Wikipedia:Reference desk/Science

Welcome to the science section
of the Wikipedia reference desk.

skip to bottom

Select a section:

• Computing
• Entertainment
• Humanities
• Language
• Mathematics
• Science
• Miscellaneous
• Archives

Want a faster answer?

Main page: Help searching Wikipedia

   

How can I get my question answered?

• Select the section of the desk that best fits the general topic of your question (see the navigation column to the right).
• Post your question to only one section, providing a short header that gives the topic of your question.
• Type '~~~~' (that is, four tilde characters) at the end – this signs and dates your contribution so we know who wrote what and when.
• Don't post personal contact information – it will be removed. Any answers will be provided here.
• Please be as specific as possible, and include all relevant context – the usefulness of answers may depend on the context.
• Note:
  • We don't answer (and may remove) questions that require medical diagnosis or legal advice.
  • We don't answer requests for opinions, predictions or debate.
  • We don't do your homework for you, though we'll help you past the stuck point.
  • We don't conduct original research or provide a free source of ideas, but we'll help you find information you need.

Ready? Ask a new question!

How do I answer a question?

Main page: Wikipedia:Reference desk/Guidelines

• The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.

See also:

• Teahouse
• Help desk
• Village pump
• Help manual

November 13

Hollow pipe stronger than solid bar

Is it possible for a pipe of a given substance (metal, say) to be stronger than an equal-diameter bar of the same substance? Interpret "stronger" as you will, though I'm really interested in bending/buckling strength. --Sean 00:32, 13 November 2009 (UTC)

If the pipe is the same material (no special alloying or special hardening) then it is equivalent to the outermost ring of the solid rod of the same diameter, and I cannot see how removing the center of a solid cylindrical rod could increase its strength. For a given weight per unit length, I would expect the pipe to be stronger than a cylinder of the same weight per length but smaller diameter in resistance to bending/buckling, but perhaps not in tensile strength/resistance to elongation. Edison (talk) 00:38, 13 November 2009 (UTC)

For any cylinder, the neutral axis is at the centre. The stress (which is what you're interested in) varies with WxL/Z for a lateral load, where W is the weight, L the length, Z the section modulus. Z = I/C where I is moment of inertia, C is distance from the neutral axis to the most distant fibre. For a shape with outside radius R, C = R, so all that varies is I. I varies with (R^4 - r^4), r being the inside radius. For the solid rod, r=0, so I is maximum - so the solid rod will always be stronger. As Edison notes though, the material near the centre contributes very little to the strength, so in practical terms a hollow shape is much more efficient in material use. If the load is from only one direction, a vertical hollow rectangle will be even better, since I there is WxH^3/12 - w x h^3/12. The buckling (vertical column compression) equations work much the same way, except there you're using radius of gyration. Franamax (talk) 00:53, 13 November 2009 (UTC)

It depends how you interpret "stronger". For example, a concrete cantilever structure is stronger if it is "ribbed", because less of its material strength is "wasted" supporting its own weight. Bending strength of a metal pipe might actually depend on how the pipe is formed - Edison's suggestion that it is identical to the outer ring of a solid cylinder might not take into account anisotropy or lattice structure. There are ASME handbooks that give empircal measurements for these sorts of parameters for pipes of different materials, wall thicknesses and diameters, because theoretical equations are poor approximations to the real material properties. Nimur (talk) 00:59, 13 November 2009 (UTC)

(ec) The above answers are correct – for a homogeneous cylinder, a solid cylinder will always be more resistant to a given buckling force than a hollow cylinder of the same material and outer diameter. A minor caution applies, however, if one is dealing with a long cylinder supported at its ends. In such a case, the weight of the cylinder itself supplies a bending force which can contribute to buckling. In such a circumstance, the strength-to-weight ratio of the cylinder becomes important, and a hollow cylinder may be 'stronger' (in the sense of being able to support a greater externally-applied force) than a solid one. TenOfAllTrades(talk) 01:08, 13 November 2009 (UTC)

Hmm, that's a good point and it could apply to my example of laying a pipe horizontally and putting weight along its length also. For a material of very low tensile strength and very high density, you could have a situation where you have a perfectly good pipe sitting there, then you stick a slug of extra weight into the middle and it nows sags under the combined weight. The smaller diameter piece you stick into the middle couldn't support its own weight, so it would load the pipe, possibly to failure. I'll have to run some numbers on that one. For a column in compression, I'm not convinced, but those formulas are way more complicated, so I might not get to them. :) Franamax (talk) 02:47, 13 November 2009 (UTC)

The OP said "Interpret 'stronger' as you will." If the pipe or cylinder is hanging down from a support and loaded, the cylinder of greater cross section would support a far greater load than the pipe. Likewise, a vertical cylindrical column should support greater weight than a pipe of the same diameter if loaded. If the member is used as a beam, and runs horizontally between supports while supporting a distributed load (like a joist or beam in a structure), only if the supported load is small relative to the weight of the member will a hollow member be "stronger" than a solid one. I agree that it is possible, depending on material , that a hollow horizontal member supported at one end or at the ends might be able to extend farther without collapsing than a solid one, if it were heavy and of low tensile strength (like what? Unreinforced concrete? Adobe? Sod? Playdough? Modelling clay?). I'm not sure that would apply to steel or wood. Joists or beams are solid, not hollow, and that is not a mistake. Edison (talk) 05:16, 13 November 2009 (UTC)

Interestingly, our pipe article has an illustration of wooden pipes, and concrete pipe is very common. Clay pipes are commonly used in many parts of the world; I doubt that they are suspended or supported only by their own material strength. Nimur (talk) 17:53, 13 November 2009 (UTC)

Neither the historic (19th century use) of wooden pipe or more recent use of concrete pipe to carry water or other liquids supports any claim that the pipe is stronger than a solid cylinder of the same diameter, particularly when in compression as a column, where the compression strength of concrete would be great. Unreinforced concrete would not do well in tension, but wood would, and I would vote for the solid cylinder in tension or shear strength. The outermost part would be more effective against buckling or in torsion than the same mass of material located near the center. Edison (talk) 20:59, 13 November 2009 (UTC)

metals and stones

ok, i have several question, but theyre all related to each other, and i did found the general asnwers, but those werent realy specific, especially since my question are actually quite specific anywaysm here goes (by the way, all of the questions are about natural, un-mixed [not artificcially made or alloyed] metals and just natural stones [doesnt matter if its carbon mixed with any other element, as long as its natural])

1. which metal AND stone have the highest melting point?

2. which metal AND stone have the highest (and lowest) density?

3. which metal AND stone have the best heat conduction? (dont answer this one if the answer is silver and diamond)

4. which metal is the hardest (non brittle) and/or toughest (hard to break, crack, bend, or dull) (?possibly based on mohs scale?)

thats it for now, i apologize if this the wrong way to do it, and i want to thank the person who is going to answer this in advance —Preceding unsigned comment added by RoYaLKiD90 (talk • contribs) 01:45, 13 November 2009 (UTC)

Category:Lists of chemical elements is a good start for finding many of the metal properties. Not quite sure what you mean by "not artificcially (sic) made" for metals...almost no metals exist in their "normal, metal form" in nature, but rather as oxides, sulfides, or other minerals and ores. However, Periodic table (standard) tells you which elements are naturally-occurring vs only known via nuclear synthesis in labs. DMacks (talk) 02:55, 13 November 2009 (UTC)

For the lowest density stone, perhaps a pumice stone ? StuRat (talk) 03:05, 13 November 2009 (UTC)

If it has to be a naturally occurring metal then osmiridium is a natural metal alloy of osmium and iridium, high melting and dense. Osmium is the hardest metal and also very slightly denser than iridium, or osmiridium, I am not sure that you will find it pure in nature though. But Osmium is also slightly brittle. reading Thermal conductivity and the condition on your question means that it should not be answered with diamond, but diamond is not actually a metal anyway. And silver is the top metal in thermal conductivity, and also does occur naturally. Graeme Bartlett (talk) 09:37, 13 November 2009 (UTC)

chicken and the egg

Is the DNA of the egg from whence the chicken comes identical to the DNA of the chicken it hatches? 71.100.0.254 (talk) 01:59, 13 November 2009 (UTC)

No. Chickens reproduce sexually, so the DNA of the chick is a combination of the DNA of hen and the DNA of the cock. --Tango (talk) 02:00, 13 November 2009 (UTC)

...er ...No, I don't mean the DNA of the chicken that lays the egg. I mean the DNA of the egg from whence the chicken comes. 71.100.0.254 (talk) 05:33, 13 November 2009 (UTC)

You may also be interested in Chicken or the egg. Red Act (talk) 02:18, 13 November 2009 (UTC)

It is an interesting page, certainly, but it has nothing to do with the OP's question. --Tango (talk) 02:20, 13 November 2009 (UTC)

Are we talking about a fertilized egg or an unfertilized egg? Bus stop (talk) 02:21, 13 November 2009 (UTC)

That depends on why the question was asked. Given the title of the question, I suspect the OP is planning on using a genetic argument to answer the riddle of whether the chicken or the egg came first. Genetically, the answer to the riddle is that the egg came first: Regardless of what precise set of criteria is used to distinguish between "chicken DNA" and the DNA of the chicken's progenitor species, the first egg that contained "chicken DNA" existed before the first bird that contained "chicken DNA". That point is made in the article I linked to.

The "no" part of your answer, BTW, is incorrect. The OP is comparing the DNA of an egg to the DNA of the chicken that comes from it, not comparing the DNA of a chicken to the DNA of an egg it lays. Red Act (talk) 03:14, 13 November 2009 (UTC)

The DNA within the egg is the same as the DNA as the chick that ultimately hatches from the egg. Technically the egg is the zygote - the first cell that forms from merging of male & female genetic material. From the DNA in that cell, the egg and the chick are formed...hence the DNA within the egg is the same as for the chick. On the other hand, the DNA in the egg is NOT identical to the DNA in the chicken that lays the egg because half of the DNA came from the male bird. SteveBaker (talk) 02:48, 13 November 2009 (UTC)

Unfertilized eggs don't contain any genetic material from the male. Bus stop (talk) 02:55, 13 November 2009 (UTC)

And if, perhaps, you asked in order to speculate on the common idiom which came first, the chicken or the egg -- I will respond to that. The question, when posed with thought, may be used to ask how and when evolutionary changes occur. Germ line mutations would allow a a pre-chicken to lay an egg which contains an organism unlike itself, thus it can be said that the [chicken] egg preceded the chicken (and, in essence, the pre-chicken, surprisingly, did not lay a pre-chicken egg). It can also be speculated that the developing, intra-egg pre-chicken developed a somatic mutation (that also affected it's germ-line), thus suggesting that the chicken preceded the chicken egg (because what the pre-chicken laid was a pre-chicken egg). DRosenbach ^{(Talk | Contribs)} 03:55, 13 November 2009 (UTC)

Chicken and egg question is addressed in Scientific American magazine, September 2009, page 77. Bus stop (talk) 03:47, 13 November 2009 (UTC)

The answer I am seeking would be the same answer as if I asked about a caterpillar and a butterfly. Also please clarify about the contents of the egg. It is my understanding that only one sperm enters the egg and therefore the contents of the egg after fertilization leaves no male DNA since it has combined completely with the femaile DNA... but of course what I mean is the combined DNA not to include a remnant of the males DNA. 71.100.0.254 (talk) 06:03, 13 November 2009 (UTC)

A butterfly has the same DNA as the caterpillar that it developed from. In general, the DNA of an animal doesn't change during a metamorphosis.

During sexual reproduction, roughly half of the DNA in the fertilized egg comes from the mother, and half comes from the father. In addition to the articles I just linked to, you may also want to read meiosis. Red Act (talk) 06:33, 13 November 2009 (UTC)

How many nuclei or cells are even in an unfertilized egg laid by a chicken? Are there any? -Craig Pemberton 07:48, 13 November 2009 (UTC)

An unfertilized egg (an ovum), being a gamete, consists of one haploid cell. This is in contrast to a just-fertilized egg (a zygote), which consists of one diploid cell. For a chicken's egg, the nucleus is in the germinal disc, which is that white spot on the yolk. Red Act (talk) 08:38, 13 November 2009 (UTC)

Deaths caused by malaria?

It's easy to find how many people die from malaria per year in modern times but I can't seem to find any numbers for a few hundred years back. I understand malaria has existed for an insanely long time but does anyone know about how many people have died from it in the past few centuries? —Preceding unsigned comment added by 99.230.206.44 (talk) 02:04, 13 November 2009 (UTC)

Since there really wasn't a precise way to analyze total deaths by any disease up until about 1850, it's difficult to give exact numbers. To be honest, I believe the way that diseases like malaria were recorded by text, but not typically, and especially in the most infected lands like Africa. If I were to estimate, I would take the total number of malaria-related deaths in today's population and make adjustments according to population and infectibiliy. For example, if 881,000 people died in 2006 from the disease, I would find the approximate population of a period in time and (do a little math) find the approximate number of deaths that could have occured. It's not precise by any means, but it's better than just guessing right? I hope this has helped!

Try this for information about malaria in general --> WHO malaria website Letter ⁷ 07:33, 13 November 2009 (UTC)

Letter 7, you're suggesting to compare apples and oranges... though I'm not even sure which oranges. :) What is the population you want to compare to which? World population today to world population back then? Not only will you have to rely on wild guesses again (how many people really lived in a specific area at a specific time?), but you also suggest that the same percentage died of malaria. That's highly unlikely assumption. The whole point of malaria medication is to reduce the infection and the death rate. Add to that improved means to protect yourself from mosquitoes (ranging from screens to all the little accessoires that supposedly keep them away), improved health care in general, improved transport (to get health care to people or vice versa), etc. etc. etc. Not to mention that people today live in different areas (more or less exposed to malaria/mosquitoes?), that human activity has had an impact on malaria/mosquitoes, etc. It's actually a pretty interesting question to wonder how much the death rate decreased. But it makes it impossible to assume that the same percentage of the population died, say, in 1700 and today!!

And one more tiny problem to find out "any numbers for a few hundred years back" - malaria is particularly virulent in areas, which "a few hundred years back" simply kept no written records. For example, I don't know if any Sub-Saharan African peoples at all recorded any numbers about malaria deaths before Europeans stepped in (and, BTW, pretty soon started influencing them). So you'll most likely have to look at records of early explorers, missionaries, etc. ... which are most likely seriously flawed (because they commonly only knew a small percentage of the population of today's countries), but it may be your best guess yet... --Thanks for answering (talk) 12:24, 13 November 2009 (UTC)

Also, malaria ranges have shrunk. Washington DC used to be a malaria infested swamp, but I doubt anyone catches it there anymore. Same with most of the rest of the US. It is probably not a common thing to catch in a lot of areas where it used to run rampant. Googlemeister (talk) 14:08, 13 November 2009 (UTC)

Funny you should use that specific example, since there were 2 autochthonous cases near Washington DC in 2002: PMID 12403407 -- Scray (talk) 02:44, 14 November 2009 (UTC)

If you google "malaria 19th century" you get some hits, like this page, that give some indication of what we know about the spread and likely prevalence of the disease in the last couple of centuries. Obviously, exact statistics will not be available for the whole world. (Though for specific countries or regions, they may be—England kept very good death statistics going back hundreds of years.) --Mr.98 (talk) 14:35, 13 November 2009 (UTC)

I imagine you could get very rough estimates of historical mortality rates by studying how much of a population has Sickle cell trait.John Z (talk) 03:34, 14 November 2009 (UTC)

Is this a springtail?

I found this little guy [1][2] in northern Arizona in August. There were several hundred under some pots near a leaking hose so the surrounding loess was damp and shaded. The local region is very arid but there are some reservoirs nearby and scrub and sage not too far out. They were all about 1/2mm long. They could jump about 3cm. I think it might be a springtail but I don't know how to tell for certain. I can't make out a furcula but it is hard to see in the photo. Thank you very much. -Craig Pemberton 03:01, 13 November 2009 (UTC)

If it looks like a springtail and it jumps like a springtail... yeah, I guess it's a springtail :) . --Dr Dima (talk) 03:26, 13 November 2009 (UTC)

My best guess puts it in Entomobryomorpha after looking at a lot of images of springtails. I think I'm confident enough to upload and tag it on commons. -Craig Pemberton 07:51, 13 November 2009 (UTC)

Any springtail that can only jump 3 cm would be laughed out of the club by the other members. StuRat (talk) 11:34, 13 November 2009 (UTC)

Not really, no. Most springtails are tiny, so for some of them 3 cm may well be over 100 times their body length. They can jump several inches, or sometimes less, depending on the species. The peak velocities and accelerations of springtails during the jump are a few times lower than those of fleas, click beetles, and grasshoppers [3]. --Dr Dima (talk) 22:20, 13 November 2009 (UTC)

The fine folks over at bugguide.net identified it as a Entomobrya unostrigata, which I've discovered to be an excellent website for those trying to identify arthropods. Also, I'll pass on this interesting tidbit:

The furca is hard to see in alive specimens since it is held underneath the body when not used. If you tease a specimen for a while and you can keep it jumping it will get exhausted after a series of jumps and then the furca will be visible as a kind of tail behind the body. ---Frans Janssens

-Craig Pemberton 09:49, 14 November 2009 (UTC)

p+ and p- mitochondrial genomes

What do p+ and p- refer to in respect to mitochondrial genomes? ----Seans Potato Business 11:28, 13 November 2009 (UTC)

p+ is a wild type circular mitochondrial DNA, while p- is a mutant DNA.--Gilisa (talk) 13:43, 13 November 2009 (UTC)

I think they are asking which gene is "p" and what is its function. --Mark PEA (talk) 15:57, 13 November 2009 (UTC)

LHC

How the LHC works? When it will start again? —Preceding unsigned comment added by ZrslX009 (talk • contribs) 11:55, 13 November 2009 (UTC)

Did you try LHC which says "Due to the time required to repair the resulting damage and to add additional safety features, the LHC is scheduled to be operational in mid-November 2009.[6][7]" and has a large section at Large Hadron Collider#Design with many links? If you don't already, you'd likely also need to know how Particle accelerators work in general first Nil Einne (talk) 12:10, 13 November 2009 (UTC)

Leukemia transfusions

For patients with luekemia, couldn't they treat it by just doing constant transfusions ? If they don't do this because it would drain the local blood supplies, how about if friends and family (with the proper blood type, of course) provided all the blood ? This would work especially well for pediatric cases, as the quantities of blood needed would be less. I realize that this wouldn't cure the disease, but I would think the patient could be kept alive as long as the transfusions continued. Not a medical advice Q, as I don't know anyone with this disease. StuRat (talk) 15:35, 13 November 2009 (UTC)

Supportive transfusions are a regular part of leukemia treatment. Generally, specific blood components (often red blood cells or platelets, though occasionally white blood cells for immunocompromised patients) are transfused to respond to specific deficiencies, rather than whole blood. Unfortunately, there are issues which would complicate treatment by perpetual transfusion. Patients who receive frequent transfusions of platelets (for example), may develop an immune response to 'foreign' platelets (in appropriate jargon, they are refractory to platelet transfusion: [4]). Finding appropriate HLA type-matched platelet donors is far more challenging than finding ABO-type matches for red blood cell transfusions. Consequently, (potentially-curative) chemotherapy and stem cell transpant are considered a much-preferred alternative to a lifetime of transfusion. TenOfAllTrades(talk) 17:40, 13 November 2009 (UTC)

I've taken the liberty of changing the title of this thread, as it contained a typo, "luekemia" instead of "leukemia". I'm doing this because I'm about to tag the "Luekemia" redirect page for deletion. We don't normally have redirect pages for typos, and I change the title to avoid a redlink.--NorwegianBlue ^talk 21:45, 13 November 2009 (UTC)

I think you are wrong -- we do in fact "normally have redirects for typos". See for example the {{R from misspelling}} template and its associated category. I have removed the speedy tag. --Trovatore (talk) 22:39, 13 November 2009 (UTC)

If you read our leukemia article carefully, you will realize that leukemia is not a single disease. It is a term that includes most or all malignant diseases of stem cells in the bone marrow. Therefore, the prognosis will depend very much on the specific type of stem cell involved, and on the age of the patient. In contrast to many other types of cancer, leukemia is always disseminated at the time of diagnosis. So you have all the problems of a disseminated cancer - a cell population that does not respect our body's normal regulatory mechanisms of cell proliferation. The cells are not localized to a specific area, and therefore not accessible to surgical excision. In addition, there is great variation in prognosis depending on cell type and patient age. Leukemic cells displace normal bone marrow cells. This will, as you address in your question, lead to anemia, and to thrombocytopenia, as TenOfAllTrades says, because megakaryocytes too are displaced. Both the anemia and thrombocytopenia can be treated by transfusion. In countries where leukocyte filtered blood products are mandatory, platelet refractoriness is seen mostly in women who have been immunized through pregnancy. Platelets, in the absence of white cells, are not very immunogenic. A blood center that has a reasonably sized pool of HLA-typed donors and that tests the exact specificity of the HLA-antibodies, will in the vast majority of cases be able to provide matched platelets to such patients. However, the bone marrow suppression also leads to immune suppression, which leads to opportunistic infections, which are a major killer. As TenOfAllTrades wrote, the only potentially curative treatment is chemotherapy, that kills most or all malignant cells, followed by a stem cell transplant. --NorwegianBlue ^talk 23:02, 13 November 2009 (UTC)

Picture of ferrofluid in oil

Hi clever science ref deskers, I'd like to pick your brains about this file: File:Ferrofluid poles.jpg (see thumb). Specifically, the image shows ferrofluid in oil, collecting near the poles of a magnet that has been placed underneath the dish. Although it depends on the strength of the magnet and the magnetisation of the ferrofluid, I've seen that this "collection" happens almost instantaneously. I'd like to find this picture a home in other articles (it's only in ferrofluid so far). Ignoring, perhaps, the fact that it is ferrofluid in oil, what principles are being illustrated here? I have some general ideas, but I'm sure there are some specifics that I'm completely missing, and my captions would probably be wrong, or at least too simplistic. Ideas? Thanks, :) Maedin\^talk 16:31, 13 November 2009 (UTC)

The interesting feature of the picture is the spontaneous formation of corrugations in the black ferrofluid above each end of the bar magnet where the magnetic field exceeds the critical strength for normal-field instability. I think other pictures the OP supplied[5] show this better. This picture shows some unexplained striations in the oil layer that look different at the two ends (poles) of the magnet. I guess these are effects of dispersed grains of magnetic material and surface tension of the oil. Cuddlyable3 (talk) 21:03, 13 November 2009 (UTC)

Yes, I was interested in the striations; I thought this must be a well-known physical property that I just wasn't familiar with. Thanks for your response. I'll try to get in contact with the author and see if he can enlighten any further. Maedin\^talk 17:22, 14 November 2009 (UTC)

On further thought, the ferrofluid may have been initially spread evenly on the surface which was then placed over the magnet. When the ferrofluid was pulled into the shape shown it left tracks of its movement in the oil film. Cuddlyable3 (talk) 18:09, 14 November 2009 (UTC)

Polyploidy in humans

Has any human survived Polyploidy into adulthood? If so, what happens normally? Is Polyploidy in humans considered a "bad" thing to happen? --Reticuli88 (talk) 19:07, 13 November 2009 (UTC)

Did you read our article on polyploidy, specifically the polyploidy in humans subsection? There's a wealth of information there, as well as a link to mixoploidy that notes adult humans with the condition. Whether polyploidy is "bad" depends on the standard you're using, though I don't think it's a difficult question to answer. — Lomn 19:19, 13 November 2009 (UTC)

It doesn't mention anything about adults. When I say bad, I mean is there something physically wrong with the adult who is afflicted with this or is it possible that one can become "super-human? --Reticuli88 (talk) 19:26, 13 November 2009 (UTC)

The condition is almost invariably fatal, and always results in sterility. Superheroes are just as likely to result from polyploidy as from ALS, synesthesia, or radioactive spider bites. — Lomn 19:43, 13 November 2009 (UTC)

Sense of impending doom

Wikipedia seems to have no article for this! It is a well known symptom in many cases, but I can't understand what on earth, biochemically, brings it about. Among other things, I hear blood transfusions (no source) can result in these, along with the classical myocardical infarction, from where I guess it is best known. Any help on this issue would really sate my curiousity; thanks in advance! =) 77.18.86.199 (talk) 19:35, 13 November 2009 (UTC)

Intravenous adenosine injection classically causes this sensation. Interestingly, lidocaine toxicity also causes this. Axl ¤ [Talk] 19:58, 13 November 2009 (UTC)

Anaphylaxis also causes a sense of impending doom (I can testify personally to this). I wonder if it's related to release of epinephrine. --NellieBly (talk) 10:17, 14 November 2009 (UTC)

Malaise tells us almost nothing. I feel one scrapes at the surface of something rather important here, but which is either left unstudied or is just so unpopular to study that the knowledge is not common. My googling efforts continue. 77.18.85.72 (talk) 15:58, 14 November 2009 (UTC)

Classically the rapid dropping blood oxygen from Pulmonary emboli gives a sense of impending doom. See dozens of references for this [6] --BozMo talk 21:10, 14 November 2009 (UTC)

The sensation described by the OP is defined as a foreboding n. a feeling of evil to come. Cuddlyable3 (talk) 12:19, 15 November 2009 (UTC)

EMP

Would an EMP kill humans? After all, we have electrical conductors in our body, yet in COD 6 the EMP detonated seemed harmless to humans. —Preceding unsigned comment added by 24.200.1.37 (talk) 19:52, 13 November 2009 (UTC)

We don't have anything in our bodies that would function as an antenna, so a EMP is harmless (unless you have a pacemaker, I suppose). --Tango (talk) 19:53, 13 November 2009 (UTC)

Electromagnetic weapon#Use against humans. It's not sourced, but it does list some possible side effects of electromagnetic weapons. Presumably how much our neurons were disturbed would depend on the strength of the pulse. It may also affect lymphocytes. ~ Amory (u • t • c) 20:07, 13 November 2009 (UTC)

As I have pointed out on the Science desk in numerous earlier EMP questions, "EMP" is very vaguely defined. In order to speculate about consequences, some parameters must be provided - the power, the duration, the frequencies, proximity to the source, etc. As it is, "electromagnetic pulse" is so vague a term, that the original question is impossible to answer. Every day, nontrivial electromagnetic pulses are emitted by mobile phones, radios, power stations, and other man-made and natural sources of electromagnetic energy. These EMPs are usually entirely harmless. There is a subset which are debated but might be harmful. Finally, at the extreme ends, very powerful doses of ionizing radiation have been shown beyond a reasonable doubt to harm humans. --Nimur (talk) 15:15, 14 November 2009 (UTC)

multiple ccd chips or cameras

If I and my friends (pretend I know Bill Gates and Warren Buffet) bought a lot of maximum megabit ccd cameras and wired their shutters to activate at the exact same moment and placed these cameras in stationary orbit (lets just say next to each other in the least light polluted and most stable place) and pointed each to the same infinite point in space then combined each image with software would this serve in the place of a parabolic mirror to intensify the image and thus allow it to be greatly magnified what magnification would be possible and would this be large enough to justify the project? 71.100.7.164 (talk) 20:04, 13 November 2009 (UTC)

Imaging in weak light of a CCD camera is limited by electrical noise generated on the CCD chip that shows as graininess in the resulting picture. If one can aim many chips at exactly the same object and combine their output signals (with no coding like JPEG in between) then the noise power can theoretically be halved with every doubling of the number of cameras. A practical objection to the scheme is the difficulty of aiming many cameras identically. Having many cameras does not provide greater magnification of the view. For greater magnification the cameras need longer-focus (telephoto) lenses which will make aiming even more critical. The area to be filled by camera bodies would be much larger than that occupied by the parabolic mirror they are supposed to replace. Cuddlyable3 (talk) 20:31, 13 November 2009 (UTC)

Actually what I am suggesting is that because you end up with a combined intensity of the same object which can be aligned exactly by software that because of the increased intensity you can perform the magnification by blowing up only a few number of ccd extremely high resolution cells which represent only a fraction of the object but are visible due to the greater intensity provided by all of the combined images performing the same function as a parabolic mirror. 71.100.7.164 (talk) 22:17, 13 November 2009 (UTC)

You may suggest that software can achieve perfect alignment but that does not make it easy. Enlarging or "blowing up" a CCD image always means reducing the number of cells per printed area. The number of cells on the CCD chip is fixed, as becomes obvious as blockiness (aliasing) when an image is greatly enlarged. If an object is larger than a point source then a few cells likely cover only a fraction of the object. It is unclear whether you are hoping to gain magnification in image size or image brightness. If the subject is stationary then there is no need to have a "lot" of cameras because one can use a single camera to take multiple pictures. A CCD camera coupled to a conventional reflecting or refracting telescope is a popular arrangement for astronomers and makes more sense than coaxing your famously rich friends to buy truckloads of cameras. Cuddlyable3 (talk) 17:59, 14 November 2009 (UTC)

For the sake of argument so as to eliminate the limitations of individual ccd pixels, although grains of silver still present this delimina, the reason for not taking multiple sequential images is to eliminate opportunity for temporal disparity. That said the way graininess is overcome using multiple cameras is by the very fact that they do not occupy the exact same location. The idea is that individual cameras can be designed to use a parabolic reflecting mirror in place of a lens to maximize magnification beyond the ability of the individual camera to distinguish a difference between light levels between adjacent cells due to the extreme magnification and then rely on multiple cameras to contribute to a measurable difference in intensity through image overlay for any wavelength of electromagnetic radiation. 71.100.7.164 (talk) 19:44, 14 November 2009 (UTC)

I believe the OP is referring to something more like an Astronomical interferometer, which is theoretically a quite powerful concept, provided you can get the components in place. Alfrodull (talk) 20:35, 13 November 2009 (UTC)

I would be surprised if the OP was thinking of interferometer because distance measurement is nowhere mentioned. Cuddlyable3 (talk) 17:59, 14 November 2009 (UTC)

You might look at MMT Observatory for a description of a similar idea (six cooperating telescopes) here on Earth. Looie496 (talk) 21:23, 13 November 2009 (UTC)

As our article mentions, there are various proposals for space based inferometers. For example Darwin (spacecraft) and Terrestrial Planet Finder and Space Interferometry Mission [7]. Then there's the rather extreme hypertelescope proposal from Antoine Émile Henry Labeyrie [8]. However these operate using multiple mirrors with one primary imaging sensor and not multiple sensors. And they all are likely to be rather expensive and require a very high degree of technology, in particular the ability to accurately position the multiple elements that we may not currently have. BTW, in terms of multiple mirror telescopes on earth, there are some other proposed ones e.g. check out Extremely large telescope, for example the Giant Magellan Telescope. There is also radical proposed stuff like a Fresnel Imager [9] although again only one camera. Nil Einne (talk) 16:20, 14 November 2009 (UTC)

Yes, mega multiple sensors with individual lenses, shutter and direction control i.e., cameras, is the system which I am suggesting. Has this ever been attempted and if not where can I submit a proposal that it be done? 71.100.7.164 (talk) 17:42, 14 November 2009 (UTC)

71.100.7.164 (talk) 05:53, 15 November 2009 (UTC)

You can send proposals for a new space-based research payload to NASA Ames Research Center or European Space Agency. Expect them to be reviewed by people who know fundamental optics such as diffraction limits, the 300-year history of refinement of the Optical telescope and the already established applications of CCD's in astronomy. You will be at a disadvantage if you cannot quantify your proposal in terms of this body of knowledge. Cuddlyable3 (talk) 12:15, 15 November 2009 (UTC)

has the lhc collided the particles yet

mid-november, we're almost in mid november but theres been nothing on it, this is one of the biggest scientific things to happen and yet theres no fanfare or anything.--Draw99990 (talk) 20:23, 13 November 2009 (UTC)

Both our article and the LHC website say that particles have circulated but not collided. DMacks (talk) 20:31, 13 November 2009 (UTC)

The article says "particles were circulating" as of October 30, but that's really an optimistic way of describing the situation, since particles aren't going all the way around. As of four days ago, they've got particles going half way around.[10] And the first high energy collisions aren't currently expected to occur until sometime in early 2010.[11] Red Act (talk) 20:43, 13 November 2009 (UTC)

You might already know this, but actually discovering new physics at the LHC will require careful analysis of months or years of collected data. There won't be a sudden jump in knowledge on the day the collisions start; there's no "moment of truth". -- BenRG (talk) 22:18, 13 November 2009 (UTC)

The Earth hasn't been swallowed by a black hole yet, so no. :-) StuRat (talk) 23:17, 13 November 2009 (UTC)

They got close - but then (believe it or not) a bird dropped half a loaf of french-bread onto the machinery - which overheated at that spot and shut the system down. So more delays... SteveBaker (talk) 23:17, 13 November 2009 (UTC)

How long does it take a bird to fly here from the future? --Trovatore (talk) 23:19, 13 November 2009 (UTC)

That depends. Is it African or European? —Akrabbim^talk 23:22, 13 November 2009 (UTC)

The LHC, like any other machine, is made of parts that sometimes malfunction and need to be fixed or replaced. This is a normal and anticipated part of the LHC's operation; it's not news. Furthermore, this story wasn't even true, according to this page at cern.ch. The mainstream media is worthless as a source of news about physics. Read physicists' blogs instead. Wikipedia is often good too. -- BenRG (talk) 02:27, 14 November 2009 (UTC)

Looking for Raccoon Penis

Now that I've caught your eye :) Seriously though, I'm preparing a presentation for class regarding raccoon anatomy, and my closer is going to be on this particular "bit". (Why? Keep reading!). I've got just about all of it covered regarding the baculum and so forth, but the thing I can't seem to find is a diagram or even a picture of how the baculum is connected, even which way is "up" on the thing, and how it appears when, errr.... in use, shall we say. All the anatomical diagrams and annotated skeletals I've found tend to omit this little feature. Online searches all return either a story about an unfortunate fellow who tried to get too friendly with a raccoon, or places to buy raccoon penis-bones which are apparently quite popular as trinkets in the Southern US. The latter is why I want to have this as my closer. I found a place that sells bags of the things, so I plan to hand them out to the class as both a visual aid, and as a sort of sociological experiment to see how they are received! :) So.... any ideas? Thanks in advance to all! —Preceding unsigned comment added by 75.227.198.51 (talk • contribs) 21:01, 13 November 2009

The article Baculum may help. You may criticize the speculation noted by Richard Dawkins that the loss of the bone in humans is the result of sexual selection by females. Your post is characterised by nervous euphemisms. A class of children will acquire such an attitude from their teacher. I'm almost certain this is a joke. Cuddlyable3 (talk) 21:45, 13 November 2009 (UTC)

Possible signs of global warming, or just common phenomena?

Hi. I'm in Southern Ontario, and recently this November I've noticed some possible signs of global warming. It is already mid-November, but some things are still occuring that one would expect in the warmer seasons. Just yesterday, I saw several dandelions, both the flowering kind and the white puffballs, as well as those in the closing stage. I also saw a flock of geese (or ducks) flying north in formation. Just today I saw around a hundred birds (either ducks or geese) resting in a small pond (although this isn't very unusual). Within the past week, I and other people in my community have seen ladybugs flying near our homes. Squirrels of different varieties are still commonly seen from day to day. Total precipitation so far this year has been the highest in the past six years, higher even than 2008, which produced a record-breaking summer rainfall and very high winter snowfall, despite having a dry spell in late August and early half of September of this year. We had a short period of warmth this November, being the second-highest recorded temperature in this period of November in the past six years (19C), second only to 2005, globally the warmest year on record. We have had only one minor snowfall this autumn of less than one centimetre, and in previous years snow has often fallen numerous times in late October to early November. Although I have noticed some of these signs in recent years, they appear to be becoming more common. Are any of my observations extremely unusual for my location and time, and could they be signs of global wrming? Thanks. ~AH1^(TCU) 21:47, 13 November 2009 (UTC)

The long-term changes to plant flowering times and to bird/insect migration patterns is certainly a very real, well-documented indication of climate change. They are subtly incidious because many animals and plants have carefully evolved their reproductive strategies around the timing and location of these kinds of event. So if a flower times it's peak nectar production by the average air temperature - but the bees that pollinate them time their spurt in worker-bee production by the length of the day - then the flowers may peak before the bees are ready to pollinate them - the flowers don't get their pollen spread around - and then when the bees do finally kick into high gear - the plants are already past their best. Both species suffer. Similar things happen with bird migration timed against insect hatchings. It's a delicate system that CAN evolve to meet change - but only so long as the change happens gradually and not at break-neck human-induced speeds.

In the flower/bee case, you'd probably just get another species of flower that flowers at a different time thriving at that latitude. We are actually getting that already. StuRat (talk) 23:11, 13 November 2009 (UTC)

The actual weather variations (ironically) are less convincing evidence. Weather is what's happening right now outside of your back door - and it's still sufficiently random to make it very hard to see whether there is a long-term trend. Climate is the average "weather" over large areas and large timescales - and the climate is what is steadily warming. The weather, locally can be unusually cold, unusually wet, unusually foggy...almost anything...because it's only the average that's climbing steadily. Here in central Texas, we've had a record number of insanely hot/dry days this year, leading to severe drought conditions - immediately followed by some of the heaviest rainfall on record...that's the hallmark of changing climate - that records (both highs and lows) tend to get broken more frequently because the weather gets steadily more chaotic. SteveBaker (talk) 22:42, 13 November 2009 (UTC)

OK, but what specifically about the dandelions in November (is this common or extremely rare at my location), and the presense of insects (just yesterday I saw housefly-like insects and what appeared to be a mosquito)? ~AH1^(TCU) 21:09, 14 November 2009 (UTC)

definition of 'oxychemical'

Google is failing me. I have seen the word 'oxychemical' twice today in peer-reviewed papers, but I can't find a definition. Here it is in context, "Fermentation microbiology with renewable resources ... has the potential to produce a large fraction of the oxychemicals and their derivatives that constitute the bulk of feedstock chemicals."

ike9898 (talk) 21:56, 13 November 2009 (UTC)

Oxy<blank> usually means <blank> with oxygen atoms as part of the molecules. See oxyacid, oxyanion, oxyfuel, etc. etc. This likely just means "compounds which contain oxygen". --Jayron32 23:41, 13 November 2009 (UTC)

You forgot Oxymoron Googlemeister (talk) 15:25, 16 November 2009 (UTC)

is anything reproduceable not part of science?

Is there anything reproduceable that isn't part of science? I mean, anything that isn't possible, so despite the fact that it can be shown and is reproduceable, is not acknowledged by science on the grounds of its impossibility. For example, was there a period of time when scientists did not acknowledge the flight of the bumblebee, as the understanding of aerodynamics at the time meant this was not possible? This is obviously just one example, a further example could be the Mpemba effect, specifically when the graduate students told their professor: The technician later reported that the hot water froze first, and said "But we'll keep on repeating the experiment until we get the right result", naturally tihs is a cue for the professor to say "that's okay, forget it", though luckily this did not happen. However, this example, like my first example, suffers from the fact that it is not contemporary. My question isn't whether there is anything reproduceable that wasn't part of science when it was first reproduceable; I'm asking if there is anythin reproduceable that isn't part of science now. So...anything? 85.181.147.202 (talk) 22:31, 13 November 2009 (UTC)

Not sure whether it answers your question but I don't think scientists ignore something just because they can't understand it. I don't think anyone ever refused to acknowledge the flight of a bumblebee. It's absurd to suggest that it's not actually flying, just because they haven't figured out the physics behind it. ----Seans Potato Business 22:59, 13 November 2009 (UTC)

The bumblebee thing is a myth. Science always accepts what can be measured and reproduced on demand under controlled conditions as "The Truth" - if the truth (such as that it's bloody obvious that bees can indeed fly) contradicts theory (that bees do not conform to the current theories of aerodynamics) - then we accept that the theory must need some adjustment. For example - just today there was a piece on www.slashdot.org talking about the Pioneer anomaly (a totally mysterious speedup of the Pioneer spacecraft as they left the solar system). The reason for this speedup is completely unknown and it appears to be breaking one or more scientific theories that we believe to be true. The phenomenon is only somewhat reproducible - some spacecraft have experienced it - others, seemingly, have not. ("While Galileo and NEAR had appreciable speed increases, Cassini and Messenger did not. Rosetta itself gained more speed than expected from its 2005 fly-by, but only the expected amount from its 2007 fly-by.") Until we figure out the cause (and there are plenty of hypotheses out there) - and do some more experiments, the best we can say is that we cannot currently explain the speedup. There could be several reasons for that:

• That one or more of our key theories (relativity, perhaps) is subtly incorrect. It would have to be a very, very subtle error though because these theories are extremely well tested.
• That there is some completely new phenomenon that we're unaware of (perhaps an undetectable source of gravitation outside of the solar system that's attracting these probes...but perhaps gremlins!)
• That there is some kind of error in the experimental data - which is why they're trying to use the Rosetta craft to do more precise measurements.
• That there is some enormous conspiracy to fake the Pioneer data...just like they faked the moon landings. (No, I don't believe that - but you can bet some conspiracy nut does).

I'm sure there are lots of things like that - that's how we end up with theories of Dark matter and Dark energy. Things we know are there because the experimental data says so - but for which we have no really good explanation yet.

You're kinda phrasing your question as if this somehow points to a horrible flaw in "Science" - when in fact, this is modern science's single greatest strength. In the last couple of hundred years, we've come up with a system for doing science that pretty much guarantees that we don't get into the kinds of horrible mess you describe with the Mpemba effect. Serious scientists most certainly DON'T keep doing an experiment until by chance it comes out the way we want. But more than that - scientists THRIVE on finding something that doesn't fit the present theories - that's the way we make progress. When every new fact fits perfectly into what we know - it's kinda satisfying that it's more evidence that we got it right - but nothing CLOSE to the joy of making a discovery that totally overturns some major theory. Everyone thinks Einstein was a genius and a hero for overturning Newton's laws of motion that had stood the test of time for hundreds of years. Einstein is considered to be one of the greatest humans ever to have lived because he found a serious problem with the status quo of science and overturned it. That's why everyone has gotten so excited over the Pioneer effect. It's an opportunity to refine what we know - and for some smart chap to make a name for himself.

SteveBaker (talk) 23:00, 13 November 2009 (UTC)

Sorry, thanks for the responses but I really did mean what I say: something reproduceable that science ignores on the grounds of its impossibility. Examples would be: any effect from a dilution (homeopathy) where the solution has been diluted so many times with distilled water that chances are there is not a single molecule of whatever you started with. Other examples would be telepathy, etc. By the way, I'm looking for an ACTUAL example, if anyone has one...instead you offered a scientific EXPLANATION for why such an example would not exist. Now the following sentence will blow your mind: if someone offers an example of something science ignores on the ground of its impossibility, will you accept this example despite your theory of its impossibility as outlined above, SteveBaker?  :) —Preceding unsigned comment added by 85.181.147.202 (talk) 23:32, 13 November 2009 (UTC)

Homeopathy is NOT reproducable. No controlled study has ever shown that homeopathic remedies produce any results above that of the placebo effect. Likewise, there have been dozens of controlled experiments on things like telepathy, which have turned up bubkis. The experiments on all of these things have been done. People are surprisingly willing to go through the trouble to do controlled experiments in these cases; which is good. Science shouldn't find any possibility off-limits, even though reasonable people would expect the negative result. Most of the time, the negative result is what happens anyways, but on a rare occasion, something interesting happens. --Jayron32 23:39, 13 November 2009 (UTC)

Other than homeopathy, can you think of anything that is reproduceable yet ignored by science? 85.181.147.202 (talk) 00:25, 14 November 2009 (UTC)

The success of the homeopathy is due to the placebo effect, selective memory, and clever marketing. All of which are well understood by modern science.

However, if you must have an example : Scientists have never adequately explained how Santa Claus delivers presents and/or coal to all the Christian children (and quite a few others) in a single 24 hour period. Yet it demonstrability happens every December between sundown on the 24th and sun-up on the 25th.

That's not to say that scientists always have a good an correct explanation for things, just look how long they thought light was carried by aether.

APL (talk) 04:21, 14 November 2009 (UTC)

That slashdot post you're quoting unfortunately confuses two different phenomena: The Pioneer anomaly is an unexplained slight additional acceleration of spacecraft in the direction of the sun, as the spacecraft head out of the solar system. The flyby anomaly is an unexpectedly large increase in the speed of a spacecraft during a gravitational slingshot maneuver. The reasons for the two kinds of anomaly may or may not turn out to be related, but the circumstances under which they occur are very different. But the main point of your post is valid, in that the existence of neither anomaly is being denied by scientists due to a current lack of a good explanation. Red Act (talk) 00:41, 14 November 2009 (UTC)

That is almost a contradiction in terms. To a very large extent checking whether something is reproducable is to engage in science. If you are saying homeopathy is reproducable you are in clear contradiction with the tests scientists have performed. Dmcq (talk) 00:34, 14 November 2009 (UTC)

No - by definition. 70.112.96.57 (talk) 00:36, 14 November 2009 (UTC)

And scientists haven't ignored Homeopathy - check out our article and you'll see any number of studies have looked for an effect and found NOTHING. So this is not a case of science ignoring something that's real - it's a case of a lot of charlatans trying to sell gullible consumers bottles of plain old water for prices that hover around $10,000 per gallon. Science has very carefully examined the claims - and they are not reproducible. Ditto telepathy, ditto all of that bogus stuff. Now you could claim that science turns it's back on what it doesn't understand - but that's demonstrably not the case - (case in point - the anomalous speeds of the Pioneer probes that I mentioned earlier). When the effect is real and can be reproduced under careful conditions - science treats it with respect and no small amount of excitement. When the effect isn't there - then it may be checked carefully and then safely ignored as bullshit...homeopathy being an excellent example of that. Cold Fusion is a good example of this. When some seemingly respectible scientists said they had this amazing effect - everyone got very excited about it. People tried hard to reproduce it - and when they couldn't - the whole thing dropped out of the realms of hard science and into the loving arms of the awaiting crackpots. The trouble is that the layman who does not understand the process sees cool idea after cool idea rejected by scientists. Perpetual motion would be cool - damn you scientists who showed that it's impossible! As science has gotten better and better at it's description of how the universe works - it's inevitable that the number of times we find an exciting and interesting anomaly gets smaller and smaller - and the excitement when we do gets bigger and bigger. In the 1800's an object moving a fraction of a percent faster than you expected was nothing to write home about. In 1900 - it would have been a curiosity worth remarking on - but nothing more. In 2000 - it's a major issue that we're about to invest a lot of time and money to track down and properly explain. Give it another 100 years and finding things that seem to outright fly in the face of existing theories is going to become very tough indeed. 70.112.96.57 (talk) 00:36, 14 November 2009 (UTC)

I can sort of think of an example, but I don't really think it counts. Way back when physicists were first discovering the concept of splitting an atom and atomic bombs, there was a big get-together. It was decided that the calculations made giving the mass needed to create a working bomb should be withheld due to the potentially dangerous uses. This didn't last long for a lot of reasons, least of all pride but especially since it became obvious that there were other, harder issues (the trigger, par exemple). Still, it was ignored so much as it was hushed for a little while. As the editors above say, if it's reproducible it's not ignored. It may not be widely studied at the moment, but those are issues more related to funding and interest. ~ Amory (u • t • c) 00:45, 14 November 2009 (UTC)

The failure of any party to claim James Randi's prize goes a long way to dispelling the notion that science might behave in such a way. -Craig Pemberton 02:24, 14 November 2009 (UTC)

Fun fact : The bumblebee thing is a myth. The boring truth is that one scientist made an error in a back-of-the-napkin calculation during a dinner party. His biologist collieges spread the story far and wide, because if there's one thing biologists love is to prove that they're smarter than those smug jerks from the physics department.

The "Fact" that bumblebee's can fly was never based on accepted actual, current, scientific thought. APL (talk) 04:11, 14 November 2009 (UTC)

In terms of the Mpemba effect, while I've read multiple conflicting claims about precisely what happens it's my understanding that the issue is that it was something that few scientists had studied or were aware of at the time and while it was known by some lay people, it's apparent that many people were not aware of it. No one demonstrated it to any scientist and since it seemed unlikely, many dismissed it when people claimed it was the case. I'm sure many scientists get people making claims which are made up, delusions or simply the result of poor methodology so it's hardly surprising that many scientists will dismiss such claims off hand without any evidence. However I'm not even aware any scientist did dismiss the claims, Mpemba was a secondary school student and he told his teacher who did dismiss it (and possibly made fun of him as a result of that) and while the teachers actions are perhaps not uncommon although also perhaps not a good thing, I'm doubtful that the teacher would fit most definitions of a 'scientist'. The first scientist who he did tell (that we're aware of) did not in fact dismiss the claim and instead asked a graduate student or technician to test it. Whatever the student/technician really said (and I suspect it's unlikely we'll ever really know) the basic idea was sound, an extraordinary claim requires extraordinary proof so many repetitions were necessary before they took it any further. Had anyone publicly demonstrated the Mpemba effect it wouldn't surprise me if it would have attracted more interest and similarly someone who would not normally be considered scientist could likely have published a paper on it if they went about it the right way and put a bit of effort into it. In other words, it's not something that scientists didn't accept rather that they simple weren't aware of and wouldn't likely not have accepted without good evidence since it didn't fit with theory Nil Einne (talk) 09:19, 14 November 2009 (UTC)

You may wish to consider the work of Rupert Sheldrake, in particular "The Sense of Being Stared At", as part of the answer to this question. --TammyMoet (talk) 15:20, 14 November 2009 (UTC)

What type of soda?

Hello desk. I am trying to make ink using a method found in some ancient Nepalese scrolls. The translation says at one point: "If one puts soda in boiling tea, this melt is said to be the best binder for ink." I finally found out what the glue liquid it keeps referring to is made up, but I don't know what type of soda the scroll refers to. According to the soda disambiguation page, it could be sodium oxide, sodium hydroxide, sodium carbonate, or sodium bicarbonate. I also see that sodium hydroxide is used in the bleaching of wood pulp. Since we're making (black) ink from fungal spores, perhaps this means it is not sodium hydroxide, or lye? I believe in another portion of the scroll it states that the same solution will congeal when it cools. What soda do you think it could be? Also, is the tea important, or do you think boiling water would be chemically sufficient? Thank you for any help! Mac Davis (talk) 22:37, 13 November 2009 (UTC)

If the solution "congeals" - then one needs to know how strong it is. Sodium Carbonate (the "normal" use of the name soda these-days) will form a decahydate - so 105g of sodium carbonate combines with 181g of water - this will melt at just 34°C - so one would not see any solid until the solution was below that temperature - so say 1 part sodium carbonate with 2 parts water will almost set solid at ambient. Sodium hydroxide is very soluble - 100g in 100g of water would be a solution which would start to crystallize at room temperature. Sodium bicarbonate is not very soluble, it will start to crystallize at ambient about 8% strength - but just throws down a white solid. My best guess is Sodium carbonate.  Ronhjones  ^(Talk) 23:02, 13 November 2009 (UTC)

Actually I think the "normal" use of the word soda is as shorthand for soda pop. Depends on where you live, of course. Somewhere you can find a map of the US and Canada, divided by where they say soda and where pop. --Trovatore (talk) 02:21, 14 November 2009 (UTC)

And they are "fizzy drinks" over here. Much more logical, we Brits are...  Ronhjones  ^(Talk) 18:41, 14 November 2009 (UTC)

Say what? I ordered a lemonade over there, and they brought me some nasty Sprite or something. --Trovatore (talk) 20:09, 14 November 2009 (UTC)

That sounds perfect Ronhjones! According to the article it is used as a bonding agent in alginate and can be easily extracted from the ashes of any plant. Mac Davis (talk) 00:31, 14 November 2009 (UTC)

That makes it even more interesting... See Potash - Plant ash would be initially potassium hydroxide, but that would rapidly absorb carbon dioxide (on cooling) to make potassium carbonate. So if the main source is plant ash then I'll plump for potassium carbonate (but there's a good chance sodium carbonate should work just as well in your application).  Ronhjones  ^(Talk) 18:38, 14 November 2009 (UTC)

Two girls, one baby (or two guys, one baby) - artificially fertilising an ovum using two ova nuclei or to sperm nuclei

Am I correct in thinking that parental imprinting would prevent the development of ova (with their original nuclei removed) fertilised with nuclei from two sperm or with the nucleus from other ovas? I expect that certain required genes would not be expressed in the correct ratios because the patterns would be the same in both sources and therefore not complementary? ----Seans Potato Business 22:52, 13 November 2009 (UTC)

Yup. I gave a pretty complete answer to this same question half a year ago: Wikipedia:Reference_desk/Archives/Science/2009_February_12#Same-sex_gametes_combining_to_form_a_zygote.3F. Someguy1221 (talk) 23:12, 13 November 2009 (UTC)

The Genomic imprinting article also describes experiments with mice to this effect. Rckrone (talk) 23:25, 13 November 2009 (UTC)

What would happen...

What would happen if less than half of the universe was nothingness? jc iindyysgvxc (my contributions) 23:05, 13 November 2009 (UTC)

It was, for part of its history. See Timeline of the Big Bang and the subarticles on the specific "epoch's" during the first few seconds. --Jayron32 23:32, 13 November 2009 (UTC)

It would rapidly collapse in a Big Crunch. That said, I don't think it is possible for the universe to reach its current size and age with that kind of density (in fact, it may not be possible for it to have that kind of density anyway - one of the results of inflationary theory is that the density of the universe will inevitably end up close to the critical density, and that theory seems to be well supported by evidence). --Tango (talk) 02:55, 14 November 2009 (UTC)

Which half? The left half or the right half? :) For some people with brain injury, see Hemispatial neglect, one side of the universe to all intents and purposes disappears and they don't seem to notice much. 12:09, 14 November 2009 (UTC)

November 14

Blood Type Compatibility

Just forestalling any possible misunderstandings, this IS NOT a request for medical advice. And now that that's out of the way, the question: Is it possible (I have heard stories places) to determine whether two people are compatible to donate blood to each other by having each prick their finger and mixing their blood on something like a microscope slide, then watching to see if it clots like crazy? Ks0stm ^(T•C•G) 03:53, 14 November 2009 (UTC)

No, it's not that simple. For one thing, clotting, or the production of a blood clot, is distinct from the agglutination reaction that indicates incompatibility. Second, while agglutination is a clear indication of incompatibility (for one or both potential recipients), more sophisticated tests are needed to ensure compatibility. -- Scray (talk) 04:31, 14 November 2009 (UTC)

Schrödinger's cat - can you actually stop observing it?

With respect to the Schrödinger's cat thought experiment, is it possible, even in theory, to set up a situation where a cat is not observable?

As a thought experiment, the Schrödinger's cat scenario is not constrained by practical limitations, but does it even make sense to have a cat so completely cut off from the rest of the universe that it is not observable, even in principle? I am curious specifically about the fact that a live cat, in contrast to a dead cat, has a metabolism generating heat, has a heartbeat, has a nervous system with electrial currents, etc., and must therefore be continuously interacting with the universe at large. I realize that the point of the thought experiment is to demonstrate the paradox, but discussions always gloss over this point. Peter Grey (talk) 06:05, 14 November 2009 (UTC)

Different assumptions would make it a different scenario. -- Scray (talk) 06:12, 14 November 2009 (UTC)

It's not necessary for the cat to be completely isolated from you, only that the effect it has on you is something that could have been a consequence of either state. I think enough insulation, or just being far away from the box would make it work. Even with full knowledge of the initial state of the system, \there will be a wide range of possible observable outcomes for each the live and dead cat. If what you observe is in the intersection of those two sets of possibilities, then the cat is to you still in a superposition of both alive and dead. Once you observe something that couldn't be caused by one of the fates of the cat (or is extremely unlikely to be caused by one of them) then you're entangled with the cat's alive/dead-ness and to you the cat is definitely alive or definitely dead. Rckrone (talk) 09:32, 14 November 2009 (UTC)

It'd pretty difficult with an object the size of a cat, never mind the ethical issues. There are proposals though to do the equivalent with a virus. Not quite so impressive having a 'Schrödinger's virus' but few people will worry about its fate. Dmcq (talk) 12:03, 14 November 2009 (UTC)

Paper here. Apparently they propose to maglev a small object like a virus and cool it down to the ground state of quantum harmonic oscillation, then put it into a superposition of the ground state and the first excited state. They don't create a superposition of internal states of the virus, much less a difference as complicated as "alive" and "dead" (whatever that would mean for a virus). This experiment is only possible because viruses are inert hunks of matter when they're not infecting a cell; you couldn't do it with a living cell because of all the chemical activity going on inside (I think). Also, a superposition of ground and first excited states is only a "superposition" in the sense that it's not an energy eigenstate. But complicated systems are never in energy eigenstates anyway. The cooling to the ground state seems more interesting than the subsequent excitation, which just makes it slightly more normal again. Nevertheless, if this experiment is performed, it will of course be reported by the media as "an experimental realization of Schrödinger's cat". -- BenRG (talk) 13:15, 14 November 2009 (UTC)

In practice it is absolutely impossible to shield something of the size and temperature of a cat from the outside world. All that's necessary for the system to become classical is that the environment contain enough information to distinguish the states in principle—whether or not that information is accessible in practice—and that's inevitable when enough particles are involved. The heat radiating from your computer case contains information about the calculations being performed by the CPU. If nothing else, the cat's gravitational field will give it away through any amount of insulation, I think. Even if the system's state remains unknown to you, you still have to model it as a classical mixed state (1/2 chance of live cat, 1/2 chance of dead cat) and not as a quantum superposition (1/√2 alive + 1/√2 dead) to reflect the fact that it has objectively collapsed by environmental decoherence. -- BenRG (talk) 13:02, 14 November 2009 (UTC)

Maybe you could set up noise around the cat, like randomly moving weights, sounds, etc, determined by a lot of different quantum measurements. Would it be possible to create enough noise so that from your perspective it would be impossible to distinguish the two cat fates even in theory from the observables available to you? Rckrone (talk) 17:23, 14 November 2009 (UTC)

Unless I'm missing something, that's impossible. Because of unitarity, the only way to eliminate the information from the environment is by, in effect, undoing the process that produced it. If that was a thermodynamic process (like blackbody radiation) then you can't undo it because of the second law. -- BenRG (talk) 18:00, 14 November 2009 (UTC)

The wave function is fully determined, but when you take a measurement, you aren't finding the full wave function. Two different wave functions can produce the same measurement. That's the idea behind interference. Rckrone (talk) 18:42, 14 November 2009 (UTC)

Noise doesn't do it. It may make it harder, or perhaps impossible to determine which information comes from the cat, and which information comes from the noise, but the information is still leaving the box. APL (talk) 21:23, 14 November 2009 (UTC)

Right, but it's not enough for information to be leaving the box, it has to be information that is determined by the fate of the cat. If the same measurement could as likely come out of the box with a live cat in it as the box with a dead cat, then making that measurement doesn't lead you be entangled with the cat's alive/dead state. BenRG is right that the measurement you're making includes any way that the box affects you which includes quite a lot of information, but I'm wondering if it wouldn't still be realistically possible to set up the box so that the measurement isn't necessarily indicative of the cat's state, at least for some short amount of time after the event. Rckrone (talk) 22:02, 14 November 2009 (UTC)

In principle it's very simple: you put the cat (in a box) in the middle of interstellar space, with the closest observer a billion miles away. The cat is then unobservable over the time course of the experiment simply because of the finite speed of light. Looie496 (talk) 18:38, 14 November 2009 (UTC)

Ahhh....but who put the cat there? Myles325a (talk) 02:21, 17 November 2009 (UTC)

No. Because ANY interaction with the universe is deemed an 'observation'. So as soon as anything observes it (or interacts with it ), the WF collapses into a definite state.--79.75.63.71 (talk) 00:50, 18 November 2009 (UTC)

origin of a cyclone

formation of cyclones —Preceding unsigned comment added by 124.43.90.158 (talk) 08:32, 14 November 2009 (UTC)

Are you asking, "How does a cyclone form?" If so, see Cyclone#Formation.--CurtisSwain (talk) 08:59, 14 November 2009 (UTC)

Ferrofluid buoyancy?

Supposing a powerful (perhaps superconducting) permanent magnet was placed over a tube of ferrofluid. Would pressure still increase with depth, and what would happen to an object of neutral buoyancy in such a liquid at different depths?Trevor Loughlin (talk) 14:19, 14 November 2009 (UTC)

It would depend on if the magnetic "up" force more than counteracted the gravity "down" force. Pressure in a liquid (condensed fluid) is just controlled by the forces acting on the fluid (gas pressure works differently). Under normal circumstances, gravity is the only force acting on it. If you had a stronger force pulling straight up, such that the net force vector on the fluid was up rather than down, I would expect the pressure gradient to act differently. Of course, since the magnet will lose strength with distance, this effect could result in some unusual pressure gradients. --Jayron32 16:05, 14 November 2009 (UTC)

Having neutral buoyancy by definition means an object neither rises nor falls from its position in a presure gradient. Cuddlyable3 (talk) 16:36, 14 November 2009 (UTC)

Supposing the magnet was strong enough to completely reverse the pressure gradient. Would an object which would normally float upward float downward? And if it was moved sideways out of the gradient (since the float is not magnetic itself this takes little energy) when it reached the bottom, would it float up again? And if it was moved sideways back into the reverse gradient when it reached the top, would it sink again, creating a mechanical over-unity device?Trevor Loughlin (talk) 12:37, 15 November 2009 (UTC)

Moving it sideways into or out of the gradient takes energy -- specifically, exactly as much energy as you get from it moving along the gradient. --Carnildo (talk) 01:34, 18 November 2009 (UTC)

Hanging

The OP is asked not to edit responses to their question. Cuddlyable3 (talk) 23:25, 15 November 2009 (UTC)

how come profesional hangings the victom goes out quick even if the neck is not broke iv watched 30 iran and german hangings they are all instent alothough they are all suspension. but suicide hangings iv seen take at least 10 secs to pass out why?

examples: http://video.google.com/videoplay?docid=7181755851454128977#

http://www.liveleak.com/view?i=317_1218265064

there are many others many in which the are slowly raised by hand as well . the result is the same. why? —Preceding unsigned comment added by 74.65.3.30 (talk) 16:34, 14 November 2009 (UTC)

There are different ways of hanging a man by the neck until he is dead. The long drop, favoured by English hangmen, produced death by breaking the neck. You may also wish to consider whether censorship was applied to the video clips you have been watching: was a long struggle cut from the end result so that it could be distributed? --TammyMoet (talk) 17:33, 14 November 2009 (UTC)

Breaking the neck does not, of course, produce instant death. What it produces is instant paralysis, sparing the feelings of the onlookers; the interested party stops moving, because he can no longer send signals to any muscles below the neck, and usually his face is covered. --Trovatore (talk) 20:53, 14 November 2009 (UTC)

The article Death erection cites from a RS that one in three hanging men have an erection. That statistic means the OP may have watched 10 males with erections but no associated enjoyment. Unless any were female or very very peculiar. Cuddlyable3 (talk) 22:54, 14 November 2009 (UTC)

The OP is asked not to edit responses to their question. Cuddlyable3 (talk) 23:25, 15 November 2009 (UTC)

bipolar disorder

percentage of people affected by bipolar disorder globally and age wise .. —Preceding unsigned comment added by Arun vvv (talk • contribs) 17:29, 14 November 2009 (UTC)

Is the information on epidemiology in our article on bipolar disorder helpful? TenOfAllTrades(talk) 18:53, 14 November 2009 (UTC)

homeostasis during illness

Hello! I've been asked to look at the role of homeostasis in the human body during health and illness. As for health, I thought this seemed quite simple - homeostatic mechanisms such as regulation of blood glucose concentration, blood pressure, serum potassium concentration, osmoregulation etc. help maitain our health and without them we would obviously quickly die. When it comes to the role of homeostasis in illness I got stuck and I need someone to point me in the right direction. What examples of homeostasis occur during illness? Would the mechanism of a fever be an example? Please help! RichYPE (talk) 19:33, 14 November 2009 (UTC)

You might look at CO₂ levels, pulseox and respiratory volume when O₂ is administered. You might look at the blood sugar levels in diabetecs when they have an infection. Edison (talk) 20:18, 14 November 2009 (UTC)

Additional pointers:

• Villous adenoma, anemia, tissue hypoxia, erythropoietin, reticulocytosis, iron deficiency
• Physical exercise, muscle hypertrophy
• Hypertension, ventricular hypertrophy
• Sound, Tensor tympani
• Infection, Inflammation, Chemotaxis, Diapedesis, G-CSF

Hope this helps. -- Scray (talk) 05:46, 15 November 2009 (UTC)

I think perhaps the article on Stress (biology) is the best place to begin. It will point you to other relevant articles, such as HPA axis. Looie496 (talk) 18:15, 15 November 2009 (UTC)

Many thanks for the contributions everyone. Scray provided a good example of what I am looking for by mentioning reticulocytosis. I'm just basically looking for some examples of homeostatic mechanisms that occur during illness. Any more ideas about the kind of thing I need to look for will be great. Thanks all! RichYPE (talk) 23:07, 16 November 2009 (UTC)

LHC beam dump

The LHC has around 8000 miles of rock and metal around and under it. The beam dump of the LHC has to absorb high particle energies, and needs to be several meters long to do so.

Why isn't the earth itself suitable for absorbing the energies of the beam? It's less absorbent than custom materials (graphite, etc) but there's miles of rock compared to meters of custom material, and a less efficient but longer absorber would presumably spread the heat dissipation over a larger volume. Heat dissipation is its main purpose, and presumably nobody really cares how warm a chunk of off-site rock at the end of a separate tunnel 50 - 175 m underground gets.

FT2 ^{(Talk | email)} 21:00, 14 November 2009 (UTC)

They may care how radioactive it gets. It could well become a safety issue. Groundwater can move radioactive isotopes to unwanted places. Graeme Bartlett (talk) 21:28, 14 November 2009 (UTC)

Rising longevity and the remaining number of years of expected survival

Its 2009, I'm X years old and I've got a 50% chance of surviving for another Y years. Going back 100 years say with a much lower longevity for the population, then to have the same chance of surviving another Y years I would have to be very much younger - I would need to be Z years old. Is there anywhere on the internet where I can see my Z-age (to coin a term) during the 20th and earlier centuries? Or get the data to estimate it? 78.147.25.95 (talk) 21:50, 14 November 2009 (UTC)

I don't know where to point you for the specific data — I could Google it but so could you. But when you find it, I think you may find that the differences are not as dramatic as you think. As I understand it the life expectancy of adults has not really risen that awfully much. The huge increases in life expectancy at birth are largely due to the fact that far fewer people die in childhood than they used to (at least in the industrialized world). --Trovatore (talk) 22:01, 14 November 2009 (UTC)

I've read that idea old chestnut several times here, but I think its not particularly true. My grandfathers for example died in their sixties probably due to unwittingly consuming too much saturated fat and alcohol and not taking much exercise. In the early 20th. century at least even people who survived childood still died much younger than currently. 84.13.173.43 (talk) 11:53, 15 November 2009 (UTC)

There certainly has been an increase in how long people that reach adulthood live, but it is small compared to the increases in life expectancy at birth. According to Life expectancy#Lifespan variation over time, the average life expectancy at birth in mediaeval Britain was 20-30 years. It is now about 80. That is an increase of at least 50 years. I can't find figures for adult life expectancy, but I think we can be sure it has increased by significantly less than 50 years. --Tango (talk) 12:13, 15 November 2009 (UTC)

Nevertheless, the lifespan for people who have for example reached the age of twenty has still been rising considerably. The number of people over 100 has risen greatly. 92.27.154.139 (talk) 13:55, 18 November 2009 (UTC)

Is X=Y in the question or is it a two parameter question? i.e. do you just want the age at which you have a 50% chance of living as long again? By the way of course the chance of you surviving for another Y years is technically unknown since we don't know what will happen to the curve of longevity in the future (obviously). Incidentally an appreciable fraction of all the people who have ever lived are still alive (bout 10-15% I think) which does not imply you have a 10-15% chance of not dying but does illustrate the growth in the population. --BozMo talk 22:09, 14 November 2009 (UTC)

X=Y?? You mean if I'm two years old I'm going to only survive another two years? You've misunderstood the question. 84.13.173.43 (talk) 11:56, 15 November 2009 (UTC)

That last statistic depends heavily on what you mean by "people". You have to draw the line somewhere, but where you draw it can make a big difference (population numbers were low in proto-humans, but they were around for so long that the total numbers are high). We have some discussion of this topic at World population#Number of humans who have ever lived. --Tango (talk) 22:27, 14 November 2009 (UTC)

The questions seems to be about the estimated lifetime remaining, conditional upon reaching a given age. Insurance and census data would be a major source, it would also depend upon other factors such as locale, health, employment, family/medical backgrounds, and so on. The question can be paraphrased (as I understand it) this way:

Holding all other matters constant: - "For any given age of a person (A) and calendar year (B), there will be an age (C) such that a person who is A years old in year B, has a 50% chance of living to C years old. Where can I find a table of (A, B) -> C?"

Or more generally: - "For any given age of a person (A) and calendar year (B), there will be a distribution (C) for eventual age at death vs. probability of dying at that age. Where can I find a table of (A, B) -> C?"

FT2 ^{(Talk | email)} 22:33, 14 November 2009 (UTC)

The article Life expectancy will help. Life insurance companies keep data for life expectancy estimates when selling a Life annuity which is a form of Longevity insurance. Cuddlyable3 (talk) 22:39, 14 November 2009 (UTC)

Life tables typically give you A->C for fixed B. What the OP wants is B->A for fixed C. I don't think that exists ready made. --Tango (talk) 23:39, 14 November 2009 (UTC)

What I'm effectively looking for are life tables for various times in the past. 84.13.173.43 (talk) 12:02, 15 November 2009 (UTC)

November 15

Lucid dreaming

How can I develop this skill? —Preceding unsigned comment added by 79.67.82.206 (talk) 01:10, 15 November 2009 (UTC)

Did you try looking it up on Wikipedia, seeing as you are here? If you had, you would have very quickly found this: Lucid dreaming#Induction methods. --Tango (talk) 02:32, 15 November 2009 (UTC)

Yes thanks dont know how I missed that. Must have been asleep when I asked the Q--79.67.82.206 (talk) 12:12, 15 November 2009 (UTC)

Lucid dreams can be very hard work. It is funny when one wakes up from a realistic dream wherein he worked harder than in real life. I woke up from dreaming about having to devise computer systems for tracking billing and document management for a law firm, and designing a complete physical plant for the firm, all of which were far removed from tasks I ever did in a job. On waking, i felt ripped off, as if I had done work without compensation. Why would you assume lucid dreaming is a good thing? Edison (talk) 03:41, 15 November 2009 (UTC)

If it were really a "lucid dream", you would have known it was a dream, so you could have just told your boss to go jump in a lake. APL (talk) 04:35, 15 November 2009 (UTC)

Indeed. I think Edison is getting confused between "lucid" and "vivid". --Tango (talk) 13:25, 15 November 2009 (UTC)

I don't think you can develop it. There is no evidence whatesoever that these dreams are indeed lucid. As we can dream just about everything, we can also dream that we are lucidly (aka consciously) dreaming, just like we can dream we that we are cold, or hungry or whatever. It's an illusion. DVdm (talk) 13:34, 15 November 2009 (UTC)

Huh? I don't quite follow you -- would there be any empirical difference between actually dreaming, versus merely dreaming that you are dreaming? I have lucid dreams occasionally (not deliberately induced), and I find that I can easily make myself wake up from one if I want to. It seems to me that that's inconsistent with what you're saying, but I'm not sure I actually understand you. Looie496 (talk) 18:09, 15 November 2009 (UTC)

"I can easily make myself wake up from one if I want to." ==> You mean that you dream that you easily can make yourself wake up.

We dream that we can can fly. Do we actually fly?

We dream that we can make ourselves wake up. Do we actually make ourselves wake up? You might think so, but I don't - we just dream it.

We can dream anything, remember, so why not this?

Perhaps this clarifies :-) DVdm (talk) 19:15, 15 November 2009 (UTC)

I lucid dream and sometimes it goes a bit all wrong, and I concetrate extremely hard on moving my real life arm instead of my in dream arm and it wakes up. Like, actually wakes me up in real life. I've done it relatively consistently so it's not just a coincidence. Plus if you're aare you're dreaming then you're aware you're dreaming, surely that's that? 82.11.245.145 (talk) 19:48, 15 November 2009 (UTC)

I don't think so. If you think you are aware you're dreaming then surely you agree that you are dreaming. Now, what are you dreaming? You are dreaming that you are aware you're dreaming. DVdm (talk) 19:50, 15 November 2009 (UTC)

But I'd say lucid dreaming is being aware you're dreaming, and if you know you're dreaming in any sense I'd say you are lucid. Generally realising you aren't awake whilst in a dream would be lucid to me in some way, even if you are dreaming you're dreaming. I get what you're saying, but it seems more philosophical/a technicality than anything. Guess it depends on how you think of the term. Jimothyjim (talk) 20:02, 15 November 2009 (UTC)

Well, starting from the premise that one can dream anything, I just apply Occam's razor in this case. I always found this a school book example.

Cheers, and sweet dreams :-) DVdm (talk) 20:36, 15 November 2009 (UTC)

Nonsense. First of all, in it's purest form, a "lucid dream" is just a dream where you're aware that you're dreaming. There's no difference between being aware of something during a dream, and dreaming that you are aware of something. Perhaps you're objecting to the idea that dreams can be controlled. That's entirely testable. (By the dreamer, perhaps not by an outside observer) People who can lucid dream often decide before they go to bed what direction they'll take a dream in. Since this is typically a direction that their dreams to not normally go in (else, why bother?) and since they are typically satisfied with the results, I deduce that lucid dreamers are getting results far better than random chance.

Incidentally, I'm not sure if this is a correct application of Occam's razor. You're positing an unusual sort of meta-dream. Why does this multiply entities less than positing a lucid-dream? APL (talk) 00:52, 16 November 2009 (UTC)

"First of all, in it's purest form, a "lucid dream" is just a dream where you're aware that you're dreaming." ==> Yes, like you say, "a dream where you're aware...". So you dream that you're aware that you're dreaming. That does not mean that you are aware.

"There's no difference between being aware of something during a dream, and dreaming that you are aware of something. " ==> Of course there is a difference, just like there is a difference between feeling cold during a dream, and dreaming that you are feeling cold.

"... the idea that dreams can be controlled. That's entirely testable. (By the dreamer, perhaps not by an outside observer)" ==> So it is entirely un-testable and, what's more important, un-falsifiable, which makes it useless idea.

"You're positing an unusual sort of meta-dream." ==> On the contrary. We can dream anything... hunger, awareness, joy, illusion of control, fear, lucidy, extasy... There is no meta-level anywhere near. That is Occam in action.

But hey, don't let me spoil your dreams. By all means enjoy the illusion that you really honestly have control. I just don't buy it :-)

DVdm (talk) 08:37, 16 November 2009 (UTC)

No, seriously. You've got logical errors here. For starters, your abuse of the word "anything" can cut both ways. I could say "If I can dream anything then I can dream precisely what I want to in a wholly interactive way." and it would be just as valid as what you said.

Secondly, not strictly a logic problem, but I still don't see how Occam's famous problem-solving technique applies here. Lucid Dreaming is entirely testable by the dreamer, (As I explained above) and many lucid dreamers claim to have done so. You're positing that they're lairs.

Thirdly, While it annoys those of us who prefer the hard sciences, you can't dismiss, out of hand, phenomena that rely on self-reporting. Otherwise you've just dismissed the largest fraction of psychology, and a significant fraction of medicine. (How do we know that painkillers work?)

Fourthly, but not finally, "Feeling cold" is a perception. Feeling cold during a dream and dreaming that you are feeling cold are the same perception, even if the causes are different, so your example in that case is flawed as well.

Finally, and most importantly, you're ignoring the fact that communication from a dream to reality is entirely possible. So lucid dreaming is entirely testable by third parties. Studies have been done where lucid dreamers have been instructed to perform certain actions, (clench their fists, move their eyes in a particular unusual pattern, etc.) and they were able to successfully do this even when polygraph machines proved that they were asleep. Two such studies, in reputable journals are used as references in the introduction to the article Lucid Dreaming.

(For the record, I cannot lucid dream, I am simply objecting to your misapplication of logic to 'disprove' a common phenomena.)APL (talk) 15:33, 16 November 2009 (UTC)

Very well put, APL. In the same vein, how could you say that the "illusion" of being aware is any different than "actually" being aware? Either way, you are perceiving the same thing. —Akrabbim^talk 15:42, 16 November 2009 (UTC)

I will only comment on your first sentence: "I could say "If I can dream anything then I can dream precisely what I want to...".

==> You still don't get my point. You can dream that you-can-dream-precisely-what-you-want, because dreaming-precisely-what-you-want belongs to "anything".

I think I have repeated myself sufficiently now. For those who still don't understand, don't worry - and don't lose any sleep over it :-) DVdm (talk) 15:47, 16 November 2009 (UTC)

"I think I've repeated myself sufficiently now. No matter how many times I keep repeating exactly the same thing people just keep pointing out the flaws in my logic, my poor understanding of the topic under discussion, and referencing legitimate scientific evidence that I am exactly wrong, It's sad really. Still, a man can only mindlessly repeat the same thing so many times before he's forced to give up on the sad souls who won't listen to his brilliance." APL (talk) 15:58, 16 November 2009 (UTC)

I had a dream once where I was going to do something illegal, but then I realized I was dreaming, so it was ok for me to do the illegal thing since it wasn't real. Ariel. (talk) 08:23, 16 November 2009 (UTC)

Yes, you had a dream once. I had one too :-) DVdm (talk) 08:37, 16 November 2009 (UTC)

I had a dream once where I was Lucid, I can't remember what I was doing, but at the same time I was listening to the TV in the real world. And I wasn't just dreaming I was listening to a real world TV, because when I woke up again I checked the NFL game and everything I had heard whilst dreaming had happened in the game. That's not technically lucid dreaming as something else, but my point is that dreaming isn't a clear cut thing, just cause you can't do it doesn't mean it's not possible. Some people can remember insane amounts of numbers and stuff, and I can't do that but I don't deny others can. The mind is pretty much impossible ot understand at the minute, but it seems odd to disregard things like Lucid dreams. Jimothyjim (talk) 11:59, 16 November 2009 (UTC)

Sure. I had the same experience many times and we probably all have. But note that I don't disregard lucid dreaming - I just find it a hell of a misnomer. DVdm (talk) 12:21, 16 November 2009 (UTC)

I think DVdm is like an ancient Greek philosopher here. He's tumbled onto an explanation of a natural phenomena that is elegant in it's simplicity and has all the grace and symmetry of the finest zen koans, and he refuses to let go of this explanation even when the real world turns out to be more complicated than his initial assumptions. APL (talk) 16:50, 16 November 2009 (UTC)

It's not any sort of explanation in the first place. There is no such thing as "an illusion of being aware". That was Descartes' irrefutable point with his famous line cogito ergo sum, "I think, therefore I am", which many people these days misunderstand.

By the way, DVdm also goes off the track a bit by equating "lucidly dreaming" with "consciously dreaming". When you are dreaming, quite obviously, you are conscious, whether it's a lucid dream or not. You are not conscious (or at least not very) of external stimuli, but that's another matter: You are able to perceive and think, even if your perceptions are internally generated. --Trovatore (talk) 20:23, 16 November 2009 (UTC)

Hunger

Why do I feel hungry about every 5-6 hours while awake, but not when asleep. When I wake up at night I may feel hungry but if I go back to sleep without eating, then, when I wake up in the morning, Im no hungrier than normally at breakfast. Whats going on here? —Preceding unsigned comment added by 79.67.82.206 (talk) 01:14, 15 November 2009 (UTC)

Circadian rhythm, or something similar - hunger isn't only caused by a need for nutrients, your body is conditioned to expect foods at certain times and not to expect them at other times. Vimescarrot (talk) 01:22, 15 November 2009 (UTC)

Sleep is a pleasure too. You have two competing pleasures — sleeping and eating. Why waste good sleep on mundane eating? Bus stop (talk) 03:47, 15 November 2009 (UTC)

You also have a much larger demand for nutrients while awake since you are actually up and about and doing things. Sleeping doesn't require much energy at all (no walking, no intense thinking), so you can make it pretty far on not very much. ~ Amory (u • t • c) 19:47, 15 November 2009 (UTC)

Phone and Paper Shredder

Many times when I receive a cell phone call in my bedroom where my paper shredder also happens to be, the paper shredder will start running (as if I inserted paper) just before the phone rings and will continue to run until I pick up the call. Why does this happen? 69.115.152.137 (talk) 01:32, 15 November 2009 (UTC)

Do the clocks start running backwards when someone rings the doorbell as well? :) Perhaps it's interference. DRosenbach ^{(Talk | Contribs)} 03:10, 15 November 2009 (UTC)

...don't you love flippant responses? Actually it is possible that pre-ringing interaction between your cell phone and the cell towers are responsible for your cell transmitting at a frequency and intensity that triggers the circuitry f the switch that belongs to the paper shredder activation circuit. For instance if the switch is based on a light sensor then the radio frequency may cause the light sensor circuitry in the shredder to activate as if the light beam were interrupted. In some cases all it take is for the signal traveling to the sensor sent by the light beam to deviate from phase or frequency to activate the circuit. 71.100.7.164 (talk) 03:29, 15 November 2009 (UTC)

It could be electromagnetic inductance from the cell phone triggering the circuit on the shredder which detects the introduction of paper to be shredded. Or perhaps the house is built over an old Indian (Native American) burial ground, and poltergeists are at work. Edison (talk) 03:35, 15 November 2009 (UTC)

Right before a cel-phone rings there is a lot of communication going back and forth between the tower and the phone. This interferes with a lot of things. Most commonly people notice this as interference in speakers. Just like speaker wires can pick up the signal, probably there's a wire between the "paper sensor" and the chip the controls the shredder that's picking up this interference. If I had to guess, I'd say that the sensor is probably analog (Optical, perhaps?) with a very tiny voltage difference between "paper" and "no paper". APL (talk) 04:33, 15 November 2009 (UTC)

The shredders I've used have had a mechanical switch that the paper operates. Any design that is capable of being turned on by simple interference sounds dangerous (even if nothing is near the paper slot, the motor could overheat). I would suggest getting rid of the shredder or at least keeping it unplugged when not actually in use. And if it operates even when unplugged, call an exorcist. :-) --Anonymous, 05:50 UTC, November 16, 2009.

Nah, most shredders today use a light sensor and a diode. Mechanical switches tend to clog. But you are right about the overheating part - I hope the motor has protection circuitry in it. There are many kinds of proximity sensors, maybe one of them is affected by strong radio waves. Ariel. (talk) 08:20, 16 November 2009 (UTC)

cancer

Cancer is a mutation of normal cells characterized by uncontrolled growth. If a GM corn or flax cell that produces insecticide gets cancer is it also characterized by uncontrolled growth? 71.100.7.164 (talk) 02:21, 15 November 2009 (UTC)

So you sort of answered your question by defining cancer as mutations that promote uninhibited growth. DRosenbach ^{(Talk | Contribs)} 03:11, 15 November 2009 (UTC)

Only if my understanding of what cancer is or does is correct. 71.100.7.164 (talk) 03:22, 15 November 2009 (UTC)

Plants don't exactly get cancer. Plants can get tumors, but it's not really cancer because it can't spread like it can in animals. Cecil Adams touches on this briefly here. APL (talk) 04:23, 15 November 2009 (UTC)

Your question would make a lot more sense if you began with "Cancer is a mutation of normal animal cells characterized by uncontrolled growth." By redefining a common term, you can make up any ridiculous question you like. For example, I could ask: "If radiation contamination is caused by any exposure to sunlight, are all GM crops grown outside full of radiation contamination?" -- kainaw™ 04:39, 15 November 2009 (UTC)

I don't disagree with you and you are making a reasonable point but where I live there are a lot of phosphate mines and a lot of unmined phosphate. It is ver common to see trees with so called tumors but due to their encompassing size in some cases the tumors are larger than the tree. Although they are usually adjacent to each other and a dividing line is hard to establish between adjacent tumors and they appear not to have been transported to other parts of the tree through the veins of the tree they are obviously uncontrolled growths everyone assumes to be from radon gas or a radiation based interference with genomes, even though hey might be the result of a tumor causing virus. 71.100.7.164 (talk) 08:14, 15 November 2009 (UTC)

Might they be galls? -Craig Pemberton 09:00, 15 November 2009 (UTC)

These nodules, growths, tumors are very large, the largest mass of tumors surround a thirty foot oak tree at the trunk from a foot above the ground to six feet above the ground, if memory serves me correctly. Unless galls are consistently this massive then I can't explain the number of trees effected. 71.100.2.243 (talk) 11:38, 15 November 2009 (UTC)

Could be nematodes or fungi. Fences&Windows 15:29, 15 November 2009 (UTC)

Plants can't get cancer as such because their cells cannot undergo metastasis. But they do get tumour-like growths such as crown galls caused by Agrobacterium tumefaciens. Fences&Windows 15:22, 15 November 2009 (UTC)

Metastasisless malignancies are still malignancies -- basal cell carcinoma is cancer even though it rarely metasticizes. If it would never metasticize, it would still be categorized as cancer because metastasis is just one of the many surrogate biomarkers signs, so to speak, of cancer. (pre)Cancer is diagnosed prior to metastisis based on histologic findings such as mitotic figures, metaplasia/dysplasia, epithelial invasion of the lamina propria, etc. DRosenbach ^{(Talk | Contribs)} 15:41, 15 November 2009 (UTC)

Why do plants get tumors from infection by other organisms only? 68.193.225.106 (talk) 16:06, 15 November 2009 (UTC)

I'm not sure if that is true. On a slightly different note, cancer is commonly linked to infection. -Craig Pemberton 08:33, 16 November 2009 (UTC)

Evolutionary advanage of nervousness?

It seems that nervousness would be a severe detriment to survival, due to making tasks which are important to survival more difficult to perform successfully. Yet somehow nervousness hasn't been eliminated by natural selection. What survival benefit does nervousness provide that has caused this? --75.39.194.221 (talk) 02:23, 15 November 2009 (UTC)

This emotion is supposed to stop the animal from doing something risky, such as showing itself in front of a predator, eating a strange new substance, driving too fast, straying too close to a cliff edge, or jumping from it. Graeme Bartlett (talk) 02:35, 15 November 2009 (UTC)

Nervousness is supposed to stop you doing whatever it is, that is the point. What important things were there for proto-humans (or earlier animals) to do that would make them nervous? I can't think of any. Anything that would make them nervous would be something that they shouldn't do. Eg. you see a big lion sleeping next to the tree you want to pick fruit from you don't overcome your nerves and creep up to the tree, you go and get your dinner somewhere else. --Tango (talk) 02:56, 15 November 2009 (UTC)

I suppose the opposite of "nervousness" would be fearlessness. "The lion is sleeping next to the tree with the fruit I want to eat. I will climb up on the sleeping lion to reach the fruit. If the lion wakes up, I will simply spit in his eye." Very brave, but the individual might not survive to pass on his genes to the next generation. Edison (talk) 03:32, 15 November 2009 (UTC)

Emotions are complex. Nervous is a general term covering many emotional states. As you point out, nervousness can be detrimental. I don't think evolution is the best place to look for evaluating nervousness. Emotions may not leave traces as easily understood over the periods of time involved in human evolution. We may not really be able to know what advantage or disadvantage various emotional states, among them the many types of nervousness, have played at the various stages in the role of human survival over the periods of time in question. Bus stop (talk) 03:35, 15 November 2009 (UTC)

Like most behaviours, nervousness can be dysfunctional in some cases, but in others there would be a survival benefit to having second thoughts, being overly cautious, or even being visibly nervous which could alert other group members or even lead to a better-qualified member taking action. Also you're only likely to overcome nervousness if you judge that the action truly is important, so it screens out casual risk-taking. Peter Grey (talk) 03:53, 15 November 2009 (UTC)

I find that nervousness is usually quite justified. What's the point of embroidering your quilt if you have the notion that a sabretooth tiger is nearby? Vranak (talk) 04:19, 15 November 2009 (UTC)

That's right, put down the quilt, grab your spear, and get yourself a nice sabertoothed fur, instead. Much warmer than a quilt. StuRat (talk) 05:12, 15 November 2009 (UTC)

I've noticed a huge difference in the skittishness of flying insects. If they are sitting on a wall when I enter a room, some will start flying and taking evasive action immediately, while others will let you walk right up and grab them. I have more trouble understanding the latter behavior. I'd expect them to give their camouflage a chance to work, but, at some point, I'd also expect them to realize I've spotted them and flee (or flea, as the case may be). StuRat (talk) 05:17, 15 November 2009 (UTC)

Maybe they were asleep. --Tango (talk) 06:15, 15 November 2009 (UTC)

And they might not be intelligent enough to cope with the unusual environment (big homogeneous wall painted with only one color) --131.188.3.21 (talk) 10:36, 15 November 2009 (UTC)

Pure conjecture here, but the presence of individuals with crippling nervousness or brash bravery in a population might be understandable in terms of heterozygote advantage and balanced polymorphism. -Craig Pemberton 08:57, 15 November 2009 (UTC)

It could be, but I think it is more likely explained by nurture rather than nature. Crippling nervousness usually has an identifiable cause (yelling at your children over minor things a lot tends to make them generally nervous, for example). I think brashness is usually caused by over-estimating ones own abilities rather than bravery - that, and being drunk. --Tango (talk) 09:06, 15 November 2009 (UTC)

Fear and Risk aversion might help, and see The psychology of risk taking behavior. Nervousness isn't per se a pathology, the balance of whether to take risks or not - which is really what underlies nervousness - is something that affects most animals. Work in animal behaviour and ecology often talks about 'neophobia', which is a version of nervousness. "What important things were there for proto-humans (or earlier animals) to do that would make them nervous? I can't think of any." New sources or types of food, crossing rivers, climbing trees, extra-partner mating, predators or other groups of hominids nearby, etc. Fences&Windows 15:13, 15 November 2009 (UTC)

How long will lunar water last?

Scientists have recently confirmed the presence of large amounts of water on the moon. Has anyone done any work estimating how long that water is likely to last if we start using it? Are we likely to hit peak water on the moon at some point? I know we don't have any idea precisely how much water there is on the moon and we don't know how much water we are likely to want to use in the future, but does anyone have a rough order of magnitude? Is there enough for a few decades? A few millennia? Millions of years? --Tango (talk) 04:46, 15 November 2009 (UTC)

I believe you are viewing lunar water as a pure consumable, not a recyclable resource. There is no reason to assume that the water harvested from the Moon won't be recycled over and over as long as it is needed. The issue, from my point of view, is not if we will use it all up. The issue is how many people can the water on the Moon support? -- kainaw™ 04:51, 15 November 2009 (UTC)

If just small amounts are used to replace losses in life support systems, that might be the case (but it probably wouldn't - the lunar bases will almost certainly be in illuminated parts of the moon, at least partially, and water that escapes there would be heated up to sufficient degree to escape the moon's gravity). If large amounts are used to make rocket fuel (which is one of the common proposals) it certainly isn't. --Tango (talk) 06:14, 15 November 2009 (UTC)

Water on Earth is not likely to leave the hydrosphere, but water on the Moon could escape if exposed to the vacuum, so it would be in part non-renewable, with a little replacement by comet impacts. Of course, right now none of it is being used. Peter Grey (talk) 05:29, 15 November 2009 (UTC)

They blasted a 60-100 ft crater with their impactor, equivalent to a volume of 100 thousand to 1 millions gallons of disturbed regolith. As a result approximately 25 gallons of water was kicked up into space in a way the satellite could detect. So we can set a lower limit on the concentration of ice in this permanently dark crater at 25 parts per million by volume (but possibly quite a bit higher). That's not a high concentration, but on the other hand, it would suggest one could get ~100-300 tonnes of water per km² in craters such as this. The space shuttle external launch tank carries about 700 tonnes of fuel for comparison. So, the dream of using water for fuel would seem possible, but not very easy since very large areas may need to be mined. Dragons flight (talk) 10:51, 15 November 2009 (UTC)

Water on the moon is really important to the future of humans in space. How long it lasts depends on what we use it for. If people merely live on the moon - then it can be recycled. We'll need oxygen to breathe and water to drink - and both to raise food - but that could all be recycled (at least in principle - there would of course be losses). With care, it could support a lot of people for a long time - but no recycling will ever be perfect - so it can't last forever. But there is another important use for lunar water. If we use cheap solar power to split lunar water into hydrogen and oxygen - we can use that as rocket fuel - very handy for trips to other planets and such like because we don't have to haul it up from the earth's gravity well. In that case, the water is certainly not recyclable and we would undoubtedly slowly consume what's there. We can't tell how long it'll last unless we know:

• How many people are using it.
• How efficiently are they recycling it (if at all).
• How much is taken off the moon in the form of rocket fuel or whatever.
• How efficiently it can be mined.

In the long run, I'd hope we'd use the moon intelligently - as a stepping stone. There is plenty of even more useful water "out there" in the form of comets, small moons, Saturn's rings and asteroids - we just need a way to get to it - and the moon is a good place to start. For example - if we mined Halley's Comet (picking a comet at random!) - it appears to be approximately 80% water and it's about 1000 cubic kilometers in size. That's a truly insane amount of water! (In reality - we'd want to pick a comet in a more nearly circular orbit.)

We need to use the water on the moon wisely to allow us take that next step.

SteveBaker (talk) 01:19, 16 November 2009 (UTC)

There has been a lot of work done in how to use lunar resources, I was wondering if anyone knew of any work done on estimating how much we would need and how long it would last. I know we can't get accurate answers, but some rough Fermi calculations should be possible to get a range of orders of magnitude. --Tango (talk) 01:28, 16 November 2009 (UTC)

At current moon water usage rates, it should pretty much last forever. Googlemeister (talk) 17:31, 16 November 2009 (UTC)

Copepod parasite?

Anterior bit of the copepod.

Higher magnification.

I found this copepod with an egg sac today. There is some sort of tubular structure in the egg sac. My first guess was that this was how they attached their eggs, but I don't see a similar structure in photos of other egg sacs. Could it be a parasite? Or maybe someone got stuck in egg adhesive and is unwittingly along for the ride? -Craig Pemberton 08:46, 15 November 2009 (UTC)

How do paramedics repair severed arteries?

When a paramedic, combat medic, or some other first response health provider encounters a person with a severed artery (or vein I suppose) that needs treatment right away (i.e cannot wait for transportation to a hospital), what do they typically do to treat the person? Do paramedics carry an "artery repair kit"? Also, how is an artery repaired and is there any difference between how a first response surgeon with limited equipment and a someone in a hospital with the full breadth of equipment would go about reconnecting an artery? I tried looking for information and some websites mentioned stitches and grafts, but I don't think I got an accurate picture of how the severed ends are actually stuck back together. 96.253.247.216 (talk) 10:04, 15 November 2009 (UTC)

They won't repair the artery. They will stop the bleeding through a combination of direct pressure, elevation, pressure points and, as a last resort, a tourniquet. The artery will be repaired by a surgeon once they get to hospital. --Tango (talk) 10:12, 15 November 2009 (UTC)

Regarding the second half of your question, the most commonly-used technique for repairing an artery was described by Alexis Carrel in 1902 (Lyon Med 1902; 98:859–863, too early to appear in Pubmed) and illustrated here. The arterial wall is fragile and all three layers (intima, media, adventitia from inner to outer) must be rejoined in the repair, because separation and retraction of one or more of these layers, i.e. delamination, is common with severed arteries. This is made even more difficult because direct clamping or grasping with forceps can damage the arterial wall and 'kill' it (it is living tissue, after all). Thus, arterial repair is a fairly demanding task - not saying it couldn't be done in the field, but it would be a serious challenge. -- Scray (talk) 15:52, 15 November 2009 (UTC)

Thanks very much for the answers! 96.253.247.216 (talk) 22:25, 15 November 2009 (UTC)

How to apply a pressure dressing 75.41.110.200 (talk) 23:14, 15 November 2009 (UTC)

Psychology

Hi, I know a person who is always very calm and it seems like nothing can surprise her.She never shows any emotions. If something strange or incredible happens, she just says "Oh." or smth like this. (Like Robin from Robin (TV series) if you know it...) Once I've heard of alexithymia but I'm not sure she has it because she can recognize other people's feelings very well. She is quite lonely and doesn't talk much to other people because she talks very silently and no one hears her. She really can't express herself and I feel sorry for her. Any ideas which illness could this be? —Preceding unsigned comment added by Atacamadesert12 (talk • contribs) 10:53, 15 November 2009 (UTC)

I afraid we can't make diagnoses here. You will need to consult a professional. --Tango (talk) 11:02, 15 November 2009 (UTC)

Template:RD medadvice This removal is discussed here -- Scray (talk) 16:02, 15 November 2009 (UTC)

The common element whenever you observe these strange behaviors is that you are observing her. If you cease observing, perhaps the symptoms will also disappear! Vranak (talk) 15:50, 16 November 2009 (UTC)

Too many possibilities. According to FlashForward she has addisons (joke), she could also have aspergers or (light) autisim. Or she's just not an emotional person, or just shy. There is no way someone on wikipedia could help you diagnose. But if you want to help, how about just sitting silently (with her) and letting her be herself before trying to change her. See what she does by herself, and then you do the same, but with/near her. Maybe you'll learn more about her. Ariel. (talk) 08:15, 16 November 2009 (UTC)

Queen Ant

I have a queen ant and she has laid some eggs. When the eggs hatch what will the little worker ants need to be fed? I know in nature they'd eat dead files or stuff, but in captivity what can I give them? —Preceding unsigned comment added by 82.43.89.85 (talk) 23:39, 13 November 2009 (UTC)

Do you know the species ? I suppose, if you don't, you can leave them a bit of everything, from leaves to fruit to meat, and they can take what they want. Leave small enough quantities so you can tell what they take. Also leave water. StuRat (talk) 13:33, 15 November 2009 (UTC)

Different ants eat different things - from leaves (actually fungus growing on the leaf) to aphid "honey", to sugar, to meat. There is a tremendous variation. I would start by trying sugar and meat. If they like the sugar don't keep feeding them that, use something else that is sweet (like an apple). If they eat fungus from leaves you probably will not be able to feed them. If you are lucky they are omnivores, and will eat anything. Ariel. (talk) 08:11, 16 November 2009 (UTC)

bipolar disorder

i am repeating this question as i didn't get relevant answer. i would like to know percentage of global people affected by bipolar disorder and age wise distribution of this disorder globally ... pl help some one .. —Preceding unsigned comment added by Arun vvv (talk • contribs) 12:33, 15 November 2009 (UTC)

You might find some figures in some countries for the number (and ages) of diagnosed cases, but I don't think anyone has attempted the difficult task of guessing the rate of occurrence or age distribution world-wide. The condition is not easy to diagnose in an individual, so it is even more difficult to estimate global figures. Is it even recognised as a disorder in some countries? I assume that you have read our article linked in answer to your previous question. It suggests that about 1% of children and 2% of the population from teenage upwards suffer from the clinical condition, with perhaps a further 2% or more having a minor form. The condition is never considered to be "cured", so an age distribution is not appropriate. Dbfirs 13:16, 15 November 2009 (UTC)

PMID 17162652 is probably the best source of up-to-date information, if you have access to it. Looie496 (talk) 17:30, 15 November 2009 (UTC)

Thanks. Is there anywhere that someone without access can read a reasonably detailed summary? Dbfirs 23:36, 16 November 2009 (UTC)

Feeling in eyes.

Do your eyes feel heat? I assume they do but I don't think I've ever though 'man my eyes feel cold' so I'm unsure. —Preceding unsigned comment added by Jimothyjim (talk • contribs) 13:22, 15 November 2009 (UTC)

It's not your eyes, but sensory neuron on your cornea -it respond to heat and so it should also respond to loss of heat. Meaning that I guess that a hit of liquid oxygen would heart (P.S. it's not the best example as such hit would also cause to extensive damage-but there is such thing as cold pain) .--Gilisa (talk) 13:41, 15 November 2009 (UTC)

Thermoception isn't a very well developed article, but it notes correctly that hot and cold thermoreceptors in mammals are in the skin. However, some animals do have thermoreceptors in their eyes, e.g. cats have cold receptors.[12] There's evidence that humans can detect cold on the cornea and conjunctiva.[13][14] Fences&Windows 14:38, 15 November 2009 (UTC)

You've never felt cold in your eyes? I have....is that unusual? Vimescarrot (talk) 15:13, 15 November 2009 (UTC)

I'd say that most people would reflexively shut their eyelids, thus reducing the stimulus that would kick ofs a response -- sort of like people who experience less tooth pain to cold air when they shut their mouth. DRosenbach ^{(Talk | Contribs)} 15:35, 15 November 2009 (UTC)

Try the opposite - if you sit close to a fire in a fireplace, you'll get a hot headache, and can often feel the heat "behind" your eyeballs (as implied above). ~ Amory (u • t • c) 19:41, 15 November 2009 (UTC)

Certainly cold water feels cold, I think. 68.193.225.106 (talk) 15:59, 15 November 2009 (UTC)

Hmm, maybe my eyes do feel cold but I just don't notice.

Looking for the name of a knot similar to the clove hitch

I'm looking for the name of a hitch knot, which is similar to the clove hitch. In the clove hitch, a part of the rope runs diagonally, compressing other parts of the rope forming the knot. In the knot I'm talking about, there's a twist in the part of the knot under the "diagonal" section. Supposedly the knot is more secure that the clove hitch. Does anyone know the name of the knot? (Sorry if my description is not very clear.) —Preceding unsigned comment added by 173.49.12.245 (talk) 15:43, 15 November 2009 (UTC)

The constrictor knot, ground-line hitch and snuggle hitch are all similar to the clove hitch, but more secure. Are you thinking of one of those? Red Act (talk) 16:33, 15 November 2009 (UTC)

The constrictor knot was what I had in mind. Thanks. --173.49.12.245 (talk) 16:49, 15 November 2009 (UTC)

activity vs sleep on mountains

i'm not asking for medical advice here, i have no intention of climbing a mountain but i'm wondering if it's true that you need to stay awake on mountains to keep your body temperature up? i'm pretty sure that sleeping well in a safe place is just as important to get your energy back up? —Preceding unsigned comment added by 87.114.162.77 (talk) 16:22, 15 November 2009 (UTC)

If you're severely hypothermic (so cold that you've stopped shivering), then falling asleep would be bad, but at that point you'd be on the verge of dying anyway. Body temperature drops a little bit during sleep automatically, but if it drops enough to be harmful, you will start shivering and that's sure to wake you up. In my experience (never been actually hypothermic), it's impossible to fall asleep if you're shivering. I have spent a few very unpleasant nights on mountains that way. Looie496 (talk) 18:29, 15 November 2009 (UTC)

If you're in a place dangerous enough that you shouldn't sleep to avoid dying, you are already very hypothermic and in danger and should calmly and carefully get off the mountain. The first step is to always avoid a dangerous situation like that by planning ahead and being safe. You will not think clearly when severely hypothermic. You should only ever go up a mountain if you have adequate shelter and warm clothing, in which case it will often be okay to sleep. ~ Amory (u • t • c) 19:38, 15 November 2009 (UTC)

I agree with what has already been said. On a related note, however, at very high altitude (eg. Everest Camp IV) sleep apparently becomes very difficult. It's not that it is dangerous to sleep, it's just difficult to get to sleep. --Tango (talk) 21:56, 15 November 2009 (UTC)

Ah ok, maybe i misunderstood what i was told then. Stay awake if you're about to die, nice lol! Tx for hypothermia link, that explains a lot. —Preceding unsigned comment added by 87.114.162.77 (talk) 23:50, 15 November 2009 (UTC) --87.114.162.77 (talk) 23:52, 15 November 2009 (UTC)

self-serve check-outs and phone answering systems

Most of these registers are manned by one cashier to four registers. In many cases this cashier is busy with another customer when a problem happens. For this reason many people are exposed to a talking register that treats them as if they were a computer. An even worse situation of computers treating people like they were computers are telephone, bank and other business and institutional phone answering systems (USPS is one of the worst). Are such systems a threat to the civility of mankind and perhaps in part responsible for indiscriminate psycho crimes like terrorism? 71.100.2.243 (talk) 16:37, 15 November 2009 (UTC)

I don't think this is a very scientific question, and I don't have a very scientific answer. These computers you speak of do not pass the Turing test, so people can consistently tell the difference between talking to a human and dealing with one of these computers; thus, I don't think any confusion between the two contributes to violent behavior. My sense is that if people relax and focus on the task at hand, the task gets done. -- Scray (talk) 16:47, 15 November 2009 (UTC)

"Are such systems a threat to the civility of mankind and perhaps in part responsible for indiscriminate psycho crimes like terrorism?" I don't think there's any evidence that such things contribute to threats against the "civility of mankind" (whatever that means), and have seen zero evidence that such systems have any responsibility for "indiscriminate psycho crimes like terrorism". I think it would be fairly idiotic to assume without any evidence that frustration with phone answering systems has any connection to terrorism. The systems probably do contribute to a decreasing satisfaction amongst consumers with customer service (I cannot stand the phone systems and find them unhelpful; if you keep pressing the zero key, you often end up with a live person, though), but and they do have economic effects (they are used to avoid hiring live human beings), but other than that, I don't see any reason whatsoever to ascribe them much influence. --Mr.98 (talk) 17:04, 15 November 2009 (UTC)

I actually prefer the self-checkout, for these reasons:

1) I can check each price and make sure it's correct. You can try this in a traditional check-out, but the display is often aimed at the cashier, not you, and the cashier may check things so quickly that you can't keep up. In almost every load of groceries, I'm overcharged on at least one item, so missing this is expensive.

2) I can bag things properly. I put the frozen items together, the refrigerated items together, etc., while many baggers don't bother.

3) I can avoid have my food damaged by the cashier and bagger. I've had bananas slammed down, only to get bruises almost immediately, and have had a greeting card placed in the leaking milk sludge on the conveyor belt, even after I handed it directly to the cashier.

That said, they really need to work on a few problems:

A) They don't assign enough people to oversee them. Perhaps one cashier for every 2 or 3 would work. However, they need to actually keep the cashiers present. They frequently seem to walk away to do God-knows what, leaving the customers totally unattended. Maybe they can put a location sensor on the cashiers and dock them pay for every minute they are out of the area ? (Or fire them if they take it off.) There has to be some way to get them to do their jobs.

B) Many tasks require a cashier that shouldn't. If I have a coupon, I have to hand it to a cashier. If I want to cancel an item I scanned, I need a cashier. If I have an item with a hand-marked price, I need a cashier (in this case they need to stop hand-marking prices).

C) Many of the automatic check-out lanes need repair. There's some where the scale doesn't work, some where the voice part is broken, etc. They continue to use these defective lanes, which cause even more time demands on the cashiers. StuRat (talk) 18:45, 15 November 2009 (UTC)

With all of your points I agree. I usually buy canned goods in bulk and people behind me in line get perturbed whenever I start scanning individual cans. One cashier refused to override and enter the number of cans saying it was against chain policy. In another instance when my card was not approved due to faulty communication link the cashier refused to return my card until I threatened to call the police and have him charged with theft. My bank backed up my contention and he would have gone to jail. The problem I experience most is that recently there is some kind of holdup every time I use the self-checkout register. Repeatedly pressing zero usually results in the phone system hanging up.

I can't seem to find an alternate system or solution. Perhaps I can find a store that will allow me to fax, email or call ahead to place an order and have it ready for me to pick up in a couple of hours. 71.100.2.243 (talk) 20:30, 15 November 2009 (UTC)

As for the dehumanizing effects, the monotone voice is high among them, especially when it says something like "Have a good day". It just doesn't work when it comes from a machine. With a cashier you may suspect that they don't mean it, but at least it's possible that they do. And a monotone voice repeating the same thing ad infinitum actually seems even worse for the people who work there; I've seen them go to extremes to shut it up. StuRat (talk) 21:02, 15 November 2009 (UTC)

Do other people get "Unexpected item in the bagging area" every time they place an item in their bag, or is it just me? Certainly contributes to the stress level. Itsmejudith (talk) 21:19, 15 November 2009 (UTC)

I have had that problem at one particular chain of home improvement stores, but it's now been resolved. I think this reflects an important aspect of these systems - they will improve when people complain and companies listen, and the improvements scale well (compared to human training, for example). While I like to see people employed, there are some tasks that are so mindless and repetitive that machines can do the job better. Scanning groceries seems like one of those. -- Scray (talk) 21:26, 15 November 2009 (UTC)

In the case of self-check outs, a human still does the scanning, it's just now the customer. StuRat (talk) 21:53, 15 November 2009 (UTC)

Point taken - thanks for setting me straight there. I do anticipate greater automation being the next step, probably eliminating checkout aisles as we currently recognize them, but I don't want to treat the RD as a forum. -- Scray (talk) 22:30, 15 November 2009 (UTC)

Do you mean like the Quick Check system used in Waitrose? That is awesome, and does pretty much eliminate the normal checkout for everything except random rescans. And it alerts you to special offers when you scan things in, which is surprisingly useful. Doesn't quite cancel the greater expense of shopping at Waitrose, though. I can see it catching on in a lot of other shops if the initial cost comes down: remember how quickly the self-service checkouts caught on? 86.142.231.220 (talk) 23:43, 15 November 2009 (UTC)

I think he means more like the self scan checkouts at ASDA and Tesco.  Ronhjones  ^(Talk) 00:23, 16 November 2009 (UTC)

Oh, I thought that was already covered in the previous comments. How do they include greater automation that other self checkouts? 86.142.231.220 (talk) 00:57, 16 November 2009 (UTC)

In the case of telephone companies who have perfected the technology to the greatest extent the monotone is almost gone but the resistance to turning the call over to a human operator even greater. (same for USPS who use this technology). To speak with an operator versus the system hanging up you first must provide your telephone number or account number, if its about data versus voice and if its data what your operating system is, what type of modem you have and on and on and on. An even more expensive lunch for the added speaking capability with even greater resistance to putting you in contact with a real live human including substantial wait time and failure to allow contact if your particular issue is not in its list. Try to get in touch with the right party to report a tree that is now so large it hs grown three inches around the cable or to report a thousand other problems. The menus are never well developed or based on proper classification principals. (see http://academia.wikia.com/wiki/Optimal_Classification) 71.100.7.189 (talk) 23:40, 15 November 2009 (UTC)

Rechargeable battery

How does the total life of a rechargeable battery compare with a non-rechargeable ? By "total life", I mean all the milliAmp hours you can get out of either battery until it's voltage drops permanently below the rating. In particular, I'm interested in AAA batteries, so I can decide whether rechargeables make sense in my walky talky. The rechargeables in question are Ni-MH and the non-rechargeables are "super heavy duty", which I think means "not alkaline". StuRat (talk) 18:06, 15 November 2009 (UTC)

I don't know about AAA batteries, but I did find this piece on how rechargeable vs. non-rechargeable AA batteries work for long term use in electronics. It recommends that for devices that are used often or "draw bursts of power" (such as a digital camera for taking a picture with flash), use rechargeables, and for seldom used or low power devices, such as flashlights or remote controls, use single-use batteries. Ks0stm ^(T•C•G) 18:49, 15 November 2009 (UTC)

The issue is that my price structure may well be different than theirs, since I can get permanent AAA cells in an 8-pack for a dollar, while I have to pay 20 times as much for rechargeables. So then, the question is if the rechargeables last 20 times longer. StuRat (talk) 18:57, 15 November 2009 (UTC)

Permanent AAAs aren't - that would be great ;-). The answer to your question depends not only on the battery type, but also on the application. Most rechargeables provide a fairly constant voltage (and current) until they are fairly drained, and then drop quickly towards (nearly) zero. Conventional batteries drop more evenly. If your walky talky is digital, it will need a certain minimum voltage, and you may not be able to use plain batteries to their full capacity. Also, most rechargeables can be used a lot more often than 20 times. As far as I can tell, for all items that use significant current and are in frequent use, rechargeables are the more economic choice. On the down side, they have a much quicker self-discharge rate, so they are unsuitable for storage or items like an alarm clock, that runs for years on a plain battery. ---Stephan Schulz (talk) 20:48, 15 November 2009 (UTC)

You seem to have assumed that both types of battery last just as long on the initial charge. I don't agree. I think rechargeables discharge faster, especially when old, but I don't know by how much. StuRat (talk) 21:06, 15 November 2009 (UTC)

No, I did not assume such. Yes, older rechargeables eventually loose capacity. As for initial capacity, look at List of battery sizes, which indicates non-rechargeables have between 50% and 20% higher initial rated capacity. But, since rechargeables hold voltage longer, they will discharge faster over the same resistance than non-rechargeables. Of course, they will typically also give higher performance. Anyways, due to the fact that they have much more than 20 recharge cycles, my point stands. --Stephan Schulz (talk) 22:05, 15 November 2009 (UTC)

The reason rechargeables are not good for slow draws, or infrequent uses is that they self discharge, and most will not last more than a month or two. Regular batteries don't self discharge (as much), because they have a higher internal resistance - but that internal resistance means that can not support a high draw without wasting energy. So it's a balancing act: do you want high power, low shelf life, or low power, long shelf life. PS. I don't think anyone makes low power long shelf life rechargables because it doesn't make sense from an economic point of view - why pay so much for a battery to sit and do nothing? Ariel. (talk) 08:06, 16 November 2009 (UTC)

The "super heavy duty" cells are zinc chloride battery and they are near useless at high current drains, which would include walkie-talkies in transmit mode. Rechargeables are much better for that. One problem with rechargeables was an "arms race" between NiMH battery manufacturers in the 1990's to make cells of higher and higher capacity, by making the insulating layer inside the cell thinner and thinner until the cells became unreliable (they lose the ability to hold a charge soon after you buy them). The cure is to buy pre-charged cells (low self-discharge NiMH battery). They have slightly lower capacity but the advertised advantage for them is they mostly eliminate the self-discharge effect (which they do), making it possible to ship them pre-charged and have them retain their charge on the retail shelf. I don't have an RS for it but I've seen stated in several places that what they basically did was go back to a thicker insulating layer, which not only gets rid of self-discharge but also makes the cells more reliable. I've been using these cells for a few years and have had very good results from them, unlike the max-capacity ones I used earlier which crapped out all the time. 69.228.171.150 (talk) 21:47, 16 November 2009 (UTC)

Human Scent

I had asked a previous question about human scent, but didn't find the answer to one part: Why can people not smell their own scent? Is there any way to make this possible? Thanks in advance... Ks0stm ^(T•C•G) 18:39, 15 November 2009 (UTC)

I suppose if anybody was in any way 'cut off' from their own scent, either by intensively using deodorant or perfume or by some mechanical means (i. e. carrying a clothes pin on your nose for a year, or any other nasty way), then I suppose after the foreign means had been removed one could become conscious of their own smell. IMHO. --Ouro (blah blah) 18:48, 15 November 2009 (UTC)

I think people can. You may get accustomed to any smell you are exposed to continuously, though, so may need a higher concentration to detect it. So, if you run a marathon and sniff your pits, I bet you will smell something. StuRat (talk) 18:51, 15 November 2009 (UTC)

It's called habituation, but when one raise his hand to enjoy the wonderful aroma of his armpit, just after intensive training in a gym, then he can smell himself very well. But if you leave him in a room filled with this odor for one-two hours, it would be more than enough to make it imperceivable. The first to describe the molecular mechanism for it (in Aplysia) was Eric Kandel and along with other studies he performed, his studies on the Aplysia's habituation mechanism actually founded the modern study of memory processes. Much more interesting thing happen when people try to tickle themselves, here-in different from habituation, the brain 'predicts' the action and it knows what areas exactly are going to be tickled, so it won't have any effect.--Gilisa (talk) 19:51, 15 November 2009 (UTC)

Everything Gilisa posted applies to females too. "Horses sweat, men perspire, women glow". Cuddlyable3 (talk) 21:46, 16 November 2009 (UTC)

a purely conceptual thought experiment

In a purely conceptual thought experiment I have discovered the CONTIUM.

The CONTIUM is simply a neutron, which instead of becoming a proton and electron or Hydrogen-1 becomes a CONTRON and a positron (a positively charged electron ).

The significance of this discovery is that external energy is no longer required to overcome the Coulomb barrier. In fact there is no Coulomb barrier.

The only way to keep Protium and Contium apart is with a polar magnetic field strong enough to do the job. When the field collapses the Protium and Contium are attracted.

My question is do they annihilate each other or do they undergo fusion and if fusion what are the most likely byproducts? 71.100.2.243 (talk) 19:22, 15 November 2009 (UTC)

Anything could happen since it's particles that dosn't exist in reality, but you may want to define their anti-particles and invoke CPT symmetry to run the reactions in reverse. It's a common line of reasoning in particle physics. EverGreg (talk) 19:29, 15 November 2009 (UTC)

We do not speculate about hypothetical things on the reference desk; and we do not encourage publication of original research - Wikipedia is an encyclopedia, not a forum for new ideas. A quick search shows that "contium" or "contron" do not appear in any prior scientific literature. Nimur (talk) 03:03, 16 November 2009 (UTC)

I understand the overpowering fear of academics being wrong and forever having that label on their coattail so let me put the question so you can provide a known answer. What force other than temperature and pressure can overcome the Coulomb barrier? 71.100.7.189 (talk) 05:25, 16 November 2009 (UTC)

Neither temperature nor pressure are a force. The coulomb barrier is a potential energy "barrier". Your use of terminology in this question is not valid, so there's no way to answer it as you have asked it. Nimur (talk) 06:38, 16 November 2009 (UTC)

All forces can "overcome the Coulomb barrier". As for Contium - if you started with a neutron (no charge), and split into a positron (positive charge), and "something" (contium), that something *MUST* has a negative charge, otherwise you violate Conservation of charge. Your "Contium" sounds very much like an anti-proton. If a proton (AKA protium) and an anti-proton annihilate each other a gamma ray will issue. Ariel. (talk) 07:59, 16 November 2009 (UTC)

Keeping the discussion factual, if the contium is basically a neutron, it will have baryon number 1. This means it must decay into a total baryon number of 1, so the contron must have a baryon number of 1. Intrincially, it has lepton number 0, so unless something very strange is happening, lepton conservation is broken. This can be solved with a(n) (electron) neutrino, but you then get n → c- + e+ + νe. Which is very like p+ → n0 + e+ + νe (merged with n0 → p+ + e− + _νe) , except not so explainable. Basically, your particle breaks known rules, or this universe. If you wish to imagine a completely different universe, fine, but you can't carry it accross to here, at least by my reckoning. - Jarry1250 ^{[Humorous? Discuss.]} 18:09, 16 November 2009 (UTC)

Type 1 Diabeetes - Sugar allowed in a can of drink

Really obscure question here, but does anyone know how muc h sugar people with Type 1 diabetees are 'allowed' to have in a can of drink? It's kind of a weird question but I'm asking for a friend :S —Preceding unsigned comment added by 82.11.245.145 (talk) 19:35, 15 November 2009 (UTC)

There is no such allowance. The source of the sugar is largely irrelevant. The amount of sugar they can have will depend on the nature of their condition (everyone is slightly different) and how much insulin they have had/will have. --Tango (talk) 19:45, 15 November 2009 (UTC)

Okay well, let me rephrase, roughly how many grams of sugar do you reckon an average type 1 diabeetes person could have in a drink without it affecting their sugar level? 82.11.245.145 (talk) 19:54, 15 November 2009 (UTC)

This is massively getting into the realm of medical advice, which we aren't allowed to give here. Suffice it to say that even for an "average" type-1 diabetic, if there was such a thing, the amount of sugar they could safely drink in a can would depend on a huge number of factors and there's no number we could give you that would be particularly meaningful without detailed knowledge of the specific situation. ~ mazca ^talk 20:13, 15 November 2009 (UTC)

This is purely hypothetical, nobodys drinking any cans of coke based on the advice here :P Also I don't mean safely, I mean literally no change in their levels, not even a safe change, just no change. Jimothyjim (talk) 20:22, 15 November 2009 (UTC)

None at all, then. Any consumption of sugar will raise blood sugar levels temporarily, in a diabetic or otherwise. --Tango (talk) 21:02, 15 November 2009 (UTC)

Okay, thanks all, I think everythings all sorted out now. More confusion over the question than anything. Jimothyjim (talk) 21:08, 15 November 2009 (UTC)

Toxicity of hydrogen peroxide

In Charlie Chaplin's film Monsieur Verdoux, Chaplin's character thinks he's pouring poison disguised as hydrogen peroxide into a bottle of red wine, but instead, he's pouring real hydrogen peroxide into the wine. He and his lady friend later drink the wine, and suffer no ill effects, save for inebriation. Is hydrogen peroxide actually toxic? Does it have any harmful effects when ingested in such small quantities (only a few centilitres)? JIP | Talk 20:27, 15 November 2009 (UTC)

One of the uses of the common 3% hydrogen peroxide solution is as a gargle, so presumably it's not very toxic. 100% hydrogen peroxide would burn you severly, on the other hand. StuRat (talk) 20:45, 15 November 2009 (UTC)

A 100% solution is hard to get and even harder to store for a long time. The most important thing is the concentration 3% or 30%. Wine has some imputities which will slowly oxidize and the hydrogen peroxide vanishes away. The small particles will also catalyze the decomposition of hydrogen peroxide. --Stone (talk) 20:51, 15 November 2009 (UTC)

Hydrogen Peroxide is most definatly not good to drink in large quantities or concentrations; which is why you gargle it. 3% solutions are generally recognized as safe, but I would still read and heed Hydrogen_peroxide#Safety. Wine may contain some measurable amount of Catalase, which would basically turn the red wine/hydrogen peroxide into Cold Duck... --Jayron32 05:45, 16 November 2009 (UTC)

Heteroaromatic Chemistry Problem

I can see from experimental results that the chlorine in 2-chloropyridine is easily displaced by nucleophiles such as amines. However, this isn't the case with 3-chloropyridine....why?! 188.221.55.165 (talk) 22:44, 15 November 2009 (UTC)

this article outside of Wikipedia explains in some detail the mechanisms of such reactions on pyridine, with electron pushing diagrams. See also Chichibabin reaction. --Jayron32 05:38, 16 November 2009 (UTC)

discoloration in schitzu's hair

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis, prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page.

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis or prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page. --~~~~

) 188.221.55.165 (talk) 23:49, 15 November 2009 (UTC)

November 16

Centrifugal force

I'm doing a lab report on ficticious forces, and something doesn't seem to make sense. The design of the experiment is as follows: a stationary channel has a ball roll slowly through it, while the channel is overtop some paper on a rotating platform. Again, the ball is NOT rotating (just going in a straight line), but it's making contact with the paper that it rotating, and every 30 ms or so the ball makes a mark on the paper, so that's its trajectory is traced out. Now according to the lab manual (and in agreement with the results we obtained), the ball will slow down as it approaches the centre, and speed up while it's leaving, and apparently this is due to centrifugal forces.

Now to me, this doesn't make much sense. The ball itself shouldn't be experiencing any forces (ignoring friction), and even in the reference frame of the rotating paper, the ficticious force acting on it should be directed towards the centre, allowing it to continue in a circular path. After all, if the ball wasn't moving at all, it wouldn't start moving away from the centre, so I have trouble believing that there would be a ficticious force acting on it. But I wasn't actually there for the lab; is it possible that it was the ball that was rotating while the paper was stationary, and that my lab partner is just an idiot? —Preceding unsigned comment added by 24.200.1.37 (talk) 00:31, 16 November 2009

In the nonrotating lab frame, the velocity of the ball relative to the paper is the velocity of the ball relative to the lab (a constant) minus the velocity of the paper relative to the lab at the point where the ball is at that moment. The paper is moving more slowly near the center of the rotation, so it's reasonable to suppose that the difference of the velocities will be smaller nearer the center. That's why the marks on the paper were more closely spaced there.

In the real world (as real as academic physics gets, anyway), that would be enough. You don't have to analyze the problem in every frame, you can just pick one and do the analysis there. But since this is a lab, I suppose they want you to repeat the analysis in a rotating frame where the paper is at rest. That seems to be a lot more complicated in this case, so if the intent of the lab is to show you the usefulness of fictitious forces then it isn't doing a very good job. In the rotating frame, the ball experiences the centrifugal force (which acts outward from the center) and the Coriolis force (which acts at right angles to the ball's velocity). You're probably supposed to ignore the fact that the ball is constrained by the channel and supported by it against gravity; the important thing is that the ball moves as it would in empty space with no external forces (other than the fictitious forces). You can write down the equations of motion and try to solve them, but it's going to be ugly. I don't see any easy way to do it aside from solving the problem in the nonrotating frame and then changing the coordinates.

In the case of an object at rest in the nonrotating frame, the centrifugal force in the rotating frame points outward, but the Coriolis force points inward and is twice as large. So the net force is inward; that's the centripetal force that keeps the object moving in a circle. In this case, too, it's easier to see what's going on in the nonrotating frame. -- BenRG (talk) 01:11, 16 November 2009 (UTC)

If the ball is stationary, then it's radial velocity is zero. Since the coriolis force is proportional to the radial velocity, how can it cause a centripetal force? —Preceding unsigned comment added by 24.200.1.37 (talk) 08:21, 16 November 2009 (UTC)

An object following a circular path with constant angular velocity $\omega$ relative to a rotating reference frame which is itself rotating with constant angular velocity $\Omega$ (where axis of path coincides with axis of rotation of frame) requires a centripetal force of magnitude

$mr(\omega +\Omega )^{2}=mr\omega ^{2}+mr\Omega ^{2}+2mr\omega \Omega$

The first term is the centripetal force that is "expected" relative to the rotating reference frame; the second term is a "correction" due to centrifugal force; and the third term is a further "correction" due to Coriolis force. In BenRG's example the object is stationary relative to the non-rotating reference frame, so $\omega =-\Omega$, the Coriolis force term is negative, and the net required centripetal force (after the "corrections") is 0. Gandalf61 (talk) 11:59, 16 November 2009 (UTC)

Stone artifact need help with what it is...

I need help with a stone that my daughter found on Myrtle Beach S.C. It is very old and it is either indian or maybe even from the stone age. We have pictures and would appreciate any help with whom we could email for assistance. Thank you for your time —Preceding unsigned comment added by Donald Cohee (talk • contribs) 00:54, 16 November 2009 (UTC)

If you post the pictures, someone here might be able to help identify the stone. Otherwise, we don't have a directory of Wikipedians with expertise in identifying Native American artifacts. —Akrabbim^talk 01:23, 16 November 2009 (UTC)

Since you actually are in possession of this artifact, you might consider talking to a history or archaeology professor at the nearest university, who may be willing to spend some time looking at it. Nimur (talk) 03:07, 16 November 2009 (UTC)

It's worth noting that removal of antiquities can be regulated in some places. -- Scray (talk) 04:59, 16 November 2009 (UTC)

tuned circuit

I'm trying to create a tuned circuit for a science project to show how 60 Hz power line frequency intensity can be monitored and displayed on a computer based osciliscope. When I calculate the wavelength for 60Hz however I get an antenna length that is way beyond a length of wire that I can mount in the yard and tune. I know there must be harmonic that I can use with a reasonably shorter antenna and with a coil and capacitor circuit to cilate and perfectly match 60 Hz but I can not find any references or information as to how to calculate the length of the size of the coil and capacitor for a specific 60 HZ harmonic antenna length that will work. Does the Wikipedia have any references for the complete calculations? 71.100.7.189 (talk) 01:52, 16 November 2009 (UTC)

You will pick up 60 Hz whether you want to or not... I have a lot of experience setting out antennas of varying sizes and we always get 60Hz interference. Our AWESOME antennas pick up 60Hz and dozens of its harmonics; you can see its antenna size and download schematics for the antennas, as well as the preamplifier and data acquisition system. I think you can even purchase the hardware and equipment at-cost from Stanford for around $500. In any case, if your preamplifier and amplifier have a good low-frequency response (e.g. similar to a high-quality audio amplifier), you'll have no trouble tuning to the 60Hz at baseband ("zeroth harmonic") even with a small ~ 1 meter antenna. Nimur (talk) 03:15, 16 November 2009 (UTC)

I assume the horizontal lines are the 60HZ harmonics but what I need is a circuit specifically tuned to 60Hz or at least the equations necessary to create the antenna, coil and capacitor to resonate at 60Hz. 71.100.7.189 (talk) 03:47, 16 November 2009 (UTC)

The links I've provided show circuit schematics for a broad-band amplifier; if you want to tune to 60 Hz, take a look at tuned circuit and Q factor. The equations are trivially easy; the difficulty is finding components and getting a good amplifier at such low frequencies. That is why I suggest using a broad-band system (like the one I linked above) and digitally processing the result to analyze the 60Hz band. Nimur (talk) 05:03, 16 November 2009 (UTC)

So are Maxwell equations but their usefulness and comprehension exceeds the elegance of their simplicity. 71.100.7.189 (talk) 05:17, 16 November 2009 (UTC)

After reviewing the few questions you have asked, I think the best advice for you is to review some basic physics; we have some good articles on electronics, electromagnetism, and atomic theory that are all very well-sourced. If you still have specific questions after you are up to speed on the fundamentals, or if you're having conceptual problems understanding parts of the articles, feel free to ask here. Nimur (talk) 06:52, 16 November 2009 (UTC)

You should not be trying to establish a pattern of thinking based on any of my questions since only two questions I have asked originated from the same member of our group. Also if you don't know the answer just say so. 71.100.7.189 (talk) 07:42, 16 November 2009 (UTC)

I would avoid constructing a passive resonator circuit for so low a frequency as 60Hz because of the inconveniently large LC product needed. It is easier to make it either as a bandpass Active filter or as a digital Goertzel algorithm. THe latter is used in DTMF detectors in telephony and might be readily implemented in your computer based oscilloscope. Nimur has given good advice above. BTW I have found that in many urban areas one need only bury a couple of earth rods a few meters apart to be able to pick up a few tens of millivolts of power line frequency between them. Cuddlyable3 (talk) 10:45, 16 November 2009 (UTC)

The phrasing of your initial question implies that you think it is necessary to have an LC circuit tuned to 60 Hz in order to "monitor and display" 60 Hz EMF. You also seem to believe that the antenna has to be resonant at 60 Hz to detect that low frequency. Responders have pointed out the error in these assumptions. You need not imply that the responders "Don't know the answer." You may just be asking the wrong question so far as your research goal is concerned. EMF is commonly measured by small instruments which allow display on PC's without some impossible 2500 km antenna. I have used them myself, and they are fairly small. I expect that some of the electronics hobbyist magazines have published "build-it-yourself" instructions for such a meter with 3 small coil antennas. A pickup coil producing 1 mV per 20 mG is available for under $5 online [15]. Edison (talk) 20:16, 16 November 2009 (UTC)

Here is a warning if the OP is considering measuring the electric field near high voltage power or overhead tram cables using some kind of homemade probing antenna. Don't. Cuddlyable3 (talk) 21:29, 16 November 2009 (UTC)

Tsar Cannon with two ton cannonballs?

Sorry about the random inquiry, was just interested with reading a random article I found. Apparently the Tsar Cannon has cannonballs placed in front of it, weighing two tons each according to my interpretation. The cannon was also fired at least once, with gunpowder, according to analysis. Although the diameter of the cannonballs is larger than the barrel diameter of 35 inches, and they were made only for the purposes of decoration, if the cannonballs could fit, would a reasonable amount of gunpowder be sufficient enough to propel a two ton cannonball? And if so, to what distance? Thanks, ♠The Ace of Spades^♣♥_♦ 02:00, 16 November 2009 (UTC)

Not a cannonball, but two tons. Nimur (talk) 03:55, 16 November 2009 (UTC)

Well, this Tsar Cannon gun maybe isn't a suitable design; but a modern battleship from the 1980s was armed with a 66-foot long main battery capable of firing a 1200 kg projectile up to twenty miles. The explosive powder propellant is much more advanced than "gunpowder" (as it would have existed in the 16th century). Our article describes the propellant as "smokeless Powder Diphenylamine (SPD)" with a "titanium dioxide and wax compound known as 'Swedish Additive'"; and polyurethane jackets placed over the powder bags. When the USS New Jersey bombarded the coast of Lebanon, the Navy referred to the projectiles as "flying Volkswagens"[16] in an effort to demoralize the enemy[17]. Targeting for these 2-ton projectiles was grossly inaccurate (blamed on calibration errors in the explosive powder mixture). Shells from this barrage missed their intended targets by many miles, resulting in massive civilian casualties; this was cited as a motivation for the subsequent attack on the United States Marine barracks in October 1983. Nimur (talk) 03:43, 16 November 2009 (UTC)

Perhaps, seeing that the grapeshot that the Tsar Cannon fired weighed about a ton and three-quarters, according to the article. bibliomaniac15 04:15, 16 November 2009 (UTC)

20 miles? ha ha ha ha ha ha ha. Lucky if it went 20 yards. Here are my calculations, first the initial assumptions;

• explosive pressure of black powder = 67 ton/m² (might need adjusting - I got that from a fireworks article)
• energy content of black powder = 3 MJ/kg
• mass of projectile = 800 kg (from article - don't know where Bibliomaniac got ton and three quarters, I don't see it)
• calibre: 890 mm
• barrel = 5.34 metres

From the calibre I get a csa of 0.622 m² and from the pressure a force of 44.3 tons. Newtons second law arrives at an acceleration of 543 m/s². From $\scriptstyle v={\sqrt {2ax}}$ we get a muzzle velocity of a measly 76 m/s - you would probably do more damage head butting the enemy. Maximum elevation and ignore aerodynamics etc gets you a flight time of 7.77s and a distance just over 300 metres. The kinetic energy on leaving the barrel is 118 MJ which, if energy is transferred 100% efficiently, requires about 40kg of black powder.

For a 2 ton projectile it comes out at 118 metres and 16 kg of charge. Of course, many subtleties are neglected here, not least of which is the assumption that the charge continues to burn all the way up the barrel and is completely used by the time the projectile exits. That can be wrong both ways, the charge could burn up before we are done accelerating the projectile, or the charge might not burn fast enough leaving part of it uselessly burning after the projectile has exited. An ideal weapon has the barrel length "tuned" to the missile you are trying to launch and the propellant you are using to launch it, but this one most probably isn't. SpinningSpark 22:23, 16 November 2009 (UTC)

Actually, I've made an error in the amount of powder calculation, it comes out the same for both cases and is less than 1kg, but I don't believe for a minute that is the correct load for this gun in reality. SpinningSpark 22:48, 16 November 2009 (UTC)

Thanks, all. ♠The Ace of Spades^♣♥_♦ 03:34, 17 November 2009 (UTC)

String theory and GUTs

Could there be string vacua that approximate the standard model without allowing proton decay? 76.67.73.245 (talk) 04:09, 16 November 2009 (UTC)

Recreating extinct species

Okay, this is mostly just a small idea that I've been toying with. With current genetics research, I am fairly sure that at some point we will have the capability to clone and reintroduce extinct animals to the wild, but only some have enough intact DNA to do this. I was just trying to think of a list of the more important extinct species that could be brought back. For example, the passenger pigeon and the Carolina parakeet have enough DNA remaining via feathers to clone them and have genetic variation, but the dodo bird likely does not. I was wondering if anybody could add to the list of animals where enough material remains to clone them and retain genetic variability in the cloned population?

1. Passenger Pigeon
2. Carolina parakeet
3. Elephant bird - long shot unless the eggs retain enough DNA.
4. Great auk
5. Thylacine
6. Quagga

Thanks, Falconus^{p t c} 05:11, 16 November 2009 (UTC)

[18] looks like an interesting read. It's currently cited in the Passenger Pigeon article. --Jayron32 05:19, 16 November 2009 (UTC)

Thanks, that was interesting. Also, apparently feathers don't actually contain DNA. Falconus^{p t c} 05:31, 16 November 2009 (UTC)

Bad idea. Eventually they'd figure out how to mate and then we'd have to listen to some flirty nonsense about chaos theory. In all seriousness though, the issue is going to be the "intact" part. DNA samples won't hold very well and the amount of reconstruction one would have to do would be enormous, to a point where you would likely have a very different animal (assuming viability). It's doable for things like the recreation of the 1918 flu since there are only 8 genes. ~ Amory (u • t • c) 13:58, 16 November 2009 (UTC)

The mammoth is often put forward as a likely candidate for the "Jurassic park" treatment. Large amounts of mammoth meat can be found deep-frozen in the north of Siberia - and it's thought that a modern elephant could provide the necessary egg & womb for turning DNA into living animal. Pidgeons & parakeets could be similarly dealt with if the DNA is in good enough shape - but finding a parent animal for an elephant bird, auk thylacine or quagga might be tough. SteveBaker (talk) 14:03, 16 November 2009 (UTC)

Steve, have a look at Quagga Project. ZUNAID●FOREVER 14:57, 16 November 2009 (UTC)

And Neanderthal genome project for a jockey?.Cuddlyable3 (talk) 21:21, 16 November 2009 (UTC)

Re-expanding a shrunk cotton shirt

Some questions regarding the hydrophilic properties of cellulose fibers such as cotton and wool:

• Why is it that materials made from cotton or wool shrink when immersed in hot water and allowed to dry? I mean, what's happening to the polymer? Does the water become permanently bound into it, resulting in permanent swelling of the fiber, thereby decreasing its length, or does the water evaporate and somehow leave behind a shrunk fiber?
• Why does this not happen with cold water?
• Is it possible to re-expand the fibers to the original length after shrinking in this fashion?

My inquiring mind was unable to find answers in the articles about cellulose, cellulose fiber, or hydrophilic. ~Amatulić (talk) 06:54, 16 November 2009 (UTC)

This is not a perfect fix but it helps if you hang a shrunk tee up wet. It would be nice to understand what is happening. My uninformed guess is that being wet allows the shirt fibers to become more disordered, increasing the entropic force of the fabric against stretching. -Craig Pemberton 08:42, 16 November 2009 (UTC)

The process of turning cotton fibers into threads and then weaving them into clothes involves pulling and twisting the fibers. As a result many of the fibers (and their constituent molecules) are distorted into an elongated state. They are weakly bound into that state by binding against other fibers and threads. Heat, water, and/or agitation (e.g. a hot wash) cause some the fibers to free themselves and relax into their natural, unstressed state. It's that act of relaxing that causes the clothing to shrink. Cotton and other organic fibers that have complex textures are more prone to stretching and shrinking than simple synthetic fibers. To a degree one can reduce / counteract shrinkage by manually stretching out the article with applied force but this will never be more than a partial solution since no about of pulling will really replicate the effects of making thread. Dragons flight (talk) 11:21, 16 November 2009 (UTC)

I guess, then, making a garment from pre-shrunk cotton thread won't prevent the garment itself from shrinking later, because the act of weaving would stress the threads. ~Amatulić (talk) 18:28, 16 November 2009 (UTC)

Flying Machine

Could this machine fly?

Are there theoretical limits on size? (I mean way beyond Spruce Moose size) TheFutureAwaits (talk) 07:26, 16 November 2009 (UTC)

The machine depicted appears to have no wing structures - even in a cutaway diagram one might expect to see spaces for their supports: is it actually meant to be an aircraft, or merely an airscrew-driven hydroplane?

If flight is postulated, I suspect it would be too heavy, especially given the old fashioned and bulky natures of many of its components. I don't think there are any theoretical limits on an aircraft's absolute size, but there must be practical limits determined by the aerodynamics of a given atmosphere and the strengths and weights of available materials. A major consideration would be the square-cube law, which dictates that as the linear size of an object increases, its surface area increases proportionallty to the square of the linear increase, but its volume (and hence weight) increases proportionally to the cube - this rapidly increases the wing loading of a conventional aircraft design beyond what will allow flight. 87.81.230.195 (talk) 08:49, 16 November 2009 (UTC)

You could try to demonstrate infeasibility by using a rough and ready calculation for the torque which would be applied to the propeller shaft, and see if any known material has the required strength. -Craig Pemberton 09:08, 16 November 2009 (UTC)

I don't see anything that indicates that this isn't just a multihull boat.-Craig Pemberton 09:11, 16 November 2009 (UTC)

The pontoons are labeled as being "retractable," which I would think would be more likely in the design for a plane than for a boat. My presumption is that it's intended to be a plane, with the wings just not visible in the cutaway. Red Act (talk) 09:22, 16 November 2009 (UTC)

Silly; any vehicle this extravagant is bound to be pimped out. -Craig Pemberton 22:47, 16 November 2009 (UTC)

Also, the rudder sticks up above the craft, not down below it like would make sense for a boat. Red Act (talk) 09:27, 16 November 2009 (UTC)

From the style of the sketch (that's all it is) especially looking at the cars, this was drawn around 1920-30. Anything can "fly" if it gets enough lift. So start by estimating what this monster weighs. Cuddlyable3 (talk) 10:21, 16 November 2009 (UTC)

From the drawing I would have thought that this is meant to be a blended wing body / flying wing aircraft. See alsoJunkers G.38. Boeing clearly thinks this to be an option for future aircraft and is designing one for 800 passengers which can use existing runways. --Cookatoo.ergo.ZooM (talk) 11:06, 16 November 2009 (UTC)

You only showed us one picture...there are more! [19] and [20]. Clearly it's not intended to be a boat. It's very clear that it wouldn't have stood a chance of flying...at least not with the internal design as shown. The artist clearly didn't understand anything about airplane design.

As a flying machine - it's pretty impractical. Using a steerable rear propeller and more props out on the "wings" for turning the thing is a really clunky idea (especially as there is no indication of how those things are powered) - and the de-icing trick results in the need for a double skin which would be heavy. There is a pathetically small fuel supply - yet the fact that there are "quarters" even for the crew and vast amounts of water storage suggests anticipated flight durations of more than just a few hours. There is essentially zero internal structure that would give the thing strength - all we see are partition walls separating rooms...no structural girders except in areas where the artists couldn't think of any useful purpose for the interior space. The weight of things like fuel and engines - plus water tanks and heavy cargo are not well-distributed through the structure - it looks like it would tear right down the middle where the super-weak elevator shaft splits the two heavy sections! The center-of-gravity of an airfoil needs to be at the same place as the center-of-pressure - and that's at the thickest part of the cross-section - this doesn't look like it would have enough weight up-front...but then with those gigantic diesel engines...who know?

There are certainly a lot of oddities to the design...the elevator motors are gigantic! Any idiot could see that if they had moved some of the cargo storage forwards into the bottom of the craft and put the reception areas and offices on upper floors - they'd have needed far fewer stairwells and elevator shafts and perhaps stood a chance of getting the center of gravity in the right place.

This is a classic example of something an engineer would never come up with. Some artist sketched a design for an interesting-looking exterior in 2 minutes flat and then spent the next couple of days carefully filling every cubic inch with something that a cruise liner might need - without giving any consideration whatever for structural strength, power-to-weight ratio, center of gravity, etc.

Bottom line: No - it wouldn't fly.

SteveBaker (talk) 11:18, 16 November 2009 (UTC)

It would make a great submarine. Cuddlyable3 (talk) 11:57, 16 November 2009 (UTC)

Especially if there was a large body of water right at the end of the runway! :-) SteveBaker (talk) 13:58, 16 November 2009 (UTC)

Look how much it's banking in that cover shot! I hope nobody is in those bathtubs! APL (talk) 16:21, 16 November 2009 (UTC)

It's an ocean liner with wings. It is designed just like an ocean liner and would probably weight as much (thousands of tonnes). There is no way to get something that heavy to fly by conventional means. It's not that it was designed by a non-engineer, it was designed before the realities of flight were well understood. It looks like it was designed by a nautical engineer (or someone with experience of ship design) thinking flight would be the same kind of thing. --Tango (talk) 20:05, 16 November 2009 (UTC)

Now I've seen the full magazine item at the page linked to below I see it doesn't have wings, per se. It is supposed to be one big wing. This seems like an obvious idea until you realise that greater weight requires greater wingspan, which means that you need to be able to increase the wingspan without increase the weight much, which means having light wings. That necessitates a design like a regular aircraft with a central thick body and thin wings (although the wings don't have to stick out the sides, they could go forward and back - there have been some interesting ideas along those lines). --Tango (talk) 21:10, 16 November 2009 (UTC)

The design is from 1932 or 1934 (the page says both), and is estimated by its designer to be 10,000 tons. Dragons flight (talk) 20:31, 16 November 2009 (UTC)

It's from '34. The article refers to an earlier design from '32. --Tango (talk) 20:59, 16 November 2009 (UTC)

BTW, we have an article on the guy that designed this thing: Hugo Gernsback. --Tango (talk) 21:17, 16 November 2009 (UTC)

not exactly dreaming?

I think dreaming refers to REM sleep, a stage that occurs after you've been asleep for a while. There's another dreamlike experience when initially falling asleep. It's possible to forget where you are and what you're doing, and confuse imagined activities with reality, while drifting off. Is there a name for that, if it's not technically the same thing as a dream? 69.228.171.150 (talk) 07:29, 16 November 2009 (UTC)

The article Hypnagogia may give you some leads, both in itself and through the links in its "See Also" section, such as Hypnopompic. 87.81.230.195 (talk) 08:34, 16 November 2009 (UTC)

Thanks, that article is great. 69.228.171.150 (talk) 21:20, 16 November 2009 (UTC)

mathematcal model of PMSM/AC servo motor

hi everybody my project is to control the position of AC servo motor by FPGA by sliding mode control so i need the mathematical model i am try to derive the model but i m facing a lot of problem i m very new to the electric machines i know the basics of the servo motor but it is three phase motor not like Dc motor which is qite simple and its modeling also so any body on wiki kindly help me i want state space modellike[A][B][C][D] matrix so that i can simulate it in MATLAB/SIMULINK and then implementation of sliding mode control technique on AC servo motor i want help about the sliding mode algoritham thanks in advance kindly reply

regard abhay

anembryonic gestation

does anembryonic gestation negatively affect further pregnancy?202.83.57.17 (talk) 09:33, 16 November 2009 (UTC)remy

Not an answer, I'm just adding a link to the Anembryonic gestation article, for others who might be interested. --NorwegianBlue ^talk 15:20, 16 November 2009 (UTC)

Perhaps you meant subsequent -- apparently, spontaneous abortion is thought to include the subset of anembryonic gestation. DRosenbach ^{(Talk | Contribs)} 17:18, 16 November 2009 (UTC)

Special Relativity

In special relativity, if you measure a particle of having an average lifetime of say n seconds as measured in the rest reference frame, and you know its speed, do you just use distance = speed x time to find the average distance it travels in the rest reference frame? —Preceding unsigned comment added by 94.193.67.204 (talk) 10:24, 16 November 2009 (UTC)

If by "rest reference frame" you mean the reference frame of the laboratory, then the average distance a particle travels as measured in that frame, is calculated as Average_speed x Average_rest_life_time x Gamma, where Gamma is 1/sqrt( 1-v^2/c^2 ). The average "time" that was measured of the "still" particles gets dilated by a factor gamma when the particles are moving. DVdm (talk) 10:48, 16 November 2009 (UTC)

The average lifetime is measured as the particle is moving, in the laboratory reference frame, so to find the average rest life time would you divide the average lifetime by gamma? —Preceding unsigned comment added by 94.193.67.204 (talk) 11:26, 16 November 2009 (UTC)

Yes, if the average lifetime is measured on moving particles. Average_rest_life_time x Gamma = Average_moving_life_time. See Time dilation#Time dilation due to relative velocity.

By the way, please sign your messages with 4 tildes (~~~~)? Thanks. DVdm (talk) 11:38, 16 November 2009 (UTC)

Hang on. I think there is some confusion here. You only need to use gamma if you are converting from one frame to another. So, if you are measuring the average life time and the distance travelled in the same frame then you can just do distance=speed*time. If the average life time is measured with the particle at rest (which is the normal value quoted) and the distance is measured in the laboratory frame, then you need to convert the life time at rest to a life time in the lab frame by multiplying it by gamma. You can multiply that by the speed to get distance. --Tango (talk) 19:40, 16 November 2009 (UTC)

Yes. To avoid that confusion I introduced the names Average_rest_life_time and Average_moving_life_time. DVdm (talk) 20:55, 16 November 2009 (UTC)

Recycling

In the United States, is it generally a problem or not to include paper envelopes with plasticine address "windows" with mixed paper recycling? Thank you --71.111.194.50 (talk) 13:10, 16 November 2009 (UTC)

No it isn't. Recycling plants have techniques for removing small amounts of contaminants like this. I can't believe I just answered a refdesk question with a link to Yahoo Answers... —Akrabbim^talk 15:46, 16 November 2009 (UTC)

Bahahahah... you're a regular though, so we have to let that slide. :-) ♠The Ace of Spades^♣♥_♦ 03:32, 17 November 2009 (UTC)

Many such envelopes have a plastic lining that makes them fairly unrecycleable. If you wet your fingers and rub the envelope, the paper will rub off and you'll see a very thin plastic sheet. Ones like that should just be thrown away. --Sean 17:17, 16 November 2009 (UTC)

I don't think you meant plasticine... --TammyMoet (talk) 19:46, 16 November 2009 (UTC)

I have seen many that simply have a hole cut in the paper, and replaced with a clear plastic piece. —Akrabbim^talk 19:59, 16 November 2009 (UTC)

Do arrows have "lift"?

My question concerns the following claim made in this version of the "Quarrel" article:

"Bolts and arrows have different flight characteristics. Bolts fall at the same rate, independent of the speed of flight. Arrows, in contrast, depend on gaining lift in flight, and hence have their centre of balance at a point about 9% of their length forward of their center. This is called 'point planing'."

No reference is (at present) cited in-line for this information. What I'm wondering is: does that make any sense?
On the "Quarrel" talk page I made the comment:

"To have lift, you need an airfoil, but the fletching article makes it clear that the fletchings are there only to "stabilize the arrow in flight" (ie., they are not wings). There is no mention of "lift" in the arrow article."

But then I started wondering about eg. paper airplanes, hang gliders, etc. – the "wings" of which do not (necessarily) seem to have an airfoil shape, either. Some of the "lift" in those cases apparently derives from "angle of attack" issues, but could that really be what's going on (in a consistent, reliable way) with arrows, too? Wikiscient 17:20, 16 November 2009 (UTC)

Air foil shape is useful for getting lift while minimizing drag. Ever see pieces of plywood flying around during a hurricane? Those are not airfoil shape and certainly have lift. Googlemeister (talk) 17:29, 16 November 2009 (UTC)

Well, that refutes my "to have lift, you need an airfoil" remark, but I had already done that myself by bringing paper airplanes etc. into it.

I'm still trying to understand better how "lift" works with arrows, if, in fact, there is any (which, presumably, would be attributable somehow to the fletchings, which neither bolts nor bullets have). Wikiscient 17:40, 16 November 2009 (UTC)

Some (but not all) crossbow bolts do have fletchings. See Crossbow#Projectiles, and this picture. Red Act (talk) 18:15, 16 November 2009 (UTC)

Ok, thanks for the clarification. I guess that just makes the statement in the crossbow bolt article which prompted my question all the more interesting or "incorrect," I'm still not sure which! :S Wikiscient 18:31, 16 November 2009 (UTC)

Wouldn't a crossbow bolt also have that same sort of lift if it was fired at the appropriate angle of attack? APL (talk) 17:32, 16 November 2009 (UTC)

I'm not completely certain of this, but I think the answer to that would be: yes, but not much! Wikiscient 17:43, 16 November 2009 (UTC)

That doesn't make sense to me - shouldn't the centre of balance be further back than the centre of the arrow in order for it to have positive angle of attack and thus have lift? That said, I think the key difference between arrows and bolts is that bolts go faster. That means they don't really need any lift in order to maintain level flight, there just isn't time for them to fall far before hitting their target. --Tango (talk) 18:31, 16 November 2009 (UTC)

Well, again, my question is about this quote (from the crossbow bolt article):

"Bolts fall at the same rate, independent of the speed of flight. Arrows, in contrast, depend on gaining lift in flight..."

There is no reason an arrow couldn't be launched with a higher velocity than a bolt, so I don't think that is the "key difference" in this case.

The "key difference" does seem to have something to do with the location along the length of the projectile of the center-of-gravity. And I am wondering the same thing: placing that forward of the center-of-length would, intuitively, seem likely to create a downwards angle-of-attack force! On the other hand, if the fletchings were providing lift the way an airfoil does (ie. even in level flight), you'd want to have your center-of-gravity forward of center-of-length to compensate for that "upwards-from-the-rear" force.

So, anyway, I'm still trying to understand what the quote in question is trying to say... Wikiscient 19:00, 16 November 2009 (UTC)

See, I'm just confusing myself with this, *sigh*...Wikiscient 19:04, 16 November 2009 (UTC)

Arrows are fired by a bow, bolts are fired by a crossbow. The ways those two devices work mean that bolts are fired faster. That is (part of) why different projectiles are used. As I understand it, the fletches make the arrow spin, providing stability by the gyroscopic effect. Since the arrow is spinning, there is no way the fletches could provide lift (any such force would rotate with the arrow and could average itself to zero). --Tango (talk) 19:31, 16 November 2009 (UTC)

I should clarify - the fletches probably are aerofoil shaped in order to get optimal torque. Each fletch will provide a force in a different direction and, since they are equally spaced, they will all cancel out so there is no resultant force, just a torque (rotational force). --Tango (talk) 19:33, 16 November 2009 (UTC)

No, both of these claims are wrong. Fletches are, modulo production errors, straight and symmetrical. They do not stabilize the arrow by rotation, but simply act as aerodynamic fins. If the arrows velocity is not parallel with its heading, the increased drag of the fletches acting on a long lever will right it again. --Stephan Schulz (talk) 22:39, 16 November 2009 (UTC)

Agreed. So, hmmm... Wikiscient 22:50, 16 November 2009 (UTC)

Assuming that an arrow/bolt behaves in a similar manner to a javelin, the center of gravity is placed relative to the center of pressure to achieve optimal lift. By sport rule, javelins have the center of gravity pushed forward to make them plummet and stick into the ground as opposed to gliding along and skipping along the ground when they land. -- kainaw™ 18:53, 16 November 2009 (UTC)

Optimal lift for an arrow or bolt would, presumably, be the amount of life required to keep the flight level (so you don't have to compensate for trajectory when aiming). That, I would think, would require the centre of gravity to be just behind the geometric centre. (Of course, arrows are sometimes fired up so they travel a greater distance and hit the enemy from above - that would have a different optimal lift, although to get maximum range I would thing it would still want the centre of gravity behind the geometric centre.) --Tango (talk) 19:31, 16 November 2009 (UTC)

Google finds many sources for the "point planing" claim and 9% figure but I leave it to others to decide if any meet WP:RS. Cuddlyable3 (talk) 20:57, 16 November 2009 (UTC)

Almost all those hits look like Wikipedia mirrors to me. --Tango (talk) 21:41, 16 November 2009 (UTC)

Has anyone found a good way to exclude those pesky mirrors from search results? A lot of them don't even say where they got it from so a simple -wikipedia doesn't work. —Akrabbim^talk 22:32, 16 November 2009 (UTC)

If you only want to exclude mirrors of a particular article, just choose a sentence from the article that doesn't sound likely to appear in other articles by change and do -"that sentence". --Tango (talk) 22:35, 16 November 2009 (UTC)

However, "-" terms don't always work in Google if the page uses frames. I think it applies the search criteria separately to each frame but returns the whole page. Unless it's changed since I asked about it and they answered. --Anonymous, 23:52 UTC, November 16, 2009.

Yes, there is a lift force that acts on arrows. There is also lift on crossbow bolts (especially those bolts that have fletching), but the lift is not as significant there.

The primary purpose of the fletching on an arrow is to provide stability. The stability is the strongest in the case of a helical fletch, which imparts a strong rotation around the roll axis. However, a helical fletch results in a slower arrow, and can cause problems with the fletching clearance on the arrow rest. For that reason, a straight fletch is often used, or an offset fletch, which is intermediate between a helical and a straight fletch.

In addition to stability, the fletching also provides lift. Fletching is not shaped like an airfoil, as a glance at the pictures in the fletching article will show, but that's not necessary for lift to occur.

To visualize the forces involved, it's convenient to first think about a horizontal arrow that you just drop, and then consider how that picture changes due to forward motion of the arrow. That won't work well quantitatively, because Bernoulli's principle makes life complicated, but it will at least help to picture some of the physics involved qualitatively.

When you just drop a horizontal arrow, the air resistance on the arrow causes an upward force, especially on the fletching, that wouldn't exist if the only force involved were gravity. That upward force is considered to be drag, which is defined as the component of the aerodynamic force acting opposite to the direction of the arrow's motion, which in this case is downward. Now suppose the arrow also has a horizontal component to its velocity. The upward aerodynamic force still exists, but now that upward force is mainly considered to be lift, since that's defined as being the component of the aerodynamic force that's perpendicular to the arrow's direction, which is now mainly in the horizontal direction. The fletching doesn't have an airfoil shape, so with a straight fletch and an arrow moving purely horizontally (implying a zero angle of attack), there would be no lift. But during the second half of the arrow's trajectory, at least, the arrow is also falling, and the air's resistance to that vertical motion counts as lift.

The quarrel article gives a poor explanation of why an arrow's center of gravity is placed where it is. The reason is that it's a tradeoff between lift and stability.

First, consider how the arrow's center of gravity affects lift. Suppose most of the arrow's mass was right near the tip. Now if you hold the arrow horizontally and let go, the tip of the arrow will drop faster than the nock end, because the upward force on the fletching is in this case much more effective at holding up the nock end of the arrow than the tip. Now consider the same arrow, with the tip still sagging below the nock end, but now with also a horizontal motion to the arrow. Due to the attack angle of the fletching, there isn't going to be as much lift on the arrow, or the lift might even be negative. So the arrow's going to take a nosedive. In contrast, if the arrow's center of mass was back far enough that it stayed horizontal when it was dropped, the loss of lift would be avoided. So for the sake of lift, it's good to keep the center of mass back away from the tip.

Now, consider how the arrow's center of gravity affects stability. Supposed most of the arrow's mass was in the nock, behind the fletching. In this extreme situation, the inertia of the nock tends to keep the nock going at a constant speed, while the drag on the fletching works to make the fletching part of the arrow lag behind. So the forces on the arrow favor the arrow turning around, in obviously a completely unstable situation. As the center of mass is moved forward, the arrow's stability improves, with the maximum stability occurring when the center of mass is at the tip.

Trading off keeping the center of mass away from the front for the sake of lift, and keeping the center of mass away from the back for the sake of stability, leads to a (somewhat empirically determined) optimal compromise between the two.

For a good discussion of the technical details of arrows, go to here, and click the "Archery Technical" link. The "Fletching Arrows" and "Arrow Rotation" articles are particularly helpful toward this question. Red Act (talk) 01:59, 17 November 2009 (UTC)

Dreaming

Why does it seam so realistic, as to be virtual reality?Accdude92 (talk to me!) (sign) 20:28, 16 November 2009 (UTC)

No one can tell you that it's all nonsense without waking you up, so what else can you believe? Cuddlyable3 (talk) 21:01, 16 November 2009 (UTC)

If it seemed unreal then you could pass off whatever messages your subconscious is giving you as being unimportant. Vranak (talk) 22:48, 16 November 2009 (UTC)

This is a Reference Desk, so let's at least attempt to supply some references, people. My only reference is the obvious Dream article which seems to have a lot of problems and does not address your excellent question. It has many, many links to other interesting articles. Comet Tuttle (talk) 23:07, 16 November 2009 (UTC)

Freud, subconscious, ego. I thought this stuff was common knowledge! Vranak (talk) 01:58, 17 November 2009 (UTC)

I have to point out that Virtual reality is not nearly as realistic as dreams. Not yet, anyway. APL (talk) 23:41, 16 November 2009 (UTC)

Don't forget that it's not your eyes that see during the day, it's your brain. If a dream is just a series of images created by your brain, well then that's no different that what happens when you look at something normally. While awake, you know and can tell the difference between what you are seeing and your imagination (the latter is probably hampered by the former) but you don't have that luxury while asleep. ~ Amory (u • t • c) 23:53, 16 November 2009 (UTC)

microwave cooker question

What would happen to a person who is standing in front of your standard home microwave for 2 minutes if it was running with the door open? I presume most of the microwaves are focused towards the center of the device and you would only encounter a few stray bits that were reflected? Googlemeister (talk) 21:16, 16 November 2009 (UTC)

The Wikipedia article on Microwaves leads me to believe you might get burns and the radiation could possible cause cataracts, though it seems no long term effects (other than tissue damage) would be suffered. Obviously nothing good can come of this, and since it is non-ionizing radiation, there's no way to get super powers 206.131.39.6 (talk) 21:27, 16 November 2009 (UTC)

Someone with metal or electrical implants might fare worse. Before microwaves were properly shielded they posed a threat to people with pacemakers. APL (talk) 21:30, 16 November 2009 (UTC)

Two summers ago I was living in a place with a shared kitchen and I used the microwave a number of times before I realized that there was a hole two-inches in diameter in the front door. I never used it again, and did not develop anything afaict. ~ Amory (u • t • c) 23:49, 16 November 2009 (UTC)

How could an infinite universe expand?

As far as I understand it the possibility of an infinite universe has not yet been removed from the drawing board but how would this play into the big bang and inflation, can infinity originate from a point and can infinity expand?Bastard Soap (talk) 22:22, 16 November 2009 (UTC)

If the universe is infinite then it as always been infinite. At the big bang it wouldn't have been a point of infinite density, it would have been an infinite volume of infinite density. However, the observable universe (all the space light has had time to reach us from) is definitely finite, so that would have been a point. People often refer to the observable universe as simply "the universe" (since it contains everything that can have any effect on us, meaning we can just ignore anything outside it), which is the cause of this confusion. --Tango (talk) 22:26, 16 November 2009 (UTC)

Think about all the real numbers in [0,1]. They are uncountably infinite. If you take a new set, 2[0,1], it is "larger", yet it is still infinite. You can do the same thing with an unbounded set such as [0,$\infty$). Cardinality theory might help you. -Craig Pemberton 22:54, 16 November 2009 (UTC)

The OP wasn't asking about different sized infinities, but rather how something of zero size can being infinite, which is a good question. Also, what makes you think the OP understands interval notation and terminology like "unbounded set"? While they might well do, it is best not to assume certain prior knowledge without good reason. --Tango (talk) 23:30, 16 November 2009 (UTC)

As BenRG puts it, universal expansion is just "stuff moving away from other stuff". Think about it that way and it shouldn't be so confusing. --Trovatore (talk) 23:03, 16 November 2009 (UTC)

Why isn't more money spent on SETI?

Why isn't more money spent on SETI, or a similar search for extraterrestrial signals? Although there is no guarantee that there are other intelligent civilisations, or that they would broadcast information that we could use in a short timeframe (rather than us having to make contact and then wait decades, or hundreds of years) - it would seem that the potentially massive technological benefit if we happened upon a broadcast of an advanced civilisation would warrant a bit more of a gamble. Billions, likely trillions, are spent every year on various kinds of scientific research, whereas it seems that SETI has a budget of around $500,000, and finding this stream of information could bypass all of that other spending. On a similar subject, is there an organised effort to transmit our knowledge out into space? I guess that it is likely that any civilisation receiving it would likely not be much less advanced than us, so it may be that our knowledge would not be useful in a pure technological sense, but would be in an athropological sense. I guess the above reasoning for spending money on SETI could also be applied to the development of AI, but it seems that workable that advances our knowledge AI is many, many years away, whereas that signal from the clever aliens could be available right now. QuickSnow (talk) 23:14, 16 November 2009 (UTC)

On the former point, it all comes down to the likelihood of success (small), the enthusiasm for donating money to it (modest), and the political difficulties of dumping public money into a program that has absolutely no realistic prospects for public rewards (difficult), and the fact that trying to communicate with extraterrestrials is rightly considered political poison (crank stuff). All of this, of course, avoids the fact that most people think there are more pressing uses for money (and there are a lot of scientific competitors out there in the "long-shots that could actually pay off" category). Add to it a squeamishness about the fact that meeting extraterrestrials does not, on the face of it, sound like the kind of thing humans would be very good at (how often has the encountering of one advanced civilization with a less advanced one gone well for the former?). On the latter point, see Arecibo message. --Mr.98 (talk) 23:29, 16 November 2009 (UTC)

Transmitting our knowledge into space might not be a good idea. If we ever contact and successfully communicate with aliens we're going to want something to trade with. APL (talk) 23:39, 16 November 2009 (UTC)

What if we're the advanced civilization and find a less-advanced one? The cost of sharing all of our technology could destroy our economy... Seriously though, SETI and similar programs don't get a lot of play because it's hard for people to see the benefit. In the long run, yeah there might be something but compared to that, living on Mars is right around the corner. People would rather see money go towards other things, and it is usually hard to justify spending billions on SETI instead of AIDS or other medical research that will have a much larger benefit much sooner, or any of a thousand other projects. ~ Amory (u • t • c) 23:46, 16 November 2009 (UTC)

I would expect any civilisation we made contact with to be more advanced than we are - we have had the ability to send and receive messages between stars for only a few decades (and even now we can only barely do it). Chances are slim that we would make contact with another civilisation during those few decades where they are less advanced than we are now.

However, regardless of who is we make contact with, we won't get any meaningful communications for a long time. The nearest civilisation might, at best, be 20 light years away, that means a 40 year round trip for any message. The first few messages will probably just be establishing a language to communicate in (it is possible the first message sent will be able to teach a usable language to the other civilisation, but I would expect a bit of trial and error to be required - as we discussed on the Language desk a few days ago, it is very difficult to learn a language (even one designed for the purpose) without 2-way communication. So it would likely be centuries before we could exchange technology. Getting funding for such long term projects is very difficult. Public funding is difficult to get for anything that won't happen before the next election. You'll only get commercial funding if you can turn a profit within a few years, certainly within the lifetime of the investor. That leaves charitable donations and you'll get limited amounts that way.

All that said, there is actually quite a lot being spent on SETI. Consider the recently launched Kepler Mission. That wasn't cheap. While it isn't solely devoted to SETI, discovering terrestrial planets would make it much easier to know where to look for ETIs (or where to send messages to them on spec).

--Tango (talk) 23:55, 16 November 2009 (UTC)

I was imagining a one way communication in the sense that a civilisation mght decide to transmit some, or all (perhaps with the exception of information it thought could be dangerous to itself or the receiver), of its technological informaton along wth the means to decode/translate it, as a constant transmission on a loop. There's no proof that such a signal exists, but it would seem very likely that advanced civilisations do exist out there and perhaps it is likely that they would choose to send such a signal (purely for altruistic purposes, no different to one country sharing its technology with another, simply for the benefit of the receiving country). I can understand that spending billions on this might not be politically sound, but $500,000 a year seems very low (I take on board your point about the Kepler mission though), as there are a lot of people who would spend close to that on a new car. When you take into account that tapping into such a signal would possbly replace decades (or perhaps even hundreads or thousands of years of research)it would seem that somebody somewhere would take a slightly bigger gamble (maybe not with public funds, but with private ones perhaps). QuickSnow (talk) 00:21, 17 November 2009 (UTC)

Finding a way to transmit a message containing instructions to build advanced technology without any pre-existing common language would be very difficult. Anyway, the receiving civilisation would need to technology to receive the message. Assuming a similar technological progression to ours, that puts them at no more than a few decades behind us, we wouldn't have much to teach them, probably nothing. Another issue is that people don't like to devote time and money to something that they won't know worked - we would need a reply to know we had achieved anything, so that's still going to take more than a lifetime for anything but the nearest stars. Also, working out what technology wouldn't be dangerous would be hard - even the simplest technologies can be harmful in the wrong hands. --Tango (talk) 00:59, 17 November 2009 (UTC)

I'm not sure why you think it is "likely". As the Drake equation does a good job of showing, there are a lot of probabilistic factors involved in whether there are even civilizations out there that could communicate with us during the tiny (tiny!) period of geologic history that we have had the ability to listen for them. Taking those and then saying, "so what are the odds that said advanced civilization has decided to broadcast their information to us with a strong-enough signal to be detected and on a continuous loop over the course of at least hundreds of years?"... to me, it doesn't look very likely. The biggest problem here is time itself—look at the history of just our own planet, and how long our civilization has been able to do this kind of thing. Now extrapolate a little bit and say that any civilization that can really grok radio-wave transmission is going to also, within a century or so, grok nuclear weapons and genetic engineering. Now extrapolate the likelihood of any given civilization to survive in a world where there are creatures that grok nuclear weapons and genetic engineering—how many centuries of a "window" does that give you before your civilization can no longer send or receive signals? Much less if we postulate them having anything like politics. Obviously all of this is intangible—we don't know how likely our situation is, much less theirs—but it does seem to imply that there is a much better chance that there is no one out there sending/listening at the same time we can send/listen. --Mr.98 (talk) 00:59, 17 November 2009 (UTC)

I hear this "alien civilisations will probably destroy themselves" argument a lot. The evidence doesn't support that. 100% of species known to have achieved civilisation are still going strong. --Tango (talk) 01:49, 17 November 2009 (UTC)

Human societies have regularly collapsed, e.g. Amazonian civilisations, Ur, Easter Island. So the premise is that if human societies can collapse so easily, so could alien civilisations. See our articles on Societal collapse, Risks to civilization, humans and planet Earth, Existential risk and Extinction event. Fences&Windows 03:35, 17 November 2009 (UTC)

I was careful to speak in terms of species. Human societies and civilisations have certainly collapsed, but they have always been replaced by others. --Tango (talk) 04:03, 17 November 2009 (UTC)

Assuming an alien civilization's lust for bandwidth is similar to ours, they compress their data, which is virtually indistinguishable from background noise. A Quest For Knowledge (talk) 03:50, 17 November 2009 (UTC)

Except it is concentrated in a specific band. However, that only refers to us overhearing their internal communications. It is more likely that we could detect signals intentionally sent into space (we are moving towards wired communication for long range communications so it is likely that other civilisations will do the same, so they would only send out significant amounts of radio pollution for a few decades, we're unlikely to be looking for them during that slot). They would hopefully start with sequences of primes or something else that would stand out from noise very clearly. --Tango (talk) 04:03, 17 November 2009 (UTC)

"It is more likely that we could detect signals intentionally sent into space". Really? Given that a) Homo Sapiens is the only known species who have intentionally attempted such a communication, and b) they've only attempted it once, what is the likelihood that another species would so such a thing? A Quest For Knowledge (talk) 04:28, 17 November 2009 (UTC)

Perhaps it is unlikely that another civilisation will send such a message, but it is even less likely that we'll detect an unintentional message. With the amount of noise we're sending out at the moment and the strength of our radio telescopes we could only detect ourselves if we were at best one light year away, so we could only detect the noise from other civilisations if there is much more of it than we emit and it looks like we aren't going to emit much more than we are now (since we're moving towards wired communications for long range things - ie. the internet vs. regular TV and radio). --Tango (talk) 04:48, 17 November 2009 (UTC)

You all forgot to mention another explanation. It is not scientific (potential benefit and probabilities) or economical (cost effeciency) but political, there is conspiracy in high level government circles to conceal the information that the ETI has been already found and possibly contacted. (Igny (talk) 04:59, 17 November 2009 (UTC))

November 17

Name of process in which complex material things appear from nowhere?

I've just forgotten this term, but I think it had "brain" in there somewhere. The idea is that in an infinite space, or infinite time, or both, you could have anything happen, including our world simply appearing out of nowhere 5 minutes ago. Myles325a (talk) 01:40, 17 November 2009 (UTC)

Infinite monkey theorem? Mitch Ames (talk) 02:06, 17 November 2009 (UTC)
(That's complex structured data of course, not real physical material) Mitch Ames (talk) 02:19, 17 November 2009 (UTC)

Maybe something to do with brane? DMacks (talk) 02:17, 17 November 2009 (UTC)

Boltzmann brain -- Coneslayer (talk) 02:26, 17 November 2009 (UTC)

OP myles back. Yep, it's Boltzmann's brain (or brane) alright. Thanks. Myles325a (talk) 03:06, 17 November 2009 (UTC)

Why is urea planar?

I've drawn the Lewis dot structure of urea, and I just don't understand how it can be a planar molecule with a double bond between the carbon and the oxygen. Why don't the two nitrogen atoms have tetrahedral structures? Is there a double bond that resonates among the O-C and C-N bonds? What's going on here?