Wikipedia:Reference desk/Archives/Science/2012 April 8

= April 8 =

Illumination in lumen additive or parallel?
If various LED light emitters is fitted within the same "bulb". Will their light intensity add up as in total_lumen = lumen_1 + lumen_n + lumen_n+1.. Or will a light source made up of many parallel light emitters never be equal to a single (incandescent) light source of x lumen? That is parallel photons will not add up into less photons with the same energy but larger amplitude? because phase synchronization will not happen? Electron9 (talk) 00:58, 8 April 2012 (UTC)


 * I believe it's additive. However, our perception is not.  That is, twice as many lumens doesn't seem "twice as bright".  When lighting a room, it's helpful to have lights in each corner, to avoid any dark corners (this is especially true with dark walls, like wood paneling, where little light reflects into the corners). StuRat (talk) 01:15, 8 April 2012 (UTC)


 * Right. Photons do not join together or combine into fewer photons of different amplitude or frequency. 71.215.74.243 (talk) 01:23, 8 April 2012 (UTC)


 * Thus the whole idea about replacing incandescent light bulbs with multiple emitters is fundamentally flawed because it just won't be the same ? Electron9 (talk) 01:49, 8 April 2012 (UTC)


 * No, that's not at all what's being said. For the same total number of lumens, and same quality of light, the room will generally be perceived as being better lit if it has multiple, lower-lumen lights in multiple locations, instead of one bright light in one location.  But if you wanted the more poorly lit look of a single light for some reason, you could just put the multiple lights in essentially the same location.  Red Act (talk) 03:29, 8 April 2012 (UTC)


 * Agreed. Also, having the light sources spread out will be perceived as more light. StuRat (talk) 03:41, 8 April 2012 (UTC)


 * Won't it be much light but no real intensity anywhere? Electron9 (talk) 14:37, 8 April 2012 (UTC)


 * A room lit uniformly (as if the entire ceiling glowed, or the ceiling an walls glowed) might not be perceived as "better lit" since the lighting effect would be very "flat," and shapes of solid objects would not be as well defined. It might seem quite blah and boring. Edison (talk) 17:34, 8 April 2012 (UTC)


 * Indeed; this is one of the efficiency advantages of lengthy fluorescent bulbs (which I can't stand at 50 Hz, for what it's worth.) 71.215.74.243 (talk) 23:14, 8 April 2012 (UTC)


 * You mean you don't enjoy experiencing epileptic seizures ? StuRat (talk) 06:26, 10 April 2012 (UTC)

Strange zoo bird
Any idea what this bird is? I've gone through all the birds on its zoo's list and none seem to be it. 71.215.74.243 (talk) 01:05, 8 April 2012 (UTC)
 * I think it may be the Chestnut-breasted Malkoha - which is on the list. AndyTheGrump (talk) 01:23, 8 April 2012 (UTC)
 * More on it here - with another video. Surprisingly, it is one of the Cuculidae - the Cuckoo family. Common in Southeast Asia. AndyTheGrump (talk) 01:32, 8 April 2012 (UTC)
 * No doubt! Thanks, I don't know how I missed it from the accurate description linked from the list. 71.215.74.243 (talk) 01:36, 8 April 2012 (UTC)
 * Cool bird! "Unlike many cuckoos, it builds its nest and raises its own young." Marking as resolved. SemanticMantis (talk) 01:57, 8 April 2012 (UTC)

Octane rating of jet fuel
What is the octane rating of jet fuel? Whoop whoop pull up Bitching Betty 02:30, 8 April 2012 (UTC)
 * Jet fuel is essentially kerosene (C8 to C16 molecules), not gasoline (C4 to C12 molecules). Octane rating is irrelevant to jet fuel, since predetonation is not a concern in a gas turbine. However, if it was measured it would be considered to be very high, since octane rating is a measure of fuel's resistance to predetonation, not its volatility.  Acroterion   (talk)   02:38, 8 April 2012 (UTC)
 * Thanx! Whoop whoop pull up Bitching Betty 11:30, 8 April 2012 (UTC)

Do different chicken breeds have different tastes?
I'm not talking about their eggs, whose taste apparently depend not on their shell color, but the chicken feed. 66.108.223.179 (talk) 02:32, 8 April 2012 (UTC)


 * If so, it must not be very noticeable, or I'd expect various brands to claim they have better tasting breeds. StuRat (talk) 03:35, 8 April 2012 (UTC)


 * This document suggests that the slower growth rates of traditional breeds gives a better flavour. Alansplodge (talk) 01:37, 9 April 2012 (UTC)


 * I've eaten many different breeds and never noticed a difference. Older chickens are tougher and have more flavor, though. --Sean 20:08, 9 April 2012 (UTC)


 * Anecdotally, I can say that they taste quite different. I live in Indonesia where two different breeds are available to buy. One is the sort that westerners are used to with the massive breast, called ayam bule by the locals, and the other is a much leaner bird called ayam kampung. 112.215.36.179 (talk) 10:02, 11 April 2012 (UTC)


 * Perhaps the Q should be whether different breeds commercially available in the OP's locale taste significantly different. StuRat (talk) 22:23, 11 April 2012 (UTC)

mercury spectrum
what elements may have a spectrum of wavelengths very similar to the spectrum of mercury — Preceding unsigned comment added by 197.255.118.206 (talk) 06:43, 8 April 2012 (UTC)
 * "Similar"? You can eyeball the visible spectra at http://www.umop.net/spctelem.htm Hg is in the lower left. 71.215.74.243 (talk) 10:16, 8 April 2012 (UTC)

sodium spectrum
what are the wavelengths of the red, yellow, yellowish-green, green, greenish-bue and violet colours of sodium. — Preceding unsigned comment added by 197.255.118.206 (talk) 08:15, 8 April 2012 (UTC)
 * This smells like homework to me, but if you can figure it out from http://physics.nist.gov/PhysRefData/Handbook/Tables/sodiumtable2.htm that's probably okay. 71.215.74.243 (talk) 10:20, 8 April 2012 (UTC)

physics
what is the difference between spectroscopy and spectrometry — Preceding unsigned comment added by 197.255.118.206 (talk) 08:31, 8 April 2012 (UTC)
 * Spectroscopy is the science of determining characteristics from a spectrum. Spectrometry is the measurement of spectra. In many cases they can be used interchangeably without too much ambiguity, but it's better to be precise. 71.215.74.243 (talk) 10:06, 8 April 2012 (UTC)
 * Specialists in the field often have heated debates. The difference I learned from them in a bar long ago is mainly that half of them take offense at one term and half at the other:) Okay, the main difference I hear when they're sober is that spectroscopy deals specifically with absorption/emission of electromagnetic radiation over a range of frequencies whereas spectrometry especially refers to "things over a range" other than EM effects but may also be used as a parent field for the other. DMacks (talk) 14:28, 8 April 2012 (UTC)
 * I think your definitions are better than mine, because there's no such thing as acoustic spectroscopy. 71.215.74.243 (talk) 20:02, 8 April 2012 (UTC)
 * Further to DMacks' point, a non-electromagnetic example of spectrometry is mass spectrometry, which involves measuring the charge/mass ratio of fragments of molecules. Nothing to do with light. Brammers (talk/c) 09:34, 9 April 2012 (UTC)

Could Kinect ever come with a force-feedback body suit?
I get to burn some extra calories with the XBox360's Kinect, but there's always room for improvement.

If a force-feedback body suit could make me feel (somewhat) what I see on the screen, there is potential to burn away even more of our bodily excesses. If a zombie pushes me, I would feel an extra urge to push him away, for example.

However, what technological hurdles would its developers need to overcome in order to make a viable force feedback body suit work as intended? --Tergigress (talk) 10:29, 8 April 2012 (UTC)


 * See Haptic technology for starters. SemanticMantis (talk) 12:29, 8 April 2012 (UTC)


 * There aren't really any hurdles except expense. It's already possible to get stationary bikes with force feedback.  Handgrips or gloves with force feedback could be built, but they would cost a lot, especially gloves. Looie496 (talk) 15:57, 8 April 2012 (UTC)

Why can't the Kinect recognize fingers and head movements?
I can't look up or down; only straight ahead. There are many RPG elements (yet to come?) that'll require you to nod or shake your head.

Moreover, you can imagine many games that would allow/require the use of your individual fingers. A "Guitar Hero"-style game for Xbox360s would finally teach the player how to play a real guitar without even needing a guitar-like accessory. However, the Kinect only recognizes arm movements, and not much more.

Would the Kinect only need a software patch update? Or would changes have to be made to its hardware that it would essentially take a "Kinect 2.0" to pick up the finer details of our bodily movements? --Tergigress (talk) 10:29, 8 April 2012 (UTC)


 * My understanding is that Kinect "sees you" as outlines of forms — as a silhouette — with some depth mapped on to that (it makes an infrared map like this and then creates the form map like this). It's extremely hard (and unreliable) to see things like fine head and hand movements with just silhouette. It would take significant changes to the way the Kinect worked to do these sorts of things. I wouldn't expect it as just a software patch. (And I would note that even well-informed air guitar is not really instructional for how to play a real guitar.) --Mr.98 (talk) 12:53, 8 April 2012 (UTC)


 * Its Z-resolution seems to be a bit better than those pictures suggest - check out the various things at http://openkinect.org/wiki/Gallery - the first facial animation shows (in its bottom left) the raw Kinect spacial data stream. That's pretty good, but its resolution is probably too poor to properly distinguish fingers, especially at a reasonable distance, for most angles of the hand. Given an order-of-magnitude improvement in resolution (which probably isn't unreasonable to expect in say 5 or 10 years) you could locate fingers for a guitar game pretty accurately. -- Finlay McWalterჷTalk 13:27, 8 April 2012 (UTC)


 * Try a google with 'kinect finger' and yoiu can see some videos of people experimenting with this. I guess you'd need a bit of intelligence about how fingers work as well as just detecting them to get it working really well but I don't see any great problem. Dmcq (talk) 13:42, 8 April 2012 (UTC)

which reaction formula is right?
For the reaction between aluminium and NaOH, I'm interested in knowing which of the two reaction formulae is correct:
 * the one listed here, under the "reaction of aluminium with bases" section: http://www.webelements.com/aluminium/chemistry.html 2Al(s) + 2NaOH(aq) + 6H2O → 2Na+(aq) + 2[Al(OH)4]- + 3H2(g)
 * or the one given in the Wikipedia article, Sodium hydroxide. 2 Al + 2 NaOH + 2 H2O → 2 NaAlO2 + 3 H2

They give different products and disagree in the initial amount of H2O. Katherine.J.W. (talk) 13:52, 8 April 2012 (UTC)


 * The section here, Sodium_aluminate, suggests they may both be right. --Tango (talk) 14:14, 8 April 2012 (UTC)
 * Looks like [Al(OH)4–] is just a hydrated form of [AlO2–]. As Tango's link says, there are lots of different forms possible with various numbers of "oxide" and "hydroxide" ligands depending on how much water is present (which makes sense, per Katherine.J.W's good observation that "the initial amount of H2O" is a key difference). DMacks (talk) 14:22, 8 April 2012 (UTC)

Mystery bird
I took a picture of this bird that was wading and fishing at Oyama Lake last July. The complete image is 15mp and actually has a fish jumping on the other side of the frame. I hope to upload it to wikipedia after I identify the bird. The fish is most likely a trout.--Canoe1967 (talk) 16:26, 8 April 2012 (UTC)
 * http://dl.dropbox.com/u/50919224/mystery%20bird%20close%20up.jpg


 * It is one of the Heron species. AndyTheGrump (talk) 16:30, 8 April 2012 (UTC)


 * Probably the Great Blue Heron. Mikenorton (talk) 16:31, 8 April 2012 (UTC)


 * Yup - If the 'Oyama Lake' referred to is the one in Canada, that makes sense. In Europe, one would expect to find the very similar Grey Heron, which is what I initially thought it was. AndyTheGrump (talk) 16:39, 8 April 2012 (UTC)


 * Thank you both. I should have mentioned which planet the lake was on. I am glad I didn't label it as a kingfisher before upload.--Canoe1967 (talk) 16:41, 8 April 2012 (UTC)


 * Er, yes - I don't think Kingfishers get that big. Actually, I may have a decent picture of a Grey Heron myself - or if not, I might see if I can take one to download (fairly common on the banks of the Thames above London, and in surrounding parklands etc). It would be nice to get a picture of one in flight - very distinctive. AndyTheGrump (talk) 16:47, 8 April 2012 (UTC)

I had the camera tilted approximately 40 degrees. I can't see a way to crop it decently to include the heron and fish with normal rotation. I will upload as is and get proposals and votes on the best way to fix it.--Canoe1967 (talk) 17:11, 8 April 2012 (UTC)


 * I managed to upload, but it seems the file is too large for thumbnails. I need to look into that. File:Heron and small trout.png --Canoe1967 (talk) 18:09, 8 April 2012 (UTC)
 * Changed to jpg upload. File:Heron and small trout.jpg. Where would I seek photgraphic opinions on how to fix the rotation, or is it fine as is?--Canoe1967 (talk) 18:59, 8 April 2012 (UTC)

✅ I asked for opinions in the graphics lab help area.--Canoe1967 (talk) 20:15, 8 April 2012 (UTC)

calcium metaborate
I'm trying to write a balanced chemical equation for the reaction of calcium oxide melted with boric acid to yield CaB2O4. Have I worked this out correctly? CaO + 2B(OH)3 = CaB2O4 + 3H2O. 86.7.42.12 (talk) 16:47, 8 April 2012 (UTC)
 * I hope we aren't doing your homework, but the oxygen count looks off .--Canoe1967 (talk) 17:15, 8 April 2012 (UTC)
 * Hmmm, I count seven each side? 86.7.42.12 (talk) 17:19, 8 April 2012 (UTC)
 * Yes, I corrected my above post. It has been a while since I have done those. I had problems with factoring trinomials even more.--Canoe1967 (talk) 17:26, 8 April 2012 (UTC)
 * Okay. And no, you're not doing my homework (I wish I were still that young!), especially as I think I have obtained the correct chemical equation anyway, just want to check for mistakes, like whether the charges are balanced or not.  It's been a while since I last worked with chemistry too.  86.7.42.12 (talk) 17:34, 8 April 2012 (UTC)

If I remember correctly, you just need the correct yield compounds and the element counts need to have the same totals on each side, so it does look okay in that respect.--Canoe1967 (talk) 18:04, 8 April 2012 (UTC)
 * None of the redox numbers change because this is not a redox reaction(which is what you're most likely thinking of when you asked about balancing the charges), so all you need to do is balance each side of the equation, which you've already done. So yes, this is correct as is. 112.215.36.180 (talk) 06:59, 9 April 2012 (UTC)
 * Thank you very much, that's just the affirmative answer I was looking for. I was thinking of redox numbers, yes.  86.7.42.12 (talk) 10:06, 9 April 2012 (UTC)

Why do cows eat grass?
The cows at a nearby farm seem to prefer almost anything over grass. If I bring my organic waste there, like banana skins, apple skins, even rotten vegetables, they come running to me from a great distance, eat all of it, hang around for a while (presumably hoping for more food), and then slowly retreat and start to eat their regular diet of grass.

So, why don't we feed cows with organic waste instead of grass? Count Iblis (talk) 17:50, 8 April 2012 (UTC)


 * Why do cows eat grass? Because they evolved in grasslands. AS for them eating other things, they may well enjoy it. They may well even get some benefit from it - in small quantities. I doubt that a diet consisting solely of 'banana skins, apple skins, and rotten vegetables' would be good for them. AndyTheGrump (talk) 18:01, 8 April 2012 (UTC)


 * In the same way that horses are crazy for polo mints, but you'd not want to feed a horse solely on polo mints. 46.208.224.194 (talk) 18:03, 8 April 2012 (UTC)
 * Not even a polo pony? —Tamfang (talk) 01:15, 9 April 2012 (UTC)

Cows are ruminant animals. Every part of their digestive tract - from the shape of their teeth to the chemistry of their multichambered stomach - has evolved to support eating fibrous plant matter, like grass. However, other plant matter, like fruit, grains, and oats, are acceptable in some quantity. Here's a good overview of cattle feed for small-scale beef farmers, Feeds and Feeding for Junior Beef Cattle Projects, from the extension program of the Animal Science department at Texas A&M - you'll hardly find a more expertly qualified organization than that to explain cattle nutrition! In addition to grass and roughage, cattle need minerals, vitamins, and nutrients that are normally provided by oats and alfalfa, and other products; apples and fruits are acceptable supplemental sources, too, but tend to be too expensive for large-scale feeding. Nimur (talk) 18:23, 8 April 2012 (UTC)


 * We don't feed cows with grass either, rather, with corn, according to The Omnivore's Dilemma. → Σ  τ  c . 20:07, 8 April 2012 (UTC)


 * Pasture fed cattle obviously eat other stuff too. Grass is sucessful because it tolerates grazing well + the cows/other grazers eliminate the grass's potential competition from other sapling plants that could grow up to shade out the grass. Sky Machine   ( ++ ) 23:55, 8 April 2012 (UTC)


 * Here in the UK, (and a lot of other countries) we got into a lot of bother by feeding cows on bits of other dead cows. Alansplodge (talk) 01:25, 9 April 2012 (UTC)


 * Cows are probably similar to primitive man, who had to subsist mainly on low-calorie veggies and grains. When they got something better, like fruit or meat, they were probably quite grateful, too. StuRat (talk) 01:20, 9 April 2012 (UTC)


 * As Nimur says above, the insides of cows are designed to eat grass and similar stuff and quite different from ours. Alansplodge (talk) 01:27, 9 April 2012 (UTC)


 * The similarity isn't in the actual diets, but that the majority of the diet of both cows and primitive humans was one thing, while both craved "treats" to supplement their meager diets. StuRat (talk) 02:10, 9 April 2012 (UTC)


 * Something I read long ago, so needs verification. I have heard that too much of very sweet or starchy foods can make cows and pigs ill by causing rapid fermentation in their guts leading to acidification and gas buildup. Staticd (talk) 06:00, 9 April 2012 (UTC)
 * See Bloat. 110.151.252.240 (talk) 21:08, 11 April 2012 (UTC)

Bayes' theorem in medical diagnostics
I'm trying to get a grasp on how Bayes' theorem can be applied to updating prior probabilities in medical diagnostics. In this context, Bayes' theorem could be written:


 * $$P(SomeDisease|PositiveTest) = \frac{P(SomeDisease) \, P(PositiveTest | SomeDisease)}{P(PositiveTest)}. \,$$

My understanding is that $$P(PositiveTest|SomeDisease)$$ is the diagnostic sensitivity of the test, and $$P(SomeDisease)$$ is the doctor's prior probability of the patient having the disease in question. I'm having problems, however, in interpreting $$P(PositiveTest)$$. Which probability should be entered here? The probability that any random person in the community that the doctor serves has a positive test, whether they have the disease or not? This doesn't sound right, as the doctor must have taken other information, such as the symptoms, age and sex of the patient into consideration, when assigning a prior probability. So, what probability, exactly, should be entered here? I am aware of the article Likelihood ratios in diagnostic testing, this question specifically concerns the use of Bayes' theorem. Thanks! --95.34.141.48 (talk) 20:17, 8 April 2012 (UTC)


 * $$P(SomeDisease)$$ is the probability that someone in a particular group has the disease. $$P(PositiveTest)$$ is the probability that someone in that same group (regardless of their disease status) tests positive. Both would be based on observed frequencies within that group. What group? It could be all the patients tested during the development phase of the test (good because it gives a large sample, making for a more accurate probability), or it could be all the patients that the doctor has ever given the test to (good if test results vary by geography etc, but bad if it results in poor accuracy of probabilities due to small sample size), or it could be all the patients of particular age, sex, and symptoms that this doctor, or doctors in general, have ever given the test to. But everything in the formula has to refer to the same one of those groups. Choosing a group depends on how good the measured probabilities are as estimates of the true underlying probability, which depends on sample size, and on how much difference it is thought to make if you limit yourself to sub-groups with particular characteristics. Duoduoduo (talk) 20:54, 8 April 2012 (UTC)


 * Thanks! That was really helpful. Would the following statement be both a correct interpretation of your answer, and correct (albeit pedantical) mathematical notation?


 * $$P(SomeDisease|PositiveTest,X) = \frac{P(SomeDisease|X) \, P(PositiveTest | SomeDisease,X)}{P(PositiveTest|X)}. \,$$


 * Where $$X$$ is the information that the patient belongs to a subgroup within the doctor's practice, that the doctor would test for the disease, for whatever reason. If the doctor is not doing a clinical study, the doctor's suspicion of the patient having the disease, or the patient's fear of having the disease, could be such reasons. --95.34.141.48 (talk) 05:52, 9 April 2012 (UTC)


 * Yes, that's right, everything conditioned on X. The problem with choosing X to be all people who this doctor has ever suspected of having the disease is that you probably don't have good data on the percentage $$P(SomeDisease|X)$$ of them who actually had the disease -- maybe all you have is the percentage $$P(PositiveTest|X)$$ who tested positive. Also you probably don't have $$P(PositiveTest | SomeDisease,X)$$ since the doctor probably has not tested everyone in X for the disease by all possible means. So it seems to me that one has to go with data from clinical studies. Duoduoduo (talk) 15:10, 9 April 2012 (UTC)


 * Thanks again! I know of course the necessity for data from clinical studies, but I am pursuing my reasoning in order to understand exactly what is going on. Therefore: would it help if I defined $$X$$ as the subgroup of patients in the doctor's practice who ever contacted the doctor with a problem that led the doctor to perform the test? If the doctor had a suitable database of all his patients, lab-tests, and results, $$P(PositiveTest|X)$$ could be calculated directly from the data, by dividing the number of positive tests by the total number of tests performed (granted, you would have to figure out how to handle repeated testing of the same patient). When clinical studies calculate diagnostic sensitivities, and these are used for calculation of likelihood ratios for updating prior probabilities etc., it appears to me that there is an implicit assumption being made:


 * $$P(PositiveTest|SomeDisease,X) \approx P(PositiveTest|SomeDisease,Y)$$
 * $$ \approx P(PositiveTest|SomeDisease) \approx Sensitivity$$,


 * If we then interpret $$P(SomeDisease|X)$$ as the doctor's pre-test probability of the patient having the disease, and $$P(SomeDisease|PositiveTest,X)$$ as the doctor's post-test probability of the patient having the disease, we end up with


 * $$P_{posttest} = \frac{P_{pretest} \times Sensitivity}{P(PositiveTest|X)}. \,$$


 * I understand, of course that these are approximations, but are there any really serious flaws in this reasoning? --95.34.141.48 (talk) 19:20, 9 April 2012 (UTC)


 * I'm not sure why you think that those approximations are implicitly being used. Suppose there's a test for heart disease. Presumably in the clinical trials if they report $$P(PositiveTest|SomeDisease,male)$$ then the sensitivity was measured separately for males and is not being approximated by the unconditional $$Sensitivity$$ or by a sensitivity conditioned on some other category Y. And on the other hand if all they report is a sensitivity conditioned on no special group, then what X means in $$P(PositiveTest|SomeDisease,X)$$ is simply the group "all people". In any event, your last equation is right provided all things including Sensitivity are conditioned on the same X. If the doctor had sufficient data about his own patients, then this X could be his own patients, or it could be his own male patients, etc. Duoduoduo (talk) 20:00, 9 April 2012 (UTC)


 * Thank you! Your responses have been very clarifying. Much appreciated! --95.34.141.48 (talk) 20:40, 9 April 2012 (UTC)

You can simply expand this probability:
 * $$P(PositiveTest) = p(SomeDisease) \, p(PositiveTest | SomeDisease) + (1 - p(SomeDisease)) \, p(PositiveTest | Not \, SomeDisease)$$

Icek (talk) 15:18, 9 April 2012 (UTC)
 * Thanks for your reply! See also Duoduoduo's replies above. It turns out that the $$P(PositiveTest)$$ term is particularly problematic, because it depends strongly on the prevalence of the disease in the doctor's practice, and also strongly on the doctor's tendency to have (unnecessary) tests being performed, "to be on the safe side". It turns out that this problemtatic term cancels out when Bayes' theorem is transformed into its Odds version, Bayes' rule. I was confused because (1) I hadn't read that article, and (2) the articles Likelihood ratios in diagnostic testing and Pre- and posttest probabilities treat likelihood ratios only in the context of dichotomous variables. See my question about this on the maths desk, and Meni Rosenfeld's reply that an approach using likelihood ratios with continuous variables is perfectly valid. So I'll experiment further with that approach. I'll be back with more questions if I run into further hurdles! --95.34.141.48 (talk) 16:03, 10 April 2012 (UTC)

Group 14 electronegativities
Why doesn't this group show any EN trend? Could someone give a detailed answer?--R8R Gtrs (talk) 20:32, 8 April 2012 (UTC)
 * Electronegativity is determined in a relative sense with all methods other than Mulliken. It's estimated as one of many contributing factors to the energy difference between products and reactants in different reactions. In other words, determining it is not an exact science. Not all of the groups give perfect patterns as the graph shows.[[Image:Periodic variation of Pauling electronegativities.png|thumb|300px|right]]. From the article on electronegativity; The anomalously high electronegativity of lead, particularly when compared tothallium and bismuth, appears to be an artifact of data selection (and data availability)—methods of calculation other than the Pauling method show the normal periodic trends for these elements. 112.215.36.180 (talk) 07:34, 9 April 2012 (UTC)
 * Sorry, but this is not really helpful. (Also, I'm talking about differences here--lower or higher is a difference issue) The Al-Ga, Si-Ge, etc. upturns can be explained (I guess) by the affect the new d-shell causes, but I don't have a systematic knowledge on this, and would love to find out more. About lead: I read that text as well. And this does not explain where does the Pauling Sn-Pb upturn comes from, which must be important. Pauling Pb figure (2.33) is greater than those of Bi, Po, and At; that's noticeable.--R8R Gtrs (talk) 12:44, 9 April 2012 (UTC)
 * The value 2.33 is for Pb(IV): the Pb(II) value is 1.87, which follows trends. Only for Tl and Pb do different oxidation states of the same element have vastly different electronegativities. Double sharp (talk) 10:30, 18 July 2014 (UTC)

A few questions from a science fiction author: Lethality of small amounts of high explosives and theoretical weapons systems
I'm currently working on a book for an RPG game developer that's in their "wish list" category, I dislike pure "pie in the sky" science fiction: I want my creation to be at least plausible.

One idea that has always intrigued me is the idea of a "utility launcher" weapon, based on the dizzying array of shotgun shells and grenades manufactured, especially the myriad special shells (flechette, HE, smoke) proposed for the Jackhammer automatic shotgun. My idea is that given the tactical adaptability needed of a 22nd century soldier (engaging rioting civilians, lightly armed insurgents, powered armor equipped enemy heavy infantry, light vehicles, etc) a common solution is a large-bore (perhaps 30-40mm) low-velocity pistol or rifle railgun. In this publisher's settings power cells have put energy levels capable of fueling a railgun in common use. The standard D-sized battery carries 180,000 KwSec of energy, as an example.

My question is threefold: First of all how practical would such a weapon system be? Would there be special challenges faced? Would they make conventional weaponry obsolete or would they be used as a side-arm in addition to a main battle rifle firing a round more like what we're used to seeing (for example a 5-8mm railgun main battle rifle)? Secondly: How much damage would a 30-40mm sphere of high explosive do? Would it be lethal enough to justify its use? What might it's kill/wound radius look like? For this I think we can assume advances in chemistry would produce an explosive 10-30% more powerful than hexogen Third: What sorts of rounds would a common soldier be issued? Obviously HEAT and HESH are likely, perhaps smoke and distraction device. Non-lethal stingball and CS rounds are other obvious possibilities, but one complaint I have with sci/fi is that there are often many advanced weapons but writers rarely look at theoretical grenades/explosives, except maybe plasma. I see no reason why they wouldn't advance along with the weapon technology. HominidMachinae (talk) 23:46, 8 April 2012 (UTC)


 * Are you thinking of something like the Milkor MGL? Alansplodge (talk) 01:04, 9 April 2012 (UTC)
 * In all honesty the fictional underpinnings of my idea come from the Scorpion pistol in Mass Effect 3 and the Pancor Jackhammer (which I consider fictional since fewer than 20 were ever made). I envision something like the sawn-off Vietnam Era variant of the M79_grenade_launcher or the XM29 HominidMachinae (talk) 02:08, 9 April 2012 (UTC)


 * The US military is already looking at explosives 28% more powerful than hexogen, so it wouldn't be unreasonable to assume that something 100% or even 200% more powerful will become available by the 22th century.
 * I really like your grenade idea. A bunch of army guys had similar ideas back in the 90's and that's how the OICW project started. 20 years later two countries are fielding (US and South Korea) computerized air burst grenades. My speculation is that these computerized grenades will gradually gain new capabilities as technology evolve and eventually become "smart grenades" that can automatically identify threats, change trajectory in mid-flight, and perhaps even switch between HE and HEAT right before impact. Just to throw some wild ideas around: sub-munitions, spherical/cylindrical grenades that can roll toward targets after landing, grenades that can turn into mines. You might also want to take a look at what other sci-fi authors came up with w.r.t. grenades:Anonymous.translator (talk) 02:17, 9 April 2012 (UTC)
 * I assume that all rounds will have a dual-use proximity switch based upon capacitance: just like the touch screen of a modern smartphone they'll know if what they stuck to is humanoid (and thus use an instant fuze) or inanimate (and thus use a proximity fuze based on capacitance), in essence they work like a very lethal Theremin. As to what other sci-fi authors have done, usually they stick to modern explosives when offered a choice of grenade, otherwise they go to using a plasma grenade.  Even settings in the far future such as Mass Effect or Halo use either fragmentation grenades much like those used since the 1800s or "Plasma" as the default "sci/fi sounding" grenade type.  I hope for a more realistic interpretation. HominidMachinae (talk) 05:17, 9 April 2012 (UTC)
 * My last sentence was actually directing you to this website with Tom Clancy's ideas about some interesting grenade rounds. I agree with you that most sci-fi books and games just keep the same old WWII-era frag grenades and make the explosion blue or something. But I guess game makers can't really put self-guided grenades in because it doesn't require player skill and might unbalance the game. Anonymous.translator (talk) 07:01, 9 April 2012 (UTC)


 * I wonder why you would only have 30% more powerful explosives. You have 180 MJ per D-sized battery (56.5 cm3), in other words 3.186 MJ/cm3 for your source of electricity. Hexogen has a heat of detonation of 83.82 kJ/mol, which means 377 J/g, which means an energy density of 687 J/cm3. Of course there are materials with much higher heats of reaction around (which do not detonate, e.g. thermite has about 17 kJ/cm3), but if you get up to 3.186 MJ/cm3, I'd really expect to see explosives much more powerful than hexogen. Icek (talk) 15:05, 9 April 2012 (UTC)


 * According to this D cells can only manage 75 KJ. The "standard" non-alkaline version only 18 KJ. A 180 MJ energy cell could drive a car at full throttle for over 20 minutes. Although I suppose it's not impossible for the standard D-sized battery to store 180 MJ in the 22nd century and be able to release it quickly and slowly that you can also plug into a gun, though it probably won't run on electrochemistry, right? Sagittarian Milky Way (talk) 23:33, 9 April 2012 (UTC)


 * The energy per atom would be at least a few thousand electron volts, so it would probably be nuclear. But I would still wonder why this couldn't be used as an explosive... it cannot be simply radioactive decay (which is used in RTGs) because you can release the energy relatively quickly. So if you can speed up the reaction, why can't you make it fast enough to get an explosive? The nuclear reactions themselves usually happen very fast. Icek (talk) 00:31, 10 April 2012 (UTC)


 * I personally think a 180 MJ battery is silly, but I am writing for a published game system that specifies that at near-future tech level that is what the batteries carry. It gets really silly when you have said battery powering devices that seem to be less deadly than simply shorting the battery.  But that's what the publisher's setting says, I'm bound by it.  HominidMachinae (talk) 04:23, 10 April 2012 (UTC)


 * Here is a 40mm hand grenade (pic). Also, I'm amused by your idea that if fewer than 20 of something was produced then it's fictional; won't the Space Shuttles be surprised!
 * I should point out that I consider speculation on the implications of wide use of the Pancor as well as its hypothetical, proposed-but-never-made, ammunition types as the realm of fiction, not the weapon itself. Sorry for any confusion. HominidMachinae (talk) 04:20, 10 April 2012 (UTC)

A couple of comments on your first question. The biggest issue I see is with the size of the ammunition. A 30-40mm shell is, obviously, 30-40mm in diameter. That limits your ammo capacity and makes the weapon pretty large. You ask about a handgun/side arm, but either of the current magazine designs (hand grip clip or revolving cylinder) become unwieldy with such large rounds. One possibility is something like what Metal Storm developed, where the rounds are carried stacked inside an interchangeable barrel. Your soldier could carry several barrels for a side arm, each loaded with rounds for a different environment. I'm not sure how well magnetic acceleration would work with a barrel like that, but if you can make 180 MJ batteries, miniature super conducting magnets should be simple.

As for rounds, a couple of other ideas: Continuous-rod warhead, Top attack charges and thermobaric are all modern warheads that are used on larger missles, but not IFAIK grenades. As was mentioned above, computerized air burst grenades are in development now, so something like steerable munitions or even autonomous guided grenades which search for the largest threat, select the correct warhead (HE/HEAT) and steer to engage the threat, are possible. What about a Kinetic Energy round (though I guess you'd need a rocket motor to pick up speed, since the recoil would be too great for a pistol/rifle). For non-lethal, how about glue traps or wire obstacle for inside buildings or cameras that either stick to buildings or can be launched on a ballistic arc for reconnaissance. Tobyc75 (talk) 15:13, 11 April 2012 (UTC)