Wikipedia:Reference desk/Archives/Science/2011 March 14

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March 14[edit]

Best tsunami strategy for boats?[edit]

Assuming you had warning, like everyone on the US west coast did, what would be the best strategy for minimizing damage to your vessel? It seems to be that heading directly out to sea would be the best choice, in order to get past the point where the tsunami begins to stack up and form a real wave. Out in open water the tsunami is only a meter high, or even less, with an enormous wavelength, right? Leaving your boat moored would be the worst choice, would it not? The Masked Booby (talk) 02:17, 14 March 2011 (UTC)

Heading out to sea is definitely the best choice. That's what most of the fishing boats in Crescent City did, as I understand it. Many, though, for various reasons were not able to do it. Looie496 (talk) 03:33, 14 March 2011 (UTC)
Concur with Looie496. See Tsunami Safety Rules (3rd from bottom), which recommends "move your vessel to deeper water (at least 100 fathoms)." But you might also take your vessel out of the water, if possible. Several fishing ports received signficant damage to vessels in port and infrastructure. See also:
Tsunami's are barely noticable in the deep ocean, so the best advice is to take it out to sea. There was an expert on NPR shortly after the earthquake discussing the physics of tsunamis and how they differ from ordinary surface waves; a Tsunami may have an amplitude of several meters, but a wavelength of 300 kilometers in the open ocean. In other words, while the crest of the wave may be taller than your boat, that crest is spread out over 300 kilometers or so; meaning that the effect of the tsunami passing under you will be negligible and indetectable. When the tsunami reaches the continental shelf, the wave gets backed up, meaning that by the time it reaches land, much of that wavelength has been "pushed together" resulting in a huge, devastating wave; so the key to surviving on a boat is to get the boats out to deep sea. --Jayron32 23:58, 14 March 2011 (UTC)

How far inland did the Sendai tsunami wave travel?[edit]

How far inland did the Sendai tsunami wave travel? —Preceding unsigned comment added by (talk) 03:33, 14 March 2011 (UTC)

Most places are saying "More than 5km". APL (talk) 04:22, 14 March 2011 (UTC)
Likely too early for a really reliable source, but see "At the scene" sidebar here. BBC reporter claims 10km (six miles), ref from 2011 Sendai earthquake and tsunami - 220.101 talk\Contribs 17:51, 14 March 2011 (UTC)
"BBC reporter claims 10km (six miles)" Ok lets do the maths on that!!

reporter = divide by 2 = 5km BBC = reduce by 20% = 4km (American media reduce by 40% Australian reduce by 55%) Bigredtoe (talk) 19:24, 14 March 2011 (UTC)

Actually 4 km would match the extent of tsunami sand deposits on the Sendai plain from previous large earthquakes, like the 869 Sanriku earthquake and tsunami. Mikenorton (talk) 19:21, 15 March 2011 (UTC)

A wave question[edit]

Dear Wikipedians:

I had been working on the following wave question:

If a sinusoidal wave has a frequency of 479 Hz and a velocity of 373 m/s, what is the distance between two points that differ in phase by π/3 rad?

My solution is as follows:

λ = v/f = 373/479 ≈ 0.7787

d = λ(π/3)/(2π) = λ/6 ≈ 0.1298 m

However, I am not too sure how valid my second step is, I basically reasoned that the phase difference tells me how much of the 2π cycle is taken up by the horizontal distance between the two points, so that the proportionality would allow me to find the original horizontal distance between the two points. Is this valid?

Thanks, (talk) 03:35, 14 March 2011 (UTC)

Your method of calculation looks OK. Graeme Bartlett (talk) 06:52, 14 March 2011 (UTC)
Yes, you are correct right down to rounding the answer to 4 decimal places. Cuddlyable3 (talk) 13:17, 14 March 2011 (UTC)
The answer is correct but incomplete. The full answer is d = λ |1/6 + n|, where n is any integer. Dauto (talk) 23:43, 14 March 2011 (UTC)

Lack of preparation for foreseeable events at nuke plants[edit]

(Title of thread changed from "Explosimeters: broader issues) There has reportedly been a second hydrogen explosion at a Fukushima 1 nuke plant (Unit 3, after the earlier Unit 1 explosion), blowing off the masonry walls and roof around a reactor containment. An Explosimeter or combustible gas detector is a gadget which detects when any combustible gas has reached the lower explosive limit of admixture with air. Utilities have used them for many decades to test tor combustible gases in enclosed spaces. Hydrogen detectors are also time tested devices. Do Japanese nuclear plants not have them installed in the outer containment buildings? If they had them, why wouldn't they vent the enclosures with outside air to keep the concentration below the amount which could cause the two violent explosions observed, each of which reportedly injured several workers? Areas which might have combustible gases usually are required in the US and Canada to have all switches, relays and contactors fully enclosed so that a spark cannot ignite an explosive gas mixture. Is thus a not a rule in Japanese nuclear plants? How can they allow two giant explosions in 2 days? Hydrogen is not an exotic substance. Large power generators (not reactors) have been filled with hydrogen for low viscosity cooling of the windings for maybe 80 years, and blowups or fires are rare because hydrogen leaks or buildups are detected and ventilated. There was a hydrogen bubble in the Three Mile Island reactor vessel, but it did not cause an explosion to demolish the building. They had the sense not to just vent it into the containment building and wait for a spark. Edison (talk) 04:17, 14 March 2011 (UTC)

They might not have wanted to risk contaminating the area with radioactive "stuff" by venting the enclosure? —Ruud 05:33, 14 March 2011 (UTC)
Nils J. Diaz, a nuclear engineer who led the United States Nuclear Regulatory Commission, blamed it on the Japanese perfectionist culture. [1]F (talk) 11:15, 14 March 2011 (UTC)
Agreeing opinion on not wishing to contaminate the surrounding area here. Nanonic (talk) 15:29, 14 March 2011 (UTC)
According to Fukushima I nuclear accidents#Explosion of reactor building: "Safety devices should ignite the hydrogen before explosive concentrations are reached but apparently these systems failed." —Ruud 05:39, 14 March 2011 (UTC)
Isn't it quite easy to put a number of large slow-burning candles in high places to ignite the hydrogen gas? -- Toytoy (talk) 12:09, 14 March 2011 (UTC)
I'm not sure they can get in to the vessel in question. And yes, I think the problem with venting is that the stuff in the reactor building is generally stuff you don't want to vent. --Mr.98 (talk) 14:31, 14 March 2011 (UTC)
So you let the thing explode instead? Sorry I just don't get the reasoning. Vespine (talk) 22:41, 14 March 2011 (UTC)
After the power fails, the backup power fails, the back-up back-up power runs out - what do you have left to run the ventilation? They brought in fire trucks to pump seawater into the reactors - until it ran out of petrol and may have resulted in a partial meltdown in unit #2. These are very desperate measures. (talk) 23:40, 14 March 2011 (UTC)
Yeah, better to let an explosive hydrogen air mix accumulate and blow the upper portion of the building off and injure people and damage pumping equipment at the adjacent reactors. Not. A completely forseeable and automatic sequence of events: they let the coolant drop below the fuel, the zirconium cladding oxidizes, hydrogen is generated as pressure in the inner reactor vessel builds, they vent hydrogen into the upper masonry enclosed space to reduce pressure in the inner reactor vessel so water can be pumped in, an explosion results when there is a spark (why allow a spark?) An alternative would be to knock 2 holes in the masonry and attach a fan powered by a portable generator, if they were so idiotic as not to have allowed for a power failure. Then the upper structure would never have accumulated an explosive hydrogen/air mixture. Power plants took great pains to avoid explosive hydrogen accumulations in battery rooms since the 1880's. How could 1970's reactor design have been so behind the times? And no one anywhere has broached the dangers from embrittlement of the metal inner reactor vessel due to years of neutron bombardment, which was a concern for reactors such as the GE Mark 1 reactors even back in the 1980's. If the steel is embrittled, and they negligently allow the water to drop below the core, then the fuel gets to several thousand degrees, then they pump in cold water, the reactor vessel is apt to fracture, leading to more problems, such as the loss of cooling water, the complete melting of the fuel, its melting through the concrete into the soil below the reactor, and a steam explosion releasing Chernobyl amounts of radioactive material. The plant operators also lost the cooling pumps on one reactor when they ran out of diesel fuel. (Gee, we should have ordered some fuel). Now a third reactor has had a hydrogen explosion which blew off the top of the building. Anyone see a pattern? Edison (talk) 01:05, 15 March 2011 (UTC)
There is no need for a spark - the vented steam is hot enough to self ignite as soon as it finds oxygen. Ariel. (talk) 01:18, 15 March 2011 (UTC)
If there were a red hot igniter by the vent, or if the vented steam were hot enough to ignite hydrogen in oxygen, then why wouldn't the hydrogen have burned off harmlessly (save for warming the enclosure)? Thus no explosion would be possible, which is counterfactual.Perhaps the vented steam was not hot enough to ignite hydrogen. Please reanalyze. How did there accumulate a sufficient inventory of unburned hydrogen to blow the sturdy masonry structures to flinders? The structure must have remained below the lower explosive limit while steam and hydrogen vented until an explosive mixture evolved, or until there was an ignition source. And how was this not foreseeable? Edison (talk) 01:27, 15 March 2011 (UTC)
There was no oxygen in the vented gas. It took a while to mix with ambient air (and probably cooled in the process). Then some fresh, hot, gas got vented and set off the whole thing. And not only was it foreseeable, they knew it would happen, but did it anyway because the outer building is unimportant. Also, I've seen no suggestion at all that they ran out of fuel (it makes no sense that they did since it's not that hard to send some fuel). Ariel. (talk) 01:48, 15 March 2011 (UTC)
"Unimportant?" It injured numerous workers and impaired pumping efforts at adjacent reactors, thus "IMPORTANT." News reports indeed said that the pumps at one reactor stopped because they ran out of fuel. I agree that the Japanese government (or most world governments) would likely have cheerfully transported some fuel if the folks in charge had requested it in a timely manner. You didn't hear about it? See [2] "Later in the day, a backup pump to a third reactor ran out of fuel, causing water levels to fall so low that the fuel rods were fully exposed." In a nuclear reactor, anyone with any knowledge at all of their operation would agree that letting the cooling water drop below the recently used fuel rods was an extremely bad idea, to be avoided at all costs. Edison (talk) 01:58, 15 March 2011 (UTC)
It's really too bad. With the latest news of a leak it looks like nuclear power may be delayed again in the US, and I'm not happy about that. I live in an area with lots of pollution from coal plants, and I would gladly trade the certainty of health problems from hydrocarbons for the risk from a nuclear plant. Ariel. (talk) 03:32, 15 March 2011 (UTC)
More precisely, the plants were designed with an electrical burner on the vent to burn off any hydrogen that was vented. Of course, with the total loss of power, that wasn't working. Dragons flight (talk) 11:17, 16 March 2011 (UTC)
I'm not sure that they have as much control over the reactor facilities as you seem to think. Sensors and vents are only useful if they're functioning and still connected to their control systems. APL (talk) 04:11, 15 March 2011 (UTC)
The lower explosive limit for hydrogen gas in air is 4%, per Flammability limit. "Control over the reactor facilities" could amount to mechanically breaching the wall of the upper nonpressure structure, or having a pair of sealable bulkhead doors which could be opened from some distance via a lever or cable. Air flowing through would then have kept the hydrogen concentration below 4%. The concept of a "hatch" is not exotic sci-fi. What is the point of having a masonry structure which cannot be ventilated when the basement floods (foreseeable) and electrical panels are shorted out (electrical fires are foreseeable and occur somewhere every day), with the pressure vessel (foreseeably containing hydrogen) vented into the structure rather than the great outdoors? Why not vent out through the roof rather than into the building? What was supposed to happen to the hydrogen inside the masonry building other than achieving an explosive concentration? The consequence of not being able to vent the hydrogen is that numerous workers have been injured by the explosions, and now the workers at the plant have reportedly exposed to radiation levels (400 mSv per hour, or 40 Rem per hour) which could cause radiation sickness in 2.5 hours or death in 12.5 hours of exposure. (I hope they are shuttling workers in and out to limit exposure, but that does not make for continuity of action, and there are only so many workers with knowledge of a plant and training to take needed actions there). Robots were used to a limited extent way back at the Three Mile Island cleanup. Do Japanese nuclear plants have any remote operated robots which could go in and do work such as extending a firehose to a spent fuel pool, or opening a valve? The authorities are now, in desperation, asking for helicopters to fly above a hazardous radiation zone and drop water on a spent fuel pool which had previously boiled away water allowing the burning of spent fuel. There are search and rescue robots and firefighting robots which could be introduced into a high radiation building and controlled from a safe distance, to extend a hose to a spent fuel pool from which the water is boiling away. Edison (talk) 15:58, 15 March 2011 (UTC)
Nuclear experts in the 1970's and 1980's noted weaknesses of this design, said there was a high probability of the vessel and containment bursting soon after a core melt, and said the concrete containment structure was not strong enough in the event of a cooling failure. Edison (talk) 18:11, 15 March 2011 (UTC)
Ah, the experts speak, per CNN at 22:37 GMT, March 15: "Plant managers were considering removing panels from the buildings housing those reactors in an effort to prevent the hydrogen buildup that officials believe caused the other explosions, the IAEA said. Edison (talk) 23:48, 15 March 2011 (UTC)

The optical properties of ptfe (teflon)[edit]

I am trying to find optical properties/ transmittance data for virgin (opaque) PTFE. Many web sites have mechanical properties but no optical. I wish to use PTFE sheet as a diffuser to measure solar radiation. Is this data available? It is not included in (talk) 05:06, 14 March 2011 (UTC)

Characteristics of crab nebula[edit]

i read in "astrophysical concepts "by (martin harwit) that the cloud which we see there in crab nebula containes pieces in volume some cube meters . thus it cannot be dust , is it so in other references?[ that was in last my question replyed it is such as oven and low density dust] akbar mohammadzade march 2011 -- (talk) 06:45, 14 March 2011 (UTC)

I can't find that in my copy of Harwit (4th edition). In which section did you find that statement? --Wrongfilter (talk) 08:53, 14 March 2011 (UTC)
that is third edition 1988 chapter nine 9-1 page420 mohammadzade(cicular and about some ten cube meter ) —Preceding unsigned comment added by (talk) 10:53, 14 March 2011 (UTC)
Third edition is on google books, but page 420 is in Chapter 10. The relevant bit in 9.1 should be here but this doesn't mention grain size. Are you sure that the number you mention doesn't refer to a density? --Wrongfilter (talk) 11:41, 14 March 2011 (UTC)

Evolution of the solar core?[edit]

The solar core is currently about 150 times denser than water, at 15 million kelvin. Over the next five billion years the Sun will gradually get hotter and larger, which I assume means that its core must get hotter and denser. As I understand the Wikipedia articles, eventually the Sun becomes a red giant following the asymptotic giant branch, until the core consists of degenerate matter and undergoes a helium flash that drives it out on the horizontal branch, but only temporarily. Apparently multiple ? helium flashes at the end of the process end up converting these huge outer red giant layers into a planetary nebula, leaving behind the degenerate core as a white dwarf.

What I wonder is, how does the solar core evolve over this process? How does its heat and density change over the billions of years before the sun becomes a red giant? How quickly does it collapse to degenerate matter as the red giant phase sets in?

Last but not least, for a sci-fi story I'm writing, I'm curious whether it is possible to save the core of sun-like star once it starts to become denser and/or hotter. For example, if you could somehow make a red dwarf star collide with the sun, would that provide fuel and abort the red giant stage in some semi sane period of time (by which I mean, less than 105 years, which I think is what it would be...[3]) If you could somehow inject the hydrogen from the star all the way to the core could it help? (though my favored hyperdrive would be hard to use that way...) Wnt (talk) 08:04, 14 March 2011 (UTC)

Regarding "...its core must get hotter and denser", getting hotter would cause it to expand, reducing density. As for adding more hydrogen, that sounds like it could work, if you can mange to carry another star there. I would think the hydrogen would find it's way to the core on it's own. StuRat (talk) 11:52, 14 March 2011 (UTC)
Stellar structure is a good place to start. StuRat's understanding of the hotter/denser issue is correct over short time scales, but fails to take into account the change in stellar core composition as the star ages. In stars similar to our Sun, the core never quite gets hot and dense enough (while it is on the main sequence) for it to start burning appreciable amounts of helium; this helium accumulates in the core, increasing the core's density. Because of this increased density, there is increased gravitational compression of the fusing material at the core, and the core gradually gets hotter as the star ages.
On the issue of how to get fresh hydrogen to the core, I'm afraid that dumping it on the surface won't work for a star like our Sun. While there is significant convective transfer of material in the Sun's outer layers, there's actually very little exchange down into the core. (Note that adding hydrogen at the surface could work for very small stars, less than 0.4 solar masses. In such stars there is convective transfer all the way down to the core—though I don't know how rapidly that exchange of material takes place.) TenOfAllTrades(talk) 13:54, 14 March 2011 (UTC)
Wow. I just read that the Sun is expected to go red giant when just 12 percent of its hydrogen is used up.[4] Yet according to red giant, I have the impression that all of the hydrogen in the core is used up. Which I think means that the core, like Tantalus, is surrounded by a near endless sea of compressed hydrogen, but in 10 billion years it never gets to drink. Which kind of kiboshes the red dwarf idea, unless maybe if it's moving really fast... Wnt (talk) 22:33, 14 March 2011 (UTC)
StuRat got it wrong. Stars actually get hotter when they get denser and get cooler when they expand due to gravitational potential energy released during the compression (or taken away during the expansion). Also, it is true that a sun sized star becomes an iland of helium surrounded by a lake of hydrogen and that the hydrogen of the added star wouldn't reach the central part, but it would increase pressure and temperature at the boundary between the core and the envelope allowing more hydrogen to burn. The island would expand at the expense of the surrounding lake, so to speak. I like the Tantalus analogy. Dauto (talk) 00:30, 15 March 2011 (UTC)
They get hotter when they get compress, yes, but then this increased heat makes them expand, reducing density. Thus you can get short term cycles of expansion and contraction as these two forces battle each other. StuRat (talk) 01:47, 15 March 2011 (UTC)
Cycles can happen in some situations but it is much more common to reach an equilibrium where higher densities correspond to higher temperatures. Stars are somewhat counter intuitive thermodynamic systems because they have negative heat capacity. Dauto (talk) 01:51, 15 March 2011 (UTC)
To expand on my earlier comment, the core gets denser and hotter as its helium content increases. The correspondingly increased energy output causes the expansion of the star's outer layers, increasing the star's overall diameter but also decreasing its surface temperature. Even while still on the main sequence, stars like our sun get slightly larger, slightly more luminous, and slightly redder as they age. TenOfAllTrades(talk) 12:25, 15 March 2011 (UTC)
It should also be said that lack of hydrogen in the star in general is not the issue with the "running out of fuel" because the driving fusion is really only happening in the core. When the core hydrogen runs out, the star begins to break out of the Main Sequence and swell, but there's still plenty of hydrogen outside the core - it just doesn't get in there - the core finds a more profitable fusion into higher elements, all the way up to iron, but the problem is that in doing this the energy release is much much lower, so the star cools.
As for the sci-fi, it's an interesting question, but as explained you can't just pump in hydrogen. Colliding it with a red dwarf will destroy the Solar System, first by gravity and then by big explodey thing, but it may actually get things mixed around the extend the fusion process in the star quite well. However, stars are very beautiful, very uniformly-behaved things, and messing with their structure to that extent will have largely-unpredicted consequences (i.e., fiction fodder?). My suggestion: if you have all that energy available, use it to push Earth's orbit back away from the Sun as it expands.
Oh wait, one more solution - you might be able to extend the star's lifespan stably if you can get it to accrete material off of a more-massive structure that you place in orbit. The problem is still that the new structure's gravity and heat (it's a star) will also destroy the Solar System. Keep us updated if you get any ideas. SamuelRiv (talk) 08:47, 15 March 2011 (UTC)
These people live inside the star, so the solar system isn't an issue. ;) Wnt (talk) 15:14, 16 March 2011 (UTC)

My BS detector ...[edit]

[During the Gulf War of 1991] ... Lieutenant Commander Michael Riley was monitoring the radar screens onboard the HMS Gloucester ... he noticed a radar blip off the Kuwaiti coast. ... He couldn't explain why, but the blinking green dot on the screen filled him with fear; ... [It was heading for USS Missouri ] ...
... The radar blip was located in airspace that was frequently traveled by American A-6 fighter jets, ... It looked exactly like an A-6 on the radar screen. ... the A-6 pilots had gotten into the bad habit of turning off their electronic identification on their return flights. ... the pilots opted for the cloak of silence over Iraqi-controlled airspace. ... [The only way to tell], they could determine the altitude of the blip. ... the type of radar that Riley was using didn't provide him with any altitude information. If he wanted to know the height of a specific object, he had to use a specialized radar system known as the 909 ... Unfortunately, the 909 radar operator had entered an incorrect tracking number shortly after the blip appeared, ...
... Riley issued the order to fire; two Sea Dart surface-to-air missiles were launched into the sky. ...
[The target was shot down.] ... the captain of the HMS Gloucester entered the radar room. "Whose bird is it?" he asked Riley, wanting to know who was responsible for destroying the still unidentified target. ... The results of the investigation were in: the radar blip was a Silkworm missile, ... Riley had single-handedly saved a battleship.
... [The British naval officers could not distinguish between the Silkworm and a friendly A-6. based on the records, until] ... the summer of 1993, when Gary Klein started to investigate the Silkworm affair. ...
... Because Riley's naval radar could pick up signals only over water -- after a signal went "wet feet" -- he was accustomed to seeing the fighter jets right as they flew off the Kuwaiti coast. The planes typically became visible after a single radar sweep. ... Unlike the A-6, the Silkworm didn't appear off the coast right away. ... it wasn't visible until the third radar sweep, which was eight seconds after an A-6 would have appeared. Riley was unconsciously evaluating the altitude of the blip, even if he didn't know he was doing it.
... There was something strange about this radar blip. It didn't feel like an A-6. Although Riley couldn't explain why he felt so scared, he knew that something scary was happening. This blip needed to be shot down.

-- How We Decide (2009) by Jonah Lehrer, pages 28 to 32

This story turns on my BS detector. I find following points very suspicious:

  • How could a radar operator fire two Sea Dart missiles and the captain did not know it?
  • Could he be in a room other than the bridge?
  • The Sea Dart's homing radar is exactly the 909 mentioned in the story. How could he know nothing about the altitude?
  • If I were an A-6 pilot and I turned off my IFF for whatever reason, why don't I turn it on if I am being locked by a British targeting radar?
  • Now, if a British radar operator used the 909 radar to lock on an unknown target, would the target turned on its IFF if he's a U.S. A-6?

The author only cited two of Gary Klein's books in his bibliography, The Power of Intuition. New York: Doubleday, 2004. and Sources of Power. Cambridge: MIT Press, 1999. I have neither of them. I checked for the index of the first book. It probably does not talk about Riley's instinct.

The author also cited Finlan, Alastair. The Royal Navy in the Falklands Conflict and the Gulf War. London: Routledge, 2004. This book mentioned Riley's story. However, it quoted The London Gazette that reads: "the ship's operation room team swiftly assessed the contact as a Silkworm missile". And it also said the missile's target was another ship beyond USS Missouri. (page 147) And the HMS Gloucester's phalanx (close-in defense system) sprayed several rounds on the USS Missouri even though no one was injured. (Now I added links!) -- Toytoy (talk) 14:30, 14 March 2011 (UTC)

The book is yet another example of the avalanche of pulp-non-fiction comming from America - very verbose quasi-textbooks that are based on dubious reasoning. They often tell things as a folksy story focused on personality. Bin them. (talk) 12:53, 14 March 2011 (UTC)
Without dredging up a full technical explanation, I'll offer something a little more substantial than 92.x's response.
  • "How could a radar operator fire missiles without the captain knowing?" First, the officer in question isn't the radar operator; a lieutenant commander is much too high a rank for that position (the operator likely isn't a commissioned officer). Rather, he's probably the second- or third-ranking officer on the ship. It's entirely reasonable that he could be the officer presently in charge. The captain can't be on duty all the time, and his subordinates will regularly give orders in his name (though they'd better not be orders that the captain needs to countermand, else those subordinates won't have a long career). Destroying an inbound missile is the sort of thing that requires a response too quickly to summon the captain if he's not presently on duty.
  • "Could he be in a room other than the bridge?" The combat information center (CIC) is another logical possibility, depending on how the Gloucester is laid out. But I think this is tied to the above, and so the particular physical locations aren't really important.
  • "The Sea Dart's homing radar is the 909..." You appear to be conflating the radar on the missile (used after launch) with one of the radars on the warship (used before launch).
  • "If I were an A6 pilot, wouldn't I turn on IFF?" You're an A6 pilot who's running under EMCON to avoid detection in enemy airspace. Your IFF is off, and all mission long you've been picking up enemy radar signals. Now you're headed home, and you're apparently lazy about turning your IFF back on -- what's one more indication of a radar signal? Your aircraft doesn't report "US radar" vs "British radar" vs "Soviet radar", it just reports "radar". Additionally, you're flying in a corridor that has undoubtedly been designated as "this is where A6s fly back; don't shoot the A6s".
  • "If a British operator locked onto an unknown target..." See above. Additionally, IFFs are generally left in an "on" or "off" setting. Pilots are usually not in the habit of fiddling with the settings on accessory electronics while flying in a combat zone. There are certainly going to be rules of engagement to reduce friendly fire beyond whether or not an IFF switch is in place (note also: what if the IFF has sustained battle damage? It's not a magic fix-friendly-fire box that never fails).
While I can't vouch for the veracity of the thing, it's not overtly a "verbose quasi-textbook based on dubious reasoning". Hope that helps. — Lomn 13:56, 14 March 2011 (UTC)
Sorry, after looking at the pages available on Amazon, it looks that way to me. It certainly is a folksy story based on personality, and is written in a very verbose manner. And, unless the author was sitting or standing there witnessing events in the command room or whatever, or is paraphrasing a witness stement, then the details must be from the author's imagination. If these things had all the uninformative padding cut out, I'd be more inclined to read them, and they'd provide a better service for the world. (talk) 14:08, 14 March 2011 (UTC) (talk) 14:02, 14 March 2011 (UTC)

According to "The Royal Navy in the Falklands Conflict ..." (p. 417), the incoming Silkworm missile was spotted by a "junior seaman". This book says HMS Gloucester's Phalanx CIWS gave USS Missouri a couple of rounds. On another web page (, see section I. Ship-to-Ship Incident), it was USS Jarrett (FFG-33)'s Phalanx that was having a good time shooting at a chaff from USS Missouri. Wikipedia's article also said so. Anyway, all the ships in that area were engaging that missile. And they knew it. This book is crap. -- Toytoy (talk) 14:47, 14 March 2011 (UTC)

Again, with reasonable speculation:
  • "Junior seaman" vs "lieutenant commander": The seaman is actually operating the radar. He says "Commander, there's an unidentified contact." Pretty simple discrepancy.
  • "Just Gloucester engaging" versus "all ships engaging": The Sea Dart has an engagement range of miles, the CIWS an engagement range of (admittedly lots) of meters. There's plenty of time for Gloucester to engage the target, alert the other ships, and those ships activate their close defenses before the missile is destroyed -- but the rough overview I see never indicates that Jarrett's CIWS was in position to engage the missile before Gloucester destroyed it. "All the ships were engaging that missile" is a somewhat different statement from "Gloucester was engaging that missile, and the other ships were alerted to its presence".
  • "Gloucester's CIWS hitting Missouri": based on other stuff, I think this is a typo for Jarrett's. We note at the Sea Dart article that Gloucester's engagement was tail-end, that is, after the missile passed Gloucester en route to Missouri. I can't think Gloucester's CIWS would have been in range. — Lomn 19:15, 14 March 2011 (UTC)
The USS Missouri article seems to say that the Silkworm and Jarrett incidents occurred on different days. But it may just be poorly written. (talk) 23:30, 14 March 2011 (UTC)

Here are the three pages from "Royal Navy in the Falklands Conflict and the Gulf War: Culture and Strategy" (2004):

FYI -- Toytoy (talk) 01:48, 15 March 2011 (UTC)

I used to work with the Chief Gunner that launched those weapons, and the description above doesn't really reflect the decision process. But to respond to the specific points.

  • The question from the CO applied to whose bird took down the Silkworm, GLOU wasn't the only potential shooter. The launch would have been noted by the CO, but he wouldn't know whether they were the only ones in the air.
  • The CO had been in his cabin, two decks up from the Operations Room. The Lieutenant Commander would have been the Anti Air Warfare Officer on watch. ships of that class carry two, and the on watch AAWO is responsible for fighting the air battle. It's a while since I discussed it by I also think he was Anti-Air Warfare Co-ordinator.
  • The T909 is a pointing radar and can be used to determine altitude, but it needs to be allocated to the correct track. It does strike me as odd that it could be allocated to the wrong contact yet the birds engaged the correct one. The Sea Dart rides a reflection from the target back. It's not out of the question that the narrative conflates the decision process with the launch process that assures the correct target prior to launch.
  • Can't comment on IFF as it would have depended on the protocols in force at the time. Nowadays IFF is required at all times, but there were changes in the 90s after a number of fratricide incidents during Granby.

ALR (talk) 10:38, 15 March 2011 (UTC)

Thank you for you input. My educated guess is that the British 909 radar caught the right target immediately. Possibly Riley's radar operator first noticed the suspicious blip and his suspicion was confirmed by 909's correct reading on the correct target. Based on radar operator's correct decision, Riley (very likely the AAWO on duty) gave the order to shoot down that bird. However, he was not sure. He was afraid that he killed a U.S. pilot. In the end, he was proven right.
The author distorted many vital parts of the story to make his point. There is no way the 909 radar would point at the wrong target and then the Sea Dart could hit the Silkworm. And there were two Silkworms instead of one. The U.S. boats also knew it and opened fire. I will never buy a book by this author.
Now, why didn't the Iraqis set their Silkworms to fly at the A-6s' altitude? Since these A-6s tend to turn off their IFFs all the way, these Silkworms could easily fake it into the fleet if they flew just a little higher. Why didn't they do this?
I think if Riley had the power to fire, he was not supposed to read the radar by himself. The radar operator was not supposed to be the decision maker. It was the nameless radar operator who noticed the strange-looking blip. Maybe he asked Riley to see it. But it's very unlikely that Riley was the radar guy. The observer and the decision maker shall not be the same person. Either Riley was the radar guy, or Riley was the AA guy. I think it is against any navy's policy to let the observer make the decision. -- Toytoy (talk) 18:08, 15 March 2011 (UTC)
The T909 doesn't "catch", it's a pointing radar rather than surveillance so needs to be allocated to a specific track number in the combat system. Also the air picture involves three individuals, although there are more than that. There are three Air Picture Compilers, an Air Picture Suprvisor and the AAWO. There is then the missile team.
In terms of process the AP team support the AAWO to identify the target, that's then prosecuted by the weapons team. The T909 can be used in picture compilation, but it's intended to be the weapon direction radar. Given that the processes are well documented it's entirely reasonable that one of the two T909s was used to identify altitude, and the other one was used to direct the missiles.
ALR (talk) 22:18, 15 March 2011 (UTC)

nuclear plant questions[edit]

Two questions from the incident at Fukushima. That BWR has a torus shaped pool, any reason it is in that shape? Why is zirconium used as cladding when it will produce hydrogen in accidents? F (talk) 11:15, 14 March 2011 (UTC)

Zircaloy's major advantage over other cladding options is that it has a very low neutron absorption cross section. TenOfAllTrades(talk) 13:21, 14 March 2011 (UTC)
A torus is a reasonably pressure-resistant shape that fits nicely around the bottom end of a sphere (the reactor containment vessel). --Carnildo (talk) 02:16, 16 March 2011 (UTC)

Sound of the Japanese earthquake[edit]

I'm not happy with this as it says nothing about how speeded up it is, or how it has been treated or created. It also appears to be a compilation of different things.

While I appreciate that the "sound" could be the seismology record rather than actual noise, is anything better available? Thanks (talk) 12:48, 14 March 2011 (UTC)

They do say that it is based USGS XML feed, I figure they have converted acctual seismic readings to sound. Not sure, if ground vibration has any particular sound in reality ~~Xil (talk) 13:59, 14 March 2011 (UTC)
Seismic wave says they travel at a maximum of about 2 km/s. Human hearing's low end is about 20 waves per second. So it seems unlikely one could hear an earthquake itself. Of course there could be all kinds of other sounds one might hear. Pfly (talk) 07:41, 15 March 2011 (UTC)
Some earthquakes make a lot of noise, such as the 1929 Murchison earthquake, which was heard more than 250 km away. Mikenorton (talk) 13:16, 15 March 2011 (UTC)

Largest earthquake in human history[edit]

Within human history - say, looking at the period since the Toba eruption - is there any evidence of earthquakes having occurred which are larger than the 1960 Valdivia earthquake, which is the largest one listed at the Richter magnitude scale article? I am thinking of cases where there might be geological evidence of major sudden earth movements, which are interpreted as having been of greater magnitude than the ones recorded over recent centuries. Ghmyrtle (talk) 12:49, 14 March 2011 (UTC)

Given that the article dosen`t list any such theory, while listing other pre-historical catastrophes, I would doubt it. ~~Xil (talk) 13:25, 14 March 2011 (UTC)
Any what such theory? Matt Deres (talk) 13:39, 15 March 2011 (UTC)
Given the question below, I wasn't treating Xil's response as authoritative.  ;-) Ghmyrtle (talk) 14:05, 15 March 2011 (UTC)
That`s somewhat unfair - there is no connection between earthquakes and electricity ;) My point, though, is based on logic, not knowledge - if there was a reason to suspect such an earthquake, authors of that article would know, if not every geek who watches discovery - apparently it would cause global devistation. Given that it states that there is no known magnitude 10 quake, you would need 9.6-9.9 magnitude, which seems too small diffrence for estimiated magnitude. Yucatan meteorite strike seems to be closest thing to what you are looking for ~~Xil (talk) 13:29, 16 March 2011 (UTC)
I think the problem is that such quakes don't leave good geological evidence. The reason is that the fault typically continues to be active, and thousands of years of subsequent quakes right on top of the original obscure any record. Just from a statistical perspective, the chances of there having been a larger quake than one in 1960, since Toba, is well over 99%. StuRat (talk) 06:46, 15 March 2011 (UTC)
However, you can look at the earthquake record along subduction zones, which is where you get the largest continuous fault surfaces on earth, and try to estimate what is the largest area that could conceivably rupture all at once, the magnitude of an earthquake is mostly a function of the slipped area. Along all subduction zones there is evidence of asperities (areas of excessive fault 'roughness') that earthquake ruptures never cross, so it should be possible to predict the largest likely magnitude. Mikenorton (talk) 14:37, 15 March 2011 (UTC)

What would happen, if wet hair would get into contact with electricity?[edit]

I just washed my hair, and pluged in blowdryer, being carefull not to get my hair tangled around it the plug. Now what would happen, if it did - is it a freak death scenario, a light shock or maybe nothing to worry about? ~~Xil (talk) 13:26, 14 March 2011 (UTC)

To be electrocuted, you would need to have a complete electrical path from your hairdryer, through you, to ground/earth. If your wet hair got all the way to the heating elements inside the hairdryer, and tied in a knot around them, somehow, and if your wet, naked leg was held firm against a pipe under the sink, then you might get a shock, but I doubt if wet hair would conduct well enough to kill you. StuRat (talk) 13:37, 14 March 2011 (UTC)
Sorry, I should have paid more attention to what I wrote, I meant, if they got tangled around the plug and pushed into the outlet ~~Xil (talk) 13:49, 14 March 2011 (UTC)
The results would be the same. Hair isn't an electrical conductor, and the small amount of water on the surface would likely only conduct electricity well enough to give you a bit of a shock, before evaporating. StuRat (talk) 14:03, 14 March 2011 (UTC)
Wouldn't the addition of a thin layer of chemicals present in conditioner, shampoo, etc. to hair significantly increase its conductivity? Like adding a bit of salt to water? It probably wouldn't make much of a difference, it still needs moisture to conduct. Plasmic Physics (talk) 23:34, 14 March 2011 (UTC)
Well, absolutely pure water is an insulator, but only a small amount of impurities make it into a good conductor. I had already assumed this to be the case, and that the water was a good conductor. However, the small quantity on wet hair still seems insufficient to cause a fatality. StuRat (talk) 00:04, 15 March 2011 (UTC)
Is there any way it could be fatal? I mean here we assume smalla mount of hair gets into contact with electricity. Imagine an unrealistic scenario - let`s say very long and very wet hair get blown by wind onto power line? ~~Xil (talk) 02:07, 15 March 2011 (UTC)
I have a hard time seeing how. Perhaps, if you're writing a story that features electrocution death due to long hair, a better set-up would be if the person gets their hair caught in a dangerous area, say in a chain-link fence with a downed, but non-energized, power line draped over it, and are thus unable to escape before for the electrical system switches to a back-up transformer and re-energizes the downed line, killing them. Be sure to have both of their hands in contact with the chained-link fence, and them standing in a deep puddle in the rain, to explain how they would make good contact with the ground. StuRat (talk) 06:39, 15 March 2011 (UTC)

Thirsty nuclear reactor[edit]

At the Fukushima I Nuclear Power Plant, the source of their problems appears to be an inability to keep the core filled with water, due to it boiling off quicker than they can refill it, because the pumps won't work, due to lack of electricity. Is there any reason why such a water-front nuclear plant can't have the core built below sea-level, so that gravity can then be used to flood the reactor with sea-water, in an emergency ? StuRat (talk) 14:01, 14 March 2011 (UTC)

I already suggested undersea nuclear plants above. I expect the reason is that it would cost more and be more difficult to run and maintain. (talk) 14:13, 14 March 2011 (UTC)
They can flood the reactor with sea water (and boric acid) and are already doing so. The problem appears to be more complicated than that. --Mr.98 (talk) 14:27, 14 March 2011 (UTC)
They are trying, but, according to the article I linked to, they are unable to keep the reactor cores submerged. This is due to lack of electricity from the shut down reactors themselves, the grid, and the backup diesel generators. Unlike electricity, you don't have to worry about a lack of gravity in a quake zone, so having a gravity backup seems like a good idea, to me. StuRat (talk) 20:44, 14 March 2011 (UTC)
StuRat, reactors are already horribly expensive. As mentioned, the (I expect) extra cost of building "below sea-level" would very likely, be prohibitive, plus in all likelyhood not a good idea operationally. Many/most reactors are already near lakes or ocean for a good supply of water for cooling (see page 8), and it would thus likely require constant pumping to keep the facility dry. The cooling needs to be done in a very controlled manner, otherwise you may end up with a cloud of radioactive steam or an explosion as has happened in Japan. - 220.101 talk\Contribs 16:28, 14 March 2011 (UTC)
I can't imagine sump pumps being a major expense, relative to the cost of a nuclear reactor. The cooling could still be done in a controlled manner, by opening and closing valves that provide gravity-fed water. The explosions they had in Japan are apparently due to the build-up of hydrogen gas, as a result of the cores not being covered with coolant. StuRat (talk) 20:52, 14 March 2011 (UTC)
I wonder if 92.15's enthusiasm for undersea nuclear plants is warranted. Imagine the crisis if a reactor had a minor technical glitch, such as a leaking valve. Recent events been demonstrated that deep sea repairs are prohibitively difficult. Of course, we could put the nuclear reactor somewhere more accessible - such as on land - and just pump in the seawater as needed.
The problem is not a shortage of coolant - that is a gross oversimplification of the serious multiple-system-failure that is currently occuring in Japan. A trivial solution is to flood the reactor with thousands of tons of coolant-water, and vent the resulting steam into the atmosphere. The fission reactor will rapidly cool, but a massive cloud of possibly radioactive steam will form - and it's not easy to estimate whether that is a safe action to take.
Many things are currently broken in the reactor, not just the coolant system. The problems could be better described in the following brief way: how do we maintain nuclear radiation containment while exchanging thermal energy rapidly enough to cool the reactor? More to the point - how do we perform the needed maintenance in a safe way, under the assumption that certain critical safety-systems might be malfunctioning? Nimur (talk) 18:02, 14 March 2011 (UTC)
I believe that the lack of coolant in the reactor cores was a critical point in the chain of failures leading to the current problems. As for underwater repairs, I believe any reactors (like the current ones) that need to be flooded with seawater are then decommissioned. Release of radioactive steam is a concern, but is preferable to a melt-down. StuRat (talk) 20:59, 14 March 2011 (UTC)
This discussion has been closed. Please do not modify it.
The following discussion has been closed. Please do not modify it.
It's so unfortunate, StuRat, that you're over here, playing armchair reactor engineer on Wikipedia, rather than over there in Japan, where you could tell them what to do and how easy it could be. Amazing how much talent is on here for designing and operating reactors! Who knew? --Mr.98 (talk) 21:04, 14 March 2011 (UTC)
I do have an engineering degree. It's mechanical, rather than nuclear, but simple mechanical problems, like how to move water, do seem to be at the core of this situation. Also, your reply seems to be saying "leave it all to the experts, they know what they are doing". Unfortunately, blind reliance on "the experts" can lead to all sorts of problems, like the current one. If they are certain that the public isn't paying attention, then they can cut corners and nobody will know, until the inevitable accident, by which time they will likely be retired. Lack of public oversight, like absolute power, corrupts absolutely. You might think that Japan's equivalent to the Nuclear Regulatory Commission would ensure that the plants are safe, but the same issues also apply to them. If the public isn't monitoring them, and forcing them to do their jobs correctly, then they won't, via regulatory capture, bribery, and other means of corruption. StuRat (talk) 06:33, 15 March 2011 (UTC)
And now you're an expert in regulation, and on Japan's nuclear industry! Please, StuRat, soapbox away! Who cares if you're just making it up as you go along... My reply does not say "leave it to the experts", it says, "you are way out of your depth"! I contend you understand neither 1. nuclear reactor engineering in general, 2. these reactors in particular, 3. the current accident except in the most superficial of terms, and 4. the Japanese nuclear industry not at all! The experts may occasionally get it wrong, but their track record is infinitely better than people on the internet who make it up as they go along! --Mr.98 (talk) 03:00, 15 March 2011 (UTC)
And what qualifies you to judge my level of expertise of nuclear reactors ? Do you have a degree in nuclear engineering ? Or are you doing the exact same over-reaching you accuse me of ? StuRat (talk) 06:33, 15 March 2011 (UTC)
Guys, nobody's challenging your qualifications. I'm sure both of you could, with sufficient specialization, be qualified to work on a nuclear reactor, with or without the on-paper "nuclear engineering" degree. The real issue is that none of us have good, complete information about the current situation. As much as our 24-hour internet-news deludes us, the actual event is very far away - and every piece of information we receive is probably funneled through a journalist who mangles up the "unimportant technical details." Unless anyone has a schematic of the particular plant, with an up-to-date assessment of the exact systems that fail, it's moot for any of us to debate the "best solution." For better or worse, we have no option except to "trust the experts" at this point. If any of you guys think you'd be well-qualified to fix the disaster, you should have pursued a full-time career as a nuclear engineer, and further specialized in crisis-response, and then sought a position with the appropriate commercial contractors or government institutions; then you could be involved in the on-the-ground technical response to the current disaster. But since none of us have done that, the best we can do is try to parse through the mangled web of misinformation that the CNNs of the world trickle back to us - understand that there are technical, language, cultural, and time barriers that all severely inhibit our ability to correctly understand the actual problem at the nuclear plant. With due respect to involved parties, I'm hiding this discussion, in the hopes that we can cool off and apply whatever technical qualifications we do have to help provide reliable reference-information for other concerned readers of the Science desk. Nimur (talk) 14:41, 15 March 2011 (UTC)
This has been my point the entire time. It is one thing to ask, "why is it so," or "what is going on?" It's another to assert things that are simply not true, and to grandstand about things one knows nothing about. And StuRat, it is obvious from your assertions that you know nothing about the details on which you are holding forth. It is trivial to tell when someone is making stuff up as they go along, far easier than actually coming up with technically informed conclusions. I do not know how to design a reactor — but I know enough to tell that you don't know anything about it either! I have no problem with you discussing the topic — I do have a problem with you claiming all sorts of things that you assume must be true (e.g. that the Japanese public must not have known what the earthquake tolerance levels were for those plants) that in fact you have not bothered to learn anything about at all. --Mr.98 (talk) 21:34, 15 March 2011 (UTC)
I'm still waiting with my $10 for you to come up with any actual proof of your claims. Put up or shut up. StuRat (talk) 07:32, 17 March 2011 (UTC)
You could put the relevant part in a dry pit that was below sea level, and in an extreme emergency open a sluice gate to flood them. I'm not sure if just cooling the outside of the pressure vessel would be sufficient. (talk) 18:57, 14 March 2011 (UTC)

How many serious nuclear incidents have occurred at sea? And what fraction of the world's nuclear power plants are seaborne? Hcobb (talk) 18:32, 14 March 2011 (UTC)

There have been 3 fatal nuclear incidents at sea, all on Soviet submarines (in 1961, 1968, and 1985). There are several other naval nuclear incidents noted, all Soviet, without deaths listed. There have been approximately 500 nuclear subs, with give or take 100 in service presently, plus 30-50 nuclear surface ships or so. There are, for comparison, 436 nuclear reactors presently used in power plants worldwide. So naval usage makes up 20%-30% or so of active reactors, and no current operator nations have experienced significant nuclear accidents. — Lomn 19:28, 14 March 2011 (UTC)
Of course, a few nuclear subs have sunk for reasons other than a nuclear reactor malfunction, but that still leaves a nuclear reactor at the bottom of the sea. See the category Lost nuclear submarines. Jc3s5h (talk) 19:38, 14 March 2011 (UTC)
If the reactor core was below water level, that would allow cooling water to initially flow into the core, even if the pumps were inoperative. But if the pumps were inoperative, how would the water flow out of the core? Dolphin (t) 21:26, 14 March 2011 (UTC)
It boils off, and leaves as steam. As stated previously, this can be somewhat radioactive, but it's usually less of a problem than a nuclear melt-down. StuRat (talk) 21:54, 14 March 2011 (UTC)
A simple problem of being unable to pump water due to lack of power just makes no sense to me. It's so easy to solve that I am certain it's not the actual problem they are having. I read they brought portable generators but the plugs wouldn't fit?? That can't be real, you either cut the wire and attach it directly - or go get a plug, it's been 4 days! I suspect the quake broke cooling lines and they are having to jerry rig something. Also, I suspect the rods are not fully inserted, because if it's just residual decay, by now the heat should have faded. Ariel. (talk) 22:09, 14 March 2011 (UTC)
Actually, I think a common problem in disasters is that things which are normally so easy to obtain that we don't think of them suddenly become an issue. Another example is communications. Land lines can go down and cell phone networks can be overloaded, both of which also interfere with the Internet. An additional case would be basic medical care. You can't just drive to the hospital to have broken arm set, since your car is flooded and upside down, the road is washed out and covered with debris, and the hospital is closed due to structural damage and a lack of power. StuRat (talk) 23:04, 14 March 2011 (UTC)
As for the problem with the plugs (I hadn't heard of that before, but trust your source is reliable), just getting new plugs might be difficult if the stores are all closed and the roads are impassible. Also, different sized plugs likely indicate that the power source is not appropriate for that device, due to different voltages or A/C versus D/C. StuRat (talk) 23:13, 14 March 2011 (UTC)

The "plug story" is complete hogwash! The scale of machinery and energy we are dealing with here is a whole different ball game. Forget about silly stories about "the plugs being different".Bigredtoe (talk) 19:38, 30 March 2011 (UTC)

Even so, after 4 days they could have any type of generator or plug they could possibly need. They have helicopters and Tokyo is undamaged. (I don't actually know if the plug story is true - I read it on the news once, and not again. Half the stuff that comes out at the beginning of an emergency turns out not to be true.) Now I read they have a stuck valve - that strikes me as more believable than not having power to run pumps. I'm still surprised at the heat though, see Decay_heat#Power_reactors_in_shutdown. It seems to me after 4 days it should basically be over. Ariel. (talk) 00:19, 15 March 2011 (UTC)
It has not been 4 days of controlled shutdown, with the fuel consistently cooled. News reports indicate the zirconium cladding has split and the fuel has melted, at least partially, while the cooling water had dropped, exposing at least several feet of the fuel rods. Japanese government officials have admitted to at least a partial meltdown, amongst backtracking, parsing and prevarication, while wishing the problem would just go away, or maybe they would wake up and it was all a bad dream. Edison (talk) 02:11, 15 March 2011 (UTC)
Human actions make no difference to decay rates. After 4 days residual decay should be pretty low, cooling or no cooling. It's pretty obvious we don't know the whole story. Ariel. (talk) 03:30, 15 March 2011 (UTC)
A 500 MW_electrical Mark I reactor has an operating thermal load of about 1500 MW due to inefficiencies. Immediately after shutdown that falls to about 100 MW_thermal, and after 5 days, it would be about 5 MW_thermal. That's a large drop-off, but 5 MW is still a significant amount of heat to dissipate, roughly equivalent to boiling 7000 kg of seawater per hour. Of course, if you have a decent pump, you can provide that much water through a large firehose, so it isn't a ridiculous amount of water. But the numbers are large enough that you don't have a ton of margin of error for things breaking and blowing up, which seems to be happening a lot at Fukushima. Dragons flight (talk) 10:58, 16 March 2011 (UTC)

Science Fiction Detachable Fingertips[edit]

Does anyone remember this story? I don't know much about it, my friend was talking of it last night, she mentioned she wished she owned it still, but she doesn't remember where she read it. There's a guy with detachable fingertips. He can point them at people, shoot them off, there's a thin coiled up wire that keeps them connected. I guess he can shoot his fingers towards people, wrap around their necks, and vuala, murder them. Cheers, --i am the kwisatz haderach (talk) 15:03, 14 March 2011 (UTC)

I think you must mean the short story Johnny Mnemonic. Specifically, it was a removable thumb tip. Gibson described the wire as a 'monofilament', and we even have an article on that: Monomolecular_wire, see the 'uses in fiction' section for other works you may be thinking of. SemanticMantis (talk) 17:06, 14 March 2011 (UTC)
p.s. I think you mean "voilà". As a word often heard but seldom read, it's easy to spell it wrong ;) SemanticMantis (talk) 17:09, 14 March 2011 (UTC)
p.p.s. I was going for the AMERICAN TRUCK DRIVER FRENCH Spelling Edition. Kushti Bok!, Good Luck in Romani --i am the kwisatz haderach (talk) 21:04, 14 March 2011 (UTC)
p.p.p.s. In Switzerland the Romani would never spell it that bad, and they're even more hick than American truck drivers! SamuelRiv (talk) 08:31, 15 March 2011 (UTC)
We don't have an article about Sixfinger. I'm shocked, just shocked. See here it was before my time but I thought there was a TV show about a guy who used one. (talk) 10:17, 16 March 2011 (UTC)

What is the difference between convection and conduction[edit]

After reading the respective articles, I'm still not really sure what the difference is. In laymans terms, what's the difference? ScienceApe (talk) 16:58, 14 March 2011 (UTC)

Conduction is heat moving between two "objects" (could be masses of air or whatever). Convection is an object moving and taking its heat with it (where it then might conduct it into some object that had been too far away). --Tardis (talk) 17:10, 14 March 2011 (UTC)

Well said Tardis, yours is the ONLY "answer" on this page that is correct! ScienceApe doesn't quite grasp it (he needs a little more illustration) but the poor sod will be totally confused and misled after reading the rest of this page.

Csmiller and StuRat both fail to understand the difference between two distinctly different uses of the word convection and therefore have confused you in the process of sidetracking themselves.

The other contributors appear to be only semi literate at best and therefore unable to understand a simple question properly, but just able to quote textbooks or lectures they don't really understand.

Take heart SciencApe it's not really that hard. Firstly just remember that the word convection is used in a couple of different ways and does not mean the same thing in every context, the word conduction more straight forward.

The fact that you have asked the question the way you have indicates you are thinking of convection in its more correct meaning, what it means when used in the same context as conduction. That is the transfer of heat.

Tardis referred to "objects", we could talk in terms of atoms and/or molecules but lets not. If you pick up a cold fireplace poker and stick the tip in the fire and hold on to the handle at the other end, the metal at the tip will absorb heat from the fire. After a while the other end of the poker (that you are holding) gets hot! The heat has traveled 2 feet (600mm is you must)by conduction. The "object" did not move but the heat did. The heat keeps moving - into your hand (ouch) because your hand is in contact with the poker. Once again conduction.

Your hang up the poker (and blow on your hand). A log in the fire place spits a glowing hot ember straight at you and you catch it in your other (cold) hand -more ouch. The heat from the ember (the object) transfers into your hand by conduction once again. HOWEVER convection occurred when the ember moved 2 feet out of the fireplace and onto your hand BRINGING THE HEAT WITH IT!!!!!

It is that simple. Yes it is that simple at its root. Don't get distracted and confused like Csmiller and StuRat by thinking of convection in terms of fluid dynamics ("hot air rises" (it doesn't aways!) etc etc) that is a whole different thing (and in as much as there is a connection they have it arse about.

So talking in molecules; if there is a continuous line of molecules (or atoms) between point A and point B and heat moves through the line (gets passed along) that's conduction. Any time a molecule (or atom) gains some heat in one place and then moves to another location carrying the heat with it That is convection. It does not matter whether the direction is up, down or side ways, it does not matter whether the object is a gas, liquid or solid. Bigredtoe (talk) 21:07, 30 March 2011 (UTC)

(edit conflict) Hot molecules vibrate faster than a colder ones. In conduction, the hot molecules bumps into their neighbours, transferring speed (heat) into them. This occurs in solids, liquids (and to some extent) in gases. In convection, hot parts are less dense than cooler parts, so in gases and liquids (but not solid) they rise (if there is gravity). CS Miller (talk) 17:13, 14 March 2011 (UTC)

Can I have an example of the two? ScienceApe (talk) 20:40, 14 March 2011 (UTC)

When you heat a pot of water on the stove, conduction moves the heat along the surface of the pot itself, and there is also some conduction of heat to the water and within the water. Within the water, you also have convection, where the hottest water at the bottom rises to the top, and cooler water drops to the bottom and then heats up, repeating the cycle.
You always have some conduction, except for when there's a vacuum between the objects. Convection, on the other hand, generally requires a fluid (liquid or gas) and enough of a temperature difference to drive it more than the currents which would otherwise prevail. For an example of where convection is almost the only method of transferring heat, look at how heat is redistributed in the atmosphere. There the distances and low density of air mean that conduction is very slow, but convection can happen quicker, with winds being the result of convection currents in air. You may have noticed that rapid temperature changes are almost always accompanied by winds. A third type of heat transfer, radiation, is also present, but, at the temperature differences between adjacent air masses, it has a very minor contribution within our atmosphere. (It is, however, pretty much the only way the air is heated from the Sun, due to the vacuum of space preventing both conduction and convection. StuRat (talk) 21:11, 14 March 2011 (UTC)
Conduction: the transfer of heat, due to the thermal equilibrium principle.
Convection: the transport of heat, due to a pressure differancial in a dynamic medium. Plasmic Physics (talk) 23:28, 14 March 2011 (UTC)
Those aren't laymen's terms. StuRat (talk) 23:55, 14 March 2011 (UTC)
Wait, I thought *advection* was the movement of the particles in space, with convection being a combination of both conduction and advection? (talk) 09:34, 15 March 2011 (UTC)
Any time a gas or fluid is convecting, it's fair to say that heat is also being transferred through conduction and radiation. "Advection" is really ultimately the same concept as "convection" - except that it can also be used to describe transfer of things other than heat. I'd use the following rough definitions:
  • Advection - bulk movement of fluid particles to transport something (heat, salinity, dissolved chemicals...)
  • Convection - bulk movement of fluid particles to transport heat
  • Conduction - transfer of heat by direct contact
  • Radiation - transfer of heat via blackbody radiation
Now, if we zoom the scale length way up or way down, we kind of break this "clear-cut" set of definitions. At the most microscopic level, there is only conduction. (Or, only radiation, depending on how you want to look at it). Energy is exchanged via scattering and collision between microscopic fundamental particles. If we zoom all the way out to astronomical scales, we again find that radiation is the most significant form of heat transfer. In day-to-day physics scenarios, like a room with a hot-air radiator, we have all the types of heat transfer: the radiator conducts heat from the iron bars to the air by direct contact. The hot air right next to the radiator starts flowing around the room (convecting). And, the radiator also emits infrared radiation, warming any object within its "line-of-sight" via electromagnetic heat transfer. Because the line of sight includes the room air (which is flowing convectively), some radiative heating is spent interacting with the convection pattern; and every individual air molecule that is part of a convective flow is also both re-radiating heat and also conducting heat to anything it's in contact with (walls, other air molecules), and so on - it's a giant muddled mess of "details" and coupled systems - which is one reason why fluid dynamics is so difficult to solve with formal mathematical treatment. Nimur (talk) 14:53, 15 March 2011 (UTC)
I wouldn't expect much direct heating of the air by radiation, since a few feet (or meters) of air absorbs a very small percentage of infrared light. Most will heat room surfaces, instead. StuRat (talk) 20:16, 15 March 2011 (UTC)

Silicon boiling point[edit]

Most places I've read give this as 2355 degrees C, but our article (Silicon) says 3265 degrees. Why the difference? Or is it a mistake? Grandiose (me, talk, contribs) 17:20, 14 March 2011 (UTC)

Made in this revision to Template:Infobox silicon (in mid-2008). Grandiose (me, talk, contribs) 17:32, 14 March 2011 (UTC)
Such infobox parameters are very hard to enforce against intentional vandalism and honest editing-errors. I always defer to a reputable source, such as the CRC Handbook of Chemistry and Physics, if I need a chemical parameter. Unfortunately I don't have a CRC handbook handy to check this number, but your lab or library almost certainly has one. Nimur (talk) 17:53, 14 March 2011 (UTC)
SI Chemical Data states 2680°C but that is fairly old. Wolframalpha gives 2900°[5]. Other random sources from google scholar give 2878°C[6], 3514K 3504K (and 3267° in a patent). Graeme Bartlett (talk) 21:02, 14 March 2011 (UTC)
Webelements has 3173 K (matching wolframalpha's quote). The German wikipedia article de:Silicium strangely cites webelements but uses 2628 K instead. -84user (talk) 23:57, 14 March 2011 (UTC)

when diesel power failed why not restart one of the reactors & it's generator?[edit]

I wonder whether they considered restarting one of the main generators after the diesels failed and while they still had enough battery power. Haven't seen this question posed, considered or commented on anywhere. Would be sad if it was a case of "just let your tires down mr truck driver"! Bigredtoe (talk) 20:04, 14 March 2011 (UTC)

Starting up a damaged nuclear reactor doesn't sound wise to me... --Tango (talk) 20:41, 14 March 2011 (UTC)

There is no evidence to suggest that the reactors themselves were damaged at all when the generators failed. The damage to the reactors only occurred some time AFTER the generators failed because without power they could not manage the reactors properly. You have missed the point of the question!Bigredtoe (talk) 15:36, 30 March 2011 (UTC)

Starting up a reactor, even under normal conditions, is not as easy as just hitting a switch and having power come out. It takes time to work them up to peak levels, make sure everything is working correctly, etc. --Mr.98 (talk) 21:00, 14 March 2011 (UTC)
Agreed. There is the question, though, of whether the decision to shut down all nuclear reactors was wise, considering the lack of reliable backup sources of electricity. Perhaps the least damaged reactor (2 ?) should have continued to be run at low levels, to provide power for the pumps, until a reliable electricity backup could be established. StuRat (talk) 21:03, 14 March 2011 (UTC)

Mr.98 (and StuRat) you are completely wrong! Hot starting a reactor IS in practice pretty much as simple as hitting a switch. Further down this page Mr.98 said to someone "You make an awful lot of assumptions about things you know very little about...!" Mr.98 should take his own advice. For further FACTS about restarting a reactor see further comments later.Bigredtoe (talk) 15:49, 30 March 2011 (UTC)

Generally it takes more power to start up a reactor than the emergency diesels can provide. It needs grid power to startup. Lots of big pumps must be operating, for instance. The emergency diesels are only sized for operation of shutdown for cooling pumps and controls.Edison (talk) 21:13, 15 March 2011 (UTC)

"Generally" you are wrong. Single reactor Nuke subs & ships are fully capable by design to COLD START their reactors using on-board secondary power systems (diesel and/or steam driven generators & pumps). In Fukushima's case by far the largest single pumping load would be the primary "cooling" circuit, (those of you that actually understand NPPs will know why I have used the quotes) however adding together all the load of the secondary and emergency cooling systems would tally to a capacity somewhere near capable of running the primary pumps. Given that Fuk No1 has six diesel gensets each one capable (by design) of fully supporting the entire secondary and emergency systems load; if several or all of the reactors were cold or even cool, you would have more than enough on site power to start a dead cold oven, let alone a hot one, and spin up an alternator. That of course assumes that your aux power supply switching has been designed and built with flexibility in mind. As for the "..diesels are only sized.." PLEASE state your source! or are you just guessing and/or assuming? I know of at least one other NPP, with larger reactors and turbines than Fuk No1, that can do a "black grid" start if needed. In any event your comments indicate you have not properly understood the question. The question specifically addresses the circumstances AFTER THE DIESELS HAD FAILED.Bigredtoe (talk) 16:20, 30 March 2011 (UTC)

SCRAMing the reactor is the default action when you are unsure whether it is going to work correctly. It's the right action. What you want to avoid is anything that will keep you from shutting it down in the future, which is essentially what happened at Chernobyl (it got too hot and they couldn't re-insert the control rods). It is far, far safer to rely on diesel or something else in that period. If the diesel doesn't work, you can always get more diesel. If the reactor won't shut down, you're in real trouble. --Mr.98 (talk) 21:20, 14 March 2011 (UTC)

Mr.98 not following his own advice again.

Your comment shows that you clearly do not understand one of the fundamental characteristics of a SCRAM. For your education the shutdowns at Fukushima were not done because anybody was "unsure whether" it was going to work. If that were the case it would not have been a SCRAM!! The shutdowns at Fukushima were initiated and fully carried out by the control system (computers). The human operators at the plants had no say in it. The control rods were fully inserted in a matter of seconds after the readings from ground acceleration sensors, at the plant connected directly to the control system, exceeded a pre-programmed level.

Your summation of the chernobyl event is also quite misleading and indicates an ignorance of the unique keys to that event. These two events have virtually nothing in common. There was a particular behaviour characteristic of the Chernobyl reactor that was not "in the instruction manual" but was inherent in its design which was key to that event.

As far as your waffle about getting more diesel fuel and the safety of relying on diesels? You appear to be blissfully ignorant of the situation on the ground at Fukushima at the time (didn't bother reading the question properly?), and I suspect you have no idea of the scale of machinery we are talking about here.Bigredtoe (talk) 17:55, 30 March 2011 (UTC)

By most reactors, the control rods system isn't linked to the emergency Diesel generators and cannot be operated without external power. If external power fail they are automatically driven in a safe position to shutdown the reactor.--Franssoua (talk) 14:54, 14 April 2011 (UTC)
(edit conflict)Against that you have to weigh the risks involved of running the reactor without an external power supply for emergencies. This article about a different Japanese BWR says the control rods must be inserted from beneath, and mentions the possibility that an earthquake may have shifted the structure such that a single control rod could not be moved. The article also suggests that the standard response to a moderate earthquake was to shut down the reactors. Actually running the reactor in this compromised circumstance carries the risk that a subsequent aftershock will shift the pile such that many control rods can't be inserted (and/or kill the hydraulics that insert the control rods); if that aftershock also knocks out the circulation system, you have what they have now, but with the reactor generating several times as much heat. Given that no-one can predict aftershocks, and plant operators have a necessarily imperfect view of what equipment in their plant still works after an earthquake, all things being equal a control-rods-fully-in posture seems to be the safest. -- Finlay McWalterTalk 21:29, 14 March 2011 (UTC)
The scramming I understand, but... if the reactor continued to stay hot, or reheats itself, as it did, why can't the cooling systems continue generating electricity? Wnt (talk) 21:33, 14 March 2011 (UTC)
I must say I was surprised by this, i thought NPPs were much more fail safe since Chernobyl. Vespine (talk) 22:02, 14 March 2011 (UTC)
They are, in that the total failure mode is much less catastrophic than Chernobyl. Even in the event of a total core meltdown, the most radioactive material (the uranium core) will remain trapped in the containment vessel, rather than catching on fire, exploding (rupturing the containment vessel), and sending burning radioactive matter up into the sky and all over the countryside. Buddy431 (talk) 22:46, 14 March 2011 (UTC)
The news reports keep suggesting otherwise. We'll see soon enough. Wnt (talk) 22:51, 14 March 2011 (UTC)
Long experience has convinced me that news reporters have no clue about anything, ever. Certainly not about anything scientific and certainly not about any rumors circulating in the immediate wake of a major disaster. -- BenRG (talk) 00:19, 15 March 2011 (UTC)
Agreed. This is not an analogous situation to Chernobyl at all. It is much more similar to Three Mile Island in its technical respects. But they are having a heck of a time getting it under control. The news reports which incessantly say, "worst since Chernobyl" are technically true, but comparing it with Chernobyl is itself quite misleading — it is not like Chernobyl at all, but it is the worst problem at a nuclear plant that has occurred since Chernobyl. --Mr.98 (talk) 02:56, 15 March 2011 (UTC)
However, the fact that all 3 active reactors are having similar failures implies that there are fundamental design flaws and/or inadequate procedures. If the reactors are only designed to withstand quakes up to X magnitude and tsunamis of up Y meters, then the Japanese public should have been told that, so they could either demand greater protection or choose to live farther from the reactors. StuRat (talk) 22:59, 14 March 2011 (UTC)
What makes you assume that the information was not a matter of public record? I'd be willing to be you $10 that the earthquake rating of those reactors is easy to come by if you read/write Japanese. You can only secure a given reactor (or dam, or chemical plant, or whatever) against certain types of risks. In many modern countries (the US in particular), exactly what those risks are is part of the environmental impact report and is part of its public documentation. You make an awful lot of assumptions about things you know very little about...! --Mr.98 (talk) 02:56, 15 March 2011 (UTC)
Well, it's possible, but then again, they may have claimed they were safer than they really were, as happened with the levies in New Orleans when Hurricane Katrina hit. I'd be interested to see any documentation you can come up with. Note that you are making the assumptions that this information was released, and was correct, so I could make the same charge that you "make an awful lot of assumptions about things you know very little about". If you can come up with proof that there were publicly available records that said that the plants could not withstand this level of quake and tsunami, then you win the bet and I will wire you $10. StuRat (talk) 06:26, 15 March 2011 (UTC)
The current US standard is that a nuclear plant should be designed to survive with no major damage from the worst natural event that is predicted to occur within 1000 years at its location, and with no hazardous release of radiation against a once in 10000 year event. I don't know what standards Japan applies, or what standards might have been in use 40 years ago when the reactors were being built. Of course, given that we don't have thousands of years of history to go on, estimating the 1000-year flood / earthquake / tsunami / tornado / etc. is decidedly something of a guessing game. Dragons flight (talk) 11:09, 16 March 2011 (UTC)
While I can't comment on the relative safety or merits of the General Electric designs used at Fukushima I compared to those at Chernobyl, I will observe that the Japanese reactors are actually slightly older than the ones in the Ukraine. Construction of reactors 1, 2, and 3 at Fukushima began between 1967 and 1970, and they entered service between 1971 and 1976. Construction of the Chernobyl facility began in 1970, and the fourth (catastrophically-failed) reactor at that site entered service in 1983. (From what I gather from our article on void coefficients, however, the boiling-water reactors at Fukushima aren't vulnerable to the same type of runaway failure suffered at Chernobyl.) TenOfAllTrades(talk) 23:07, 14 March 2011 (UTC)
Age was not the problem with Chernobyl. The problem was poorly trained operators mixed with a very dangerous reactor design. I don't know the specifics of the Japanese designs, but the fact that they have full containment buildings automatically makes them much safer than Chernobyl, even ignoring the different nuclear setups. --Mr.98 (talk) 21:40, 15 March 2011 (UTC)
Wnt's question above is the important one. Is it possible to restart just the steam plant of a scramed reactor to generate power from the decay heat, and in the process cooling that very reactor. I suspect that it is possible as long as emergency power is available during the start-up, but that without such power you might not be able to bootstrap the system. Are the condensate & feedwater pumps and sea water cooling pumps to the condenser all driven by steam or by electric power? Even if they are all steam driven, start-up without external power might not be possible depending on conditions such as condenser water level and temperature. -- (talk) 00:58, 15 March 2011 (UTC)
I don't think they can. The steam turbines are designed for lots of steam. The small amount produced here can not run them. However they do have steam powered pumps which were used to directly pump water to cool the plant. Ariel. (talk) 01:14, 15 March 2011 (UTC)
There are multiple reasons why this wouldn't work. Big generating plants aren't designed to run at a low fraction of maximum power. If you don't have nearly full output from a reactor, the generator isn't going to run right. The generating system may already be damaged from the earthquake and tsunami. Even if there were no damage and the generating system were happy to run at a fraction of full power, running a generation system on its own output is mathematically unstable; you can't keep it running easily without an external power source. Finally, clearly power is not the problem. If their only problem was how to power the cooling system's pumps, they would not be in the mess they are in. Something else is wrong: damage to the cooling system, damage to the core, etc. It's unlikely that running the steam plant would be any help at all.--Srleffler (talk) 04:25, 15 March 2011 (UTC)

Srleffler -where do I start? You have let the cat out of the bag that the automotive industry has been defying the laws of mathematics for decades!!!! and the rotten sods have sold us millions of cars that are mathematically unstable! It is just a con man's trick that we have to pay for alternators etc. When our cars electrical system dies it really is that secret chip inside the car getting triggered by a secret message from the car factory to turn off the secret (invisible) power system inside our car!!! (and then they send another secret message to the invisible "real" power system in our car at the same time as we pay for a new alternator?)

As far as big not being able to run at "low fraction of max power" - nonsense.

The real screamer though is "If you don't have nearly full output from a reactor, the generator isn't going to run right." You obviously have no idea of the elegant beauty of a large steam turbine alternator!

And finally, CLEARLY POWER WAS THE PROBLEM. Until they lost their diesels they were IN CONTROL. Contrast No1 to No2!!! Daini did NOT lose their diesels, (they did loose grid power too) and they achieved full cold state without significant damage or leakage.

And finally finally (and for about the tenth time) UNTIL AFTER THE DIESELS FAILED THERE WAS NO CORE DAMAGE. soooo frustrating when people blabber before reading properly.Bigredtoe (talk) 17:15, 30 March 2011 (UTC)

I doubt they would have been able to restart the reactor so soon after a SCRAM from full power. From a reactor physics perspective, even if the plant operators had full confidence in the reactor following the earthquake and had wished to restart it, they would have had the problem of reactor poisons. These are fission products (such as xenon-135) which act as strong neutron absorbers and remove reactivity from the core. Often, reactors have to wait several days in order for sufficent posions to decay before they have a sufficient reactivity margin to restart. HighOrbiter (talk) 09:35, 15 March 2011 (UTC)

Not true! The only time reactor poisons would prevent a restart after a SCRAM (or any shutdown) even very shortly after, is if your reactor was very near the end of its fuel cycle and therefore you had close to zero "reserve" power in your pile. There is one fully documented case I recall where a full sized commercial power station reactor was restarted inside 3 minutes of a SCRAM. Wrists were slapped some time later but the reactor and power station suffered ZERO negative effects or technical complications.

It is SOP for reactors in nuke subs to complete a restart within 7 minutes of a SCRAM. Bigredtoe (talk) 16:34, 30 March 2011 (UTC)

Has one or more transmission lines had power restored to the Fukushima 1 switchyard, so there is offsite power? The tsunami flooding the basements and shorting out the reactor controls and aux power is a separate issue from having grid power available. I would expect there to be high voltage transmission in 2 or 3 directions from the transmission yard,as is typical for any nuclear plant, and it is unlikely every line would have suffered complete disruption beyond what a day or 2 orf repairs could correct. If the transmission was restored, when did that happen? Edison (talk) 21:19, 15 March 2011 (UTC)
As I understand it, the reactors are in an area hit by the tsunami. I would not be surprised to find that the power lines are destroyed for tens of miles in all directions. --Carnildo (talk) 02:25, 16 March 2011 (UTC)
"Tepco sounded a rare optimistic note by saying engineers would soon restore an electrical connection from the national grid - which should allow them to re-start water pumps, provided they have not been damaged by the tsunami or the hydrogen explosions." 16 March 2011 20:16 GMT BBC


So, I flipped over my mattress yesterday and started using the other side, because a spring was sticking out and poking me in the back. I noticed that it feels much, much harder on the flipside (the side I've been using for years had a nice, comfy and me-shaped indentation), which I guess is how the thing felt when it was new (though I don't really recall).

Question - what's the current thinking with regards to buying the best mattress? Does the medical profession still advise that one should buy a really hard mattress, for improved spinal health? Personally, I've always purchased the hardest one that I could bear lying on - figuring that it will take longer to go soft and thus last longer. --Kurt Shaped Box (talk) 23:21, 14 March 2011 (UTC)

A mattress which is too hard can also lead to medical problems, as pressure points can lead to bed sores, or wake you up often, causing a lack of sleep. If the flipped mattress is too hard, I suggest putting more fabric between you and it, such as comforters. Another option is to buy a pillow top mattress pad: [7]. Either should work until the mattress softens back up. Note that the spring poking through could also be repaired. However, if the mattress is on it's last legs in other ways, it may not be worth the trouble. StuRat (talk) 23:53, 14 March 2011 (UTC)
Na, it's not too hard. Just feels harder than the side I've been sleeping on. One side seems like new, the other is completely knackered and beat-up. Just wondering in general what the current thinking was, re: mattress firmness. Years ago, 'they' (as 'they' do) used to say that it was best to get the hardest one that you could manage on... --Kurt Shaped Box (talk) 00:44, 15 March 2011 (UTC)
Modern mattresses usually have a defined "up" side. Even when new, the side you are intended to sleep on is softer than the other side. Older mattresses could be used on either side, and in fact the manufacturers recommended flipping them over every few months so they would wear evenly.--Srleffler (talk) 04:38, 15 March 2011 (UTC)
This indicates that medium-firm and firm mattresses allow better spinal alignment, but did not indicate that spinal alignment had any affect on the body (in patients with no back problems). Effect of firmness of mattress on chronic non-specific low-back pain: randomised, double-blind, controlled, multicentre trial (F Kovacs et al., 15 November 2003, The Lancet, 362:9396, p.1599-1604) mentions in the introduction that 95% of orthopaedic surgeons surveyed believes "that mattresses played a part in the management of low-back pain, with 76% recommending a firm mattress. However, evidence supporting this advice is lacking." due to few studies and poor methodology. That study found that replacing an old mattress with a firm, or especially a medium-firm mattress, lead to patients with chronic lower-back pain having less pain and reduced drug usage. There are several other studies which produces similar results. As for very hard mattresses, I did come across a couple of pieces of research which found that sleeping on a wooden board was not as good as using an actual mattress (shocking, I know!) --Kateshortforbob talk 16:53, 15 March 2011 (UTC)

What you should also test is if the mattress you intent to buy does not depress a lot more when you push a lot harder on it. If you lie on your back on the mattress, it will depress a certain amount around the hip area. Then, if you flip over and lie on your side, it will depress a bit more because the exerted pressure increases, but it should not depress a lot more. Count Iblis (talk) 17:03, 15 March 2011 (UTC)

Do you mean, it should follow Hooke's law? — Sebastian 19:51, 15 March 2011 (UTC)
If your matress follows Hook's law, it will depress perhaps 4 times more when you flip on your side, which would be very bad. Count Iblis (talk) 15:11, 16 March 2011 (UTC)

Since this is the Science desk, I'd recommend experimenting. Select Comfort makes mattresses that allow you to change their firmness. (I usually avoid commercial external links, but I feel differently about them for reasons that would be off topic here.) So you could experiment and see at which firmness you feel best the next day. — Sebastian 19:51, 15 March 2011 (UTC)