of the force is indeed constant, the direction of the force changes as the direction of the electron's velocity changes. Red Act (talk) 20:59, 11 January 2012 (UTC)

I think I understand in now. Thank you very much. Chaosandwalls (talk) 23:01, 11 January 2012 (UTC)

As always, elementary physics courses teach electron gyro motion in the form of a spherical cow. The problem specifies a dramatically simplifying assumption: a perfect and uniform magnetic field that is encountered instantaneously and with no edge effects or fringing or transient field intensity rise. In reality, no magnetic field behaves like this; but in reality, the motion of charged particles in magnetic fields is very hard to analyze. So, the physics student should work within the parameters of the canonical problem definition and solve the equations of motion, using the Lorentz force. The solution to this equation is circular motion with a specific angular frequency that only depends on the intensity of the magnetic field, the charge, and mass, of the electron. Note that the electron's kinetic energy (... ergo, its velocity) does not affect the resonant frequency. This result is important and empirically useful, because it still applies fairly well even when the other simplifying assumptions do not. In more advanced studies, you may encounter other invariant plasma parameters - derived observables that are independent of other variables in the system. Nimur (talk) 22:08, 11 January 2012 (UTC)

Buying a Telescope : list of celestial objects versus magnification required

My friend is planning to buy a telescope. Is there a site/page which lists as a table the magnification (and aperture or other parameters) versus the objects (planets, nebulae, saturn's rings, jupiter's red spot, its satellites, pluto ;) asteroids, comets) that can be seen. This to decide what magnification(and diameter) to buy assuming he already has a list of bare minimum celestial objects he wants to see. (Budget is also limited). I suggested that he visit a planetarium, but he wants to make it a regular hobby. Cplusplusboy (talk) 16:56, 11 January 2012 (UTC)

As a rule, you should completely ignore any mention of magnification when shopping for a telescope. Further, any telescope that puts the 'magnification' in the biggest type or in the most prominent place on the packaging gets a major red flag, and is apt to be toy store junk. (High magnification factors also make the telescope harder to aim, will need to be re-aimed more often as objects will move faster across the tiny field of view (unless you have a properly-set-up motor drive), make faint objects fainter by spreading out their light over a larger area, and accentuate any optical defects in the telescope or eyepiece.)

Our article on Apparent magnitude has a table with the brightnesses of a number of solar system objects (planets, asteroids, moons) as well as some important stars, galaxies, and nebulae.

The following web sites offer advice on buying a telescope:

• Astronomy Today] has an excellent, multi-part FAQ
• Heretic's Guide - offers quick recommendations for a given price range, though you really should get to the more-detailed (but still brief) FAQ.
• Scope Reviews has advice for the beginning amateur astronomer—it's worth it to scroll to the bottom of the page to see the 'reality check' comparisons between what you'll be able to see at the eyepiece and professional astrophotos.

A big consideration is how and where your friend plans to use his telescope. Some scopes will fit in a lunch box or a large purse, some need a van and three people to move. A lot fit between those two extremes. TenOfAllTrades(talk) 17:33, 11 January 2012 (UTC)

Just to explain a little further, far more significant than the magnification is the amount of light the telescope can collect, which means the size of either the mirror (reflecting telescope) or the objective lens (refracting telescope). A good telescope will come with a range of magnification options.--Shantavira|^{feed me} 17:50, 11 January 2012 (UTC)

Light is much much more important than magnification. Department stores usually display telescopes claiming to get something like 500x magnification, but that's just nonsense; while you may get the 500x magnification, all you'll see is extremely blurred images. Go to a proper store and get a decent light collecting scope. With patience and experience, you'll be able to see almost all the planets and many nebulae. Just don't expect too much out of a small telescope; you won't be able to see any features on Venus and Mars (Jupiter and Saturn look great though), and the nebulae take a lot of practice. You'll also be doing your friend a favor by gifting him a good, steady mount. Lynch7 18:19, 11 January 2012 (UTC)

To spend a fat wad of cash on a really nice telescope if you live in and will use it in an area with lots of light pollution would also be a waste. 69.243.220.115 (talk) 19:31, 11 January 2012 (UTC)

Partly true; where I live, the light pollution is so high that I've never been able to see Polaris in my life (not kidding there). But the Moon and objects near the zenith look great. Lynch7 19:38, 11 January 2012 (UTC)

I agree with previous speakers. Any good telescope will come with a set of exchangeable eyepieces and, using the right eyepiece, you can get any magnification you want. Whether you can see anything at that magnification, that really depends on the diameter of the lens/mirror.

You did not specify your budget, but, based on the description above, a 6-inch or a cheap used 8-inch reflector should do the job, a basic one of these could be had for about US$250 (if you opt for a manually aimed model, that is, without an electric motor and a computerized aiming system.) --Itinerant1 (talk) 20:44, 11 January 2012 (UTC)

Pure energy

Hi, in popular science settings I sometimes hear the phrase "pure energy". From what I can gather, this actually means electromagnetic radiation. Is that correct? Is there any other form in which so-called "pure energy" could exist? Furthermore, given the equivalence between matter and energy, how is electromagnetic radiation any more "pure energy" than, say, a lump of rock? 86.179.113.11 (talk) 18:40, 11 January 2012 (UTC)

I think you're right to be skeptical of the term "pure energy". Energy is a property of a system or an object, not an object or substance in and of itself. Everything which is known to exist always has additional properties besides energy. For example, photons have a nonzero spin. If you want to describe a particle with a zero rest mass, then the way to say that is that the particle has a zero rest mass. The phrase "pure energy" is meaningful as a disco group and as an album, but it's not a good physics term. Red Act (talk) 19:04, 11 January 2012 (UTC)

Interestingly, the Turkish word for "lip synching" is pronounced "positive energy". --Trovatore (talk) 19:07, 11 January 2012 (UTC)

Electromagnetic radiation isn't even pure energy, like everything else it has energy. For that matter, what is impure energy? Plasmic Physics (talk) 23:13, 11 January 2012 (UTC)

"wrought iron" vs "forged iron"

What is the difference between "wrought iron" and "forged iron"? Is there any? --82.113.98.208 (talk) 18:56, 11 January 2012 (UTC)

Wrought iron is an iron alloy with a very low carbon content, and fibrous inclusions known as slag. Forged iron is iron which has been forged. One term refers to the metal's composition, the other term refers to how the metal was shaped into the desired shape. Some wrought iron is forged, but not all wrought iron is forged, and not all forged iron is wrought iron. Red Act (talk) 19:17, 11 January 2012 (UTC)

It depends on the sense in which you mean wrought iron. According to our article, the term can refer to the composition of iron, or to the methods used to make a certain piece. The two are conflated, because iron products made by bending required the iron to be malleable enough not to crack. In particular, in modern usage, it seems to mostly apply to the method, not the source material:

"Wrought iron is no longer produced on a commercial scale. Many products described as wrought iron, such as guard rails, garden furniture and gates, are made of mild steel. They retain that description because they are wrought (worked) by hand."

For modern products, "wrought iron" usually means "mild steel worked by hand". SemanticMantis (talk) 19:28, 11 January 2012 (UTC)

steroids before steroids

Basically, I'd like to know whether there were other methods of chemically enhancing performance of athletes back before steroids were invented? How far back? What were these substances called? How effective were they?

An argument came up recenly in an online debate that I participate in that http://www.sandowplus.co.uk/Competition/Pandour/pandour.htm this guy, Bobby Pandour, could not have juiced because he died before 1927. Would he have access to drugs or whatever they called it in those days that improved performance (made his muscles bigger, etc.)?

Thank you, Agtren. — Preceding unsigned comment added by 68.8.168.251 (talk) 23:20, 11 January 2012 (UTC)

Are identical twins common in any non-mammalian species?

I understand that identical twins are common in mammals such as cats, sheep, ferrets, and deer. Are identical twins common in any non-mammalian species?82.31.133.165 (talk) 23:29, 11 January 2012 (UTC)