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May 18

CO2

Why does a can of pressurized carbon dioxide (in a liquid state) down so much when it is released (in a gaseous state)? Thanks. 173.179.59.66 (talk) 03:44, 18 May 2010 (UTC)

If by "down" you mean "get cold"; when a liquid evaporates into a gas it goes through a phase transition which involves Enthalpy of vaporization. In short, it takes energy to change a liquid into a gas, the energy is the heat in and around the canister which is absorbed by the carbon dioxide as it evaporates into a gas. The reason this might seem "strange" is because the boiling point of carbon dioxide is 57 degrees Celsius below freezing, we think 0 degrees C is some special "low" energy point, but it's actually 273 degrees Kelvin so still has a lot of energy for something like carbon dioxide. Vespine (talk) 04:19, 18 May 2010 (UTC)

The process by which a liquid or gas is allowed to expand freely is called throttling. During throttling the temperature changes and this is called the Joule–Thomson effect. Whether the temperature increases or decreases during throttling depends on the gas’s Joule-Thomson coefficient and its inversion temperature. Hydrogen and helium at room temperature warm as they are throttled to a lower pressure. Carbon dioxide, nitrogen and oxygen at room temperature cool as they are throttled to a lower pressure. Dolphin (t) 05:10, 18 May 2010 (UTC)

Are you saying that if you had a gas bottle with liquid helium in it and you released it, the gas bottle would not get cold? That doesn't sound right. I've never heard of Joule-Thomson effect (which isn't saying much) but looking at it, it seems to specifically refer to the temperature of the gas in situations where there is no heat exchange with the environment, which is certainly not the case when you just let gas out of a gas bottle, or a can. Vespine (talk) 06:34, 18 May 2010 (UTC)

A gas or liquid can be allowed to change from a higher pressure to a lower pressure in a variety of ways. The change can take place with no heat transfer to/from the surroundings (adiabatic), or it can take place with heat transfer. The change can be reversible, such as when it accompanies the raising of a weight and takes place slowly; or it can be irreversible, such as when it is allowed to "explode" out of its container. A reversible, adiabatic change takes place at constant entropy and the resulting temperature can be determined accurately by knowing that the entropy of the gas doesn't change. See isentropic process. An irreversible, adiabatic change is called throttling and takes place at constant enthalpy. See isenthalpic process. The resulting temperature can be determined accurately by knowing that the enthalpy of the gas doesn't change; also this resulting temperature will be significantly different to the isentropic process. The Joule-Thomson effect is the change in temperature during the isenthalpic process, not the isentropic process. The original question does not specify precisely what process is intended, but it talks about a can of liquid CO2 being discharged to the gaseous state. The idealized process which best represents this process is the throttling process, even though the isenthalpic process involves no heat transfer whereas discharging a can of CO2 will involve a small amount of heat transfer in the brief period of time that the discharge takes place. Dolphin (t) 12:48, 18 May 2010 (UTC)

To clarify, there is an important distinction between a case where helium gas is allowed to expand starting from room temperature, and where liquid helium is allowed to boil. The two cases are distinguished first by the fact that the latter involves a phase change (liquid to gas, soaking up enthalpy of vaporization) and second by the fact that they will occur at vastly different temperatures (the critical temperature of helium is about 5 kelvin, so you're never going to have liquid helium above that temperature — liquid helium will always be at a temperature below its inversion point if you're working under atmospheric pressure). TenOfAllTrades(talk) 13:12, 18 May 2010 (UTC)

By down I meant a decrease in temperature, I'm not too sure where the "down" came from lol. But thanks a lot for the explanation! 173.179.59.66 (talk) 05:52, 18 May 2010 (UTC)

When liquids boil, they absorb energy to change in the gaseous state. When air is pressurized it gets hotter. I can feel on an air pump sometimes that it gets hotter. Some gases may not behave in that way, but I think liquid helium becomes cold when it is released due to the rapid boiling, cooling it to very low temperatures. --Chemicalinterest (talk) 11:58, 18 May 2010 (UTC)

That's a good answer. Going into detail about isentropic processes and entropy and Joule–Thomson effect is way, way overboard for the question actually asked. Vespine (talk) 03:45, 19 May 2010 (UTC)

I think the anwers above are unclear, the throttling explanation seems to be about the temperature of the exiting gas after expansion, the question was about the temperature of the can and that has more to do with boiling and maybe isentropic expansion. Gr8xoz (talk) 00:21, 20 May 2010 (UTC)

percent of atmosphere

What percent of the entire Earth's atmosphere including that which is absorbed and released by water, etc. is released by human lungs of an average adult male upon exhaling? 71.100.0.29 (talk) 04:27, 18 May 2010 (UTC)

From Atmosphere of Earth we have total mass of 5×10¹⁸, from Lung volumes we have average male Tidal volume (Vt) of 500ml, from Density of air we have 1.2  kg/m³. A cubed meter is 1000l so 500ml of air is 1/2000th of 1.2kg = 6×10⁻⁴kg per breath. So it's just (6×10⁻⁴) / (5×10¹⁸) x 100 to get your percentage, i'm no good with so many zeros, my guess is 1.2×10⁻²⁰%, but I could be off by an order of magnitude or two. Someone better at maths can help me out. ;) Vespine (talk) 06:27, 18 May 2010 (UTC)

Your calculations look correct. --Chemicalinterest (talk) 12:00, 18 May 2010 (UTC)

Strange. I was no good with symbolic equations which contained space and used x's in place of *'s. I consulted with several of my friends as did you and they advised that I use the following symbology and syntax to get the following results. Many thanks human. May we also have exchange good like this in future time. (6 * (10^(-4))) / (5 * (10^18))) * 100 = 1.2 × 10-20 —Preceding unsigned comment added by 71.100.0.29 (talk) 18:54, 18 May 2010 (UTC)

Best extrasolar planet candidates for habitable moons based only on irradiance?

What discovered extrasolar planets are the best candidates for habitable moons
based on the heat/irradiance they, the planets, receive from their parent star?
1366 W/m² being the Earth's solar constant, therefore also the Moon's.
Clarifying: since it doesn't seem obvious to everyone,
I meant only possible habitable temperature, based on albedo/emissivity similar to the Earth,
and irradiance comparable to what the Earth receives.
24.78.178.235 (talk) 06:44, 18 May 2010 (UTC)

Presumably, what you are getting at is the habitable zone, because this level of stellar radiation would yield a temperature near the triple point of water. We have a nice listing at Extraterrestrial liquid water#Beyond the Solar System. At this time, extrasolar planets are on the bare edge of detection; I know of no research claims about detection of a moon around an extrasolar planet. On the other hand, moons seem commonplace in our own solar system, so it seems plausible that any large extrasolar planet (and some dwarf planets, too) could be capable of having "habitable" moons in stable orbits. Of course, a necessary precursor to the question is, "define habitable". Nimur (talk) 09:08, 18 May 2010 (UTC)

With present detection methods, it's unlikely we're going to be able to detect moons around extrasolar planets unless they are truly gigantic and very close to the parent star - or perhaps are in an eclipsing orbit from our perspective and are large compared to the parent planet (like our moon or the Pluto/Charon pair). The odds of either of those things being true seem rather slim. If we're going to try and guess, we'd have to think in terms of large planets in the habitable zone of their parent stars - and just kinda hope that they'd have large enough moons with inhabitable atmospheres - but we don't have much evidence of the probability of that happening because we only know about the planets in our own solar system...of which there is just one (or arguably two or three) in the habitable zone. We have: List of extrasolar planets which contains all the data you need to estimate which are in the habitable zone - but it doesn't look like anyone did the actual calculations to enter that fact into the tables. SteveBaker (talk) 13:29, 18 May 2010 (UTC)

A note about the "habitable zone". This refers to a planet which is the proper distance from the star for liquid water. In the case of a moon around a huge planet (the only ones we can currently detect), the moon is not only heated by the star, but also from radiation and tidal warming from the planet, so the moon could be further away from the star and still have liquid water. StuRat (talk) 21:38, 19 May 2010 (UTC)

Nice point, but a very different question from the one I asked, did you read it? 24.78.178.147 (talk) 09:30, 21 May 2010 (UTC)

I did read it, several times. But, even with the clarification, I still don't quite know what you're asking. StuRat (talk) 15:09, 21 May 2010 (UTC)

Candidate Chart

Planet	Radius (Sol)	Photosphere Temperature (K)	Semimajor axis (AU)	Orbital eccentricity	Perihelion Irradiance	Average Irradiance	Aphelion Irradiance	Period (Yrs.)
Mars	1.0	5778	1.523	0.0934	52.45%	43.11%	36.06%	1.8795
HD 141937 b	1.06	5821	1.52	0.41	151.57%	52.76%	26.54%	1.79
HD 187085 b		6011	2.05	0.47	191.84%	53.89%	24.94%	2.7
HD 23079 b	1.13	5848	1.65	0.1	68.65%	55.61%	45.96%	2.02
ups And d	1.631	6212	2.55	0.32	124.54%	57.59%	33.05%	3.56
HD 99109 b		5272	1.105	0.09	71.72%	59.39%	49.99%	1.20
HD 10697 b	1.72	5641	2.16	0.1	77.76%	61.60%	49.99%	2.947
HD 147513 b	1	5701	1.26	0.52	279.84%	64.47%	27.91%	1.48
HD 213240 b	1.5	5984	2.03	0.45	219.53%	66.41%	31.58%	2.6
HD 45364 c		5434	0.8972	0.0974	82.15%	66.93%	55.57%	0.939
HD 196885 b	1.79	6340	2.37	0.462	231.99%	67.15%	31.42%	3.65
HD 210277 b	1.1	5532	1.1	0.472	258.97%	72.20%	33.32%	1.21
HD 136418 b	3.4	5071	1.32	0.255	188.72%	74.90%	39.91%	1.27
HD 183263 b	1.21	5888	1.52	0.38	196.35%	75.48%	39.63%	1.73
HD 160691 b	1.245	5700	1.5	0.128	103.07%	78.37%	61.59%	1.76
HD 125612 b	1.05	5897	1.2	0.39	213.56%	79.47%	41.13%	1.37
HD 28185 b	1.03	5482	1.03	0.07	93.69%	81.03%	70.77%	1.05
HD 190228 b	3.02	5176	2.31	0.43	262.13%	85.17%	41.65%	3.09
Gliese 876 c	0.36	3350	0.132	0.266	162.61%	86.65%	53.73%	0.083
HD 188015 b	1.1	5520	1.19	0.15	120.50%	87.06%	65.83%	1.25
HD 16175 b	1.87	6000	2.1	0.59	548.49%	92.20%	36.47%	2.71
HD 100777 b		5582	1.03	0.36	237.79%	97.40%	52.66%	1.05
Earth	1.0	5778	1.0	0.01671022	103.43%	100.00%	96.74%	1.0
HD 108874 b	1.22	5407	1.051	0.07	119.47%	103.33%	90.25%	1.08
HD 155358 c		5760	1.224	0.176	155.02%	105.26%	76.11%	1.45
HD 142415 b	1.03	5834	1.05	0.5	425.29%	106.32%	47.25%	1.06
HD 20367 b	1.18	5929	1.25	0.23	185.73%	110.12%	72.79%	1.37
HD 82943 b	1.12	5874	1.19	0.219	182.79%	111.50%	75.03%	1.21
HD 221287 b		6304	1.25	0.08	136.29%	115.36%	98.90%	1.25
HD 45364 b		5434	0.6813	0.1684	167.83%	116.07%	85.02%	0.62
HD 92788 b	0.99	5559	0.97	0.334	221.33%	117.95%	73.13%	0.89
HD 153950 b	1.34	6076	1.28	0.34	329.92%	143.71%	80.04%	1.37
HD 69830 d	0.895	5385	0.63	0.07	166.74%	144.22%	125.96%	0.54
Venus	1.0	5778	0.723	0.0068	193.93%	191.30%	188.73%	0.6148

These are all from Luminosity article.

$L=4\pi R^{2}\sigma T^{4}\,$

$L=4\pi f\ d^{2}\$

If Radius/Temperature unknown, then:

L_star = 0.0813 · dist_star² · 10^{(−0.4 · m_star)} · $L_{\odot }$

Therefore:

$f=(R^{2}\sigma T^{4})/d^{2}\$

I don't mean to show anyone up, I was looking for anyone else who could do this,
and this should have been easy for anyone who presumed to answer here. 24.78.178.147 (talk)

Best ref desk candidate for being a jerk based only on attitude in answering own question? 63.17.50.130 (talk) 01:02, 23 May 2010 (UTC)

Attitude? - These are formulas. Check that attitude of the people who answer, they all want to change the question so they can lecture on their opinions, it's pathetic. Why if they couldn't answer they question did the assume their opinion mattered?
Change it to the "opinion desk" and I'll admit I'm wrong on that. 24.78.178.147 (talk) 02:15, 23 May 2010 (UTC)

By the way "retard," it sounds like you were saying I as a "jerk" to myself.24.78.178.147 (talk) 02:18, 23 May 2010 (UTC)

• OP gave some examples, but technically the question was not answered. 24.78.166.69 (talk) 06:25, 29 September 2010 (UTC)

annealing aluminium from H-18 to H-O

We are blanking aluminium circles. We use alloy 1050 and 3003. During blanking we use H18 coils (hardness is H-18). After blanking we want to anneal these circles from H-18 to H-O temper. We have box type (batch type) Oven. We know we need to keep this in 343° to 413° C temperature to anneal these from H-18 to H-O but how much time is required to be kept in this temperature in a box type oven  ? Can anybody help us out in this ? —Preceding unsigned comment added by Ashvora (talk • contribs) 07:31, 18 May 2010 (UTC)

Not sure, but might I suggest trial and error ? That is, anneal it a bit, take it out, cool it, and test it, then anneal it some more, until you figure out the right length of time. StuRat (talk) 21:33, 19 May 2010 (UTC)

Type of intermodal container

These containers seem common in trains in japan [1] (not the tanks - the boxes). http://commons.wikimedia.org/wiki/File:JRF_19D-33700.JPG or http://commons.wikimedia.org/wiki/File:JNR_Container.jpg I don't think they are '10ft ISO's', but maybe they are? - does anyone know what standard they are? Can they be stacked..? Thanks. Sf5xeplus (talk) 12:00, 18 May 2010 (UTC) I think its something to do with this http://ja.wikipedia.org/wiki/JR%E8%B2%A8%E7%89%A9%E3%81%AE%E3%82%B3%E3%83%B3%E3%83%86%E3%83%8A%E5%BD%A2%E5%BC%8F - are these stackable? any compatability with ISO containers. Also does anyone know why 12ft length seems so popular when elsewhere 20ft+ is normal.? Can anyone give a link to background on this topic? thanks. (in particular: why was ISO standard not used) Sf5xeplus (talk) 13:47, 18 May 2010 (UTC)

length of menstruation

Why does menstruation take 2-7 days, rather than a short time (e.g. an hour or so)? After reading the articles on menstruation and the menstrual cycle, it states the normal length of the menstruation is 2-7 days, which I knew. But what I am curious is about is WHY it takes this long. I'm not sure if this is easy to answer, but it seems that it is a process that could happen quite quickly, rather than taking a few days, but it doesn't. Ballchef (talk) 12:33, 18 May 2010 (UTC)

Given the discomfort level many women feel during (and prior) to their menstruation, I'm not sure compressing that into a shorter timespan would be such a great thing - pain might multiply while the time divides, you know? In evolutionary terms, it might simply be better for women to be moderately uncomfortable for a longer period of time than extremely uncomfortable for a shorter, but still sizable, period of time. Matt Deres (talk) 14:09, 18 May 2010 (UTC)

Unscientific answers.
The following discussion has been closed. Please do not modify it.
It's serious business, and serious business generally isn't over in the blink of an eye. Vranak (talk) 14:34, 18 May 2010 (UTC) That's not a reason. Vimescarrot (talk) 17:06, 18 May 2010 (UTC) Well if sexuality was a light and breezy affair, then people wouldn't have any reason to menstruate, let's put it that way. Vranak (talk) 21:16, 18 May 2010 (UTC) That makes absolutely no sense. --Tango (talk) 21:35, 18 May 2010 (UTC) Exactly. Vranak (talk) 21:52, 18 May 2010 (UTC)

Per Menstruation#Evolution, the length of time has to do with the rate of cell growth for the uterine lining. This sort of low-level biological parameter is not easily changed - cells simply can not divide and multiply significantly faster. Our article links to some evolutionary biology research on the advantages and disadvantages of the process, e.g. The evolution of endometrial cycles and menstruation. Mostly, this evolutionary process was driven by the balance between the utility of internal fertilization versus the energy and nutrient cost to sustain this very complex process. Keep in mind that evolution is not a steady progression towards "optimal" - it is simply survival of the fittest random mutation during every intermediate step - so the development of modern menstruating mammals is the result of prior forms. See also, estrous, for a related process in other mammals. Nimur (talk) 00:58, 19 May 2010 (UTC)

Brilliant answer thanks! But still it wont stop my girlfriend from complaining. Ballchef (talk) 03:33, 19 May 2010 (UTC)

See Menstrual extraction for a quick painless method —Preceding unsigned comment added by 79.76.203.64 (talk) 18:56, 19 May 2010 (UTC)

And possibly illegal, depending on the Jurisdiction... Buddy431 (talk) 03:42, 20 May 2010 (UTC)

physics

when a hole is made from north pole of the earth to the south pole of the earth and a ball is put into it what is the time period of the oscillation of the ball —Preceding unsigned comment added by Mai ca lal jai kison (talk • contribs) 14:24, 18 May 2010 (UTC)

Question has come up before:

• http://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Archives/Science/2009_September_17#Gravity_at_the_center_of_a_body
• http://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Archives/Science/2009_September_11#Path_through_Earth

Answer in second link - some simplfiying assumptions are made to get an answer.77.86.10.27 (talk) 14:34, 18 May 2010 (UTC)

There's some more explane here http://answers.yahoo.com/question/index?qid=20080519084940AAMjRd0 77.86.10.27 (talk) 14:40, 18 May 2010 (UTC)

There's a step by step guide to one derivation in "A: The basic setup" http://amath.colorado.edu/courses/2460/2007fall/Labs/lab2/ 77.86.10.27 (talk) 14:40, 18 May 2010 (UTC)

Reliable looking answer here http://physics.ucsd.edu/students/courses/summer2008/managed/physics2a/documents/chap15.pdf Question 70 page 15 "The magnitude of the gravitational acceleration inside Earth is given..." 77.86.10.27 (talk) 14:43, 18 May 2010 (UTC)

But how would it be possible to keep such a hole from being completely flooded? :-) 67.170.215.166 (talk) 01:07, 19 May 2010 (UTC)

People here are not saying it is possible, just assuming no water or air, or lava in the hole. :-) Graeme Bartlett (talk) 12:43, 19 May 2010 (UTC)

Alkali acids

Is an alkali like NaOH an acid? --Chemicalinterest (talk) 15:37, 18 May 2010 (UTC)

OH- as an acid : see this quote :"The oxide ion, O²⁻, is the conjugate base of the hydroxide ion, OH⁻"

Na+ is also a weak lewis acid

In water it's always a base, the opposite of an acid.77.86.10.27 (talk) 15:42, 18 May 2010 (UTC)

So that means that OH^- is the conjugate acid of O^2-? --Chemicalinterest (talk) 15:58, 18 May 2010 (UTC)

Yes.77.86.10.27 (talk) 15:59, 18 May 2010 (UTC)

I plan to improve the articles dealing with chemicals that have a pH above 7. Do you think it would be good to add it, or it would just confuse people saying that a base is also an acid? --Chemicalinterest (talk) 16:03, 18 May 2010 (UTC)

Probably not a good idea to add - since any molecule with a hydrogen is potentially an acid - eg methane, hydrogen gas, etc. too many

It's sort of mentioned already in Superbase.

As far as I can tell the definition at Alkali is 100% correct already.

I think Alkali salts would be better moved to Basic salt : that's the only change I can see needs doing - not sure what other people will think.77.86.10.27 (talk) 16:19, 18 May 2010 (UTC)

Square wheels

Can anyone provide a proof/derivation for why the square wheel riding on catenaries thing works, as shown in the article? 173.179.59.66 (talk) 15:39, 18 May 2010 (UTC)

It looks like the wheel corner gets "stuck" in the down curve, but just rolls right out. Round wheels probably wouldn't work on there unless they are much bigger. --Chemicalinterest (talk) 16:05, 18 May 2010 (UTC)

And a round wheel would provide a bouncy ride (i.e., would never "work" in the same way): as it rises and falls over each bump, the axle does too. When the size of the square is perfectly matched to the dimensions of the catenary, the axle remains at a fixed height. Proof is just a bunch of calculus: probably start by assuming length of one side of the square is the same as the length of one arch of the catenary (they remain touching as the roll past each other). That means at any x position, you know the height of the catenary and also (by some trig) the offset of the center of the square from that x. And then (by some more trig) the distance from the center straight down to the height of contact. Our catenary article says square or any larger polygon can be used, and has a cite to more reading about this unusual geometric phenomenon. DMacks (talk) 18:43, 18 May 2010 (UTC)

One possibly non-obvious assumption that (I think) will need to be made is constant ratio of angular velocity to linear velocity. no idea what can happen if this isn't assumed (disclaimer: I've assumed what I've said is correct rather than actually knowing). not right on second thoughts.77.86.10.27 (talk) 19:50, 18 May 2010 (UTC)

I started trying to prove the catenary equation from the height of the axle, but then I found a much neater and more elegant proof here (along the lines suggested by DMacks above). The method can be extended to any regular polygon by truncating the catenary at a point corresponding to the exterior angle. Dbfirs 20:36, 19 May 2010 (UTC)

Planetary rings

Why some planets have rings and others do not have? —Preceding unsigned comment added by 113.199.143.2 (talk) 17:43, 18 May 2010 (UTC)

We don't know. Planetary rings are a big mystery. --Tango (talk) 18:28, 18 May 2010 (UTC)

But our Planetary ring article does have some information about the origins of them. DMacks (talk) 18:32, 18 May 2010 (UTC)

Note that planetary rings tend to be associated with gas giant planets such as Saturn; this suggests (but does not in itself prove) that there's a certain minimum size of planet below which it cannot acquire a ring. FWiW 67.170.215.166 (talk) 01:11, 19 May 2010 (UTC)

In fact, all of the gas giants in our solar system have rings: Rings of Jupiter, Rings of Saturn, Rings of Uranus, Rings of Neptune. Buddy431 (talk) 03:40, 20 May 2010 (UTC)

Dark Chocolate icing

I have a chocolate icing made of 49% dark chocolate and 51% melted margarine. After leaving it in the fridge for too long it turned to moose(?). Heating the sauce in a microwave caused the margarine and chocolate to separate so now there is melted chocolate sludge in a pool of melted margarine. How do i get the two to become one sauce again? Btw, 5 minutes of mixing did nothing. Simply south (talk) 18:30, 18 May 2010 (UTC)

A high speed electric whisk should emulsify it again hopefully. (maybe like this http://www.cookingtime.co.uk/index.php?act=viewProd&productId=1095 ? )77.86.10.27 (talk) 18:32, 18 May 2010 (UTC)

Adding some (or a lot) of cream might help as well.77.86.10.27 (talk) 18:35, 18 May 2010 (UTC)

I would like to still use it as icing but will try the whisk. Thanks. Simply south (talk) 18:38, 18 May 2010 (UTC)

According to http://chocomap.com/chocolate-making-tempering.php it's "chocolate seize" and cannot be reversed - I think cream may help solve this though..77.86.10.27 (talk) 18:40, 18 May 2010 (UTC)

If it has seized (and not just separated out) there are a thousand and one things you can try.. http://www.google.co.uk/search?q=chocolate+seize&hl=en&start=10&sa=N 77.86.10.27 (talk) 18:44, 18 May 2010 (UTC)

Thank you. Simply south (talk) 18:47, 18 May 2010 (UTC)

Turned to moose!!! Goddarn, take the dang thing outside and shoot it!!!! If it turned to mousse then follow the suggested advice. Caesar's Daddy (talk) 20:24, 18 May 2010 (UTC)

Swedish Chef tried it.DMacks (talk) 21:39, 18 May 2010 (UTC)

"First moose, then squirrel!" Edison (talk) 21:51, 18 May 2010 (UTC)

Aether vs. Quintessence

How did the powers that be determine that "aether" was not an acceptable term for "quintessence", when their definitions are from the same classic Greek idea? —Preceding unsigned comment added by 165.212.189.187 (talk) 18:44, 18 May 2010 (UTC)

They're not the same -

• aether http://en.wiktionary.org/wiki/aether means air
• qunntessence http://en.wiktionary.org/wiki/quintessence means fifth essence

Classical elements only have 4 elements - thus air cannot be a fifth essence ??? 77.86.10.27 (talk) 18:55, 18 May 2010 (UTC)

The aether wikipedia article refers to it as a proposed "fifth element" why? —Preceding unsigned comment added by 165.212.189.187 (talk) 19:00, 18 May 2010 (UTC) I'm not talking about semantics I'm talking about the ideas and theories behind the words. —Preceding unsigned comment added by 165.212.189.187 (talk) 19:04, 18 May 2010 (UTC)

Sorry my mistake (Ἀήρ was normal air) here Aether (mythology)

Quintessence is another term for aether ???77.86.10.27 (talk) 19:25, 18 May 2010 (UTC)

What exactly is it you are talking about? do you mean that Quintessence (physics) is different from definitions of aether ?77.86.10.27 (talk) 19:28, 18 May 2010 (UTC)

Giving them the same name would be confusing because they are used for completely different scientific theories. --Tango (talk) 19:32, 18 May 2010 (UTC)

In the Roman and medieval natural philosophy deriving from Aristotle, aether and quintessence were indeed synonymous—see Aether (classical element)#Fifth element. Who is it who "determine[d] that 'aether' was not an acceptable term for 'quintessence'"? Deor (talk) 21:53, 18 May 2010 (UTC)

As for why Aristotle posited such a fifth element, C. S. Lewis explains it well (The Discarded Image, pp. 3–4):

Aristotle, being interested both in biology and in astronomy, found himself faced with an obvious contrast. The characteristic of the world we men inhabit is incessant change by birth, growth, procreation, death, and decay. And within that world such experimental methods as had been achieved in his time could discover onlty an imperfect uniformity.... But the world studied by astronomy seemed quite different.... So far as he could find out, the celestial bodies were permanent; they neither came into existence nor passed away. And the more you studied them, the more perfectly regular their movements seemed to be.... It seemed reasonable to suppose that regions which differed in every observable respect were also made of different stuff. Nature was made of the four elements, earth, water, fire, and air. Air, then (and with air Nature, and with Nature inconstancy) must end before Sky began. Above the air, in true Sky, was a different substance, which he called aether.

—Deor (talk) 23:28, 18 May 2010 (UTC)

Tango, what are the two different theories, just the basics, thanks.98.221.254.154 (talk) 00:54, 19 May 2010 (UTC)

See luminiferous aether and quintessence (physics). Both of them are supposed to pervade all of space (and time), but aside from that they have nothing in common. -- BenRG (talk) 07:07, 19 May 2010 (UTC)

At an attempt at clarification - "aether" is a defunct theory for most scientists - so reusing a synonym won't be a problem for the majority of people.

If you want to know who repurposed the word I think the article Ostriker, Jeremiah P., and Paul Steinhardt, "The Quintessential Universe", Scientific American, vol. 284, no. 1 (January 2001) may be the place to start.

http://iopscience.iop.org/0264-9381/17/13/101/fulltext this article dates from 2000 - was that the original aim? to find out who coined the term 'quintessence' relating to dark matter?77.86.10.27 (talk) 11:42, 19 May 2010 (UTC)

This was in the aether theories article: The general attitude to this amongst physicists[who?] today is that although it is purely a matter of semantics, Einstein's comments stretch the word "aether" too far: it is argued that an "aether" with no mechanical properties doesn't correspond to the historical idea of aether, and so it is potentially misleading to apply this name to the spacetime field of general relativity.[citation needed]. Note the [who?] and [citation needed]. If it is so well known that the two theories are not the same why not update these? —Preceding unsigned comment added by 165.212.189.187 (talk) 13:26, 19 May 2010 (UTC)

Is this the sort of thing you wanted - [2] [3] , if the problem was different please be WP:BOLD or discuss on the relevant talk pages. I'm not sure what you want but I don't see anywhere in the articles problems. 77.86.10.27 (talk) 20:25, 19 May 2010 (UTC)

Whatever, even after reading both articles several times i still cant see a definitive difference between the two. Its like saying that originally a cucumber was considered a vegetable but now that it really is a fruit it should be renamed. —Preceding unsigned comment added by 98.221.254.154 (talk) 01:17, 20 May 2010 (UTC)

(Please link to the pages you are talking about)

The terms "Aether" and "Quintessence" are practically synonymous in their original meaning. But, they are not synonymous in later usages of the word.

If you want more info. please be more specific than 'i don't get it' because nobody can help you with that problem.!77.86.108.78 (talk) 11:00, 20 May 2010 (UTC)

So youre saying that meanings change over time. That is what I don't get. If their original meanings are practically identical then WHAT happened to change the meanings???165.212.189.187 (talk) 14:39, 20 May 2010 (UTC)

Yes, meanings of words change over time. This happens a lot.

In the meanings of the words in Aether (classical element) and Quintessence are synonymous only when "aether" refers to a fifth form of matter: because quintessence means "fifth essence", in later uses of the word "aether" such as Luminiferous aether where it does not refer to a fifth state of matter the two words are not neccesarily synonymous. Similarly Quintessence does not directly have the same meaning as Aether (mythology).

The earliest meanings are

• Aether - name one of the gods - see Aether (mythology) and a reference to "upper air" (at least as early as Hesiod 8th century BC)
  • Aether - as an element - comes later = probably by Aristotle - 5th century BC - approx 300 years later.
• Quintessence - means "fifth element/essence"

They're not the same meaning except when refering to Aether (classical element) when they happen to have the same overall meaning.

If you need more explanation please ask on the humanities or language desk as they would be better placed to explain the etymology, origins and meanings of these words.

To put it brutally to you - when you say "when their definitions are from the same classic Greek idea? " you were originally completely wrong : if you drop that assumption and read the articles everything should become clear. 77.86.115.45 (talk) 15:11, 20 May 2010 (UTC)

Native American Cradle Board and Infant Behavior Differences

Someone told me that when infants were placed in these cradle boards before they were able to walk that these infants were much less fussier and happier than of those infants who did not grow up these? Is this true? Please let me know if I did not make myself clear. Reticuli88 (talk) 18:51, 18 May 2010 (UTC)

It seems clear enough. But I don't know off hand of any scientific reason for this.--Chemicalinterest (talk) 21:04, 18 May 2010 (UTC)

See swaddling. StuRat (talk) 21:26, 19 May 2010 (UTC)

Right angles

Obviously not at a right angle to the ground if you're standing right next to it, but when viewed from far away, is this close enough?

Do right angles occur naturally? Jacob Lundberg (talk) 20:07, 18 May 2010 (UTC)

It depends on how perfect you want the right angle to be. Halite, for example, forms an isometric crystal, but as you'll see from the pictures, some of the angles are not quite exact. Matt Deres (talk) 20:18, 18 May 2010 (UTC)

Galena, too; and staurolite crystals can be twinned at right angles, as in the infobox image. Deor (talk) 21:44, 18 May 2010 (UTC)

Some fossils such as trilobites and strophomenid brachiopods (e.g. File:Leptaena sp + Rhynchonella sp.2 - Silurico medio.JPG) come pretty close to having right angles, such that they can be used to measure angular strain in deformed rocks by structural geologists. Mikenorton (talk) 20:47, 18 May 2010 (UTC)

A vine hanging to the ground, or a tree like the one to the right (if viewed from far enough away)? Comet Tuttle (talk) 22:08, 18 May 2010 (UTC)

If you break a silcon wafer (as used to make integrated circuits) that is 1-0-0 orientation, many of the pieces will form perfect right angles. --Phil Holmes (talk) 07:39, 19 May 2010 (UTC)

There are three right angles in space.77.86.10.27 (talk) 11:43, 19 May 2010 (UTC)

Yes they do, they are just rare. For example is two rocks are smashed against each other by waves, and a piece breaks off one, there are huge number of angles the corner where the piece broke off could take. It might by wild chance be 90 degrees, but it's unlikely. It's extremely unlikely to be 72.143554 degrees as well. There are just so many that any one happening is wild chance.--92.251.177.211 (talk) 20:42, 22 May 2010 (UTC)

Fear of the dark

What does the latest research have to say about fear of the dark? Has evolutionary psychology tackled this topic? Barbara Ehrenreich popularized the fear of predators explanation in Blood Rites (1997), but surely Steven Pinker and others have opined on the matter? Any pointers would be helpful. Viriditas (talk) 21:05, 18 May 2010 (UTC)

In an earlier discussion on ghosts in the archive, it says that people generally use the sense of sight to detect most objects. In the dark, they don't have that sense fully, so they are restricted. The sense of hearing becomes much better, so a floorboard creacking could sound like someone sneaking up. It unsettles you. --Chemicalinterest (talk) 21:07, 18 May 2010 (UTC)

Yes, that's true. But many children are afraid of the dark, such that they imagine monsters and see fearful shapes in everyday objects, such as trees. Ehrenreich's explanation, that as primates, we were once prey for predators at night, explains a great deal. I'm wondering if anyone has followed up on this line of thought (early humans as prey) since 1997. Viriditas (talk) 21:11, 18 May 2010 (UTC)

I can't seem to find any more recent research than what you point out. Ehrenreich's hypothesis doesn't make a great deal of sense to me, what would be the point of being scared of the dark before we had a way of making light ourselves (i.e. fire)? What's more, being scared of the dark, and presumably making a fuss to your parents, would be disadvantageous as any predators out there would be directed right to you. CI's suggestion seems reasonable, being in the dark makes you more sensitive to other senses and can make you more paranoid. Perhaps children haven't learnt what all the possible sounds that they hear in the dark could represent, and being on the safe side, are therefore scared of them. 86.7.19.159 (talk) 21:45, 18 May 2010 (UTC)

Why would the predators be directed at you if you make a fuss or increase your alertness? I think they'd have an easier time if you stand still, fearless, while taking no precautions against the mysterious shape sneaking up on you. --99.237.234.104 (talk) 04:02, 19 May 2010 (UTC)

I don't think it requires any special explanation. We are primarily visual animals: that's how we find food, notice dangers, etc. Being in the dark takes away our primary means of sensing the world outside out bodies - heck, even within our bodies. When you stub your toe, you don't try using proprioception and inner pain sensors to determine how badly it's hurt, you twist your leg into an ungodly position and risk falling flat on your ass to see it. Like the posters above, I'm not too impressed with Ehrenreich's idea; like David Jones' An Instinct for Dragons it seeks to provide a theory when the bald facts might be explanation enough. Matt Deres (talk) 22:48, 18 May 2010 (UTC)

As I remember from my childhood, fear of the dark is mainly fear of what might be hidden in the dark. Ehrenreich's explanation seems so, well, obvious, that I'm surprised there is any controversy about it. It's not clear how it could be tested by an experiment though. Looie496 (talk) 00:50, 19 May 2010 (UTC)

Sorry for hitching a ride on someone else's question, but what possible explanations might there be for a person (such as myself) actually being more comfortable in the dark than in daylight? As a child I was scared of many things (dogs, bulldozers, power-line towers, etc., etc.), but I was never really scared of the dark -- I was actually more comfortable in the dark than in daylight. Thanks in advance 67.170.215.166 (talk) 01:18, 19 May 2010 (UTC)

I find darkness calm and relaxing too, maybe you associate it with peace and rest. Not every single little aspect of human nature necessarily has to have a categorized condition. I'm not an expert so I could be wrong about this one. But I mean, NOT being afraid of spiders isn't a "condition" right? So why would NOT being afraid of the dark be one? Maybe the condition you are looking for is "slightly uncomfortable during the day time", maybe you have daytime anxiety disorder.  ;) Vespine (talk) 05:36, 19 May 2010 (UTC)

Reduction of alkali metals

Why can some alkali metals be reduced by weaker reducing agents? An example would be cesium caesium reduced by magnesium. Does it have something to do with gaseous equilibrium? --Chemicalinterest (talk) 21:50, 18 May 2010 (UTC)

If entropy can be increased so that the Gibbs free energy is positive then things that seem to go against the energy barrier can happen. So yes if cesium can be produced as a low density gas in the reaction it will depart from the scene and not react back the other way. Graeme Bartlett (talk) 08:45, 19 May 2010 (UTC)

PS I hope you are not trying this at home. Graeme Bartlett (talk) 08:46, 19 May 2010 (UTC)

No I only have tiny amounts of lithium that burn brightly but I saw in cesium production that cesium dichromate is reacted with zirconium metal to yield cesium gas. I thought the dichromate would be a much stronger oxidizing agent than the Cs⁺ ion. But the cesium ion oxidizes the dichromate to form cesium gas. --Chemicalinterest (talk) 11:58, 19 May 2010 (UTC)

That sounds an unlikely mechanism, more likely the zirconium reduces the dichromate and the cesium ions. If you make that cesium compound hot enough it will make cesium vapour all by itself. When you get brown dwarfs or giant planets you will find alkali metal vapour lines in the spectrum. Graeme Bartlett (talk) 12:32, 19 May 2010 (UTC)

It doesn't mean the alkali metals are in the planet, it could mean that compounds of them exist. (Both Na and NaCl release a specific spectrum.) --Chemicalinterest (talk) 21:39, 19 May 2010 (UTC)

algae or other plants

Is there an algae or other plant that will grow in the arctic or elsewhere in sufficient quantities to absorb all of the excess carbon dioxide now produced by fossil fuels? 71.100.0.29 (talk) 22:43, 18 May 2010 (UTC)

Lichens grow in the Arctic some places. But they will not make any measurable difference to the carbon dioxide concentration. BTW, fossil fuels only put out a miniscule section of carbon dioxide compared to natural sources. If there is more carbon dioxide, plants will grow better, consuming more of it. (This may not be NPOV). --Chemicalinterest (talk) 22:46, 18 May 2010 (UTC)

That's not NPOV, it's false (unfortunately!) see soyface and have a read of Co2#Role_in_photosynthesis. Admittedly on a global scale it is very uncertain, along with changes in cloud cover, the response of forests to co2 is the biggest unknown in climate change models. 86.7.19.159 (talk) 08:05, 19 May 2010 (UTC)

Have you read Geoengineering and the various links? The most common proposal when it comes to using plants is ocean nourishment. Other proposals generally involve growing plants in a more normal fashion and then encapturing the carbon dioxide in some manner so it isn't released for a long time like Biochar and Bio-energy with carbon capture and storage. Nil Einne (talk) 23:08, 18 May 2010 (UTC)

But doesn't CO2 storage intail with it the long term danger of accidental or unintended release that would result in the deaths of trillions of animals, if not render animal life extinct? 71.100.0.29 (talk) 00:53, 19 May 2010 (UTC)

The straightforward method of "storage" is to grow plants such as trees, and then bury them underground. Calculations show that a depth of 10 feet would take them out of circulation for hundreds of years. I think its pretty clear that any unintended release from this reservoir would be extremely gradual. In any case, to get a fix on the numbers, compensating for the CO2 we add each year would require removing several billion tons of carbon from the system, and there is no way that can be done with lichen. Looie496 (talk) 00:57, 19 May 2010 (UTC)

Well I do know of a case in Florida in which a lot of tress were found underwater that had been there for a long time. When the trees were removed they were found not only to be free of decay but strong enough to use for building material. Not only that the trees had taken on aesthetic qualities which allowed them to be used to build furniture that was highly valued and returned to the excavators hundreds of fold of their initial investment. On those ground the idea might not only be good for sequestering carbon dioxide but making your descendants thousands of fold rich, owing also to inflation. 71.100.0.29 (talk) 01:18, 19 May 2010 (UTC)

Looie, I know this has been suggested (biochar) but what's the point in this until we stop digging up coal?! Why waste energy storing trees when they could just be burnt instead and the coal could be left in the ground? 86.7.19.159 (talk) 08:05, 19 May 2010 (UTC)

You can't make furniture out of coal. 71.100.0.29 (talk) 16:19, 19 May 2010 (UTC)

Exactly. It's really worse than that. Just look at the amount of coal it takes to feed a single power plant. It's something like one or two mile-long trains full of coal per day! Now, for carbon sequestration to work, you'd need AT LEAST one or two mile-long trains full of tree timber to be buried someplace PER DAY. It's actually an awful lot more than that because trees contain water and the carbon is reacted with oxygen and other stuff that means that to sequester the carbon from one ton of coal requires more like three tons of old-growth trees or five tons of pine or other fast-growth trees. So just imagine your little power station - covering a few hundred acres - then think about the size of forest and the scale of activity you'd need to fill up maybe 10 mile-long trains with cut lumber every single DAY, 365 days out of the year!! (And to do that sustainably!) In previous Ref Desk questions, I've done the math on this - and to cover the current coal consumption (ignoring gas and oil) of the USA alone, you'd need to plant an area more than twice the size of the USA with trees and harvest and bury them all every 15 years! Furthermore - you'd have to do all of that harvesting, hauling and sequestering without using any more energy in the process...or you'll need even more area and even more harvesting, hauling and sequestering!! Plus, you can't just dump trees in a handy lake someplace - it'll fill up amazingly fast - and besides, trees have this annoying tendancy to float! This is so far from being a practical proposition that it's completely laughable. SteveBaker (talk) 15:03, 19 May 2010 (UTC)

I believe it would be feasible to remove carbon biologically at a cost of $100 per ton or less. The problem is that currently coal itself only costs a bit more than $100 per ton (it was up to $150 before the economic crisis hit, but was as low as $30 back in 2000). That means that to finance the removal of all the carbon you'd have to impose a tax of close to 100% on coal, which is obviously a problem. For any other energy source it would be far less of a burden though. Even for crude oil you'd only have to charge about a 20% surtax, by my calculations. I doubt that the political will is there, but I feel this is something the world could handle if it decided to. Looie496 (talk) 20:41, 19 May 2010 (UTC)

That's just bullshit! It can't possibly work! It's not enough to "remove" this carbon "biologically" - it's still got to go someplace. You burn the two mile-long coal trains worth of coal - you somehow capture the many cubic kilometers of CO2 that this produces (every day!) and "biologically" you do what with it? The material has to go somewhere - conservation of mass and conservation of energy guarantees that! If your magic biology turns the CO2 back into carbon then it's going to need considerably more energy to do that than you got out of the coal in the first place (conservation of energy). If you're planning on using photosynthesis as the source of that energy than you have to use sunlight to do that - and you STILL have 10 mile-long trains full of whatever residue your biological process leaves behind...but hey - if that stuff is so rich in carbon - why not burn it? Well, if you can produce/capture more energy/carbon with your biological process - then why bother burning the coal in the first place? Simply build a closed-loop system where you burn a gazillion tons of bio-residue, turn it into CO2 - which your mysterious process then (photosynthetically) turns back into bio-residue that you can then burn. No coal, no coal-trains, no mining disasters, etc. What you've just invented is a solar power plant. The idea of taxing coal and all that nonsense would magically go away - and since your process can capture the CO2 from burning $100 worth of coal (or bio-residue) for just $100 - the process you describe should be just as cheap as burning coal. So either what you are talking about is complete bullshit - or you've just solved the world's energy crisis and we can shut down all of the coal-fired power plants. I suspect, it's not the latter! SteveBaker (talk) 15:04, 20 May 2010 (UTC)

The way to get rid of the biocarbon is to bury it. The problem with using plant carbon directly as a power source is that it doesn't burn very well and isn't easy to transport-- it would probably have to be converted to charcoal, which is an expensive process. As I said, I believe it would be feasible to grow trees or other high carbon plants, harvest them, and bury them, for a cost on the order of $100 per ton of carbon. I'm not at all sure it would be possible to make a ton of charcoal for $100. Making biofuels (i.e. synthetic oil or alcohol) is at least an order of magnitude more expensive.Looie496 (talk) 17:33, 21 May 2010 (UTC)

Put simply, no, because if there was a plant or algae that could grow there it already would be. Take a look at antarctic flora - very few plants can grow there. Reasons for this are multiple: enzyme reactions become very slow, photoinhibition increases, photosynthesis decreases and water is less available at cold temperatures. To fix CO₂ plants need to open their stomata but if there is no water available (or if it's ice) then this won't happen. If (when) the arctic ice cap melts in the summer, more CO₂ will be fixed but the change in albedo from ice to water will far outweigh any benefit of increased photosynthesis. A more promising idea is to use cacti growing in deserts (which use the water efficient CAM photosynthesis) to fix carbon and sequester this elsewhere. But as I said above, doing this while still using fossil fuels is pretty pointless. 86.7.19.159 (talk) 08:05, 19 May 2010 (UTC)

• Strange that you should ask that question, as this has already happened in the past, see azolla event causing a global cooling catastrophe. Graeme Bartlett (talk) 08:43, 19 May 2010 (UTC)

It's worth pointing out that the original "sequestration" was the biogenic creation of fossil fuel in the first place: algae and peat absorbed atmospheric carbon by normal methods - photosynthesis and plant respiration (but over the course of hundreds, thousands, or millions of years). Then, those plants died and were buried (all the while, containing the carbon that they are made out of). Over geologic timescales, this kerogen turned into petroleum and other fossil fuel by geochemical, thermal, and even biological alteration. Now we are re-extracting this former plant-matter. The problem is that we have become so good at extracting it, that we can pull carbon out of the ground at a rate significantly faster than ordinary/natural plant life-cycles and geology can put it back into the ground. (At least, this is our concern, evidenced by the growing carbon concentration in our atmosphere). This is why there is research into carbon sequestration - we are looking for other ways to help improve the rate of carbon "re-absorption" - whether those methods are biological, mechanical, or otherwise. When we contemplate the scales, though, it just boils down to this: something must put the billions of tons of carbon that we extract back in the ground. Nimur (talk) 13:50, 19 May 2010 (UTC)

Interesting, DYK that only 70 years of photosynthesis were ever stored as fossil fuels? (Can't find the figures at the moment, but it does show that we could in theory remove CO₂ from the atmosphere relatively quickly once we stop producing it.) 131.111.30.21 (talk) 15:43, 19 May 2010 (UTC)

The key point here is that it's not enough for the plants to grow (thereby absorbing CO2). Something has to happen to the plants when they get old and die. If they simply sit there and decay - or are eaten by animals or are burned in a forest fire or something - then the carbon that they locked away will simply be released back into the atmosphere again and we're back to square one. If (somehow) the plant gets buried and instead of decaying and producing more CO2 and methane and other nasty greenhouse gasses - they get (ultimately) sequestered and after a gazillion years turn into coal and oil. This locks away the carbon and so long as no stupid humans come and dig it up again and burn it - it can be quite effective. But simply growing some moss and doing nothing else would only have a short-term benefit - roughly of the order of the lifespan of the first generation of plants...after that, the rate that these plants are absorbing CO2 would be balanced by the rate at which the extra plant decay adds to the CO2/Methane levels. SteveBaker (talk) 15:03, 19 May 2010 (UTC)

May 19

Nitroglycerin final ph

many people take Nitroglycerin for heart problems and its also added to gunpowder. since its made from nitric and sulfuric acid. wouldent it burn the mouth of the patient taking it and cause corrosive damage to the gun barrel? —Preceding unsigned comment added by Tom12350 (talk • contribs) 00:31, 19 May 2010 (UTC)

Reviewing several nitroglycerine MSDS safety sheets from various sources, nearly all list "not applicable" for the pH. For example, Nitroglycerin MSDS from Duke University. There are other hazards, including flammability and shock sensitivity; for skin contact, the MSDS suggests immediately flushing with water (though this is contraindicated by the typical medical application, rubbing it on the skin - but medical nitroglycerin is often dissolved in propylene glycol and is not pure). I would speculate that pure nitroglycerine has an almost perfectly neutral pH, if anybody bothered to measure it, gauging from its chemical structure; keep in mind that just because a precursor chemical was a strong acid does not mean that the final product is also a strong acid. As far as reactivity with metals, no metals are counter-indicated on the MSDS. Nimur (talk) 00:49, 19 May 2010 (UTC)

Seenitroglycerin manufacture. Oxide atoms are basic, but they are "locked up" in the glycerol structure. When the strong H⁺ ions attack the glycerin (along with the nitrate), the oxide atoms react with the hydrogen ions to form water, which is neutral. --Chemicalinterest (talk) 11:55, 19 May 2010 (UTC)

It's true that there are components that act as acid and base and give water in the reaction process (leading to neutral product), but the question wasn't about why glycerin doesn't make things basic. Also, please read the production section you mentioned to see how it actually happens--the mechanism you explain is not correct. DMacks (talk) 14:14, 19 May 2010 (UTC)

There is no reaction on that page that shows how the acids are added to the glycerol to form an ester(an ester is the compound of an alcohol and an acid, it doesn't specify whether it's inorganic or organic). If it is esterification, then they react to form the ester(glyceryl trinitrate) and water. I'm just saying that the acids are neutralized, so there is not harm from protons like there is in the free acid. --Chemicalinterest (talk) 21:37, 19 May 2010 (UTC)

To quote the article, "The sulfuric acid produces protonated nitric acid species, which are attacked by glycerin's nucleophilic oxygen atoms. The nitro group is thus added as an ester C-O-NO2 and water is produced.". That's...pretty clearly not "Oxide atoms are basic, but they are "locked up" in the glycerol structure. When the strong H⁺ ions attack the glycerin (along with the nitrate), the oxide atoms react with the hydrogen ions to form water". The nitrate is what attacks the H⁺; the glycerin O remains within the structure. DMacks (talk) 23:13, 19 May 2010 (UTC)

This esterification reaction involves the replacements of the OH^- groups in the glycerol with NO₃- groups. The H₂SO₄ acts as a catalyst. The H⁺ from the nitric acid and the OH^- from the glycerin react to form water. So the simplest(not the mechanism of reaction, just the difference between reactants and products) formula would be glycerol + 3 nitric acid → glyceryl trinitrate + 3 water. You can see how the acid is neutralized. What makes nitro explosive is because the reducing carbon group is bonded to the oxidizing nitrate group. --Chemicalinterest (talk) 11:19, 20 May 2010 (UTC)

Aircraft repairs

Would a blowtorch burn in a monsoon? I'm planning to write a novel about a flight around the world, and in one of the proposed scenes the pilot, while getting ready to depart from Calcutta on the first day of monsoon season, discovers that the plane has been sabotaged at an earlier stop in Pakistan by clipping the generator wires, and decides to repair it by soldering the wires together. Unfortunately there's no power available to run the electric soldering iron (the plane's battery is dead, and the generator is obviously non-functional), so the soldering iron has to be heated using a soldering torch, which has to be used a safe distance away from the fully-fueled aircraft, in the torrential rain. What (if anything) is wrong with this picture? Thanks in advance! 67.170.215.166 (talk) 01:37, 19 May 2010 (UTC)

Twist the wires together along with a strand or two of soldering wire and then heat with the blow torch directly until the solder melts, that would work. I'd be more worried about taking off in a monsoon then soldering some wires together near a fueled plane, especially since presumably everything's going to be pretty wet. I've arced a battery under the hood of a "fully fueled" car by accident more then a few times without any explosions so far. I'm pretty sure you can even weld under the hood without too much risk, unless you directly contact the fuel lines or components. Vespine (talk) 03:35, 19 May 2010 (UTC)

Just a note that doesn't really answer your question. Cutting the generator wire may not be a logical way to sabotage an aircraft - piston aircraft do not need a functioning battery or alternator (which is the generator that charges the battery) to remain flying with the engine(s) running. They use magnetos. Without a functioning battery, you have to hand-prop the aircraft (which means turn the magnetos on and turn the propeller(s) by hand until the magnetos engage and the engine is running by itself, which I should mention is dangerous if you are not trained in doing that), because the starter won't work and the turn coordinator, radios, navigation equipment, lights, and some of the other gauges, such as the fuel guages, would not function. If the attitude indicator is electronic (which is typically not the case, at least not on single engine aircraft such as the one I fly), that would not work either. Vespine brings up a good point. You want your electronics working if you are going to be flying through clouds. A good pilot will make the choice not to fly for any reason if the weather is dangerous, but since it's a book, you have a lot of leeway ;-). Falconus^{p t c} 03:42, 19 May 2010 (UTC)

I think Falconus would agree that 90% of pilots in this situation would unhesitatingly hand-start the aircraft, because that's the macho thing to do. The least likely part of the whole scenario sounds like the pilot taking off in a monsoon at all. Comet Tuttle (talk) 06:01, 19 May 2010 (UTC)

Um, no, I would not agree with that at all... I was talking about what is technically possible, not what is the smartest thing to do. While there is not an inherent risk to flying without the electrical system (heck, some aircraft don't even have an electrical system), that is only under optimum conditions (excellent weather, no need to fly through airspace requiring a radio, etc). I personally would not be comfortable doing that even if I knew the area like the back of my hand. If the weather was going to be bad, the pilot would have to be a certifiable madman to make the decision to fly without the electronic navigational devices, various gauges, radios, and the electrical instruments. I seriously doubt that many pilots would choose to fly with no electronics for a long distance flight (I could see with a GPS, and a backup GPS) even in great weather. It just isn't worth it. There are a couple of pilots that are "macho" and they are the ones that end up in the news. Maybe a handful (I'm guessing) would seriously consider flying in a foreign land with an aircraft that does not have any of the equipment that they typically rely on, but of these, I can only hope that very few would be stupid enough to attempt it in poor weather. Most modern pilots operate under the "err on the side of caution" philosophy. People don't realize that, because those pilots don't end up in the news. Falconus^{p t c} 06:28, 19 May 2010 (UTC)

Also, I should mention that hand-propping works (in theory) on all piston aircraft, but is rather dangerous to attempt on tricycle gear aircraft, just because when you lean forward to push the prop down, your head gets way too close to the arc. That is another reason why I would never attempt it on the aircraft I fly (reason 1 being that nobody has ever shown me how). Falconus^{p t c} 06:33, 19 May 2010 (UTC)

If the airplane was sabotaged in Pakistan, how did it get to Calcutta in India? And if the sabotage was so minor that the pilot simply flew from Pakistan to Calcutta, why doesn't he just fly on to his next port and fix the damage there, or somewhere else where it will be more convenient and miles away from the monsoon? Dolphin (t) 12:14, 19 May 2010 (UTC)

To answer your questions in the order asked:

1)The presumable intent of the saboteur(s) was not to prevent the plane from taking off altogether, but to cause a dangerous failure once in the air (the Paki saboteur was presumably angry with the pilot for breaking sharia law and then resisting arrest);

2)To this effect, the wires on the generator (mounted on the starboard engine in this model of aircraft) have been cut and then loosely re-attached in such a way as to vibrate loose during flight (also, the machine screw holding one of the valves on the portside engine has been loosened, which will cause a failure further down the line), therefore the sabotage has gone unnoticed until after landing in Calcutta;

3)During the flight from Pakistan to India, the weather is for the most part CAVU, so one could get by without electrical power, whereas from Calcutta to the next stop (Bangkok) it's close to zero-zero -- therefore, for this flight it's absolutely imperative to have fully functioning flight instruments and a working power supply. 67.170.215.166 (talk) 23:43, 19 May 2010 (UTC)

Guys, the question has little to do with the above answers. All he wants to know is if a blowtorch will work in a torrential downpour. Googlemeister (talk) 12:53, 19 May 2010 (UTC)

Oxy-acetylene torches will even work under water (see underwater welding), because they provide both fuel and oxidizer. If the wind were very strong, it is conceivable that the flame would blow out, but I think it's reasonable to say the rain is not an issue. Nimur (talk) 13:52, 19 May 2010 (UTC)

The following "retro" methods of soldering are not suggested as being safe or practical for actual usage, and are only presented in the context of possible use in the fictional work described above. In practice, there would be danger of burns or of starting something on fire, and hazard from inhaling lead fumes. If the electric soldering iron is heated while the wind is blowing and it is getting rained on, it will cool off too much to melt the solder by the time the hero has run several paces from his "safe open flame" location to where the wires are. In the early 20th century, there were soldering irons which were designed to be heated by a torch, (see some at [4]), and they had several ounces of copper in the business end. They would stay hot a bit longer. Something with several ounces of metal and an insulated handle or a handle that could be gripped with Visegrip or similar pliers could be heated with a torch or fire and might stay hot enough to heat the copper wire as well as melting the solder (needed to avoid a cold soldered connection). Maybe a golf club could be pressed into service as such an improvised soldering iron (though with an unwieldy long handle) or a small hammer with a metal handle and a leather grip further insulated with rags could be used, but a larger torch than a little propane torch would be needed to heat it. Maybe some aviation fuel could be burned in a can to heat the found soldering iron. A soldering iron, to melt solder, does not need to be red hot, so if heated red hot, it would still be at working temperature after it cooled a bit. Another old soldering trick is the solderpot. The wire connection was twisted together and left dangling downward. The solder was melted in an iron pot over a flame, and lifted up so the wires dunked into the solder. If there is enough solder, and a metal can, like a metal measuring cup and any sort of fire, and pliers to hold the can with, this would be an easy solution to the problem. If you Google ehow solder pot there are detailed instructions for using a solder pot. Edison (talk) 15:31, 19 May 2010 (UTC)

Thanks everyone, I think I'll have my hero(ine) use a torch-heated soldering iron that he/she has in the toolkit as a backup for the electric iron. BTW, if it's safe to heat the wires directly with a blowtorch on a fully-fueled twin-engine plane that has more than a thousand gallons of 100-octane avgas on board (as Vespine claims), I don't see why using a torch to heat the soldering iron while in close proximity to said fully-fueled plane would pose a significantly bigger danger of "setting something (i.e. above-mentioned plane) on fire" -- if anything, the danger would be less in this case. And as for hazard from inhaling lead fumes, it's very much overblown -- lead is not so volatile as to give off more than a tiny bit of fumes at the temperatures involved, so the pilot's exposure won't be significant (even if said pilot is a pregnant woman) from doing this job just one time. IMHO a bigger danger would be either setting the plane on fire with the blowtorch, or getting your fingers chopped off afterward when hand-propping the engine. FWiW 67.170.215.166 (talk) 00:01, 20 May 2010 (UTC)

Notes like the one about lead fumes are just ass coverage in case someone in the future reads a good-faith ref desk posting and does something idiotic like sitting in a small closet with a boiling pot of lead solder for hours, then wants damages paid from the person who posted information. We live in a litigious society. The US government has regulations to prevent children eating bicycle gears which contain lead. Personally I like the narrative having the person take a pipe cap and make it into a solder pot, heated over some burning fuel. Edison (talk) 19:04, 20 May 2010 (UTC)

Above seems about right. Comment - in the context of this story the whole thing seems a little like overkill - just as easy to strip the two wires, force them together, and tape up - and weak connections will spark and tend to just spot weld the wires together, additionally solutions such as finding a jubilee clip of similar clamp seem a lot simpler for our hero..77.86.115.45 (talk) 16:48, 21 May 2010 (UTC)

Good point about twisting the two wires together and taping the joint, that's another option for making the repair. However, jubilee clips are used on hydraulic lines, not on electrical wires (easy to see why, 'cause they're made of metal and thus conductive). 67.170.215.166 (talk) 04:19, 22 May 2010 (UTC)

soap labels

i noticed that some liquid soap bottles have a paper label. (dr. bronners is one i think but there are others as well) that label dosent dissolve even in my shower.

A) what kind of paper do they use that dosent dissolve and B) what kind of ink do they use that dosent run and C) what kind of glue do they use that dosent dissolve but it also safe for skin contact ect. —Preceding unsigned comment added by Tom12350 (talk • contribs) 02:40, 19 May 2010 (UTC)

FYI...Dr. Bronner's paper labels do most certainly dissolve, which might explain why they don't use them as much anymore in their liquid soap products under the half-gallon size. Sounds like your bottle isn't getting wet. Long-term users of the good doctor will often buy the soap in bulk and transfer it to smaller bottles, which often lacks a label. It's true that the paper labels on the old bottles didn't come off easily, however, and could take up to six months or so if you reused the bottle as I describe above, so maybe there was some water-resistant protection, but I think the company phased out the paper labels on the smaller bottles to save trees. Viriditas (talk) 04:21, 19 May 2010 (UTC)

i dont use Dr. Bronner's that much but other soaps labels i have dont come off that easily . in general what are they made out of? —Preceding unsigned comment added by Tom12350 (talk • contribs) 05:31, 19 May 2010 (UTC)

The new bottles have silk-screened labels, so no paper. Keep in mind, this is one of the most famous liquid soap labels in the world, so you should be able to find out what the old label was made of very easily. You can contact the company here. There's a phone number listed on that page as well. Remember, DILUTE! OK! Viriditas (talk) 06:49, 19 May 2010 (UTC)

can we stop talking about dr. bronners. i said i have other soap labels i have dont come off that easily . in general what are they made out of? they are a type of paper im holding one right now. —Preceding unsigned comment added by Tom12350 (talk • contribs) 08:39, 19 May 2010 (UTC)

Our Waterproof paper article is extremely sparse, but it does have a couple of references. The Times Higher Education link ([5]) describes a recent breakthrough in making waterproof paper. Making paper waterproof--and writable from CNET says, "Manufacturers today produce waterproof labels, but it requires embedding polypropylene fibers in paper. The process is expensive but also makes the paper waxy and tough.". Apparently the big push is to make waterproof labels which are also ecologically friendly.

Sadly, Waterproof ink and Waterproof glue are redlinks; this suggests that one way of making waterproof ink is to add glue to it, but it doesn't go into much detail.

There appears to be a wide spectrum of waterproof glues from make your own! (Cheese required) to Clues to Waterproof Glue Found in Antarctic Creature. It actually seems as though the glue may be the most straightforward of the three to create. --Kateshortforbob _talk 15:18, 21 May 2010 (UTC)

Could it be that both the paper and the ink are impregnated with waterproof glue to increase the water resistance? That would be the most logical solution for me. 67.170.215.166 (talk) 04:22, 22 May 2010 (UTC)

Lung cancer tumor eroding bone in rib

Hi There, My father was recently diagnosed with non-small cell lung cancer. The doctor said this has not spread to the bones but that it has eroded the rib at the tumor site. My question is what is the mechanism whereby the cancer causes the bone to erode? This is not a request for advice, I am wondering about the physiology of the bone deteriorating. Thanks! —Preceding unsigned comment added by 64.234.6.24 (talk) 04:41, 19 May 2010 (UTC)

I believe the erosion is simply due to pressure from the tumor, but I can't seem to find a citation to back this up. Regards, --—Cyclonenim | Chat  06:35, 19 May 2010 (UTC)

I would say metastasis (Lungs, bones, liver, and brain are the most common metastasis locations from solid tumors). AFAIK Lung cancer frequently sends metastasis to other organs through blood circulation. Metastasis are colonies of amorphous tumoral cells that substitute, in this case, bone tissue, making it more fragile. --151.51.20.38 (talk) 17:43, 19 May 2010 (UTC)

The docs were very specific, based on PET scan, that the cancer had not metastisized, rather the tumor had caused the bone to deteriorate. We will see the doc Monday and I will ask him about the mechanism of this as it seems the question is more difficult than I imagined. Thanks! —Preceding unsigned comment added by 64.234.6.24 (talk) 01:01, 20 May 2010 (UTC)

Perhaps the tumor is sucking too many nutrients from neighboring tissues? 67.243.7.245 (talk) 04:16, 20 May 2010 (UTC)

This section is a perfect example of why Wikipedia policy forbids giving medical advice. Looie496 (talk) 14:20, 20 May 2010 (UTC)

I don't believe this is an instance of a poster seeking medical advice, though you're welcome to take this up on the talk page, Looie496. (Granted, the reliability of the answers here is certainly dubious. Responders should remember that our goal is to provide detailed, factual, referenced responses to questions — not guesses.) TenOfAllTrades(talk) 15:09, 20 May 2010 (UTC)

In general, tumors (primary tumors and metastases) don't generally directly attack bone. Instead, they may secrete factors (proteins) which locally or systemically up-regulate the activity and growth of osteoclasts: cells that normally resorb bone at a carefully-maintained level. (While bones look static, they're actually continuously being taken apart and regenerated at a microscopic level. Osteoblasts build new bone, while osteoclasts trim it back; it's a dynamic equilibrium that responds to stress, strain, and fracture.)

There's a whole alphabet soup of different proteins which can be involved in shifting the balance from bone maintenance to bone destruction. Here's one paper – that I've linked to primarily because the fulltext is free – which specifically fingers MCP-1 in some non-small cell cancers; the discussion section towards the bottom of the article also lists a large number of factors identified in other studies.

To further complicate matters, the tumors don't have to secrete the osteoclast-stimulating factors themselves — the presence of an invasive tumor can trigger an inflammatory response in nearby cells which in turn drives osteoclast activation. This latter model is similar to a process of bone loss seen in inflammatory arthritis: [6] (that paper deals with cholesteatomas, but the idea is the same).

In other words, there are a number of mechanisms which can ultimately lead to overstimulation of osteoclasts and bone loss. I can't speculate on which might be active in any particular patient, and your father's oncologist is the one to talk to about treatment or prognosis options. TenOfAllTrades(talk) 15:54, 20 May 2010 (UTC)

Great, just what I was looking for. Thanks Ten! —Preceding unsigned comment added by 64.234.6.24 (talk) 16:57, 20 May 2010 (UTC)

safety of tinned food

Is it safe to eat tinned food that is past the use-by date? I have some tinned tomatoes that are about 4 years out of date, but it's a "best before" date rather than a use by date. I've checked the article, but it doesn't say there. Thanks in advance, It's been emotional (talk) 06:41, 19 May 2010 (UTC)

By definition, goods are not considered safe for consumption after the use by date.--Shantavira|^{feed me} 07:17, 19 May 2010 (UTC)

This article suggests that that may not be necessarily true: "Canned food retains its safety and nutritional value well beyond two years, but it may have some variation in quality, such as a change of color and texture. Canning is a high-heat process that renders the food commercially sterile. Food safety is not an issue in products kept on the shelf or in the pantry for long periods of time. In fact, canned food has an almost indefinite shelf life at moderate temperatures (75° F and below). Canned food as old as 100 years has been found in sunken ships and it is still microbiologically safe". Ghmyrtle (talk) 07:21, 19 May 2010 (UTC)

The integrity of the container is of paramount importance. Any rust? any dents? Discard the can. 218.25.32.210 (talk) 08:09, 19 May 2010 (UTC)

In part this will depend on how the canned food was sterilized. Some are irradiated thoroughly to kill off practically all microbes within the can, and this can leave the food with a use by date into tens of years. Whether it'll still taste good is a different matter. Regards, --—Cyclonenim | Chat  11:08, 19 May 2010 (UTC)

There is a reason they put a "best before" rather than a "use by". The former means that the texture or flavor may not be at it's absolute peak after that date - the latter means that you need to toss it out. So I would expect this stuff to be perfectly OK to eat. Most canned goods retain their edibility for decades. However, whether it still tastes OK is a different matter. Open one and find out! If it's been rotting for two years, you'll definitely know! SteveBaker (talk) 14:44, 19 May 2010 (UTC)

I would argue against the "just try it" method. Rotting is obvious, yes, but not all dangers come from rotten foods. Bacteria may set in that haven't really produced noticible decay. Bascially, the "use by"/"best before" date is the longest a company is willing to assert that the food is fresh and safe. Beyond that, you're taking a risk with the product. — The Hand That Feeds You:^Bite 15:15, 19 May 2010 (UTC)

With tomatoes one concern is corrosion of the can. The acid in tomatoes will quickly corrode an unprotected can. This is solved in the short term by lining the inside of the can with enamel or a layer of polycarbonate (yes, there's BPA in food cans). These will only last for a short time. After a while, they'll no longer be sufficient to protect the metal from acid errosion, and your tomatoes will get an off "metallic" flavor, or become unfit for consumption. -- 174.24.200.38 (talk) 16:13, 19 May 2010 (UTC)

I'd put inspection way over any date for determining if it's good. Is the can corroded, dented, bulging ? Toss it. If not, open it up. Are the tomatoes gray and bad smelling ? Toss them. If it looks and smells good, take a taste. If it tastes bad, toss it. If not, eat up. I've also had many items go bad before the USE BY date, it's more of a question of being 100% sterilized or not. If not, the food is unsafe almost right away. StuRat (talk) 17:57, 19 May 2010 (UTC)

If a can has been properly sterilized, there won't be even one single living microorganism in the whole thing. The "best before" dates are related to possible deterioration of the nutrients, not to bacterial growth. The speed of deterioration is tremendously dependent on temperature, though, so it's hard to set fixed time spans for usability. Looie496 (talk) 20:22, 19 May 2010 (UTC)

It's not just microorganisms that can be dangerous though. As Mr. 174 pointed out, there could be metal leaching into the food, perhaps to an extent to be harmful to the OP's health. It's not like canned tomatoes are that expensive; buy a new can. Buddy431 (talk) 04:25, 20 May 2010 (UTC)

Can coyotes co-exist with elk for any duration of time, without attacks?

Sorry for all the "wild animal kingdom" questions, but I'm on vacation and thought this board would have some biology experts about. Anyway, all I'm basing my question off of is what I could see through my binoculars and a Maglite pointed into the dark. A coyote was barking/howling about 20 feet away from me (I'm on a high porch facing a valley); he was loud enough to scare the daylights out of me when I was inside, and I quickly went out to listen to him. I could hear him sort of "quietly" grunting (when not howling). He stopped... so I ran inside to get the binoculars and flashlight, and when I returned, he was gone. However, a small herd of elk was grazing about 50 feet off to my right, and I saw two or three pair of "floating" eyes in the distance on the left. That meant the coyote was standing amidst this small herd, and I stood out there for probably 20 minutes waiting for a pack to take down one of the elk. But nothing happened. Is this ... normal? Any ideas what was going on? Was the coyote trying to spook the elk away? Cause it didn't work lol. Thanks so much in advance. And also if any birders are around, I'm still hoping for a bird call identification up in my "Loons in Colorado" question above. – Kerαunoςcopia^◁_galaxies 08:37, 19 May 2010 (UTC)

If the coyotes had just eaten, they might not want to eat the elk. But that doesn't explain why the elk weren't scared of them. --Chemicalinterest (talk) 11:42, 19 May 2010 (UTC)

I would be pretty surprised if a single coyote was any threat at all to an adult elk. That could explain their apathy, especially if the herd did not have any young. Googlemeister (talk) 12:48, 19 May 2010 (UTC)

Exactly. I don't like the chances of a coyote bringing down an elk, even if they have a partner, unless there is some exceptionally vulnerable herd member around. Those antlers aren't just for show. Vranak (talk) 12:57, 19 May 2010 (UTC)

Agreed, you'd need a wolf pack to hunt adult Elk. StuRat (talk) 17:50, 19 May 2010 (UTC)

Googlemeister, there was only one coyote from what I could tell, so maybe that's it. And I've seen entire roads closed off with signs saying "Closed until summer for elk calving", so maybe there weren't any young yet. I'm directly in the path of the elks' migration as they're always coming through here. So maybe one coyote decided to get a little possessive of his territory or something, it was kind of amusing. Thanks all for your replies, I greatly appreciate it. – Kerαunoςcopia^◁_galaxies 19:32, 19 May 2010 (UTC)

To be honest, I doubt the coyote calls had much to do with him trying to warn off the elk; it probably had more to do with letting other coyotes in the area know that he had claimed that bit of property. Matt Deres (talk) 20:32, 19 May 2010 (UTC)

Interesting. The Coyote article though mentions the territory thing doesn't happen until fall, and it's spring here now. But if that's the case, I kind of hope he returns. – Kerαunoςcopia^◁_galaxies 20:55, 19 May 2010 (UTC)

Turning off car

Over here in my city, we have timers on traffic signals that show how long till the signal turns green or red. I turn off the car when the timer is over 30 seconds( for it to turn green). I know that starting the car back on consumes fuel, but my question is how much time on the timer would make it feasible to turn off an average family sedan (mine is a 2000 Honda Civic). Thanks.--119.155.30.13 (talk) 10:34, 19 May 2010 (UTC)

Besides the cost in fuel, you should also calculate in the extra wear and tear on your starter. The starter for my Jeep is pretty cheap and it's a breeze to replace but yours might be different (more difficult/expensive). Dismas|^(talk) 10:55, 19 May 2010 (UTC)

An idling 4-cyl consumes around 1 liter per hour. Let's say you managed to save 10 minutes idle time each workday, it's around 40 liters annual savings. Is it worth it? If the car is out of warranty period, think of what Dismas said. IMO, if idle time becomes a financial (not just ethical) concern, you need to reconsider your daily route, place of work etc. East of Borschov (talk) 11:30, 19 May 2010 (UTC)

Recent BMWs turn of the engine automatically at any stop, and start it again when the accelerator is depressed. So the wear on the starter cannot be that bad. --Stephan Schulz (talk) 11:40, 19 May 2010 (UTC)

From what I had explained to me by a BMW salesman, the engine doesn't turn off-off. It's just a sort of really low "state". Rimush (talk) 13:11, 19 May 2010 (UTC)

I haven't seen an idle-shut-off feature listed on any of the marketingese at the BMW website; I suspect there's a misconception here. The Toyota Prius, however, does have the capacity to shut down when idle - but it has a completely different engine design, called the Hybrid Synergy Drive. In fact, it has no "starter motor" - the hybrid motor is the starter. This complete re-engineering changes the fuel-consumption/wear-and-tear tradeoff equation very significantly. But in an ordinary car, I would think that the extra wear on your starter is not worth the small fuel savings you may be getting by shutting down when idle. Nimur (talk) 13:39, 19 May 2010 (UTC)

They definitely had the feature on the BMW 1 Series in 2007-08. Maybe they discontinued it, or it's an Euro-only thing. Rimush (talk) 13:41, 19 May 2010 (UTC)

It is certainly a feature of some BMW cars.

On older cars without computer-controlled fuel injectors, I think the extra fuel used to restart the engine made it not worthwhile to stop the engine for the duration of a traffic signal. But modern cars can inject just exactly the right amount of gas to restart an already warm engine - so there is almost zero penalty for doing that - and killing the engine for even a brief stop turns out to be worthwhile.

However - there are some weird legal issues in some US states over cars that do this automatically - and the car manufacturers won't make different designs of cars for different states - so if just a couple of states have stupid laws, everyone is screwed (think about that the next time someone advocates increasing state's rights over federal government!). But certainly there are plenty of cars in Europe that do this. The MINI (which is a BMW brand) has different software in the USA and in the rest of the world specifically for this reason. The law here in Texas was designed to outlaw those remote starters that some people in cold climates use to start their cars 5 minutes before they go outside so that the engine and passenger compartment are nice and warm when they go to drive off. These things can be dangerous if someone leaves the car in gear by mistake or something. It seems that this law was written stupidly such as to disallow any device that causes the car to start without someone inside the car specifically commanding it to do so...or some such madness. Anyway - on my MINI (bought in the US), it doesn't do it - and on my sister's almost identical one (bought in the UK), it does. The Prius got away with it by saying that the engine doesn't directly drive the wheels - so technically it's just a generator. The answer to this question is that, yes, it does save gas to do that - and no, it doesn't noticably shorten the life of your starter motor. Even if it did, it, it also lengthens the life of the rest of your engine, clutch, water pump, belts, etc, so it would be a net win in any case. The latest MINI goes even one step further - when the engine has automatically stopped - and you push gently on the gas pedal, it rolls the car forwards using only the starter motor! Hence, when you are in heavy stop-start traffic, edging forwards a couple of feet at a time, you effectively have an electric car! It only restarts the engine when you get over one or two miles per hour, or if the battery is getting low, or if the cabin temperature gets high enough that the A/C has to turn on. I'm really pissed that some stupid outdated law prevents these kinds of intelligent fuel-saving ideas from being sold in the US market - even on cars that have all of the hardware to do it! SteveBaker (talk) 14:39, 19 May 2010 (UTC)

I see my error! Assuming that auto start-stop was a "luxury" feature, I checked the highest-end 7-series BMW, which does not have the option. Apparently auto start stop is only available on smaller BMWs - 1- through 3-series. Nimur (talk) 21:15, 19 May 2010 (UTC)

From occasionally driving and often being driven in a 2-3 year old 3-series BMW, I can, with very very very high certainty, state that at least the German model does indeed completely switch of the engine automatically when idling. It also switches off fuel injection completely if the car is engine-braking. --Stephan Schulz (talk) 18:45, 19 May 2010 (UTC)

The no-fuel-injection-during-engine-braking thing is a pretty common and well-established feature on cars with electronic fuel injection. My 1994 Civic did it, and I don't think it was particularly novel at that time. -- Coneslayer (talk) 19:58, 19 May 2010 (UTC)

How much does a starter typically cost? And how many starts does it take to wear one out? Thanks.--221.120.250.69 (talk) 18:52, 21 May 2010 (UTC)

http://www.google.co.uk/products?hl=en&q=starter%20motor&um=1&ie=UTF-8&sa=N&tab=wf

~£100 / $150

lifespan is long - starter motors are (I think) DC motors - so eventually the brushes may wear out or need replacing. I would guess the clutch or the contacts that turn it on/off would fail first.77.86.62.107 (talk) 19:03, 21 May 2010 (UTC)

My old auto shop teacher said, as a general rule, one minute of gas would be used by starting up the car. But you really have to take this with some salt, because it depends entirely on the car in question; obviously a big-arse Cadillac with a V8 is going to be different than a Yugo is going to be different than an Aston Martin is going to be different from a van, and the model year has a lot to do with it on account of increasing efficiency. And the temperature of the engine, temperature of the day, all that junk has to be taken into account as well. ZigSaw 12:25, 24 May 2010 (UTC)

Nuclear fuel

I read that Iran is swapping enriched uranium for nuclear fuel. What is the difference basically?--Mudupie (talk) 11:00, 19 May 2010 (UTC)

Enriched uranium discusses this at length, with diagrams to match. Regards, --—Cyclonenim | Chat  11:06, 19 May 2010 (UTC)

It's the level of enrichment—or, rather, the proportion of the isotope U-235 to the isotope U-238. Basically Iran is giving away a large storage of low enriched (3-5%) nuclear fuel, in return for a small amount of (ideally carefully controlled) fuel that is enriched to 20%, which is considered "highly enriched" even though it is not "bomb grade". The enrichment level determines in part what you can do with the fuel. 20% enriched fuel can run different types of reactors than 3-5% enriched fuel. In this case, I believe they want the 20% fuel to run a reactor that will make medical isotopes. (This is not a bad thing, in and of itself. Medical isotopes are good things.)

The reason for all of this is that ideally people don't want Iran to be able to enrich fuel to 20% on their own. The reason is not that 20% fuel can do anything interesting from a weapons point of view (it can't), but because the difference between 5% to 20% enrichment is actually a LOT larger than the difference between 20% and 90% enrichment. (This is, as first glance, counterintuitive—why should 5 to 20 be more than 20 to 90?—but it is because enrichment is exponential, to put it simply. This post goes into more detail as to why this is the case.) 90% enrichment is bomb-grade. So the goal here is to keep Iran from enriching their own material to 20%, because if they do that, they'll basically know how to make bomb-grade uranium. Giving them the 20% by itself is not necessarily dangerous, if it is monitored (so that it is not more enriched) and if they don't know how to enrich up to 20% on their own. Getting Iran to give away their existing stock ideally puts a limit on how much more enrichment they can do to it, and depletes the total number of bombs they could make if they enriched all of that fuel.

Note that there are some pretty obvious plans with the deal. Iran still intends to learn how to enrich its uranium to 20% anyway, and has kept enough low-enriched fuel that, if they did enrich it to 90%, they could have a bomb's worth of uranium. The U.S. analysts have largely viewed this as a "stalling" measure on Iran's part—to "give" a little bit so that sanctions don't kick in, while they work on their enrichment ability all the while. --Mr.98 (talk) 15:49, 19 May 2010 (UTC)

If you really believe that they want 20% enriched uranium to make "medical isotopes", then you must have your head under about two meters of sand. The thing is, 20% enriched uranium can actually do some interesting things from a weapons point of view without needing further enrichment -- if you stick it into a breeder reactor along with a lot of depleted uranium, then you can make "medical isotopes" indeed... 67.170.215.166 (talk) 00:15, 20 May 2010 (UTC)

Dirty bomb? --Chemicalinterest (talk) 11:12, 20 May 2010 (UTC)

That requires additional processing facilities and know-how that they likely don't have (nobody is alleging they have plutonium facilities), and the 20% they'd get from Turkey/Brazil would be heavily safeguarded anyway. I don't think there's any danger there other than them stalling. The risk of dirty bombs is exaggerated and certainly not what they are going after here. They do want the medical isotopes, in part because they want to be able to claim they've been doing civilian work on this all along. Their strategy from the beginning is to slowly get the infrastructure necessary to build multiple weapons if they wanted them. They wouldn't take the 20%, break safeguards, turn it into plutonium, and then try to turn that into a single weapon (if you could even get that out of 120kg of 20% fuel—the amount of plutonium produced even in a breeder reactor is small relative to the whole of the fuel mass, but I don't know the exact numbers). That would be the dumb approach. The smart approach would be to take the 20%, turn it into medical isotopes, show everybody how peaceful they are, drag out the UN process, continue developing U-235 enrichment capacity, divert other LEU into that, and get to the point where they could develop, say, a warhead a month if they wanted to. Then they have stealth nuke capability (like Israel), but have not yet violated the NPT in an explicit way, thus avoid sanctions, possibility of war, etc. Which is just a way of saying, one need not be blinkered about Iranian intentions to think that the 20% stuff is not going to be a military problem (it won't be). --Mr.98 (talk) 14:39, 20 May 2010 (UTC)

Also bear in mind that even "legit" medical isotopes (Sr-90, Tc-99, I-131, etc.) can, if produced in sufficient quantity, be used in a dirty bomb. You don't need plutonium for one of those things -- and if you're making plutonium, it makes much more sense to use it in a real nuke. BTW, regarding plutonium manufacture, Iran has actually been building a breeder reactor near Isfahan (and another one in Natanz near the main enrichment plant, so I've heard); I don't know if that thing is ready for use, though (they've had big delays with getting parts from Russia). FWiW 67.170.215.166 (talk) 04:35, 22 May 2010 (UTC)

Dirty bombs are, again, over-hyped, which basically every expert agrees on. Iran is not going to leave the NPT for a dirty bomb. A dirty bomb is not a sufficient deterrent, in any case. Again, the problem here is not about Iran taking this 20% material and doing bad things with it, the problem is that this is a move meant to derail other efforts to get Iran's stuff under control, and the more time they waste on that, the further they can get ahead in their domestic program. They've shown zero interest in any kind of short-term bomb; they want an independent production capability, if anything. --Mr.98 (talk) 21:30, 23 May 2010 (UTC)

Thank you for the explanation. --Mudupie (talk) 11:13, 20 May 2010 (UTC)

Reverse of hydraulic diameter?

While modelling fluid flows often the hydraulic diameter concept is used to model a non-circular duct as a circular one. I need to model a circular pipe as an equivalent rectangular one. So 1)Can this be done? (2)If so will it be modelled only as a square or can it be modelled as a rectangular section with any width to height ratio I choose? (3)Is this done in simply a reverse manner to how the hydraulic dia is calculated or is there some other technique (or does it depend very much on my fluid flow process and cannot be generalized)? Thanks —Preceding unsigned comment added by 125.17.148.2 (talk) 12:34, 19 May 2010 (UTC)

What exactly are you modeling? In general, you can model anything as anything - you can model your pipe as a spherical cow if you like. The question really is, "what parameters and results will you derive from your model," and as a followup, "what errors are introduced by your modeling assumptions/simplifications?" For example, if you intend to solve your flow with a FDTD solver and derive a fluid-flow rate for the pipe, your effective pipe shape will dramatically affect the resulting flow-rate. But if your procedure approximates the rate by simply calculating a cross-sectional area, the actual shape is irrelevant. So - what parameters do you hope to derive from your model? Once we know those, we can help direct you towards estimating the errors that result from your modeling approximation. Nimur (talk) 13:32, 19 May 2010 (UTC)

I am modelling the pressure loss in a cyclone separator. I have a correlation which is based on the entry duct being rectangular whereas my actual duct is circular. the pressure drop is dependant (at least according to the relation) mainly on the width of the rectangular entry duct and only to a smaller extent on height. so how do i change my circular duct to an equivalent rectangular one? If i know that the ideal/ general width to height ratio is 1:3 can i form that equiv rectangle? or since the model is dependent on a particular dimension (width) rather than area i cannot model it at all? Thanks once again. —Preceding unsigned comment added by 122.172.10.93 (talk) 16:31, 19 May 2010 (UTC)

If it is the pressure loss in the cyclone separator it self and not the pipe I don't think there are any generic translation. This depends on the mixing of fluids with different velocities at different radius in the cyclone. You will need a empiric formula CFD-simulation or very complex calculations. As an approximation I would guess between the pressure loss for a square with the same side as the diameter and a square with the same diagonal as the pipe diameter. —Preceding unsigned comment added by Gr8xoz (talk • contribs) 22:08, 19 May 2010 (UTC)

engineering

What is the scope of jobs if i do electronics in engineering<BE>?? —Preceding unsigned comment added by Swet69kak (talk • contribs) 13:21, 19 May 2010 (UTC)

Electrical engineering is huge. I mean, really huge. If you obtain an undergraduate degree in electronics engineering, you may be qualified to work in semiconductor manufacturing, MEMS, analog circuit design, digital electronics, computer architecture, system integration, firmware programming, software engineering, image processing, information theory, telecommunications, radio science, energy, and more. Have you looked at our article, electrical engineering? Nimur (talk) 13:26, 19 May 2010 (UTC)

Electronic engineering is really huge. Sometimes confused with Electrical eng —Preceding unsigned comment added by 79.76.203.64 (talk) 18:49, 19 May 2010 (UTC)

Note that this vocabulary distinction differs by region. In the US, at least, electronics engineers often have a degree in "electrical engineering", though they have extensive training in electronics. Comet Tuttle (talk) 23:00, 19 May 2010 (UTC)

The great thing about doing a BE is that it teaches you to think like an engineer. In any real job, you rapidly find yourself applying the thinking skills to information that goes into greater depth than you learnt in your course. After a while, it becomes possible to apply that process effectively to fields that didn't feature in the course at all (I can point to Electronic Engineering graduates who, 20 years on, spend most of their day doing Aeronautical, Marine, Automotive and Hydraulic engineering mixed with project management).

Proving you can cope with the academic rigour of a BE course also makes you attractive to all sorts of non-engineering employers (accountancy firms always used to like employing recent engineering graduates). Zeusfaber (talk) 19:27, 19 May 2010 (UTC)

moist towelettes

I watched the movie "The Book of Eli" back when it was playing and one thing that was a big trade item were moist towelettes, like the kind you use to clean your hands at a BBQ restaurant. I was wondering if those are a reasonable substitute for bathing in situations where a shower might not be available, like on a camping trip? I mean will one packet significantly reduce the BO, or would they need so many of the things that it would be inconvenient to haul dozens of them around? Googlemeister (talk) 13:38, 19 May 2010 (UTC)

The towelettes really vary in terms of the amount of liquid in them and they also gradually dry out over several months/years - even "sealed" as they are. I don't think they'd reasonably be useful for reducing BO, though; there's just too much "you" and not enough moisture in the packets to cover it all. Using one under each arm and one around the face/neck and one around the crotch might take some of the edge off, but after you've been sweating and in camp smoke for a few days, the stank (to use the technical term) is basically all over you - even your hair. Matt Deres (talk) 14:44, 19 May 2010 (UTC)

Exactly. And remember one of the opening scenes, where Eli says the good thing about no showers is that "You can smell hijackers a mile away", right before he's ambushed by the very same. Still, I think moist towelettes were a comfort item in that film, to, like Matt says, 'take the edge' off. Similar to the shampoo that Gary Oldman's character gave to his wife. Vranak (talk) 20:24, 19 May 2010 (UTC)

You'd be better off finding a stream or pond to wash off with (not necessarily in, mind you). In dryer climates, just rubbing sand on you can help clean off the sweat & grime, though it won't do quite so much for the smell. — The Hand That Feeds You:^Bite 15:28, 19 May 2010 (UTC)

You can always use a shower in a can to cover up the smell. 131.111.30.21 (talk) 17:23, 19 May 2010 (UTC)

Look in the baby aisle of your local supermarket - they'll have packets of moist wipes used for cleaning pooh off of babies rear-ends. That stuff is antibacterial so it should handle BO - and you get like 100 of them in a small container without a gazillion foil wrappers to lug around. SteveBaker (talk) 14:49, 20 May 2010 (UTC)

Beans growing on Crete

Does anyone know the name of the beans which grow on Crete and are used in locally produced "Coca-Cola" look a like called Fimi, these beans are also used by Nestlé. I forgot what they were called... I saw them growing in the wild in Crete... Sεrvιεи | T@lk page 16:54, 19 May 2010 (UTC)

Carob? Ghmyrtle (talk) 17:05, 19 May 2010 (UTC)

Still used, rusty aquaduct pipe lying in creek

At the tail end of a lake, the water rushes through a waterfall before continuing down a creek into the massive city-used reservoir eight miles away. Lying on top of some of this creek is a rusty pipe that is "picking up" some of the water and acting as an aquaduct to take it elsewhere (not sure where). The pipe is just resting on the surface of the creek; it's kind of gross. Are there any potential environmental or health concerns from this pipe touching future-drinking water? The pipe is slightly orange-ish in hue, with spots and discolorations on it. – Kerαunoςcopia^◁_galaxies 19:40, 19 May 2010 (UTC)

Almost certainly not - the orange patches are certainly rust - and iron is not a harmful element.77.86.10.27 (talk) 20:31, 19 May 2010 (UTC)

Even after it's oxidized? Is the amount of iron controlled at some point then? – Kerαunoςcopia^◁_galaxies 20:52, 19 May 2010 (UTC)

Rust is fairly insoluble in normal water, so it stays stuck to the pipe. If it goes into a water supply for humans it may be filtered to remove flakes and other gunk. Graeme Bartlett (talk) 21:16, 19 May 2010 (UTC)

Rust isn't harmful; it is a natural occurrent in the earth's crust. See hematite, the natural form of rust. --Chemicalinterest (talk) 21:33, 19 May 2010 (UTC)

Well, you can have too much of a good thing. I wouldn't expect the concentration of iron in the water coming off the pipe to be remotely high enough to be harmful, though. --Tango (talk) 21:46, 19 May 2010 (UTC)

If you are really concerned contact your local water authority or enviromental health agency (whatever they are called in your country) - better safe than sorry. The fact that a pipe links a water course to somewhere else raises the possibility of pollution by 'bad water' running in the opposite direction. In general though a rusty pipe in a water resovoir is not going to be a big problem.77.86.108.78 (talk) 11:03, 20 May 2010 (UTC)

Botfly

What actually happens if a human carries a botfly to full term in their flesh? Is there actually any lasting damage or health implications? No, not asking for medical advice here - I don't have botfly, nor does anyone I know. Just simple curiosity. --Kurt Shaped Box (talk) 20:21, 19 May 2010 (UTC)

Extracted human botfly larva. The arrow points to the larva's mouthparts

Dermatobia hominis captures a mosquito and lays an egg on it. Then when it feeds on a human the egg is transferred and a larva starts to develop (pictured) by feeding on flesh. Once it reaches full term it forces its way back out through the skin, falls to the ground and pupates. There was a great BBC Nature documentary showing it happen to a cow but I can't remember which it was. Searching the literature, the only problem caused seems to be myiasis (the larva feeding on your flesh). Adding "complication" to a search only comes up saying that it does not normally cause any complications. The danger comes if somebody attempts to remove the larvae and does a bad job, if the gut contents are spilled into your blood you could end up with a nasty infection (but having looked I can't find any recorded cases of what type of infection). So basically, like a good parasite should (to try and keep plenty of its hosts alive), it doesn't seem to cause any lasting damage. I spent the summer with some tropical biologists and heard a story of a professor who became so used to having the larvae that he no longer cared, once when at a football game, the larva decided it was time to leave, he took of his cap and out popped the grub, much to the disgust of those around him! That should probably be taken with a pinch of salt but I think it makes it clear that while being disgusting, they don't do any harm. 86.7.19.159 (talk) 21:45, 19 May 2010 (UTC)

Cracked disagrees. The bottom of this article says they can eat your brain. Of course, that problem wouldn't specifically be related to carrying it full-term... Vimescarrot (talk) 05:58, 20 May 2010 (UTC)

Hmm, that doesn't look like the most reliable source in the world. It also says that bullet ants "shriek" before they bite, but through personal experience I know that's not the case. It also has a picture of driver ants when its talking about the army ant, Eciton burchellii. Obviously if the mosquito happens to bite you in an important place then losing that bit of your body might be annoying - how exactly is the larva supposed to get through the skull though? —Preceding unsigned comment added by 86.7.19.159 (talk) 07:59, 20 May 2010 (UTC)

Certainly not a reliable source itself, but Cracked usually references some other source within its articles (I can't see it from here, it's blocked on this network). I think the idea was that to get to the brain it would simply float aruond the body (through blood vessels? I don't really remember) until it found somewhere it liked, then it'd settle down for a feast. 212.219.39.146 (talk) 08:02, 20 May 2010 (UTC)

That wouldn't work as they develop in the subcutaneous layers of the skin and don't enter the bloodstream. There are no sources in the article at all. _{To make things worse, they even stole the driver ant picture off this guy breaking the GFDL.} 131.111.30.21 (talk) 13:46, 20 May 2010 (UTC)

Through your ears? According to Myiasis#Clinical_presentation_in_humans, at least. Though this doesn't seem to be specifically referring to botflies. --Kurt Shaped Box (talk) 15:56, 20 May 2010 (UTC)

This article in Time discusses someone getting infected in their ear but it doesn't sound like they would be able to get into the brain through there. It seems more likely that the image in Cracked is of a Screw-worm fly - they can travel through the blood "Unlike the botfly, these larvae can enter the bloodstream and travel to distant sites such as the brain, lungs, heart, maxillary sinuses, inner ear, and even bone. If they remain localized, they feast on the host's tissues and can produce deep disfiguring wounds". That really wasn't a very good article! 131.111.30.21 (talk) 16:39, 22 May 2010 (UTC)

That quote came from this by the way there's no abstract available but if you search for "botfly brain ear" in google scholar it's the first hit. 131.111.30.21 (talk) 16:42, 22 May 2010 (UTC)

Evolution of movable eyeball

I know how the eyeball evolved, as per the WP article, but I can't think of an path for the eyeball to detach itself from the flesh around it, so that it can be moved. Is there there some speculative ideas on this? A google search [7] turns up a few hits, mainly from creationists questioning this. CS Miller (talk) 20:49, 19 May 2010 (UTC)

I have no idea how it actually happened, but it doesn't seem too difficult to me. Even a small amount of movement is beneficial, so it could start with an attached eyeball with a little flexibility and an appropriate muscle and gradually get less and less attached and more and more precise muscles until you reach the current state. --Tango (talk) 21:37, 19 May 2010 (UTC)

The most useful approach would probably be to compare the lamprey and hagfish, considered the two types of vertebrates with the most primitive body plans by most biologists. Lampreys have large movable eyes, but hagfish have lensless eyes with no exterior eye muscles. Looie496 (talk) 21:53, 19 May 2010 (UTC)

I've searched for some articles but it doesn't seem to have been discussed in any journals from what I can tell. This is because it is bound to be speculative and would be difficult to test so can't really be published in a journal. Tango's answer sounds very plausible, remember the amounts of time that evolution has to play with (unless you are an young earth creationist) and would be able to make infinite numbers of adjustments that would be either neutral or an improvement on previous eyes. Because eyes are so important, the selective pressure to improve would be strong. The creationist argument of irreducible complexity is pretty poor, this, the first hit in your link says that even the first eyes were complicated but ignores the fact that the simplest eyes would never have been fossilised! That also says "The fascinating thing about the evolution of the eye is its apparent sudden appearance" - this needs to be thought of on a geological time scale though - there have been huge changes to live today in the last few million years. There does not appear to be a convincing exact mechanism to show how the movement of the eye evolved, but remember that absence of evidence is not evidence of absence. The previous link ends with "For non-evolutionists there is no debate" - this is absolutely useless! You can't say that a theory is wrong without providing some alternative, more plausible explanation. Sorry for the rant - sounds like we're not really sure about it. 86.7.19.159 (talk) 22:10, 19 May 2010 (UTC)

It's of note that the eyeball is not totally detached by any definition. It is receded and has muscles that allow it to be pointed in different ways, but it still very much connected to the flesh. Receding into flesh would seem to make sense from a protection point of view; muscles to manipulate its location would also make sense. One can easily see how "half" of this capability would still be useful (humans only have "half" of the capability of, say, a chameleon), so that throws irreducible complexity out of the window (it is not an "all or nothing" type of thing). --Mr.98 (talk) 22:21, 19 May 2010 (UTC)

• I was under the impression that to get to the the the pin-hole state the retina evolved into the flesh, rather that the folds evolved outwards. It's the path from a lens-covered pit to a muscle-attached organ that I'm after.
• If the pit already had a lens before the sphere was moveable, then pointing the lens only at the object of interest is likely to reduce focusing accuracy.
• I can see that if the eyeball was on a stalk (a bit like snails'), then moving it into the body would be an advantage.
• 86.7--- / Mr98 - I'm not invoking argumentum ad ignorantiam, I'm trying to dispel my ignorance. CS Miller (talk) 22:58, 19 May 2010 (UTC)

The eyeball is still a lens-covered pit, isn't it? It's just a lens-covered pit that's also somewhat free to move from the surrounding flesh. I agree it's probably useless for the lens to be moved alone. The whole apparatus has to be moved together, which is why it might become somewhat less attached to the surrounding flesh. If you're thinking that the lens developed into the whole eyeball and the pit developed into the eye-socket that doesn't seem to make sense to me, although I'm just speculating. Rckrone (talk) 23:56, 19 May 2010 (UTC)

No, it is not necessary for the whole apparatus to move together. Salticidae have developed eyes where the lens is immobile but the retina moves. Of course Salticidae are arthropods, not chordates, and their eyes are not homologous to the eyes of the chordates. But no, the whole apparatus does not have to be moved together. Lampreys (already mentioned by Looie) indeed have an eyeball that is moved by extraocular muscles. (To be fair, lampreys have 5 extraocular muscles while most craniates -- from fish to mammals -- have 6; also, in contrast to most craniates, lamprey eyes are also focused by the extraocular muscles; AFAIK lampreys lack ciliary muscles in their eyes). This may suggest that lamprey eyes are indeed the most primitive "proper" craniate eyes extant. (Hagfish, on the other hand, is something of an enigma; either their eyes are the basal chordate eyes, or they have lost the advanced eyes their ancestors possessed, as the hagfish ecological niche does not require vision. There are reviews on that subject in literature. I recommend "Evolution of the vertebrate eye..." by Lamb, Collin, and Pugh, Nature Reviews Neuroscience (2007) v.8 pp. 960-975). This brings us back to the original question, how did the eyeball of the craniates evolve from the "cup" eyes of our basal deuterostome ancestors. Indeed, one mechanism by which hagfish may have lost the advanced eyes is neoteny. Larval stage of a lamprey has primitive eyes much like the hagfish; it is only during the lamprey metamorphosis that the proper eyeballs develop. Following the lamprey metamorphosis gives us a pretty good idea of what the eyeball evolution may have looked like. What happens is (1) light sensitive layer balloons laterally, forming a vesicle, (2) surface ectoderm is modified to form a lens, and (3) the extraocular muscles are formed from the mesoderm and the neural crest. Hope this helps. --Dr Dima (talk) 22:14, 20 May 2010 (UTC)

Trichlor illegal?

Is trichlor outlawed? It says so in the sodium hydroxide article. Thanks.--Chemicalinterest (talk) 21:32, 19 May 2010 (UTC)

it means trichloroethane (not Trichloroisocyanuric acid) , I've corrected the article [8]. Yes CCl3CH3 is outlawed.77.86.10.27 (talk) 21:59, 19 May 2010 (UTC)

Thanks. --Chemicalinterest (talk) 22:35, 19 May 2010 (UTC)

I still have some! Will I be arrested? Dbfirs 07:26, 20 May 2010 (UTC)

I think that it outlawed its production and sale, not its use (like halons). Naughty. You aren't concerned about the environment.--Chemicalinterest (talk) 11:06, 20 May 2010 (UTC)

Only a very small quantity - too little to be worth destroying (if that's possible). It has a very attractive odour, but I avoid inhaling it. Dbfirs 11:15, 20 May 2010 (UTC)

Which one is it? --Chemicalinterest (talk) 12:21, 20 May 2010 (UTC)

the 1,1,1 form was the most common - I used to have some Carbon tetrachloride - it too had a lovely smell - like many halocarbons (most of which are now banned or very heavily controlled) - you could hand it in to the local enviromental agency if you want rid of it (as an individual I doubt they would charge) - but company's probably have to pay to get rid of the stuff.77.86.115.45 (talk) 12:29, 20 May 2010 (UTC)

Yes, 1,1,1 (Liquid Paper thinner). Dbfirs 23:09, 20 May 2010 (UTC)

Wow, haven't seen any of that for over 2 decades - I think they banned it in the UK long before 1996 and replaced it with water or something - kids at school were sniffing it, - apparently the hallucinations they experienced interfered with paying attention in class or something...77.86.115.45 (talk) 23:47, 20 May 2010 (UTC)

Don't smell carbon tet! Can give you liver cancer. --Trovatore (talk) 23:50, 20 May 2010 (UTC)

Yes, almost all these compounds are toxic - and I don't think any are available any more for that reason. Possibly Methyl bromide is still used for fumigating silos for lack of an alternative but is heavily controlled. Dichloromethane is still available as a 50/50 mixture with methanol as paint stripper (in the UK) - I think it (should be) only a matter of time before the sale of that is banned too.77.86.115.45 (talk) 00:00, 21 May 2010 (UTC)

Here in the USA, we're still allowed to use dichloromethane as an industrial degreasing solvent (OSHA rules require good ventilation and the mandatory wearing of protective gloves, though, and there are EPA rules limiting emissions). Our policy is based on limiting the amount of pollutant emissions, rather than blanket bans on entire classes of substances which cause more harm to the economy than our mitigation-based approach. 67.170.215.166 (talk) 05:33, 21 May 2010 (UTC)

Atomic mass unit

"A single atom of carbon-12 has a mass of 12 u exactly, by definition", according to Wikipedia's article on the atomic mass unit. Because electrons contribute slightly to the mass of an atom, the mass of the nucleus of a carbon-12 must be slightly less than 12u. But this would seemingly imply that protons and neutrons have a mass that's slightly less than 1u, but in fact they have a mass greater than 1u. So what's going on here? Is this a relativistic effect involving potential energy reducing mass, or what? 173.179.59.66 (talk) 22:46, 19 May 2010 (UTC)

Electrons generally wouldn't count in the mass number. The total mass of the electrons in an atom carbon-12 would be 0.003291 (approx.) u. --Chemicalinterest (talk) 22:58, 19 May 2010 (UTC)

Terminology clarification: mass number is just the number of protons and neutrons and is an integer. The original poster is talking about the atomic mass, the actual mass of an atom, typically measured in atomic mass units; and yes, this includes the electrons. --Anonymous, 04:02 UTC, May 21, 2010.

A free carbon atom weighs slightly less than 6 loose protons + 6 loose neutrons. See nuclear binding energy. CS Miller (talk) 23:05, 19 May 2010 (UTC)

What you are observing here is that the mass of the assembled nucleus is less than the sum of the masses of the constituent particles. There is a loss of mass! See Mass defect where it says When the nucleons are grouped together to form a nucleus, they lose a small amount of mass, i.e., there is mass defect. The lost mass has been converted to energy according to Einstein’s formula $E=mc^{2}$ to hold the nucleus together against the electrostatic forces trying to disperse the positively-charged protons.

One amu is defined to be one-twelfth of the mass of a carbon-12 atom. As a consequence of the mass defect, the mass of a free neutron or proton is greater than one amu.

The mass defect is different for different elements, and different isotopes of any element. For example, the mass of the hydrogen-6 isotope is not 6 amu as you might expect from the definition of amu, but 6.045. Less mass is lost per nucleon in assembling a hydrogen-6 atom than in assembling a carbon-12 atom, possibly because hydrogen only has one proton so only one electrostatically-charged particle in its nucleus.

The mass of an electron is only 1/1836 that of a proton so the mass of all the electrons in an atom is not significant in the mass of the atom. Dolphin (t) 02:39, 20 May 2010 (UTC)

Whenever a net energy input is needed to pry something apart into its constituent pieces, conservation of energy together with E=mc² implies that the mass of the bound system must be less than the sum of the masses of the parts. This also applies to electromagnetically bound objects like atoms and to gravitationally bound objects like planets. "The lost mass has been converted to energy [...] to hold the nucleus together against the electrostatic forces trying to disperse the positively-charged protons" is incorrect. You have the sign backwards. If you have to spend energy to force like-charged objects together against their mutual repulsion, the binding energy/mass is positive, not negative. The negative binding energy of nuclei comes from the nuclear force. Electromagnetism contributes a positive binding energy, but not enough to make the binding energy positive overall. -- BenRG (talk) 03:38, 20 May 2010 (UTC)

May 20

Reservoirs for pumped storage hydroelectricity?

About what proportion of water reservoirs are presently configured for pumped storage hydroelectricity? How many are suitable? Enough to support 100% wind power in most countries? 71.198.176.22 (talk) 00:11, 20 May 2010 (UTC)

The article says there's 21.5 GW worth of capacity in my country -- not nearly enough to support 100% wind power. In any case, nuclear power would be much more reliable, practical and economical than wind power (though wind power could be used to supplement electricity production). 67.170.215.166 (talk) 01:03, 20 May 2010 (UTC)

I'm more interested in how many reservoirs could be converted to pumped storage during a transition to wind. I think you may be mistaken about the cost of nuclear. 71.198.176.22 (talk) 04:15, 20 May 2010 (UTC)

This article was published by Climateprogress.org, which is a self-described progressive environmentalist blog, and was also outspoken in its defense of Al Gore -- so they stand to benefit politically from supporting renewables in the face of all evidence against such policies. Clear conflict of interest, and anyone reading this article should take it with a big grain of salt. 67.170.215.166 (talk) 05:44, 21 May 2010 (UTC)

And pretty much bog-all in my country. Pretty much one, in fact. Again, not nearly enough to support "100% wind power". Tonywalton ^Talk 01:14, 20 May 2010 (UTC)

There's also Cruachan, Foyers and Ffestiniog in the UK. Loch Lomond/Loch Katrine (via Loch Arklett) could provide around 2.5hrs of average-load for the whole of the UK, for a 10m drop in water level (13km*1km at 300m elevation), however Loch Katrine is the major source of Glasgow's water supply. As for the OP's original question, as long as the tail race discharges into a large enough body of water, of the same salinity, then any conventional storage hydro station could be converted to pump storage. Another way to store electricity is to use giant sub-sea airbags, sodium sulfar batteries or to make hydrogen during windy periods. CS Miller (talk) 11:34, 20 May 2010 (UTC)

Pumped storage is more cost-efficient due to economies of scale. It could also be used for conventional hydropower when not being used for energy storage. 67.170.215.166 (talk) 05:48, 21 May 2010 (UTC)

Deepest manmade pool

Listening to NPR this evening brought a question to mind. They were talking about the Deep Horizon oil spill and how much pressure the human body can take under water. So, my question is what is the deepest manmade pool ever made? By "deepest" I mean from the surface of the water to the deepest point in the pool. And by "pool", I mean any manmade hole or container which was built/dug specifically to contain water. Or a quarry or other such excavation that was later filled/allowed to fill with water. Dismas|^(talk) 04:54, 20 May 2010 (UTC)

Nemo 33 holds at least one record. Viriditas (talk) 09:44, 20 May 2010 (UTC)

Another type of record: Lock (water transport)#Very large locks says "the Oskemen Lock on the Irtysh River in Kazakhstan has a drop of 42 m".[9] The reference says it is the deepest lock. PrimeHunter (talk) 13:27, 20 May 2010 (UTC)

From Open-pit mining I came across the Big Hole which has been closed since 1914 if I understand the article correctly (and I presume was allowed to fill up with water since then) but has only filled up to a level of 40metres. I don't know if the level is stable or of hundreds of years from now it could be over 200m.

Then there's Adams Mine "the deepest being 183 m (600 ft), placing it below the water table; it is currently half filled with water" so I guess that's ~90m.

Finally I found Berkeley Pit which our article says "is filled to a depth of about 900 feet (270 m) with water" so I guess that's the winner so far. I wouldn't want to swim or dive in it though since our article also says it's "heavily acidic (2.5 pH level). The pit is laden with heavy metals and dangerous chemicals, including arsenic, cadmium, zinc, and sulfuric acid". It may have been higher except "In the 1990s plans were devised for solving the groundwater problem. Water flowing into the pit has been diverted to slow the rise of the water level. Plans have been made for more extensive treatment in the future. The Berkeley Pit has since become one of the largest Superfund sites."

Edit: I also came across Mir mine which I guess is filling with water although I don't know to what depth. [10] appears to show it with water (based on our article and the details mentioned I'm pretty sure it's the same thing even if they say it's in Eastern Serbia when it's actually in Eastern Siberian).

Nil Einne (talk) 15:39, 20 May 2010 (UTC)

Do you count artificial lakes formed by dams ? Some of the tallest dams are around 300m high, so the lakes behind them are probably of similar depth. Gandalf61 (talk) 15:46, 20 May 2010 (UTC)

Super-Kamiokande's detector-pool is just over 40m deep. I'm sure either NASA (weightlessness training) or the oil-rig safety companies (dropping a helicopter body into a pool) have deeper ones. CS Miller (talk) 21:49, 20 May 2010 (UTC)

While it is not an open pit, the former coal mine at Springhill, Nova Scotia has been refilled with ground water at 18 Celsius and is now used as a massive geothermal reservoir. One shaft goes to 1325 metres depth. LeadSongDog come howl! 21:24, 21 May 2010 (UTC)

What does "Da" mean?

Link: [11] What does "Da" mean?174.3.123.220 (talk) 05:07, 20 May 2010 (UTC)

Dalton (unit). DMacks (talk) 05:28, 20 May 2010 (UTC)

In what language? use the language ref. desk not science. —Preceding unsigned comment added by 165.212.189.187 (talk) 14:36, 20 May 2010 (UTC)

In every language:) It's a scientific unit of measurement, per the cited context, not an arbitrary word. DMacks (talk) 14:43, 20 May 2010 (UTC)

Also, it means yes in Russian. --Ouro (blah blah) 19:18, 20 May 2010 (UTC)

And since (as in "since x, therefore y") in German. 67.170.215.166 (talk) 05:52, 21 May 2010 (UTC)

For readers without an easy way to see SVG diagrams, the relevant link is: File:Formation of tholins in Titan's upper atmosphere.svg. Astronaut (talk) 14:30, 21 May 2010 (UTC)

A Wikipedia search for "Da" is redirected to "DA", a disambiguation page which lists the aforementioned Dalton (unit).

-- Wavelength (talk) 14:45, 21 May 2010 (UTC)

Da also means yes in romanian.174.3.123.220 (talk) 21:56, 22 May 2010 (UTC)

Spinning Tesla egg and stability

http://www.youtube.com/watch?v=brNBVDCeECg&feature=related Okay, so in this vid, the egg is initially spinning about one axis, but as it rotates faster it its axis of rotation (relative to the body) switches. I was wondering why this happened. I know that an object spinning about a principal axis with a minimum or maximum value for its corresponding moment of inertia will remain stable, but an egg has two moments of inertia that are equal, so I don't know what happens in this case. Thanks. 173.179.59.66 (talk) 05:40, 20 May 2010 (UTC)

Our article Tesla's Egg of Columbus cryptically refers to "gyroscopic action". The whole article is pretty poor; I don't even understand why a rotating magnetic field would cause a copper egg to rotate (does it set up induction currents in the egg that create their own field, and interact with the external one?). Buddy431 (talk) 12:44, 20 May 2010 (UTC)

You don't need to mess around with copper and magnets and all that stuff. Just take two regular hens' eggs. Hard-boil one and leave the other raw. Now spin them on their sides as fast as you can. The hard-boiled egg will gradually roll until the pointy-end is pointing straight up...the raw one will remain on it's side and stop spinning rather quickly. SteveBaker (talk) 14:44, 20 May 2010 (UTC)

That the raw egg will stop spinning is pretty clear to me. What I still don't understand is why the other egg will change orientation. I tried something with Euler's equations which I'm not sure is correct, but maybe it will be on the right track. Let the axis that runs through the end of the egg be axis 1, the axis that the egg is initially rotating in be axis 2, and axis 3 be perpendicular to the first two. These three axes will be principal axes, so Euler's equations can be applied:

${\begin{matrix}I_{1}{\dot {\omega }}_{1}+(I_{3}-I_{2})\omega _{2}\omega _{3}&=&0\\I_{2}{\dot {\omega }}_{2}+(I_{1}-I_{3})\omega _{3}\omega _{1}&=&0\\I_{3}{\dot {\omega }}_{3}+(I_{2}-I_{1})\omega _{1}\omega _{2}&=&0\end{matrix}}$

Initially, most of the spin will be in ω₂, but owing to perhaps to some pertubations or whatever, ω₁ and ω₃ are small but non-zero. Because they are small, the second term in the second Euler equation can be ignored, and we get that ω₂ is constant. Likewise, because I₃ = I₂, dω₁/dt=0 and ω₁ remains constant. However, if we differentiate the third equation and substitue the first equation into it, we arrive at the equation

$I_{3}{\ddot {\omega }}_{3}+{\frac {(I_{2}-I_{1})(I_{2}-I_{3})}{I_{1}}}{\omega _{2}}^{2}\omega _{3}=I_{3}{\ddot {\omega }}_{3}=0$

Meaning that ω₃ will increase at a constant rate. If so, then the pointy end of the egg will begin to rotate, either moving up or down depending on the sign of ω₃. However, there are still some pieces missing: first, for the egg's tip to move up, ω₃ will have to be positive, but Euler's equations seem to imply that it can just as easily be negative;, second, what causes ω₁ to increase; finally, are Euler's equations even applicable here, considering that the principal axes are themselves rotating with respect to the laboratory frame? Actually, I can see that ω₁ would increase to preserve the orientation of the egg's angular momentum, but Euler's equations seem to contradict that (and really, this is just an exercise in applying Euler's equations, so I would like to know why they don't work, or if there's a way to make them work). 173.179.59.66 (talk) 17:39, 20 May 2010 (UTC)

The difference compared to hard-boiled is a good clue--suggests that having the internal material be fluid might be key. Especially important might be that the yolk has a different density and is mobile within the object. DMacks (talk) 18:46, 20 May 2010 (UTC)

Oh, I get why the raw egg stops spinning. Centrifugal forces push the yolk to the edges of the egg, increasing the egg's moment of inertia, and so on. What remains a mystery (at least to me) is the behaviour of the hard-boiled (or copper) egg. 173.179.59.66 (talk) 18:56, 20 May 2010 (UTC)

ok stevebaker is right about the hardboiled egg (slightly excited person) another - clearly the overall axis of rotation stays the same - so angular conservation of momentum is preserved..

actually the explanation of why this happens is complex - handwaving more handwaving - it seems that instabilities in the rotation of the egg + friction lead to precession maybe not - and eventually the egg stands up (in a circularly symmetrical arragement that is stable with respect to the frictional effects that made it stand up in the first place...) - quite how the friction causes the precession effect is beyond me - perhaps someone else could give a proper explanation...? The two mathematicians were Moffat and Shimomura - perhaps someone on the maths desk has a better handle on this. (It's certainly not trivial to explain - and quite a acchievement to prove - I'm still not sure if this is finished with Critics attacked the paper because... one for the maths desk )

As for the electromagnetic - spinning - yes - it's an induction motor basically - this video http://www.youtube.com/watch?v=pgkxAQ3fPzg shows the same effect with a slightly less confusing allen key in the second half - works for most things that conduct basically.

Question - as I understand it the induction motor shouldn't work when the copper egg stands on its end since the egg is circularly symmetrical in the centre of rotation of the field - since the torque requires anisotropy in the field.. Can anyone help me with this - does the egg slow once it's upright - at most the induced electric current would rotate - but since the rotation is about the centre of symmetry of the egg when upright there will be little resistance to it changing - and little or no torque?? (ie would a copper ball spin in the same experiment??) Anyone know??77.86.115.45 (talk) 19:47, 20 May 2010 (UTC)

So does my jumble about Euler's equations have any bearing? 173.179.59.66 (talk) 01:58, 21 May 2010 (UTC)

I've asked for assistance on the maths desk about this - I'm scratching my head - I expect the explanation to be simple - but I'm not sure it is. 77.86.115.45 (talk) 02:35, 21 May 2010 (UTC)

Pressure drop in branched pipe flow

I have a Y branch (both 45 degree) entering into a main duct. What is the associated pressure drop of the branch when (1)no fluid is flowing in the main duct (ie the branch is actually a sort of 'entry')? (2)fluid is flowing in the main duct? I would be grateful if anybody could give me either a correlation modelling the flow or the equivalent k factor or a relation in terms of bend loss etc Thanks —Preceding unsigned comment added by 125.17.148.2 (talk) 06:56, 20 May 2010 (UTC)

Ants

I woke up this morning to find Ants crawling all over my kitchen. I'm not sure how or why they got there as there is nothing for the blighters to eat except perhaps a few crumbs and I live two floors above ground so I'm surprised they made the effort.

Anyway, what's the best way of getting rid of them? My local hardware store has ant powder and also a spray of liquid for ants but which is better and how long will these take to work? They're only ordinary black ants, the type that are very common. GaryReggae (talk) 09:11, 20 May 2010 (UTC)

In the UK we have something called Nippon, which is a sort of gel. You put a blob of it where you saw the ants, and they are attracted to the stuff, which they consume and carry back to the nest, which then kills all the ants. It's quite funny watching all these ant drunkards queueing up to get to this stuff, and then staggering about trying to find their way home! It's about the most effective stuff I've found yet. --TammyMoet (talk) 09:25, 20 May 2010 (UTC)

Quite funny? Sounds like sadism :P Rimush (talk) 10:00, 20 May 2010 (UTC)

We occasionally get ants in our house, and use a prepackaged solid chemical composition in a plastic container. After a few hours, the ants get attracted to the trap. In a couple of days, you can see the ants are moving slower and diminishing. In a week, they should be completely gone. --Chemicalinterest (talk) 11:08, 20 May 2010 (UTC)

(edit conflict) Most sprays and powders kill ants pretty much in a few minutes - a good idea is to put in where they are getting in - like a minefield.

Other anti-ant products contain a poison that the ants carry back to the nest - thus killing the queen or whatever. These work in the longer term - and usually come in a box with a hole for the ants to get in. This is the type chemicalinterest mentions above

Googling the name of the products will probably get you the answer - the MSDS of each product should be available online - it's fairly likely that many products use the same poison - it will be mentioned in the MSDS.77.86.108.78 (talk) 11:11, 20 May 2010 (UTC)

Of course, in the long term, they'll probably keep coming back until you eliminate whatever brought them there in the first place. You know the drill: keep the kitchen clean, keep food in sealed containers (flour, sugar especially), wipe up spills immediately, etc. Buddy431 (talk) 12:39, 20 May 2010 (UTC)

I have found that putting a line of Raid around wherever they are coming in seems to work pretty well. It kills a bunch of them but presumably not the whole colony. But I don't recall getting repeat business from the same colony. --Mr.98 (talk) 14:30, 20 May 2010 (UTC)

Thanks for all your help folks! I would have bought some 'Nippon' as it is apparently very good and kills the whole colony, however my local hardware shop didn't have any so I got a spray instead which contains 'Cypermethrine'. Spray it on an ant and it kills it almost instantly. I can't figure out where they are coming in but I have sprayed the surfaces around where there seemed to be a lot of ants. I also realised what they were coming in for - I had left an empty bottle on the side with some dregs of fruit juice in - this actually proved a very effective trap - there were literally DOZENS of dead ants in there! Anyway, a couple of hours after spraying and I haven't seen any more ants. Fingers crossed! GaryReggae (talk) 18:23, 20 May 2010 (UTC)

If the ants do not carry it back to the queen, the nest doesn't die though. --Chemicalinterest (talk) 20:34, 20 May 2010 (UTC)

_{If you want to have some fun battling with them, an interesting thing to notice is that ants won't cross a line of black pepper. I have good fun in my house finding where they are getting in and lining it with black pepper and then responding to how they get around it. Not overly effective, but a good way to turn pest control into good fun.--Jabberwalkee (talk) 03:55, 21 May 2010 (UTC)}

Most of the common ant killer products are just a mix of borax, sugar, edible oil (usually peanut oil) and perhaps something fruity to get their attention. It's often sold premixed in small tins with ant-sized openings just to make extra sure that kids and pets can't get at it. Thanks for the reminder, I've got to do something about a colony in my yard. LeadSongDog come howl! 20:12, 21 May 2010 (UTC)

NaI (Tl) temperature effect

hello, it is observed that the light output from thre NaI (Tl) crystal falls with either rise or fall of temperature. can any body help why tis happen. and what is the mechanism that causing the phenmena. 59.90.213.38 (talk) 11:23, 20 May 2010 (UTC)

Thallium iodide article says that conditions to avoid are heat, so it may decompose into the elements when heated. The thallium iodide article says the NaI crystals are doped with TlI, but the NaI article says that the NaI crystals are doped with Tl (elemental?). --Chemicalinterest (talk) 11:38, 20 May 2010 (UTC)

Thallium is probably in the form of Thallium iodide - a description of the background is here [12]

Quote: Bob immediately sent off for some pure sodium iodide, and obtained a quantity of thallium iodide as well from Fort Belvoir, Virginia, where research on crystal counters was being conducted. He placed some NaI together with, as he put it, a "pinch" of thallium iodide in a crucible, and simply torched the powder. When it cooled down, he placed a small amount of the resulting glaze on a photographic plate, together with naphthalene, and repeated the irradiation experiment with the radium source. The response of the NaI(Tl), Bob told me, was tremendous. He knew then that he had found a wonderful scintillation material.

The search temp should be "Sodium iodide thallium effeciency temperature" or similar - this turns up http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B73DP-4V3M8DT-X&_user=10&_coverDate=04/15/1982&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=5c38b40ce51202ea554194ce49ce42ae which states a positive efficiency gain with temperature, which is explained in terms of emmision of light being related to adjacent thallium ("thallium dimers") in the crystal. (The article is not free on the web unfortuntately). I don't know if this theory is considered broadly correct but assume it is.

For the role of Thallium dimers in the scintillation process the key article appears to be by "Van Sciver" (Name: W. J. Van Sciver) : searching "van sciver thallium dimers" helps here.

This article is typical http://ieeexplore.ieee.org/Xplore/login.jsp?reload=true&url=http://ieeexplore.ieee.org/iel5/23/4324068/04324090.pdf%3Farnumber%3D4324090&authDecision=-203

I can't find any free resources on this on the internet. This isn't my subject - hopefully someone more expert will be able to explain more.77.86.115.45 (talk) 12:08, 20 May 2010 (UTC)

Karma

Is there any way to disprove the existence of karma? TheFutureAwaits (talk) 11:59, 20 May 2010 (UTC)

I don't think so - at the simplest level : "cause and effect" most scientists would eaily accept it to be broadly true, at more human or abstract levels; such as karma obtained through thoughts or words it is probably too subjective to be scientifically analysed to the level of proof or disproof.77.86.115.45 (talk) 12:14, 20 May 2010 (UTC)

Good things happen and bad things happen. In the immediate present our actions can result in positive and negative consequences, so if I punch a bouncer at a nightclub, the chances are I'll get beaten up in return. But if the consequence is entirely unrelated to the initial good or bad deed, there is clearly no link to a magical force. It's just two random events colliding with human irrationality (just as some people believe in good luck charms). Regards, --—Cyclonenim | Chat  12:57, 20 May 2010 (UTC)

No, definitely not. Most (if not all) versions of karma allow for the effect to come in a different life than the cause (see reincarnation). To disprove karma we would have to either disprove reincarnation or show that even if reincarnation exists, it doesn't include a concept of karma. Neither of those is falsifiable. --Tango (talk) 13:56, 20 May 2010 (UTC)

I don't honestly think so. I reckon, point of fact, that it would be easier to make a convincing case for its existence, than to break the same. Immoral people do tend to attract bad outcomes for themselves, from what I have witnessed. Having a reckless disregard for other people's feelings often means you are inattentive to matters that could set you back. Vranak (talk) 14:38, 20 May 2010 (UTC)

Karma simply means that actions have consequences. You don't need to have much life experience to realize that's true. Belief in rebirth, caste, etc is not a prerequisite to appreciating the truth of karma.--Shantavira|^{feed me} 15:13, 20 May 2010 (UTC)

It's probably far too broadly defined. To disprove something you need a specific claim. You could disprove specific claims about karma. For example you could take a thousand murderers and a thousand confirmed nice people and have them play games of chance against each other and see if the nice people are more likely to win, but if that shows no proof of Karma, someone who believed karma existed would simply say that it doesn't work like that.

Beyond that, some definitions of Karma are less about mystical forces, and more about the reactions and interactions of the people around you. For those definitions of karma it's actually a real effect caused by human's social instincts.

This sort of thing is why scientists try at all times to be very specific about their definitions. Laymen often interpret it as nit-picking, or trying to wiggle out of making a firm statement, but it's really just an important first step. APL (talk) 15:19, 20 May 2010 (UTC)

I think it would be fair to make a very reserved, but testable, claim that captures the overall principle: for example, "people who do nice things for others tend to get rewarded." Now, even this claim has some issues. What counts as a "nice thing"? What counts as a reward? To what extent do we intend to show a correlation? To what extent do outliers discredit the hypothesis? (There are plenty of nice people who have come to tragic ends). But at least this makes a stride towards a falsifiable, testable hypothesis. A scientist can then proceed to test the validity of the hypothesis. Game theory has contributed a significant body of research modeling and estimating peoples' behaviors and rewards. Surely there are also sociological papers that research this effect: The modeling of sharing: Effects associated with vicarious reinforcement, symbolization, age, and generalization. Now, to what extent does this capture the concept of karma? Karma is a vaguely defined semi-philosophical/semi-religious concept with thousands of interpretations. But if you want to restrict the claim to the concept that good behavior statistically yields better outcomes (with numerous caveats and exceptions), then that is a scientific claim with a good deal of evidence to support it. Nimur (talk) 16:23, 20 May 2010 (UTC)

Certainly one could imagine a statistical test for this. However, I suspect that the results would "prove" that Karma exists - in as much as people who do nice things tend to do better in life. But separating out the psychological feeling of well-being you get from doing someone a good turn from some mystical/religious interpretation would be much harder. How would you eliminate this "placebo effect"? There is also the issue of correlation versus causation. Could it be, for example, that people who are doing well in life tend to be nicer towards others? That seems like a reasonable hypothesis. We'd also have to be much more careful about the meaning of the term than is generally accepted. For example, we might try to devise a kind of double-blind study where people perform some act which they think is a good act - but which for reasons they aren't told is actually either "good" or "utterly evil"! If you found that those people that unknowingly were behaving in an evil manner did worse in life than the ones doing actual good in the world - then you'd have a very different conclusion than if they each performed equally. But do the "rules" of Karma say that merely having good intentions is enough to win you the rewards even if your actions are doing horrible things? If so then we can't use that test. SteveBaker (talk) 21:02, 20 May 2010 (UTC)

I'd argue the opposite of what most people seem to be saying. Bad things happen to good people. Wars and natural disasters don't spare "good people". Of course then you could argue that good people get a better afterlife or reincarnation, including that makes it completely unfalsifiable. Forgetting the subjectivity of what it means to be "good" to begin with..Vespine (talk) 22:35, 20 May 2010 (UTC)

Bad things do happen to good people - the question is whether they happen disproportionately to good people versus bad people. But this question isn't about whether Karma is 'real' or not - it's about whether you can test the hypothesis scientifically. Also, the "reincarnation" thing is a red herring - according to the believers, good karma brings rewards in this life as well as future reincarnations. Read Karma for a proper description. Note in particular: "In Eastern beliefs, the karmic effects of all deeds are viewed as actively shaping past, present, and future experiences."...if that's a true belief, then the effect should be measurable in "this life" and should not require the additional testing of any reincarnation hypotheses. If one were able (for example) to provide strong statistical evidence that karma doesn't work in this life - then you would have disproved the present belief system that surrounds it.

It is of course always possible (indeed probable) that the religious nuts would then back off a bit in a typical "god-of-the-gaps" fashion and say "Well, we're really talking about 'karma-2.0' in which the benefits of the good deeds you do in this life only affect you in subsequent reincarnations". But that would be a significant restatement of their present position - and I would argue, a different kind of karma than the kind they are telling us is guaranteed right now. However, even the 'karma-2.0' definition could (in principle) be testable (although it would be extremely difficult). You could have an entire generation of all of humanity do nothing but good deeds for their entire life - and have their children do nothing but evil their entire lives. Then you could measure the statistical improvement in the lives of the subsequent generations as the do-gooders died off and were reincarnated, then the evil-doers died and reincarnated. If the 'karma-2.0' theory is correct then the graph of newborn babies doing better than expected, then worse than expected should precisely match the graph of the deaths of the do-gooder and do-evil generations. So the hypothesis is falsifiable...but not by any practical experiment. SteveBaker (talk) 12:56, 21 May 2010 (UTC)

Defocus calculation

I have a lens which is focused to 5 feet. There are two points of light, one 3 feet away and another 6 feet away. How would I calculate the defocus blur (like the spread) of those points of light at the film plane given a focal length and aperture? How would I generalise this to work at all focus distances, including infinity? Lewis Collard! (lol, internet) 12:15, 20 May 2010 (UTC)

Probably the easiest way to see how to do the calculation is to draw a diagram. Light spreads from the point and hits every part of the lens. All the light that hits the lens gets redirected toward the focal point, so the size of the beam just past the lens starts out at the full size of the aperture and then decreases linearly down to zero between there and the focal point. Past that it grows again at the same rate. Use the formula on the focal length article to find the proper distance of the screen from the lens to get a focused image for the light at 3 feet, and compare that to the actual distance. Rckrone (talk) 17:13, 20 May 2010 (UTC)

There might be a suitable formula in Circle of confusion depending on exactly what info. you needed.77.86.115.45 (talk) 18:45, 20 May 2010 (UTC)

An easier way to see what's going on is to trace rays backwards from the film. All rays from a point on the film are refracted in the lens and reconverge to a point in the focal plane, then diverge beyond that. This traces out a double cone with one base at infinity and the other base at the aperture (and with the aperture's size and shape). Any light source inside that cone (and only those light sources) will make a spot on that point of the film. This is easy to remember and visualize and it tells me what I usually want to know: how much blurring will happen at a given distance, in units of physical length at that distance. It also tells you the behavior at infinity: the angular confusion at infinity is the apex angle of the cone. If you want the size perspective-scaled to a different plane for some reason, then you need to multiply by d/D, where d and D are the distances from the lens to the plane of interest and the plane of the light source, respectively. If d is the film plane, and you want to calculate it from the focal plane distance L and the focal length f, then d = 1 / (1/f − 1/L). Only these more complicated formulas appear in the circle of confusion article, together with more complicated diagrams, making things look much harder than they really are. -- BenRG (talk) 21:55, 20 May 2010 (UTC)

(more complex/accurate method) If you want to know the 'shape' of the defocus blur (ie the distribution of light in the focal plane) - you can do this mathematically - you need a good understanding of vectors/trigonometry/equivalent - (I assume the light points are on the focal axis) - you need to calculate the path of light as it travels from light source, is refracted in the lens, and then the intersection of the ray with the focal plane - this equation needs to be found as a function of angle the light ray makes with the lens axis - then obtaining the distribution (blur spread equation) by integrating over angle from 0 to the angle at which the ray makes with the aperture (at a given f stop)...

For parallel lines (ie point at infinity) you may need to use a slightly different integration (though assuming the light intensity of the parallel rays is constant with distance off axis is a good approximation for all normal lens) - (unless you are good enough at maths to have made your equations so that they don't "go silly" when point source distance = infinity.

You can also use a computer to help you do this (numerical integration) - there are also commercial products that do this - ray tracing or optics design - I don't know of any free ones - but no doubt they exist if you look hard enough (ask...)

Technically you need the forms of the len(s) you are using (ie the equation of the surface of the lens) - but you can simplify by just assuming a simple single lens even if your actual set is complicated and compound.. Ask if you need more..77.86.115.45 (talk) 18:17, 20 May 2010 (UTC)

Are you after a Depth Of Field Calculator? .. Vespine (talk) 22:29, 20 May 2010 (UTC) I corrected the displayed name of your link and hope you don't mind. Cuddlyable3 (talk) 23:16, 20 May 2010 (UTC)

particle board desk.

i have a particle board desk. i noticed there is "lip" where the top meets the edge there is a small gap where the veneer is glued. there are small white granules in there that appears to be a glue. is this Urea Formaldehyde? or some other type of glue. some came out and it is sticky. —Preceding unsigned comment added by Tom12350 (talk • contribs) 13:11, 20 May 2010 (UTC)

Probably the glue (aka resin) - Particle_board#Manufacturing suggests a number of possible glues, of which urea-formaldehyde is one likely possibility, I don't know of an easy way to distinguish the different glues.77.86.115.45 (talk) 14:41, 20 May 2010 (UTC)

Oh - if it's the glue holding on the veneer it may not be the same as the glue used to make the board - for wood veneers standard "wood glue" is applicable, for non-wood veneers (ie waterproof type plastic veneers) I don't know what sort of glue they use commercially.77.86.115.45 (talk) 17:59, 20 May 2010 (UTC)

For plastic veneers, it's usually some kind of contact-adhesive, I believe. Certainly when you do the job yourself, that's what the DIY stores recommend. SteveBaker (talk) 20:30, 20 May 2010 (UTC)

Yes - I've used araldite to mend these - I think (certain in some cases) the plastic veneers are produced with one side already coated with adhesive (and a peel off protective film) (ie like sellotape but much stronger) - this wouldn't be likely to produce any "white granules" - I think they will be from the particle board itself.77.86.115.45 (talk) 21:06, 20 May 2010 (UTC)

In some cases the edges are applied with hot-melt adhesives, which are usually white. If you can heat one of the droplets it may turn soft and sticky. Contact adhesives will rarely behave that way. LeadSongDog come howl! 05:22, 22 May 2010 (UTC)

i though hot-melt adhesives were clear —Preceding unsigned comment added by Tom12350 (talk • contribs) 05:45, 22 May 2010 (UTC)

What's the deal with ants and icing sugar?

Inspired by the ant question above. Is it true that ants will refuse/be unable to cross a line of icing sugar poured on the ground/floor upon which they are marching? Never had enough ants in my house to bother trying it, never felt the urge to dick around with the ants outside - but it's a factoid (folk wisdom?) that I've heard various people repeating over and over again down the years. --Kurt Shaped Box (talk) 16:04, 20 May 2010 (UTC)

Mmmh according to [13] it's a line of chalk not sugar - though I would guess they wouldn't cross a sugar line since oncee they found it their journey would be complete ("mission complete.found sugar.return to base.bring friends")...

Another possibility is ants dislike for fine powders .. eg Diatomaceous earth (also Boric acid Borax) - all of which look like sugar - could this be a source of the story??77.86.115.45 (talk) 16:17, 20 May 2010 (UTC)

I don't think that ants will refuse to eat icing sugar. Boric acid and borax are toxic to ants. --Chemicalinterest (talk) 17:33, 20 May 2010 (UTC)

Not quite the same subject but something I am curious about relating to ants - would double-sided tape be an effective way of catching them? Would they walk across it? If they refused to cross it then I imagine putting a line of it across where they enter would stop them from coming in.GaryReggae (talk) 18:25, 20 May 2010 (UTC)

Possibly.. depending on the glue used you might even find that they like the taste of it and are eating it..77.86.115.45 (talk) 18:32, 20 May 2010 (UTC)

Ants live their lives on a different scale to us. I wouldn't like to say for sure whether something that's sticky to us will also be sticky to their tiny feet... --Kurt Shaped Box (talk) 23:49, 20 May 2010 (UTC)

Thanks very much for the answers so far, folks. Seems to make sense... --Kurt Shaped Box (talk) 23:47, 20 May 2010 (UTC)

Blood work accuracy

How can you tell if a lab provides accurate blood test results or just randomly spits out numbers ? Are they rated for accuracy in any way ? I'm in Michigan. StuRat (talk) 17:47, 20 May 2010 (UTC)

There some letters after the name, and stuff listed here Medical_Laboratory_Scientist#Certification_and_licensing - one way to tell if the lab is legit.. 77.86.115.45 (talk) 17:50, 20 May 2010 (UTC)

That's about whether individual technicians are qualified to do the tests, I'm more asking if the labs actually bother. If nobody outside the lab double-checks them or if there's no consequences for just faking the tests, I'd be worried about the results. My brother does delivers for such a lab, and they don't bother keeping frozen samples frozen, so that makes me wonder about the labs in general. StuRat (talk) 18:25, 20 May 2010 (UTC)

Um we're referring to the US here, the land of the massive lawsuit. Do you really think there's no consequence for just faking the test? Also if your lab uses certified or licensed medical laboratory scientists then they would surely have some obligation to ensure they don't just 'fake the test' and if they do, are likely to suffer similar penalties that other professionals failing in their professional obligations would. If you want to know if you lab has any such people on staff, you'd best ask them. Forgot to mention that I'm guessing many may also have a pathologist or two or more on staff or perhaps even in charge who is a doctor so of course has the same professional obligations as other doctors.

Edit: I'm presuming of course you've already read the obvious article Medical laboratory which mentions such things as "Accreditation is done by the Joint Commission, AABB, and other state and federal agencies. CLIA 88 or the Clinical Laboratory Improvement Amendments also dictate testing and personnel" and "Now many labs have a compliance officer with mandatory annual meetings about compliance for all employees" (although that appears to be more about defrauding the US governments and insurers and stuff), but still want more info?

Nil Einne (talk) 18:49, 20 May 2010 (UTC)

Well I don't know about the US but here in the UK as a lab scientist I'm not going to just be churning out random numbers, we churn out the results we get from our experiments. If there are discrepancies in the results, they would be done again. Most labs have individual benchmarks for each test for what is normal, i.e. how much of everything should be in the blood of someone in the condition that's presented to them. I suppose it could be different in the UK because the NHS will have shared generic lab values, but I don't see why it'd be that different in the US. Regards, --—Cyclonenim | Chat  19:13, 20 May 2010 (UTC)

Hmmm, knowing "how much of everything should be in the blood of someone in the condition" could easily lead to faking the results, a true blind test would be better, in my opinion. StuRat (talk) 14:36, 21 May 2010 (UTC)

The doctors sending samples to that lab would very quickly realise if the results they were getting didn't match the symptoms their patients were presenting with. --Tango (talk) 20:31, 20 May 2010 (UTC)

Yes, but I don't trust doctors or accreditation boards, a few bucks under the table will probably shut up any investigations. And this is the US, so I have to assume full regulatory capture of any agency tasked with regulating the labs, meaning they now work to cover up any problems found at the labs, rather than to protect the public. As for lawsuits, it seems to me that it would be impossible to question a lab's results, especially if they destroy the sample, once testing is completed. And they could always claim the doctor gave them the wrong sample. So, how can I personally verify whether a given lab gives accurate results ? Are there websites like, say, "RateMyLab.com", where people can report problems ? StuRat (talk) 21:13, 20 May 2010 (UTC)

If you don't trust doctors, why are you worried about lab tests? Surely you don't use the healthcare system, so don't have any tests run. --Tango (talk) 22:06, 20 May 2010 (UTC)

I'd like to have some simple tests done (cholesterol and such), and would rather bypass a doctor entirely, if possible, if I could find a lab that I can actually trust. StuRat (talk) 22:29, 20 May 2010 (UTC)

The thing is that doctors do not get into medical school to cause harm. If a lab scientist sent dodgy results, the doctor would know. If it's the doctor who is changing the lab results, why would they in the first place? Sure it might help some statistics ("oh look everyone in Michigan doesn't have high neutrophil counts" or something) but it would also mean putting your health at risk, and if something were to happen, others would then look at your results and find the discrepancy.

I just see no real, valid reason why labs would need to be tested for authenticity or accuracy. Regards, --—Cyclonenim | Chat  01:31, 21 May 2010 (UTC)

If you had two tests done and the results were the same then you could fairly assume that both labs were ok. If they differed then one (or both) were wrong.. Can't you get home tests for chloresterol etc nowadays anyway?? (I assume you have some faith left in the chemists that produce these? or are they under suspicion too ? :) ! )77.86.115.45 (talk) 23:13, 20 May 2010 (UTC)

I would have slightly more faith in a test which can be done completely at home (versus one you must mail back). The reason is that they could be easily double-checked for accuracy by the consumer. StuRat (talk) 23:26, 20 May 2010 (UTC)

I'm just not seeing the reason to have any mistrust in the labs themselves -- they have absolutely no motive to alter such tests, and they have the best equipment at hand to make sure the results are as accurate as possible. It should be noted that home tests can still provide false negatives and positives, and in any case, no complicated blood work can be conducted at home. The most you can do is check your glucose levels. Regards, --—Cyclonenim | Chat  02:09, 21 May 2010 (UTC)

We seem to have a fundamental difference, you inherently trust everyone until (you become aware that) they have violated that trust, whereas I don't trust anyone or anything until they prove they are trustworthy. I sure hope you don't give your bank account numbers to "rich Nigerian princes" who e-mail you that they want to deposit money in your account. :-) StuRat (talk) 14:41, 21 May 2010 (UTC)

Also, is there any evidence of the accreditation boards actually suspending or revoking lab accreditation for any cause other than lack of payment of dues ? That would help to restore my faith (somewhat). Otherwise, I have about as much faith in them as in financial rating services which provided top notch ratings to failing banks. StuRat (talk) 21:17, 20 May 2010 (UTC)

It seems to me you have a rather large distrust of the entire US health care system. If you don't trust the people who are actively out there each day to save lives and help people, who do you trust? Surely not a bureaucracy or regulatory agency... Regards, --—Cyclonenim | Chat  22:09, 20 May 2010 (UTC)

You must have missed it when I said it before, so I will repeat it.

1) I would tend to trust consumer ratings over "official" ratings, any day. So, is there a web site where labs are rated by consumers ?

2) I also said that, while I inherently mistrust them, I could be convinced that the "official" agencies are actually doing their jobs if there was some evidence that they do, such as suspensions and revocations of accreditation (for causes other than nonpayment of dues). So, is there any such evidence ? StuRat (talk) 22:26, 20 May 2010 (UTC)

In Australia, the vast majority of pathology is done by a small handful of large chain labs, or it might now even be just one: Healthscope, since they purchased Gribbles Pathology a few years ago, which was "the other" big lab. These places would have strict operating procedures and audits and stuff. I really just can't believe a lab would get away with faking tests "wholesale" for very long. What would be their motivation? To save money by just printing off tests instead of really doing them? And doctors and the regulatory organizations would "cover up" their fraud? What would be their motivation for that? The lab is paying them all off? That's just ridiculous. Sure there would be cases of negligence, or even fraud, but to suggest it's "institutionalized", with the participation and support of the WHOLE health community is what I'd call paranoia. Where I WOULD distrust blood tests is if they are provided by a naturopath or some other "alternative health" practice not in a well known accredited lab, in that case I think you have good reason to be sceptical about any blood work you get done. Vespine (talk) 22:55, 20 May 2010 (UTC)

I think you're taking me a bit too literally. I doubt that any labs fake all their results, but perhaps some fake a few, and others just do sloppy work (like the one where my brother works that never bothers to keep samples frozen, even thought they must be for accurate results). But I'm just interested to know if any action is ever taken against bad labs. That is, do they have any incentive to do a good job, or is keeping their costs down their only goal ? StuRat (talk) 23:16, 20 May 2010 (UTC)

A problem I foresee with a "consumer rating" of pathology labs is that consumers on the whole would not at all be qualified to judge the validity of lab results. You would get all the conspiracy nutters who believe in chem trails and the whole big pharma genocide rubbish giving their 2 cents when their doctor give results that doesn't confirm their paranoia. That's kinda why we trust specialists in the 1st place, like doctors, which is kind of a vicious circle. If there are no doctors you trust, maybe you should have considered a career in medicine yourself, or at least find some doctors you might get to know and trust. That's why I look at blogs like science based medicine, because there are doctors there who's opinions I trust. Vespine (talk) 00:30, 21 May 2010 (UTC)

While individual doctors and lab techs may well be competent and want to do a good job, the management of the company may work against them. For example, if a test requires 10 minutes to perform competently, but their management threatens to fire them if they take more than 5 minutes on each, then they have the choice of rushing each and doing a half-assed job, doing half of them properly and just faking the results on the other half, or being fired and replaced by someone else who will do one of those things. If a company is only concerned with short-term profits, this type of management pressure is a real concern. StuRat (talk) 14:32, 21 May 2010 (UTC)

I agree that individual consumers may well be nut-jobs, but the consensus of the whole should nonetheless be useful info, much like individual purchasers of stocks are often idiots, but nonetheless the stock market, in total, does a good job determining the long term value of companies, perhaps better than professional rating agencies, specifically when the effect of bribery is considered. While any small group can be bribed, or perhaps just cover up a problem that would otherwise "bring disrepute into our field", there's no way a large cross section of consumers can be bribed or act against their own interests. StuRat (talk) 14:23, 21 May 2010 (UTC)

I agree with Mr. 77.86: send your blood to two labs (or more, if you really want to be sure) and compare the results against each other. If they match reasonably well, then it's likely that they actually did some sort of test. Buddy431 (talk) 05:06, 21 May 2010 (UTC)

See http://www.bloodbook.com/ and click on "ABOUT US". -- Wavelength (talk) 05:48, 21 May 2010 (UTC)

Lab statistics

OK, let me ask another way. See chart:

Lab name      % of results within 10%
============  =======================
ABC Lab       93%
Quack Labs    12%
XYZ Labs      98%

Is there a place where I can get results like this ? Better yet would be a break down of how accurate each individual test is when performed at the various labs. StuRat (talk) 14:52, 21 May 2010 (UTC)

... Within 10% of what? Presumably, you mean some kind of gold-standard, trustable set of ideal and perfect measurements from a reliable laboratory. But who verified that set of results? (Presumably they are compared against another, "platinum-standard", ultra-trustable laboratory?) As you can see, the problem boils down to a degree of trust and verification. Web of trust describes a decentralized trust model - you can see that the problem has been thought about - but at some level, you must accept somebody on good faith alone - unless you can create and administer every part of the test individually. Nimur (talk) 15:49, 21 May 2010 (UTC)

Within 10% of the actual value. For example, if they are giving an RBC count, there should be an actual correct number of red blood cells. How do you determine what it is ? Taking an average of the lab results from many labs would work, possibly tossing out the values farthest from the average. StuRat (talk) 03:43, 22 May 2010 (UTC)

I can't be bothered to reply in different parts of this thread so I'll just post my reply down here.

"Hmmm, knowing "how much of everything should be in the blood of someone in the condition" could easily lead to faking the results, a true blind test would be better, in my opinion."

This simply is not possible. How can you define what is normal with a blind test? You need to establish what is normal based on average test results over time. You can't just take a blood sample and go "ooh looks a bit busy here with respect to leukocytes" -- you have to know how many leukocytes should be in the blood for a person in that condition! Bottom line, you need benchmarks to compare results against, otherwise you're just staring at a number which means nothing!

I completely disagree. The lab should not be given any clues as to what values are expected, they should just report the levels they find, and the doctor and/or patient can then decide if that's normal for them or a cause for concern. StuRat (talk) 04:01, 22 May 2010 (UTC)

"We seem to have a fundamental difference, you inherently trust everyone until (you become aware that) they have violated that trust, whereas I don't trust anyone or anything until they prove they are trustworthy. I sure hope you don't give your bank account numbers to "rich Nigerian princes" who e-mail you that they want to deposit money in your account. :-)"

The difference is that these rich Nigerian princes are people who lack any credentials whatsoever _{and usually have Yahoo! mail accounts!} The doctors and lab scientists are trained and are there in your best interest for the most part. To inheritly distrust them seems silly when 99.999% of the time they're working with your best interest at heart.

99.999% ? Really ? You only think maybe 1 in 100,000 people would ever take a short cut that's not in the best interest of the customer ? I believe more than that many will be actual murderers, based on statistics and my assumption that lab techs are just as susceptible to human failings as any other person. I'd guess at least 1 in 10 would take occasional shortcuts. Your estimate seems absurdly low. I sure wish there was a way we could tell for sure, but that's rather the whole point of my question, isn't it ? StuRat (talk) 03:56, 22 May 2010 (UTC)

The problem with your little chart is that the chances are all of those labs are using very similar, if not identical, procedures, and so assuming fully competent lab scientists, they're all going to be around the high 98-99% range. ALL TESTS have a degree of error, it's called the standard error, but the vast majority of tests in hospitals have such a small degree of error involved that the results are almost always perfect. I'd venture to say you are probably in a small minority for distrusting inheritly these officials, and I doubt there are any statistics on specific lab accuracy because they're all going to be roughly the same. Regards, --—Cyclonenim | Chat  16:28, 21 May 2010 (UTC)

If all the labs come out with about the same accuracy, that would still be valuable info that I'd love to see. StuRat (talk) 03:45, 22 May 2010 (UTC)

[Cyclonenim, please see wikt:inherit and wikt:inherent. -- Wavelength (talk) 16:44, 21 May 2010 (UTC)]

Argh, sorry. I'm usually such a pedant for vocabulary and grammar, too. Blame the 40 hours without sleep. Regards, --—Cyclonenim | Chat  17:46, 21 May 2010 (UTC)

I did a Google search for blood test accuracy, and found HowStuffWorks Videos "Accuracy in Blood Test Data" (14:02) by World Business Review on the topic "Blood Test Data Management". Wikipedia does not yet have an article specifically about blood test data management, but that expression can be useful in further searches on the World Wide Web. -- Wavelength (talk) 17:35, 21 May 2010 (UTC)

Breathing in Helium

Why does breathing in helium cause the human voice to become squeakier? I've gone through some websites on the matter, and they all say that it's because the speed of sound in helium is greater than in air, but I'm a little unsatisfied with this. It's not really an explanation; I still can't "see" why helium produces this effect. I figure that there are specific resonance frequencies in our voice box, and that changing the speed of sound in the voice box will change the resonance frequencies, but I'm at a loss as to why the frequencies will be shifted upwards with an increase in the speed of sound. Can anyone give a better description of what's happening? 173.179.59.66 (talk) 19:03, 20 May 2010 (UTC)

The shape of the larynx determines the wavelength of the sound. The vibrations aren't produced by the tissue in the larynx itself vibrating (as in a guitar string), but rather by allowing the air to vibrate within the space it creates (as in an organ pipe). That's why you won't get any vibration without air flow. Higher speed of sound with the same wavelength means higher frequency. Rckrone (talk) 19:28, 20 May 2010 (UTC)

What I said seems to be contradicted by the vocal folds article, so to be honest I'm a bit confused about this myself. The resonant frequency of the vocal folds should not depend on the type of gas that's next to them. Rckrone (talk) 19:42, 20 May 2010 (UTC)

First of all, here's a nice thing on speed-of-sound calculations and the Straight Dope relevant article. Taking in helium puts some of the gas in your vocal tract which does mean the speed of sound is faster. However, the difference in pitch should come about more when the sound leaves your mouth (which may be why, and I'M NOT AN EXPERT ON ACOUSTICS, you don't hear yourself with a high voice as much as others do). Your vocal cords vibrate with the same frequency and the energy of the wave should stay the same which gives it a longer wavelength, so when it transitions to the slower speed of normal air, that's when the frequency of the sound wave increases, resulting in an overall higher pitch. This is what I think occurs.

The relevant equation, by the way, is c=f*L, or the speed of sound equals frequency times wavelength, and E~c*f, or energy is proportional to speed of sound times frequency. When energy stays equal but the speed of sound drops between helium and air, the frequency must increase (energy is conserved). SamuelRiv (talk) 19:36, 20 May 2010 (UTC)

... so if you listened in helium, everyone speaking in air would have a deep voice? The "Straight Dope" article sounds confused to me. I think they mean that helium doesn't change the wavelength of the sound, but I'm not an expert on acoustics either, so I'm confused too! Does anyone know the truth? Dbfirs 00:01, 21 May 2010 (UTC)

No, you don't hear wavelength, you hear frequency. (At least, assuming you don't have helium in your cochlea; not sure offhand how that would affect things.) When sound of a given frequency crosses the air/helium interface, its frequency stays the same but its wavelength changes.

On the other hand, you generate sound of a given wavelength, because it's related to the geometry of the resonating chamber. --Trovatore (talk) 00:08, 21 May 2010 (UTC)

Ah, the article says the cochlea is "filled with a watery fluid". If that were replaced by helium, my guess is that you would go totally deaf, and the question would be moot. --Trovatore (talk) 00:10, 21 May 2010 (UTC)

So my understanding is that the wavelength of emitted sound doesn't change when breathing in helium, meaning that the frequency emitted is higher. But then why isn't the pitch of the sound affected? 173.179.59.66 (talk) 01:56, 21 May 2010 (UTC)

The pitch is effected... your voice sounds higher! The speed of a wave equals it's frequency times it's wavelength. Since the wavelength remains the same, and clearly the speed remains the same, then it must be the frequency that changes (a.k.a. the pitch?) Regards, --—Cyclonenim | Chat  02:11, 21 May 2010 (UTC)

Except that most articles that I've read suggest that it is the timbre of the sound which is affected, rather than the pitch. 173.179.59.66 (talk) 02:31, 21 May 2010 (UTC)

I'd say it's quite clearly not timbre in it's official definition. Timbre is just the quality a specific note has, so if you play a guitar you can play the same note on the fifth fret of the A string and the twelfth fret of the D string, and the pitch is the same, it just sounds ever so slightly different. Pitch is another thing entirely and relates to the distance between the peaks in a wave, and is responsible for different notes. When you inhale helium, it's not just the quality of the sound you produce that changes, it's the pitch/notes you produce. Regards, --—Cyclonenim | Chat  03:33, 21 May 2010 (UTC)

I don't think the speed remains the same, not exactly the same anyway. We probably have an article on the speed of sound that explains what determines it. If I remember correctly, the effect of the mass density cancels out, but there's a difference between monatomic and diatomic media. --Trovatore (talk) 02:17, 21 May 2010 (UTC)

Don't get confused by timbre. You have to remember that the sound produced by any natural source will normally be a combination of more than one simple frequency. A change in frequency/wavelength (whatever we decided it was) will certainly affect the timbre. But the more obvious change will be in the pitch (which is just the frequency most prominent in our hearing of the tone).--Jabberwalkee (talk) 03:47, 21 May 2010 (UTC)

So are you saying that the pitch will change? That seems to contradict the Straight Dope article listed above, the author of which was fairly adamant that pitch is unaltered (he has several audio files to support his claims, although admittedly I thought the pitch did change). Likewise, Wikipedia's article on helium states that pitch is unaffected. 173.179.59.66 (talk) 04:06, 21 May 2010 (UTC)

The only thing that is guaranteed to (almost) stay constant is energy, as I stated before, and the sources I linked did not address this fact directly. The frequency with which your vocal folds vibrate determines the base frequency with which sound is emitted, and the associated energy can be used to determine the wavelength given the speed of sound. So if, as we know, energy stays the same but the medium of the sound wave changes to one with a lower propagation speed (speed of sound in air is about 1/3 of that in helium), then either wavelength must decrease or frequency must increase or both. In all except the most controlled thermodynamic environments, both will occur, and more detailed calculations can predict the ratio with which they change - it certainly depends on the interface between going from air with a lot of helium to air with virtually zero helium. Point is that frequency definitely increases, so pitch increases. SamuelRiv (talk) 07:27, 21 May 2010 (UTC)

No no no. Energy isn't going to help you. Energy gets dissipated; energy gets reflected from the interface. Energy is absolutely not the right thing to consider here.

The important things to think about are frequency and wavelength. The relationship between frequency and wavelength is controlled by the speed of sound in the medium, in an obvious way (the wavelength is the distance along one full cycle; the frequency is the reciprocal of the time that one full cycle takes; work it out from there). Energy is a distraction; you might be able to rephrase things in terms of energy somehow, but I don't see the point.

As I said above, what you hear is frequency, not wavelength. So the question is, which, if either, remains constant when you do the same thing with your vocal apparatus with a breath of air, as opposed to helium.

As someone said above, the vocal folds, which drive the whole thing, should not be affected much by the helium — they should put out the same spectrum of frequencies (not wavelengths) in either environment.

However, the way your resonating cavity responds to the driving from the vocal folds, is controlled by wavelength. It's a question of which wavelengths fit nicely into the cavity. So if the vocal folds drive the resonance with a noisy spectrum, some of the frequencies will be selected and some will not, and this depends on their wavelengths. --Trovatore (talk) 18:18, 21 May 2010 (UTC)

I would have thought that the same wavelengths get "selected" regardless of medium the sound is propagating in, because the resonance wavelengths are dependent on the geometry of the vocal tract alone. Then, if the speed of sound is greater helium, by the relationship f = c/λ the frequency must increase as well, resulting in a higher pitch. However, several sources have stated that pitch doesn't change, but personally, based on the reasoning given above as well as my own experiences with helium, I would have to disagree with their assessment. 173.179.59.66 (talk) 20:02, 21 May 2010 (UTC)

Trovatore is on the right track. The human vocal tract has four major resonance spaces of different dimensions. Assuming your larnyx remains in its usual place and you form the usual vowel shapes with your mouth, tongue, and soft palate then they will resonate at normal their wavelengths (or higher frequencies), but the pressure sawtooth wave pulse train generated by the opening and closing of the vocal folds will be at a fundamental frequency that is close to normal. The harmonic series of overtones above that fundamental will be at near normal frequencies, but the specific harmonics that resonate in each of the cavities will be those close to the (now temporarily higher) natural frequency of those cavities. LeadSongDog come howl! 19:58, 21 May 2010 (UTC)

To be perfectly honest I didn't really understand your explanation. Here's what I got from it: 1) the resonant wavelenghts of sound in the vocal tract will be the same; and 2)The frequency of the sound produced from the vocal flaps will be roughly the same. The rest about the harmonics confused me a bit. My (apparently flawed) understanding of what was happening was something like this: air produced from the lungs travels through the vocal folds, producing sound waves at a variety of frequencies. These sound waves then entered the vocal tract, where certain wavelengths (and hence certain frequencies) were selected by resonance, depending on what sound the speaker wished to make. My impression from what you said is that the sound from the vocal tract and from the vocal folds independly contribute to the final sound quality, but I'm not sure. Maybe if you showed me where my picture is wrong I would be able to finally understand what's going on. 173.179.59.66 (talk) 05:47, 22 May 2010 (UTC)

Natural undersea oil spills

The oil leak in the Gulf is apparently a major ecological disaster, resulting from a relatively tiny opening to the seafloor from an oil deposit below the sea. Are these oil deposits immune to natural processes which could create an opening, such as an earthquake creating a fracture which allows flow up into the ocean, or a volcano which fractures the thick rock dome above the oil? Do geologists find evidence that there has ever been a significant natural undersea oil leak? Even in ancient times, people found natural seeps on dry land. Wouldn't there be similar underwater oil seeps of varying flow rates? Edison (talk) 19:10, 20 May 2010 (UTC)

Yes. Oil does ooze naturally from shallow deposits as this article discusses - and it doesn't take a volcano or even an earthquake to make that happen. There are plenty of places up on dry land where this happens too (See La Brea Tar Pits, for example) - humans have been scooping the stuff up and using it for thousands of years (See Oil_industry#Early_history). Although the magnitude of this seepage is tiny because the pressures are so small. In the gulf right now, you have to understand that the drilling rig had bored down through 18,000 feet of rock below the 5,000 feet of water. So the likelyhood of oil coming through all that rock in that area naturally is pretty slim! But the weight of 18,000 feet of rock pushing down on the oil - means that it is squirting upwards with tremendous pressure. Our article on the oil spill points out that the total oil reserves at that site are 50 million barrels...but if it's really coming out at 100,000 barrels a day - as some are estimating - that reserve is shrinking noticably! SteveBaker (talk) 20:27, 20 May 2010 (UTC)

See Tarball (oil) - some of the refs mak it clear that these are found naturally as well as man made

eg http://pubs.usgs.gov/of/2009/1225/ (unfortunately searching for "tarball" in the oil sense is difficult - due to computer usage of the term.) I've heard of them before and believe them to be well known to beachcombers.77.86.115.45 (talk) 21:14, 20 May 2010 (UTC)

(ec)See also Asphalt volcano for an example of a past natural underwater oil seep. People involved with exploring for hydrocarbons make use of satellite photos to identify natural oil slicks from such underwater seeps to show that there is a working source rock down there. They have to do repeat surveys, of course, to try and remove the unnatural ones (ships cleaning tanks etc.). Mikenorton (talk) 21:16, 20 May 2010 (UTC)

newtonian fluids

Is Mercury a newtonian fluid —Preceding unsigned comment added by 82.201.241.168 (talk) 21:35, 20 May 2010 (UTC)

on the whole yes [14] 77.86.115.45 (talk) 21:43, 20 May 2010 (UTC)

Biomedical control systems

hello i am searching for an application of the control systems in the biomedical field but i'm stuck and i cannot get all what i want, it must have block diagram and meaningful description,,,,,any one could help me?? —Preceding unsigned comment added by 41.196.197.43 (talk) 22:04, 20 May 2010 (UTC)

You need to be a little more specific. Manufactoring control systems, or control systems pertaining to regulations? Regards, --—Cyclonenim | Chat  22:15, 20 May 2010 (UTC)

Publishing scientific literature.

I just have a few questions about publishing research.

1. ) How is it decided what journal any piece of scientific research will get published in? Does the research team just pick one they think is the most suitable? I've heard reference to top tier, and 2nd and 3rd tier journals.
2. ) Is there a process to decide which tier they will try to be published in? Surely no one says "my research is pretty dodgy, I'll try to publish in 3rd tier"?
3. ) What happens if a paper is not accepted for publishing? Are there costs involved in submitting a paper to a journal if it is rejected?
4. ) Can you just keep trying less and less reputable journals until you hit one that will publish your research?
5. ) Is there some place where these kind of introductory questions to this subject are addressed? I've read the Academic publishing and Scientific literature but they don't really cover these "idiots guide to publishing scientific literature" kinds of questions. Vespine (talk) 23:15, 20 May 2010 (UTC)

The researchers (or institution) submits a paper to the journal of their choice - in general they will pick one that is applicable, some are more prestigious than others, some are more "technical" than "theoretical" etc. The submitted paper is reviewed before publishing by the publisher, and other researchers. Peer review is key here. I'm not aware of charges for submission of papers - most journals publish the rules of submission online eg [15]. Yes you can keep trying until someone accepts it...(better if you know your limits at the start) Last question - probably a good way would be to pick a journal, and look up their submittence method online - should give a good idea of the method if not the practice.. Another good way would be to ask here :) I anticipate many other people will be able to give much more insight into the process here. (oh.. you often need a referee to support your submittal of a paper to a journal - usually someone old and well respected in the field etc ... or at least the department you work in will exert some control over what you put forward for publishing - they don't want you submitting any old tat and giving them a bad name .. etc .. this probably varies a lot from place to place) 77.86.115.45 (talk) 23:26, 20 May 2010 (UTC)

eg here are some of the info pages for Angewandte Chemie specifically to do with how referees judge the article and decide if it's recommended for acceptance [16] . I'm not sure about tiers - (don't think they are 'official') - but see Impact factor . Was there any field you were thinking of in particular? 77.86.115.45 (talk) 23:37, 20 May 2010 (UTC)

In general: 1. when you are in a field, you know what kind of article will work with what kind of journal. You know which articles of yours are worth sending off to Nature and you learn which ones go in Proceedings of a Very Limited Subfield of My Discipline. Tiers generally reference the size of the audience and likelihood of future citation ("impact factor")—Nature and Science are at the top because basically all scientists read them and cite them. 2. It's less of a "my research is dodgy" calculation than a "will these editors be interested in my paper" calculation. "Is this paper sufficiently interesting/important to get into the biggest and best?" is the sort of calculation made. The comment above regarding some journals being more specialized in different ways or for different audiences (e.g. more theoretical, more technical, etc.) is correct as well. 3. There are no costs to being rejected born by the submitters other than time. There are costs in terms of time of reviewers. There are a number of ways you can be rejected—from flat out rejection to "revise and resubmit" requests. 4. Yes, but it does take time to submit things, and getting a reputation for this sort of thing is probably not ideal. 5. Advisors, generally speaking. An advisor (at a university) in a given field usually knows the landscape of that particular field and tells their students how it works. It is slightly different for every particular field (they have their own norms, their own idea of which journals accept which types of articles, etc.). --Mr.98 (talk) 03:21, 21 May 2010 (UTC)

Note that if you submit research in a given field, the number of experts able to review it is limited, and, by the birthday paradox, there is a good chance that the same reviewer will get your paper again. In that case it should really show that you took his previous comments into account, or your reputation will suffer. I've put together a number of workshop programs and journal issues, and I once had a comment from a reviewer that yes, he can review a certain paper easily, as he already had rejected it 4 times. This is not good for the chances of the paper or the author... --Stephan Schulz (talk) 12:42, 21 May 2010 (UTC)

It is not generally the case that the reviewer will "hold a grudge" against a paper he has reviewed before for the same (or a different) journal. More than once I reviewed a manuscript for a journal and cited the shortcomings in the research (such as potential confounds) or its presentation (such as alternative explanations for the results). The researcher did additional experiments(to rule out confounds), and added additional explanations of procedural details to remove ambiguity, and then I recommended acceptance of the manuscript. In the end, the work became a much-cited article. The funny part is that the writer may be an important, distinguished and well known figure in the field, and the anonymous reviewer may be a lowly grad student, yet the researcher has to jump through hoops to satisfy the reviewer's objections. The researcher will typically try again with the more important journal, correcting the flaws (or pointing out the idiocy of the objections) rather than shopping the manuscript to lesser journals, since the prestige of the journal is important in getting tenure or getting a grant renewed. This is probably different from a writer of a piece of fiction, since the fiction writer might have an "artistic vision" which he would not want to compromise, just as a painter might not want to add paint to his canvas to satisfy a critic and get into a particular exhibition. Edison (talk) 15:10, 21 May 2010 (UTC)

There are generally no monetary costs for submitting to most scientific journals. (Some do charge for the paper to be published, open-access journals for example.) The main cost when submitting a paper for publication is temporal. Getting it reviewed, fixing/touching up/totally redoing what reviewers point out might take a lot of time. Also, flat out rejection means you have to try for another journal (Note: you can not submit the same paper to multiple journals at the same time) trying for another journal is starting over time-wise. Most researchers don't want to waste time doing this, so they generally submit to the "best" journal that is appropriate that they also except to have a good probability of being accepted. --Rajah (talk) 05:17, 22 May 2010 (UTC)

Even distinguished journals commonly have "page charges" and may charge to print an article sooner. Going down the pecking order to non prestigious journals, there are those which are vanity press and print any paper that is submitted, for a large fee. Edison (talk) 19:44, 22 May 2010 (UTC)

May 21

Absorbent glass mat (AGM)

can i get a Absorbent glass mat (AGM) battery 4 my honda accord —Preceding unsigned comment added by Tom12350 (talk • contribs) 04:16, 21 May 2010 (UTC)

It would probably be more expensive than an ordinary one, and you won't see much difference if it isn't a hybrid. --Chemicalinterest (talk) 15:37, 21 May 2010 (UTC)

Actually, quite a few modern non-hybrid cars use these batteries - they last longer and are both smaller and lighter than a regular car battery. So even on a non-electric car, they save energy just by making the car lighter. My car has one - on previous MINI Cooper'S models there was no space under the hood for the battery - so it had to go into the trunk - I was surprised not to find it there...and doubly surprised when I couldn't see it anywhere under the hood either! On my car, the amazingly tiny AGM battery is tucked away in an extremely hard-to-reach place (against the fire-wall right beneath the lower-right edge of the windscreen, hidden in the ducting and air-vent metalwork). The claim is that they are reliable enough to never need replacing...We'll see!

I don't see any reason why you shouldn't be able to replace a conventional battery with one of these gizmo's - weight savings are always a good thing! But it might be wise to check with your local Honda dealer before you do it...you never know what weird stuff is different with them. SteveBaker (talk) 20:19, 21 May 2010 (UTC)

Photon clocks in GR

According to the equivalence principal, in a uniform graviational field, clocks at different heights will run at different speeds. If two identical photon clocks (a clock consisting of two mirrors seperated by a fixed distance with a photon reflecting between the two to measure time) are placed at different heights, then it seems that they too must run at different rates. But this would seemingly imply that the speed of light changes with height, which is obviously not true. So what gives? 173.179.59.66 (talk) 08:02, 21 May 2010 (UTC)

I assume you mean at different heights in a spherically symmetric gravitational field (which is not uniform as the direction and strength of the field both vary). If you have two photon clocks at different heights then the curvature of spacetime is different and light travels along different geodesic paths within the two clocks - so you need to think about what you mean by "identical" photon clocks. Parallel transport may be a useful concept here. Gandalf61 (talk) 08:21, 21 May 2010 (UTC)

No, I meant a uniform gravitational field. 173.179.59.66 (talk) 16:58, 21 May 2010 (UTC)

Along with time dilation, you also have length contraction. So the distance between the two mirrors will be shorter in the clock in the stronger gravitational field. Ariel. (talk) 20:07, 21 May 2010 (UTC)

Are you sure you got that the right way round? Would not the stronger field be time dilated, compared to the weaker field, and therefore have a bigger mirror spacing to get the same time delay. You could get the same idea by measuring wavelength. Graeme Bartlett (talk) 20:55, 21 May 2010 (UTC)

And the gravitational fields are the same for both clocks, no? Unless you meant potential...173.179.59.66 (talk) 21:19, 21 May 2010 (UTC)

If you really do mean a uniform gravitational field then the two clocks are indeed equivalent and run at the same rate from the point of view of any observer. You will only get a difference in time dilation rates if the gravitational field is non-uniform. Gandalf61 (talk) 21:28, 21 May 2010 (UTC)

I have to disagree with you on that one. Replace the uniform gravitational field with a uniformly accelerating rocket, with a clock A at its front and a clock B at its tail. If clock A emits light pulses at a uniform rate, then the time it takes for any pulse to reach point B from point A will L/(c+v), were L is the distance between the two clocks (which remains constant). Because v increases , the pulses will take increasingly less and less time to reach clock B, so an observer at B will conclude that the clock at A is running faster. Equivalently, redshift still occurs in a uniform graviational field, so relative time dilation must necessarily still occur. 173.179.59.66 (talk) 05:32, 22 May 2010 (UTC)

It's not clear to me what a "uniform gravitational field" would be in general relativity. The closest thing is flat spacetime in Rindler coordinates, which is not uniform inasmuch as the acceleration needed to stay at the same (x,y,z) position varies as a function of x. Trying to apply length contraction and other concepts from special relativity to this problem is hopeless. (Length contraction barely makes sense in special relativity, in my opinion, but that's a different question. It makes even less sense in general relativity.) There's no difficulty in the definition of identical clocks as long as they're small compared to the scale of variation in the gravitational field (which is the usual assumption).

When people say that the clocks run at different rates, what they mean is that if you send periodic signals ("ticks") from the clocks to a common location, the received signal rate at that location will be different for the two clocks. This is the same as saying that there is gravitational redshift. Light clocks essentially define what time means at a given location, so you can't say that they run fast or slow in any absolute sense. If you do a local speed-of-light measuring experiment with a light clock and a meterstick, you'll get c. -- BenRG (talk) 22:23, 21 May 2010 (UTC)

I'm not very well aquainted with general relativity, but I'm using as an approximation a gravitational field equivalent to a uniformly accelerating rocket, which is simple enough so that I can understand with my current level of knowledge. In that case, two observers at different altitudes will the other's clock run slower or faster depending on the relative height of the observers.173.179.59.66 (talk) 05:37, 22 May 2010 (UTC)

Time dilation due to constant acceleration depends on rate of acceleration and initial velocity, but not on initial separation - see Time dilation#Time dilation at constant acceleration. Therefore, if your definition of "uniform gravitational field" is "equivalent to constant acceleration", then the time dilation in your "uniform gravitational field" will not depend on separation either. So all (stationary) clocks in this "uniform gravitational field" will run at the same rate. What makes you think they will not ? Gandalf61 (talk) 14:18, 22 May 2010 (UTC)

In the wikipedia article you linked to, the observer is outside the rocket, and so the time dilation in that case is just a special relativistic effect. In my scenario the observers are both inside the rocket. The thought experiment that I mentioned above shows how two clocks at different heights in an accelerating rocket will run at different rates. If you don't trust me, then here's a more comprehensive article: http://www.peaceone.net/basic/Feynman/V2%20Ch42.pdf173.179.59.66 (talk) 18:10, 22 May 2010 (UTC)

Wind Turbine and surface drag

I read an article on a new paint that reduces wind resistance [17], and one of the applications mentioned was wind turbines. My first thought was that you would not want to reduce wind resistance on a turbine or the air would just slip by without turning it. Then I began to wonder whether the turbine is turned by a pressure difference rather than friction with the air, and if so does the creation of the pressure difference rely on friction? Even if the wind resistance is not responsible for the effect, is it in any way detrimental? I am now completely confused as to what actually makes a wind turbine turn! -- Q Chris (talk) 09:29, 21 May 2010 (UTC)

It depends on the type. Some wind turbines work by redirecting the air flow sideways, creating torque via Newton's third law. These usually have flat vanes angled into the wind. Most modern high-performance turbines have an airfoil profile and generate torque by the pressure difference caused by the different speeds of air travelling over the more curved leading side and the straighter trailing side. In either case, energy lost to friction just warms the blade and does not contribute to the generating capacity. --Stephan Schulz (talk) 09:40, 21 May 2010 (UTC)

Thanks Stephan. I can see that the energy that just heats the blades will not aid generation, but will it be detrimental to the generation? As far as I can see the air will be slipping off in the same direction that the blades rotate, so it won't make much difference either way. -- Q Chris (talk) 10:03, 21 May 2010 (UTC)

What friction will do is slow down the airflow. Thus, somewhat simplified, you have a reduced "effective wind". In the case of simple vanes, for example, the induced sideways motion of the downwind air will be less (part of the energy is lost to friction), and hence the opposing force acting to turn the vanes will be less. A similar argument can be made for the airfoil. --Stephan Schulz (talk) 11:33, 21 May 2010 (UTC)

Also, friction can result in turbulence, which can wiggle the blades and cause heating and wear and tear on the bearings. Thus, laminar flow is preferred. The blades themselves may also tend to get pitted more if grains of sand are dashed against them, due to turbulence. This could in turn cause more friction and turbulence, and also unbalance the blades. StuRat (talk) 15:05, 21 May 2010 (UTC)

What is this weird creature?

Opossum

Opossum

River otters

weird creature Kittybrewster ☎ 11:21, 21 May 2010 (UTC)

Here's some more pictures: [18]. Most of the comments (i.e. here) I've seen are saying otter or possum, or possibly a nutria or groundhog. Buddy431 (talk) 12:35, 21 May 2010 (UTC)

I vote for "exceptionally ugly/drowned looking opossum." Compare with this beauty queen. Either than or an otter whose lost a lot of fur on the snout. (The skull is very otter-like.) --Mr.98 (talk) 12:37, 21 May 2010 (UTC)

If it's 'playing possum' it's overdone it.. Really appears to 100% dead possum. cf image seach for "possum skull" - note the lower 'canine' - not otter as far as I know.

Does anyone know what happens to the hair - is it common for it to fall out of dead animals in water? eg this [19] 77.86.115.45 (talk) 16:29, 21 May 2010 (UTC)

The face looks like a wolverine's, but the article says "The creature's tail is like a rat's tail and it is a foot long.", which suggests possum. Maybe a hybrid? Wolverines don't have rat-like tails do they? Vranak (talk) 17:59, 21 May 2010 (UTC)

I'd vote for otter - perhaps with mange, perhaps something else - decomposition? - causing the fur loss. The face looks very otter-like to me, though I'm curious about the tail. Of course, if hair loss also occurred on the tail, it could well look like a rat tail. Matt Deres (talk) 19:39, 21 May 2010 (UTC)

I don't think anyone would look at an otter tail and say it was rat-like though. Vranak (talk) 19:51, 21 May 2010 (UTC)

Comparing to the pictures to the right (feel free to adjust the formatting, I can't figure it out), I think the snout is too short for an opossum, and the ears too small. Also, the place where the whiskers would be doesn't seem quite right either. I'm voting tentatively for the river otter. Perhaps without fur on the tail, someone who has not seen a rat recently would say it looked like a rat tail. The river otter's ears look closer to me, as does the snout and the whiskers. Falconus^{p t c} 21:03, 21 May 2010 (UTC)

Note: I revised inaccurate captions on the pictures. I am fairly sure, for example, that the bottom picture is not a badger, but rather a river otter.Falconus^{p t c} 22:06, 21 May 2010 (UTC)

Bovine Tubersulosis versus the Human Form.

During my research into my family history I've discovered that my grandfather lost three of his siblings over a 5 year period at the turn of the 20th. Century. I am wondering if occupation conveyed a part of the other siblings immunity? I know, for example the Jenner discovered that immunising someone with Cow Pox gave them a marked immunity to Smallpox, hence my curiousity regarding T.B.11:47, 21 May 2010 (UTC)~ —Preceding unsigned comment added by 2.102.26.59 (talk)

Assuming that contact with Mycobacterium bovis can generate resistance to Mycobacterium tuberculosis (the more typical cause of tuberculosis in humans), it is important to take a major difference between M. bovis and the cowpox virus into account: the latter doesn't cause a typically life-threatening disease, while the former does. This is what made inoculation so useful. – ClockworkSoul 16:55, 22 May 2010 (UTC)

0t,1t 2t bend test / galvanized/colour coated coils

Does anyone recognise what is being asked here Wikipedia:Reference_desk/Miscellaneous#Bend_test ? 77.86.115.45 (talk) 11:57, 21 May 2010 (UTC)

Oil spill - quick drying cement?

Why cannot the source of the oil spill just be covered with a large amount of quick drying cement. After the first batch has hardened, another batch, then another. This is not a silly question - cement does set under water. 92.28.253.142 (talk) 14:32, 21 May 2010 (UTC)

I believe the force of the oil, which is coming out under pressure, would push the concrete out of position before it could harden. StuRat (talk) 14:58, 21 May 2010 (UTC)

As do many polymers, going back to the wet-climate-set Chinese lacquer. My guess is that the big question is how to put a big heavy block onto a big hole spewing crud at very high pressure and not just having it get knocked to the side by the spray. Consider how hard it is to stop the water from coming out of a hose with your thumb. SamuelRiv (talk) 15:07, 21 May 2010 (UTC)

As an extension to the above idea - first cover the flow with large chunks of broken stone - so that the oil is diffused out between the gaps in the stone - the concrete would be less likely to be swept away before setting due to the reduced local flow rate.. In practice once completed the flow would probably just exit below the stone - and scour the (loose?) sea bed, creating its own channel.

I wonder if a rheopectic substance or Dilatant would help here (probably not).77.86.115.45 (talk) 16:13, 21 May 2010 (UTC)

Along these lines, Google for: bp oil "junk shot". DMacks (talk) 16:29, 21 May 2010 (UTC)

I wonder if they've considered using (hydraulic?) clamps to 'crimp' the end of the pipes to restrict the flow? - are the pipes made of a workable steel or a brittle steel?77.86.62.107 (talk) 16:57, 21 May 2010 (UTC)

Not a good idea, it could break the pipes. Even workable steel has a limit to which it could be cold-worked before it starts to crack (generally no more than 20% deformation), so "crimping" the pipes won't work. 67.170.215.166 (talk) 05:05, 22 May 2010 (UTC)

And is it possible that it is impossible to close this oil spill until all the oil has run out? Mr.K. (talk) 16:00, 21 May 2010 (UTC)

No, just until the pressure drops. Are they not planning to drill nearby to relieve the pressure? Dbfirs 17:19, 21 May 2010 (UTC)

"They" (we) are planning to do just that, but it could take up to several weeks due to the great depth of the well required and also the difficult rock formation. (Well, I don't know all the particulars -- I work on the refining end, not the extraction end -- but that sums up what I've heard from the company management.) FWiW 67.170.215.166 (talk) 05:00, 22 May 2010 (UTC)

I believe the amount of oil shooting out of the broken pipe would prohibit this sort of remedy. And it's a little sloppy too, just pouring heaps of cement over a leak. Reminds me of Chernobyl. And just getting the cement out in the middle of ocean, and then down miles beneath the surface, is rather more problematic than, say, trying to plug Old Faithful in the same manner. Which, come to think of it, seems rather problematic in itself. Mind you one is a pipe, the other, a natural geyser -- apples and oranges and all that. But the point remains, pouring cement at those depths, that far from land -- not entirely trivial. But ultimately, I feel that the force of the oil is the critical factor. From all I have read, pumping drilling mud into the aperture is the way to go. Vranak (talk) 17:50, 21 May 2010 (UTC)

If I understand it correctly, the advantage of injecting heavy mud is that it can flow down the borehole against the oil counterflow. As the depth of the borehole fills with mud it creates a backpressure to gradually reduce the oil flow while also narrowing the part of the borehole through which the oil is flowing. The other approach, of capping the pipe, can only work if the pressure inside the cap is kept below the surrounding water pressure. Given the amount of dissolved gas from this well, that's not a trivial thing either. As the gas rises and expands it undergoes adiabatic cooling (like the working fluid in a refrigerator or air conditioner). On mixing with water this cold gas can form ice crystals that clog the pipe to the surface platform. This appears to be what happened to the first attempted cap. LeadSongDog come howl! 19:31, 21 May 2010 (UTC)

Not exactly ice crystals but methane clathrate, which is less dense than pure water ice. The mud (it's actually synthetic) is made extra dense by adding the mineral barite to it, which is how highly pressured oil and gas are controlled when they are first encountered when drilling. Mikenorton (talk) 19:55, 21 May 2010 (UTC)

The key problem here is three-fold. One is pressure - the oil isn't just slowly washing out - it's coming out at some ungodly pressure. Below the seafloor, there is about 18,000 feet of solid rock pressing down on the oil reservoir - that's an incredible amount of pressure. Nothing like wet cement is going to be able to resist that. Second is temperature. This oil is incredibly hot. Third is that there is a lot of debris there - for starters, there is 5,000 feet of crumpled up pipe that fell from the rig onto the well-head. Then there is debris from the rig itself. So wet concrete is out of the question. Even dropping a very large concrete block onto the well-head won't work because the oil is under such pressure, it would just channel a route through the sand and stuff underneath it and squirt out around the edges. So you'd have not one neat little pipe to cap - but the entire perimeter of the concrete block. The various domes and such they've tried (and failed) with would have to have the oil continually sucked out of them - with a suction more powerful than the pressure of the oil - so as to 'suck' them onto the sea floor. These are all very difficult solutions.

The one I could imagine working would be to construct four vast rolls of flexible water/oil-proof fabric or plastic sheeting - each 5,000 feet long by (let's say) 100 feet wide - and to unroll these from the sides of ships to create four curtains around the well-head - then to heat-seal or 'zipper' the edges together as they are unrolled to make a vast, square-cross-section, floppy tube that could eventually rest on the seafloor far enough from the well head to avoid the debris field and the immediate heat/pressure of the oil. (You'd have to weight-down the bottom edge of each strip). This container would start to fill up with oil - which could then be pumped out from ships on the surface. The large width of the tube would ensure that the oil had room to expand and to relieve the pressure. Since oil is less dense than water, and we're pumping out the inside of this giant tube - any small leaks would have water flowing in - not oil flowing out. The technical difficulty is in handling such enormous amounts of fabric - and how well the stuff performs at the very low temperatures at the bottom of the ocean - also, how the pressure of ocean currents would work to push the thing out of shape.

SteveBaker (talk) 20:03, 21 May 2010 (UTC)

You're hired. Get your ass to the Gulf of Mexico. Comet Tuttle (talk) 20:16, 21 May 2010 (UTC)

Well, there's theory, then there's practice. I should think that Red Adair was so good at capping blowouts because of his experience in the field, not so much a sound theoretical background. I also imagine that too much theory and not enough experience was one of the chief causes for this mess in the first place. Vranak (talk) 20:20, 21 May 2010 (UTC)

The oil coming out now is actually at low pressure. It's being dumped into the ocean as quickly as the weight of the rock is able to force the oil into the well, and so there is very little accumulation of pressure. (Even given the large weight of the sea floor, oil will move slowly through the pore spaces in oil bearing rock.) If you are losing "only" 100,000 barrels per day through a 50 cm pipe then the average flow rate is only about 1 m/s (2.2 mph), which would imply the pressure difference of only about 500 Pa between the well and sea floor. Any person with a stout piece of plywood could actually block that off. The problem is that the weight of the sea floor will continue forcing more oil and gas into the well space even after you block the opening, so pressure will buildup and unless your obstruction is very sturdy the well will blowout again. Dragons flight (talk) 00:08, 22 May 2010 (UTC)

Why can't they just use a wider (4 -5 ft) pipe from the source to the surface and that would no doubt solve the problem of slushing up the pipe with frozen methane? —Preceding unsigned comment added by 98.221.254.154 (talk) 02:05, 22 May 2010 (UTC)

Actually the pipe would still slush up, it would just take longer. 67.170.215.166 (talk) 05:21, 22 May 2010 (UTC)

I would like to clear up a scientific inaccuracy that seems to be floating around in the above posts. The reservoir pressure is not exactly caused by the weight of the 18,000 feet of rock overhead. Rock is not a fluid (not a good one, at least); it does not behave like a hydraulic head; although the weight of the rock does contribute to the pressure, the real defining equations for pore pressure are a lot more complicated. The pore pressure contributes to, but must be converted into, an effective reservoir pressure. Finally, this can be used to estimate a pressure at the wellhead on the seafloor. The Terzaghi equation, in conjunction with reservoir characterization and geomechanical measurements, can be used to calculate the reservoir pore pressure; or an empirical law relating pore pressure to some other geomechanical property or observable from a borehole logging measurement. Finally, the fluid seep into the borehole needs to be modeled and eventually a hydraulic head can be calculated to determine the pressure at the exit point of the wellhead (on the seafloor) or at the ocean surface. To do all this, you need to know a lot of details about the fluid composition in the bore (probably drilling mud and other debris at this point), as well as details about the reservoir that only a privileged member of the BP E&P team would have access to. I just want to make sure nobody is thinking of applying the old "P = ρ g h" static pressure-head equation with the density of rock in a feeble effort to calculate the fluid pressure - it is unfortunately much more complicated than that. The short answer is, we don't know what pressure the oil is under as it rises to the well-head - the fact that there was a blowout indicates that neither did BP or its subcontractors. Nimur (talk) 02:44, 22 May 2010 (UTC)

We do know that at the time when it started to flow that the pressure in the reservoir was somewhere between the hydrostatic pressure (the pressure at the base of a column of water equal to the depth) and the lithostatic pressure (the pressure at the base of a column of rock equal to the depth). Most reservoirs are 'normally pressured' and lie close to the hydrostatic pressure, taking into account the column height of the hydrocarbons involved. Some reservoirs are 'overpressured' and lie closer to the lithostatic gradient but never reach it because high pressures will cause fracturing of the top seal (the impermeable layer that helps form the top of the 'trap') and this is known as the fracture gradient, so again we know that it will be less than that. After flow has started the pressure will start to reduce, something known as depletion, but the amount of depletion depends on the extent to which water flows into the reservoir as the hydrocarbon is removed, something known as 'aquifer support'. As to the blowout, the gas may have come from a shallower formation (unless this is associated gas i.e. coming out of solution from the oil), which should have been held back by the cement liner or casing in the wellbore above the reservoir. Mikenorton (talk) 13:12, 22 May 2010 (UTC)

I don't udnerstand why they can't just bring another rig to that location, send a pipe down and resume normal operations. Why not?--92.251.177.211 (talk) 20:30, 22 May 2010 (UTC)

BP are currently drilling two 'relief wells' to try and intersect the original wellbore, but it takes time and the target is rather small. Mikenorton (talk) 20:36, 22 May 2010 (UTC)

Field Strength of LHC Magnets

I am told that the magnets at the 27 km circumference LHC operate at 8.3 Teslas, while the protons contained in the beam have an energy of ~7 TeV (see Wikipedia LHC article). Trying to match these data up using simple physics fails, and so I'd like to know where my mistake(s) is/are.

As protons are travelling at near the speed of light:

$mv\approx {\frac {E}{c}}$

$F={\frac {mv^{2}}{r}}=Bqv\implies B={\frac {mv}{rq}}\approx {\frac {E}{crq}}$

Substituting in values:

$B={\frac {7\times 10^{12}{\mbox{ eV}}\times 1.602\times 10^{-19}{\mbox{ J eV}}^{-1}}{3\times 10^{8}{\mbox{ m s}}^{-1}\times 4300{\mbox{ m}}\times 1.602\times 10^{-19}{\mbox{ C}}}}=5.4{\mbox{ T}}$

I presume I've missed off some relativistic effects, but even when I tried to account for some of them, I still got around 5.4 Tesla. Any suggestions? --80.229.152.246 (talk) 15:46, 21 May 2010 (UTC)

(altered/corrected your ref tags - no reference section at bottom of this page)

Is it possible that the figures you've used are maximum operational limits - eg the magnets can go up to 8.3T safely ? (but are operated at a lower figure?)77.86.115.45 (talk) 16:19, 21 May 2010 (UTC)

there doesn't seem to be a reference for the 8.3T figure to get its context from.77.86.115.45 (talk) 16:23, 21 May 2010 (UTC)

There are a few mentions of 8.3 T being the required field in LHC: The Guide. --80.229.152.246 (talk) 17:38, 21 May 2010 (UTC)

Mmmh actually - plan B - the magnets aren't actually completely circular are they?? ie it's magnet/straight/magnet/straight etc? Thus the turning circle at the magnetic turning sections must be smaller than the radius of the machine - hence a higher magnetic field required - ie the colider shape in not a circle but a n-agon (polygon) (with rounded corners) - surely this must be the case? So radius is less than 4300m. 77.86.62.107 (talk) 18:31, 21 May 2010 (UTC)

I'm pretty sure it's quite circular. But what about length contraction? The magnet slightly ahead of the current position of the proton is length contracted toward the proton, so the radius might be lower than what you calculate. But it's not totally ahead of the proton, just slightly, so the contraction is only a fraction of the total speed. Ariel. (talk) 20:16, 21 May 2010 (UTC)

Fairly certain polygonal eg [20] states 1232 15m dipole magnets - so that's 18.5 km of bending magnets - but the circumference is 27km. 77.86.62.107 (talk) 20:27, 21 May 2010 (UTC)

(ec) That's correct. The bending magnets occupy only a portion of the ring's total circumference. The remainder contains quadrupole focusing magnets, experiments, and gaps between magnets. In total, the LHC contains 1232 dipole bending magnets, each with a length of approximately 15 meters. (That PDF link contains a number of other important specs for the bending magnets, as well.) 15 meters times 1200 magnets accounts for just 18 kilometers (about two thirds) of the total tunnel length. TenOfAllTrades(talk) 20:33, 21 May 2010 (UTC)

...back of envelope attempt at getting radius of curvature of magnetic sections - since for each turn (2pi/1232 radians) angle is small I assume sin x=x and cos x=1

r_effective=4300m , L=(27000m-18500m)/1232 (length of each straight section), A = 2pi/1232 (angle radians)

r=radius of curvature of magnetic sections

I get r_effective/r = (rA+L)/rA using similarity of triangles (approx since cosA~1)

solving for r (using pi=22/7)

gives r=4300x(15/22)

Thus using the original equation with the new r I get magnetic field = 5.4 x (22/15) = 7.92 (pretty close to the 8.3 quoted)

Looks like this method is probably along the right lines.?77.86.62.107 (talk) 21:36, 21 May 2010 (UTC)

I should probably point you back to the PDF that I linked in my response — it actually has more precise values for the length of each magnet, as well as explicitly specified bending radius and angle per magnet. The real magnet length is actually a bit less than 15 m — the specs say 14.3 m — which probably just about accounts for the discrepancy between your calculated field value and the nominal. TenOfAllTrades(talk) 03:11, 22 May 2010 (UTC)

doh, silly me I should stop skimreading - yep my estimate came out at ~2930m - the pdf gives ~2800m .. giving an unsuprising 8.3T for the required field which is spot on.77.86.62.107 (talk) 03:23, 22 May 2010 (UTC)

Thanks everyone. I'm glad to see it's not down to awkward relativistic effects like length contraction and the like (I did consider that but didn't think it'd have a large enough effect, plus I have no idea how to work that out...). --80.229.152.246 (talk) 15:45, 22 May 2010 (UTC)

Iron in high oxidation state

Is there any way to create iron compounds with an oxidation state of more than +3 using household chemicals? --Chemicalinterest (talk) 20:57, 21 May 2010 (UTC)

Potassium ferrate - you would probably only have access to the sodium compounds - sodium ferrate is more unstable (see http://library.sciencemadness.org/library/ferrates.html)

In sweden you can produce it from bleach possibly http://sv.wikipedia.org/wiki/Natriumferrat ?? seems to be confirmed by youtube http://www.youtube.com/watch?v=pUvdETUQPuo (I think this is probably true) 77.86.62.107 (talk) 21:49, 21 May 2010 (UTC)

I tried adding KOH and household bleach (NaClO) to ferric oxide but it didn't react. (Oh and I boiled it).--Chemicalinterest (talk) 22:42, 21 May 2010 (UTC)

Watch the youtube video linked above - you need strong bleach, and they boiled it.77.86.62.107 (talk) 22:47, 21 May 2010 (UTC)

Oh.. and the step were they add ammonia at the end - don't try that if there is excess bleach ammonia can react with it to make hydrazine - explosions can potentially follow... alternatively the reaction produces chloramines - which are toxic.. (or nitrogen trichloride even which too is explosive) In fact I wouldn't try this at home - boiling bleach sounds like a recipy for disaster in one form or another..77.86.62.107 (talk) 22:56, 21 May 2010 (UTC)

Pushing or pulling Asteroids

Lets say we have a spaceship that's powerful enough to move asteroids. Is it easier for it to push it or to pull it? ScienceApe (talk) 21:04, 21 May 2010 (UTC)

A joule is a joule is a joule. Presently, I don't believe we even have any technology that is capable of such a feat, so it's a purely speculative issue at this point, yes? Vranak (talk) 21:07, 21 May 2010 (UTC)

It would be easier to pull using the gravity inherent in the ship's mass, because that would not use any external energy. dude❶❽❶❽ (talk) 21:11, 21 May 2010 (UTC)

You still have to use energy to keep the gravity tractor in the right place. --Tango (talk) 21:13, 21 May 2010 (UTC)

Pushing is easier. Dauto (talk) 21:17, 21 May 2010 (UTC)

From an energy point of view it's the same, but from an engineering point of view pushing is easier. For two reasons: One you can just push the asteroid, and don't need some method of attaching to it. Two: If you pull, your exhaust gases will impact on the asteroid, which will push it back - you'd need some way to reroute your exhaust around the asteroid. Ariel. (talk) 21:42, 21 May 2010 (UTC)

Ok. But think of failure. If your're gunning it full steam towards an asteroid and the 'link', whatever that may be, fails, then you're going to crash into it (unless your distance is great, or you have good retro rockets, etc). If you're pulling it, you just go in the opposite direction. Vranak (talk) 21:44, 21 May 2010 (UTC)

That assumes pushing from a distance. If the asteroid is strong enough to be pushed from a single point without breaking up, the spacecraft can be brought right up against it first (in effect a soft landing) and then start pushing. However, you would need to keep the pushing force accurately aligned with the center of mass. --Anonymous, 23:08 UTC, May 21, 2010.

Exactly. In any case, a worst-case scenario looks a lot worse when you are pointing towards the 'roid, rather than away from it. Well, if it were remotely-operated, I suppose a hull breach isn't necessarily curtains. Vranak (talk) 00:16, 22 May 2010 (UTC)

I too would pull - for using you need a structure to transmit the pushing force from the front of the spaceship - but the force propelling the spaceship is probably at the back - would need a strengthened airframe - you also can't see where you are going..

For pulling all you need is some ropes - these can be attached close to the propulsion source - ropes can be long - gas back draft shouldn't be a problem..77.86.62.107 (talk) 21:46, 21 May 2010 (UTC)

Gas back draft most certainly is a problem. Or earth if you go far away the air disperses the gas. Not so in a vacuum. The gas will go directly toward the asteroid, and will totally cancel out the effect of the propulsion. It would be like trying to move a sailboat by attaching a fan to the boat and blowing on the sail. Ariel. (talk) 23:43, 21 May 2010 (UTC)

That depends on whether the gas molecules collide after being ejected - if so the gas will disperse (in a 'cone' shape) - I think it would be hard to make a rocket nozzle that outputs molecules that do not collide with one another - would require low gas densities - though it would be the most efficient.77.86.62.107 (talk) 00:34, 22 May 2010 (UTC)

For pushing you have to locate and get exactly behind the asteroid's center of mass or the thing will start spinning instead of going the direction you expect. For pulling this is not a problem. Cuddlyable3 (talk) 22:24, 21 May 2010 (UTC)

It's exactly the same problem for pulling. If the force, whatever the direction, doesn't go through the centre of mass then you will introduce a torque. If you are using a gravity tractor, then the force is automatically through the centre of mass, but if you are pulling it using a rigid scaffolding or something, then it could be a problem. If you are pulling it using a flexible cable, then the torque will be temporary and it will soon end up going through the centre of mass. You can avoid a torque when pushing by having the engine attached to the asteroid via a gimbal - that way you can make sure the thrust is straight "up", which means it goes through the centre of mass (actually, that may only be precisely true for a spherical asteroid, but I think the principle can be generalised). --Tango (talk) 22:39, 21 May 2010 (UTC)

Also for turning - if the spaceship has weak turning thrusters and powerful main engine fixed on axis then it is easier to pull since "thrust vectoring" can be used - whereas when pushing the turning thrusters would be required to turn the entire combined mass - depends on what sort of spaceship you're using I suppose...77.86.62.107 (talk) —Preceding undated comment added 22:34, 21 May 2010 (UTC).

see: Pendulum rocket fallacy.—eric 23:10, 21 May 2010 (UTC)

I don't think that fallacy is relevant. The IP is correct - if you are pulling the asteroid using a cable then all you need to do to turn is change the attitude of the rocket. If you are fixed to the asteroid, thrusting in a fixed direction and pushing it along then you would need to turn the whole asteroid. However, if you are fixed to the asteroid but can change the thrust direction of the main engine then you can use the main engine to turn the asteroid and it becomes pretty easy (in fact, it's probably just as easy as in the pulling case, since in both cases you will use the main engine to turn the asteroid). An alternative would be to push the asteroid using a rocket than can move around on the surface (probably hopping around - there is so little gravity on a typical asteroid that the thrust required to hop would be minimal, you could probably do it with an air horn!). --Tango (talk) 23:25, 21 May 2010 (UTC)

(I was assuming that someone would be steering the ship . but it is an interesting link)77.86.62.107 (talk) 00:37, 22 May 2010 (UTC)

I like the idea of pushing with a clamp-on linear accelerator, which mines the asteroid, ionizes it, and accelerates a small portion of it to near the speed of light as a source of propulsion, all powered by nuclear reactors, or better yet, a matter-antimatter reactor. StuRat (talk) 04:15, 22 May 2010 (UTC)

Car Mechanics...... power steering

Hi evry one ... my car power steering system breaks down .... so i tried to find out how it works , i googled it , to find this ... that the system use a pump attached to the engine (use engine power to compress hydrulic oil) in the system to maximize your hand power and make it easier to rotate the car .... so while searching i found that the oil pump compress the system faster at higher rpms (revolve per minute) .... which leads to more sensitive steering at higher speeds ... should'nt it be the other way around ...? as a safty measure the steering should have a slower response at higher speeds ...? --Mjaafreh2008 (talk) 21:47, 21 May 2010 (UTC)

Did you read in the article Power steering this: "...at high engine speeds the steering would naturally operate faster than at low engine speeds. Because this would be undesirable, a restricting orifice and flow control valve are used to direct some of the pump's output back to the hydraulic reservoir at high engine speeds." ? Cuddlyable3 (talk) 22:19, 21 May 2010 (UTC)

May 22

If Earth was great big ball of magnetism

If the earth was magically replaced with a new earth made totally from a strong magnetic material like neodymium what sort of impact would that have on the solar system? I know that gravity is really weak compared to the other forces so i'm just curious would an earth of neodymium pull other planets towards it? Would it have any effect on the sun? Mike --87.112.183.70 (talk) 01:17, 22 May 2010 (UTC)

I don't think so -- at the sorts of interplanetary distances involved, the gravitational force would still be much more of a factor than the magnetic force. Keep in mind, too, that the other planets would still be non-magnetic. FWiW 67.170.215.166 (talk) 05:17, 22 May 2010 (UTC)

This is a terrific question that I know will have several people puzzling. I can't speak much to the change in Earth's natural magnetic field at all - I will defer to someone who knows more about it - and I'm not sure how the polarity is set up in those Nd magnets. That said, most planets have natural magnetic fields, and if the field lines from two bodies reinforce each other, they will attract according to the cube of the distance from each other. This tapers off much more quickly than gravity, but even if it didn't, Earth's field may be strong but even Jupiter's, the strongest in the solar system, is relatively weak and will likely not result in much orbital disturbance.

It takes two good fields to magnetically tango. When magnets pick up pieces of metal like paperclips they do it by inducing a temporary field in the paperclip, because the iron in a paperclip is something that can quickly align as a magnet and then fall back out of it, depending on what other fields are in the environment (so it can attract itself to either pole of a magnet by rearranging itself, for example). A planet is not made out of this "ferromagnetic material". Most of them have heavy cores of iron or nickel, but those are far too high temperature to hold an attractive arrangement together to attract itself to the Nd Earth. However, Nd magnets are strong enough to induce magnetic fields in even non-ferromagnetic materials, even humans, and thus can make for neat household tricks (try dropping one down an iron tube).

In conclusion, I don't think this giant Nd Earth will have much direct effect on other planets, though someone will probably prove me wrong. SamuelRiv (talk) 05:24, 22 May 2010 (UTC)

I think that the neat trick you're thinking of involves dropping a strong magnet down a copper tube. The magnet will simply stick to an iron tube. APL (talk) 07:42, 22 May 2010 (UTC)

Now you've got me curious. What happens? Vimescarrot (talk) 07:57, 22 May 2010 (UTC)

assuming you've not already google'd it - here's a youtube video of what happens. (http://www.youtube.com/watch?v=30oPZO_z7-4) ny156uk (talk) 09:13, 22 May 2010 (UTC)

Nifty! Vimescarrot (talk) 15:27, 22 May 2010 (UTC)

rust forceps

i bough some German stainless steel Surgical OCHSNER Forceps. i put them on my sink counter. a few weeks later a small amount of rust appeared. hows that possible. —Preceding unsigned comment added by Tom12350 (talk • contribs) 04:57, 22 May 2010 (UTC)

What's your sink counter made of? If could the rust have come from that and not the forceps? This used as a source in stainless steel only says that stainless steel rusts less easily than normal steel. I'm no chemist though, hopefully someone can explain in more detail. 131.111.30.21 (talk) 08:59, 22 May 2010 (UTC)

Stainless steel is very resistant to oxidation by oxygen gas, where it forms a thin protective layer of chromium(III) oxide. If there is acid, the coating dissolves, starting the corrosion (although the rust dissolves too). If there is strong alkali, the coating dissolves, and some rust forms which is insoluble in alkali (iron is not amphoteric). But you shouldn't have strong acids and alkalis on your sink. --Chemicalinterest (talk) 10:51, 22 May 2010 (UTC)

[21] [22] Rust spots on stainless steel happen, for a variety of reasons.77.86.62.107 (talk) 14:51, 22 May 2010 (UTC)

Weather recce

What's an aerometeorograph, and what atmospheric parameters does it measure? 67.170.215.166 (talk) 06:06, 22 May 2010 (UTC)

From here "A self-recording instrument used on aircraft for the simultaneous recording of atmospheric pressure, temperature, and humidity." APL (talk) 07:30, 22 May 2010 (UTC)

Can the acoustic guitar hurt your hearing?

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis or prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the talk page discussion (if a link has been provided). --TenOfAllTrades(talk) 13:40, 22 May 2010 (UTC)

TenOfAllTrades(talk) 13:40, 22 May 2010 (UTC)

Too fast to be an Iridium flare... so what was it?

I sat beneath the stars tonight for about an hour. I no longer have a grasp of the night sky, so all I can say is I was facing southwest (the Big Dipper was behind me somewhat). At one point, I saw what looked like a camera flash go off, but it was a pinpoint of light. It was extremely quick, no "few seconds" or "trail" that the Satellite flare article talked about. Then I noticed something peculiar... I kept staring at that spot and there was a second, almost imperceptible flash, just a hair to the left of the original flash. Huh! Anyway, time goes on and I'm staring to the northwest, closer to the Big Dipper, and again, there is a microburst of light way up in the heavens. This time I stared and stared, hoping to corroborate the secondary flash, and sure enough, after a few seconds, and just a fraction of some unknown stellar distance from the original flash was a second "pop" of light... What's up there, and is it rotating? I've seen dozens of "normal" satellites that are a constant reflection, a dot moving slowly across the night sky. I've never seen this before in my life. Any ideas? SR-71 taking pictures of me? :D – Kerαunoςcopia^◁_galaxies 09:17, 22 May 2010 (UTC)

It might be an airplane doing combat manuevers in the air. It also could be a meteor. Firecrackers? --Chemicalinterest (talk) 11:06, 22 May 2010 (UTC)

Without having seen it, it's hard to say for certain. It's also worth remembering that one's eyes can play tricks under low-light conditions. (For example, the second 'flash' might be just some sort of afterimage that you're seeing just because you're looking very hard for it. As well, to dark-adjusted eyes an object doesn't have to be particularly bright for it to look quite bright.) A couple of guesses: a meteor following a trail aimed almost directly at you, so that it didn't appear to move appreciably as it rapidly brightened and then disappeared. If the rock happened to break into more than one fragment, you might see a second flash. Another explanation could be tumbling space debris — the solar panels on a retired or 'lost' satellite, etc. That reflection would tend to have a much faster 'rise time' than an Iridium flare, and you might get a second flash as the satellite tumbled around. TenOfAllTrades(talk) 13:12, 22 May 2010 (UTC)

A fundamental problem we have here is not knowing how high was the artefact that caused the brief flashes. It could indeed be something as simple as a plane at altitude and you caught a solar reflection, you don't say how long after sunset this occurred. However the fact that it happened again in a different part of the sky makes me believe that it was some sort of image created by your eye or optic system. There are several non-pathological causes for the effect of "seeing stars" in a medical sense and I am not inferring that you have a medical condition that requires attention, I suggest this may be a possible reason for seeing microflashes of light. Richard Avery (talk) 14:59, 22 May 2010 (UTC)

How many carbon black add in polypropelene polymers from protection SUN LIGHT

Dear, Plese, find answer headline and give me reply. thanks, Mr. jatin —Preceding unsigned comment added by Mjhirpara (talk • contribs) 12:14, 22 May 2010 (UTC)

More carbon black produces increased uv resistance.

This product [23] uses 3% carbon black.77.86.62.107 (talk) 15:03, 22 May 2010 (UTC)

See this book [24]77.86.62.107 (talk) 15:06, 22 May 2010 (UTC)

Iodine oxidation

Is sodium hypochlorite strong enough to oxidize elemental iodine (in its dilute state as household bleach)? --Chemicalinterest (talk) 12:19, 22 May 2010 (UTC)

Look up the reduction potentials for Cl⁺¹ → Cl⁰ or Cl^–1 compared to I⁰ → I⁺¹ to see which is stronger/able to oxidize or reduce which when you have these two redox half-reactions balanced. DMacks (talk) 15:06, 22 May 2010 (UTC)

There's a number of issues with this reaction:

• hypochlorite solutions are strongly basic - so the standard electrode potentials will need converting, or may not be applicable
  • particularily : Iodine disproportionates in alkaline solution to iodide and iodate
• Additionally Iodine reacts with chloride to form I₂Cl- and other reactions.

There's some more detail on iodine redox here [25] 77.86.62.107 , the chlorine potentials are also in this book a few pages before. (talk) 15:24, 22 May 2010 (UTC)

I never find the reduction potential for OCl^- + H₂O + 2 e^- → Cl^- + 2 OH^-; only see it for reduction to Cl₂. The iodide probably will be oxidized by NaClO when it is formed. --Chemicalinterest (talk) 17:04, 22 May 2010 (UTC)

It's in the above link, page 74 section C E=0.890V (in basic solution - not at [H+] = 1mol/dm3)

Probably the reason why it's never found as a standard E is that ClO- is unstable under standard (ie acidic) electrode conditions.87.102.18.191 (talk) 17:11, 22 May 2010 (UTC)

FWIW, "put a drop of solution on starch/iodide paper" is a standard test my students use for presence of hypochlorite in solution; turns dark if there is oxidizer available. See starch indicator and iodine test for some backround on what this might mean chemically. DMacks (talk) 18:55, 22 May 2010 (UTC)

Wembley Stadium grass - too dark?

Are the problems with the Wembley Stadium pitch simply due to the fact that the design of the stadium (high walls, roof) means that the grass does not get enough sunlight to grow properly? 92.28.248.33 (talk) 13:06, 22 May 2010 (UTC)

It seems unlikely, grass doesn't require a particularly high level of photosynthetically active radiation to grow. In fact at my house, the grass grows longer in the shade since there is more water available due to less evaporation. I'm not familiar with stadiums but I can't believe that Wembley is particularly different to any others and you'd think that they would have thought about it during the design stage. Reading this it sounds like it is more of a problem with it not being laid long enough before a game is played for a strong mat of roots to grow and form a good surface. 131.111.30.21 (talk) 16:33, 22 May 2010 (UTC)

The roof of Wembley was specifically designed to maximise the sunlight on the pitch, for the grass - that's why it's retractable. Vimescarrot (talk) 17:46, 22 May 2010 (UTC)

The stadium is in London, which is on the same latitude as Newfoundland, so it would not get as much intensity of sunlight as similar designs of stadium would in most parts of the United States for example. The grass is also 4 metres lower than it used to be, and the old design was more raked and roofless as far as I recall. 92.15.9.117 (talk) 18:04, 22 May 2010 (UTC)

dimple above penis

I have noticed that some men have a slight dimple just above the spot where the penis meets the pubis (this is normally only apparent if the pubic hair is shaved). Is this a medically recognised anatomical feature, and if so, what is it's name? Little radiolarian (talk) 13:14, 22 May 2010 (UTC)

The origin of life!!!!!!

I want to know how it was successfully verified that life on earth has arisen from complex molecules such as methane and oxygen was not present during the initial formation of life on earth? —Preceding unsigned comment added by Hitarth21 (talk • contribs) 14:58, 22 May 2010 (UTC)

Hi, your sentence is very confusing, can you rewrite it? Thanks. Beach drifter (talk) 15:00, 22 May 2010 (UTC)

Our knowledge and understanding of abiogenesis is very limited. There are some educated guesses about how it might have happened (see that article for details), but we don't really know. --Tango (talk) 15:50, 22 May 2010 (UTC)

TWO SCIENTIST DID AN EXPERIMENT: they took a round bottom flask, put two electrodes in it,filled it half with water, and put some rare gasses in same proportion they thought would have been present at the time of origin. they kept this setup for weeks at 100degree Celsius. electrodes are used for sparking mimicking lightning. and after weeks lo and behold1 TYHEY found key compounds needed to let life exist. THIS EXPERIMENT WAS CALLED MILLER'S EXPERIMENT ON THE NAME OF ONE OF THE GEEK. GOOGLE IT --Myownid420 (talk) 15:53, 22 May 2010 (UTC)

You're thinking of the Miller-Urey experiment. It was an important step in thinking about how life came about, though people today realize that the actual composition that they used probably wasn't very representative of Earth's early atmosphere. However, similar experiments have been done using other compositions, sometimes with interesting results. Buddy431 (talk) 16:23, 22 May 2010 (UTC)

Here are some of the problems with your original post:

1) Methane and oxygen aren't complex molecules, they are simple molecules (CH₄ and O₂). Oxygen, of course, is also a chemical element, O, but isn't normally found as a single atom.

2) The "complex molecules" you were probably thinking of are amino acids, the building blocks of proteins.

3) Then when you ask about whether scientists "verified that life on earth has arisen" from this process, you must realize that scientist can only propose a hypothesis that this is how it happened, as there's no fossil record of the original life forms. StuRat (talk) 16:30, 22 May 2010 (UTC)

The initial stages of the origin of life are still not clearly understood. To me it seems most likely that deep ocean vents are where the action took place. Regardless of that, there is very strong evidence that significant oxygen levels didn't show up until about a billion years ago -- the rocks that formed at the surface prior to that are not oxidized as they would be if high levels of oxygen had been present. Looie496 (talk) 16:52, 22 May 2010 (UTC)

Germ cell tumor

Whats the prognosis of a metastatic germ cell tumor —Preceding unsigned comment added by 24.97.164.250 (talk) 15:13, 22 May 2010 (UTC)

I assume you've read "Germ cell tumor#Prognosis"? Remember that Wikipedia does not give medical advice (see WP:MEDICAL). Gabbe (talk) 17:10, 22 May 2010 (UTC)

planets coming in align

in how many years does all planets come in one line. is it even possible or not? When they will align, will not it anyhow efffect Earth's life? if so then how.

<IN MY CLASS TEST ONCE I MADE ALL THE PLANETS IN ONE LINE AND MY TEACHER ASKED ME "WHAT IS THE PROBABILITY OF THIS". I SAID "MAY NOT IN COMING THOUSANDS OF LIGHT YEARS BUT SOME DAY IT WILL HAPPEN". I WANNA KNOW I WAS CORRECT OR NOT>

See Syzygy. How often it happens depends on how precisely you want them to line up. If you're happy with them just being in the same quadrant (ie. a 90 degree wide sector) then it will happen far more often than if you require them to be within a 1 degree sector, say. As for what effect it would have - none at all. About 70% of the combined mass of the planets is Jupiter, so all the planets acting together couldn't do anything significantly more than Jupiter can do on its own, which isn't much (as far as the Earth is concerned). --Tango (talk) 15:57, 22 May 2010 (UTC)

And when you consider the relative gravitational influence of solar system bodies on the Earth, you stop caring after the moon and the sun. Jupiter isn't even the most influential planet (it's 1/10th the effect of Venus), but none of them are meaningfully relevant. — Lomn 19:44, 22 May 2010 (UTC)

Ah, yes, I forgot it's tidal forces, not direct gravitational forces, that matter, so we need the cube of distance not the square. I believe Jupiter has the largest gravitational force out of the planets on Earth, just not the largest tidal force. Thanks for the link! --Tango (talk) 21:25, 22 May 2010 (UTC)

And a light-year is a unit of length, not of time. --Магьосник (talk) 16:37, 22 May 2010 (UTC)

Solid phase extraction and Chromatography

Hi, I have just read both Solid phase extraction and Chromatography pages but I haven’t found the difference between techniques. I mean, they do the same thing and exploit the same principle or not? Thanks so much in advance, I ‘m studying Forensic pathology for next month exam.--151.53.91.218 (talk) 16:51, 22 May 2010 (UTC)

SPE deals with making the desired analyte specifically soluble/extracted or insoluble/stuck-to-solid-phase, the other starts and ends with the desired analyte in solution merely passed through. The key to SPE is where that article states "either the desired analytes of interest or undesired impurities in the sample are retained on the stationary phase" (emphasis mine) as opposed to the more general idea of chromatography "passing a mixture [...] through a stationary phase, [...] Subtle differences in a compound's partition coefficient result in differential retention on the stationary phase". Differential retention causes elution time to vary vs "retained or not-retained". DMacks (talk) 18:50, 22 May 2010 (UTC)

updates based on scientific fact

Shrimp are bottom feeders meaning their diet may include toxic substances including radioactive particles. However, since 1970 shrimp have been farmed in non-toxic environments. Consequently do any of the religions which in the past have excluded them from the diet now permit such non-toxic shrimp to be labeled "Kosher"? 71.100.3.228 (talk) 19:53, 22 May 2010 (UTC)

Toxins possibly being present in food has nothing to do with the food being or not being Kosher. Beach drifter (talk) 20:00, 22 May 2010 (UTC)

I think the toxin example is a bad one because it presumes to know the intent of the law, which would not sit with a religious person terribly well. (It assumes they have secular goals behind them; that is how an outsider views such things, not an insider.) But there are modern updates to things like kosher laws—for example, there is an entire industry of appliances designed to conform with Sabbath strictures as they are interpreted to apply to modern technology. See: Sabbath mode. In Judaism, there are rabbis who get together and debate whether or not, say, flicking a switch violates the strictures against "work", or whether setting an oven to heat up violates strictures against lighting a fire, and so on. --Mr.98 (talk) 20:52, 22 May 2010 (UTC)

magnetism versus temperature

what is the formula that relates and objects temperature to its magnetism? 71.100.3.228 (talk) 20:01, 22 May 2010 (UTC)

I'm not aware of one - maybe you were thinking of the Curie temperature .87.102.18.191 (talk) 20:25, 22 May 2010 (UTC)

Niel ?

I keep thinking I've heard of a "Niel temperature" - but search shows nothing. (Not Niels Bohr - I think it was a surname)

Is there a similarly name temperature or point - I'm sure it was a transition or phase change temperature.87.102.18.191 (talk) 20:27, 22 May 2010 (UTC)

Annealing temperature? --BozMo talk 20:34, 22 May 2010 (UTC)

:) (no) 87.102.18.191 (talk) 21:20, 22 May 2010 (UTC)

The Néel temperature is the temperature above which an antiferromagnetic material becomes paramagnetic. Cuddlyable3 (talk) 21:29, 22 May 2010 (UTC) Cuddlyable3 (talk) 21:29, 22 May 2010 (UTC)

Yes thanks. 87.102.18.191 (talk) 21:49, 22 May 2010 (UTC)

Resolved

What metals were thrown out by the icelandic volcano?

What heavy metals were ejected by the icelandic volcano?--92.251.177.211 (talk) 20:55, 22 May 2010 (UTC)

The material ejected by the volcano would have been basically basalt, which has metals in the form of silicates and oxides but none of the heavy metals are likely to be present other than in trace amounts, as far as I know. Mikenorton (talk) 21:26, 22 May 2010 (UTC)

Is there any animal that can 'emit' fire?

Years and years ago I saw a wildlife documentary that featured a rainforest insect of some kind which (IIRC) as a defence mechanism was able to squirt a stream of *something* from its hindquarters which then spontaneously ignited in contact with the air, producing a small jet of flame. For some reason, I ended up discussing this with someone today, who insisted that I was wrong and asserted that there is no such and never has been any such creature. I'm open to the possibility that my memory is playing tricks on me and that I've mixed up something like a bombardier beetle (I looked that up first, thinking that it may have been what I was remembering) with Pokemon, or dragons - or that I saw it in a dream, or whatever.

So, does anyone know if there really is a bug, or anything else out there that can do this? --Kurt Shaped Box (talk) 21:05, 22 May 2010 (UTC)

Black hole paradox

After watching an explanation of the black hole paradox from Leonard Susskind, the explanation made first at sense, but further thought has left me only more confused. First, a quick explanation of the paradox:

• When person 1 watching person 2 enter into a black hole, person 2 appears to freeze, and time for him stops due to the gravity. Person 2 will never progress beyond the event horizon from person 1's view.
• Time, however, does not stop for person 2; from his perspective, he will sail right past the event horizon.
• Point 1 appears to conflict with point 2. Thus anything done by person 2 inside of the horizon will be irretrievably lost to the outside world - this shouldn't happen though. Physics says that, in theory, person 1, with a perfect view of what's occurring, should be able to reconstruct person 2's past perfectly.
• The solution, as explain by Susskind and apparently mostly accepted by physicists, is that the information is stored on the surface of the event horizon, an unfathomably hot place where matter is squished into a two-dimensional (or essentially two-dimensional) plane.

What I don't understand is this:

1. For person 2, time on the outside world should go faster and faster. Right before reaching the event horizon, the world will speed up to infinite time. What then to make of what person 2 observes after passing the even horizon? (this situation, by the way, is far from just theoretical: the spaghettification on a smaller sized black hole apparently won't occur on supermassive black holes).
2. What of the matter towards the center of the collapsing star that becomes a black hole? That matter has no way of being "stuck" on the event horizon and as such wouldn't be visible as the event horizon slowly evaporates.
3. What happens to matter immediately inside the event horizon upon collapse? The gravity there would insist on a field faster than the speed of light. This seems to violate the laws of nature.

Magog the Ogre (talk) 21:25, 22 May 2010 (UTC)