Wikipedia:Reference desk/Archives/Science/2010 May 11

= May 11 =

Minimum energy for brute force attack
In the article for Brute force attack it says

The so-called Von Neumann-Landauer Limit implied by the laws of physics sets a lower limit on the energy required to perform a computation of ln(2)kT per bit erased in a computation, where T is the temperature of the computing device in kelvins, k is the Boltzmann constant, and the natural logarithm of 2 is about 0.693

So how can the minimum energy required be 0.693? 0.693 is just a number. Shouldn't it has a unit of J? 139.130.1.226 (talk) 00:22, 11 May 2010 (UTC)


 * The Boltzmann constant has units of J K−1. Looie496 (talk) 00:27, 11 May 2010 (UTC)


 * Also, it is easy to see that this limit can be violated, so it is not a fundamental limit at all. Count Iblis (talk) 01:40, 11 May 2010 (UTC)
 * That paper seems like a meaningless moving of the goalposts. If their bit reservoir is thermal then their bit-clearing protocol doesn't work. Whatever is forcing the reservoir into a non-thermal state ought to be treated as part of the system. To put it another way, a reservoir of N bits each with an independent probability p of being zero contains N (1 + p log p + (1−p) log (1−p)) bits of known value. Their "erasure" protocol swaps the memory bit with a known bit from the reservoir, which just foists the erasure off on whatever device is replenishing the known bits in the reservoir. (And if nothing is replenishing the bits then the reservoir might as well be treated as part of the demon's internal RAM.) The only way to get p ≠ ½ in a thermal state is to have an energy difference between 0 and 1, which takes us back to square one. Maybe I'm missing something. -- BenRG (talk) 08:42, 11 May 2010 (UTC)


 * I'm not a mathy guy but it seems to me you are completely misreading the sentence. It's saying that "the natural logarithm of 2 is about .693". Which is true. It's not saying that the total energy required is .693; it's still defining all of the variables. The next sentence discusses the actual energy that this equation would imply (in joules and gigawatts and etc.). --Mr.98 (talk) 13:27, 11 May 2010 (UTC)

Help required with this code
Hey! Can anyone please explain me this matlab code for uniform quantization?

Thanks in advance.--111.68.97.146 (talk) 04:11, 11 May 2010 (UTC)


 * I've taken the liberty of formatting your source-code as MATLAB code and fixing some mis-leading indentation. This code runs two separate trials, with 5 and 6 quantization intervals, seeking to quantize a function.  It appears that the quantization intervals are designed to be non-uniform width - but uniform in the number of inputs that get binned into that interval, based on an input probability distribution function.  The code then demonstrates this by computing the quantization intervals (results are stored in the vector c), and applying it to quantize the input function, then plotting the results.  Such quantization (with non-uniform intervals) makes optimum use of the number of bits stored, but at the expense of complexity and (deliberate) variable precision of each interval.  The hard part was noting what "uniform" refers to.  In this case, what is uniform is not the width of the interval, but the probability that a given input will bin into that interval. Nimur (talk) 10:35, 11 May 2010 (UTC)

Lasso Physics
Okay, so this is a homework question, but I've managed to get an answer myself that I wanted to confirm here. If I'm wrong, then hopefully you can identify where I made my error. The question goes as follows:

A thin loop of mass M and radius R is suspended from a string through a point on the trim of the hoop (the setup looks like a lariat trick/lasso). If the support is spun with a high angular velocity ω, the hoop will spin with its plane nearly horizontal and its center nearly on the axis of the support (the support here refers to what the string is attached to). The sring makes an angle α with the verticle.
 * (a) Find approximately the small angle β between the plane of the hoop and the horizontal.
 * (b) Find approximately the radius of the circle traced out by the center of mass around the vertical axis.

Here are the answers I found. If I'm wrong, let me know and I'll provide my reasoning so that you can perhaps let me know where I've made any incorrect assumptions. For (a), I got β = g/(Rω2), and for (b) I got r = √(Mgtanα/ω). 173.179.59.66 (talk) 07:21, 11 May 2010 (UTC)


 * Can you clarify what you mean by "the support is spun". Do you mean the support is twisted like a drill? And the whole setup is rigid? Or do you mean spun like a lasso is spun - i.e. the loop makes a circle, and the string (support) traces out a cone shape? Ariel. (talk) 09:43, 11 May 2010 (UTC)
 * The former, but the cone opens downward. 173.179.59.66 (talk) 16:08, 11 May 2010 (UTC)
 * Upon further reflection I believe the answer to (a) may be β=g/(Rω2 - gtanα). 173.179.59.66 (talk) 21:23, 11 May 2010 (UTC)

Can a continent be subducted?
Is it possible for one continent to be subducted beneath another? As far as I can tell from Geology of India, India has slowed down a lot since colliding with Asia, but what will is likely to happen in the future? Will it simply stop eventually or end up disappearing altogether? I've checked plate tectonics, plate reconstruction and obduction but can't find any information. Continental collision looks to be the place to look but doesn't make it clear what the ultimate fates of the continents are. 131.111.30.21 (talk) 09:17, 11 May 2010 (UTC)
 * JuandeFucasubduction.jpg
 * Usually, oceanic crust subducts, because it is denser than continental crust. In the case where two continental crust zones are colliding, as in India, the two plates have comparable density, so neither is "easily" forced down relative to the other.  Eventually, given enough geological time, it seems plausible that some continental crust might be forced downward, but it would be a lot messier, with more deformation of both plates, than your typical picture of a nice, contiguous sheet as you see in the classic diagrams.  In the short term, the deformation of the plates results in the Himalayan orogeny zone - more of an inelastic deformation of both plates than a clean subduction.  Nimur (talk) 09:34, 11 May 2010 (UTC)
 * Followup - this letter from the journal Nature, The possible subduction of continental material to depths greater than 200 km (2000), puts a little bit more quantitative spin on the problem. The continental crust has to overcome a density gradient, so it can only be forced downward if the collision gives enough energy and downward momentum to the continent to overcome its buoyant force.  (The momentum-, energy-, and time-scales for these sort of inelastic collisions are all huge).  This letter indicates some geochemical and mineralogical observations that might put some bounds on how deep continental crust can be forced down.  They claim continental crust has been subducted to depths of "150 km", and up to 300 km using "indirect observations".  This paper,  The Himalayan Arc: large-scale continental subduction, oroclinal bending and back-arc spreading (1986), which I'm having a hard time finding a PDF of, might be of interest.  They seem to suggest that paleomagnetic data indicate a rotation and subduction of the entire Indian subcontinent.  This paper,  Cenozoic Volcanism in Tibet: Evidence for a Transition from Oceanic to Continental  Subduction, presents geochemical evidence for subduction.  They present the idea that, in India, the only two ways to relieve the strain are continental subduction (India goes under Asia), or convective thinning (India "melts" from the bottom up, and its continental crust is slowly absorbed back into the asthenosphere). Their claim is that the geochemical evidence suggests subduction.  Nimur (talk) 09:39, 11 May 2010 (UTC)
 * Cheers for that, one reason I was asking was because I wondered if any continents have disappeared in the past - reconstructions of plate movements often look like they have big gaps in them making me wonder if other continents have been subducted, taking all their fossils with them. I guess we'll never be able to tell. Try this DOI link it gives me a pdf of the paper you couldn't find. Gotta love that someone modelled the collision with plasticene! 131.111.30.21 (talk) 10:25, 11 May 2010 (UTC)
 * I know that I'm a bit late onto this but, anyway. Most continent-continent collisions involve at least short-lived subduction of continental crust, the leading edge of a continent may go down to quite impressive depths but they can't stay there due to their relative bouyancy. In the Western Gneiss Region of Norway, there are areas of continental crust that are exposed at the surface now but contain eclogites, with inclusions of coesite and diamond. These indicate that this particular chunk of continental crust went down at least 80 km during the Caledonian orogeny. There is still a lot of uncertainty about exactly how it returned to the surface, but it rose quickly back up through the mantle (at fairly constant temperature) before being progressively exhumed during Basin and Range style extension. This recent paper goes it into a lot more detail than you probably need but it addresses the general problem of how to get continental crust so deep and then how to get it back to the surface. Mikenorton (talk) 22:50, 13 May 2010 (UTC)
 * Awesome, Figure 2 seems to show that large chunks of continental crust can definitely be subducted then, even if some remnants survive in a highly altered state. What could have been very useful fossils must have been destroyed, what a shame! 131.111.30.21 (talk) 09:08, 14 May 2010 (UTC)

I, Ant
I've been killing a lot of ants recently. A) Are ants certain to be too tiny-brained to have any sense of self? B) Would a modern computer be capable of mimicing an ant brain in real time? Although I expect the ant-brain circuitry has not been perfectly mapped yet. 78.146.87.143 (talk) 11:26, 11 May 2010 (UTC)
 * List of animals by number of neurons says that ants have 10000 to 100000 neurons, certainaly a modern PC could do a fair job of simulating that --Digrpat (talk) 11:41, 11 May 2010 (UTC)
 * Brains are funny things. So funny that there are guidelines as to what does and what does not deserve the moniker, and the central control of insect nervous systems are called ganglia as opposed to a brain for a reason.  I don't have first hand knowledge of every organism type, but I believe that invertebrates as a group are said to have ganglia as opposed to brains -- this could very well be incorrect, though.  It's likely that rules and regulations of what we term psychology do not traverse into the realm of invertebrates in any sense other than instinct and the like (except for some exceptions, such as high level cephalapods, etc.)  DRosenbach  ( Talk 11:54, 11 May 2010 (UTC)
 * It might be possible with the computational power we have (but keep in mind that a neuron is more complex than a node in an artificial neural network), but I've never heard of any research that has even started mapping out insect central nervous systems (I bet this is because it's impossible with current technology), and we understand so little about the way that brains work that simulating an ant is an impossible dream for now. Paul (Stansifer) 14:00, 11 May 2010 (UTC)


 * Any animal that is physically capable of biting itself (as an ant is) needs to have enough self-recognition to prevent that from happening. Ants can do a lot more than that:  they can distinguish ants belonging to their own colony from ants belonging to other colonies.  The ant system for passing chemical messages is quite sophisticated.  Their brains are small but they pack a lot of computation into that tiny space. Looie496 (talk) 14:56, 11 May 2010 (UTC)
 * When we think of how to get a universal computer to do something like determine when not to bite something, or how to distinguish some detected creature from another, it often ends up being very hard to do. Now consider if you had to make a device that wasn't universal, but instead had only one task to do (like tell you if a room is light or dark).  This sort of specialized device can exist in nature, too, so it's not always fair to compare a computer to anything that demonstrates some level of intelligence.  Consider, as a more direct example, the recent work being done on calculations at the atomic level: this article is about how we can use an iodine molecule to perform a fairly sophisticated math equation in a very short amount of time.  Are we going to replace a general purpose CPU in a computer with a single iodine molecule any time soon?  Its utility, while amazing, is incredibly narrow. --Jmeden2000 (talk) 15:27, 11 May 2010 (UTC)


 * As to A, it's really not possible to say without you yourself being an ant. They do not take kindly to harassment though, so I think that qualifies them for (very tiny and minor) personhood. Vranak (talk) 15:21, 11 May 2010 (UTC)


 * One method used to see whether something has a sense of self is to show it a mirror - if it recognizes that this is a reflection then this is meant to be proof that the creature has a sense of self (rather than the more obvious proof that the creature has a sense of 'mirrors'). Do this with ants. If they can't recognize themselves, stomp away! :) --  KägeTorä - (影虎)  ( TALK )  15:50, 11 May 2010 (UTC)
 * That seems like a rather limited assessment. Apparently blind people have no sense of self, either! --Mr.98 (talk) 16:37, 11 May 2010 (UTC)
 * The actual experiment that KageTora is referring to here is a lot more complex than that - but it's certainly flawed. Animals like Bats that "see" with sonar may well not recognize that they are even looking at a bat because it has the wrong three dimensional curvature, etc.  Dogs are often the same - most (but not all) dogs are really unimpressed by their own reflection in a mirror...presumably because it doesn't smell anything like a dog.  On the other hand, birds are completely taken in by mirrors - we had a Red Cardinal in our backyard a few years ago who evidently thought that his own reflection was another male impinging on his terratory - and spend weeks and weeks battering himself against the window trying to scare himself off.  If the reaction to the mirror itself is so variable, it's hard to say that an ant that fails the test is somehow lacking a sense of "self" - when the lack of pheromones coming from the reflection mean that the reflection doesn't seem like an ant at all - self or otherwise.  It would be like saying that humans are not self-aware because we cannot recognize the smell from a vial of our own sweat as being our own...a dog would find that test pretty convincing! SteveBaker (talk) 17:04, 11 May 2010 (UTC)
 * Exactly the point I was trying to make - that the mirror experiment is designed from a very human perspective and cannot tell us much if anything about the existence or lack of a creature's sense of self. --  KägeTorä - (影虎)  ( TALK )  17:22, 11 May 2010 (UTC)
 * Just FYI, it would seem that the European Magpie (ref in article) is aware that the bird in the mirror is its own reflection. I'm not exactly sure if it's the same for some of the larger parrot species (e.g. macaws, African Greys) - but some of them do certainly seem to become aware with time that the reflection is not another bird - in a way that say, Budgerigars or Cockatiels do not. --Kurt Shaped Box (talk) 17:19, 11 May 2010 (UTC)


 * E.O. Wilson's recent piece in the New Yorker, "Trailhead" explores, to some extent, the question of what ants "think" about. It's labeled as a work of fiction, appropriately, but given that Wilson is probably the world's foremost expert on ants, it is safe to assume that it is rooted pretty heavily in fact. His ant is basically a "programmed" creature—it does not think in a way that is analogous with humans (or mammals), though it is not "dumb". I don't know what a "sense of self" is supposed to mean in a scientific setting but I don't see much evidence for ants having one. They are instinctual automatons, albeit ones that can learn and do rather complicated things:.
 * If the Trailhead Colony could not understand the history of its own species, how much did it understand of its current condition? How could it make the right decisions for survival? In fact, the Trailhead Colony knew a great deal. Worker ants are far more than automated specks running around on the ground. Even with a brain one-millionth the size of a human’s, an ant can learn a simple maze half as fast as a laboratory rat, and remember the directions to as many as five different destinations when she forages away from the nest. After exploring a new terrain, a worker can integrate all the seemingly haphazard twists and loops she made and, amazingly, return to the nest in a straight line. She can learn and recall the special odor of the colony to which she belongs. The Trailhead Colony, when all the learning and thought of its workers came together, was very smart, by insect standards—and, with the unifying power of its Queen lost and its population growth plummeting, it needed to call on that group intelligence to regain its balance.
 * Which goes along with a lot of what Wilson has long said about ants—the colony, taken as a superorganism, is really the unit to be worried about, not the individual ant. --Mr.98 (talk) 16:37, 11 May 2010 (UTC)


 * Better yet, consider the whole ant colony as a being. An individual ant is just a cell of it: drop a chemical that means "I'm dead" on one ant, and all the others will quickly carry it out to the "burial place/dump". It hurries back to the nest, and the whole process is repeated again and again, the carriers never realizing that the kicking and is not quite dead. I doubt that individual ant are capable of learning anything. I'm curious weather someone can give counterexamples. --131.188.3.20 (talk) 17:10, 11 May 2010 (UTC)


 * I am getting the sense that underneath a lot of this discussion is a desire to throw all of ant-kind into the bin marked 'unremarkable', 'unworthy' and the like. Well I for one think they are pretty cool creatures, and would not advise harming them out of hand. At least not the innocent small black kind we get in the Pacific Northwest. Fire ants, bullet ants, and so on -- different story perhaps. Which leads me to ask 78 - are the ants bothering you by their presence alone? Is it an inherent dislike? Or are they making predations onto your territory? Eating your precious sugar, burrowing into the woodwork and so on? Vranak (talk) 18:02, 11 May 2010 (UTC)


 * It's remarkable how these sorts of discussions tend to evolve. The OP asks whether ants might have a sense of self, and a dozen replies later, without the OP having said anything more, they are being accused of disliking and disrespecting ants. Looie496 (talk) 18:25, 11 May 2010 (UTC)


 * Well he says he's been killing a lot of them lately. If that's not disrespect, well I guess it's sheer indifference. Vranak (talk) 18:28, 11 May 2010 (UTC)

Fox's diet
Do foxes eat weasels?Jameslpeterson (talk) 11:28, 11 May 2010 (UTC)
 * Weasels' main predators are raptors, but foxes would eat weasels.  DRosenbach  ( Talk 11:56, 11 May 2010 (UTC)

Pitta bread and heat
Why is pitta bread so hot to the touch after coming out of the toaster? I'm assuming it has something to do with the air pocket inside it, but would like a proper explanation. Your regular slice of toast, for example, doesn't even get remotely near as hot. Hammer Raccoon (talk) 12:59, 11 May 2010 (UTC)
 * The air pocket sounds reasonable. I'd also think the texture and density have a lot to do with it.  Pita bread is denser than standard toast (thus carrying more energy at a given temperature), but perhaps more importantly, has a reasonably solid surface.  When you pick up a piece of toast, most of the surface is actually exposed air pockets, which can quickly cool (and which make a good insulator anyway).  Contrast with pita, where all you touch is hot bread. &mdash; Lomn 13:20, 11 May 2010 (UTC)
 * Mostly agree with Lomn, but also consider that steam will get trapped inside those air pockets, while toast's open structure will allow more of the steam to escape. Same mechanism, it's just that steam holds an awful lot of heat. Matt Deres (talk) 13:31, 11 May 2010 (UTC)

In addition to more moisture in the pita. A pita is also much denser than a piece of white bread. the more holes the more heat dissipates quicker. The denser it is the more heat it retains.165.212.189.187 (talk) 14:24, 11 May 2010 (UTC)


 * Before jumping to a conclusion about steam, I'd like to pose a question &mdash; is the pita hotter, or does it just seem hotter? In other words (and Lomn's implicitly response touched on this) is there a difference in the heat conductivity and heat transfer properties of pita bread versus regular toast?  If the pita can transfer energy to your fingers more rapidly (due to greater density, differences in water content, more surface in contact with your skin, or what-have-you) it will feel hotter even if it is at the same surface temperature as the toast.  Consider the perceived 'hotness' of the air in an oven with the perceived temperature of a metal rack inside the oven &mdash; similar temperature, but very different heat transfer properties.
 * Incidentally, if you're curious about the effects of the air pocket inside, you can repeat the experiment with the pita sliced in half (across its diameter) so that the inner pocket is unsealed. TenOfAllTrades(talk) 14:27, 11 May 2010 (UTC)

Read our articles on specific heat and humours. I am not going to put two and two together for you, for fear of angering the locals, but if you reflect on what emotional personality a representative sample of a cross section of Americans are statistically likely to attribute to an anthropomorphic cartoon representation of pita bread and a piece of toast, respectively, and how this relates to the two articles, I think you will find yourself no nearer to, and perhaps even inexorably estranged from the answer you seek. 92.224.204.126 (talk) 14:34, 11 May 2010 (UTC)
 * ... what? Nimur (talk) 10:32, 12 May 2010 (UTC)


 * My experience is that when you pick up a toasted pita, it's hard to avoid squeezing it a bit, which causes steam to come out, and it is the steam that burns you if you aren't careful. Looie496 (talk) 14:59, 11 May 2010 (UTC)

The flat surface of pita transfers heat efficiently to your fingertips, especially since heat causes a little vegetable oil to migrate out to the surface. Vranak (talk) 15:19, 11 May 2010 (UTC)

Thanks for the responses everyone! Very informative. Hammer Raccoon (talk) 17:25, 11 May 2010 (UTC)

Giant King Grass
when i search for giant king grass, the article under wikipedia does not appear but a totally unrelated article. —Preceding unsigned comment added by 75.172.158.69 (talk) 13:25, 11 May 2010 (UTC) :The help desk might be a better place to ask your question. --Chemicalinterest (talk) 13:34, 11 May 2010 (UTC
 * Giant King Grass is a red link. Page 8 of this presentation says that China Giant King Grass is a hybrid between elephant grass and another grass. Miscanthus giganteus is also a hybrid between two species, but I'm not sure if it shares all the characteristics in the presentation about CGKG. If someone can find more information (there is none on google scholar) a redirect should be made to a relevant article (maybe just to Miscanthus if nothing else can be found. 131.111.30.21 (talk) 14:41, 11 May 2010 (UTC)
 * This says that Giant King Grass is a trademark, that's why we won't be able to find out what actual species it is a hybrid of. Probably shouldn't have an article yet as most info looks like press releases but maybe a redirect to Miscanthus wouldn't go a miss. 131.111.30.21 (talk) 14:48, 11 May 2010 (UTC)

Giant King Grass appears to be a hybrid of Pennisetum purpureum and another unrevealed species. The developers of it are purposefully vague about the "other grass" that contributes to the hybrid, probably to try to protect their commercial IP. Miscanthus x gigantueus is a naturally occurring hybrid between Miscanthus sinensis and Miscanthus sacchariflorus. The green credentials of Giant King Grass appear to be being deliberately overstated. The supposed yields are wet weight - so you need to reduce them by 60% to start with. Then you need to reduce them further because there is no evidence of the actual level of production per hectare on a commercial scale rather than just in trials. Then you need to build in a negative for the energy cost of drying the material before use. Then you need to build in another negative for the fertiliser that will have to be applied at least annually. Because if it is of value as animal feed as advertised, then there will be nutrients being removed with the harvest that have to be replaced through application of fertiliser. And lastly, you need to build in another negative for having to reestablish it every 7 years. Miscanthus x giganteus in comparison has low moisture content at harvest time, translocates almost all its nutrients back down to its rhizomes prior to harvest, and can continue to be harvested for at least 15 years, and possibly a lot longer than that, without needing to be replanted.

PoCl2 oxidation
This is purely out of curiosity. In the polonium dichloride article, it says that polonium dichloride reacts with nitric acid to form a dark red solution and a flaky white precipitate of unknown composition. This may be the reaction: 4 HNO3 + 6 PoCl2 → 2 H2O + 4 NO + 3 PoCl4 + 3 PoO2 Any suggestions whether it is or not? --Chemicalinterest (talk) 13:32, 11 May 2010 (UTC)


 * The statement is referenced to a 1955 article in J. Chem Soc. Did you check out that article?  It may have more info in the article.  Furthermore, there are analytical techniques which are commonplace now which were unavailible in 1955.  A simple literature search may turn up more recent studies on polonium halide salts where the nitric acid reaction has been more thoroughly analyzed.  -- Jayron  32  16:35, 11 May 2010 (UTC)
 * A quick google taught me that PoCl4 is a yellow solid that seems to be fairly water-soluble (or susceptible to hydrolyis) and eaily forms soluble complexes. The Po+2/Po+4 electrode potential is 1.1 V (0.72 V in HCl as an ion complex) and Po+4/Po+6 1.5 V. How does that fit with your proposal of nitric acid oxidizing Po+2 to Po+4? DMacks (talk) 17:01, 11 May 2010 (UTC)

I wrote polonium dichloride. I have the paper in front of me and it states:

"The dichloride dissolves readily in dilute hydrochloric acid to a pink solution which rapidly autoxidises to the quadrivalent state and is immediately oxidised by hydrogen peroxide or chlorine water. Addition of potassium hydroxide solution to this solution gives a dark brown precipitate (solubility 1.4 mg. of 210Po/l.) which may be the hydrated bivalent oxide or hydroxide and which is very rapidly oxidised to the quadrivalent state. With 0.1 N -nitric acid it gives a dark red solution and then rapidly a white flocculent precipitate, the composition of which is not known."

Make of that what you will.

Ben (talk) 17:46, 11 May 2010 (UTC)

Name of plant, please
I remember a plant which had curved narrow grey twigs. It would sit in a cupboard for years and on being brought out, put in a bowl and given some water, would come back to life. Named something like a Judea plant or a Lebanon plant. Kittybrewster  &#9742;  18:12, 11 May 2010 (UTC)
 * Could it be any of our Resurrection plants?   D b f i r s   18:16, 11 May 2010 (UTC)
 * Brilliant and spot on. Anastatica. Kittybrewster  &#9742;  18:21, 11 May 2010 (UTC)

Fissile elements used nuclear reactors
What elements apart from uranium and plutonium are used, or could be used, to supply energy? Does plutonium require a different kind of reactor than uranium? Do other elements require different reactor set-ups? Thanks--92.251.166.171 (talk) 18:29, 11 May 2010 (UTC)


 * It is possible to run a molten salt reactor with the thorium fuel cycle, which uses a thorium/uranium fuel cycle. -- Finlay McWalter • Talk 18:38, 11 May 2010 (UTC)
 * But it's still uranium that's providing the power. The thorium absorbs neutrons produced by the fission of U-235 and creates U-233, which could then be used for generating more power. The thorium itself is not fuel, but it can be turned into fuel. --Mr.98 (talk) 22:27, 11 May 2010 (UTC)


 * In principle, any element that's radioactive (which is most of them - if you pick the right isotopes) could hypothetically be used to power a nuclear reactor of some kind. But the problem is that the radioactive isotopes of some elements are so rare that you can't obtain them in nature, others have such spectacularly short half-lives that even if you could find them, they'd be gone within milliseconds - and yet others have such a long half-life that they give up their energy too slowly to be useful and can't create the desired self-sustaining reactions.  If you could find a source of (for example) Mercury's isotope 194Hg, it's radioactive, it has a half life of 450 years and the byproduct is gold!  Sadly, the only way to get 194Hg is to make it by irradiating some gold...so we're not likely to see any mercury reactors around in the near future!  You most certainly do need different reactors for different nuclear fuels - but the reactor isn't the biggest part of a nuclear power plant - so perhaps the cost to refit one to a different type of fuel might not be horrific. SteveBaker (talk) 20:17, 11 May 2010 (UTC)
 * Correct me if I'm wrong (I know very little nuclear physics) but from our nuclear reactor article a reactor sustains a nuclear chain reaction by definition, for an ordinary fission reactor (as opposed to a fusion reactor) this would surely mean that the fuel would need to be either fissile or fertile, rather than simply radioactive. An atomic battery on the other hand could hypothetically use any radioactive isotope.131.111.185.68 (talk) 22:20, 11 May 2010 (UTC)


 * Steve, using random radioactive elements for heat is not the same thing as powering a nuclear reactor. You need fissile materials if you are going to have an actual chain reaction. Yes, if you had ungodly quantities of very radioactive materials you could get the waste heat off of them like in an RTG but that won't be efficient for large-scale power production. There are very different principles behind such designs. An RTG is not a nuclear reactor. --Mr.98 (talk) 22:27, 11 May 2010 (UTC)
 * I agree, Steve is confusing RTGs and nuclear reactors. --Tango (talk) 23:03, 11 May 2010 (UTC)


 * See the article fissile. Basically it is just uranium and plutonium, but you can use the neutrons created (say, from U-235 fissions) to breed other isotopes of uranium or plutonium. As for different reactor designs... yes, basically. Different fuels behave differently. Different reactor designs are optimized towards specific types of fuels, and some won't work if you put in the wrong fuel. Some reactor designs are more flexible; reactors that use LEU can also use MOX fuel in many cases. But you can't just mix-and-match willy-nilly. --Mr.98 (talk) 22:27, 11 May 2010 (UTC)
 * There are other elements with fissile isotopes (eg. Curium), but I believe they are all synthetic, which means they are only available in small quantities. If you want enough for a significant nuclear reaction, you are going to have to go with either uranium or plutonium. --Tango (talk) 23:03, 11 May 2010 (UTC)


 * Actually, looking a little closer: Fast-neutron reactors use transuranics beyond plutonium as "fuels" in a the sense that they breed them and then fission them. Apparently these are known as the minor actinides. That's interesting to know. --Mr.98 (talk) 01:37, 12 May 2010 (UTC)

Chalcogenide reduction potential
It seems that chalcogenides (oxide, sulfide, selenide, telluride, polonide) become stronger reducing agents the bigger the molecules get. Oxide is very weak, sulfide is moderately weak, and telluride is quite strong. Is there a pattern? --Chemicalinterest (talk) 20:34, 11 May 2010 (UTC)
 * Try looking at their electronegativities, there may be a correlation. Oxygen is the most electronegative, which makes it very difficult to remove electrons from it (as a reducing agent, it would have to donate electrons to some other species) and hence is not a very good reducing agent.24.150.18.30 (talk) 22:22, 11 May 2010 (UTC)
 * What about calaverite, a gold telluride? Presumably it contains gold in the +1 oxidation state and tellurium in the -2 oxidation state. I thought that since telluride is such as strong reducing agent (see sodium telluride, where it is oxidized by oxygen readily) and gold(I) is such a strong oxidizing agent, that gold telluride would be extremely unstable, possible even explosive. Why is it found naturally though? Normally very reactive chemicals are not found in the earth's crust. Thanks. --Chemicalinterest (talk) 22:51, 11 May 2010 (UTC)
 * It is quite possible that the gold is not in the +1 oxidation state, nor is the Te in the -2 oxidation state. Things like sodium chloride may be considered to have very ionic character, with the sodium and chlorine atoms each having an almost full positive and negative charge respectively.  The transition metals, and those elements down near the bottom of the periodic table behave differently, and I suspect that in this case there will be some metallic bonding, or even some covalent character given that tellurium is a semimetal.  The electron rich atoms (Te2-) can donate electrons (or electron density, it doesn't have to be a whole number of electrons) to the electron poor atoms, resulting in a decrease in the charge separation.  Effectively, you could have Au(+0.5)2 Te(-1), or some variation which makes the tellurium less of a reducing agent and gold less of an oxidizing agent.  This should show that the reducing ability of 'telluride' (or anything else in the series) is dependent on the the actual chemical species and not just on the fact that there is tellurium present.  Take a look at our Wikipedia page on Bonding in solids: .24.150.18.30 (talk) 23:36, 11 May 2010 (UTC)

Zintl phase might be a good point to start.--Stone (talk) 15:47, 12 May 2010 (UTC)
 * I was always told that group VIA (16) elements tend to form compound with a -2 oxidation state. Tellurium doesn't seem to do that readily. Only oxide commonly does it. Group VA (15) elements are supposed to have a -3 oxidation state, but the elements are not predominately -3. Nitrides are not easily formed, phosphides are reactive, arsenides, antimonides, bismuthides are rare. It doesn't seem like there is much periodicity in the groups. --Chemicalinterest (talk) 16:07, 12 May 2010 (UTC)
 * Oxidation states are only of interest if you do not form bonds between the elements. In Zintl phase compounds you form bonds between the elements. The I3- is a ion shows this concept even with water soluble compounds. For your problem with the Group 15 elements is understandable, but you ave always two noble gas electron shells to go to the left and to the right. You can either give away five electrons and end with the electron shell of the previous noble gas or you can add three electrons and get to the the electron shell of the next noble gas. Giving is easier for the electropositive elements, large electron shell makes elements more electropositive, so this is the way the heavy and large group 15 elements go. The opposite is true for the light electronegatives.--Stone (talk) 14:41, 13 May 2010 (UTC)

Identify drill bits
On this page is a selection of drill bits. On the bottom right of the image are some bits that look like flat-head screwdrivers with points shooting out of the centre. What are they? --78.148.181.99 (talk) 21:18, 11 May 2010 (UTC)
 * Wood bits (that is to say, bits for drilling holes in wood). DuncanHill (talk) 21:21, 11 May 2010 (UTC)
 * See Drill bit. DuncanHill (talk) 21:23, 11 May 2010 (UTC)

Psychological term for the "deification" recently deceased people get?
When someone dies, especially someone young, you are almost certain to hear others describing them as wonderful, so talented, having had limitless potential, etc etc etc. Suddenly, in death, each individual's traits become a long list of superlatives. Clearly, there are people to which not all of these things really apply - and their surviving relatives & friends (to me) seem rather caught up in the moment. Is there a psychological term for this process of instantly forgetting all the negative qualities of a person and thinking of them as some sort of perfect angel once they die? 61.189.63.174 (talk) 22:30, 11 May 2010 (UTC)


 * I don't want to be a psychologist, but you sound like you are upset, it might help to talk to someone in person, rather than over the internet. But to answer your question: From : "The Talmud contains advice for those who deliver the eulogy. Its aim should be to call attention to the achievements of the deceased. A little exaggeration was felt to be in order. In a eulogy, it is permitted to imply that the deceased was rather more generous and pious than he really was, but the kind of insincere praise which everyone present knows to be false must be avoided. One talmudic rabbi said to a man well known as a gifted eulogizer: "Give warm expression to your feelings when you eulogize me for I shall be present there." And ".... give the deceased a little more credit than they deserve. The Taz (Rabbi David Segal, 1586-1667) was troubled by this apparently disingenuous leniency. In his landmark commentary on the Shulchan Aruch, he offered several possible reasons as to why embellishment may be permitted in a eulogy. Firstly, he warned that if we were forced to stick to the plain truth without any exaggeration at all, zealous people would be overly cautious. They would stint in their praise of their loved ones; shortchanging them of the praise they had deserved. He also pointed out that even in the most intimate relationships, there is so much that goes unsaid. None of us can be aware of every good deed that someone else did during their life, so we have to leave a margin of error to account for the many private acts of kindness that they may have done. Finally, he suggests that good people deserve credit for their good intentions even if these were never fulfilled, for had they only known the infinite value of a good deed they would certainly have done it. When speaking of our dead relatives, we can afford to be generous." I don't think people actually forget, so there is no specific term like what you are looking for (not that I know of anyway), but people prefer to focus on the good. Ariel. (talk) 00:00, 12 May 2010 (UTC)


 * Seems like a perfectly reasonable question to me (have you noticed that every single British soldier killed in Afghanistan has been a hero? Not one of them was an ordinary bloke who only signed up to escape the dole.) Anyway, the general concept is de mortuis nil nisi bonum. DuncanHill (talk) 00:07, 12 May 2010 (UTC)
 * Recently in Australia, Carl Williams was fondly remembered at his funeral with "touching" eulogies, before being buried in his imported gold casket.. I mean he was still a human being with a (ex)wife and kids.. I suppose kids could grow up to hate their parents, but even scumbags can love their kids and be nice to them and be fondly remembered by them, even if they were hated by everyone else, that's all it would take. I think the effect you are thinking of is related to cognitive dissonance theory, not sure what it would be specifically. Mourning for the dead is instinctive, you have to really really hate someone not to mourn them when they die. So mourning for someone and the fact that they were (sometimes/often) a big jerk would cause cognitive dissonance, so to justify it you would gloss over and forget anything unpleasant and only remember the great things about them. Vespine (talk) 01:35, 12 May 2010 (UTC)


 * Yeah, it's called don't speak ill of the dead. It's not a psychological pathology, it's called having respect for others. Vranak (talk) 13:55, 12 May 2010 (UTC)


 * There are worlds of difference between respecting someone, not speaking ill of them, and piling superlatives on a person just because they've croaked. Only this last thing is the point of the question and it's a reasonable one. So we don't speak ill of the dead (not that it's going to bother them now, is it?); why add false praise? It's a bit like what goes on when someone retires ("John worked tirelessly to improve grommet margins .2% above expectations over his forty years at this company...") - especially sports and media figures ("Howard Cosell was the greatest TV broadcaster in the history of the medium and I don't mind saying so now that the son-of-a-bitch is finally off the air..."). You can be respectful without completely throwing away your objectivity. Matt Deres (talk) 16:34, 12 May 2010 (UTC)


 * In many or most cases, eulogies, or eulogy-like words, are spoken by people who had some relationship to the deceased, or at least knew the person, when they were alive. There is a tendency to speak well of such a person, because you genuinely miss their good qualities, and their bad qualities are understood to no longer be a presence. Bus stop (talk) 16:49, 12 May 2010 (UTC)
 * I disagree with the OP's statement that grieving is the "process of instantly forgetting all the negative qualities". We could question the assumption that people delivering eulogies actually believe what they are saying. They may knowingly stretch the truth because they thought it was socially acceptable or prescribed behavior. If this is true, this behavior would be a case of Observational learning122.169.152.60 (talk) 18:00, 12 May 2010 (UTC)
 * I'd normally not repeat myself but I think you guys totally missed my point. Most of the stuff you are saying like "why add false praise?" and "bad qualities are understood to no longer be a presence" seem to me to be very well explained by cognitive dissonance theory. Mourning someone while at the same time remembering all the bad things they did would cause dissonance. To resolve the dissonance you either not mourn them, which is hard to do since mourning is such a primitive reaction, so you justify away any negative views you might have had and exaggerate the good things they did. This would predict that the nastier someone is, the more people would have to exaggerate the good things they did to justify their mourning. This is one of those strange "counter intuitive" things that happens which is otherwise difficult to explain. Obviously there would be a tipping point where you can no longer justify the nasty person and the option of not mourning them becomes easier, this would happen much sooner for someone who totally hated the person to begin with, but a lot later for the person's children or parents. Vespine (talk) 22:30, 12 May 2010 (UTC)


 * Just a side note, to eulogise is, by definition, to speak well of -  Adambrowne666 (talk) 22:01, 12 May 2010 (UTC)

Common magnets
Are the common magnets found in shower curtains, speakers, etc. ceramic magnets? They crack easily. If they are ceramic, do they just contain barium/strontium carbonates and iron oxides, as the article says? They dissolve in hydrochloric acid slowly with minimal bubbling to form a yellow solution, which gets more orange after time. It seems like iron oxide, then cobalt oxide. The yellow could be nickel oxide dissolving then reacting to form NiCl42-, which is yellow. Any thoughts? --Chemicalinterest (talk) 22:46, 11 May 2010 (UTC)
 * Ferrite magnet is your article on this. They are cheap without exotic rare earth elements. Graeme Bartlett (talk) 11:09, 12 May 2010 (UTC)
 * Why the reddish color when they are placed in hot hydrochloric acid? Barium chloride is colorless, strontium chloride is colorless, and iron chloride is either light green or yellow. Do they have cobalt oxides in them? --Chemicalinterest (talk) 13:00, 12 May 2010 (UTC)
 * You should be able to precipitate the barium or strontium by adding sodium sulfate. To distinguish coblat and iron, ammonium thiocyanate causes a blue or red colour.  Iron thiocyanate complex can be removed by adding fluoride, to form FeF63- ion in preference.  You need to read about Analytical chemistry, Bead test (which need a lot of work) and Qualitative inorganic analysis.  Prospectors are very interested to tell if a mineral contains cobalt, so you can mimic what they do, ferrite is an artificial mineral. Graeme Bartlett (talk) 22:12, 12 May 2010 (UTC)
 * The iron(II) chloride gets oxidized to iron(III) chloride, which is more yellow-brown. Sintered materials contain a material with a lower melting point to glue the particles together, this might give the colour. Another possibility would be a coating of the material. The rare earth magnets are normally plated with nickel.--Stone (talk) 14:49, 13 May 2010 (UTC)