Wikipedia:Reference desk/Archives/Science/2010 March 24

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March 24

Bone marrow donations

Now that I'm 18, in the UK I'm eligible to sign up the bone marrow donation register next time I go in to donate blood. I've heard there are two separate methods of donation: bone marrow harvest directly from your pelvic bone, or stem cell donation after a few days of injections (by normal blood extraction methods).

My question is what are the advantages of bone marrow harvest over stem cell donation, and vice versa? Presumably there are advantages to both methods, or the bone marrow harvest would not be performed (as it's done under general anaesthetic and therefore inherently carries more of a risk). Thanks. Regards, --—Cyclonenim | Chat  00:57, 24 March 2010 (UTC)

A little terminology nit-pick: "bone marrow donation" clearly is extraction of bone marrow. But the goal is usually to get stem cells from it, so that's why extraction from blood is an alternative. Bone marrow transplant#Risks to Donor following Peripheral Harvesting of Stem Cells looks like it has some info. Also, "after a few days of injections" could have effects other than boosting the amount of harvestable cells (as well, having an elevating effect might itself have side-effects...not sure). DMacks (talk) 01:44, 24 March 2010 (UTC)

Thanks, interesting link. If anyone has any information on the advantages of using bone marrow harvesting specifically, that'd be great. Regards, --—Cyclonenim | Chat  08:57, 24 March 2010 (UTC)

We're not supposed to answer medical questions. I suggest asking the people where you go to donate blood. They probably know more about it than we do. — DanielLC 05:03, 24 March 2010 (UTC)

We're not supposed to answer medical advice. You're allowed to answer questions by which no harm could come from answering. Me asking the advantages of bone marrow donation over stem cell donation is not something that could harm me. Regards, --—Cyclonenim | Chat  08:54, 24 March 2010 (UTC)

(ec)Actually we are supposed to answer medical questions as long as they don't require medical advice. Kainaw's criterion is a good rule to follow. AlmostReadytoFly (talk) 08:58, 24 March 2010 (UTC)

I expect that if you are ever found to be a donor match to someone that your doctor will talk you through the various options for donation. By then a different method may be used. 137.73.4.211 (talk) 13:36, 24 March 2010 (UTC)

From the Cochrane database: "Bone marrow harvest versus peripheral stem cell collection for haemopoietic stem cell donation in healthy donors". It's quite a long document. Of note:-

• Pain prior to the donation procedure was experienced by peripheral blood donors only.
• More bone marrow donors experienced pain at donation site in comparison to peripheral blood donors.
• Pain subsequent to donation was experienced by both groups of donors. Bone marrow donors experienced more back pain and peripheral blood donors experienced more skeletal pain.
• Bone marrow donors are more likely to develop haemorrhage, anaemia and hypotension in comparison to peripheral blood donors.
• Bone marrow donors tended to experience more days of restricted activity, had more mean discomfort and a greater number were still experiencing restricted activity 14 days post-bone marrow harvest. Peripheral blood donors experienced greater difficulty in functioning within the first seven days.
• Bone marrow donors are more likely to require hospitalisation than peripheral blood donors.
• Both bone marrow and peripheral blood donors experienced psychological morbidity. Both groups had increased fatigue and reduced energy and anxiety following the procedure.
• The number of donors reporting any adverse events, was greater in the bone marrow group in comparison to the peripheral blood group.
• No life threatening adverse events were reported.

Axl ¤ [Talk] 18:36, 24 March 2010 (UTC)

Thanks, great summary of the disadvantages of both marrow donation, but are there any advantages? I haven't found any, and if that's the case, why is it still used commonly (though not as commonly as peripheral blood donation)? Regards, --—Cyclonenim | Chat  19:22, 24 March 2010 (UTC)

About coefficient of mastication

Could you please through some light on the term " Coefficient of Mastication " Kasiraoj (talk) 05:53, 24 March 2010 (UTC)

I think it means how thoroughly you chew your food when eating. FWIW 24.23.197.43 (talk) 07:01, 24 March 2010 (UTC)

Sounds like a term of art in the fletcherizing sciences. --Sean 12:43, 24 March 2010 (UTC)

An article about A model for comparison of masticatory effectiveness in primates includes a coefficient of masticatory effectiveness (E) the value of which increases with effectiveness of exposing new food surface area with each chew. Cuddlyable3 (talk) 22:25, 24 March 2010 (UTC)

Question on Scientists

Is it true that Watson and Crick, may have discovered the double helix on acid(LSD)? —Preceding unsigned comment added by Hmrnkng901 (talk • contribs) 06:05, 24 March 2010 (UTC)

FYI, LSD does not have a double helix structure -- that would be DNA. I think you might have confused the two acids. FWIW 24.23.197.43 (talk) 06:59, 24 March 2010 (UTC)

No, Hmrnkng means "is it true that they may have been taking LSD when they discovered the structure of DNA?" This discussion thread from 2007 at snopes.com discusses the claim without reaching a clear conclusion. It seems as though the claim originates from this article from the British tabloid The Mail on Sunday. It asserts that Crick told someone he was on LSD (and then this claim is treated as truth for headline purposes), but when asked about it by the reporter, Crick denied it. --Anonymous, 08:30 UTC, March 24, 2010.

I'd be pretty sure they weren't - it took a lot of work and thinking, it wasn't just an afternoon's "eureka moment". Aaadddaaammm (talk) 09:25, 24 March 2010 (UTC)

is there any reliable evidence/a good citation that either of them had EVER used LSD? 82.113.106.90 (talk) 10:01, 24 March 2010 (UTC)

Of course they were on LSD - at that time it was the acronym for the Sterling money system of pounds, shillings and pence! --TammyMoet (talk) 11:39, 24 March 2010 (UTC)

LSD really didn't become a recreational or even common drug until the 1960s. Watson and Crick discovered the double helix in 1953. Their work was built up of incremental steps and careful reasoning, not one "OH, DUDE" moment. I would say, "signs point to no," or at least, "a second-hand account in a British tabloid is not very convincing to me." As for whether either of them ever did LSD later—it's entirely possible, of course. Both lived long lives! --Mr.98 (talk) 13:17, 24 March 2010 (UTC)

James Watson would probably want it pointed out that he is still living a long life! – ClockworkSoul 23:06, 28 March 2010 (UTC)

Editing Wikipedia

I am new to editing Wikipedia, though I have been using it for several months now I did my first edit a few weeks back. I have a few questions: Our organisation has over 40 thousand computers connected on Internet in different locations in the city and I dont use one particular computer. I could use several computers in a period of one month.

But when I saw recently a messsage it said some entries that were made were removed and so on. My question is I never made these entires but someone using the same internet network could have done so. Is there a way I can make my own comments/ edits and retain my uniqueness without Wiki mistaking me for someone else? —Preceding unsigned comment added by 213.130.123.30 (talk) 06:55, 24 March 2010 (UTC)

Questions about Wikipedia itself should generally go to the Help Desk, rather than here at the Reference Desk. That said, basically the solution to your issue is to create a user account and login. [1] It's free, provides a variety of benefits, and requires no personal information (not even an email address). As long as you are logged in, the edits will be uniquely associated to that account regardless of what computer you use. Dragons flight (talk) 07:27, 24 March 2010 (UTC)

Create a user account. You see over at the top-right of your browser window where it says "Log in / create account"? Click on that - then on "Don't have an account? Create one." - click on that - then follow the instructions. Now, when you log in, your contributions are credited to your account - and not to a bunch of nameless IP addresses that change when you move from place to place or (possibly) whenever you reboot your computer. Doing this has other benefits - it lets you hook up your email address so other Wikipedians can email you - and it also makes it possible to create new articles and do a bunch of other things that are forbidden to 'anonymous' users. Ironically, having a user account actually makes you MORE anonymous because Wikipedia hides your IP address. Right now - I can tell (because your IP address is 213.130.123.30) that you're posting via Qatar Telecom - so you probably live in or around Doha. If we look at Dragons flight - the only things we know are what he or she decides to put on his/her user page. You get to control what you reveal. In my case, I chose to reveal my real name (Or did I? You'll never know!) SteveBaker (talk) 13:13, 24 March 2010 (UTC)

But somehow I suspect there may be more than just the one Steve Baker in the world. StuRat (talk) 13:21, 24 March 2010 (UTC)

There is a way to make it one less (video at 1:04). Cuddlyable3 (talk) 22:12, 24 March 2010 (UTC)

This video contains content from MyVideoRights (Mr Bean), who has blocked it in your country on copyright grounds. Vimescarrot (talk) 10:01, 25 March 2010 (UTC)

The video plays in my country.Cuddlyable3 (talk) 13:16, 26 March 2010 (UTC)

I agree with Dragons flight and SteveBaker. There is also another benefit in creating your own account - as well as a User page (on which you might choose to post a little information about yourself) you also get a User Talk page. Other Users can send you a message on your User Talk page, and that message will usually be about edits you have made to an article. Other Users can make suggestions or ask you questions. That is always a better alternative than merely deleting something another User has written. (To see a User's Talk page, simply click on the blue word (talk) following immediately after the User's name.) Dolphin51 (talk) 22:36, 24 March 2010 (UTC)

thanks everyone for the replies... i would log in and create my user name and do it the proper way henceforth. appreciate all the reply. thanks Steve for given a detailed reply though you called one of my earlier questions nonsense ( which in my assessment was a very valid and scientific q) neways thanks everyone and I liked cuddlyables comment too ;))213.130.123.12 (talk) 10:26, 25 March 2010 (UTC) done that. Thanks again everyoneFragrantforever 10:37, 25 March 2010 (UTC) —Preceding unsigned comment added by Fragrantforever (talk • contribs)

DC supply in tripping circuits

Why Dc circuits are used in Tripping of Circuit breakers instead of AC circuits? —Preceding unsigned comment added by 109.82.139.192 (talk) 08:57, 24 March 2010 (UTC)

I think you are mistaken. Some circuit breakers may have a digital control system which runs on a DC power supply, but the overwhelming majority of circuit breaker elements are totally passive, and trip mechanically when overcurrent is detected. See Circuit breaker#Types of circuit breaker for more information. Nimur (talk) 09:13, 24 March 2010 (UTC)

In electrical generating stations and substations, there are large batteries which supply direct current for tripping and closing circuit breakers and other switching devices. Sophisticated and sometimes computerized relay systems, perhaps with communication from relays at the other end of the line, determine when a breaker should trip, and operate backup breakers if it fails to trip. In a home , the electrical panel has circuit breakers with magnetic elements (coils or solenoids) which can trip instantaneously for an extremely high fault current, and thermal elements which allow a smaller overload to persist for a short time, as when a motor is starting. No DC supply is really needed for their operation. DC for tripping of such small breakers would require expensive batteries and chargers, with additional possible failure modes from old or overcharged batteries, and additional maintenance. It is also possible to keep a capacitor charged from a rectifier to provide DC for tripping a breaker. I'm not sure what the benefit is. Some large utility breakers used a tank of compressed air to provide energy for tripping. Some 12 kv breakers use a spring for tripping energy. DC is typically used to trigger the stored energy mechanism. Edison (talk) 20:01, 24 March 2010 (UTC)

Screw Compressor

Why screw compressor make more noise as compared to reciprocating compressor?203.199.205.25 (talk) 10:03, 24 March 2010 (UTC)

Who says they do? This page says just the opposite. At any rate, according to this document and many others it's not the case. A huge factor is going to be whether it's an oil-flooded screw compressor where the oil itself will dampen the sound. Another important distinction is what "more noise" means; screw compressors run faster so have a higher pitch, but that's more readily muffled than higher-output low pitch sounds. --Sean 13:38, 24 March 2010 (UTC)

testicles

Can a human being created without testicles. If he does can he able to bear (give birth) to a child. A man with very small size of testicles can give birth to a child? —Preceding unsigned comment added by 196.200.103.5 (talk) 11:05, 24 March 2010 (UTC)

For your first question, it happens all the time. For your second question, a woman with a properly developed reproductive system and of appropriate age will usually be able to bear a child, but most will object to being refered to as 'he'. For your last question unless the man has a female reproductive system (in particular the parts essential for carrying and giving birth to a child like a fully developed uterus and vagina) it is obviously impossible for them to bear and give birth to a child. In some cases a person may have ovotestis but I don't know if there's ever been a case where someone with ovotestis (let alone testes) has had a fully developed uterus and vagina however if such cases do occur while the person is likely to be naturally infertile it may be possible for them to bear and give birth to a child using IVF with donated eggs (and a partner or someone else's sperm) or embryos and likely appropriate hormone treatment. However they may not identify as being 'a man' and it would be inaccurate (and probably offensive) to simply say they have 'small size testicles' Nil Einne (talk) 11:12, 24 March 2010 (UTC)

A boy can be born without testes. This is called Anorchia. Men do not bear (give birth to) children, but can normally father them. AlmostReadytoFly (talk) 12:47, 24 March 2010 (UTC)

All women and a very few men are born without testicles. However, there is a lot more to bearing a child than not having testicles - you need a womb and ovaries and a bunch of other stuff that men don't have. Hence a man isn't going to be able to bear a child no matter what's happening in the testicles department. SteveBaker (talk) 13:03, 24 March 2010 (UTC)

I think the OP wanted to ask "Can a male be born without testicles? If so, would they be able to father a child? What if the testicles were very small rather than absent - would they be able to father a child?"--Frumpo (talk) 14:58, 24 March 2010 (UTC)

Just a wild guess, but perhaps our questioner is from a culture that does not consider females as human beings...? alteripse (talk) 00:45, 25 March 2010 (UTC)

I think a more generous guess is that the questioner, being in Eritrea, doesn't speak English fluently and is confused by the distinction between 'man' (relating to mankind and replaceable with 'human') and 'man' (meaning male). AlmostReadytoFly (talk) 09:10, 25 March 2010 (UTC)

Rarely, women have had babies delivered alive from ectopic pregnancies attached to the abdomen outside the uterus or fallopian tubes. Could such an abdominal ectopic pregnancy be successfully transplanted to a man, particularly if he did not have male hormones circulating? Edison (talk) 20:06, 24 March 2010 (UTC)

The Wikipedia article Male pregnancy answers definitely maybe perhaps. It's harder if you want baby and dad to survive. Cuddlyable3 (talk) 21:57, 24 March 2010 (UTC)

Sorry, let me ammend may question. Can a man without a testicle or with a small size of testicle be fertile (become a father). —Preceding unsigned comment added by 196.200.103.9 (talk) 10:43, 26 March 2010 (UTC)

1) (without testicle) No, 2) (small testicles) Probably, and in either case it's fun trying. Cuddlyable3 (talk) 13:11, 26 March 2010 (UTC)

Apart from the "fun trying" answer, the others are probabilities, as not all men with normal sized testicles have normal sperm. The infertility rate in apparently normal adult men is a few percent I think. In contrast the infertility rate in men with small testicles is higher because there are a number of conditions in which the testicles do not develop right and do not make sperm. Examples are Klinefelter syndrome, Kallman syndrome, gonadal dysgenesis, and hypopituitarism. The actual probability for our non-medical-advice-seeking questioner varies by "how small". For a twenty year old man with testes 4cc or less, the expectation of infertility would be well over 75%. alteripse (talk) 19:51, 26 March 2010 (UTC)

has anything impossible ever happened for sure, well verified, with scientific consensus (there will be a followup question)

My first question is whether anything considered, then and today, scientifically impossible for the time, ever nonetheless for sure happened, in a way that is well verified, and for which there is scientific consensus that it happened in that impossible way. It doesn't have to be effects that depend on the power of the mind, or something paranormal, the only criterion I'm looking for is that it must be scientifically impossible, yet nonetheless have happened, and that the scientific community should be in agreement on both these points. ie I'm talking about something "supernatural" or "miraculous", but with consensus both on the fact that it's impossible ("a miracle") and also on the fact that it must have happened in that impossible way. Then I will have a followup question. Thank you. 84.153.234.218 (talk) 12:03, 24 March 2010 (UTC)

Are you meaning things that were once considered 'scientifically impossible' but are now considered possible? Or are you meaning things that were (and still are) considered 'scientifically impossible'? 194.221.133.226 (talk) 12:07, 24 March 2010 (UTC)

As I tried to say with my words "considered, then and today, scientifically impossible for the time", I mean that not only whenever it occurred, it should have been considered impossible then for it to have occurred, but also today it should still be considered impossible for it to have occurred then the way that it did. Nevertheless, my crucial second point is that there there should be full, well verified scientific consensus that it in fact did in fact occur in the way that is impossible. 84.153.234.218 (talk) 12:11, 24 March 2010 (UTC)

I think the question is flawed. If the scientific community agrees that a certain thing actually happened, then there's no way they would also agree that it was impossible. The very fact of it having happened proves that it is possible. If the thing in question had previously been in the category of "miracles" (by definition beyond scientific explanation), then it would be removed from that category quick smart. Such corrections have often occurred throughout science. -- Jack of Oz ... speak! ... 12:13, 24 March 2010 (UTC)

American Revolutionary War patriot and hero Ethan Allen wrote "In those parts of the world where learning and science have prevailed, miracles have ceased; but in those parts of it as are barbarous and ignorant, miracles are still in vogue." Wikipedia offers an article Miracle. Cuddlyable3 (talk) 12:21, 24 March 2010 (UTC)

first of all I disagree completely with your saying that the question is "flawed". That is akin to saying it is a "flawed" question to ask "are there any even primes greater than a million?" That question is not flawed in the least. 84.153.234.218 (talk) 12:26, 24 March 2010 (UTC)

(edit conflict) It's more like asking if there's a number that's known to be prime, but has multiple prime factors. -- Coneslayer (talk) 12:32, 24 March 2010 (UTC)

Fine. That question is not flawed in the least either, it is perfectly sensible and meaningful and has a well-defined answer. Viz, I'll post it now. Note: despite the fact that it is not flawed in the least, and an infinite AI intelligence would answer "no", not meaningless or flawed or undecidable question or division by zero or anything else, it is possible the math reference desk will sputter out an answer more like this latter. If so, that will be a flaw in their contributors, not in the question, as the question is very easy to answer, though AI that can do so is still fifty years away. 84.153.234.218 (talk) 12:38, 24 March 2010 (UTC)

Ok, the question isn't flawed, the answer is just so obviously "no" that you are wasting everyone's time asking it. --Tango (talk) 12:42, 24 March 2010 (UTC)

Thank you, I know it might seem like I'm wasting people's time (I've removed the math reference desk question now) but that is why I stated right in the original question that there will be a followup question. It simply depends on this question. 84.153.234.218 (talk) 12:48, 24 March 2010 (UTC)

By the way, it is trivial for existing "AI" software to answer your question. Any worthwhile software proof assistant will be able to detect bare contradictions such as "prime number with prime divisors" and say that such a number does not exist. Staecker (talk) 12:57, 24 March 2010 (UTC)

The reason I said 50 years is the exact phrasing "asking if there's a number that's known to be". For the simpler question "do any numbers satisfy the condition: x" where x is the above (or, more simply "number is both 7 and the number is 8), can you link me to AI that will answer questions of this form? (ie of the form "are there any numbers that" but which will answer "no" for obvious answers such as "are both negative and positive" and so forth.) This question is important enough for me that I've asked it on the computing reference desk.84.153.234.218 (talk) —Preceding undated comment added 14:27, 24 March 2010 (UTC).

As Staekcer said, any proof assistant will be able to spot that there is a contradiction and thus no solutions. --Tango (talk) 17:42, 24 March 2010 (UTC)

Okay, it seems from the two responses given so far that the only two possible answers modern, Western science has to an observed miracle, ie an observation of something impossible are: "It did not happen as observed" or else "It happened as observed but what was observed is therefore not now considered impossible". In other words, is what you're both saying that there is no third option: "It happened as observed, and what was observed was and is now impossible." Is it correct to say that this third italicized option is simply not one that Science has? 84.153.234.218 (talk) 12:31, 24 March 2010 (UTC)

That statement is not one that anyone can make (consistently), because it contradicts itself. If something happens, it is not impossible. Tinfoilcat (talk) 12:37, 24 March 2010 (UTC)

Yes, that third option doesn't exist. You only need to look up "impossible" in a dictionary to verify that. --Tango (talk) 12:39, 24 March 2010 (UTC)

It sounds like you're using some nonstandard definition of the word "impossible". Maybe you mean "unexplainable"? or "unexpected"? (These latter are words typically used of "miracles". People who believe in miracles shouldn't call them "impossible"-- if you believe in miracles then you believe they are possible.) Staecker (talk) 12:45, 24 March 2010 (UTC)

While his/her wording may be technically incorrect, I think I understand exactly what his/her intent is. The trouble is that if something is "scientifically impossible" but actually happened (i.e. God circumvents the laws of physics), scientists would be so busy trying to retroactively come up with new laws that they would never realize it. Near Death Experience is something that certainly is recognized by mainstream scientists, but there are many people (including some scientists) that feel that there is no (and never will be) scientific explanation. The mere fact that every person in the country hasn't taken it as a sign to embrace a faith shows that they are far from "proving" this to be unexplainable. Also, in science, nothing has ever been proven, only strongly supported. Falconus^{p t c} 12:48, 24 March 2010 (UTC)

Do you have a source for the claim that there are scientists who feel that there will never be an explanation for near-death experiences? Zain Ebrahim (talk) 14:13, 24 March 2010 (UTC)

Near death experience#Spiritual viewpoints names a scientist that believes that conciousness survives after death. To be fair, it doesn't say that he says there is no scientific explanation. Also, I never said that anybody says that there will never be an explanation; I was referring to scientific explanations. Falconus^{p t c} 14:58, 24 March 2010 (UTC)

Yes, I'm also only referring to scientific (or "natural") explanations. You claimed above that there are people (including scientists) who believe that there will never be a scientific explanation. I'd like to see a source for that. Zain Ebrahim (talk) 15:11, 24 March 2010 (UTC)

Perhaps I was wrong, I haven't been able to verify my statement. I'm smiting it. Falconus^{p t c} 22:05, 24 March 2010 (UTC)

The problem here is that scientists do their work based on evidence. If there is solid evidence (observations) that something is happening that does not fit our current understanding of the laws of physics (or whatever) then we don't say "Something definitely impossible just definitely happened!" - we say "Huh! I guess our laws must be broken someplace." - and we rush off with great excitement to try to figure out what's wrong with those laws so we can fix them. So when the Michelson–Morley experiment showed us that the speed of light is a universal constant - we didn't say "Newton's laws of motion forbid this - so it's impossible" - we said "Something is wrong with our understanding of the universe". Eventually, we discovered that "Newtons laws of motion are wrong" and "Einsteins' theory of relativity is right".

Because we think that way - the hypothetical situation your question supposes couldn't happen. That's not because we know everything that it's possible to know and that our laws are perfect and therefore nothing "impossible" can ever happen - it's because once something happens that clearly contravenes those laws, we immediately say "One or more of those laws must be wrong". Things that violate known laws are sought out eagerly because it's only by 'breaking' a law that we find out that there is something wrong with those laws. Scientists get very excited when that happens because that's always really interesting - and it's the way you make a name for yourself and earn a Nobel prize!

SteveBaker (talk) 12:56, 24 March 2010 (UTC)

What about the discovery that the speed of the light is always the same? According to newtonian physics (the one which was universally accepted at the time) this was impossible.--Pokipsy76 (talk) 13:04, 24 March 2010 (UTC)

The OP has said, and clarified, that they are looking for things that are still considered impossible. --Tango (talk) 13:09, 24 March 2010 (UTC)

Continuing along Falconus's line of reasoning, if the entire world were just a virtual machine (The Matrix) and someone figured out how to exploit a buffer overflow in the rendering of physical objects, and by precisely crafting a certain physical object (on an atomic scale) were able to achieve so far just one single effect, which is to make that physical object disappear as an exception is thrown. So all the person can do so far, after years of trying to program something better, is to make a certain arbitrary physical object disappear upon being produced (we're talking about something on the scale of a processor, where the pattern is very small also). So they are frustrated and want more money so they can hire some engineers to help them, they want to rule the world. They approach the James Randi company with their claim: They are not going to tell you the pattern until an agreement on the test methodology, but the claim is that they can make a solid physical object by steps, that will be an existing, actual, physical CPU-like, physical object, and by adding one little bit more to it it will disappear, the supernatural claim. Now this is a very supernatural claim, that you can just make a large physical object disappear from the universe, but my problem is that what's to stop the James Randi company from agreeing, and then, once the preliminary test had been done, stating: "You know what, actually we cheated. We had so many scientists looking at this preliminary step that this object-disappearing thing is now known to be physically possible. I bet you could do it in a repeatable way a million times over. In fact, so could anyone else - we even photographed the pattern you used, and we're trying to reproduce it again." So they don't agree to a final test. Moreover, why would they ever agree to the final test, once the preliminary test has been shown to be physically possible? Isn't the moment you do something, even if it is by means of hacking the physical world on a supernatural level, doesn't the moment you share that with the world means the physics jumps to encompass the metaworld as well? In short, I think for this reason that the James Randi proposition is inherently fraudulent, it does not appear to me to be made in good faith. If it is made in good faith, can someone explain to me how someone with the object-disappearing insight I have conjectured above could use it to get $1,000,000 from the Randi corporation? Thank you. 84.153.234.218 (talk) 13:58, 24 March 2010 (UTC)

I think Randi's offer is clearly regarding things that are deemed supernatural now. That science will try (and probably succeed eventually) to explain it shouldn't be a factor it determining whether something qualifies. --Tango (talk) 14:25, 24 March 2010 (UTC)

As a mathematician of course I think the answer is "no, by definition" and indeed Polkinghorne often says that even the Resurrection is not impossible or miraculous to Christians, but "inevitable" when you have the most complete and consistent way of looking at the universe. --BozMo talk 14:39, 24 March 2010 (UTC)

Time to tell us your follow up question, even though you didn't get the answer you wanted... Dauto (talk) 14:28, 24 March 2010 (UTC)

Agree, whats the follow on? --BozMo talk 14:39, 24 March 2010 (UTC)

Among the learned, meteorites were considered "impossible" until the 19th Century. 63.17.46.33 (talk) 04:26, 25 March 2010 (UTC)

the followup question

it seems we have established it is the scientific consensus that whatever happens, ipso facto was possible when it happened. But if the latter word, possible, means anything at all in a physical sense, it must mean that other things were not possible.

Let me reiterate "in a physical sense." I don't mean, in terms of how people thought, or in terms of what was expected, or had been experienced previously, or was predicted in someone's equation. I mean, what was possible in terms of reality; of physical truth; of the actual way things are (as opposed to are understood), the facts of the situation, the physical nature of reality.

In this latter sense, what is possibility? —Preceding unsigned comment added by 84.153.234.218 (talk) 15:04, 24 March 2010 (UTC)

First of all, have you read possibility? It links to several sub-definitions, from a philosophical and logical point of view. The closest we can come for a definition in a scientific context is probably from "logical possibility" - something to the effect of "A logically possible proposition is one that can be asserted without implying a logical contradiction." It is up to the scientist to define the relevant axioms which might be contradicted. Typically, scientists axiomatically assume that there is some degree of consistency in the laws of physics, and that our observations of the universe reveal facts about our surroundings. These are pretty basic axioms; all the rest of science is built on those two ideas through the scientific method.

SteveBaker, Tango, and the others have stated this very well above. Anything at all is certainly possible. Scientists use the recorded body of observed evidence to evaluate how likely something is (assuming, of course, that the universe has some level of consistency and predictability). If you spend a good amount of time reading proper scientific literature (textbooks, peer-reviewed publications, and so forth), you'll see that any well-respected, disciplined scientist is very careful about how they use terminology when describing the hypothetical. I don't think I ever read a textbook that said, for example, that a violation of physical law is impossible. Sometimes, there will be conditional possibility; "antigravity boots are impossible unless our understanding of conservation of energy is flawed," for example, is a logical deduction that forces a scientist to weight a claim against a well-tested and widely-understood idea. This uses scientific analysis of consequences in order to tease out the inherent implications of certain possibilities. Ultimately, these careful and detailed explanations point out that modern science is based on generalizing ideas about the things which we have already observed, and not excluding the things which we have not. At the same time, an intelligent scientist has reservations and skepticisms, which are necessary to keep an open mind well-disciplined. Nimur (talk) 15:31, 24 March 2010 (UTC)

The OP's promise of follow-up questioning suggests they seek a debate about the place of supernatural miracles in modern Western science. This Ref. Desk is not the place for such debates that tend to founder on strawman claims like Science has failed to prove that my God doesn't exist. Below is a taxonomy of scientific interpretations of observations. It seems the OP will argue from classical premises that there can be supernatural causation. Post-classical science including quantum mechanics never claims to have eliminated the supernatural but neither does it invalidate the stance of atheism.

SCIENCE EVOLUTION     | CATEGORIES OF OBSERVATION             XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
==============================================================XXXXXXXXXXXXXXXXXXXXXXX/           \XXXXXXXXXXXXXXXXXXXXXXXXXXXX
Pre-intellectual      | Visible or          | Unknown cause   XXXXXXXXXXXXXXXXXXXXXXX SUPERNATURE XXXXXXXXXXXXXXXXXXXXXXXXXXXX
                      | remembered cause    |                 XXXXXXXXXXXXXXXXXXXXXXX\           /XXXXXXXXXXXXXXXXXXXXXXXXXXXX
----------------------|---------------------|-----------------XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Primitive             | Known cause         | Unknown cause   XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
----------------------|---------------------|-----------------------------------------------------XXXXXXXXXXXXXXXXXXXXXXXXXXXX
Enlightened classical¹| Known cause         | Knowable cause  |	Unknown	    | Unknown unknowns XXXXXXXXXXXXXXXXXXXXXXXXXXXX
----------------------|---------------------|-----------------|----------------|----------------------------------------XXXXXX
Post-classical        | Known cause         | Analyzable cause| Fundamentally  | Unknown unknowns | Unknowable unknowns XXXXXX
                      |                     |                 | indeterminate² |                  |                     XXXXXX
------------------------------------------------------------------------------------------------------------------------------

¹Unknown unknown - Donald Rumsfeld 1932 -

²Uncertainty principle - Werner Heisenberg 1901 - 1976

Cuddlyable3 (talk) 15:47, 24 March 2010 (UTC)

I fixed your ASCII art, it was broken. Nimur (talk) 16:48, 24 March 2010 (UTC) Thank you. Cuddlyable3 (talk) 21:39, 24 March 2010 (UTC)

One fine point we should make is that when the seemingly impossible happens, it hasn't changed what is actually possible, just our (formerly incorrect) view of what is possible. Therefore, nothing really impossible has, or can, happen. StuRat (talk) 15:54, 24 March 2010 (UTC)

See also Kiri-kin-tha's First Law of Metaphysics. -- Coneslayer (talk) 16:53, 24 March 2010 (UTC)

no, I had absolutely no inkling of an intention to start any debate. On the contrary, I expect all of the answers to my mundane physical questions to be quite uncontroversial. It is only for my personal edification, being as how I lack the funds for a first-rate education through the college and maybe masters (in philosophy of course) level. 84.153.234.218 (talk) 18:02, 24 March 2010 (UTC)

Magicians make a living demonstrating things that are impossible according to known laws of science. I have seen a close up magician sitting at a table with several observers make an ordinary baseball appear in an ordinary teacup which was clearly empty before the trick was done, a clear violation of the laws of physics. I expect he used slight of hand. Stage magicians have made elephants appear on stage, and have travelled through solid walls, or have levitated themselves or volunteers. Again, I expect this is done through machinery and misdirection. That would be the common answer to other seeming violations of the laws of physics: it was a trick. When a scientist announces he has demonstrated cold fusion, or an inventor announces his motor/generator produces more electricity than the batteries put into it, it is attributed to errors in measuring the energy input and output (or to simple chicanery). When someone announces he has discovered a way to do something thought impossible, modern science calls for him to writeup the method, and for others to be able to replicate the work in their own labs. Edison (talk) 20:17, 24 March 2010 (UTC)

I agree with the above by Cuddlyable3 but I think for completeness you should consider the question about whether people exist, in the sense of whether the appearence that we are conscious and able to decide or act is a delusion. I think you will only really get a handle on what is and isn't supernatural or "God" or anything once you have reconciled your view of what people are with the fact people are also incapable of doing anything "impossible". --BozMo talk 22:17, 24 March 2010 (UTC)

The answer is no. Impossible things do not happen, by definition. There are things that have happened (and still do happen) which science has no explanation for, there may be things that happen for which science will never have an explanation, but if science says something cannot happen, and it does happen, then scientists change their theories to fit the observed evidence. Science isn't some magical claims about ontological truths; science is an ongoing effort to understand the world through careful, reasoned observation. --Ludwigs2 23:02, 24 March 2010 (UTC)

I feel the urgent need to mumble something about the multiverse in reply to the question "what is possibility". Things which are not possible in our universe may be possible in a variation of it. However, logical contradictions remain impossible, since their meaning is undefined. The laws of physics in the multiverse could perhaps resolve to the set of everything logically possible (as Nimur said), which removes the problem of the set of possible things being arbitrary. 81.131.4.31 (talk) 16:01, 25 March 2010 (UTC)

Someone may have written this before, cannot be bothered to read all above, but the Catholic church requires impossible things - ie a miracle - to happen when it creates a new saint, such as this man http://online.wsj.com/article/SB10001424052748704896104575139691810314722.html?mod=WSJ_hp_editorsPicks as an aethiest I think its silly. When an impossible thing happens, it becomes possible, and is no longer an impossible thing. So heavier-than-air flight was once an impossible thing, but now it is not. Edit: someone must have deleted the 'signature' information, making it seem that the below paragraph was written by me. I've added the 'signature' again here: 78.144.250.185 (talk) 16:08, 28 March 2010 (UTC)

The fact that something has happened doesn't mean that it is "possible" existentially. Right now the earth is in a certain spacial relationship to every other body in the solar system, including asteroids, comets, and everything in the Kuiper belt; this relationship "has happened." However, it is impossible that it will ever happen again. Yes, it was "possible," but it no longer is -- and something that is impossible in the future is impossible, existentially. The past doesn't exist anymore and will never exist again. 63.17.79.42 (talk) 04:10, 28 March 2010 (UTC)

How much of the Sun's energy is used for light and how much is used for heat?

I just read in "Living in the environment" by G. Tyler Miller Jr. that only 5% of the electrical energy that comes into a light bulb is used to get light, while 95% is becoming heat energy. What is the equal relationship for the sun? //moralist 12:25, 24 March 2010 (UTC)

According to Luminous_efficacy, the sun comes in at about 12%...however, that article says that a 110volt incandescent lamp has an efficiency of between 0.7% and 2.6% (depending on the wattage) and that only photographic and projector lamps get up to 5%. Compact florescent lamps make 8 to 11% efficiency and LED lamps can reach 12% - so you can do better. Anyway there are some nice tables at the end of that article that summarize this stuff very nicely. SteveBaker (talk) 12:41, 24 March 2010 (UTC)

The sun is very nearly a black body with a temperature of 5800 K. It emits a mostly continuous spectrum with a maximum at around 500 nm. Light bulbs are also approximately black bodies, but radiate at between 2000 and 3300 K, meaning that their maximum emission is around 800 nm or longer, already outside the visible spectrum. This is further complicated because the eye does not perceive all visible wavelengths equally. If you look at Luminous efficacy, you can see that light bulbs have a luminous efficiency between 0.7% and 5.1%, the sun has an efficiency of 12%, and sunlight has an efficiency of 14% (the difference is that sunlight is filtered through the atmosphere, which removes mostly frequencies outside the visible range, improving the nominal efficiency, see File:Solar_Spectrum.png). --Stephan Schulz (talk) 12:50, 24 March 2010 (UTC)

Okay, thank you for your excellent answers! What about the heat energy, thought? The heat is also very important both in light bulbs and especially the sun, so how much of the sun's energy becomes heat? Is it the rest? And in comparison with for example radiators, how much of the energy used to radiators is used to heat up? //moralist 13:07, 24 March 2010 (UTC)

The image I linked (File:Solar_Spectrum.png) has the visible part of the spectrum marked. The majority of non-visible radiation is in the infrared and longer for the sun, but a significant part is ultraviolet (that's why we get sunburns ;-). For light bulbs, very little of the energy is in the ultraviolet. If you are not afraid of formulas, check out Planck's law for the gory details. --Stephan Schulz (talk) 13:23, 24 March 2010 (UTC)

Pretty much all energy ends up as heat eventually. Whenever electromagnetic radiation, of whatever frequency, is absorbed it heats up whatever it is absorbed by. Even the visible light will end up as heat once it is absorbed. So, any heater will be 100% efficient. The heat may not go where you want it, but it will definitely heat something up. --Tango (talk) 13:24, 24 March 2010 (UTC)

I want to point out that Luminous efficacy includes a factor related to the human eye's sensitivity which seems foreign to the quation asked. Most of the sun's energy is acctually in the form of visible light. Also worth pointing out that "heat" in this context is electromagnetic radiation and therefore division between light and heat is also dependent on the human eye'e inability to see those longer wavelengths. Dauto (talk) 13:42, 24 March 2010 (UTC)

This correlates with another question I thought of before, so I continue: The heat death of the universe is a known thing, but what happens with all the other kind of waves (those you talk about above) in the heat death? I mean, will all the lightwaves become entropy (some sort of disorded light or something) too, or will they eventually become heat? And what about sound waves, will the heat death of the universe have a constant disorded noise-sound? //moralist 18:44, 24 March 2010 (UTC)

Entropy isn't a thing, it's a property of a system. If the universe goes into a heat death (which isn't certain, but it does seem the most likely fate) then there will be electromagnetic radiation just flying around very rarely interacting with anything (which is a high entropy state). If the radiation is absorbed by something and heats it up then it will emit more radiation (as thermal radiation) anyway, so the radiation will never disappear. The expansion of the universe will result in the radiation gradually getting longer and longer wavelengths (that is, corresponding to cooler and cooler thermal radiation). Sound is pressure waves, so it needs a medium to travel through. There is no such medium in space, so there is no sound ("In space, nobody can hear you scream."). --Tango (talk) 18:50, 24 March 2010 (UTC)

standing on one leg with eyes closed

I can stand on 1 leg for more than 30 seconds easily. But, if I close my eyes, I can only do it for 10 seconds max. Why is this so? Obviously I understand that vision has an important part in helping us see where we are going when moving but I assumed it was of limited use in keeping our balance when standing up, after all we don't have to look at our feet to maintain balance when standing. Any suggestions would be great, thanks. RichYPE (talk) 13:19, 24 March 2010 (UTC)

Eyesight is actually a very important part of balance. You have a sense of balance from your inner ear and you have proprioception (the sense of where your various body parts are from the feedback from your muscles), but eyesight is more precise than either of those and will override them. That is why it is difficult to walk when what you can see around you is moving in a way that makes your brain think it is you that is moving (science museums sometimes have demonstrations of this). If you close your eyes, you can walk fine, since your brain relies on balance and proprioception, but with your eyes open it assumes your vision is right and your balance/proprioception wrong, and you fall over. --Tango (talk) 13:30, 24 March 2010 (UTC)

WOW!! I was going to test it and expected to reply that maybe the OP just has some personal neurological issue or something. I stood on one leg with my eyes open, and started timing with my mobile phone, then surfed the web a bit and so on, until I got bored. It was easy, well over a minute etc. Then I switched legs, started the timer, and closed my eyes. It very quickly got very very hard, and by second 12 I had lost my balance (that's when I opened my eyes and looked). WOW.

The most amazing thing about this is that while standing on one leg it was no effort, it was 100% stable, not like walking a tightrope. But with the eyes closed it was like walking a tightrope.

The answer is that there is a totally subconscious feedback mechanism with the eyes. You THINK that you aren't looking at the background when standing on one leg and looking at the mobile phone, but in fact your subconscious is doing feedbakc on the BACKGROUND you see. While doing the same with the eyes closed, the information disappears, and only your uh ear balance sensory organ thing shows you which way you're facing, and the feedback becomes like tightrope walking. AMAZING. 84.153.234.218 (talk) —Preceding undated comment added 13:31, 24 March 2010 (UTC).

I've often wondered how it is that birds are so much better at balancing on one leg than humans are. Not only can they stand on one leg for hours at a time - but they can actually sleep whilst standing on one leg, *with their heads turned through 180degrees*. Believe it or not, if they do this, it's an indication that they're relaxed, healthy and getting a nice, deep sleep! Any ideas how they manage this, folks? --Kurt Shaped Box (talk) 14:10, 24 March 2010 (UTC)

That's an easy one. They have a lower center of gravity. It's the same way that it's easy to balance 10 matches on the head of a match - you just arrange them so that the center of gravity is real low. My hypothesis is that it's much easier to crouch on one leg while closing your eyes. Let me test it... 84.153.234.218 (talk) 14:41, 24 March 2010 (UTC)

I was under the belief that birds could lock their legs and feet so that they could effortlessly perch in position, but I'm having trouble coming up with anything in Bird anatomy or reliable sources to support this belief. -- Coneslayer (talk) 15:01, 24 March 2010 (UTC)

Yes, I've read that (somewhere) too. When a bird sleeps, the muscles/tendons in its feet 'lock' so that it doesn't fall off its perch. It's a slightly different issue from being able to maintain balance on one leg though... --Kurt Shaped Box (talk) 15:27, 24 March 2010 (UTC)

Only some birds can perch on branches like that. Not all of them have locking feel. By the way, did you ever see a goose perched in a tree? --Cheminterest (talk) 21:10, 26 March 2010 (UTC)

I found something similar recently, its very easy to walk along a balance beam, using both feet, but the moment I closed my eyes it became incredibly difficult--Jac16888^Talk 14:55, 24 March 2010 (UTC)

This is the principle behind Romberg's test. Axl ¤ [Talk] 18:40, 24 March 2010 (UTC)

Another experiment which I've tried before: try balancing a broomstick upside-down on the open palm of your hand. It's easy enough if you keep your eyes fixed at the top (bottom) of the broom. The minute you close your eyes or look away, e.g. look down at the palm of your hand, you are unable to balance it properly. Zunaid 22:04, 24 March 2010 (UTC)

I was able to maintain my balance for much longer, but with significantly more wobbling than with my eyes open. 67.243.7.245 (talk) 22:27, 24 March 2010 (UTC)

Another one that always bothered me is that I can fill a glass 90% full of water - and walk around at full speed without spilling a drop - all without looking at the glass. Turn the lights out and you can't take three steps without spilling it. SteveBaker (talk) 00:19, 25 March 2010 (UTC)

I've long suspected that the ability to do this is unconsciously practised by carrying beer in the brim-full measure beer glasses customary in the UK. I wonder if a study comparing this ability's levels in the UK to those in countries (such as Germany) where beer glasses are customarily not filled to the brim would reveal significant differences. I'd like to offer my availability as one of the test subjects. 87.81.230.195 (talk) 09:49, 25 March 2010 (UTC)

I bet it's because when your eyes are open you know the exact direction "up" (due to the doors etc), and that this benefit would disappear in a special room that was all monitors showing all different skewed directions - you could only not spill the water then if you were looking at it directly. It would be interesting to verify somehow. 84.153.234.218 (talk) 10:02, 25 March 2010 (UTC)

You could verify it by carrying a glass through a room with flat floor but everything that should be vertical tilted a few degrees. I believe such experiments have been done and it does make it difficult to balance. --Tango (talk) 12:31, 25 March 2010 (UTC)

A wonderful example of this is a carnival trick where you walk through a rotating tunnel. You're walking on a perfectly stable raised platform, but everything around you is spinning around the axis of the direction you're trying to walk. With your eyes open it is extremely difficult to walk straight and upright because your eyes are telling you that you're falling over. (They've got one of these at the Ripply's Believe It Or Not museum in Orlando. It's probably the most Authentic thing in the place.) APL (talk) 02:13, 26 March 2010 (UTC)

How long does it take to see changes in blood cholesterol levels?

When a person switches from a very high cholesterol diet to a very low one, is the change immediately visible on blood tests? If someone is told they need to fix their cholesterol intake, then does so, how long should they wait before getting re-tested? 202.10.89.185 (talk) 14:54, 24 March 2010 (UTC)

The medical professional that told them they needed to get their cholesterol levels down would be the best person to ask. It won't necessarily be the same for everyone. --Tango (talk) 18:51, 24 March 2010 (UTC)

Hardly a reliable source or a good study, but a TV program in the UK took a healthy man with a good diet, and an overweight man who had a terrible diet, and switched their diets. Within, I think, two weeks - the healthy man's cholesterol was worse than that of the overweight man. Should I Worry About...? was the program. Here is a description of the episode. Anyway, I just thought this might give you a rough idea of the timeframe involved. Vimescarrot (talk) 09:52, 25 March 2010 (UTC)

Another vacuum cleaner drive belt bites the dust

Vacuum cleaners with rotating brushes at the carpet-vacuum interface commonly use a rubber "drive belt" to transfer rotary motion from the motor spindle to the brush. When the brush is prevented from rotating due to, for example, a shoelace becoming ensnared and wrapped around the brush, the motor spindle continues to turn while the drive belt slips. The drive belt is heated until it fails and breaks, disconnecting the brush from the motor. Are there no alternatives that do not require the replacement of belts but use a mechanism which slips when unable to turn? ----Seans Potato Business 14:59, 24 March 2010 (UTC)

It depends on whether you live in a Communist or a Capitalist country. In a Communist country linear programming is used to allocate resources such that a thermal or torque cut-off switch would probably be included to make the system operate more soap bubble/wire frame like. In a Capitalist system you want belts to burn out fast as possible so you make the contact surfaces extra rough and small radius. 71.100.11.118 (talk) 15:06, 24 March 2010 (UTC)

Your rant is off-topic, but I'm curious: is there any evidence that communist countries produce longer lasting products? I understand the logic, but it doesn't seem to happen in practice. --Tango (talk) 19:05, 24 March 2010 (UTC)

@Tango evidence Exhibit AK-47: In service 1949-present. Number built: 100 million. Exhibit M14 In service 1957-present. Number built: ~1.5 million. Cuddlyable3 (talk) 21:30, 24 March 2010 (UTC)

@Cuddlyable3 evidence Exhibit Big Rigs: Over the Road Racing: Without a shadow of doubt, the worst computer game ever written by far - developed by a team in the Ukraine. Just amazingly, spectacularly inept. Actually - the disks last for an unrivalled number of years...but only because nobody is stupid enough to play them. SteveBaker (talk) 00:15, 25 March 2010 (UTC)

My favorite part is the complete lack of collision detection except for the start/finish line, where half the time you win when you cross the line to start. Horribly made but incredibly entertaining! -Pete5x5 (talk) 03:40, 25 March 2010 (UTC)

The claims on the back of the box and the screen-shots of things that completely don't exist in the game are quite impressive - they claim you'll be evading the police and smashing through roadblocks...but there are no police or roadblocks anywhere in the game! I also like the way the programmers limited the speed of your truck to 100mph or so - but forgot to check for large negative speeds. Hence you can accelerate in reverse to literally unlimited speeds! SteveBaker (talk) 02:02, 26 March 2010 (UTC)

Tetris vs Boulder dash. --Polysylabic Pseudonym (talk) 10:07, 25 March 2010 (UTC)

Soviet vacuum cleaners suck blow but this hardware trumps any software so now All your base are belong to us. Cuddlyable3 (talk) 18:41, 25 March 2010 (UTC)

Off-topic-y: It's definitely the case that the Soviet design ethos worked better in some cases than others. With regards to weaponry, the Soviets were pretty good. Their rifles, tanks, planes, etc. were usually not as high-performing at US models, but were cheaper to develop and produce, and could generally be serviced by people with far less training than high-performance Western models. The Soviet ethos was to make things that could be serviced in the field by someone with about as much training as an auto-mechanic, and would last forever. That comes with some performance cost, but allows you to make up for it in volume and overall lower investment cost. There are lots of academic papers on this in regards to things like jet development, firearm, rockets, etc. --Mr.98 (talk) 13:06, 26 March 2010 (UTC)

A mechanical carpet sweeper uses a drive wheel (driven by the user moving the thing back and forward) to run a belt or gears which rotates its brushes. People still swish their vacuum cleaners around as if they worked this way, so you could always put this mechanism back into powered cleaners. -- Finlay McWalter • Talk 18:30, 24 March 2010 (UTC)

71.100.11.118 offered an informative answer wrapped in an entertaining joke (though I didn't get every aspect of it. Joke aside, I can't see evidence cleaner manufacturers are motivated to sell large quantities of replacement drive belts.)

Many motors in industry do not burn out their transmissions in the event of a jam. If the motor drove the brush directly, or through a gearbox, I think the motor could usefully be fitted with a power cut off. A clutch could usefully slip (though that would eventually burn out too), this is essentially a role that the drive belt plays. A magnetic drive would have a maximum torque before slipping (though would still generate some heat.) However, I suspect that my ideas are more expensive than occasionally replacing a drive belt - it is a cheap alternative to wrecking a bearing or the motor windings.

I think Finlay McWalter's idea is more cost effective.

--Hroðulf (or Hrothulf) (Talk) 19:13, 24 March 2010 (UTC)

Compare the Trabant with the Reliant Robin. You get an extra wheel under Communism. 78.149.198.14 (talk) 00:49, 27 March 2010 (UTC)

household voltage and frequency

If the world (or a new [artificial] planet) had it to do over again what would be the most efficient voltage and frequency (with all other things considered like interference and danger) for household consumption? 71.100.11.118 (talk) 15:01, 24 March 2010 (UTC)

60 Hz @ 240volts. This frequency produces low saturation of transformers (as opposed to 50 Hz) and so reduces power loss, and so can be made smaller. This makes cabling cheaper for carrying same amount of power. 240v needs smaller conductor cross section for the same amount of power (the resistance gets proportionaly smalller as you increase the volatge). Voltages higher than this increase electrocution risks to unacceptably higher levels (assuming the 240 volt tolerance is no more than + 6 % or 254v which is what it is likely to be at the sub-station).--Aspro (talk) 15:35, 24 March 2010 (UTC)

400 Hz @ 230 volts r.m.s. The higher frequency as used in avionics allows size and cost savings on transformers and filters. For starting anew, the electric power net will carry Internet data and accurate time and frequency reference signals. Cuddlyable3 (talk) 16:52, 24 March 2010 (UTC)

I though 400 hz was already in use with avionics but was declining due to skin and proximity effect resulting in the need for special (hollow stranded or thicker) conductors to reduce resistivity. 71.100.5.192 (talk) 20:36, 24 March 2010 (UTC)

Going from 60 to 400 Hz the skin depth reduces to 39%, e.g. in copper it is 8.5mm@60Hz and 3.3mm@400Hz. That means thicker cables for long-distance transmission but not more expensive copper because the resistivity of the cable core is largely immaterial. See Aluminium Conductor Steel Reinforced. Cuddlyable3 (talk) 21:25, 24 March 2010 (UTC)

High tension at 400 Hz?!!
The current carried by the corona is determined by integrating the current density over the surface of the conductor. You'd be limited to lower voltages in high tension cables. The voltages are at their maximum for the newer 50 and 60 Hz grids.--Aspro (talk) 23:45, 24 March 2010 (UTC)

Power transmission lines are dimensioned to carry a desired voltage and there is no maximum limit if one is building afresh. Why should corona loss increase on going from 60 to 400 Hz at the same peak voltage? Increasing the radius of a cable reduces the corona current. Cuddlyable3 (talk) 18:22, 25 March 2010 (UTC)

I don't disagree with any of the above answers. I think an important consideration is that there is no best solution to the problem. Lowering the voltage has safety benefits and lowers the cost of insulation but it requires higher currents and that, in turn, requires more copper and hence more weight and more cost for the copper. Alternatively, raising the voltage causes lower currents and requires less copper and hence less weight and less cost. However, raising the voltage requires more weight and cost for insulation, and progressively there is reduced safety. That explains why there is a proliferation of voltages and frequencies around the world. There are even situations where direct current is preferred over alternating current, but for household consumption I believe alternating current is better because of the ability to transform voltages from high voltage for long-distance transmission to low voltage at the point of consumption. Dolphin51 (talk) 22:20, 24 March 2010 (UTC)

History explains best why there is a proliferation of voltages and frequencies around the world. They were based on the best compromises that technology provided and economics allowed at the time that each system was originally founded. The trade off's and compromises are well understood. The next grids (as economics allow) will be DC. As for local distribution around the house, who knows, as 400 Hz does then have advantages ( but the main circuit frequency will still remain at 60 Hz or 50Hz for the reason I have previously given). Well have to wait until China is ready to tell us what the new standards will be. The service life of capital equipment is 25 to 50 years, so I don't think there is a terrific urgency --Aspro (talk) 00:09, 25 March 2010 (UTC)

population stratification in a normal sample of the general population

This question relates to genetic research. I am looking for a scholarly reference (or several) that discusses the issue of 'population stratification' in a 'normal sample'. I have searched the library databases for these and related terms (like 'population substructure'). I am not interested in a discussion of the issue in a case-control design or in a family-based study and have attempted to remove these terms with a Boolean search command. I found one PowerPoint presentation by someone at the Centers of Disease Control that said that population stratification was less of an issue in a normal sample but there was no citation for that particular bullet point and no name on the file. I assume there are statistical reasons why population stratification might be less of an issue when people vary on a continuous phenotype but that stratification is still an issue if there are different ethnic groups (or any genetic substructure) in the sample tested.

Citations (partial or complete) and explanations of the reasoning behind this issue are especially welcome. Thanks!Becstudent (talk) 15:25, 24 March 2010 (UTC)

Dentists identifying need for fillings by x-ray

(not after medical advice just wondering). I was at the dentist today and my dentist checked my teeth in the usual way (sharp metal stick, mouth open, little mirror) and said 'they all look ok' then they said they'd wait for the x-rays back. They get the x-ray back and within seconds i'm now at the dentist for 3 treatments - 3 fillings! My assumption is that the x-ray is finding 'hidden' decay that is perhaps covered by an existing filling or is between teeth or whatever. Anyhoo my questons...Is this quite new a new technique? (in my 27 years of dentisting i've never had a check-up like it)...Is my assumption in the right ball-park? Cheers 15:36, 24 March 2010 (UTC) —Preceding unsigned comment added by 194.221.133.226 (talk)

In my experience (in the USA), no, this is pretty common. The x-rays can find things that are not large enough to be easily seen, and they can identify "problem areas" that have not yet matured into full cavities yet. My anecdotal experience is that some dentists are more enthusiastic about dealing with minor cavities or problem areas than others. --Mr.98 (talk) 15:43, 24 March 2010 (UTC)

To elaborate, both common and not particularly recent (for the US). I've had x-rays at routine dental visits for at least 25 years, though I seem to recall that as a child they weren't a feature of every visit (perhaps every second or third), I assume to reduce radiation exposure. These days I get them snapped at every 6-month check, and the "film" is instead some x-ray-reactive USB dongle that immediately uploads to a PC monitor beside the table. Pretty slick. — Lomn 15:53, 24 March 2010 (UTC)

See also Dental radiography. TenOfAllTrades(talk) 16:28, 24 March 2010 (UTC)

Well I don't know where you are, OP, but I've been having dental X-rays since 1980 in the UK... --TammyMoet (talk) 09:16, 25 March 2010 (UTC)

Dentist here -- certain lesions (areas of demineralization that are commonly referred to as cavities) are evident only clinically (that is, by physically looking at the teeth in the mouth) and others are evident only radiographically (that is, they can be seen on an x-ray film) and others are evident both clinically and radiographically. Generally, occlusal caries (decay on the biting surface of teeth) can be seen clinically, but if such decay is small-to-moderate, it might very well not be detectable radiographically -- this is because the buccal-lingual dimension of the tooth in question (that is, the thickness of the tooth in the cheek/lip-to-tongue dimension) is too much to detect small changes in the mineralization of the tooth structure. Such decay is usually detected either visually or with an explorer (and there is certainly a bulk of literature debating the specificity and sensitivity of such a "sticky catch" method of detecting such decay). Another type of region of decay is interproximal decay that exists on the surface of a tooth that is adjacent to another tooth. Such an area, as you can probably see for yourself in the mirror, is hardly visualized in a clinical exam and especially for posterior teeth (premolars and molars), radiographic detection is really the only way to visualize such demineralization. I have frequently checked a patient's mouth and told him or her that they appeared all clear only to find 3, 5 or even 10 "cavities." This photo montage is a great example of what appears to be very slight clinical decay (a mere dot in the central fossa of a maxillary molar) but what is really a ridiculously large interproximal lesion that was actually contiguous with the surface of the root (see C in the montage) after I removed tooth structure only from the top of the tooth (i.e. the side hole was already there). Such a situation occurred because this case was from a location at which I worked in which practitioners would routinely not take radiographs and treat patients on a clinical basis only. The little black dot didn't seem too bad and so it had gone untreated for probably over a year (decay is very slow). The tooth was extracted because the patient could not afford the cost of restoring the tooth with crown lengthening, root canal therapy, post and core and crown. DRosenbach ^{(Talk | Contribs)} 20:09, 26 March 2010 (UTC)

What's in a can of tuna?

While eating a can of tuna for luch, I was curious and decided to look at the ingredients, and what I found confused me. According to the Percent Daily Values label, one serving is 56g of drained meat, but the figures add up to a lot less than 56g — it's 1g fat, less than 1g of carbohydrates, less than 1g of fiber, and 11g of protein, and the only other figures (cholesterol, sodium, and potassium) add up to 300mg. What could the other 40g+ of substance be? Is it all water? Nyttend (talk) 16:15, 24 March 2010 (UTC)

Calories/Energy? 194.221.133.226 (talk) 16:23, 24 March 2010 (UTC)

Yep, it's water. This site gives the water content of canned tuna as 73%, give or take. TenOfAllTrades(talk) 16:25, 24 March 2010 (UTC)

Water will be present in drained tuna as Ten states. And 194, calories/energy are recorded as fat, carbohydrates, proteins and alchohol (which I presume tuna will not actually contain). Googlemeister (talk) 18:35, 24 March 2010 (UTC)

Most forms of animal life are 60-75% water. So virtually all meat that hasn't been cured or dried in some way will have a similar discrepancy between the tally of caloric content and the per serving weight. —ShadowRanger ^(talk|stalk) 20:52, 25 March 2010 (UTC)

Not all substances in foods contain calories. Cellulose, for example, is not metabolized, so it does not contain calories.--Cheminterest (talk) 21:04, 26 March 2010 (UTC)

supermarket salt + vinegar

Using this combination quite often to make marinading brines, I wonder how much a hazard sodium ferrocyanide in consumer salt is? John Riemann Soong (talk) 17:57, 24 March 2010 (UTC)

I see that Morton salt sells a no-additive "canning and pickling salt" so there may actually be an issue or at least a perception that there is an issue. Rmhermen (talk) 18:59, 24 March 2010 (UTC)

I think the no additive is because it does something to the pickle, not because of the hazard. It's not very hazardous. There is little of it in there, and cyanide in general is not super hazardous in low quantities. Some poisons have cumulative damage (arsenic or lead for example), but cyanide doesn't since the body can metabolize it. So as long as it doesn't kill you it's not damaging. Ariel. (talk) 19:34, 24 March 2010 (UTC)

Morton says the canning salt is due to the anti-caking agent settling at the bottom of your jars of pickles. Recipes I've read that call for it say the same thing. --Sean 19:58, 24 March 2010 (UTC)

The WP article actual provides a link to a toxicology report. [2] As Ariel points out: Cyanides are metabolised. It also occurs widely in nature including in the foods we eat. [3]. So I can not see an issue. Mind you... why should it be in brine? Manufactures buy what ever salt is the cheapest and don't need to specify anti-caking salt.--Aspro (talk) 23:24, 24 March 2010 (UTC)

I interpreted this as being about making your own pickles, not store-bought ones. Rmhermen (talk) 00:17, 25 March 2010 (UTC)

Ferrocyanides and ferricyanides aren't very toxic, unlike cyanides, because the iron is bound strongly to the cyanide, preventing its release.--Cheminterest (talk) 21:03, 26 March 2010 (UTC)

Unusual rock

Several years ago, I found an unusual rock in Riley County, Kansas on the shores of Tuttle Creek Lake. I'll do my best to describe it.

It's about the size of my hand. It's dark and very porous (like those lava rocks that people use in landscaping) and it has all kinds of different smaller rocks stuck in it. One side of it is more porous than the other side which is rougher and less porous. I broke it in half and you can clearly see how the layers have different porosity. I've never seen a rock like this in Northeast Kansas since most of the rocks here are light colored limestone.

I'm no geologist, but it almost seems like a volcanic rock to me. I was under the impression that there weren't any igneous rocks in Kansas. Could it have been something carried here by glaciers during the ice age? Is it a meteorite?

I took several pictures of it, but the lighting is bad and they're out of focus. I did the best I could.

http://img232.imageshack.us/img232/5144/dscn0190j.jpg http://img413.imageshack.us/img413/8402/dscn0193t.jpg http://img689.imageshack.us/img689/5870/dscn0194j.jpg http://img715.imageshack.us/img715/2195/dscn0200.jpg http://img291.imageshack.us/img291/9512/dscn0201z.jpg http://img339.imageshack.us/img339/7301/dscn0202.jpg http://img708.imageshack.us/img708/7194/dscn0208e.jpg http://img718.imageshack.us/img718/8140/dscn0216b.jpg http://img689.imageshack.us/img689/2358/dscn0217y.jpg —Preceding unsigned comment added by 63.245.168.34 (talk) 23:32, 24 March 2010 (UTC)

It looks volcanic to me (though I'm not an expert). Kansas doesn't have any active volcanoes, and hasn't for tens of millions of years. It's possible the rock you found is in fact very old (dating to an age with local volcanism), but it is more likely that is was transplanted there. Kansas and much of the American Midwest is downwind of the Yellowstone supervolcano. Geologically recent eruptions at Yellowstone (i.e. during the last 10 Myr), created multi-meter thick ash deposits in parts of the Midwest. Most of that ash would be very fine material, but larger rocks thrown great distances would occur too. In fact, the fertility of the soil in the region has actually been enhanced by those ancient ash falls. So you certainly can find igneous rocks in Kansas, though relatively large rocks would be rather uncommon. Dragons flight (talk) 00:48, 25 March 2010 (UTC)

If its a bit of furnace slag there will probably be more bits near by. However, a couple meteor types are called “slag” due to their similarity. It does look promising. [4]. Suggest you would be better off doing a little study and then contacting meteor experts. Remember, they not only have a scientific value but a monetary one as well. You should at least be able to get a auto-focus camera out of it and a descent lens. --Aspro (talk) 00:51, 25 March 2010 (UTC)

Er, sorry but I think you've misread that page. It says slag is commonly MISTAKEN as a meteor. Vespine (talk) 21:51, 25 March 2010 (UTC)

Gosh! You right. I must get that lens prescription filled! Well, suppose we can safely discount furnace slag then.--Aspro (talk) 18:28, 26 March 2010 (UTC)

If it's volcanic, it's not from Kansas. I've done some research on Kansas geology and the only igneous rocks in Kansas are miles beneath the ground. The surface rocks where I live are from the Permian era and they're all sedimentary. There are ash deposits out west (and I even own some Yellowstone ejecta I found there), but there's no ash in Riley County. As for the meteorite thing, I highly doubt it. I found a smaller piece of similar material in almost the exact same spot several years before I found this one and the chunks of softer material embedded in it doesn't seem to fit with a meteorite. I suppose it's important to note that I found it on a rocky beach on Tuttle Creek Lake. It may have been washed there. Being so porous, I wouldn't be surprised if it floats (I've seen lava rocks that float).

Also, since I wrote my first post, I've noticed that some of the smaller objects stuck in it appear to be limestone, but I could be wrong about that. There's still other chunks stuck in it that are so hard that I can't even scratch it with my pocketknife. —Preceding unsigned comment added by 63.245.168.34 (talk) 01:09, 25 March 2010 (UTC)

It seems like a composite rock, to me. It may have started out as igneous rock, then spent some time at the bottom of a body of water next to pebbles, and was cemented to them via sedimentation. StuRat (talk) 01:23, 25 March 2010 (UTC)

My sediments exactly. Edison (talk) 14:46, 26 March 2010 (UTC)

OP here again. I found something very interesting. Read this article:

http://vulcan.wr.usgs.gov/LivingWith/VolcanicPast/Places/volcanic_past_kansas.html

Apparently I was wrong that there are no native volcanic rocks at the surface in Kansas. I was surprised to find out that there's a few Kimberlite formations in Riley County! Kimberlite is the rock that diamonds are found in, and it's notable because it's formed in the earths Mantle.

It would seem to fit with what I found since kimberlite is known for collecting many xenoliths as it plows through the layers of rock on its journey to the surface. That would explain the wide variation in the xenoliths too (some of them are so hard I can't scratch them with a pocketknife, while others are soft and powdery).

Could the rock I found be a chunk of kimberlite? Could I be holding here in my hands a piece of the Earths mantle? —Preceding unsigned comment added by 63.245.168.34 (talk) 20:40, 26 March 2010 (UTC)

If you really think you might have diamonds in there, try scratching a piece of glass with them (obviously not any glass you care about). If it won't scratch glass, then it's not diamond. If it does, then more testing would be required to prove they are diamonds. Note that most diamonds are ugly and discolored, not like the pretty ones you see in a jewelry store. StuRat (talk) 20:49, 26 March 2010 (UTC)

No, you misunderstand. I don't think I've found any diamonds in it, and the resources I've found on the Kimberlites here say that they don't contain diamonds. I just want to know if what I found is a piece of Kimberlite. —Preceding unsigned comment added by 63.245.168.34 (talk) 21:11, 26 March 2010 (UTC)

Finding amount of chloride in a solution using ion-selective electrode

I want to use an ion-selective electrode to find the amount of chloride in an unknown solution. I will obviously need to use the chloride-ion selective electrode, but where can I find the method and procedures for such an experiment? —Preceding unsigned comment added by 142.58.43.153 (talk) 23:39, 24 March 2010 (UTC)