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February 25

Hermitian condition in Dirac notation

A Hermitian operator satisfies

$\int \operatorname {d} x\left[(A\psi )^{*}\psi \right]=\int \operatorname {d} x\left[\psi ^{*}A\psi \right]$

How do you write this in bra-ket notation? --superioridad ^(discusión) 02:01, 25 February 2012 (UTC)

Is this homework? You need to use the fact that $(A\psi )^{*}=\psi ^{*}A^{*}\!$. -- BenRG (talk) 02:24, 25 February 2012 (UTC)

This is not homework. So is it then just $\left\langle \psi \right|A^{*}\left|\psi \right\rangle =\left\langle \psi \right|A\left|\psi \right\rangle$? --superioridad ^(discusión) 02:42, 25 February 2012 (UTC)

Yes. Though you could also write $(A|\psi \rangle )^{*}|\psi \rangle$ for the left hand side. You don't have to use $(A\psi )^{*}=\psi ^{*}A^{*}\!$, it just makes it look nicer. If this were homework they would probably want the nicer looking version. -- BenRG (talk) 02:47, 25 February 2012 (UTC)

Electric trains and rails

Since electric trains put the return current to the running rails, is there any danger of shock if someone touches the running rails with a train nearby? Does the return current go to the ground directly under the track, or does it travel along the running rails? 169.234.111.180 (talk) 02:37, 25 February 2012 (UTC)

Yes, there is danger. See Third rail. RudolfRed (talk) 04:33, 25 February 2012 (UTC)

Assuming there's a third rail present, that would be dangerous. Inadequately-bonded running rails might present a danger, but I don't know what difference in potential might normally be present between the running rails and ground. Probably not much, if any, given that people walk over tram rails all the time in wet weather, or across rails at station platforms. I have no definitive information to offer, though. Acroterion (talk) 04:39, 25 February 2012 (UTC)

So just to clear things up, the current from the third rail/overhead lines is picked up by the train, and is returned through the wheels of the train, to the rail, and then to the ground; and the current doesn't have to return to the power station through the running rails, right? 169.234.111.180 (talk) 04:57, 25 February 2012 (UTC)

From this paper, it sounds like most modern systems (DC at least) do use the running rails to return the current, which can lead to dangerous shocks, but the lines are equipped with special devices which measure the potential between the rails and the earth, and open a connection if the potential gets dangerously high. Smurrayinchester 11:30, 25 February 2012 (UTC)

In DC traction systems, it is a lot harder to keep the current in the rails and out of the earth, than it is for AC, but it is still the aim. DC systems are a nightmare for causing corrosion in any metal (rails, pipes, buildings, whatever), and causing all manner of problems and safety issues in nearby AC and low voltage systems. DC Traction is a very old and obsolete system devised when the only way to vary the speed of an electric traction motor without punishing loss of efficiency was the Ward-Leonard motor-generator-motor system http://en.wikipedia.org/wiki/Ward_Leonard_motor_control_system. As soon as magnetic amplifiers were developed (1930's to 1950's) AC could be used at lower cost, and DC traction became obsolete, much to the relief of engineers everywhere, and the distress of litigation lawyers. From the 1960's onwards, semiconductor control (TRIAC/SCR) was available, giving extremely high reliability and efficiency with AC power. Keit60.230.195.53 (talk) 12:50, 25 February 2012 (UTC)

DC traction is certainly an "old" system, dating back to about 1895, but hardly an "obsolete" one, since many of the larges urban rail systems use DC, and plan to retain them for the indefinite future. See List of current systems for electric rail traction. Agreed, AC is the typical choice for new electrification, especially in less dense population areas and for long distance transportation. The simple regenerative braking of DC allows a train slowing down or going down a grade to power a different train on the system which is accelerating or going up a grade, rather than just dumping the energy into resistor banks on the train or into heating up brake linings. AC regeneration is far more complicated.Edison (talk) 23:02, 26 February 2012 (UTC)

Competent electrical engineers never design systems so that significant current returns to the power station or substation via the earth - earth current only occurs during certain fault conditions. This is because earth current causes a wide range of problems, including interferance and hazardson telephone lines (even if overhead and not buried) and hazardous conditions on metal pipelines. The rails thru which the locomotive return current flows are connected at regular interavls to a return cable system, which "drains" off the current. In the overhead feed system, transformers are installed each couple of km or so to force the return current out of the rails. With overhead systems, it is not in the least dangerous (electric shock wise) to touch the rails - of course being run over by the train is another matter. With 3rd rail systems, yes - touch the 3rd rail (which is the energising rail), and you can die. Fortunately 3rd rail systems are not very common in most countries, due to performance issues, problems with interference to other services due to the necessarily low voltage & high current, the need to securely fence off and gate the railtrack, and residual serious safety issues (what happens if the train breaks down? Usually passengers get fed up after a while and want to get off - Don't ever do that) 3rd rail systems are used most often in coutries like Britain, whose focus of safety and reliability, due to cultural standards & industrial history, is lower. In countries with a greater focus on performance and safety (eg Australia), 3rd rail feeding is not allowed. Keit60.230.195.53 (talk) 05:55, 25 February 2012 (UTC)

I think that you will struggle to find evidence that there is a lower focus on safety and reliability in Britain than Australia. The main issue with both the original electrification of urban railways in Britain and converting the existing network is bridges and tunnels - the cost of rebuilding these would be enormous. Mikenorton (talk) 14:50, 25 February 2012 (UTC)

There might be other reasons than "a greater focus on performance and safety" for Australia not having the third rail systems found in the US and Britain, such as not having dense urban areas needing electrification of rail systems as early on. The assertions sounds a bit chauvinistic. As for side effects of the current used to power rail systems, I agree that DC leakage promotes corrosion, but AC causes inductive interference with phone and other signal systems. "Competent engineers" realize induction is also a problem with AC powered trains, especially with thyristor or other solid state controls, since the rails are used as returns and transposition is not the simple affair it is with overhead power transmission systems. Edison (talk) 23:02, 26 February 2012 (UTC)

There's heaps of evidence that reliability and safety is less a priority in Britain than in Australia, for cultural and historical reasons. One of the more well known examples known to electrical and electronic engineers in Australia is colour TV. Britain was first, Australia didn't go colour until 1974. There was immense pent up demand. To meet it some companies decided to import British-made sets. These didn't last long in the market - they were rubbish compared to Australian and Japanese sets - too many faults, too many safety compromises, too expensive to repair due to rough construction & old-fashioned circuitry. One set, "Decca", shortly after market release in Australia, was banned by the Authorities, because not only was it liable to give electric shocks if only minor wear & tear defects occurred, it had a transformerless half-wave rectifier power supply, causing DC in your house earth, which causes corrosion and earth system failure in the street MEN earthing system. A truely disgusting thing - yet it was a major volume seller in Britain. Those of us of my generation remember British cars, before they were driven out of the Aust market when Japanese designs began to be imported and made locally in Australia in the 1960's. British cars in comparison to Jap and American - sourced cars were cheap, nasty, unsafe, had high failure rates, and poor finishes that didn't last. Before WW2, Britain had a huge export market. After WW2, little exported. Why? Because by pre-war standards, British products were on a par, but during WW2, other countries used their experience in making high quality war materiel to improve quality, but Britain was economically damaged, and resumed with pre-war standards and expectations. Another good example: motorcycles: In the 1960's Japanese bikes (Honda, Yamaha, etc) became available in Australia. That was the end of British bikes (BSA, Triumph). British bikes had poor finish, high failure rates, and vibrated. Jap bikes had high standard of finish, better handling and brakes, very low failure rates, and were smooth. I could go on and on with many many more examples. Australia has, ever since WW2, been economically much stronger than Britain, with a higher standard of living. That has allowed Australia to spend the money to do things right. Yes, it cost a lot of money to put in Overhead feed AC rail traction. Australia just went ahead and did what was necessary for a reliable safe system. Keit60.230.195.53 (talk) 16:19, 25 February 2012 (UTC)

The vast majority of UK electric stock that does not run underground uses overhead (Great Northern Electrics uses overhead and switches to 3rd rail underground - a matter of a few miles). Safety is a complex issue and the comparison between two countries can't be dealt with easily (there is some interesting background comparing DV/AC and UK US on Talk:Vacuum_tube). The sad fact is that the three pin system, for example, used in the UK and Australia (with different plugs) is being undermined by two-wire devices suitable for the US and mainland Europe, which are significantly less safe. Although the British manufactures post war certainly took a much smaller share of the world market, and quality was a problem (which was mainly about the Far Eastern improvement in quality, as you say) none of these things generalise that well. We see, for example, cycles in the competitiveness and quality of other producers, and we see an increase in the demands of standards bodies such as the IEEE regulations. Earth bonding requirements in the UK, for example, have changed radically in the last 50 years. Rich Farmbrough, 20:30, 25 February 2012 (UTC).

In Australia at least, if the plug does not have an earth pin, the appliance must conform to the requirements of "double insulated", and must display the symbal. This makes it more safe than an earthed appliance, not less. The reasoning for the 3-wire eath system is that if appliance metal work thru a fault becomes live, the user is protected from electric shock because the appliance metalwork is as low in voltage as anything else nearby. But this assumes that the appliance and the house wiring is not otherwise faulty, and the house is multiple earthed per code requirements. If this is not so, or the source is a portable generator (which makes earthing rather a theoretical exercise), the user can still be electrocuted. There are other, admittedly quite uncommon, circumstances too complex to explain here, where you can be electrocuted with earth-pin/3-wire systems that are not faulty. With double insulated appliances, it is virtually impossible for such faults to occur, and thus virtually impossible for users to be electrocuted. In any case, in Australia, the use of ELCB's for ALL wall outlets installed for portable or mobile appliances is mandatory. Lastly, IEEE is an American professional body for engineers (broadly similar to IET in Britain), and has nothing to do with the UK. Keit121.221.230.136 (talk) 00:36, 26 February 2012 (UTC)

The IEEE article seems to disagree with your characterization of it. 75.41.110.52 (talk) 21:31, 26 February 2012 (UTC)

Despite what you may have or have not misread or read in either my posts above or in any Wiki article, it is a fact that the IEEE, as an AMERICAN association of professionals, cannot and does not control how things are done in Britain (or any other country) any more than the BRITISH standards bodies can expect to control how things are done in America - that is the point I made. Basically, both are associations of professionals extablished to maintain professional standards by dissemination of information, however they differ in detail as to how they do that, and what they do. If you work in Britain, you will have to conform to any applicable British mandatory standards, which will in many aspects require you to violate some aspects of American standards. This does not mean either standard is wrong, as they will have been written in different contexts. The same with working in America - you will have to conform to NEC etc, not British standards. This is not to say you cannot use the standards of another country as a GUIDE to good practice, should a local or international standard to cover the subject not exist. Generally, if there is a local standard, comply with that, if no local standard comply with an applicable International (eg IEC) Standard, if no international standard, comply with an applicable voluntary industry code of practice, if no industry code, use a subject applicable standard or code from another country if in your profesional judgement it seems fit, if not, just use your best professional judgement. Keit124.182.21.71 (talk) 02:03, 27 February 2012 (UTC)

"more than 400,000 members in more than 160 countries, about 55% of whom reside in the United States" from the article with two references. If you have better references please improve the article. 75.41.109.190 (talk) 20:08, 27 February 2012 (UTC)

The data on membership is totally non-relevant to both the OP's question and the points I've made, however the reasons for the membership is very interesting. As a practicing consulting engineer based in Australia but with some limited international work, I am a member of both the IEEE and the IET. Neither have any "control" in the countries my customers are located in, but a) membership gives me access to their journals so I can keep current on scientific developments etc, and b) membership gives me some international credibility. The equivalent Australian institution is the IEAust. Keit124.182.55.62 (talk) 09:02, 28 February 2012 (UTC)

I removed the excess "E" from my post, and refer the hon. IP to the IEE/IET regs BS 7671. I note that these are also the standards for "Mauritius, St Lucia, Saint Vincent and the Grenadines, Sierra Leone, Sri Lanka, Trinidad and Tobago, Uganda, Cyprus". Also that they have a requirement for RCDs on all household sockets. Double insulation is no match for a properly earthed device, there is no reason, of course, that a properly earthed device can't also be properly insulated. Rich Farmbrough, 02:56, 27 February 2012 (UTC).

Incorrect - a double insulated appliance, which may have exposed metal work, SHALL NOT HAVE THIS METAL WORK EARTHED, as that defeats the whole idea of double insulation. If you earth it, you will reduce safety, not increase it, as earthing it allows the user to be electrified due to the house or whatever earth/nuetral wiring being at voltage above earth either due to faults or in circumstances where a good MEN system earth is not possible. Double insulation, as difined in standards, is, atleast with the Standards I am familaier with (eg Australian Standards) is not a matter of being "properly insulated" or good insulation, it is a set of construction and testing requirments that make an appliance fault that electifies exposed metal work, or metal parts that can be exposed without the use of a tool, virtually impossible. For example, the complete failure of any single insulation item shall not be possible or shall not enable such electrification. See my post on this above. Note: I have added the word "otherwise" which was inadvertantly left out on a previous post of mine. BS7671 would be a British Standard, not an IET publication. In any case I cannot access it without paying money, which I will not do just for a RefDesk debate - can you post the title of the standard and the relevant paras, should you feel I've got something wrong somewhere? Keit58.170.170.136 (talk) 03:36, 27 February 2012 (UTC)

The OP may be interested that in the New York City subway there are what looks like short snips of limp metal cable connecting all the expansion gaps in the regular rails. I've also seen things spaced at regular intervals on the running rails which appears to be where the power goes after passing through the train. You must be rather close to the train for all three rails to be electrified. I've heard on the news of people electrocuting themeselves on the third rail. However, I don't think I've ever heard of someone being electrocuted by the running rails, even being saved in the nick of time from the train by a Good Samaritan, which happens sometimes (you know, very large population, a crazy bum tries to kill themeselves, even other people). Unless you're under the influence of a substance it's likely intentional if you get electrocuted as the TR's covered on 5 out of 6 sides. (and Mythbusters has busted that you can get electrocuted from peeing on it) Sagittarian Milky Way (talk) 00:32, 28 February 2012 (UTC)

"Things spaced at regular intervals" may be the drain system I mentioned in my post near the start of this thread. The drain system is designed to take the return current out of the rails so that it doesn't normally try and return via the earth - that ensures that the return rails stay at very low voltage compared to earth, and you can't be electrocuted. However short snips of cable as described across the rail expansion gaps are required in any case to ensure end-to-end good rail conductivity within sections for signalling purposes - when the train is near, and passing a road crossing, it electrically shorts the rails together and this is detected by the signalling controller box to bring the barriers down & turn the lights and bells on, so that the cars & trucks halt to let the train thru. Keit124.178.178.1 (talk) 06:56, 28 February 2012 (UTC)

Extreme oxidation states

Is the +9 oxidation state (or any other oxidation state higher than +8) possible? (Talk:Potassium nonahydridorhenate suggests CoH₉, RhH₉ and IrH₉.) What about oxidation states lower than -4? Double sharp (talk) 07:09, 25 February 2012 (UTC)

The highest I've ever heard of is +8 (Xe(VIII)), but my ignorant mind is certainly not all-knowing. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 14:31, 25 February 2012 (UTC)

No idea about what's possible, but the Oxidation state article mentions +8 and –4 as the currently-known extremes. DMacks (talk) 15:50, 25 February 2012 (UTC)

Well, with enough energy and the right equipment you can zap any number of electrons from an atom (see Ionization energy) - so your maximum "oxidation state" there is +Z. However that's quite an artificial set-up - I guess you're thinking about states found in actual, stable molecules. LukeSurl ^{t c} 00:08, 26 February 2012 (UTC)

Yes, I am thinking about states that could (hypothetically) be found in a stable molecule. How stable would Ir(IX) probably be? (Co(IX) and Rh(IX) would probably be less stable, but what about Am(IX) and Mt(IX)?) Double sharp (talk) 04:34, 26 February 2012 (UTC)

This paper thinks Mt can have a +9 oxidation state: Himmel, Daniel; Knapp, Carsten; Patzschke, Michael; Riedel, Sebastian (2010). "How Far Can We Go? Quantum-Chemical Investigations of Oxidation State +IX". ChemPhysChem 11 (4): 865–9. doi:10.1002/cphc.200900910. PMID 20127784. Ratbone60.230.199.111 (talk) 13:17, 29 February 2012 (UTC)

Transistor question

for a transistor the current amplification factor is 0.8 ,when transistor is connected in CE configuration . calculate the change in the collector current when base current changes by 6mA? — Preceding unsigned comment added by 117.252.66.67 (talk) 15:23, 25 February 2012 (UTC)

No. You calculate it...it's your homework not ours. DMacks (talk) 15:49, 25 February 2012 (UTC)

Can you multiply 6 by 0.8?--92.29.192.13 (talk) 20:35, 25 February 2012 (UTC)

I know that this is just a homework problem, and the OP needs to run with the figures given, but does a current gain of 0.8 make any sense in a common emitter circuit? Transistor beta states: "It is typically greater than 100 for small-signal transistors but can be smaller in transistors designed for high-power applications." In practice, would you ever see a CE current gain of less than unity? -- ToE 09:12, 26 February 2012 (UTC)

does the Q mean the alpha of the transistor insted of the beta?--92.29.200.31 (talk) 11:57, 26 February 2012 (UTC)

It took me a moment to realize that by "Q", you meant Q, not Q. -- ToE 12:19, 26 February 2012 (UTC)

The terms "alpha" and "beta" (although beta is still in common use) have been obsolete for decades - Alpha was a useful property with the very earliest of transistors. Yes, the current gain in CE mode (termed hfe) is usually much greater than unity (may be as much as 100,000 or more for very small "supergain" transistors, up to 1000 for small discretes intended for audio premaps), but it can be significantly less than unity for very high voltage switching power transistors. So, the question should probably be taken as written. Unless the correct standardised symbols are used (hfe in this case), it is impossible to be certain. Keit124.182.18.249 (talk) 12:32, 26 February 2012 (UTC)

What's the point of the "being" portion of Human Being

I know "human" refers to our genus, Homo, but I don't know what the point of the "being" is. It doesn't refer to our species, sapiens, so what's the point? I know you can refer to other animals in the genus Homo as human, but are they "Human Beings" as well? ScienceApe (talk) 19:29, 25 February 2012 (UTC)

Well, it's not a scientific term. I would hazard to say it is simply idiomatic — that is, the "being" doesn't mean much other than "I am implying this individual human has a soul of some sort," or something similarly meant to imply a notion of "dignity." The OED says that a "human being" is simply "a person, a member of the human race; a man, woman, or child." This implies to me that while you could drop the "being," it's that last part that matters — you're implying personhood, you're implying some specificity (man, woman, child), you're implying that they're alive (or invoking their formerly living status explicitly), you're implying something more than a pure zoological classification. The term dates back to at least the 17th century. --Mr.98 (talk) 19:36, 25 February 2012 (UTC)

Back to the days when adjectives were not usually used as nouns. "Human" has become a noun, but it was originally an adjective describing a type of creature, or being. We still sometimes hear the expression "alien being", but it's usually abbreviated to "alien". Same thing with human creatures or beings. "Creature" has a mainly pejorative use, so "being" is preferred. -- Jack of Oz ^{[your turn]} 20:52, 25 February 2012 (UTC)

Some folk think of human as an adjective only, like Latin humanus (although the OED cites substantive uses back to the 16th century), so they need to use "human being" for the noun (Latin homo). Deor (talk) 21:07, 25 February 2012 (UTC)

I will just note that the use of human as a noun goes back to the early 16th century. So it's not that recent, though of course usage patterns vary. Ngrams suggests using human as a noun was not uncommon but far less common than using "human being".[1][2] (just two variants I used to try and gauge relative frequency) --Mr.98 (talk) 21:43, 25 February 2012 (UTC)

You have anologies in other languages, too: human <=> human being; Mensch <=> menschliches Wesen; humain <=> un être humain. As above "pre-scientific" notation. 213.169.162.159 (talk) 09:16, 26 February 2012 (UTC)

...and 'ser humano' in Spanish. Richard Avery (talk) 14:08, 26 February 2012 (UTC)

Being. ~AH1 ^(discuss!) 18:53, 26 February 2012 (UTC)

And "istota ludzka" in Polish. Equivalent terms exist in practically all European languages. They are all calques for Latin philosophical terms from Aquinas that are in turn calques for Greek terms from Aristotle. Dominus Vobisdu (talk) 18:59, 26 February 2012 (UTC)

Actually, isn't "being" a verb? Maybe we should take this to the Language desk. ;) Wnt (talk) 19:42, 26 February 2012 (UTC)

No. It's a noun derived from a verb. Specifically, a Gerund. Dominus Vobisdu (talk) 19:45, 26 February 2012 (UTC)

It just sounds better, wouldn't you say? Vranak (talk) 03:11, 1 March 2012 (UTC)

Oxosulphuric acid

What is the name for the analog of sulphuric acid with oxygen in place of sulphur (H₂O₅)? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 20:15, 25 February 2012 (UTC)

Sulphuric acid is H2SO4.--92.29.192.13 (talk) 21:19, 25 February 2012 (UTC)

Super oxygenated water is all I can find. Apparently, it is not very stable.--92.29.192.13 (talk) 21:23, 25 February 2012 (UTC)

Oxygen doesn't form that sort of structure ("O with four bonds to atoms"). H₂O₅ is all linearly attached "hydrogen pentaoxide", not a "sulfate-like core". DMacks (talk) 21:32, 25 February 2012 (UTC)

That acid can't exist, so I assume it is a hypothetical acid, in which case you'll have to invent a new name, possibly peroxygenic acid. Plasmic Physics (talk) 21:36, 25 February 2012 (UTC)

February 26

Molality calculation

A mass of 168 g of manganese dibromide is dissolved in 225 g of water. What is the molality of the solution — Preceding unsigned comment added by Nanceninja (talk • contribs) 02:28, 26 February 2012 (UTC)

Please see Molality and Molar mass. If you still have trouble with this homework problem, show us your work so far, and point out where you are stuck. -- ToE 02:45, 26 February 2012 (UTC) (I also shortened the title of this section.)

..., and is manganese dibromide a synonym for Manganese(II) bromide, MnBr2? -- ToE 02:49, 26 February 2012 (UTC)

... apparently so (NIST MML). I went ahead and created the redirect: manganese dibromide. If a chem-head tells me it's wrong, I'll speedy WP:G7 it. -- ToE 05:26, 26 February 2012 (UTC)

Lightning in Hawai'i

A friend of mine who lives in Hawai'i says that he rarely sees lightning there. Is there data to support this and if it's true that there is little lightning there, what's the cause? Dismas|^(talk) 07:56, 26 February 2012 (UTC)

There are very few lightning storms over the ocean and Pacific islands in general. Quoting from NASA, The ocean surface doesn't warm up as much as land does during the day because of water's higher heat capacity. Heating of low-lying air is crucial for storm formation, so the oceans don't experience as many thunderstorms. The Hawaiian islands are presumably small enough that the weather there is more ocean-like than land-like. Someguy1221 (talk) 10:12, 26 February 2012 (UTC)

The areas of the world that see the most lightning (I'm going to use Florida, USA, which is the state with the most annual lightning strikes, as an example) experience it so often because they are prone in their respective warm seasons to produce localized "garden variety"-type storm cells—Someguy's link describes the upwards motion needed to initiate convective weather activity. Synoptic weather events (large-scale low pressure systems, cold fronts, tropical cyclones) can also produce lightning, but because they occur much less often in a given location, regions where pop-up thunderstorm cells are rare have to rely on these synoptic systems for their fill of electric storms. This is the case for Hawaii, but interestingly, due to the tropical environment surrounding the islands, storm systems that are capable of producing lightning there often go all-out; see here, for example, which discusses such events as 21,000 lightning strikes in five hours. Juliancolton (talk) 20:24, 27 February 2012 (UTC)

How do they measure genetic proximity for unrelated individuals?

In Steven Pinker's The Blank Slate, there is a fairly lengthy discussion of the contribution of genetics, family environment, and "unique" environment to an individual's personality and abilities. The contribution of each is measured according to its role in explaining the variance: more fully, the proportion of variance of the response variable of the sample that is attributable to that characteristic. Note that the three contributions add to 1 (the third is determined by subtraction, I think). I can make easy sense of this when we are dealing with measures that vary continuously, which would include the response variables, since personality measures can be made continuous. But surely the same has to apply for the independent variables, or else we need a categorical variable for each individual. How do they measure, in particular, genetic proximity as an independent variable? I know there are measures of consanguinity, like the coefficient of relationship, but you can only measure a small handful of people on the same scale like this. Furthermore, this is only defined by relationship, not in any absolute sense, so what reference point do you use? What do you do when you are using a large sample of unrelated people? For that matter, how do they measure the family environment? Is it just two categories, "same" and "different"? IBE (talk) 22:17, 26 February 2012 (UTC)

I'm having a little trouble parsing your question (which is probably why nobody else has answered it, as well), but to your basic question of isolating genetic relatedness as an independent variable, isn't the answer to this simply by using twin studies? --Mr.98 (talk) 22:35, 27 February 2012 (UTC)

Is that what the OP was on about? My first reaction was "Eh? wot? wot langwidge is dis?". My second reaction was: This is some kind of joke ripping us off, or the OP just likes the sound of his own words. Wickwack121.215.46.219 (talk) 00:25, 28 February 2012 (UTC)

Twin studies does give a good overview from what I can tell. The language of my post, imho, is that of mathematics, expressed in words, by someone who doesn't fully understand the concepts involved, hence the question. I also claim to be way ahead of my time, which is why Wickwack can't understand me ;). As for the maths, I can understand when it's presented, but I'm used to one type of study (simple regression, from my undergrad days), and I could see that twin studies didn't fit that particular mould. Twin_studies#Methods has the main particulars, so I'll get my head around that and then I'll ask stuff again if still needed. Thanks for the link - I should have checked first, but I'm not used to finding such good details on methodologies, even knowing the WHAA.. principle. IBE (talk) 04:29, 28 February 2012 (UTC)

February 27

Time travel

I have heard it's possible to travel in time if we can somehow travel faster than light. It has been proven scientifically and mathematically. But i don't understand how it all works? Can someone explain it in the way that any ordinary people can understand it? Thanks!Pendragon5 (talk) 04:37, 27 February 2012 (UTC)

"Can someone explain it in the way that any ordinary people can understand it?" Probably not. Then again, it has also been "proven scientifically and mathematically" that we can't travel faster than the speed of light in the first place. Why do you think the universe should be understandable by "ordinary people"? It doesn't seem to make that much sense to those that spend their entire careers trying to understand it... ;-) AndyTheGrump (talk) 04:44, 27 February 2012 (UTC)

(edit conflict) It has not been proven scientificially, in the sense that science doesn't really "prove" anything, it provides evidence that it happens. Insofar as no experiment has ever been done to confirm time-travel, and so-far only one tenuous experiment has possibly confirmed FTL travel at all (the Faster-than-light neutrino anomaly) I would say that the empirical evidence of either faster-than-light travel or time travel is simply not there for it to be "scientifically proven" (again, for whatever you take "proven" to mean, which science doesn't really do). Mathematically, sure, there are all sorts of ways to manipulate equations to show that time travel is possible, if faster-than-light travel is possible, but empircal evidence for the latter condition is super tenuous, and the connection between FTL travel and time travel is unexplored (except mathematically), I would say that the jury is not just out on time travel, I'd say there hasn't even been an arraignment... --Jayron32 04:46, 27 February 2012 (UTC)

What do you mean by that science doesn't prove anything?? Science is always a tool for human to prove things, it's by far the most acceptable method around the world to prove stuffs.Pendragon5 (talk) 19:37, 27 February 2012 (UTC)

Strictly speaking, Jayron is correct. Science helps us develop models to predict the outcomes of experiments, but since there are always multiple models to explain any occurrence, nothing is strictly proven correct, although certain models will inevitably be disproven. Someguy1221 (talk) 10:22, 28 February 2012 (UTC)

Also (edit conflict). I'm not sure if you could say it's been "proven", it's probably safer to say that it fits certain interpretations using current models. We have an article which addresses what you are talking about Time_travel#Via_faster-than-light_.28FTL.29_travel Vespine (talk) 04:50, 27 February 2012 (UTC)

(edit conflict) It has never been proven, in that no one has actually done it. Mathematically and theoretically, it comes down to the relativity of simultaneity (you can also read Special_relativity#Causality_and_prohibition_of_motion_faster_than_light). Basically, as you'll surmise from the first article I linked, the order in which events appear to have occurred is not sacrosanct in special relativity (i.e. reality). There are situations in which the order that events occurred is different for different reference frames. But if you allow things to move faster than the speed of light, you can get some ridiculous observations, mainly effects occurring before their cause. My college special relativity text used the example of a projectile being sucked out of its target and back into the cannon that fired it. Such things can be interpreted as objects, such as that projectile, traveling backwards through time. Someguy1221 (talk) 04:51, 27 February 2012 (UTC)

It's not really true. The "proofs" you've seen start from unstated assumptions that are inconsistent with faster-than-light travel, and proceed to assume the existence of faster-than-light travel. From that, you can prove anything (ex falso quodlibet). The reason people write about amazing things that physics "proves" is the same reason they write about miracle diets and angel sightings. There's a market for it. It's not because of any scientific merit. -- BenRG (talk) 07:14, 27 February 2012 (UTC)

I don't think there's anything in the derivation of the tachyonic antitelephone that's logically inconsistent with faster-than-light travel. If there is, please enlighten me.

The assumptions may be inconsistent with faster-than-light travel plus currently understood physics, but that's quite a different matter. --Trovatore (talk) 02:13, 28 February 2012 (UTC)

Well, we have managed time travel! Ok, perhaps not quite, but this experiment was very interesting. http://en.wikipedia.org/wiki/Hafele%E2%80%93Keating_experiment They managed to get a clock to travel nearly 40 nanoseconds in to the past/future. Ok, it's not time travel as such... Zzubnik (talk) 10:48, 27 February 2012 (UTC)

That's "time travel into the future", aka the twin effect/paradox. It's a totally different beast from traveling to the past. -- BenRG (talk) 19:45, 27 February 2012 (UTC)

Hi BenRG. I'm aware of that. I thought it might be an interesting read to the OP. Personally, I think that time dilation like this is the closest that we will ever get to "travelling in time". — Preceding unsigned comment added by Zzubnik (talk • contribs) 10:17, 28 February 2012 (UTC)

If I'm playing snooker ball and move it back as it moves backward in time its an example . Thanks Water Nosfim — Preceding unsigned comment added by 81.218.91.170 (talk) 13:33, 27 February 2012 (UTC)

Here's a simple way of thinking about it. As you accelerate, time starts to slow down for you. At everyday speeds, this is entirely imperceptible, but once you get up near the speed of light, it ramps up and becomes noticeable (from your point of view, time will pass normally, though). As you go faster and faster, approaching the speed of light, time slows further still, and if you were able to travel at exactly the speed of light, time would stop completely. What this implies... is absurd, and just one of the many reasons why you cannot travel at the speed of light. But if you could then accelerate even more, time would begin to go backwards. The faster you went, the faster back through time you would go. Again, from your point of view, time would proceed normally. Goodbye Galaxy (talk) 15:21, 27 February 2012 (UTC)

I meant it has been proven scientifically and mathematically if we can somehow manage to travel faster than light. And yep as with our technology today, we are no where close to the speed of light. A lot of people today would say travel faster than time is impossible. But impossibilities always have changed over time, it is impossible right now doesn't mean it will be impossible in the future. A thousand years ago, there were a tons of stuffs that consider as impossible but we can do them with ease today. I'm not saying certainly time travel is possible but we don't know for sure it's impossible either. So basically theoritically it's possible if we can travel faster than light but practical is we will see in the future or our descendants will??Pendragon5 (talk) 19:37, 27 February 2012 (UTC)

@Goodbye galaxy: Why the faster you move = the slower than time is? I don't understand the concept that0 if you travel faster than light then why is it that time is running backward?Pendragon5 (talk) 19:37, 27 February 2012 (UTC)

Goodbye galaxy is wrong about that (see my reply below). As for the rest I don't know what to say except what I said above. -- BenRG (talk) 19:50, 27 February 2012 (UTC)

The time dilation factor is ${\sqrt {1-(v/c)^{2}}}$. This does go to zero as v → c, but it goes imaginary, not negative, when v > c. In fact, negative values of the factor correspond to speeds less than c; it's only by convention that the positive square root is used. Special relativity, without additional assumptions, has no concept of going "forward" or "backward" in time. -- BenRG (talk) 19:33, 27 February 2012 (UTC)

LOL then we just make an assumption that time connected to speed? I don't see how they connected, time has nothing to do with speed. Time is something always happening no matter what we do. As we travel faster and faster, how can it possible effect the flow of time? Time is just a concept that humans have came up with, it's arguable of what time actually is. As i can understand, we still have a poorly understand about time. We still have long way to go if time travel is possible. But the time travel concept many famous scientists have came up with really confused me.Pendragon5 (talk) 20:00, 27 February 2012 (UTC)

"As we travel faster and faster, how can it possible effect the flow of time?": Few if any people understand it completely, but it does. This is part of Einstein's theory and it has been confirmed by accurate clocks in spaceships. They travel at great speed, and their clocks go a little slower than clocks on earth. The theory of relativity is mind-boggling, but it does work. It makes accurate predictions. You are right that real time travel (i.e. backwards, because we always travel forwards anyway) is usually based on poor understanding of the theory. -- Lindert (talk) 20:21, 27 February 2012 (UTC)

Well the concept of the faster we go = the slower the time flows is just mind crunching, i don't think i can make any sense out of it. I see no connection between the two, no matter of faster you travel, it is only get you to one place to the other faster not travel in time. Even if we can travel faster than light, i don't see how it can possibly travel back in time. Perhaps there is something else is effecting it and we don't even have any knowledge about it yet, such as dark matter and a bunch of other predicting particles that scientists think it must be there so the whole thing can make sense. As i can see, we still have a lot of assumptions. I don't mean to say human race is stupid, we are the smartest species in the Earth indeed but i think we are still very stupid "compare" to the universe as the whole. I feel like as it is right now i only consider that we barely know anything about the universe yet, there are still a lot of things left unexplained or doesn't make sense to human's conscious. Plus what we think is right for now may be proven wrong in the future. It always have been like that, that's the natural of science. I wonder if there is an absolute truth that will forever never be proven wrong nor can it be improve one day.Pendragon5 (talk) 23:41, 27 February 2012 (UTC)

You're thinking about time in the wrong way. You're thinking of time (change) as more primitive than everything else in the world. That's why you don't understand how the laws of physics can "affect time". Actually, time is an aspect of the world on the same footing as distance. Clocks tick off the seconds, and people think and perceive the world and grow older, by means of physical interactions between their various parts. If you think of time in that way then there's nothing strange about special relativity at all. As someone who does understand it, I assure you that it's not nearly as amazing, or interesting, as it might seem at first. -- BenRG (talk) 01:34, 28 February 2012 (UTC)

Along that line, I used the phrase relativity is "a basic consequence of geometry" when a question came up a week or two back. If you work out the math to its logical conclusions, you'll see that there's no other way things could work - there'd be an inconsistency somewhere. That's why we have things like length contraction or time dilation. As far as physicists are concerned, conundrums like the barn door paradox are less inconsistent than the consequences if we did not make relativistic corrections. For example, if the speed of light were not constant, as observed from any reference frame, the natural consequence would be that some reference frame is the canonical one, and everyone else is wrong; the laws of physics would change from place to place and person to person. Not only is the idea of a canonical universal "correct" reference frame a profoundly unsettling concept for many physicists, it's also not what we measure. We use relativity (in both special and general forms) because it is internally consistent (the math all works out) and externally consistent (it matches our experiments). All the equations and the mathematical abstractions about relativity are simply tools to help us formally explore the consequences of our observations. Nimur (talk) 02:08, 28 February 2012 (UTC)

Hopefully these explanations have disabused the OP of any notion that the highly questionable (at best) nature of the concept of time travel is in any way comparable to the well understood and experimentally verified nature of the feature of our universe that is time dilation. The OP may wish to read Poul Anderson's classic hard science fiction novel Tau Zero, which prominently features, explains, and is titled after time dilation (to the extreme). If they have sufficient self-discipline, they should postpone reading our article until they have completed the novel; it is a good read. The OP may also find our Twin paradox article interesting. -- ToE 13:23, 28 February 2012 (UTC)

Don't really understand the concept at all. There could be some unknown factors that affect the clock to go slower but the time is not actually going slower. Humans made clocks to keep track of time so it may not totally define time. It's really hard to explain what i'm going to get at. I don't even sure of what i'm talking about, it's just something in my mind that... I think we, humans, have assumed that we know time enough but maybe we are not and we don't realize it. Every single concepts that we know are the products of our humans' conscious or imagination. We made up a lot of stuffs to explain things in our universe, what makes sense to us may not be in fact the truth. As we're getting more advance and more advance we started to realize many flaws we had in the past, it is keep improving over time. As it is right, i think we are no where close to perfect. We still have a long way to go, maybe 1 thousand more years or 1 million more years or we could be extinct one day? Anything be happen but i think if we have reached to the point where we understand the universe completely then we, human race or perhaps all individuals, will probably be immortal until the universe dies on its own. I seriously don't think we understand what time is yet, perhaps we think we have strong understand about it but doesn't mean it's 100% correct yet.Pendragon5 (talk) 19:44, 28 February 2012 (UTC)

With all due respect, your response comes across as simultaneously naive yet supremely arrogant for a high school sophomore who has expressed interest in becoming a professional astronomer (per previous discussions) to make. (Seriously, haven't you come across this concept before in popular science television shows? What have you thought relativity was all about?) This is a reference desk and we have provided references and have filled in the context explaining that this is a well established and scientifically understood field. Have you read our Special relativity, Time dilation, and Tests of special relativity articles? They are not overly heavy in math, but don't just stop if you run into a formula that doesn't make sense; push on, as there may be useful text further down the article. Once you have read those, you are welcome to come back and ask for more references. Perhaps someone here can recommend a popular physics book (as in a book targeting the non-mathematical populace) which addresses your questions. We understand that the concept seems counterintuitive to you, but that does not mean that it is not the way things are. Conversely, no one, particularly no scientist, is claiming that everything is known or that all scientific theories currently believed to be valid will hold for all time. Special relativity, however, so precisely predicts that which we observe experimentally that there is no strong motivation to replace it with anything else, and should experimental discrepancies ever be found that do force a change in our understanding of special relativity, that change will not be a whole-scale one, but will be a refinement, much as special relativity is a refinement of Newtonian mechanics, which itself does a good job explaining the laws of motion at speeds which are small compared to that of light. -- ToE 23:59, 28 February 2012 (UTC)

The truly strange thing is that the speed of light is the same for all observers, regardless of their velocities with respect to one another. Once this is accepted as experimentally proven, then length contraction and time dilation follow as natural consequences; it's the only way it all makes sense. If the OP does choose to major in astronomy at university, they will work simple special relativity problems in Freshmen-level Physics. A fuller understanding will come in their Junior year when they study classical electrodynamics. (The "classical" here distinguishes it from quantum electrodynamics.) Having mastered a text such a Griffiths', the student will understand the derivation of special relativity, and should be able to easily work most relativistic problems of motion, but it won't be until they study a graduate level text, such as Jackson's, that they will be in a position to work more complicated relativistic electrodynamic problems. General relativity is a much different story. Its consequences will be discussed in many an astronomy course, but its fundamental mathematics isn't really tackled until graduate level physics.

I'm no science historian, but I suspect that most physics graduate students will understand special relativity as well as Einstein, and those specializing in general relativity will likely understand it better than Einstein ever did. The profession marches on, and long past are the days when only a handful of people on Earth understood Einstein's work.

Finally, the OP should not assume that an undergraduate degree in astronomy is the best route towards graduate studies and a profession in that field. In my experience at university, I found that the astronomy majors were much less proficient at math than the physics majors. Both took the same Junior-level Classical Electrodynamics and Classical Mechanics classes, and grades were bimodal. I believe that the students who either double-majored or majored in physics and minored in astronomy had a much better chance of being accepted into a good graduate program, and those who were most interested in cosmology were often applying to physics departments, where that sort of work is mostly done. -- ToE 22:09, 27 February 2012 (UTC)

Just as an historical note: special relativity wasn't the one that required heavy mathematical work. That was the one where people just didn't like the conclusions. One of the main criticisms was that it was mathematically simplistic — a trick of algebra — as compared with, say, the kind of math you needed to calculate vortex stability in luminiferous ether flows. General relativity was the one that required some more mathematical ability than your average physicist had at the time, and was first embraced by heavily mathematical physicists in England primarily for this reason. (The British had a stronger mathematical physics tradition at the time; the Germans were mostly about very careful experiments.) Later generations of physicists would become increasingly mathematical and theoretical. (Even they didn't work on GR, though. GR more or less wasn't even taught from the 1920s through the 1970s, or something along those lines — I can't recall the exact dates. It wasn't a hip area of physics.) --Mr.98 (talk) 02:12, 28 February 2012 (UTC)

Anecdotally, I can confirm that my alma mater's physics department offered an undergraduate course in general relativity. I don't imagine that it was a large class, but there are at least a few undergrads each year who can handle GR. TenOfAllTrades(talk) 00:38, 29 February 2012 (UTC)

Many times the particle goes back and forth in time. When he starts moving faster, the average of time begins to run down, and see the parallel universes which is related only to the speed of C, what remained of the particles that move backward and forward in time remains to one parallel universe . Thanks Water Nosfim — Preceding unsigned comment added by 81.218.91.170 (talk) 05:39, 28 February 2012 (UTC)

Binocular vision and microscopes

Is there a known condition whereby one cannot look through the microscope with both eyes simultaneously? How is this phenomenon called? What are the treatments if any? Thank you. Gidip (talk) 11:10, 27 February 2012 (UTC)

The same issues should apply to both microscopes and binoculars. Therefore, what you are looking for is the section Disorders of binocular vision in the binocular vision article. It lists several relevant disorders of the eye. As for treatment, the reference desk is not allowed to give medical advice. You would have to consult a professional Orthoptist. EverGreg (talk) 11:32, 27 February 2012 (UTC)

There are too many disorders listed there (I browsed this page before posting my question). I can't figure out which disorder is the relevant one. If someone can suggest one or a few specific disorders that would really help. Thanks. Gidip (talk) 11:57, 27 February 2012 (UTC)

Before we get into medical disorders, consider that it might just be improper setting of the microscope. The eyepieces have to be exactly the right distance apart or you have to move one way and the other to see through them. If you can't see through the microscope with both eyes at the same time, obviously you don't know that the current setting is correct. I'd say, keep trying. Wnt (talk) 12:53, 27 February 2012 (UTC)

He fathered seven point five children in one night and about Genghis Khan he only laughed

• http://www.youtube.com/watch?v=pzmI3vAIhbE

Er zeugte sieben Kinder in einer Nacht		He fathered seven children in one night
Und über seine Feinde hat er nur gelacht		And about his enemies he only laughed
Denn seiner Kraft konnt keiner widerstehn		Because nobody could resist his strength
Hu, ha...		Hu, ha...
		-- Dschinghis Khan by Dschinghis Khan

http://www.dailymail.co.uk/sciencetech/article-2106776/No-wonder-theres-violence-world-Hundreds-millions-people-related-despots-claims-study.html

... One historian believes that Yangdi, the 6th-century Sui dynasty emperor, for example, had children with 100,000 women.

The Emperor Yang of Sui (569-618) died when he was 49 years old. When he was 12, his father established the short-lived Sui Dynasty. So he was a prince when he was ready for having babies. He must have slept with at least 7.5 women each night for 37 years to father 100,000 kids. I mean from age 12 to age 49 and not a single miss.

Who is that historian?

Emperor Yang of Sui was 5 centuries before Genghis Khan. I guess he was unable to laugh at a man who could only father seven children each night. -- Toytoy (talk) 11:24, 27 February 2012 (UTC)

The Daily Mail references the anthropologist Laura Betzig. She mentions Yang in this article: "Yangdi, the Sui Dynasty emperor who built the Grand Canal and rebuilt the Great Wall, was credited by an official historian with 100,000 women in his palace at Yangzhou, alone, and when the Yuan dynasty founder, Kublai Khan, put up a capital at Beijing, he left a summer palace at Xanadu behind, with room in the excavations for another 100,000 (Wei, 2008)." So, he kept an enormous harem, but there is no claim that he had children or even slept with all of these women. --Wrongfilter (talk) 11:59, 27 February 2012 (UTC)

And it probably should be noted that estimates of population sizes (e.g. army sizes, harem sizes, city populations) by ancient historians are often off by an order of magnitude or so, either out of error or for dramatic/propagandistic effect. (Heck, we still do it today when estimating death tolls — the estimates before bodies have been counted in any systematic way, in either war or disaster, are often an order of magnitude off of the actual counts, in my anecdotal experience.) --Mr.98 (talk) 13:09, 27 February 2012 (UTC)

It is probably impossible to do that many women... to have many kids. I have read many Vietnamese and Chinese histories. Hundreds of children are typical for emperor but i never ever heard about any emperor has reached a thousand children mark yet. So 100,000 children = not even close to be possible. There were always some people who try to exaggerate stuffs about the kings so the king can favor them. Perhaps that emperor likes people to think he does a lot of woman. And as the emperor in any where of the world back there then they can basically say whatever they want and forced people to believe it. If you don't believe in it, the consequence will be really bad... Possibly deaths.Pendragon5 (talk) 19:44, 27 February 2012 (UTC)

Are you sure this is a literal description, rather than a gullibility of speech? After all, they say an emperor built a pyramid and nobody ever saw him hauling any bricks. Can't he have 100,000 children the same way? Wnt (talk) 00:57, 28 February 2012 (UTC)

I know nothing about 6th century Chinese medicine. But as to Chinese medical belief of early 20th century, I think many people, under Taoism influence, believed that one drop of semen equals to maybe 10 drops of blood or so. As a result, a playboy may be "sucked up dry" by women if he sleeps with too many of them for too many nights. I think many athletes still keep themselves from women before they are going have a big fight.

Sex is a very important subject in Chinese medicine and philosophy. Today's Taoists still practice a way to keep themselves from ejaculation during an orgasm. They trained not to "shoot" in order to enjoy sex and preserve their valuable bodily fluid. They did it to promote themselves to a higher degree of consciousness. An imaginary goal for some mysticism practioners is to "dominate" 100 women for a night without losing a drop of semen ("御百女而不洩"). I don't think there was feminism 1500 years ago, sorry.

There were very high ranked officials to decide who should sleep with the emperor each night. I don't think an emperor was allowed to waste his "dragon's essence" by sleeping with 100,000 women. If you play so much, you'll end up like a zombie! An emperor might have 100,000 women in his harem. However, the majority of these women were living in so-called "Cold Palace" ("冷宮"). They were not allowed to have sex with the emperor unless they were chosen. They end up marry an eunuch when they got too old to serve the emperor. The emperor could have several women with him each night. He was not allowed to ejaculate to all of them. On the other hand, if he ejaculated to the specially chosen woman, an eunuch outside was ordered to register the exact time of ejaculation in order to have the time reviewed by an astrologer. At least it was the practice of China's last Dynasty, Qing Dynasty.

Wang Zhaojun (50BC?-?) was a extremely beautiful lady-in-waiting of Han Dynasty. It is said that she refused to bribe a painter. As a result, she was painted as an ugly woman. The emperor did not know her before she was given to the Huns. ...... Well, the painter was sentenced death and she was sent far north .... Never been enjoyed by the emperor ......

I don't want to blame a scientist for her ignorance of Chinese history and philosophy, even though having 100,000 kids certainly is beyond science, logic and imagination. Not even a NBA basketball player could come even close without artificial insemination. I just want to know who's that historian? Ha! Ha! Ha! -- Toytoy (talk) 07:38, 28 February 2012 (UTC)

I don't think eunuch can have sex, their main sex organ is gone.Pendragon5 (talk) 19:15, 28 February 2012 (UTC)

While I agree that 100,000 children is beyond the realm of possibility, your numbers of 7.5 women a night for 37 years is off given that twin, triplets, etc. are also possible. 203.27.72.5 (talk) 01:41, 29 February 2012 (UTC)

Can a Silicon atom get split into smaller atoms, like a carbon and oxygen atoms?

Hi, Is there any way to split a silicon atom (14) into a carbon atom (6) and an oxygen atom (8)?

Or is the fusion of lighter atoms (< 26) a one-way process towards iron (26) only?

Thanks --InverseSubstance (talk) 23:27, 27 February 2012 (UTC)

This kinda rings a bell. Have you been reading something like this:Biological transmutation. Neutron bombardment can transmute Si to phosphorous but as to the other theories I want to keep clear of them.--Aspro (talk) 23:51, 27 February 2012 (UTC)

Ah. Nothing sucks-seeds like a toothless biggie. With the aid of my dowsing pendulum I have found this... [3]. Well, it seems one learns something new every day ;-) --Aspro (talk) 00:06, 28 February 2012 (UTC)

Thanks - Not sure if the above is to be taken seriously? I not looking for a wacko nut job's outrageous claim. It seems physics basically says, once an atom has fused, it can never get defused.

Phosphorous (15) is higher than Silicon (14). I'm just wondering if light atoms can only ever become heavier atoms. That is, they can't ever migrate backwards towards lighter atoms. Just wondering. --InverseSubstance (talk) 00:21, 28 February 2012 (UTC)

Bombarding a nucleus with energetic particles (e.g. cosmic rays) can sometimes cause even relatively light nuclei to break apart. For example, the traces of Beryllium-10 found on Earth are mostly caused by cosmic rays breaking apart nitrogen or oxygen in the atmosphere. Dragons flight (talk) 00:42, 28 February 2012 (UTC)

For reference, the process is called Cosmic ray spallation Vespine (talk) 01:21, 28 February 2012 (UTC)

The Discovery_of_fission section of our Nuclear fission article alludes to "splittings" or fissioning of light elements achieved when the phenomenon was first investigated. Although Silicon is not explicitly mentioned, I can think of no reason why it should be any less fissionable than other light elements. {The poster formerly known as 87.81.230.195} 90.197.66.193 (talk) 02:09, 28 February 2012 (UTC)

All right! Thanks. Because now it seems possible to change sand into oil. Theoretically at least. I'll keep grinding away... --InverseSubstance (talk) 05:15, 28 February 2012 (UTC)

I don't think so. In theory, you can take any atom of your choice (eg silicon), and hit it with any atom or particle of choice (eg electron, gamma photon, thru to the largets atom possible). For each combination of traget atom and incident particle, you'll get smaller atom plus one or more particles and some energy radiated. Just what you get is governed by certain rules. More often than not, the smaller atom wil not be nuclear stable, and within microseconds to kiloyears, depending on the target and incident combination, decay into something else - this may continue several times. Problems: a) not all combinations have been tried, b) the technology to select and use the optimal combination may not exist, and c) we know enough to know what you get is seldom convenient. So, in practice transmuting silcon into carbon is not possible, and nor is the reverse. Ratbone124.178.178.1 (talk) 07:22, 28 February 2012 (UTC)

It's definitely possible to go from stable silicon to stable carbon, it just might not be possible to do directly. Regardless, the energy costs would be obscene compared to the energy you'd get from burning the resulting oil you plan on making. If you're already cool with the process being energy inefficient, you are much better off making oil out of carbon dioxide, which is easily doable. Someguy1221 (talk) 07:27, 28 February 2012 (UTC)

You can't make oil out of just carbon dioxide - you would need some hydrogen from somewhere. Water would be the obvious source. Then you're just doing the usual combustion reaction backwards. If combustion works, then combustion backwards should work, you just need to put enough energy into it (and somehow prevent the newly formed oil and oxygen from immeadiately combusting back into carbon dioxide and water - that would probably be the tricky bit). --Tango (talk) 12:34, 28 February 2012 (UTC)

The carbon and oxygen maybe radioactive depending on which isotopes are generated. The desired reaction pathway is also unlikely to be only one, so there may be other radioisotopes from side reactions present in the mix. For making oil, you don't just need the right element; the chemical state of the newly created carbon is also important. Transmutation of silicon sounds like a horrible choice of a carbon source to make synthetic oil. As mentioned above, why not just use carbon dioxide? 203.27.72.5 (talk) 02:01, 29 February 2012 (UTC)

February 28

can an exothermic reaction create ice?

could an exothermic reaction underwater create, as a byproduct, ice: however, doing so by decreasing the density of the affected area greatly.

I am thinking of a cubic centimeter of water that we mark so we can trace it. Then an explosion of that cubic centimeter into a cubic meter. The greatly reduced density could cause it to freeze, could it not, yet the explosion from cubic centimeter from cubic meter is, well, explosive. Which leads to the question posed above. Please let me know if I seem to indicate that I am laboring under false assumptions of either physics, chemistry, or thermodynamics. Thanks. (Note that I don't make any assumptions about the actual process involved! It could be a special chemical, a physical process, whatever...just that it's exothermic. I also don't care if, as a result, the water outside our new 'cubic meter' gets hotter/undergoes an increase in entropy: indeed I expect it to.). --80.99.254.208 (talk) 06:54, 28 February 2012 (UTC)

This is quite possible if pressure is sufficient. All you need is for the heat removed by the expansion to be greater than the heat needed to be removed as heat of sublimation. If the water is super critical, ie the pressure is above the critical pressure 22.064 MPa for water, the heat of sublimation is essentially mimimum (about 6 MJ/kmol) when the triple point temperature is reached. However, if the pressure is well above critical, the specific heat of the super critical phase is mimimised, making it harder to make ice. This is quite easy to see if you look at a plot of temperature versus internal energy. Ratbone124.178.178.1 (talk) 07:08, 28 February 2012 (UTC)

I'm confused, 1 milliliter into 1000 liters, wouldn't that just vaporize the water not freeze it? Maybe I'm not understanding what you mean by "explosion". Vespine (talk) 21:52, 28 February 2012 (UTC)

Vespine, obtain a graph of temperature versus internal energy, and compare it with the phase diagram for water, and it will become clear. At standard pressure (~1 atmosphere), water transistions from ice/solid, to water/liquid, thru to gas/steam. But at sufficiently high pressures the liquid will be a supercritcial liquid, which is a liquid that is someting like a gas (you can expand it and reduce its temperature) but does not comply with the ideal gas laws - that it the normal straitforward relationship between volume and temperature doesnot hold. So, under high pressure, the liquid H2O becomes supercritical - and temperature drops without vaporisation. Ratbone120.145.22.14 (talk) 02:00, 29 February 2012 (UTC)

"The greatly reduced density could cause it to freeze, could it not(?)". No, it could not. I don't know why you think it would. The only thing that comes to mind is the negative thermal expansion of water, but you have to keep in mind that this only occurs between 0°C and 4°C and is not a reduction in density in the order of magnitude that your talking about. I agree with Vespine that increasing the volume will just vaporize the water. To increase the volume (explode) the 1mL of water you can either heat it (which in and of itself is by definition an endothermic process) or decrease the pressure, in which case it will vaporize and expand to fill the void (also endothermic). 203.27.72.5 (talk) 03:45, 29 February 2012 (UTC)

Vespine, did you look at the phase and internal energy diagrams as I suggested? If the water is above critical pressure, it can be expanded without vaporisation, by definition. Liquids are only "incompressible" if outside the critcal region. Ratbone124.182.60.34 (talk) 04:49, 29 February 2012 (UTC)

That IP is not me.. but I still don't get it..I found a phase diagram for water, I can't find "temperature versus internal energy" for water. I'm not sure what it's going to show.. What I don't understand is how you are keeping the water "above critical pressure" while expanding its volume by six orders of magnitude? Vespine (talk) 06:10, 29 February 2012 (UTC)

It would be difficult indeed to keep it above ~22MPa while expanding 6 orders of magnitude. But the 6 orders of magnitude came form the OP, not me. I assumed that wasn't the core of what he was asking - he was just clarifying his idea. For water, at triple point temperature, you only need to extract 6MJ/kmol to freeze it. So if its only just above that temperature, you only have to expand it enough to remove 6MJ/kmol. That won't require 6 orders of magnitude expansion, it won't need even 2:1 expansion. Now, if I knew how to insert a picture, I would give you a temperature - internal energy diagram - but I don't. Ratbone124.182.159.25 (talk) 07:57, 29 February 2012 (UTC)

Semi conductors

Substances whose conductivity lies between that of a conductor and an insulator is called semi-conductor.But why isn't it called semi-insulator. — Preceding unsigned comment added by Aditi keerti (talk • contribs) 08:29, 28 February 2012 (UTC)

It could have been. Go find the person who chose that convention and shoot him with a semi-manual gun. StuRat (talk) 09:26, 28 February 2012 (UTC)

The definition of a conductor is that which has charge carriers (typically valence electrons fully mobile within crystals), can be ions in liquids), thereby permitting the carrying of current. You can thus have a material with not very freely available carriers (typically mid-valence electrons & missing electrons partially/semi mobile with crystals), so "semi-conductor" makes some sense in this case.

The definition of an insulator is that which has NO charge carriers, so cannot carry ANY current (in practice, with the right instruments, very minute currents may be detected, due to impurities, leakage thru contaminants on the surface, etc). It's just semantics, I guess, but semi-nothing doesn't make as much sense in English. Semi-something is still something; semi-nothing is an oxymoron at best. Ratbone124.182.55.62 (talk) 09:58, 28 February 2012 (UTC)

At sufficiently high electric fields, even the best insulators will start conducting (Breakdown_voltage) - a perfect conductor exists in reality (superconductor) but a perfect insulator doesn't. 83.134.160.77 (talk) 06:33, 29 February 2012 (UTC)

But breakdown hardly affects the explanations given, as the explanations are based more on the quirks of the english language than the properties of materials. Having said that, with the exception of breakdown within a sealed container, breakdown means permanent chemical damage to the insulator - it is no longer an insulator because at least part of it has been changed to a different chemical form. While gaseous breakdown, breakdown is due to a change to plasma; as soon as you take the voltage away, it changes back to the original insulating gas. You can push current thru semiconductors and conductors as many times as you like without the slightest chemical change, subject to not overdoing it and overheating. And you never see in insulators current varying in proportion to voltage, but you always do in conductors, and you also see it approximately so in semiconductors. Ratbone138.217.245.71 (talk) 07:37, 29 February 2012 (UTC)

A ball rolling down an incline

When a ball rolls down a incline, how do we know how much of the potential energy gets converted into kinetic energy and how much gets converted into rotational energy? Widener (talk) 11:52, 28 February 2012 (UTC)

See Moment of inertia and List of moments of inertia. Dolphin (t) 12:08, 28 February 2012 (UTC)

If you know the radius of the ball, it is easy to calculate (if it isn't gliding, but rolling) what the relation is between the rotation- and movement velocities. Using the moment of inertia calculated for the ball, you can derive the ratio between rotational and kinetic energy. -- Lindert (talk) 12:37, 28 February 2012 (UTC)

How does one use the moment of inertia to calculate the ratio between kinetic and rotational energy? Widener (talk) 20:39, 28 February 2012 (UTC)

The rotational energy is (1/2)Iω², where I is the moment of inertia and ω is the angular velocity. The translational kinetic energy is (1/2)Mv². If the object is rolling without sliding then v = rω where r is the radius, so the ratio of the translational kinetic energy to rotational kinetic energy is Mr²/I. Rckrone (talk) 00:42, 29 February 2012 (UTC)

Oh, I see; it makes sense that v = rω Widener (talk) 06:24, 29 February 2012 (UTC)

(edit conflict) You also need take friction into account. Is there sufficient friction that the ball is purely rolling or will it also slide a bit? If there is no sliding, then you can easily relate the linear velocity to the rotational velocity (distance travelled in one rotation equals the circumference of the ball). Once you've got the velocities, you can work out the kinetic energy using E=1/2mv² and the rotational energy using the moments of inertia Dolphin links to. If there is sliding, then it gets rather more complicated (friction, generally, is complicated - there are massive simplications usually taught in schools that might get you somewhere, but to get it accurate is really hard). --Tango (talk) 12:40, 28 February 2012 (UTC)

What does Lidocaine have to do with wood?

Other names for the anesthetic lidocaine are "xylocaine" and "lignocaine". The prefixes xylo- and ligno suggest this has something to do with wood, but the Wikipedia article doesn't say anything about it being made from, or being chemically similar to, some substance extracted from wood. What, if anything, does lidocaine have to do with wood? -- Finlay McWalterჷTalk 13:16, 28 February 2012 (UTC)

According to the Oxford English Dictionary, 'xylocaine' got it's name because of the chemical relationship with xylene (and cocaine), which in turn is obtained from wood-spirit ('Crude methyl alcohol obtained from wood by destructive distillation'). It is also called 'lignocaine', because ligno- is the Latin equivalent of 'xylo'. -- Lindert (talk) 13:35, 28 February 2012 (UTC)

distance and time to orbital velocity at tourist-acceptable G's at sea level, assuming vacuum?

If the Earth were a perfect sphere and had no atmosphere, then a pod could accelerate fast enough to reach Orbit right at sea level, couldn't it? (well, a few inches/feet above sea level, let's say). So, at g's that are acceptable to tourists/passengers, how long would this acceleration take, both in terms of time taken and distance travelled in terms of our physical geography/Earth miles or kilometers? What if we increase the acceptable G's from tourist/passenger to whatever is the human maximum, however uncomfortable? Then how long would it take and what distance would be covered? Thanks. 188.6.78.231 (talk) 14:19, 28 February 2012 (UTC)

also could some confirm my premise itself, that at the right speed, orbit a few cm/feet above sea level in a perfect-sphere (uniform) earth without an atmosphere scenario is possible? 188.6.78.231 (talk) 14:27, 28 February 2012 (UTC)

Orbital speed for a circular orbit at zero altitude is about 7.9 km/s. If we assume a lateral acceleration of 5 m/s² (half a g, equivalent to the acceleration in a fast car) then it would take about 1600 seconds or about 27 minutes to reach this speed, in which time you would have travelled around 6,400 km, which is a little more than the distance from London to Chicago. Gandalf61 (talk) 15:00, 28 February 2012 (UTC)

Thank you! Do you think this is reasonable for a tourist/passenger to undergo for 27 minutes? (The acceleration of a fast car?) Would it be possible I don't know to have the pod turn toward the direction of travel, so everyone just feels a bit heavier instead of being pushed BACK (and not down) into their seats? Do you think this is a reasonable tourist experience? Thanks again for the calculations. 188.6.78.231 (talk) 15:17, 28 February 2012 (UTC)

On the other hand, at a crushing 10g, it would take 80 seconds and 3000 km. SpinningSpark 15:14, 28 February 2012 (UTC)

wow. Okay, here's one. How long would it take at a g so low that you can't notice that you're moving? Would you already go around the earth / several times before you reached orbital velocity at such a speed? 188.6.78.231 (talk) 15:17, 28 February 2012 (UTC)

Just as an aside: the slower you accelerate, the more energy you waste to gravity burn. Using the "high school algebra" formulation, as discussed in this excellent NASA page from Glenn Research Center, you need to modify your ideal rocket equation, yielding a loss term proportional to the time of the burn, "-g0*tb" - energy (or, fuel, or, dollars), that is purely wasted and gains absolutely nothing for the final orbit height or velocity. Nimur (talk) 18:00, 28 February 2012 (UTC)

To reach orbital velocity at sea level you'd likely use something like a maglev train in a vacuum tube, which should deal with gravity more efficiently than a rocket. OP should make plots of time vs horizontal g-forces (sqrt(radius of earth * gravitational acceleration) / time) vs distance-to-orbital-velocity (.5 * sqrt(radius of earth * gravitational acceleration) * time^2) to see what's plausible. --81.175.230.91 (talk) 18:44, 28 February 2012 (UTC)

How should a maglev train "deal with gravity more efficiently than a rocket"? Do you have a reference for this statement, or did you simply decide that you could ignore the principle of conservation of energy? Perhaps you are confusing non-conservative work against gravity with structural load bearing by a hypothetical "space elevator." Nimur (talk) 19:42, 28 February 2012 (UTC)

How much energy do ordinary trains spend not falling down? --81.175.230.91 (talk) 22:00, 28 February 2012 (UTC)

Indeed. Maintaining a constant altitude doesn't use energy. The whole reason gravity drag is a bad thing is because the energy is wasted - if it were a conservation of energy thing then it wouldn't matter how long it took you to get into orbit, the energy requirements would be the same. --Tango (talk) 00:19, 29 February 2012 (UTC)

If you travel around the earth's axis of rotation (in the same direction as the earth's rotation) at the earth's widest point, then you are already travelling at about 0.5km/s. That means you'd only need to accelerate to ~7.4km/s which takes only 1480 seconds (24 minutes 40 seconds) and during that time you'd only travel about 5500kms which would be from Dakar in Senegal to Manaus in Brazil. 203.27.72.5 (talk) 04:22, 29 February 2012 (UTC)

Animal fat fuel

So I was cooking some ground beef the other day, and I drained the fat, and I looked at the slimy mess and I thought to myself, "Is it possible to fuel a car with this stuff?". So is it possible? ScienceApe (talk) 15:34, 28 February 2012 (UTC)

Animal fats can be turned into fatty acid esters (fatty acid methyl esters, in particular) that make suitable biodiesel. Using the fat directly would present practical difficulties. 148.177.1.210 (talk) 15:43, 28 February 2012 (UTC)

Animal fats used to be used for all sorts of things, including as a cooking and lighting fuel. See Tallow, Lard, Schmaltz, Suet, for some animals fats which have both culinary and non-culinary uses. Also see Soapmaking#Soap_making_processes. Making soap from animal fat is an ancient, and relatively simple, process. Soak woodashes in a bunch of water. Filter off the ashes; the water now contains a bunch of alkali. Put a bunch of the alkali water together with a bunch of tallow. Heat for a few hours, seperate the glycerin layer; and let it cool. What you're left with is soap. --Jayron32 21:11, 28 February 2012 (UTC)

Slaughtering with a guillotine

What speaks against slaughtering animals with a guillotine? It seems more reliable, faster and less painful than stunning and cutting the throat. XPPaul (talk) 18:34, 28 February 2012 (UTC)

Probably not faster because it takes time to position the head correctly in the guillotine, adding to the distress the animal feels and increasing the risk of injury by slaughterhouse personnel. Also, the guillotine would have to be checked, cleaned and reset after each operation. Dominus Vobisdu (talk) 18:40, 28 February 2012 (UTC)

That don't make sense. Cattle in slaughter houses for years have been lead in to a squeeze to have their throats cut. A guillotine at this stage could likewise be automated. The problem with a guillotine would be is now one has a carcass in two parts. This requires an extra operations to recover the head and that complicates the following processes of carcass inspection, because the are two bits which need to be kept together for veterinary inspection (check for diseases extra, which is legal requirement in many countries). So, this imposes extra costs and chances of getting parts mixed up. It is reckoned that cattle loose consciousness before that realise what has happened with the current process. This requires the knives to be kept sharp, just like a guillotine blade. If guillotines were better they would already be in use. Gosh, all this talk of food is making me feel hungry again and I'm supposed to be on a strict diet. --Aspro (talk) 23:54, 28 February 2012 (UTC)

They'd almost certainly be conscious for far longer after being guillotined than they are after being stunned. Dmcq (talk) 00:29, 29 February 2012 (UTC)

Decapitation would require slicing through the spinal cord or even brain stem which may release disease causing prions that are known to exist in bovine and other ruminants. 203.27.72.5 (talk) 04:27, 29 February 2012 (UTC)

Real, Physical Status of Odyssey Moon

I was reading about the Google X Prize team entry Odyssey Moon that submitted its entry on December 6, 2007 to send a probe to the moon. The Wikipedia article has nothing as to the current status or if the team has actually built anything so far (note, the picture in the Wikipedia article is not their thing), and as far as I am able to tell, their official website doesn't plainly say how much they have actually done either (or maybe they have, I'm not fluent in marketerese). What have these people actually made as of the asking of this question? Have any of the people in that fundraising engineering operation released any estimate of a possible launch date in any way, shape, or form? 20.137.18.53 (talk) 19:06, 28 February 2012 (UTC)

Apparently nothing concrete. Their latest press release says that they teamed up with Paragon to establish a "Lunar Oasis", or greenhouse on the moon. Sounds impressive until you see it: [[4]]. Lots of marketing pie-in-the-sky talk, but still in the fundraising stage. Dominus Vobisdu (talk) 19:25, 28 February 2012 (UTC)

How much of time dilation is a consequence of signal lag?

http://en.wikipedia.org/wiki/Time_dilation In the two mirror experiment when the light returns to the bottom mirror it would take some time for this event to propagate back to the observer. Is time dilation a consequence of this delay? Please clarify — Preceding unsigned comment added by 199.89.103.11 (talk) 19:29, 28 February 2012 (UTC)

The relationship you're calling "signal lag" is expressly and rigorously defined as the retarded time, which is a crucial intermediate concept that you can use while deriving the lorentz transform from classical electromagnetic wave theory. Time dilation is a consequence of the fact that we observe Maxwell's equations to be valid in all reference frames, including those frames that are moving relative to our own frame. As a result, the relationship between the change in an electromagnetic field with respect to both space and with respect to time follow the same law in both reference frames. (In fact, this applies in all reference frames). To satisfy this constraint, we must define an adjusted time, whose value depends on the relative motion between reference frames. If you work the math, you find that this adjusted time is defined by the lorentz transform. Nimur (talk) 19:48, 28 February 2012 (UTC)

I guess what I'm asking is whether in time dilation experiment the time is measured using retarded time. If not then what would be the consequences if retarded time is used? 199.89.103.11 (talk) 20:04, 28 February 2012 (UTC)

In which time dilation experiment? For example, the NIST Physics lab for time and frequency measurement has a great webpage explaining practical details of Two Way Time Transfer. Indeed, in actual experiment, most of the time, the effects of special relativity are dwarfed by practical engineering considerations. In this 2007 paper published in the journal Nature, Test of relativistic time dilation with fast optical atomic clocks at different velocities, time is measured using ion-counters and a frequency-domain technique (which is really the state of the art). So, "no, retarded time is not used." In as few words as possible, accurate modern clocks use differential frequency measurement to experimentally validate and constrain relativistic time dilation. Nimur (talk) 20:30, 28 February 2012 (UTC)

In the moving mirrors thought experiment: http://en.wikipedia.org/wiki/Time_dilation does the observer compute the speed of light using retarded time? If not what what be the outcome if he measured it using retarded time? 199.89.103.11 (talk) 20:44, 28 February 2012 (UTC)

Signal lag doesn't enter into the definition of time dilation. The time in time dilation is the coordinate time, which is defined by means of a bunch of comoving synchronized clocks. There's a clock near every event of interest, and the coordinate time of an event is the time reading that you see on the nearby clock at the same time that you see the event. This removes any dependence on how far you are from the event, how fast you're moving, or anything else about you. Only the event and the nearby clock factor into the measurement.

Time dilation is the fact that if you have three clocks moving like this:

       A  B  C
       |  | /    ^
       |  |/     |time
       |  *      |
       | /|      |  
       |/ |       -------->
       *  |       position
      /|  |
     / |  |

where A and B are Einstein-synchronized, then the difference between the readings on C at the two crossing points (the asterisks) is smaller than the reading on B at the second crossing point minus the reading on A at the first crossing point.

This is geometrically the same thing as the fact that if you have two vertical lines and a diagonal line, the distance between the crossing points along the diagonal line is larger than the difference between the Y coordinates of the two crossing points. In fact the ratio of the two values is ${\sqrt {1+(run/rise)^{2}}}$, while the relativistic time dilation factor is ${\sqrt {1-(v/c)^{2}}}$, and the similarity of those formulas is not a coincidence.

Of course, the measurements made in actual experiments depend on the experiment. In the Hafele-Keating experiment, the clocks A and B are the same clock and C crosses that clock's worldline twice. This probably should not technically count as "time dilation". It's more like a version of the twin effect/paradox (which is geometrically the same as the fact that a straight line is the shortest distance between two points) -- BenRG (talk) 22:49, 28 February 2012 (UTC)

In the moving mirror thought-experiment there are Einstein synchronized stationary clocks at A and C to establish the coordinate time of the stationary frame. This is practically the same setup as the example I gave above. You could eliminate the mirror at B and move C to its mirror-image position in the diagram (above and to the right of B) or you could eliminate C and put the clocks at A and B, which amounts to the same thing. The advantage of the mirror is that you only need one clock (moving with the lower mirror) to measure the round-trip travel time in the moving frame. Otherwise you would need a moving clock at B also, and once you have two clocks you need to synchronize them, which would make this thought-experiment less convincing since the usual synchronization process uses beams of light. -- BenRG (talk) 02:10, 29 February 2012 (UTC)

Nuclear disasters

Was Fukushima or Chernobyl worse? --108.227.26.244 (talk) 22:00, 28 February 2012 (UTC)

Define "worse". --Jayron32 22:08, 28 February 2012 (UTC)

See Comparison of Fukushima and Chernobyl nuclear accidents. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 22:11, 28 February 2012 (UTC)

Independent of definition: Chernobyl was worse, with more direct and indirect deaths, and more radiation released. XPPaul (talk) 22:27, 28 February 2012 (UTC)

Chernobyl also has a larger affected area, but more of Fukushima's reactors were involved. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 23:35, 28 February 2012 (UTC)

I can't think of a reasonable definition of worse where the number of affected reactors is significant in itself... --Tango (talk) 00:22, 29 February 2012 (UTC)

There were more alarms up on the control room operator's DCS screen at Fukushima. 203.27.72.5 (talk) 04:36, 29 February 2012 (UTC)

I would argue that Fukushima was worse in at least one measure, namely the sigma level, i.e. the "unlikelyhood" of the event (and thus the induced shock in the general public). A major disaster in the Soviet Union was more or less expected, at least it did not come as a too big surprise. Fukushima on the other hand was pretty much a perfect storm. This does not only refer to the sequence of events leading to the scenario, but also that it should happen to such a high-tech nation as Japan. 109.149.46.78 (talk) 01:28, 29 February 2012 (UTC)

Surprising to whom? That's always the question. I think it was surprising to most people that Soviet engineers would almost purposefully blow up their own reactor. I think Fukushima was not as surprising as it ought to have been to the people who had already run flood simulations on the reactor setup and found that it was severely lacking in adequate protections. Fukushima wasn't a "perfect storm" — it was a reactor that was known to be in a seismically active zone, yet was not equipped to deal with heavy flooding after a tsunami, and the engineers were inadequately trained for emergency situations. --Mr.98 (talk) 03:34, 29 February 2012 (UTC)

The air-powered car isn't around - lobbyist conspiracy?

http://www.mylovetechnology.com/others/airpod-car-runs-on-compressed-air/

A car that can go long ranges on compressed air - something Big Oil would hate.

Why isn't that car happening in mass-numbers already? Perhaps it's because Big Oil Lobbyists went to congress to prohibit these cars on a pretext of something inconsequential and different. (If you try to argue to the contrary, are you working for Big Oil?)

And lobbyists could also gag the media from saying a thing about it, now could they?

There is a lot of explaining to do here, you all. Thanks. --129.130.208.81 (talk) 22:50, 28 February 2012 (UTC)

I see no evidence of a conspiracy - just a lack of evidence for practicality. Can you start by explaining why a system that "uses a small motor to compress outside air to keep the tank full" should necessarily be any more efficient than one that used the 'small motor' in a more conventional way - to turn the wheels? AndyTheGrump (talk) 22:57, 28 February 2012 (UTC)

This IEEE Spectrum article written 3 years ago seems like a much more realistic evaluation of the AirPod. Vespine (talk) 23:08, 28 February 2012 (UTC)

I doubt that Big Oil can indeed prohibit, or lobby for the prohibition of, a harmless invention. No matter if it's the air engine (which is doable, but seems impractical) or if it's the water powered motor (which is the invention of some crackpot). XPPaul (talk) 23:22, 28 February 2012 (UTC)

And America doesn't dominate car production like it once did. The conspiracy would need to reach deep into every other car company and nation where cars are produced. StuRat (talk) 02:54, 29 February 2012 (UTC)

Actually, Compressed-air vehicles seem to pre-date 'big oil'-powered ones: "In 1903, the Liquid Air Company located in London England manufactured a number of compressed-air and liquified-air cars. The major problem with these cars and all compressed-air cars is the lack of torque produced by the 'engines' and the cost of compressing the air". AndyTheGrump (talk) 04:25, 29 February 2012 (UTC)

Adding/subtracting sine waves of the same frequency

Hi all, what's the simplest formula for adding or subtracting 2 sine waves of the same frequency? I know that you can add or subtract two arbitrary sine waves and get a fairly complex formula like on this page (under Constructive and Destructive Interference), but if I understand correctly, two waves of the same frequency should result in a simple sine wave expressible in the basic form $y(t)=A\cdot \sin(\omega t+\phi )$. Is there a way to get that simple function for the resulting added (or subtracted) wave? Thanks! — Sam 66.31.201.89 (talk) 22:53, 28 February 2012 (UTC) (Yes, I know I first posted this in WP:RD/MA, but it's really a physics question, and that forum has only had one person post in over four hours and not even had a single actual answer all day...)

As the instructions at the top of the page say, it can take several days to get a complete answer. We're all volunteers and answer questions as and when it is convenient for us, so please be patient. That said, I don't understand your question - the first formula on the page you link to in the section you name is a formula for sine waves of the same frequency... --Tango (talk) 00:26, 29 February 2012 (UTC)

This is very easy to do if you understand vectors. But if not its still easy. If each sine wave is specified by an amplitude and a phase angle, convert each to a vector, then add the two vectors, then if required convert back to amplitude and pahse representation. For any sinewave of y volts at angle a, the vector is R = y sin(a) and I = y cos (a). You then add the two R's and I's. The ammplitude of the combined wave is the square root of [(R1 + R2)^2 + (I1 + I2)^2]. Keit121.221.233.252 (talk) 00:55, 29 February 2012 (UTC)

Tryptophan in milk

If we ingest milk, or some other food which contains tryptophan, will this tryptophan reach our brains and have an effect?XPPaul (talk) 23:12, 28 February 2012 (UTC)

Why do you think warm milk is one of the things recommended for trouble falling asleep? Or why the most popular day for taking a nap in US is the fourth Thursday in November? (Turkey is rich in tryptophan). The injested tryptophan ends up being converted into the neurotransmitter serotonin, which has a calming effect on the mind. Dominus Vobisdu (talk) 23:20, 28 February 2012 (UTC)

I was asking because it could be a common misconception. Being recommended doesn't mean a thing. We get every kind of crazy recommendations. XPPaul (talk) 23:27, 28 February 2012 (UTC)

Read the serotonin article for details. There is a section of the effects of food content. Dominus Vobisdu (talk) 23:33, 28 February 2012 (UTC)

It looks like you are wrong. — Preceding unsigned comment added by XPPaul (talk • contribs)

(edit conflict) Tryptophan is an amino acid and quite commonly present in many proteins, including meat and dairy proteins. It is an Essential amino acid, which means that a) you need it to live and b) your body cannot synthesize it; which means that you must get it from your diet. Contrary to the urban legend that dietary tryptophan can make you "sleepy" or have other psychoactive effects, tryptophan's main use in your body is to basically do what all amino acids do; which is to act as primary building blocks for making proteins and enzymes. Now, it is true that tryptophan is a precursor to certain neurotransmitters like seratonin and melatonin, which are involved in maintaining circadian rhythms (i.e. day-night cycle). Here's the important bit: Without tryptophan, you probably couldn't make melatonin; however an excess of tryptophan does not directly lead to an excess of melatonin. Your body makes melatonin as needed, not merely because there is an excess of tryptophan around. There is always an excess of tryptophan around, and your body uses it for lots of things. Because tryptophan is converted to melatonin, and melatonin is associated with sleep cycles, people make the erroneous conclusion that dietary tryptophan leads to sleepiness or other effects on the brain. In reality, you either get enough tryptophan or you don't, and under normal circumstances, having more than the minimum requirements doesn't lead to any extra effects on the brain. Lots of this information, as well as the "dietary tryptophan causes drowsiness" myth, are covered in the tryptophan articles. In summation: yes, tryptophan is used in processes which go on in the brain, yes you need to get it from diet, but these "effects" are a part of the process known as "being alive" and there isn't anything "extra" that tryptophan does when you eat it. It has an important role, but eating lots of it doesn't make it do those jobs "more". There's also nothing special about tryptophan from milk. It's the same molecule regardless of where it comes from. --Jayron32 23:30, 28 February 2012 (UTC)

Thanks. XPPaul (talk) 23:50, 28 February 2012 (UTC)

The above answer is very good, but I already found this reference so I'll still post it: From Serotonin#Biosynthesis: Tryptophan and its metabolite 5-hydroxytryptophan (5-HTP), from which serotonin is synthesized, can and does cross the blood-brain barrier. Vespine (talk) 23:39, 28 February 2012 (UTC)

yes, but it hasn't any direct effect. So, no glass of warm milk --> getting sleepy association.— Preceding unsigned comment added by XPPaul (talk • contribs)

Yeah, the issue is that tryptophan itself doesn't have any direct effects on the brain; it needs to be converted into something else, and the rate of conversion into those other things isn't directly affected by the concentration of tryptophan. It is to a point, in the sense that too little tryptophan will hinder the conversion into melatonin and seratonin; however having excess tryptophan, above what is being demanded at any given time, does not directly lead to drowsiness or other effects. --Jayron32 23:58, 28 February 2012 (UTC)

February 29

Compressed water

Why aren't people in the army or who might be traveling for a long time in the desert for some other reason issued tablets of compressed water - just take one and it contains as much water as a full water bottle? Wouldn't that allow your average soldier to carry lots more water than he could otherwise? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 00:29, 29 February 2012 (UTC)

Water is an incompressible fluid. XPPaul (talk) 00:38, 29 February 2012 (UTC)

I see whoop whoop is getting bored again and is asking questions he already knows the answer of, thereby probably driving away people with genuine questions. Stop it! 58.169.242.219 (talk) 00:41, 29 February 2012 (UTC)Wickwack

Not everyone knows that, the answer is not evident for all. XPPaul (talk) 00:42, 29 February 2012 (UTC)

Paul is actually incorrect. Water is only approximately incompressible. However, that approximation is extremely good. If you were to compress water at 10,000 atmospheres, you would get room temperature ice that is only 70% denser than liquid water at room temperature. Regardless, the limitation in carrying rations is the weight, not the volume. Someguy1221 (talk) 00:45, 29 February 2012 (UTC)

Looking into this more, just getting water to be 1% denser would require 200 atmospheres [5]. Someguy1221 (talk) 00:48, 29 February 2012 (UTC)

OK, I was not completely right, but I'd say I was approximately correct, water is not an incompressible fluid, it's only approximately incompressible. Anyway, it's incompressible for all practical purposes. XPPaul (talk) 00:50, 29 February 2012 (UTC)

One of the tricks to answering questions well on the ref desk is working out what level of detail the OP actually needs and not unnecessarily confusing them with extraneous information. Your answer, while less accurate than one that talks about what happens under 10,000 atm pressure, was a better answer. --Tango (talk) 00:54, 29 February 2012 (UTC)

Precisely! Now, whoop whoop is a frequent poster of questions and responses, sometimes intelligent, sometimes stupid, sometimes Dorothy Dixers, that it seems obvious the he himself would already know the answer to this one (another Dorothy Dixer), and so he requires no answer at all. Wickwack01:43, 29 February 2012 (UTC)

Are you suggesting the OP is insane? ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:09, 29 February 2012 (UTC)

No. Just a nuisance. I'm concerned that there may be people who know stuff and could spare the time to post good answers will not bother if they sense that the OP does not have a genuine need. Similarly, there may be people who would like some help with a realy good question, who won't bother if they think this is just a DD place. Wickwack58.169.241.13 (talk) 02:28, 29 February 2012 (UTC)

Link for non-Aussies: Dorothy Dixer. XPPaul (talk) 02:16, 29 February 2012 (UTC)

For non-Aussies again: The Wiki articale on Dorathy Dixers gives the original meaning of the term, and the one used in Australian Press (and in the UK) when discussing Govt ministers, but common street meaning include questions that the questioner already know the answer to, or questions asked at a meeting designed to stir people up rather than to get an answer. Wickwack58.169.241.13 (talk) 02:35, 29 February 2012 (UTC)

This sounds like a variation on the old elementary-school-level joke. A kid takes an empty can to show-and-tell. He says it's condensed H2O. Just add water! ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:51, 29 February 2012 (UTC)

Even if you could compress the water by any appreciable amount under a billion atmospheres of pressure and place it in a strong enough tablet sized container made from a digestible and non-toxic material, and even if you were having your soldiers march on the moon so weight is less of an issue and volume is important to minimize, then what happens when you take the pill? The container is breached and explosive decompression happens...in your gut. 203.27.72.5 (talk) 05:01, 29 February 2012 (UTC)

I imagine you could just decompress it into any old container first. Vespine (talk) 06:03, 29 February 2012 (UTC)

Why? So you could use it as a fragmentation grenade? The pressures involved are enormous. 203.27.72.5 (talk) 06:57, 29 February 2012 (UTC)

Elemental Composition of Clay

Hello. I was looking for detailed information on the elemental composition of clay (or various types of clay). All the sites I've found give qualitative information, whereas I am looking for quantitative information. Many thanks. 114.77.39.141 (talk) 00:53, 29 February 2012 (UTC)

Clay is mostly made of silicates (phyllosilicates to be precise). You can read more at clay minerals. --Tango (talk) 00:57, 29 February 2012 (UTC)

That will vary enormously from sample to sample, and there's no generallyy useful answer. What do you need this information for? It's a lot easier to help you find an answer when we know exactly what you need. Dominus Vobisdu (talk) 01:02, 29 February 2012 (UTC)

A few types of clay include Kaolinite (Al₂Si₂O₅(OH)₄), Chlorite ((Mg,Fe,Al)₆(Si,Al)₄O₁₀(OH)₈) and Illite (K,H₃O)(Al,Mg,Fe)₂(Si,Al)₄O₁₀[(OH)₂,(H₂O) which as you can see may contain a wide variety of elements.Tobyc75 (talk) 01:08, 29 February 2012 (UTC)

copper sulphate

In an oxidizing chalcopyrite (CuFeS2)system producing CuSO4 is there a point when an ion exchange could occure producing CuO and CaSO4? — Preceding unsigned comment added by 187.146.184.128 (talk) 02:22, 29 February 2012 (UTC)

Do your own homework. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 02:24, 29 February 2012 (UTC)

Other than water, expand as they freeze?

Does anything, other than water, expand as it freezes? Eomund (talk) 04:22, 29 February 2012 (UTC)

Yes. Silica glasses do. 203.27.72.5 (talk) 05:06, 29 February 2012 (UTC)