Wikipedia:Reference desk/Archives/Science/2011 January 27

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January 27

Best way to dissolve methane in a liquid that mixes with scintillation fluid

Hi,

I'd like to be able to "trap" 14-C methane in some kind of solvent so that I can mix that solvent with scintillation fluid and be able to determine radioactivity. What would be the ideal solvent for this situation? Ideally, I'd like a liquid that can trap all of the methane in the tube but also mixes with the scintillation fluid.

Thanks a lot for your help.

Ccarlst (talk) 03:50, 27 January 2011 (UTC)

Methane isn't going to be soluble to a great extent in any liquid (it is arguably more soluble in a nonpolar solvent like benzene than in water, but only in relative terms. Its not terribly soluble in either). Furthermore, even soluble gases will never completely dissolve in a liquid. Your best option is to react the methane with something, preserving its carbon, but making that carbon now bound to be part of a liquid compound rather than gaseous methane. I'm not sure how feasible it is based on the equipment you have availible, but something like Free radical halogenation would work; the article lists free radical halogenation as a method used most commonly to create chlorinated methanes like dichloromethane (methylene chloride) and trichloromethane (chloroform) both of which are actual liquids. --Jayron32 04:12, 27 January 2011 (UTC)

Try converting the methane to a methanide salt, which is soluble in polar anhydrous solvents. --Plasmic Physics (talk) 09:07, 27 January 2011 (UTC)

Yeah, but methanide salts would be much more difficult to work with than methyl halides. Alkyl salts are metastabile at best, I would expect all of them to be so highly alkaline as to be pyrophoric in air. The nice thing about methylene chloride is that it is fairly easy to work with (it is a low-boiling liquid, so you'd have to work in a cool room, but otherwise is very unreactive). --Jayron32 14:00, 27 January 2011 (UTC)

What's the source of the methane? Does the gas also contain other methane (not containing C-14) and is there anything else that does contain C-14? Google gives lots of literature hits for liquid scintillation of C-14 methane over the past few decades (sample search: 14c methane scintillation). Doesn't necessarily answer your direct question (as others have noted, it's "hard"), trying to figure out solutions to the larger situation. DMacks (talk) 09:36, 27 January 2011 (UTC)

At the moment, the source of the methane is a 1mCi vial I bought from American radiolabeled chemicals- well, at least they say is 1mCi with a specific activity of 50mci/mmol. The reason I am concerned and think that the 1mCi may be off is because according to my calculations, [1mCi X 1mmol/50 mCi X 22.4 ml/1mmol = 0.448 ml] the volume of methane I should have gotten should be around 0.5 ml, when in fact it came in a vial that looks to be about 6-7 ml. They claim there are no other gases there (and they are terrible about answering questions, so I have yet to find out if there is cold methane there too). So, I need a way to test that what they claim is there is actually what is in there. In the future, I was planning to use the 14-C methane in an experiment that is supposed to evolve 14-CO2, which I plan to trap using NaOH and then run in a scintillation counter. Thanks to everyone for your suggestions- it sounds like some of them would work well, but the problem is that it would be hard to do that kind of chemistry in a biology lab..Ccarlst (talk) 01:14, 29 January 2011 (UTC)

Of course, your 22.4 mL/mmol figure presumes the contents of the vial are at atmospheric pressure. It seems to me that if one were going to ship an expensive specialty gas in a small vial, it would be beneficial to have it well below atmospheric pressure so the pressure difference helps maintain the seal. Also, if the vial is supposed to produce a precise amount of radioactivity, they have to have some way to adjust the amount of gas they put in it, so they have to adjust the pressure anyway. Given that, they might as well have low pressure, and adjust the exact pressure when filling the vial, to hit the radioactivity target.--Srleffler (talk) 02:35, 29 January 2011 (UTC)

Geographic center of the world

Hi. I know that the geographic center of the contiguous United States is near Lebanon, Kansas {{coord|39.828175|-98.5795}} Could you, please, tell me the coordinates of the geographic center of the whole world? I searched the internet but couldn't find anything. If you don't know, could a science geek calculate the coordinates using a world map such as File:BlankMap-World6.svg and a good piece of software? --41.178.235.216 (talk) 03:50, 27 January 2011 (UTC)

To my admittedly sometimes muddled mind it seems there is no centre of the surface of a sphere. HiLo48 (talk) 03:54, 27 January 2011 (UTC)

There is, but it's not on the sphere. The center of mass of the earth is located, unsurprisingly, at the center of that sphere, not on its surface. The geographic center is defined as the center of mass of a uniform, two-dimensional cut out of the section of land in question. However, as you correctly note, it makes no sense when dealing with a sphere, only with the (planar approximation) of parts of that sphere does it make sense. --Jayron32 03:57, 27 January 2011 (UTC)

(edit conflict) I mean the center as if the whole world was flat (projected on a surface). It is probably some point in the Middle East but I need the exact coordinates. --41.178.235.216 (talk) 03:59, 27 January 2011 (UTC)

That involves some arbitrary map borders. To make the world appear flat on a map involves choosing edges, which don't actually exist, and flattening curved bits. HiLo48 (talk) 04:02, 27 January 2011 (UTC)

To expand, while a lot of maps do seem to have the Americas on the left, and Asia on the right, this one gives another perspective. HiLo48 (talk) 04:27, 27 January 2011 (UTC)

The proper way to calculate it over the whole globe is to use the (two-dimensional) circular mean. See also land hemisphere, which is nearly synonymous. --Tardis (talk) 05:02, 27 January 2011 (UTC)

For the centre of a conventionally made "flat" map, you're asking for the intersection of the prime meridian and the equator, this article has a story and pictures of a visit there (it's far out at sea off the coast of West Africa). Many world maps show more of the Northern than the Southern hemisphere, for such maps, the centre would be further north. I guess you could also calculate the centre of all the land masses in the world, this is maybe what's described in Tardis' post above. Jørgen (talk) 08:55, 27 January 2011 (UTC)

Further reading at Extreme_points_of_Earth#Center and geographical center.--Shantavira|^{feed me} 09:01, 27 January 2011 (UTC)

Greenwich, Mecca, or Jerusalem have been regarded as being the centre points of the world. At Greenwich you can stand astride the piece of metal the marks the boundry between the eastern and western hemispheres, and its where GMT comes from. 92.24.187.66 (talk) 12:21, 27 January 2011 (UTC)

Surely, the answer is wherever you are at that particular moment? --Dweller (talk) 14:25, 27 January 2011 (UTC)

Actually, the answer is wherever I am at that particular moment! --Stephan Schulz (talk) 17:17, 27 January 2011 (UTC)

I assume DWeller meant where you are. DMacks (talk) 17:25, 27 January 2011 (UTC)

Actually, I suspect it has something to do with the barycenter of the planet. Damn you, chocolate! --Stephan Schulz (talk) 17:33, 27 January 2011 (UTC)

Hmmm, despite the absurdity of it, this question is theoretically answerable. Imagine you make a globe where all the world's land surface is accurately represented by a homogeneous layer of material. Wrap it in a much lighter layer over the whole sphere to hold it together. Now put it on a smooth floor and let it roll to a stop. The point on the bottom should be "the center point of all land on earth", and the point on top should be "the center of all Earth's oceans". An industrious person could probably do this on a computer in a jiffy, but alas... Wnt (talk) 18:01, 27 January 2011 (UTC)

I think that method would find a centre very close to (but not exactly at) the centre of the land hemisphere mentioned above by Tardis. --Tango (talk) 22:12, 27 January 2011 (UTC)

According to this web page, "If you've ever wondered where the geographic center of the world's land area is, the coordinates are latitude 34 deg 26 min North and longitude 27 deg 19 min East. This puts it in the eastern Mediterranean Sea about halfway between Athens and Alexandria.".Looie496 (talk) 01:01, 28 January 2011 (UTC)

I wonder if what they mean by that is "the point at which the sum of the distance (along the surface) from there to the center of every 10 arc-minute² area of land (maybe defined as just "not-ocean"?) is minimized." WikiDao ☯ 01:32, 28 January 2011 (UTC)

If we define the problem as:

${\vec {x}}_{center}=\int _{-\pi /2}^{\pi /2}\int _{0}^{2\pi }{\vec {x}}(\theta ,\phi )\delta _{land}(\theta ,\phi )\,sin(\phi )d\theta d\phi$

Where $\delta _{land}(\theta ,\phi )$ equal 1 over land and zero otherwise, and then take the ray extending from the origin through ${\vec {x}}_{center}$, I get that it intersects the surface at 43.5222 N and 28.5470 E. That happens to be in Bulgaria at the edge of the Black Sea. That's a well-defined, non-trivial answer, though admittedly it is about as arbitrary and useless as any other answer. Dragons flight (talk) 05:04, 28 January 2011 (UTC)

That's actually the same definition that I had in mind above, though I had a well justified fear that I might foul up with three-dimensional polar coordinates, and I don't know where you found the delta(land) database.

To recap, the definitions so far cover:

• The center (barycenter) of the Earth
• The center of the land hemisphere drawn to contain the most land and least sea
• The location where you could site a "Transcontinental Congress" so that the total travel miles of delegates from evenly sized small districts throughout all the land on Earth (via great circle route) would be minimized
• The location directly above the spot deep inside the Earth where you could site the Transcontinental Congress so that the total teleportation miles of all delegates (via straight lines) would be minimized

To this I can imagine adding at least one more:

• The location directly above the spot where the barycenter of the Earth would be, if all volatiles (water, air, ice, maybe fossil carbon) were stripped away from the planet, as projected from the current barycenter.

This last one, in essence, is a way to average where the center of all the Earth's water is taking into account how deep the oceans are at each point, or where the center of all the Earth's land is taking into account how high the mountains are.

All these methods, except for the trivial answer of the barycenter, imply a dipole in the Earth between land and sea, with one centered at one spot and the other centered at the diametric opposite point.

What seems extra surprising to me is that there seems to be a close analogy between this and the philosophical issues of act utilitarianism (the "transcontinental congress" methods) and rule utilitarianism (the land hemisphere method); there are different ways of trying to decide on the "true" center depending on exactly how the "greater good" is defined. Wnt (talk) 06:11, 28 January 2011 (UTC)

For practical reasons I would add

• The location directly above the spot deep inside the Earth where you could site the Transcontinental Congress such that the sum of each delegate's squared teleportation miles would be minimized.

Least squares is a lot easier to compute, because it's just the arithmetic mean of all the land points in Cartesian coordiantes. To minimize the sum of absolute distances you'd probably need some kind of iterative approximation, and are we even sure that a local minimum would also be global? –Henning Makholm (talk) 06:37, 28 January 2011 (UTC)

Hmmm... I didn't think about that. I assumed that the "teleportation miles" (4th definition above) would work out to be the same as the average of all land areas as calculated by Dragons flight above, but is that true for the summed distance, or the summed squares of the distances, or...? Wnt (talk) 16:02, 28 January 2011 (UTC)

In one dimension it is easy to see that least squares gives the arithmetic mean, and least absolute distances gives the median. It is still the mean for least squares in higher dimension, but it is not clear to me that the median has a similarly nice generalization. –Henning Makholm (talk) 11:10, 29 January 2011 (UTC)

I don't understand the maths above, but the way I would do it would be for every point on the earth, you calculate the weighted sum (eg inverse square or whatever you choose) of the surface distance of every other point on the earth *provided* they are not more than half a circumference away, with 0 for water and 1 for land. Then the point with the highest weighted sum is the "centre of the world". What wrong with that? 92.29.125.152 (talk) 14:02, 30 January 2011 (UTC)

There is nothing wrong with it, except that it can be difficult to find the point with the best sum without doing an inordinate amount of work. (Note that nothing on a sphere is more than half a circumference away). Basically what we're discussing is which difference it makes to choose different formulas for the "weights" (in your terminology), since there are choices that makes it possible to find the resulting center with less effort than computing your sum for each possible point on the globe. –Henning Makholm (talk) 14:32, 30 January 2011 (UTC)

ORME Orbitally Rearranged Monoatomic Elements

There is some ideas on the web, but what is actually "Orbitally Rearranged Monoatomic Elements (ORME)"?, there is no information on english Wikipedia, usually it the best place to serch, would you explain please?Ghrmsn (talk) 06:23, 27 January 2011 (UTC)

It looks like it's not something real. One user attempted to write an article about it: User:Sloth_monkey/ORMEs and was deleted : Wikipedia:Articles_for_deletion/ORMEs and Wikipedia:Articles for deletion/Monatomic elements. Maybe you can glean some information from the deletion comments and the article draft. Ariel. (talk) 08:59, 27 January 2011 (UTC)

Actually it is true, there is information un many languages, although, I don't know why Wikipedia is not accepting this info. There is many more things less important or ridiculus, but not this, it is for real, probably some kind of goberment complot, trying to hide information.Ghrmsn (talk) 16:34, 28 January 2011 (UTC)

See WP:FRINGE and WP:RS for starters. DMacks (talk) 17:17, 28 January 2011 (UTC)

Mean distance in a square

Maths have always been my Achilles' heel, so I'm having trouble trying to figure out a problem with a square.

Let's imagine a big 100 sq. ft box divided into one hundred 1 sq. ft boxes. In the centre of each small box there is a candle. If I were to calculate the average distance from each candle to all other candles, would I get the same result for all the candles, or would there be a divergence depending on the location of the candles within the big box? Intuitively, I think candles located along the edges would have a greater average distance to all other candles, but I can't find a way to prove it mathematically.

Thanks to whoever can help. Leptictidium (mt) 08:55, 27 January 2011 (UTC)

When you have a problem like this simplify it. Imagine a line with just 3 squares in it, and calculate the average distance for each of those 3 candles. Ariel. (talk) 09:04, 27 January 2011 (UTC)

It would be ideal for a simple Basic program, such as SmallBasic. 92.24.187.66 (talk) 12:54, 27 January 2011 (UTC)

It's not clear from your phrasing what geometry you mean, but you will get different answers for a 1X100 rectangle of boxes compared to 10X10. The issue at play here is the perimeter to area ratio, and more generally the notion of boundary_(topology). For instance, if you put the small boxes on the surface of a sphere (and measure distance along the same surface), then all candles would share the same mean distance to the others. SemanticMantis (talk) 15:06, 27 January 2011 (UTC)

First, it has been noted that there are 100x100 10x10 1 square foot boxes in a 100 square foot box. Regardless, this is a very simple program to write. The output for a 5x5 box is:

3.31  2.83  2.67  2.83  3.31 
2.83  2.31  2.14  2.31  2.83 
2.67  2.14  1.95  2.14  2.67 
2.83  2.31  2.14  2.31  2.83 
3.31  2.83  2.67  2.83  3.31

As you can see, the mean distance to all other candles is not constant. -- kainaw™ 15:19, 27 January 2011 (UTC)

It is interesting to see the calculations, thanks. Also, I think you mean 10X10 1 square foot boxes in a 100 square foot box :-) SemanticMantis (talk) 18:29, 27 January 2011 (UTC)

And in the limit (as you use smaller candles and pack more of them) the average distance from a corner is exactly twice the average distance from the center. This is because to compute the average distance from the center, you can cut the square into 4 smaller squares, and only consider one of them by symmetry. So the average distance from the center is the same as the average distance from the corner of a square with half sides. 98.248.42.252 (talk) 18:57, 29 January 2011 (UTC)

Religion, mental health and education

Is religion correlated more positively with mental health in people with higher education? I ask this because it would test my hypothesis that approaching the ultimate nature of humanity or the universe is hazardous to a person's mental health, and that religion is a way of defending against that hazard. (I agree with Richard Dawkins' assertion that religion itself is a mental illness, but I'm not sure I agree that it's a more severe mental illness than the alternative.) NeonMerlin 11:05, 27 January 2011 (UTC)

Who's to say what the "ultimate nature of humanity or the universe" is? I don't think physicists are more crazy than other people, except in cartoons. 92.24.187.66 (talk) 12:56, 27 January 2011 (UTC)

Is this the religious version of "You can't handle the truth"? HiLo48 (talk) 14:03, 27 January 2011 (UTC)

I read an article about this in the last few weeks; the author claimed that religion (particularly the fervent, born-again type) is measurably more popular among undergraduates at Britain's most prestigious universities than at other, less rarefied institutions. His interpretation was that unusually bright people under intellectual stress are more likely to turn to religion. Anecdotal and unscientific, but it did strike a chord. It could have been in The Guardian or maybe the Financial Times; I can't find anything online ATM but I'll try to dig up a reference for you. Karenjc 16:04, 27 January 2011 (UTC)

Sorry, tried hard but couldn't find the original article - my post-Christmas recycling binge seems to have claimed it. Karenjc 10:07, 28 January 2011 (UTC)

Interesting comments regarding "unusually bright" students turning more to religion. From what I've seen, most studies show a strong negative correlation between "intelligence" (as measured by IQ) and religious faith. -- Mesoderm (talk) 16:16, 27 January 2011 (UTC)

Yes, given the strong negative correlation between religiousness and intelligence, it presumably isn't those students' intelligence that's causing them to turn to religion, so much as their highly competitive, high-stress environment. And a high-stress environment does increase a person's risk for developing other forms of mental illness (see Causes of mental disorders), so a stress/religiousness correlation would seem to fit Dawkins' religion-as-mental-illness paradigm in at least that regard. Red Act (talk) 17:36, 27 January 2011 (UTC)

Were I to try and identify a confounding variable in the relationship between university status and proportion of students who are religious believers, I would look at the number of international students. High status universities in the UK attract international students from all over the world, including countries with much higher religious observance rates than the UK. Itsmejudith (talk) 15:50, 28 January 2011 (UTC)

Correlation is not causation (Propter hoc fallacy), and doubly so when dealing in false syllogisms. If I say "I love you, and I love cheese, therefore you are cheese" you can see the rediculous leaps of logic needed to reach that conclusion. However, I have no idea why, replacing random nouns and verbs in that statement, it suddenly becomes a reasonable proposition. Lets try it "Stress causes religiousity, and stress causes mental illness, therefore religiousity is mental illness." Nope, its still a patently stupid conclusion to reach. --Jayron32 18:05, 27 January 2011 (UTC)

I did not use that syllogism. You incorrectly extrapolated what you thought I meant from what I said. I will explain what I meant more clearly.

Biological contributions to the etiology of mental illnesses are of course very important, but to make the logical content of the following clearer, pretend that stress is the only cause of mental illness. Then if you take Dawkins' paradigm as being valid, you can use the syllogism "the cause of mental illness is stress, religiosity is a mental illness, therefore the cause of religiosity is stress" to predict that there is a positive correlation between stress and religiosity. So if a study shows that there really is a positive correlation between stress and religiosity, that suggests that the model of religiosity as a mental illness may have some predictive value, in that it could have enabled you to predict the positive stress/religiosity correlation ahead of time, from just knowing the cause of mental illness. This alone isn't enough to conclude that it's useful to model religiosity as a mental illness, since it may be purely coincidental that the religion-as-mental-illness paradigm led to the correct prediction that there is a positive stress/religiosity correlation. That's especially true because mental illness in reality has multiple causes, so one has to deal with messy correlations instead of clean Boolean logic as in the syllogism above. But this could validly be used as one element of a set of information used in determining how valuable it is to model religiosity as a mental illness. Red Act (talk) 21:13, 27 January 2011 (UTC)

There is a strong correlation between citing studies linking low IQ to a group of people 'and' your personal dislike of these groups. Quest09 (talk) 18:10, 27 January 2011 (UTC)

Red Act (talk) 21:15, 27 January 2011 (UTC)

This isn't quite what you asked for, but I did stumble across this study that attempted to measure the effect of religion on physical (rather than mental) health while also controlling for the effects of age, income, education, etc. They found that religious practice had a positive and statistically significant association with health even after controlling for other variables. (Probably not surprising.) However, they also found that those holding self-reported "conservative" ideologies were on average less healthy than those with moderate / liberal religious beliefs, even after controlling for other variables. They speculated that religious conservatives may be more reluctant to seek out medical treatment when problems arise. They also found that people with higher levels of education where more likely to engage in regular religious practices (e.g. praying, going to services, etc.), but paradoxically less likely to report feeling "closeness to God". Dragons flight (talk) 18:16, 27 January 2011 (UTC)

The elephant in the room here is, how do you define "mental health". I mean, Jesus and his followers undertook many actions that they pretty well could guess were going to get them nailed to a cross waiting for a cold, cruel end. Any competent mental health professional could argue that that made them "a threat to themselves or others", right? But it was about more than physical survival. Now a person can look at a far-gone mental patient and say that there the pattern of actions is totally pathological, not productive, not for some grand and noble purpose, but how can anyone accurately draw a precise line between what behavior is less than human and what is more than human? Wnt (talk) 06:23, 28 January 2011 (UTC)

Though the behavior of Jesus and the apostles is not really germane for talking about modern religion. Most practitioners are not founders. Practically zero Christians actually behave like Christ is supposed to have. --Mr.98 (talk) 20:16, 29 January 2011 (UTC)

Anal sex in the 1800s

I watched Total Eclipse (film) the other day and was confused about something. When Verlaine is in court and a doctor tests whether he was having anal sex, the doctor says there was proof that he was having both active and passive sex. I understand how the doctor could tell that Verlaine was having passive sex, but how could he ever know that Verlaine was also having active sex? Or were they just saying that to further incriminate him...? Thanks, this has been bothering me for some time! 129.3.178.228 (talk) 14:06, 27 January 2011 (UTC)

Was something like syphilis involved? (Which was common enough at the time) Wnt (talk) 18:11, 27 January 2011 (UTC)

I can't find anything saying he ever had syphilis, no. 129.3.151.117 (talk) 18:45, 27 January 2011 (UTC)

According to the article on Verlaine at French Wikipedia he did have syphilis. --Antiquary (talk) 23:39, 27 January 2011 (UTC)

I've heard first hand accounts about how doctors belonging to certain religious groups would tell adolescent males (from families that also belonged to that group) that they had "symptoms" of having masturbated so they should cut it out. Obviously, chances are the majority of males by a certain age have at least tried masturbation so the doctor wasn't really taking a wild guess. Maybe this was a similar case where they were just making a broad assumption, obviously chances were probably less but that doesn't change much. Vespine (talk) 00:12, 28 January 2011 (UTC)

Medical textbooks of that age did actually sometimes give lists of symptoms, as here. ("...circulatory disturbances of both motor and sensory nature; irritability; insubordination and outbursts of inexplicable anger... a decided bashfulness and reserve in society; averted gaze; and lack of manly bearing... a tendency to avoid company or the joining in youthful sports, but rather to retire alone or with a single companion, upon whom the suspicion of being an accomplice should rest; in study hours there is dullness, drowsiness, preoccupation, faraway gaze, and lack of application, with often pronounced weakness of memory and absent-mindedness..." and it goes on.) Marnanel (talk) 00:46, 28 January 2011 (UTC)

The doctor was talking bullshit obviously, he could not know that. --Lgriot (talk) 13:12, 28 January 2011 (UTC)

How long after the sex act did they perform the "test". I don't want to be gross, but bathing wasn't exactly a big thing in 19th century Paris, right? Matt Deres (talk) 22:39, 28 January 2011 (UTC)

Sky photography

I stumbled upon this image during one of my Wikipedia strolls, and I was surprised to learn that it was a photograph. It looked like a negative or even a diagram to me. To what purpose would an astronomer use such a picture as opposed to a more usual (to my lay eyes) photograph such as this one ? What are those "negative" images useful for ? Thank you, have a nice day. 130.79.160.112 (talk) 15:33, 27 January 2011 (UTC)

Many astronomers would find it simpler to pick faint black specks out of a white background than vice versa, particularly if you're working by hand rather than with digital photo processing equipment. — Lomn 15:47, 27 January 2011 (UTC)

Technically, it is the negative (or a print of a photograph of the original plate); the 'raw' image collected on film at the telescope would look exactly like that, as bright stars would create dark spots. From the standpoint of working with the image, it's usually easier to pick out a small dark spot on a white (or clear, on the original film/plate) background than it is to pick out a slightly-less-dark spot on a black background. (This applies both to manual examination and to automated discrimination.) When printed non-photographically, the negative version uses less toner (or ink), and is more forgiving of printing flaws. When annotating the image, it's much easier to add dark text and symbols to the clear background (particularly when dealing with physical copies of the image) than it would be with a positive image. TenOfAllTrades(talk) 16:32, 27 January 2011 (UTC)

When I was measuring faint structures in deformed minerals on electron micrographs (more decades ago than I care to remember) I always used the negatives directly - you always lose some information when you print. Mikenorton (talk) 18:11, 27 January 2011 (UTC)

(Edit Conflict) In addition to the previous answers, an important factor is that every time a non-digital image is processed (such as when making a positive print from an original negative) degredation of the image occurs. Similarly, every extra lens that an image has to pass through will reduce the inherent quality of the image. For these reasons, professional astronomers from the earliest use of telescopes and of astrophotography generally did not add an extra lens into their eyepieces usually necessary to convert the inverted image into an upright one, and worked with original negative plates (film tended to distort more so was not used for astrometry). Thus astronomers have always been used to dealing with such images, which also have the advantages previously described. 87.81.230.195 (talk) 18:16, 27 January 2011 (UTC)

Even just on my computer screen, I find it a lot easier to see faint spots when it is black-on-white than it is when it is white-on-black. I suspect the human eye is measurably better at the former than the latter. --Mr.98 (talk) 20:37, 27 January 2011 (UTC)

I asked a similar question while studying for my (astrophysics) degree. Yes, it is easier to pick out faint detail (pale grey wisps) against a light background. Also, you get less distortion/artifacts during measurements, if using the original (negative) photographic plate. Astronaut (talk) 16:06, 29 January 2011 (UTC)

Thank you very much for those explanations ! (says the OP on another computer) Have a nice day, 85.169.175.167 (talk) 17:23, 30 January 2011 (UTC)

incipient fusion

A google search suggests that in geology or materials science or something like that, there is a concept called "incipient fusion". But Wikipedia has no article with that title. Can someone say what it is?

There is a joke I heard many years ago, in which a school principal visits a class and tries to ascertain what they're learning. He asks the pupils what they would expect to find if they dug down to 4000 miles below the ground. Nobody could say anything. Then the teacher assisted. He asked them:

"What is the state of the center of the earth?"

They all responded in perfect unison:

"The center of the earth is in a state of incipient fusion."

Michael Hardy (talk) 19:10, 27 January 2011 (UTC)

I don't think that's a joke, it's just an incorrect fact. You can read the definition of "incipient" at Wiktionary. "Incipient" means that something is just starting. The material at the center of the Earth is part of the inner core, and is a solid (or solid-like) mass of mostly iron and nickel. Some scientists have speculated that radioactive or nuclear processes deep inside the Earth may contribute to the net planetary heat flux; but I have never heard a reasonable geologist pass off fusion as a plausible nuclear reaction occurring inside the Earth. Nimur (talk) 19:22, 27 January 2011 (UTC)

It is a joke, but it's true: It sometimes (often) happens that students learn to recite memorized answers to memorized questions, without understanding them. This is just parodying that phenomenon. Michael Hardy (talk) 19:35, 27 January 2011 (UTC)

And, "Nimur", you're missing the point. Nuclear fusion is obviously not what the word "fusion" refers to in this case, as you'll see if you google "incipient fusion" in quotes. It's about a different kind of fusion. "Fusion" generally means joining together. That can refer to lots of different things. Michael Hardy (talk) 19:36, 27 January 2011 (UTC)

Fusion originally means "melting" (hence Heat of fusion and Fuse (electrical)), and by extension to join by melting (and resolidifying). -- 119.31.126.67 (talk) 00:45, 31 January 2011 (UTC)

I never heard this one, but it ties in with the question about Jupiter that was asked last week or so - as very large gas giants approach brown dwarf status during their initial formation, one might say one expected "incipient fusion" near their centers? (Whereas Earth, with a big iron core, is not fusing anything, no matter what) My feeling on reading this is that the joke implies their teacher has drilled something into the kids which is just plainly wrong. Wnt (talk) 19:20, 27 January 2011 (UTC)

For earth-specific geological-scale nuclear reactions, see geothermal gradient - heat sources. Most of the (nuclear-related) heat is simple radioisotope decay - more like an RTG than a reactor. A few scientists speculate that there may be fission in the deep mantle, and many scientists believe isolated patches of Earth's crust have experienced natural nuclear fission. Nimur (talk) 19:25, 27 January 2011 (UTC)

I think this thread of discussion is going away from the OP's question. From the brief google search I did, incipient fusion seems to be to do with materials joining together, not with energy release as a result of nuclear fusion. --Tagishsimon (talk) 19:31, 27 January 2011 (UTC)

From an article on brick making "incipient fusion, when the clay particles become sufficiently soft to stick together in a mass when cooled" [1] --Tagishsimon (talk) 20:43, 27 January 2011 (UTC)

Thank you, Tagishsimon. (Amazing how Nimur and others missed the point so clumsily. I wonder if they know that nuclear fusion has only been known for less than a century but the word "fusion" is (obviously) much older than that.) Michael Hardy (talk) 00:50, 28 January 2011 (UTC)

Irrelevant here, I guess, but it might be worth pointing out that yet another meaning of "fusion" is simply melting, as seen in the term heat of fusion. --Anonymous, 11:27 UTC, January 28, 2011.

this reminds me of one of the messages in Richard Feynman's “Surely You’re Joking Mr. Feynman!”, which was that students should be taught to understand and not only to memorise. The OPs 'joke' is an example of what happens when taught only to memorise. see http://www.hpcnet.org/cgi-bin/global/a_bus_card.cgi?SiteID=305793 —Preceding unsigned comment added by 80.168.88.74 (talk) 13:47, 28 January 2011 (UTC)

Practicality of experimental procedure for measuring microwave wattage

Is there anything about the following procedure that in actual practice would make its results significantly inaccurate? Thanks in advance.

Procedure for finding the wattage of a microwave with no labeling whatsoever:

1) Place 0.1 kg (100 mL) of water in a beaker and measure the initial temperature T1.

2) Heat water in the microwave for 10 s.

3) Quickly measure temperature of water T2 and find dT = T2 - T1.

4) Calculate energy transferred to water Q = m*c*dT using c = 4.187e+3 J/kgK.

5) Divide Q by 10 to get wattage (J/s).

76.27.175.80 (talk) 19:15, 27 January 2011 (UTC)

It sounds plausible, but it will need experimental checking. For example, this is a net measurement of the wattage absorbed by the water, but the microwave packaging probably gives a gross wattage to make it sound bigger, and so as not to overly dwell on whatever losses occur in the walls of the oven, etc. Packaging for food probably follows the manufacturer's packaging.

And of course, be sure to stir the water thoroughly. Wnt (talk) 19:24, 27 January 2011 (UTC)

100 mL of water beaker might not be enough to get average energy (assuming a standard kitchen-sized microwave oven, with a cavity of a few 10s of cm in each dimension). One of the reasons ovens now have carousels and other waveguide tricks is because the microwaves are not evenly distributed in the cavity (and these tricks only partially compensate). The plausible values for a household model do not cover that large a range, so you need to make sure you are not sitting in a particularly high-energy or low-energy region (being in a cool spot could create noticeable experimental error). How does your approximately 4x4x6 cm sample compare to the wavelength of microwaves, and are you likely have Nyquist–Shannon sampling theorem problems? DMacks (talk) 19:47, 27 January 2011 (UTC)

You want as big a ΔT as possible without errors from evaporation. So you need to do some preliminary experiments to see how fast the water heats up. A big hint: you don't really want the water to go above 60 °C (140 °F), or you'll have all sorts of practical problems in the measurements, not to mention safety issues if you're doing this as a class experiment. But don't restrict yourself to 10 seconds heating, you might get better results from a longer time. Physchim62 (talk) 19:59, 27 January 2011 (UTC)

In addition to any experimental error in finding the average power delivered to the food, you must also consider what the power will be used for. Naturally the oven will not be 100% efficient, so the power delivered to the food is less than the power drawn from the electrical mains. If you are trying to determine whether the circuit breaker supplying the oven is adequate, this must be allowed for. Also, recipies that mention the power of the oven might refer to the actual power delivered to food, or to the power drawn from the mains; you will have to figure out which meaning the recipie uses before deciding upon any modification to the recipie. Jc3s5h (talk) 20:04, 27 January 2011 (UTC)

It would be interesting to correlate the calculated absorbed energy with the actual calculated electrical draw (an ammeter on the mains line and its voltage). I don't know the typical efficiency of a consumer-grade magnetron, but that sounds like something one could find in a library or online reference (maybe even the spec sheet of an actual device?). And then consider that there are one or more motors and lights being powered in addition to the microwave source itself. Gauge the overall efficiency of the oven as a food-heating device. DMacks (talk) 20:15, 27 January 2011 (UTC)

I checked an old microwave cookbook I've got lying around, and the test there is:

1. Place two cups (500 ml) of room-temperature water in the microwave.
2. Set the microwave for a long period of time (ten minutes or more).
3. Measure the time until the water starts boiling.
4. Find the nearest time in the cookbook's chart. This gives the approximate wattage of the microwave.

Unfortunately, the page containing the chart is missing.

This procedure has some practical advantages over yours: the greater quantity of water increases absorbtion of microwaves, while the greater heating time makes for a more accurate measure of temperature (and the use of "boiling point" means you don't need a thermometer, but does introduce errors from evaporation). --Carnildo (talk) 00:49, 28 January 2011 (UTC)

Thanks all for the responses. I tried out the experiment as I described it, but with 500 mL (0.5 kg)and for 90 s. The rotating carousel carried the pyrex pitcher over a good volume of the space in the microwave continuously, so I assume I got a good sampling of whatever "hot" and "dead" zones there were in the microwave. The initial temp was 15.6 C and the final was 48.9 C for a dT of 33.3 K. So the total energy was 69.7e+3 J which over 90 s comes to about 774.6 W. I found the documentation for the microwave, which claims it's an 1100 W microwave, which, if it's true, means that it was about 70.4% efficient at putting its energy into my water. ~70% seems realistic to me, and not knowing what kind of stuff people will be putting into their microwaves, it seems logical for the manufacturer to advertise the wattage made available instead of any estimated final wattage absorbed by the food. 76.27.175.80 (talk) 17:51, 28 January 2011 (UTC)

Have you repeated the experiment, not just with the same water volume and time to see if you get the same temperature change, but with different water volumes and times to see if you get the same computed value? -- 119.31.121.84 (talk) 02:16, 31 January 2011 (UTC)

For maximum power transfer from the waveguide to the water, the water in the cavity (oven space) must present a matched load to the waveguide. In this case, the same energy will be dissipated in the water load as in the anode of the magnetron. Im not sure how microwave ovens powers are specified: Is it the maximum power that can be transferred into a matched load?--92.25.98.49 (talk) 23:05, 28 January 2011 (UTC)

Marketing can usually be counted on to trumpet the best case scenario. 76.27.175.80 (talk) 20:26, 29 January 2011 (UTC)

Safe to store water in garage?

We have some blue 55-gallon water barrels to store water for an emergency. I have heard that you should not store these in the garage because of gasoline fumes (assuming your car is in the garage). Are there some authoritative sources that state that water barrels should not be in the garage? I cannot find any. All I can find is to make sure the barrels are not sitting directly on concrete. Thanks, Alanraywiki (talk) 20:05, 27 January 2011 (UTC)

Don't both your drinking water barrels, and any gas cans you have laying around, have lids that seal? APL (talk) 20:27, 27 January 2011 (UTC)

Yes, the water barrels are well sealed. The plastic on the barrels is thick. I think the permeability of the plastic may be the concern. But, I can't find any sources to corroborate. Alanraywiki (talk) 20:39, 27 January 2011 (UTC)

The LD50 of gasoline would require a 75 kilo person to drink about 1.5 liters of it to have a 50% chance of dying. That's a lot of gas to seep through thick plastic to even get in the ballpark. Like using non-food-grade barrels for this kind of thing, it seems like a minor concern if you change the water now and then and don't make a habit of undergoing emergencies. --Sean 20:55, 27 January 2011 (UTC)

The LD/50 isn't the only issue with gasoline toxicity, I'm pretty certain people have been seriously injured by less due to chemical burning of the esophagus and stomach. The listed symptoms at drugs.com seem to confirm this: abdominal pain, bloody stool, vomiting (with possible hematoemesis), throat swelling, difficulty breathing, ect. It also says expected treatment will probably include an endoscopy to check for burns. That said, to the original question, with that much water in an impermeable container I wouldn't worry personally, the only problem if a small amount of vapor did seep in would be one of taste. Keep in mind that garages typically aren't innundated with fumes and are far from airtight. 65.29.47.55 (talk) 21:40, 27 January 2011 (UTC)

I cannot see the logic of the alleged problem. Gasoline isn't that sneaky. HiLo48 (talk) 21:04, 27 January 2011 (UTC)

Maybe they mean the exhaust fumes? And maybe it's not a "it will kill you" but a "it will taste really unpleasant" thing. Just guesses. Vespine (talk) 21:31, 27 January 2011 (UTC)

With small amounts of gasoline, I'd be more worried about carcinogenicity than acute toxicity. Gas contains significant amount of benzene.

The scary thing about carcinogens is that you can never be sure whether they've hurt you or not. With a lot the standard acute poisons, say cyanide or strychnine or carbon monoxide, if you live 48 hours, you're probably over the hump (not a guarantee, I suppose, but the major concern is over). With benzene, who knows? It could come back to haunt you years later.

(That's not to say that the acute poisons are actually better. In an emergency situation where I had to drink contaminated water to live, I'd probably pick the one with gas in it over the one with cyanide.) --Trovatore (talk) 06:36, 28 January 2011 (UTC)

If you're in the sort of emergency where you need hundreds of gallons of fresh water that you can't get any other way, minor contamination from exhaust fumes would be the least of your worries! Physchim62 (talk) 10:52, 28 January 2011 (UTC)

Why can't the barrels be placed on concrete? If water is in a closed, non-permeable container (which all water barrels should be, at least here in Finland), the placement shouldn't matter at all. Of course you do'nt want them to freeze or get a funny taste from sitting in direct sunlight. --Albval (talk) 10:29, 28 January 2011 (UTC)

Smallest meaningful length

Hello. The Planck length is the length scale at which the structure of spacetime becomes dominated by quantum effects. But, unlike the Planck time, it is not seen as the smallest unit which can exist. What is the smallest possible distance which can exist? Thank you. Leptictidium (mt) 20:42, 27 January 2011 (UTC)

Sorry to be pedantic, but you'll have to qualify the meaning of 'exist' in this context. For example, operating under mathematical realism, the so-called 'real numbers' are actual real entities, and there is no such thing as a smallest distance, i.e. there is no smallest positive real number. You may be interested in exotic types of math where true infinitesimals exist.SemanticMantis (talk) 21:28, 27 January 2011 (UTC)

As is touched on in the last paragraph of Planck time#Physical significance, and the first paragraph of Planck length#Physical significance, the physical significance, if any, of either one of those quantities is debatable. There are various theories that predict various things, but physicists really do not yet have a solid understanding of what goes on at that scale or smaller. Red Act (talk) 21:38, 27 January 2011 (UTC)

Possibly, a smaller distance than the planck length cannot be measured due to quantumn effects. To discuss smaller distances would not make sense, as it is impossible to distinguish fractions of this distance from each other. Like quantumn super position, you can't measure it, but it does exist; smaller distances cannot be measured with any certainty, but they do exist, for different reasons of course.

Statistics play a major role, you're simply cannot be certain of the absolute length, if it is smaller than the planck length.

If the planck length is the smallest quantisisable distance, then would that put a cap on the maximum energy of a photon which can be quantisised? --Plasmic Physics (talk) 22:26, 27 January 2011 (UTC)

Yes, there's an energy limit. The nature of a photon as we currently understand it wouldn't make sense at energies above the Planck scale. Red Act (talk) 22:56, 27 January 2011 (UTC)

Isn't the photon-as-we-know it supposed to last only up to the electroweak scale (far below Planck)? –Henning Makholm (talk) 00:46, 28 January 2011 (UTC)

I'm way out of my depth here, but after reading electroweak interaction and electroweak epoch, and noting that the expected mass of the Higgs boson is around that of the electroweak scale (so that energies higher than that can't necessarily be made to "disappear" by just doing a Lorentz boost), and reading that in theories with extra dimensions, the fundamental scale of gravity is lowered from the Planck scale to the electroweak scale[2] (again making it impossible to make higher energies "disappear" with a simple Lorentz boost), I'm thinking you're probably right. Red Act (talk) 01:47, 28 January 2011 (UTC)

What you said about energies higher than the electroweak scale not being boostable is not correct. I don't understand how you got to that conclusion but I know it is not correct. 71.101.41.73 (talk) 04:46, 28 January 2011 (UTC)

The link above says that in theories involving extra dimensions, the fundamental scale of gravity is lowered from the Planck scale to the electroweak scale. My thinking was that whenever you get to a scale where you need to take gravity into account in any way, you can't simply apply a boost to the description of a high-energy photon such that in the new frame of reference, the high-energy photon simply looks like a normal low-energy photon. The point being that gravity isn't something that takes place within a simple Minkowski space (although linearized gravity can be treated that way), so expecting to be able to apply an arbitrary Lorentz transformation at that scale and have the physics look the same would seem iffy at best. But like I said above, I'm way out of my depth here. I think I've got a decent grasp of general relativity and non-relativistic quantum mechanics, but I don't even really understand quantum field theory, much less physics beyond the standard model, so if I'm full of shit on this one, I'm completely unsurprised. Red Act (talk) 06:32, 28 January 2011 (UTC)

My ignorance is of about the same order as yours, but what I think I understand is that the problem is not with the photon humming along all by itself through the vacuum, but what happens when it interacts with something else. In the latter case it is meaningful to ask about the energy in the center-of-mass frame. I think the electroweak interaction article says that when this energy is high enough, pertubation-based QED loses validity, and you need to treat the photon as a superposition of W° and B° bosons, which have different interactions. But my grasp of spontaneous symmetry breaking is infinitely fuzzy and heuristic, so don't take any of that as gospel. –Henning Makholm (talk) 07:18, 28 January 2011 (UTC)

Doesn't the energy of a photon depend on your point of reference? — DanielLC 03:11, 30 January 2011 (UTC)

Well, that's certainly true in general when considering a photon traveling through a flat vacuum. What I was trying to look at was the scale at which "flat" breaks down, and what Henning was considering is a situation where "vacuum" doesn't apply (in which case the energy is taken to mean as measured in the center of mass frame). Red Act (talk) 08:53, 30 January 2011 (UTC)

It's far from clear that "smaller distances cannot be measured…but they do exist". String theory postulates additional dimensions that might come into play at distances around the Planck length (nobody really knows), and at least most if not all of the extra dimensions are probably compactified, although I think one or more additional large dimension(s) haven't quite been conclusively ruled out, and even the standard four dimensions of spacetime use a metric tensor that isn't even positive definite. So our whole intuitive Euclidean notion of "distance" may well work very poorly at that scale. Red Act (talk) 23:47, 27 January 2011 (UTC)