Wikipedia:Reference desk/Archives/Science/2011 October 2

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October 2

Does it hurt getting shot?

I mean, a broken bone will hurt, but what if you get a clean straight shot, only perforating the flesh? Could that be the same case like getting a needle stick by an able med professional, without pain? Wikiweek (talk) 00:06, 2 October 2011 (UTC)

No, because a bullet produces a relatively large permanent cavity and therefore destroys large amounts of tissue, releasing lots of chemicals which stimulate the pain receptors in your arm. A needle is much narrower, produces a much smaller permanent cavity, and produces much lower amounts of chemicals, which translates into much less pain. Also with a needle, much of the small amounts of chemicals that are produced are reabsorbed by non-nervous cells, and never get a chance to stimulate pain receptors. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 00:20, 2 October 2011 (UTC)

From what I've heard, getting shot feels a lot like getting punched, only worse. 67.169.177.176 (talk) 00:21, 2 October 2011 (UTC)

Getting shot is a combination of multiple types of pain. There is the puncture of the skin, which is a sharp pain. If a bone is hit, there is damage not only the bone, but also to the joints around the bone. Then, just to piss you off, there is a sever burning if the bullet remains near the skin. For an anecdote... I've been shot 3 times. All three times, it hurt a hell of a lot. I've had countless shots and donated blood multiple times each year. I don't flinch when a needle is put in my arm. -- kainaw™ 01:58, 2 October 2011 (UTC)

THREE times?! Ouch! Was it part of an especially nasty wiki-dispute? 67.169.177.176 (talk) 02:06, 2 October 2011 (UTC)

You mean, you were shot three times one bullet or at one occasions three bullets? In the former case you seem to have a pretty bad luck (or good luck of being alive, depending on how you see it). Wikiweek (talk) 02:05, 2 October 2011 (UTC)

Three separate and very different occasions. However, it isn't notable any more than a stupid little anecdote. -- kainaw™ 02:11, 2 October 2011 (UTC)

Adrenalin can override pain. Don't forget about shock. Plasmic Physics (talk) 02:23, 2 October 2011 (UTC)

My obsessive punning brain read that as "admins can override pain". --jpgordon^{::==( o )} 18:47, 2 October 2011 (UTC)

I don't think that's correct but correct me if I'm wrong here. My understanding is that the sympathetic nervous system would be activated in response to a stressful event. If that event was something like getting shot, epinephrine and norepinephrine would be released in a sympathetic response while the endocrine system would release endorphins. So while epinephrine would be pumping through you after getting shot, it would actually be the endorphins killing the pain. I can't think of a receptor site for epinephrine to kill pain, though I could maybe think of ways in which it might stimulate certain neuronal activity to ignore pain signals, but that's a bit of a stretch in my understanding. N^oformation ^Talk 23:23, 6 October 2011 (UTC)

Photon-tachyon interactions

A photon travels directly towards a tachyon moving directly towards it (the photon). They collide. Since the tachyon travels faster than the photon and the photon therefore cannot bounce off it and travel forwards away from the tachyon (because the tachyon will be continuously overtaking it), is the photon destroyed, does it pass through the tachyon, or does it swerve to avoid the tachyon? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 00:14, 2 October 2011 (UTC)

Tachyons don't exist in real life, so the question has no right answer. 67.169.177.176 (talk) 00:23, 2 October 2011 (UTC)

Absence of evidence≠evidence of absence. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 00:25, 2 October 2011 (UTC)

Tachyons are purely theoretical. There is no way of knowing how they would interact with other particles. There is a flaw in your logic though. If tachyons behave anything like any other particle one would assume that if it contacted another particle it would be deflected as well. Thus both particles would end up traveling in different directions, avoiding the problem. --Daniel 01:00, 2 October 2011 (UTC)

The tachyon has more momentum than the photon and would therefore overpower it. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 01:05, 2 October 2011 (UTC)

Good point... maybe. Tachyons lose energy as they speed up so it might depend on speed of the tachyon. From what I understand by reading the article is that to if one calculates a tachyon interacting with a normal particle you end up with imaginary numbers which have no meaning in our universe. --Daniel 01:13, 2 October 2011 (UTC)

I can't see any particular reason why a tachyon would have more momentum that a photon. It's moving faster, but that's not the same thing. In fact, I'm not sure their momenta are even comparable. In some formulations, a tachyon has imaginary mass. Doesn't that mean it would also have imaginary momentum? It doesn't make sense to ask whether a real number or an imaginary number is larger. Even if you are right and the momentum is greater for the tachyon, that doesn't mean it would "overpower" the photon. Typically, they would both be deflected, just the photon would be deflected more. --Tango (talk) 11:55, 2 October 2011 (UTC)

If a train rams a car, the train does not start moving in the other direction. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 14:07, 2 October 2011 (UTC)

But it might well get derailed and go off to the side (if it weren't for the rails, it almost certainly would go off to the side). That's what we mean by "deflect". The collision isn't going to be perfectly head-on, so the particles will each be deflected to opposite sides. If it were a perfect head-on collision, then I think you would just end up with the photon following the tachyon as though the tachyon had gone straight through it. There isn't a problem there before photons don't actually bounce, they are absorbed and then re-emitted. There is nothing to stop the photon being on the other side when it gets re-emitted. (That is all based on some wild guesses about how tachyons behave that come from extrapolating our existing theories to particles that they don't really make sense for, so it should be taken with a very large sack of salt.) --Tango (talk) 17:07, 2 October 2011 (UTC)

A tachyon that couples to the electromagnetic field would emit Cherenkov radiation as it moves through vacuum. The recent OPERA results suggesting that neutrinos move faster than light can be ruled out because of this effect, see here. Count Iblis (talk) 01:14, 2 October 2011 (UTC)

"Tachyon! Duck!" "THAT'S NOT A DUCK! And don't call me Tachyon!" Whoop whoop pull up ^{Bitching Betty | Averted crashes} 01:43, 2 October 2011 (UTC)

I don't understand that paper at all. They seem to assume that the neutrinos are straight-up QFT tachyons with E² = p² + m² and m² < 0. But I haven't seen anyone suggest that as an explanation for the OPERA data. QFT tachyons aren't superluminal. The proposed explanations I've seen are quantum gravitational, and I don't think this QFT argument would apply to them, not that I know anything about quantum gravity. -- BenRG (talk) 05:15, 2 October 2011 (UTC)

They assume that you can describe Lorentz invariance violation as is done in this paper. Count Iblis (talk) 22:56, 2 October 2011 (UTC)

Weighing the atom

How much does a single atom weigh? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 00:15, 2 October 2011 (UTC)

Depends on what kind of atom. See the articles Atomic mass, Chemical element and Isotope for more info. 67.169.177.176 (talk) 00:25, 2 October 2011 (UTC)

Thanks. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 00:28, 2 October 2011 (UTC)

To find the answer for any specific atom, go to the periodic table, find the atomic weight of an element, and then do the following calculation: Atomic weight/(6.02X10^23). So for instance for hydrogen you would do 1.008/(6.02X10^23). N^oformation ^Talk 23:31, 6 October 2011 (UTC)

Bacteriophages as antibiotics?

Would bacteriophages be useful as a practical replacement of chemical antibiotics? Because they produce more of themselves whenever they kill bacteria (and become inactive and are flushed out of the system when all the bacteria are dead), while chemicals require repeated treatments to eliminate the infection, it seems that they'd be much more efficient. --70.250.214.149 (talk) 01:25, 2 October 2011 (UTC)

See the article Bacteriophage therapy. It appears that bacteriophages can indeed be used to treat infectious diseases, but only if the exact strain of the disease-causing bacteria involved is known with certainty. For this reason, it would probably be ineffective against infections that involve a rapidly mutating bacterial strain, or several strains at the same time (as is often the case, e.g. with tuberculosis). 67.169.177.176 (talk) 01:35, 2 October 2011 (UTC)

Terrarium vs. tank

If I'm getting a ball python, is there any advantage of a regular fish tank set-up vs. a glass terrarium set-up? DRosenbach ^{(Talk | Contribs)} 01:30, 2 October 2011 (UTC)

You'd be paying the same for a larger terrarium, right? Go with that and give it a stick to climb. 69.171.160.198 (talk) 03:40, 2 October 2011 (UTC)

AK47 vs. Bulletproof glass

Will bulletproof glass withstand multiple hits at the same point from an AK47? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 01:39, 2 October 2011 (UTC)

Given enough hits at the exact same point, even the strongest bulletproof glass can eventually be breached. It all depends on how strong is the glass, and how many hits it takes at the same point. 67.169.177.176 (talk) 01:50, 2 October 2011 (UTC)

Hopefully you are not holding an AK47 at this moment... Whoop whoop pull up ^{Bitching Betty | Averted crashes} 01:53, 2 October 2011 (UTC)

The question can only be answered with yes, for any material, unless you limit the number of shots. Wikiweek (talk) 02:03, 2 October 2011 (UTC)

Or unless you're shooting at a gravitational singularity... Whoop whoop pull up ^{Bitching Betty | Averted crashes} 02:10, 2 October 2011 (UTC)

Is there any hypothesized method for damaging or altering such a phenomenon? ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:29, 2 October 2011 (UTC)

Only hawkings radiation can make it decay, and that would take a long ass time. ScienceApe (talk) 05:13, 2 October 2011 (UTC)

AK-47 shot at bullet proof glass. As the warning at the front states, There is no such thing as 100% "bulletproof glass" - all glass is bullet resistant according to the standards set by the National Institute of Justice and/or the European Committee for Standardization. Buddy431 (talk) 04:59, 2 October 2011 (UTC)

That was only 1 hit at any one of the three points. 67.169.177.176 (talk) 01:39, 4 October 2011 (UTC)

And for the record, there is nothing illegal about owning or holding an AK-47 in many jurisdictions around the world. In the US for example, they are legal in many areas provided they do not have full auto capability. Googlemeister (talk) 14:11, 3 October 2011 (UTC)

Global warming and future

What will the effects, as can be scientifically predicted from present climate scenario, of global warming to human civilization in 2100 and later? Will islands like Mauritius and coastal areas like Sunderbans sink? --DinoXYZ (talk) 05:56, 2 October 2011 (UTC)

Yes. Hence why representatives of the most low-lying island nations were pretty much disgusted at the failure to produce a resolution in the 2009 United Nations Climate Change Conference.

See Climate change in Tuvalu and Maldives#Environmental Issues. -- Obsidi♠n Soul 06:42, 2 October 2011 (UTC)

Wind instruments

Wind instruments do not have all their notes perfectly in tune with corresponding notes on the piano. There is a chart published indicating the discrepancies with respect to alto and tenor saxophones. It would interesting to have similar charts for, at least the B flat trumpet and the slide trombone. — Preceding unsigned comment added by 82.44.58.70 (talk) 09:01, 2 October 2011 (UTC)

Do you have a question? Plasmic Physics (talk) 11:33, 2 October 2011 (UTC)

No, he doesn't. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 12:15, 2 October 2011 (UTC)

I'll ask it then. Does anyone have a link to a chart for various instruments indicating the discrepancies between their notes and those of a piano? I know that there are many secondary-adjustments sax and clarinet players use, various combinations of keys and tone holes distant from the main ones used for the standard fingering, so would also be useful to know how much this counteracts the discrepancy. Trumpets have a tuning slide that can be kicked in or out while playing to fix certain notes. And a trombonist could just slide a little in or out and match any arbitrary frequency exactly, no? DMacks (talk) 16:16, 2 October 2011 (UTC)

Not unless the trombone is also perfect (i.e. undented). Whoop whoop pull up ^{Bitching Betty | Averted crashes} 20:32, 2 October 2011 (UTC)

Comment: "perfectly tuned" is a bit of pseudoscience. Though musicians will adamantly insist that there is such a thing as a true "perfect pitch" - and then furthermore attest that certain humans are "endowed" with a flawless capability to discern exact pitches - anybody with an engineering background will scoff at the idea.

Musical instruments have timbre - they are not monotonal - which means that their frequency spectrum is very complicated. A peak frequency exists (the root note), but it always (always) has a bandwidth. It is physically impossible to construct a real, non-theoretical instrument (including electronic synthesizers) that deliver a pure monotone sine wave. (To do so would require a musical instrument that never started or stopped playing - to have zero bandwidth tone, i.e. "exactly one specific frequency," the extent of the signal must propagate to ±∞ time. Nimur (talk) 18:45, 3 October 2011 (UTC)

Inflation-Adjusted Cost of Electricity?

Is there a way to calculate (or find) the Inflation-Adjusted Cost of Electricity in the US or EU for the past 50 years or so? On a similar note, is there a way to find the inflation-adjusted cost of lighting? --CGPGrey (talk) 10:31, 2 October 2011 (UTC)

You got it. Summary: about 8 cents per kilowatt hour, but recently headed down under 7. 69.171.160.9 (talk) 19:35, 2 October 2011 (UTC)

By which methods and how accurate can we predict the properties of an unknown isotope?

I'm just a bit curious about some sites that claimed like "In case no experimental data is available, trends in the systematics of neighboring nuclides have been used, whenever possible, to derive estimated values"--Inspector (talk) 11:19, 2 October 2011 (UTC)

That kind of guessing is one of the main strengths of the arrangement of the Periodic Table. We've come a long way from Mendelejev and his Eka-aluminum, but the system still pretty much works the same. Take neighboring elements and extrapolate, mainly. I cannot tell you which Algorithms are used in the creation of such data, sadly, but the system in general is pretty sound. I cannot comment of the reliability of any such specific data though. --Abracus (talk) 15:25, 2 October 2011 (UTC)

I depends on the properties you are trying to predict. Look for example at figure 2 here. One can see that while properties across the periodical table are not exactly continuous or obvious, there are trends, so that if you knew some "goalposts", you could try to work backwards to extrapolate the remaining parts. There are other forms of regularity that can be extrapolated ahead of time — e.g. magic numbers. This doesn't mean that these things are understood greatly — there are often surprises (imagine trying to extrapolate the phase diagram of Plutonium only knowing Uranium and Curium, in the aforementioned figure 2) but you can often get a pretty good idea of what the possible and/or likely cases are (in the case of the U and Cm, you'd know that something weird was going to be happening there, because you've got two radically different phase diagrams — Pu, as it turns out, is something of a juncture point in the higher actinides, making it metallurgically quite interesting). Depending on the properties you are investigating, there are probably more or less reliable ways of deducing from other nuclides. --Mr.98 (talk) 17:07, 2 October 2011 (UTC)

For example, the half-lives?--Inspector (talk) 09:14, 3 October 2011 (UTC)

Nuclear half lives fall into the domain of nuclear physics (or "nuclear chemistry"); so the periodic table (which really is a taxonomy of electron behaviors) is sort of inapplicable. To study half-life quantitatively, you need to use a lot of nuclear physics theory, but most of the time, the simple theories can't accurately predict nuclear stability. Loads of experimental correction factors are used, based on known, measured properties. Consider reading: about isotopic stability. Nimur (talk) 18:52, 3 October 2011 (UTC)

future binary solar system?

Given the enormous gravity of Jupiter and the available hydrogen/deuterium in space, how much larger would Jupiter have to be, or how much time would it take, for Jupiter to reach sufficient mass to trigger internal fusion reaction and become a sun/star? Has anybody ever figured this out?, or is this just a stupid question?190.149.154.16 (talk) 12:43, 2 October 2011 (UTC)

It's a perfectly sensible question and has been extensively studied. The article Brown Dwarf should get you started, and will have further relevant links. {The poster formerly known as 87.81.230.195} [[Special:Contributions/90.197.66.7Insert non-formatted text here0|90.197.66.70]] (talk) 12:56, 2 October 2011 (UTC)

Definitely not time, mass yes. Time has no effect on whether fusion initiates or not. There is a net loss of mass from Jupiter not a net gain, so unless its mass is artificially increased significantly, it will not happen. Plasmic Physics (talk) 12:57, 2 October 2011 (UTC)

Thanks guys. But I'm a little confused about the(Jupiter's mass loss) statement because atmospheric escape indicates that Jupiter's great distance from the sun, It's enormouse magnetic sheild, and large mass/gravity would minimize or eliminate mass loss, even though it doesn't mention jupiter specifically. Now since an enormouse amount of space hydrogen must be attracted by Jupiter's gravity it seems that the mass must be increasing. Please help.190.56.17.233 (talk) 16:00, 2 October 2011 (UTC)

The mass Jupiter is losing is probably very small, but it isn't attracting much either. The inter-planetary medium, especially out as far as Jupiter, is extremely thin. I think Jupiter gains more mass from meteors than the inter-planetary medium, but it will never get anywhere near enough to become a star. It would need to become about 80 times as massive as it is now. There isn't enough matter in the entire the solar system (excluding the Sun) to do that. --Tango (talk) 17:15, 2 October 2011 (UTC)

Is there a reliable source saying that Jupiter is losing mass? μηδείς (talk) 17:27, 2 October 2011 (UTC)

A good point Medeis. I tried several titles but could not find anything indicating Jupiter mass loss. Bearing in mind the enormous gravitational influence of Jupiter, It's clear that it's influence cannot be limited to the space volume within the solar system, and must also effect a large volume of interstelar space, and even though those atoms of hydrogen are widely seperated there must be a lot of matter available to Jupiter. Anybody have anything on that?190.56.17.233 (talk) 18:39, 2 October 2011 (UTC)

P.S. It has been asertained that Jupiter is giving off more heat energy than it gets from the sun, but that's not the same as loosing mass. Or is it?190.56.17.233 (talk) 18:48, 2 October 2011 (UTC)

It was in last my talk that human can change the Jupiter to be a star. Although its effect and brightness will be very poor and only it will appear in day and create shadow. No more energy and week light than moon. If we send any space craft to explode Metis (one of Jupiter moons) to fall on Jupiter then its mass will increase to be a star. --Akbarmohammadzade (talk) 05:06, 4 October 2011 (UTC) The mechanism of this event is carrying Metis to Roche limit --Akbarmohammadzade (talk) 05:15, 4 October 2011 (UTC)

Recently we are studying on solar system planets moons and Kuiper and asteroid belt, our work shows a bit mass increasing of jovian planets, after acceptance of such calculations I can say it here. --Akbarmohammadzade (talk) 05:51, 4 October 2011 (UTC)

No, Metis is a very small moon, and so will not be of sufficient mass to initiate fusion in Jupiter to turn it into a star. The gas giants may be gaing mass, but it will never be nearly 80 times as large as it is now. 190.56.17.233: Remember the energy-mass equivalce. Plasmic Physics (talk) 06:18, 4 October 2011 (UTC)

Antimatter vs. black hole

Would it be possible to destroy a black hole by sending a gigantic lump of antimatter, the same mass as the black hole, into it? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 12:53, 2 October 2011 (UTC)

No. Why should it? Plasmic Physics (talk) 12:57, 2 October 2011 (UTC)

Adding mass to a black hole only makes it stronger. Plasmic Physics (talk) 12:59, 2 October 2011 (UTC)

Adding enough antimatter would annihilate the black hole's singularity, causing the black hole to stop existing. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 13:45, 2 October 2011 (UTC)

Rubbish. Annihilation of matter and antimatter leaves energy, which has the same mass as the original matter and antimatter - see mass-energy equivalence. So you have simply added more mass to the black hole, as Plasmic Physics said. Gandalf61 (talk) 15:04, 2 October 2011 (UTC)

Would the antimatter even make it from the event horizon to the singularity? I thought anything added to a black hole after it forms stays suspended in the infinitely extended spacetime. Or is that just from the antimatter's frame of reference? 69.171.160.9 (talk) 19:33, 2 October 2011 (UTC)

In the frame of reference of the object falling into the black hole, it reaches the singularity within finite time. It is in the frame of reference of an object far away from the black hole that objects falling in seem to become frozen just above the event horizon. --Tango (talk) 22:44, 2 October 2011 (UTC)

Similar question:) HOW to destroy a black hole? -Ewigekrieg (talk) 13:19, 2 October 2011 (UTC)

Add antimass, which has never been proven to exist; or increase the Hawking radiation flux, which there is no known way to accomplish. Plasmic Physics (talk) 13:33, 2 October 2011 (UTC)

Doesn't antimatter HAVE antimass? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 14:32, 2 October 2011 (UTC)

No, anti-matter has normal mass. Dauto (talk) 15:01, 2 October 2011 (UTC)

Can some sort of very strong gravitation waves destroy it? - Ewigekrieg (talk) 13:55, 2 October 2011 (UTC)

No, very strong gravitation waves are produced by coloding black holes, they merge not vanish. Plasmic Physics (talk) 14:00, 2 October 2011 (UTC)

I try to explain. So, we have a bath full of water. We open the plug and create a whirlpool ("black hole"). Now we make really big wave ("gravitation wave"), and the whirlpool collapsed. Can we repeat this with real black hole? -Ewigekrieg (talk) 14:12, 2 October 2011 (UTC)

No. Read my comment below. Dauto (talk) 15:03, 2 October 2011 (UTC)

Anti-matter and gravitational waves both have positive energy and will only make the BH bigger. Note that the singularity is not made of matter. It is a space-time singularity. Think of it as a part of the structure of space-time itself, not as an object located somewhere in space-time. Dauto (talk) 14:18, 2 October 2011 (UTC)

So ram a white hole into it. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 14:43, 2 October 2011 (UTC)

A white hole is just another name for a black hole. read the article you linked (specially the 3rd paragraph) for an explanation. Dauto (talk) 15:10, 2 October 2011 (UTC)

It might be indistinguishable. It might be different though (if it exists). ScienceApe (talk) 15:54, 2 October 2011 (UTC)

See also here. Count Iblis (talk) 15:36, 2 October 2011 (UTC)

Exothermic reactions in warm-blooded creatures

What are the chemical equations of some exothermic reactions that take place in the bodies of some warm-blooded animals? Please use common sense and understand that I am aware that lots of exothermic and endothermic reactions take place in the bodies of both warm-blooded and cold-blooded animals, but by my question I of course am only interested in reactions that are significant enough to be ones relevant in heat output to be one of the reactions that cause the animal to be considered by humans as warm-blooded (and again, yes, I am aware that the term has fallen into disuse; humor me). Peter Michner (talk) 13:42, 2 October 2011 (UTC)

This explains it pretty well. For shivering thermogenesis, it's basically the waste energy released during ATP hydrolysis. In non-shivering thermogenesis, it's the disruption of oxidative phosphorylation (creation of ATP) by UCP-1 which enables the mitochondria to "waste" substrate, generating heat instead of storing them in ATP as it normally would.

I'm sure there are more detailed breakdowns of the reactions mentioned in the linked articles or somewhere else, but you'd probably be better off looking for them yourself. My brain shuts down when I see diagrams of metabolic reactions, I disliked biochem :P -- Obsidi♠n Soul 15:41, 2 October 2011 (UTC)

Newton's laws of motion

Isn't Newton's first law of motion simply a special case of his second law of motion, where f=0? And would massless particles still be affected by the first law, because they have no mass and therefore no force is needed to produce any given acceleration (because $f=0a$, therefore $0=0a$, so any value of a satisfies the equation)? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 14:21, 2 October 2011 (UTC)

1. Yes, the first law is just a special case of the second.
2. No, massless particles also follow the fist law.

Dauto (talk) 14:58, 2 October 2011 (UTC)

I like to think of the "first law" as the definition of inertia, rather than as an equation. The second law is the definition of force in Newtonian physics; and the third law is the formal statement of Newtonian kinematics.

When you compare the "Three Law" statement of Newtonian physics to alternative formulations of classical physics, (i.e., the principle of least action), you see that these three items are explicit. For example, inertia does exist conceptually, when we study Lagrangian physics; but it's not defined so succinctly.

When viewed this way, the shortcomings of Newtonian physics become blatantly obvious: for example, force is defined in terms of mass and acceleration, but mass is never defined. (Nor is acceleration, for that matter!) Newton assumed mass was an innate property of the universe! And he didn't consider wacky spatial geometries where acceleration is poorly defined. Extending the Newtonian definitions to account for these properties leads to general relativity. Nimur (talk) 19:03, 3 October 2011 (UTC)

Infinite Regress and General Relativity

It is often asserted in arguments related to the existence of God that an infinite regress of events is not possible. This to me seems to just be a bare assertion, but I would like a more specific demonstration that an infinite regress is at least theoretically possible to use as a clincher in such arguments. Has someone ever mathematically proved that an infinite regress does not violate General Relativity? Rabuve (talk) 15:00, 2 October 2011 (UTC)

The argument does not refer to an infinite regress of events, but rather to an infinite regress of causes. General Relativity has nothing to say about that. Looie496 (talk) 15:19, 2 October 2011 (UTC)

What I mean is a chain of events each caused by the one before it Rabuve (talk) 16:35, 2 October 2011 (UTC)

In classical theories an infinite regress (in a finite amount of time) is possible. This has been shown rigorously for classical mechanics, and I think in General Relativity there is a similar result. Count Iblis (talk) 15:18, 2 October 2011 (UTC)

What does infinite regress mean in physics?

You have it backwards. The Universe exists because there was nothing to prevent it. μηδείς (talk) 17:24, 2 October 2011 (UTC)

I'm not asking why the universe exists; I'm asking if there is a proof that having an infinitely long string of events casually linked doesn't violate General Relativity. Rabuve (talk) 20:08, 3 October 2011 (UTC)

See Steady State theory for relativistic theories with an infinite past paradigm. --Modocc (talk) 19:26, 4 October 2011 (UTC)

Worried about eating gnats

So I bought some cinnamon rolls, and I ate one. Then the next day, I see inside the box a whole bunch of flying insects. I was so disgusted, I have no idea how they got in there because the box was closed and in a plastic bag that was wrapped tight. Anyway I got rid of the bugs (They were quite small so I think they were gnats), and considered throwing out the rest. But they tasted really good, and I decided that they were probably harmless so I ate the rest. Now I'm a bit worried (hypochondria?), is there any possibility that they have any parasites in them or diseases? Could they have layed their eggs in the cinnamon rolls? ScienceApe (talk) 15:15, 2 October 2011 (UTC)

We cannot give medical advice here as a general rule. If you are worried about parasites, please ask an appropriately qualified medical professional. --Abracus (talk) 15:27, 2 October 2011 (UTC)

Wow. The question "do gnats carry parasites or transmit disease" is a medical question? --jpgordon^{::==( o )} 15:32, 2 October 2011 (UTC)

Yeah I didn't think this was a medical question lol. If you want, just ignore my little backstory and tell me if there's any danger to consuming gnats or food that gnats were crawling around on. ScienceApe (talk) 15:47, 2 October 2011 (UTC)

See The Food Defect Action Levels by the FDA. [Most unintentionally ingested] insects "pose no inherent hazard to health" except to people who may have allergies to them. -- Obsidi♠n Soul 16:00, 2 October 2011 (UTC)

With this sort of question, the problem is that if we tell you not to bother to seek medical advice and then you get sick, we are partly to blame. So if you are in any doubt it's best you call NHS Direct or the equivalent in your country.--Shantavira|^{feed me} 16:03, 2 October 2011 (UTC)

Like I said, just ignore my backstory dude. :) ScienceApe (talk) 18:58, 2 October 2011 (UTC)

Good point, you reminded me of this article where it says (halfway through) that frozen broccoli is filled with bugs. As the FDA article says there can be more than one aphid/thrip/mite per 2 grams of broccoli. Considering that these are similar to gnats (they feed mostly on plants) it would seem unlikely you'll come to any harm. As the link above shows, you could in fact be a pioneer of entomophagy in the west! (Obviously if you do feel ill go see a doctor). SmartSE (talk) 20:39, 2 October 2011 (UTC)

Insects do not spontaineously generate parasites or other disease causing microbes. They simply convey them from one animal to another. so if those insects do not feed on animals/humans and just like to eat sugar,then that just makes them sweeter.190.56.17.233 (talk) 16:27, 2 October 2011 (UTC)

So, it's secure to eat cockroaches and flies? Quest09 (talk) 16:30, 2 October 2011 (UTC)

As long as they haven't been eating mold, oleander seeds, or something else toxic. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 16:34, 2 October 2011 (UTC)

Cockroaches and flys do feed on animal matter, including feces. And how many orleander seeds do you think a gnat could eat.190.56.17.233 (talk) 16:40, 2 October 2011 (UTC)

Part of one. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 16:44, 2 October 2011 (UTC)

pretty harmless then, Huh?190.56.17.233 (talk) 16:58, 2 October 2011 (UTC)

Do you have ANY idea how toxic oleander is?! Whoop whoop pull up ^{Bitching Betty | Averted crashes} 20:21, 2 October 2011 (UTC)

Well our article suggest that it is not that highly toxic. I suppose if you ate a meal of cockroaches, and they had all fed on Oleander seeds, then you might be at risk. Dbfirs 07:38, 3 October 2011 (UTC)

Alcubierre drive vs. black hole

What would happen f you rammed an Alcubierre drive into a black hole? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 16:19, 2 October 2011 (UTC)

The Alcubierre drive is not permitted by the laws of physics and violates causality. When you can violate causality you can do anything, including, I suppose, destroying black holes by preventing their original formation. However, I think that the Alcubierre drive, as usually defined, has no mass, so just tossing one haphazardly into a black hole wouldn't grow or shrink the hole. -- BenRG (talk) 18:23, 2 October 2011 (UTC)

So I was wondering why I had never heard of that drive before, and now I see why. It's a useless piece of non-sense. Dauto (talk) 19:18, 2 October 2011 (UTC)

Wouldn't the expansions and contractions of space-time ahead of and behind the drive yank at the space-time of the black hole enough to seriously perturb it? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 20:23, 2 October 2011 (UTC)

As BenRG says, the drive can't actually exist (at least, not without some pretty serious changes to our understanding of physics). That means it's meaningless to try and describe how it would work, except as a mathematical exercise. Black holes certainly can be perturbed, in as much as the event horizon won't always be spherical (collisions between black holes are a good example of this), but that won't destroy the black hole. --Tango (talk) 22:50, 2 October 2011 (UTC)

The principle of general covariance implies that the event horizon of a black hole is not fundamentally different from any other place in the universe. An Alcubierre drive would pass through it just like any other region of spacetime. But because it exceeds the speed of light, the usual rule that "what happens inside the event horizon stays inside the event horizon" doesn't necessarily apply any more. Maybe it could shrink the hole by transporting out infalling matter before it hits the singularity. Regardless, the Alcubierre drive requires exotic matter with a negative mass density, and if you've got that you could simply drop some of it into the hole to shrink it, no warp drive required. -- BenRG (talk) 04:29, 3 October 2011 (UTC)

Shot three times

How was User:kainaw shot three times? What are the chances of that happening and the chances of surviving? Quest09 (talk) 16:25, 2 October 2011 (UTC)

It would depend significantly on what part of your body is hit each time, as well as the calibre and type of bullet and the medical care available (and how near it is). There is no way you can come up with a single number. You could theoretically come up with the number of people who have been shot three times and see what percentage of them survived but I doubt those statistics are easy to come by (and whatever statistics you have are likely to be somewhat flawed anyway, e.g. if you go by hospital visits some people aren't going to go to hospital unless it is severe), and the number it self is fairly meaningless. Nil Einne (talk) 16:47, 2 October 2011 (UTC)

That rather uncouth chap 50 Cent was shot nine times and survived with only minor long term effects so even multiple bullet wounds are survivable. Quintessential British Gentleman (talk) 17:01, 2 October 2011 (UTC)

I realised I forgot to mention how deeply the bullet penetrates will also often have an effect, which will depend on the first 2 I mentioned but also things like the type of gun and distance it was fired from. BTW just to emphasise 'part of the body hit' isn't a simple thing. Obviously a shot which actually penetrates he heart is likely to be fatal and the brain isn't good either but it seems likely you have a greater chance of surviving some shots to the body then a shot whick knicks the Femoral artery. Incidentally I found this very mildly related article [1] Nil Einne (talk) 18:24, 2 October 2011 (UTC)

As Nil Einne states, two of them were small caliber and didn't even break the bone they hit. I grew up playing in woods where hunters were always shooting at anything that moved. The third was a larger caliber, but it was a ricochet into my shoulder. So, it was travelling relatively slow. I know that getting shot isn't common - most people aren't raised around guns - but I don't find this notable. I was raised in an area full of hunters and then I served in the U.S. Marines (they have a few guns too). Now, I work in a hospital, so I have more concerns about infections than guns. -- kainaw™ 17:17, 2 October 2011 (UTC)

Well, as I asked whether being shot hurts, I didn't mean such cases: 2x hitting a bone, 1x ricocheting bullet, and therefore not straight. I thought about a clean high energy straight shot, maybe just hitting your waste fat (only skin and fat), getting in and out. Wikiweek (talk) 19:43, 2 October 2011 (UTC)

I see somene mentioned 50cent. Iremember once in the 1990's reading in a science magazine (or science section of a periodical) that on average there is a 50% chance of death per bullet wound over the general population. Paradoxically, that doesn't mean your chances of survivng one bullet wound is 50%. μηδείς (talk) 17:20, 2 October 2011 (UTC)

This guy survived being "executed" by a firing squad who shot him 9 times including being shot straight in the head - there is a pic here! If you search for "El Fusilado" you'll also find a song telling his story by Chumbawamba _{(much better than a song I can be fairly sure 50 cent will have made about him being shot)}. SmartSE (talk) 20:53, 2 October 2011 (UTC)

Vladimir Vysotsky also has a song about a guy who survives an execution by firing squad because one of the soldiers refused to shoot. 67.169.177.176 (talk) 01:22, 4 October 2011 (UTC)

Gov Connalley of Texas got shot like 3 times with 1 bullet and lived, if you believe the experts. Googlemeister (talk) 14:00, 3 October 2011 (UTC)

Radar display updating in "real-time"

I watched an episode of Mayday (TV series), and noticed that the airplanes on the Air Traffic Controller's radar display were moving "live", very smoothly. However, there was also the familiar slowly rotating green strike going across the display, indicating the antenna orientation; the motion of the dots just was in no way related to the rotation of the radar. Sometimes the dots even changed direction between the sweeps. Is this how the (modern) radars actually work, or is it just an artist's misconception? I've seen it in numerous other episodes of Mayday, too, and it really sticks out. Thanks! ›mysid (☎✎) 18:55, 2 October 2011 (UTC)

What you see on a radar is called a "track" (well, you see many tracks). Radars rarely work alone. The controlling computers gather information from other radars also. So, you have information even when your radar isn't sweeping an area. Further, the controlling computers predict what will happen between sweeps and show that. When an aircraft behaves in an abnormal manner, it will jump. In reality, it didn't jump. It is just that the computer predicted it would be in one place, but it showed up in another. That isn't as easy as it seems. What if an aircraft dropped chaff to make it look like it is somewhere it isn't? What if it was two aircraft all along and they were real close to one another and then they suddenly separate? All in all, the person at the radar station is seeing the best guess of the computer, not real radar information. -- kainaw™ 19:09, 2 October 2011 (UTC)

Thanks for the info! But what role does the green strike play, then? It was only shown for one radar. (And does this system have a name? Our article on radar tracker doesn't mention one where the dots are moving smoothly) ›mysid (☎✎) 19:25, 2 October 2011 (UTC)

Perhaps the regulations for that kind of a device are old and require it to be there. --145.94.77.43 (talk) 20:12, 2 October 2011 (UTC)

Civilian trackers definitely are not required to display the antenna swipe, at least in Europe. Moreover, in all but the most basic installations, multi-radar tracking is the norm, so there is no single swipe. There are two possible sources for the "stripe". First, if it really was rotating, it may just have been artistic license - they asked a prop man to provide a display, and he programmed a fake. If, on the other hand, the stripe went up (or down), it may just have been interference between the radar screen and the movie camera. --Stephan Schulz (talk) 21:17, 2 October 2011 (UTC)

The green sweep display is just from one radar system of which there are usually several available, and the display is there with controls so that the sweep region can be adjusted or controlled in an emergency. The smooth operational display system displays are multilateration from all the radars that aren't under manual control for the Short Term Conflict Alert, transponders, and communications systems. 69.171.160.45 (talk) 03:35, 3 October 2011 (UTC)

At a non-military control tower, they are mostly looking for the aircraft transponder to tell them where they are, not so much actually bouncing radar beams off of the aircraft. However, they could very well keep that radar system operating in case some doctor is flying his Cessna around without a transponder so mostly the sweep radar is a secondary system. Googlemeister (talk) 13:54, 3 October 2011 (UTC)

Aircraft transponders actively providing position information is ADS-B, a technology that is currently being phased in, but which is not yet supported by all airframes, and rarely used exclusively. Secondary Surveillance Radar uses transponder replies, but still computes the position from the antenna azimuth (i.e. direction ;-) and the signal run time, just as a classical primary radar. The difference is that it take the known latency of the transponder into account (and, of course, the fact that the transponder provides identity and barometric altitude, or, if it is a modern Mode-S transponder queried by a Mode-S Radar, everything from the stock of coffee in the pantry (separated into decaf and regular) to the frequency and duration of the pilot's rest room visits). --Stephan Schulz (talk) 17:55, 3 October 2011 (UTC)

Confining the electron

Would it be possible to confine an electron enough that it is possible to know exactly where it is? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 20:03, 2 October 2011 (UTC)

No, because of the uncertainty principle. Dauto (talk) 20:04, 2 October 2011 (UTC)

But what if the electron is confined to such a small space that it can only follow one possible track for any given momentum, making it possible to precisely measure both its position and its momentum? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 20:07, 2 October 2011 (UTC)

can't be done because of the uncertainty principle. An electron is not a tiny little ball that can be confined and will have a track. It is a wave that fills the available space without a clearly defined track. Dauto (talk) 20:13, 2 October 2011 (UTC)

An electron is a PARTICLE. It has diameter and mass. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 20:14, 2 October 2011 (UTC)

And a wave: wave-particle duality. Any effort to highly constrain an electron must necessarily result in a particle whose momentum is highly uncertain (or more accurately, one whose wavefunction is spread over a very wide range of possible momentum states simultaneously). Dragons flight (talk) 20:31, 2 October 2011 (UTC)

What about an electron that is confined to one single point in space and not allowed to move, thus determining its exact momentum (zero) and its exact position (the position of the point it is confined to)? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 21:08, 2 October 2011 (UTC)

Not possible. Put an electron in a box. Now make that box smaller over time. The smaller you make the box, the more kinetic energy must be transferred to the electron. In the limit that the box contracts to a single point, the kinetic energy of the electron becomes infinite. It is not possible, even in principle, to make a trap that can completely confine an electron to a single point in space. Unlike classical physics, quantum mechanics teaches that a confined electron must have non-zero kinetic energy at all times. Dragons flight (talk) 21:24, 2 October 2011 (UTC)

A diameter ? Sean.hoyland - talk 20:34, 2 October 2011 (UTC)

See quantum tunneling, I'm sure some users here might take issue with this, but for layman's purposes, imagine the electron can teleport through physical walls. So it's impossible to confine in a physical space. At most you can alter its probability cloud with electric fields. ScienceApe (talk) 23:22, 2 October 2011 (UTC)

You can actually measure (and observe) the exact moment when everything classical goes out the window and quantum rules. When you say, "an electron is a particle. it has diameter and mass", you're using a classical language. That can be very effective in some contexts. But when you start talking about sizes of a certain scale, then you have to switch to a fully quantum vocabulary and reasoning. And that means uncertainty. There is a lot of interesting work on physics at that boundary between the classical and the quantum — it turns out to be pretty important in nanoscale engineering. See Mesoscopic physics. Your idea of the box is a classic way to think about it. At a macroscale, you can talk about an electron being "inside" a box, sure. But as you start to shrink it, when you hit the mesoscale, suddenly that language starts to get really problematic, and stops being correct at all. --Mr.98 (talk) 00:23, 3 October 2011 (UTC)

Building "life expectancy"

How long do buildings are expected to last? Excluding things like meteorites, earthquakes and such. Wikiweek (talk) 20:57, 2 October 2011 (UTC)

Often a very long time, look at the Kremlin or the White House. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 21:13, 2 October 2011 (UTC)

That's certainly right, but not the most common case. I was thinking more about concrete office buildings or normal brick and mortar houses. Wikiweek (talk) 21:26, 2 October 2011 (UTC)

For tax purposes, the US convention (since 2010) is to assume that most new construction will have a 50 year useful life. Obviously some buildings continue to be used well beyond that, while others are replaced after much less than 50 years, but 50 years is probably a decent rough estimate. Dragons flight (talk) 21:39, 2 October 2011 (UTC)

So, what about all those pre-war Manhattan buildings? Are they worthless? I suppose that for tax purposes you needed a rule to amortize it. The lawmakers chose 50 years, but could have chosen more or less years. Quest09 (talk) 22:11, 2 October 2011 (UTC)

They're not worthless at all, but they've been renovated at some point, if only to update the systems and the roof, doors and windows. Acroterion (talk) 14:33, 3 October 2011 (UTC)

The White House? It's barely 200 years old... I know Americans think that is old, but it's really not. America doesn't have old buildings. I live in London. You can't walk for 10 minutes here without tripping over buildings far more than 200 years old. --Tango (talk) 23:00, 2 October 2011 (UTC)

You know: 200 years is old in the US, 200 miles is far in Europe. Quest09 (talk) 23:07, 2 October 2011 (UTC)

Very true! --Tango (talk) 00:46, 3 October 2011 (UTC)

There is some distinction that should be made between the 'remains standing' lifetime, the 'still usable' lifetime, and the 'roughly the same, functionally, as new construction' lifetime. While it is certainly the case that buildings 200 years old remain in service, many have limitations which would not be acceptable (or even legal) in new construction. Older buildings (or sometimes just their shells, or even their street-facing facades) are often retained and retrofitted at great cost and inconvenience for the purposes of 'historical preservation' and so forth. I don't dispute that older buildings can have value as works of art and can form an essential part of a street or city's character and be worth retaining on that basis—but by the purely practical measure of cost, it would make more sense to demolish them and replace them with new construction.

Any building older than two or three decades faced much more limited requirements for accessibility by disabled persons. Doorways (and even hallways, if one looks at construction more than a hundred years old, especially in very densely-packed cities) aren't wide enough to admit wheelchairs. Ramps and elevators may be absent or extraordinarily inconvenient. Methods used for heating two hundred years ago were very different from those used today. Retrofitting modern heating, air conditioning, ventilation, elevators, fire containment, fire suppression, electrical supply, lighting, computer networking, handicapped accessibility, and plumbing isn't trivial; building occupants are often forced to make an unpleasant choice between astronomical cost and tolerating inconveniences, discomforts, and hazards—and even if they do spring for the upgrade, it can mean that the building is partly or wholly unusable for months or years of construction anyway. TenOfAllTrades(talk) 11:36, 3 October 2011 (UTC)

If wood-and-masonry buildings can last hundreds of years, I see no reason why steel and concrete buildings wouldn't last longer. So, the answer is very very long, specially if you maintain the building properly and avoid things like water damage. Quest09 (talk) 23:07, 2 October 2011 (UTC)

Indeed. If they are well-maintained, they can last pretty much forever. Such buildings are often demolished when they still have plenty of life left in them in order to be replaced by new buildings. That's far more common that them getting too old (unless they've been abandoned for some time). --Tango (talk) 00:46, 3 October 2011 (UTC)

An interesting book that touches on this topic is How Buildings Learn. Pfly (talk) 04:50, 3 October 2011 (UTC)

European castles made of solid blocks of stone will start decaying in a few decades if unmaintained. The roofs are the weakest part since they are made of more fragile materials. Then the rainwater will flood places that were intended to remain dry. Internal rooms will no longer be protected from very low temperatures, so that water will start freezing inside the cracks of the stone, cracking them even more. Certain stones will crack way sooner than others, if left unrepaired they will damage surrounding stones. Damaged pillars will fall on other stones, cracking them, sometimes adding weight in places not designed for it. Stones in the middle of a wall will debilitate stones above it and will eventually cause the falling of whole wall sections. Usually, the cracks among stones are covered with masonry stuff, which gets destroyed in a couple of decades. If the cracks are kept well covered, stone walls may last millenia. Some stone buildings in Egypt were covered in sand and forgotten, and have been preserved magnificently for 4000 years or so. Now they are been eroded slowly by wind/ice and might last a few centuries if unmaintained. Summary: good frequent maintenance works because it prevents damage to buildings before it happens. Bad unfrequent might repair the most damaged parts but it will not prevent damage to parts that are still in good shape. --Enric Naval (talk) 14:18, 3 October 2011 (UTC)

Any well-constructed building that receives conscientious maintenance should remain standing indefinitely, absent an environmental disaster. That said, the economic life, as calculated by the span between major renovations, can be quite short. For retail buildings, built on the cheap with inexpensive HVAC and roof systems, 15 years is fairly standard. For higher-quality commercial buildings, 30 years may pass before the structure is obsolescent. For public buildings such as schools it may be 40 or 50 years. Bear in mind that most low-slope roofing must be replaced every 15 to 25 years no matter what, and even very durable roof systems rarely go more than 50 years without significant work. Building code requirements or building standards for accessibility, life safety, earthquake or storm resistance, or for energy efficiency may render a building non-competitive in the marketplace or perceived as unsatisfactory. For specialized buildings (again, such as schools) changes in usage requirements may make the building unsatisfactory in a shorter period of time. Technology may affect usage (i.e., air conditioning and artificial lighting may remove requirements for airshafts, or may result in their adaptation for other uses). Few buildings go for more than 50 years without some kind of more-than-routine maintenance. Acroterion (talk) 14:28, 3 October 2011 (UTC)

A couple of cents:

• just because you know some pretty old buildings (+100, +200 or even +300 years) it doesn't mean that buildings on average last that long: you simply don't know how many didn't make it up to our time.
• A life span of 50 for tax purposes doesn't mean the building will probably last 50 years or that it will be worthless in 50 years. It means buildings lose on average 2% value each year, which sounds perfectly normal for me. If you keep repairing that per-war loft, that Quest09 mentions above, it can get even more valuable. For an apartment worth $200,000, you'll have to set aside $4,000/year on average. Just remember that a new HVAC, a new roof, new plumbing, a new elevator, and many other things; all cost some thousand dollar. As the building gets older the costs get higher.

Trustinchaos (talk) 15:58, 3 October 2011 (UTC)

Just on the matter of the White House, other than the outer shell, it is only about 60 years old. See White_House#The_Truman_reconstruction. It's the old problem of the Ship of Theseus paradox; sure, there has been a structure known as The White House for 200 years, but it is constantly renovated and updated (and occasionally almost completely rebuilt from scratch), so what you see now is not, except for some cosmetic bits here and there, really all that old. The same is likely true for many really old buildings.--Jayron32 18:54, 3 October 2011 (UTC)

The White House was burned by our British friends in the war of 1812 and rebuilt about 1820. American sometimes read [2], [3], [4] that it was "white" only because it had to be painted after the burning to hide the soot stains, but in fact it was painted white from the beginning,because of the porousness of the exterior stone, and there was little left to paint after the burning. All that remained of the original building was the foundation and a portion of the south wall. By about 1900 the interior was in danger of collapse and was extensively rebuild. The roof and its support structure was replaced in the 1920s because it was collapsing. By 1948 Truman found it necessary to completely gut it, preserving only the walls and the 1920's roof, and replaced the interior with steel and concrete construction. In each incarnation before the Truman rebuilding, it was ready for condemnation and demolition every several decades, had it not become a national symbol. In the late 1800's its survival as a presidential palace was in doubt, not for structural reasons, but because it was judged obsolete and old fashioned, and there was serious consideration of building a "modern" presidential palace on another site in DC, and converting the building to offices. Edison (talk) 19:51, 3 October 2011 (UTC)

Angle of repose

Does the angle of repose depend on gravity or not ? I thought the consensus was that it doesn't.

I happened to be looking at this digital terrain model of a barchan on Mars today. It's angle of repose seems pretty low, ~20° or less after many avalanches. Puzzled, I had a search and came across this experiment that suggests that perhaps there is a dependency on gravity. Thoughts ? Sean.hoyland - talk 21:34, 2 October 2011 (UTC)

According to this, gravity has an influence. hydnjo (talk) 23:41, 2 October 2011 (UTC)

..yes but the changes in the shear stress and normal stress due to gravity cancel eachother out so the coefficient of friction just depends on the angle for a given material or so the story goes... Sean.hoyland - talk 05:50, 3 October 2011 (UTC)

N-terminal signal sequences in Archaea

I am analysing a protein sequence from from the Archaeon Thermotoga maritima...

MGSDKIHHHHHHMMGLKAHAMVLEKFNQPLVYKEFEISDIPRGSILVEILSAGVCGSDVHMFRGEDPRVPLPIILGHEGAG
RVVEVNGEKRDLNGELLKPGDLIVWNRGITCGECYWCKVSKEPYLCPNRKVYGINRGCSEYPHLRGCYSSHIVLDPETDVLKVSEKD
DLDVLAMAMCSGATAYHAFDEYPESFAGKTVVIQGAGPLGLFGVVIARSLGAENVIVIAGSPNRLKLAEEIGADLTLNRRETSVEER
RKAIMDITHGRGADFILEATGDSRALLEGSELLRRGGFYSVAGVAVPQDPVPFKVYEWLVLKNATFKGIWVSDTSHFVKTVSITSRNY

QLLSKLITHRLPLKEANKALELMESREALKVILYPEG

What's the role of the 6 histidines from AA 7 to 12? It can't be a nuclear localisation sequence can it? I thought Archaea lacked organelles? elle _{vécut heureuse} ^{à jamais} (be free) 23:12, 2 October 2011 (UTC)

Looks suspiciously like a His-tag, used for protein purification. The protein is an alcohol dehydrogenase, the histidines don't appear to be part of the protein. Hzh (talk) 00:31, 3 October 2011 (UTC)

Yup, on checking, pretty sure it is a His-tag, i.e. something artificial added to make protein purification easier. The sequence MGSDKIHHHHHH appears to be called Thio6His6 tag. Hzh (talk) 00:57, 3 October 2011 (UTC)

Definitely an added tag. The record for T. maritima aldehyde dehydrogenase here shows the sequence starting with MMGLK...—which would be right after the His tag. (When in doubt, BLAST it....) TenOfAllTrades(talk) 01:31, 3 October 2011 (UTC)

Probably a bit redundant at this point, but yes.. unquestionably an affinity tag. (+)H₃N-Protein\Chemist-CO₂(-) 16:06, 3 October 2011 (UTC)