Wikipedia:Reference desk/Archives/Science/2011 September 6

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September 6

Physiatry vs physiotherapy

What is the difference between physiatry and physiotherapy? I know a physiatrist is a physician, but a physiotherapist is not a physician. But what is the difference between their job profile as they work in the same field? --DinoXYZ (talk) 03:14, 6 September 2011 (UTC)

We have articles on both physiatry and physiotherapy. SpinningSpark 06:42, 6 September 2011 (UTC)

MLB pitchers and atlatls

I have been curious about the interaction between a major-league baseball pitcher — say, Nolan Ryan — and an atlatl, or, more precisely, one of these ball-launchers for dogs. They are basically arm extenders, which give the common human more leverage to throw the ball that's cupped at the end of the device; but how much would they accelerate a ball thrown by the likes of Nolan Ryan? His wrist action and arm motion during a pitch must differ a lot from their action during an atlatl throw, but I expect they would still let him accelerate pitches to some extent? (This sounds like a Mythbusters candidate, since it's so easy to test for somebody who can get access to, well, Nolan Ryan.) Comet Tuttle (talk) 04:03, 6 September 2011 (UTC)

The answer can likely be found in the sport of Jai alai. The best baseball pitchers get right around 100 mph as a top speed on a fastball (maybe a few MPH more). The best jai alai players get in the 170-180 MPH range, so the "xistera" or basket they use to accelerate the ball seems to be worth about 70-80% extra on the speed of an arm by itself. --Jayron32 04:07, 6 September 2011 (UTC)

Actual speed of heavenly bodies versus their speed as perceived here on Earth.

Greetings!

I've been wondering about how quickly certain planets, asteroids, comets, etc. seem to move to an Earthbound observer, and how this may differentiate from their actual velocities.

I'm (vaguely) familiar with how a tropical day (24 hours—in which the Earth completes one whole rotation) varies from a sidereal day (23 hours, 56 minutes, 4 seconds—in which the Sun transits completely through the ecliptic) but what about other celestial objects?

Does, for instance, Mercury appear (to us) to transit the 12 constellations of the zodiac in 90 days or so—as opposed to its actual revolutionary period of 88 Earth days? Also, does this in any way relate to phenomemon known as retrograde?

Please let me know whether any articles, or external references, cover this in detail.

Pine (talk) 04:44, 6 September 2011 (UTC)

Orbital period covers some of this, but its a bit hard to follow. What you sound like you are asking for is the "synodic period" vs. the "sidereal period". The first is the time it takes for the object to appear in the same spot in the sky relative to our view here from Earth, and the second is the time it takes for the object to appear in the same point in its orbit around the sun, relative to the background stars. Also, there is a distinction between true retrograde motion, which is when an object moves in the opposite direction to other objects in its neighborhood, and apparent retrograde motion, which occurs when one object "overtakes" another as it moves around the sun. --Jayron32 04:54, 6 September 2011 (UTC)

The difference is caused by the Earth's orbit around the Sun: since the Earth's revolutions and orbits are in the same counter-clockwise (view from north) rotation, a day's worth of orbit compensates to remove four minutes from the period in which the Sun is at the same position as seen from Earth. (since this would cause a shift of 24 hours every 360 days though, I'm not quite sure how it works) During lunar orbit, the Moon has to catch up to Earth during every orbit, so that its actual orbital period (sidereal) becomes longer. As for apparent retrograde motion, this occurs when the Earth speeds ahead of a planet like Mars at close approach (it only works for planets farther away) and the planet appears to be trailing westward rather than the usual west-to-east motion encountered when Earth is mostly moving towards or away from said planet. [1] ~AH1 ^(discuss!) 23:14, 6 September 2011 (UTC)

Tora Bora

If we had dropped a nuke on Tora Bora instead of trying in vain to get those incompetent Northern Alliance fighters to storm it, would it have ensured the cave's complete destruction along with everyone inside? If so, what would be the minimum yield in kilotons to do the job properly?67.169.177.176 (talk) 05:15, 6 September 2011 (UTC)

Using a nuclear weapon on Tora Bora would have undoubtedly killed many people effectively, but the political outcome of such an action may not have been worth it. --Jayron32 05:25, 6 September 2011 (UTC)

You may be interested in reading our article Nuclear bunker buster -- 110.49.241.217 (talk) 06:20, 6 September 2011 (UTC)

Yes, I'm aware of the B61Mk11 nuclear bunker-buster. The one question I have is, would it have destroyed Tora Bora, or is it buried too deep? I asked this because, as you are probably aware, there are some bunkers that are practically impervious to nuclear weapons. 67.169.177.176 (talk) 07:03, 6 September 2011 (UTC)

Er... that Tora Bora was some massive, man-made, efficient underground fortress like the volcano bases of movie villains is a myth perpetuated by the press with adjectives like 'sprawling', 'death trap', 'extensive', 'impregnable', etc. The reality is that Tora Bora caves were really just a bunch of small primitive caves hiding a handful of raggedy fighters. It was all hype. -- Obsidi♠n Soul 08:43, 6 September 2011 (UTC)

I know it's not like the Cheyenne Mountain bunker at all, but still... 67.169.177.176 (talk) 00:53, 7 September 2011 (UTC)

Reality check: Do you really expect us to consider the US dropping a nuclear bomb of sufficient yield to destroy an underground mountain complex located just 10km from the the border to Pakistan, itself one of the world's least stable nuclear powers? Cuddlyable3 (talk) 08:48, 6 September 2011 (UTC)

Why not? I mean, the Pakis hate us all anyway, don't they? And if it's a choice between collateral damage to those people or unnecessary losses to our people, then the choice is clear. 67.169.177.176 (talk) 00:56, 7 September 2011 (UTC)

The failure to capture bin Laden there stemmed from Bush's inattention, not how tough the caves were. 66.108.223.179 (talk) 11:47, 6 September 2011 (UTC)

Actually, it stemmed from the Northern Alliance fighters sitting on their asses instead of storming the cave complex like they've been darn well told to (and which they could've done, too). 67.169.177.176 (talk) 00:58, 7 September 2011 (UTC)

The Tora Bora article, as well as the article's first reference,[2] may help a little, although not really enough to actually answer the question. Red Act (talk) 12:06, 6 September 2011 (UTC)

On the question of yield: the toughest part about earth penetrating nukes, from a technical standpoint, is that the geology of caves and underground bunkers and etc. can vary quite a lot.[3] There are equations that tell you how deep a given blast will penetrate into a given material; I don't know the relative values to plug in for Tora Bora, but these should be discoverable somewhere. One of the key elements here though is that with large, sprawling, heavily rock-based complexes, whatever you do there will be a huge level of uncertainty. This makes nukes a very unattractive option, since the bad PR would be huge (both domestically in the US, or Pakistan, but also with regards to the goals of the Afghan mission). You also would have a very hard time defining what "success" in such a situation ought to be — it isn't like the bombings of Japan, where a surrender ultimatum would be agreed upon. --Mr.98 (talk) 14:51, 6 September 2011 (UTC)

Nuclear weapons are a great way to kill lots of people but a terrible way to make sure somebody is dead. Once you've blown up your favorite cave in Tora Bora, how do you figure out after the fact whether Osama bin Laden was in it? Maybe it was just a few mujehaddin and he was in another cave half a mile away, which got nothing more than a dusting of fallout... Wnt (talk) 22:34, 6 September 2011 (UTC)

On second thought, dropping a large amount of napalm on the entrances and vent shafts could be more effective (and more appropriate in terms of suffering caused to the terrorists, too...) 67.169.177.176 (talk) 01:01, 7 September 2011 (UTC)

Sheesh. I mean seriously. Tora Bora was not a 'massive cave complex' with '2000 men', technologically advanced or otherwise. It was a cluster of small primitive caves, neither complex nor terribly resistant with something like 200 men.

Times article by Matthew Forney, who visited the caves after the battle:

These weren't the five-star accommodations with internal hydroelectric power plants and brick-lined walls, areas to drive armored tanks and children's tricycles, and tunnels like capillaries that have captured the world's imagination. Such commodious quarters might exist higher in the White Mountains, but these were simply rough bunkers embedded deep into the mountain. They were remarkable nonetheless.

Interviews with US special forces Detachment Alpha (ODA) 572 who were part of the assault:

Again, with the caves, they weren't these crazy mazes or labyrinths of caves that they described. Most of them were natural caves. Some were supported with some pieces of wood maybe about the size of a 10-foot by 24-foot room, at the largest. They weren't real big. I know they made a spectacle out of that, and how are we going to be able to get into them? We worried about that too, because we see all these reports. Then it turns out, when you actually go up there, there's really just small bunkers, and a lot of different ammo storage is up there.

Bombing it with a bunker-buster nuke would have been like trying to swat a fly with a grenade. All of it was based on faulty intelligence worsened by media publishing increasingly elaborate 'plans' of the supposed 'fortress' which the higher ups (*cough Donald Rumsfeld *cough*) in US politics in turn, believed. If the US had nuked Tora Bora, it would have been supremely embarrassing afterwards that they just rendered a large stretch of land uninhabitable for hundreds if not thousands of years on a rumor.

This, this, and this were fairytales by journalists and politicians who watched one too many James Bond movies.-- Obsidi♠n Soul 02:16, 7 September 2011 (UTC)

The whole point of Al Qa'ida's operations is to provoke the US to overreact, allowing them to recruit more followers. Count Iblis (talk) 21:19, 7 September 2011 (UTC)

What makes you think so? 67.169.177.176 (talk) 02:02, 8 September 2011 (UTC)

Whether or not Count Iblis' statement is true, nuking Tora Bora and making the land uninhabitable for decades, and unusable to nomads for years, would cast severe doubt on the U.S. claim that it promotes liberty and human rights. So would deliberately using a cruel method of killing the terrorists, like 67.169.177.176 was suggesting. --99.237.252.228 (talk) 06:32, 9 September 2011 (UTC)

That's not the point of fighting the War on Terror -- the main objective is (or should be) to kill terrorists and deter the rest of the enemy population from joining them (i.e. make sure their fear of our military strength overcomes their innate hatred of our culture). Deliberately using a cruel method to kill the terrorists (in this case, napalm) would have served both purposes extremely well, although using a method that inflicts unnecessary amounts of collateral damage (in this case, bunker-busting nukes) may be counterproductive. In any event, deliberate cruelty toward terrorists (as opposed to the rest of the enemy population) has no bearing on human rights whatsoever -- terrorists don't count as people. 67.169.177.176 (talk) 00:46, 10 September 2011 (UTC)

would it be possible (to convert rotation to linear motion)

hi friends , i am proposing that whenever the bolt as shown File:Bolt.bmp moves round,it would be able to move the plate up. File:C:\Documents and Settings\Administrator\Desktop\TRAINEE GET\missfix\plate.bmp is there any kind of mechanism already availaible. basically i need to convert rotatory motion into linear motion in perpendicular direction.The space is very constrained 20mm for whole assembly. plz help .. thanx.. 203.197.246.3 (talk) —Preceding undated comment added 08:34, 6 September 2011 (UTC).

You've given the filepath to images on your local machine, they have not been uploaded here and are not viewable by other editors. You may wish to see WP:Uploading images, but other than that it's unclear what you are asking Jebus989^✰ 09:48, 6 September 2011 (UTC)

(I added to the question title to make it useful.) From your description, it sounds like you want to change rotary (circular) motion into linear motion. Do you want reciprocating (back and forth) linear motion or movement in one direction only ? If the motion is desired in only one direction, does it need to be steady, or can it be "jerky" ? StuRat (talk) 15:44, 6 September 2011 (UTC)

For reciprocating motion, there's a cam (placed over the bolt) with a vertical cam follower. For jerky motion in one direction, you could combine a cam with a second concentric riser shaft that is pushed by the cam follower in one direction, but not the other, say with saw teeth on both that lock in one direction but slide in the other (you'd need a fixed sleeve around both vertical shafts to keep them in contact, and it would also need to have saw teeth to lock with the riser shaft to prevent it from falling back down as the cam follower descends):

 _________________
|______PLATE______|
___ / \     / \ ___
| / / \ \F/ / \ \ |   
|S/ /R\ \O/ /R\ \S| 
|L/ /I\ \L/ /I\ \L| 
|E/ /S\ \L/ /S\ \E| 
|E/ /E\ \O/ /E\ \E| 
|V/ /R\ \W/ /R\ \V| 
|E/ / \ \E/ / \ \E|
        \R/
            
        <CAM>

The above is an exploded front view, with the cam rotating about the center of the C. The riser could be made of rubber, with both the cam follower and sleeve made out of a rigid material, like plastic or metal. Not shown above is a small connecting link between the M in the CAM and the bottom of the cam follower, which would pull the cam follower back down.

For smooth, continuous motion in one direction, you might want to replace the cam with a rotating rubber cone, which drives another rubber cone, at a 90 angle. This rotating vertical shaft could then have a screw thread which drives another concentric vertical shaft (either inside or outside the first):

  _______
 | PLATE |
 | | _ | |
 | || || |
 |_|| ||_|
   _| |_
   \   / 
__|\\ /
    \v
__  /
  |/
 

The side view is shown above (threads not shown). Of course, this approach would only move the top plate vertically by the length of the threads. How high do you want to lift the plate ? Also note that rotating the bolt/cam/cone in the reverse direction would bring the plate back down with this arrangement, while the first arrangement has no method of lowering the plate back down. StuRat (talk) 16:01, 6 September 2011 (UTC)

It looks to me like you are trying to make a standard worm gear that is commonly used in garage door openers and lifts. The motor applies torque to rotate a threaded gear alongside a long threaded bar. The bar moves in a linear direction perpendicular to the rotation of the threaded gear. -- kainaw™ 18:26, 6 September 2011 (UTC)

My understanding is that a worm gear alone causes rotation along the secondary shaft, not translation. However, if the secondary shaft is threaded, that can then drive a threaded concentric shaft, as in my cone arrangement above. StuRat (talk) 19:26, 6 September 2011 (UTC)

Perhaps Kainaw is describing a Leadscrew, sometimes called a Jackscrew (even when not on a jack). It is a shame that those articles do not include a photo of any application other than jacks. -- 110.49.243.48 (talk) 21:49, 6 September 2011 (UTC)

Placebo effect

Why does it occur?How? what is the mechanism?It is difficult for me to understand why and how is it that when you think that something will make you feel better, it will, just like that...--209.188.5.244 (talk) 09:04, 6 September 2011 (UTC)

I don't think you'll get any more comprehensive an answer then there is at Placebo_effect#Mechanism_of_the_effect Jebus989^✰ 09:44, 6 September 2011 (UTC)

Placebo#Mechanism of the effect is detailed, but quite technical and may not be easy to understand. The Skeptic's Dictionary has a good article[4], and UK Skeptics have a shorter one[5]. To summarise: scientists don't have a full understanding of how it works, though there are various theories. Some people think it's purely psychological, while recent research suggests that there may be a conditioned response that causes endorphins to be released when you receive medical treatment; and the reduction of stress from knowing you're being treated may itself help. --Colapeninsula (talk) 09:51, 6 September 2011 (UTC)

Just a thought here - there is also the opposite effect known as the nocebo effect, where if people are told something will adversely affect them it does. How do these effects square with white-coat hypertension? --TammyMoet (talk) 11:45, 6 September 2011 (UTC)

Pump type efficiencies?

Is there any good efficiency comparision for different pump types like centrifugal, scroll compressor, piston etc..? Electron9 (talk) 10:12, 6 September 2011 (UTC)

Have you looked at Comparison of pumps? There are too many variables, such as what is pumped, how fast, at what pressures, in which direction and the power source, that a general efficiency comparison is difficult. Pump manufacturers usually provide data on the performance of their products under intended conditions of use that you can use to calculate efficiency and to compare different pumps. Cuddlyable3 (talk) 11:19, 6 September 2011 (UTC)

Thx! Electron9 (talk) 12:31, 6 September 2011 (UTC)

If the honey badger's skin really is so tough

(See Honey_badger#Relationships_with_humans) Why not make a bulletproof out of it? Imagine Reason (talk) 11:45, 6 September 2011 (UTC)

'Cause it's not bulletproof. --Mr.98 (talk) 12:03, 6 September 2011 (UTC)

Also, you have to catch them first and they're a bit feisty. It's probably easier to just keep walking through thousands of spider's webs until you've got your bulletproof suit completed, any decade now. Sean.hoyland - talk 12:08, 6 September 2011 (UTC)

Honey badgers have a reputation for spectacularly violent objections to attempts at depriving them of their skins. Roger (talk) 13:26, 6 September 2011 (UTC)

We farm and skin lots of other animals, though. Imagine Reason (talk) 15:09, 6 September 2011 (UTC)

Trying to run a honey badger farm could be a lot of fun. It seems that efforts to make peace with them were initiated in South Africa with the Honey Badger Friendly Initiative. Not sure what to make of the fact that they stopped issuing newsletters in 2004. Sean.hoyland - talk 16:09, 6 September 2011 (UTC)

It says that their skin can resist arrows and spears, not bullets. People used to use steel armor back before firearms were developed. Back then, perhaps honey badger skins, especially several layers, might have been a lighter alternative to steel armor. I suspect it wouldn't have been quite as effective, but the lighter weight and thus enhanced mobility of the wearer might have made it a good choice. StuRat (talk) 15:38, 6 September 2011 (UTC)

Though it is unclear how said armor would compare to more easily produced leather or woven armor. It's also not clear what kinds of arrowheads or spearheads that sentence is referring to — are we talking obsidian shards or sharpened steel? --Mr.98 (talk) 16:43, 6 September 2011 (UTC)

Following on from the idea that you can make a bulletproof suit from spider silk....it is true that such a suit would not be penetrated by bullets but it will not save your life. Spider silk is so flexible that the impinging bullet would drag the material into the victim's body, possibly exiting on the far side, still enclosed in the entirely undamaged silk. Colin Tudge addresses this very issue in The Variety of Life. SpinningSpark 17:06, 6 September 2011 (UTC)

Edema

Is airway edema and air edema one and the same thing ? 12:11, 6 September 2011 (UTC) — Preceding unsigned comment added by Aniketnik (talk • contribs)

It doesn't really look like "air edema" is actually a medical term. A Google search for that phrase mainly turns up a lot of instances where there's punctuation in between those two words, and a few cases where the phrase is clearly a typo for "air enema". Are you sure you weren't misreading the phrase "air enema"? Red Act (talk) 12:34, 6 September 2011 (UTC)

I can't see how "air edema" could mean anything. Edema is swelling due to fluid accumulation. Airway edema is swelling that interferes with the airway. But what could "air edema" be? Looie496 (talk) 14:38, 6 September 2011 (UTC)

"Edema" is a build-up of water and other bodily fluids, mostly in the extremities of a person. Could a painful build-up of intestinal gas be "air edema"? ~AH1 ^(discuss!) 22:55, 6 September 2011 (UTC)

"Air edema" is indeed not a medical term, and is probably a misreading or other mistake. So there's no need to make up meanings for what is essentially a meaningless phrase. "Edema" is excess fluid in tissue; the analogous term for air in tissue is subcutaneous or tissue emphysema.- Nunh-huh 23:02, 6 September 2011 (UTC)

One thing is for sure "air edema" is not a medical term. All the inputs given above were very useful and of great help 08:02, 7 September 2011 (UTC) — Preceding unsigned comment added by Aniketnik (talk • contribs)

Deaf-mute

Are there or have there been people who have been born (as opposed to becomng such later in life) incapable of both hearing and of speech? If so, how rare is it? Lexicografía (talk) 12:28, 6 September 2011 (UTC)

Such people certainly exist. Pretty much any congenitally profoundly deaf child will have difficulty acquiring speech naturally. See prelingual deafness. The phrase deaf-mute, by the way, is considered politically incorrect nowadays. Red Act (talk) 12:49, 6 September 2011 (UTC)

I think a key question is what the OP means by being born mute. Do they refer to physical muteness? Everyone is born without speech, it's something that needs to be learnt which is as you say, is difficult for those born deaf or who lost their hearing before the age speech is normally acquired. Nil Einne (talk) 12:57, 6 September 2011 (UTC)

I would imagine that it probably used to be much more common given that scarlet fever often resulted in deafness for very young children before they had acquired speech. Sean.hoyland - talk 13:15, 6 September 2011 (UTC)

To address the rareness portion of your question, in Italy, at least, the prevalence of prelingual profound deafness is about 0.72 out of every 1000 children.[6] Prelingually profoundly deaf children can generally be taught speech, but in general it requires appropriate training, rather than the child acquiring speech naturally the way hearing children do, and not all prelingually profoundly deaf children in the world have access to such training, although I'm having difficultly finding statistics about the prevalence of that situation. Red Act (talk) 13:39, 6 September 2011 (UTC)

To clarify: I was in fact referring to people who are incapable of both hearing and speech, not just difficulty in one caused by incapability of the other. Lexicografía (talk) 13:43, 6 September 2011 (UTC)

The historical term "deaf-mute" refers, of course, to deaf people who never learnt to speak. This used to be much more common when specialist teaching was less available. I would think that inability to make the sounds required by speech, combined with deafness, has always been quite rare, though I don't have any figures to support my claim. Dbfirs 18:32, 6 September 2011 (UTC)

ferro resonance

what is the phenomena of ferro resonance — Preceding unsigned comment added by Saicharan.gedela (talk • contribs) 13:53, 6 September 2011 (UTC)

See Ferroresonance in electricity networks, or see here[7] for a more detailed, technical description. Red Act (talk) 14:13, 6 September 2011 (UTC)

It is a particular worry for electric systems which have underground cables feeding unloaded transformers, with not all the phases switched on at the source. The resonance of the capacitive cable and inductive transformers can result in voltage several time the normal voltage causing the cables to fail or the transformers to explode in a ball of burning oil. It is minimized by using only certain transformer connections; by using three-phase devices for energizing and de-energizing circuits, by limiting the length of underground cable to be energized, by keeping the capacitive reactance much higher than inductive reactance, by having resistors in the transformer neutrals, or by adding a resistive dummy load at the transformer. Edison (talk) 15:11, 7 September 2011 (UTC)

Why don't they destroy the last remaining stocks of smallpox?

Why are they keeping them? Isn't it more dangerous to keep them around? The article says, "Some scientists have argued that the stocks may be useful in developing new vaccines, antiviral drugs, and diagnostic tests". I'm not sure how that's possible though. ScienceApe (talk) 13:56, 6 September 2011 (UTC)

One of the great things about wikipedia is that you can look up the ref supporting a statement like that and see exactly what the (presumably reliable) source says to explain it. The full article appears to be available for free there. DMacks (talk) 14:17, 6 September 2011 (UTC)

The technology to re-create the virus from its known DNA sequence already exists. Only simple virusses have been synthesized in the lab, but there is nothing that would prevent one from re-creating the smallpox virus after all stocks have been destroyed. Count Iblis (talk) 15:47, 6 September 2011 (UTC)

Sure, but wouldn't virus synthesis from a DNA sequence require a ton of $ and special equipment, whereas if you already have the virus, you can work with it much, much cheaper. Googlemeister (talk) 16:29, 6 September 2011 (UTC)

Various military units (eg USAMRIID) around the world preserve biological weapons for research purposes.Anonymous.translator (talk) 17:45, 6 September 2011 (UTC)

I don't recall the novel (definitely not War of the Worlds) or the author (possibly Clarke), but there was something about living viruses (possibly the last of the smallpox stocks) being used to defeat an extraterrestrial enemy. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:31, 7 September 2011 (UTC)

Smallpox and monkeypox don't cross the species boundary all that well - extraterrestrials are probably off the menu. They're more likely to hear about it on the news report, confiscate it and use it on us! We've seen that the U.S. has been very slow to destroy chemical weapons as well - see United States and weapons of mass destruction; the Chemical Weapons Convention calls for destruction of remaining chemical stocks by 2012 but it's not clear the deadline has been met. (OTOH the release of mustard gas from the sinking of the SS John Harvey in the Air raid on Bari has been credited by some for the development of alkylating antineoplastic agents...) It is hard not to see a smallpox stock, as a potential military asset under certain desperate conditions, and something that certain former superpowers might be very reluctant to give up. Wnt (talk) 12:17, 7 September 2011 (UTC)

In the novel I'm thinking of, the live virus was used to defeat a computer somehow (obviously science fiction). There is more practical logic in keeping deadly stuff around: How do we know the enemy doesn't also have it? And even if, why should we give up a strategic advantage? ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:27, 7 September 2011 (UTC)

It was 3001: The Final Odyssey, and I was misremembering it. They used a computer virus to defeat the enemy. However, Clarke did postulate stashing viruses of all types on the moon, i.e. keeping them off the earth - and keeping them around "just in case". ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:33, 7 September 2011 (UTC)

The article you linked to says that's a myth. --Sean 14:56, 7 September 2011 (UTC)

Back in science land, there's a large debate in academic circles about this. This NPR series is a good summary. Shadowjams (talk) 21:47, 9 September 2011 (UTC)

Removing an ankle tendon a minor surgery?

[8] Imagine Reason (talk) 15:08, 6 September 2011 (UTC)

Our plantaris muscle article may help you understand why. Looie496 (talk) 15:45, 6 September 2011 (UTC)

Yes, the source you provided seems to say so - "Vermaelen has undergone a minor procedure to remove an inflamed plantaris tendon from his left ankle." Rcsprinter (talk) 15:46, 6 September 2011 (UTC)

Nuts and bolts

Why does a system of two nuts prevent a bolted joint from unscrewing during vibration? — Preceding unsigned comment added by 49.244.24.52 (talk) 15:21, 6 September 2011 (UTC)

This question was asked and answered a couple of months ago, see Wikipedia:Reference desk/Archives/Science/2011 July 15#Double nuts on bolt. Looie496 (talk) 15:49, 6 September 2011 (UTC)

Or to save you a click, see this page.--Shantavira|^{feed me} 17:27, 6 September 2011 (UTC)

Like a hot knife through...

What is happening, at the molecular/atomic level, when a sharp knife slices through some softer material? Blakk and ekka 16:01, 6 September 2011 (UTC)

Just a point of clarification: Are you only referring to a "sharp" knife, or also a "hot" knife? (Although I will admit that it is pretty clear that you are only referring to "sharpness".) Bus stop (talk) 16:10, 6 September 2011 (UTC)

I was indeed thinking mainly of 'sharpness'. The Blade article's 'Physics' section is rather limited in its explanations. Blakk and ekka 16:15, 6 September 2011 (UTC)

An ideally 'sharp' knife has an edge one molecule thick. An unused disposable Razor blade is nearly this sharp and a fractured glass edge may be the sharpest edge attainable. The material being cut is subjected to Shear stresses in opposite directions away from each side of the blade. The blade will become blunt if its material cannot withstand the shear stress produced by friction as it moves through the material being cut. Cuddlyable3 (talk) 19:38, 6 September 2011 (UTC)

Obsidian blades are still used in surgery because of their perfection compared to any metal edge, having been measured at just 3 nanometres thick. Mikenorton (talk) 19:49, 6 September 2011 (UTC)

More what I was wondering was why is a 'one atom blade' better at cutting than a thicker one that, after all, has a greater number of bonds to break? Blakk and ekka 08:28, 7 September 2011 (UTC)

One thing to note is that knives, in general, are not used to break strong chemical bonds. They are used to separate materials bound with weak bonds like hydrogen bonds, dipole-dipole interactions, etc. This is why you use a different tool to cut things with strong bonds like metal and minerals. --Sean 14:22, 7 September 2011 (UTC)

My reasoning (especially after reading the above) would be that sharpness means that fewer bonds need to be broken at a time for progress to be made. A dull blade is indiscriminate in its breaking of bonds. It breaks many more bonds than necessary. But a sharp blade is only breaking the minimum number of bonds necessary to accomplish division of the material. Bus stop (talk) 14:45, 7 September 2011 (UTC)

wow. Thank you. As someone from a humanities field this helps greatly with a "how does it work" angle, and integrates high school bond types (metals, versus weak interactions between covalent molecules) with hardness. Many thanks! Fifelfoo (talk) 01:59, 8 September 2011 (UTC)

Making UPS

How can i make a good quality UPS with 1kVA capacity? Help me with circuit diagram and explanation of the circuit.... — Preceding unsigned comment added by Subhachakra (talk • contribs) 16:39, 6 September 2011 (UTC)

They are fairly simple. You will find some circuit diagrams in our article on uninterruptible power supply. There are plenty of websites that will get you started. Just Google "build your own UPS".--Shantavira|^{feed me} 17:34, 6 September 2011 (UTC)

Most UPS are designed around a control chip and the chip manufacturers publish application notes that are rich in circuit diagrams and design help. Here are search results for application notes. I checked a couple of them and they give the kind of information you need. Cuddlyable3 (talk) 19:20, 6 September 2011 (UTC)

why the structure of the galaxies is plane?

why the structure of the galaxies is plane? I mean, why it isn't spherical?for example? Exx8 (talk) —Preceding undated comment added 18:36, 6 September 2011 (UTC).

A primary reason is rotation. Most galaxies are described as flat rotating disks - not flat stationary disks. -- kainaw™ 18:53, 6 September 2011 (UTC)

Galaxy formation and evolution has some nice explanations as well. --Jayron32 19:03, 6 September 2011 (UTC)

There are plenty of elliptical galaxies that are approximately spherical. The article on galactic morphology is good. Blakk and ekka 19:06, 6 September 2011 (UTC)

It's a combination of gravity and rotation, with gravity crushing the sphere into a disk while rotation keeps the disk from crushing inwards. Goodbye Galaxy (talk) 20:21, 6 September 2011 (UTC)

AFAIK only the part of the galaxy you see is a plane - the dark matter in which it is embedded is approximately spherical. This is important for explaining why the galaxy spins more like a solid disk than like a solar system. Wnt (talk) 22:28, 6 September 2011 (UTC)

As for the solar system, see our article formation and evolution of the solar system. ~AH1 ^(discuss!) 22:49, 6 September 2011 (UTC)

theoretically, there is an option of Irregular spherical galaxy ?Exx8 (talk) —Preceding undated comment added 23:18, 6 September 2011 (UTC).

Elliptical galaxy. One great example: Messier 87. ~AH1 ^(discuss!) 23:37, 6 September 2011 (UTC)

Nutrition of cartilage

Just having finished off a chicken carcass, I wonder if there's any nutritional benefit to eating the cartilage. It doesn't appear to have much bad stuff, like fat and cholesterol, but does it have any good stuff, like protein, fiber, or minerals ? (I suppose, if nothing else, it will help to fill up my stomach.) StuRat (talk) 19:31, 6 September 2011 (UTC)

For starters, cartilage has a lot of collagen, which is a protein that makes up the extracellular matrix. SemanticMantis (talk) 20:13, 6 September 2011 (UTC)

I don't think it's digestible unless you grind it up into mush or powder (I don't have a reference for that statement though). Looie496 (talk) 20:44, 6 September 2011 (UTC)

Oh, but cartilage is wonderful stuff. Cartilage will, when treated with relatively low heat for a long time, convert into gelatin which any cook will tell you is what makes food taste good. The conversion of cartilege into gelatin is what allows tough cuts of meat turn into succulent, unctuous barbecue; what makes long-cooked stews and soups so tasty, etc. etc. What you can do with cartilage and bones when you are done eating the chicken is throw the carcass into a pot with a mirepoix and create chicken stock which you can filter, freeze, and then take out to add deliciousness to lots of things. --Jayron32 21:14, 6 September 2011 (UTC)

Cartilage contains chondroitin sulfate, a probably useful supplement for sustaining, well, cartilage. Wnt (talk) 22:26, 6 September 2011 (UTC)

It is certainly edible, and may contain calcium. ~AH1 ^(discuss!) 22:47, 6 September 2011 (UTC)

OK, thanks all. StuRat (talk) 17:18, 9 September 2011 (UTC)

Fusion power

In a hard sci-fi setting, which would be more plausible as a practical future energy source: helium-3 fusion or muon-catalyzed fusion? --207.160.233.153 (talk) 20:14, 6 September 2011 (UTC)

Clarke's third law says that it doesn't matter. --Jayron32 20:48, 6 September 2011 (UTC)

Helium 3 fusion isn't a method to fuse. Helium 3 is just one of the fuels used. But the most likely source of fusion power will likely come from magnetic confinement fusion. This isn't something that can be carried on a vehicle though, the surrounding hardware is too large. Go with muon-catalyzed fusion for that. ScienceApe (talk) 22:07, 6 September 2011 (UTC)

Muon-catalyzed fusion only works with isotopes of hydrogen, so is there any way to get around the problem that D-D and D-T fusion give off neutrons? --76.211.90.74 (talk) 22:18, 6 September 2011 (UTC)

Hmmm, if you control the fusion reaction with enough precision, can you control the direction in which the neutrons are emitted? You could concentrate all your shielding in one thin little pencil line that way. Wnt (talk) 22:23, 6 September 2011 (UTC)

Neutrons are uncharged, so it's pretty hard to control where they will go. But don't worry, beryllium makes an excellent neutron reflector and is very light. Also, lithium-6 absorbs neutrons efficiently, while at the same time generating more tritium. So you could go with a lightweight 2-layer shield: a layer of lithium-6 on the hot side to absorb the neutrons and generate tritium, and a layer of beryllium on the cold side to reflect any neutrons that leak through the lithium layer. 67.169.177.176 (talk) 00:43, 7 September 2011 (UTC)

(ec)It's a matter of personal choice. There's no predicting which way science will go, so you can simply choose your favorite method of fusion arbitrarily. Then identify the obstacles (like "the hardware is too large") and ask yourself what would fix that. Maybe your people harvest magnetic monopoles and covalently bond them into carbon nanotube frameworks to create micro tokamaks or something? Actually, looking at the article, I see there's an older technology called a stellarator that fell out of favor for a long time - it's a cool-sounding name, and I like the idea of old technologies rediscovered to solve problems, and when I look at the article, people actually have gotten reinterested in them and have been building some! So I'd make sure that fits in there somewhere, and research the ideas are behind the recent projects, and then throw in the monopoles, room temperature superconductors, or whatever other bits of plausible magic I want to pull it over the top. Wnt (talk) 22:21, 6 September 2011 (UTC)

Magnetic monopoles theoretically should be able to catalyze proton decay, so if you have monopoles, you don't even need fusion. Any matter can be turned into energy. 24.186.108.251 (talk) 05:35, 7 September 2011 (UTC)

That could make a nice plot twist -- a runaway magnetic monopole reaction that catalyzes proton decay in the ship's structure. I don't see how your superhero could save the ship from destruction in this scenario, though... 67.169.177.176 (talk) 06:11, 7 September 2011 (UTC)

Or maybe you could have some unwitting victim get sucked into a virtual black hole and spat out again as a mass of subatomic particles... :-) 67.169.177.176 (talk) 06:28, 7 September 2011 (UTC)

Another idea (just had it when going off shift today): those magnetic monopoles could be used in some kind of "disintegrating blaster" that uses them to create a short-lived virtual black hole on its target, instantly reducing said target to microscopic powder. Maybe this can be used as a top-secret alien weapon that both the good guys and the bad guys are after? 67.169.177.176 (talk) 01:57, 8 September 2011 (UTC)

I have a crape myrtle in my yard

I didn't realize it and never even suspected. But I asked a question unrelated to that on the Science reference desk and finally got an answer somewhere else. More here. And once I knew how to recognize a crape myrtle, I found out I had one. I don't know where it came from but it has always been there. I just never noticed the blooms because there are so few at this point.Vchimpanzee · talk · contributions · 20:52, 6 September 2011 (UTC)

And to update my original question, the "peas" are back on the trees near my house.Vchimpanzee · talk · contributions · 20:58, 6 September 2011 (UTC)

Do you have a question we can answer for you about crepe myrtles? --Jayron32 21:07, 6 September 2011 (UTC)

I'm updating a question that was archived.Vchimpanzee · talk · contributions · 21:20, 6 September 2011 (UTC)

I could ask, since the Wikipedia article doesn't have it. Why have I never seen blooms? I cut the branches regularly so the top ones won't interfere with my cable, telephone or electric lines. And so it will look better without the branches getting long.Vchimpanzee · talk · contributions · 21:28, 6 September 2011 (UTC)

According to your linked previous questions, it looks like you have seen blooms as per this quote: "Anyway, there apear to be small white blooms on some of the trees, with tiny yellow blooms in the middle. They sort of look like daisies. Thie other Crape myrtles, if that's what they are, have poink or purple blooms." As for why you may have not seen blooms this year: pruning can massively interfere with bloom cycles. For instance, some plants only bear fruit on second-season twigs, and your pruning regimen may have removed them. I do not know that crape myrtles have this habit, so alternatively, not every tree/ shrub blooms every year, some plants will only bloom when conditions have been favorable for a year or more. Thanks for the update though :) SemanticMantis (talk) 22:02, 6 September 2011 (UTC)

To answer the question on non-blooming crepe myrtles, I typed "How to get crepe myrtles to bloom" into Google (see here, and got lots of decent results. This is one example, which explains several things which may influence the blooms on crepe myrtles. Regarding the flower color, I have seen crepe myrtles in several color varieties: White, red, purple, and pink are all prevelent around here. --Jayron32 02:26, 7 September 2011 (UTC)

It's actually spelled crape myrtle. That could limit your search results, though I suppose the GOOG is smart enough to adjust for that. --Trovatore (talk) 02:27, 7 September 2011 (UTC)

It is actually spelled both ways, as noted at Lagerstroemia, and +"crepe myrtle" returns 1,040,000 hits on Google, and +"crape myrtle" returns 628,000. So, both spellings are in wide use, but "Crepe Myrtle" is more prevalent. Unquoted and unplussed google searches catch both spellings, however, so my search results end up being identical as if I had spelled it using your, less prevalent, spelling instead. --Jayron32 02:33, 7 September 2011 (UTC)

It's on the north side of the house, so it's not getting enough sun. I don't know how it got there, but thanks.Vchimpanzee · talk · contributions · 13:36, 8 September 2011 (UTC)

Three-body problem

Does the three body problem is relevant to theoretical "moon of a moon"? Is there a four body problem? Exx8 (talk)

Yes and yes -- see n-body problem. Looie496 (talk) 23:07, 6 September 2011 (UTC)

Lagrangian point, Hill sphere and horseshoe orbit may be relevant, depending on the circumstances of orbit. ~AH1 ^(discuss!) 23:34, 6 September 2011 (UTC)