Wikipedia:Reference desk/Archives/Science/2008 January 21

= January 21 =

MEDICAL X-RAYS
AFTER DOING A TUBE WARM UP, THEY ALWAYS HAVE A "SOAK" TIME, BEFORE YOU ARE SUPPOSE TO ENTER THE X-RAY ROOM. IN LIEU OF THIS, I WAS WONDERING HOW LONG, AFTER TAKING AN X-RAY OF A PATIENT, DOES THE IONIZING RADIATION STAY IN THE ROOM? WHEN IS IT REALLY SAFE FOR THE TECH TO GO BACK INTO THE ROOM. —Preceding unsigned comment added by 216.54.56.99 (talk) 00:52, 21 January 2008 (UTC)
 * Who says it's unsafe? Ions react very fast, and the only thing you'll maybe notice is a faint ozone smell. Read about it for its dangers. --Rwst (talk) 10:07, 21 January 2008 (UTC)


 * Never heard of soak time. X rays are only produced when the HT is applied to the tube. As with most pulsed energy Pulsed power systems I would think this happens for only a small fraction of a second X-ray_tube--TreeSmiler (talk) 15:26, 21 January 2008 (UTC)


 * For diagnostic x-rays, the ionizing radiation stops as soon as the tube current goes off. With megavoltage x-rays (gamma rays) used for clinical radiotherapy (cancer treatment), traces of short-lived radioisotopes can be generated in the treatment room and their activity will persist for a few seconds after the beam goes off.  (Typically the time required to open the room door or navigate the maze entry is sufficient to allow the bulk of these radionuclides to decay.)


 * You should probably talk to the tube manufacturer about the purpose of the soak time and what hazards – if any – are present. It's not a radiation problem.  A word to the wise&mdash;typing in ALL CAPITAL LETTERS is often seen as 'yelling' in online conversations; as a courtesy to others you should generally use mixed-case type in electronic communication.  TenOfAllTrades(talk) 15:43, 21 January 2008 (UTC)


 * I agree with that sentiment. If you've been told by someone in charge of safety there is a soak time, you really should observe it until you've confirmed with someone who definitely knows what they're talking about. Relying on wikipedia volunteers for stuff like this is a bad idea Nil Einne (talk) 17:23, 23 January 2008 (UTC)

mineral identification question
i am looking for the mineral name of a pyrite/marcasite associated mineral that has a slang of popp rock or bujistone,,,its a metaphysical use material that forms in a dome shape like 2 vanilla wafers stuck together and commonly sells as a male and female variety the mail having a rougher surface,,it is mined/found in Kansas City,Mo.,,,,,can anyone help???

– — … ° ≈ ≠ ≤ ≥ ± − × ÷ ← → · § 71.137.5.106 (talk) 02:26, 21 January 2008 (UTC) rainboroc71.137.5.106 (talk) 02:26, 21 January 2008 (UTC)


 * See Boji stone. SWAdair | Talk 03:13, 23 January 2008 (UTC)

THANK YOU,,,,,

Creatine and Fibromalagia
Sorry, but we can't offer you treatment advice for your mother's fibromyalgia. You should encourage her to speak to her physician or pharmacist for information about how any supplements may interact with her condition or with any drugs she may be taking. TenOfAllTrades(talk) 15:22, 21 January 2008 (UTC)


 * Its sad how you relate everything to medical advice. I was not asking if or how creatine would help my mom. Your one of those poeple that makes the reference desk suck. If you were to really look at the question, you wouldnt be making a fool of yourself. Let me ask you my original question again without mentioning fibro...: Do creatine monohydrate and phosphate turn into the same thing by the body when consumed. —Preceding unsigned comment added by 71.105.67.123 (talk) 04:53, 22 January 2008 (UTC)

Oh yeah and about the physician thing, I think you also don't understand that most doctors are fools. I work at a pharmacy and we have doctors that give the wrong doses all the time. My doctor gave me a prescription for a childrens strength inhaler when I'm an adult. We have had doctors call in artificial eye drops for their patients. Everyone knows they are over the counter. Even many specialists dont know much and quite often don't stay on top of the latest research. —Preceding unsigned comment added by 71.105.67.123 (talk) 04:56, 22 January 2008 (UTC)

Pegasus
A mind exercise: Assuming all things being equal (i.e. hollow bones, etc.), what would Pegasus' wingspan be in order to fly as described in the myth (including carying an adult human)? —Preceding unsigned comment added by 216.154.18.118 (talk) 02:55, 21 January 2008 (UTC)

I love this sort of question! I'm just an amateur, but I'll give it a shot (somebody please improve this answer...) —Preceding unsigned comment added by Vultur (talk • contribs) 03:42, 21 January 2008 (UTC)

Wing chord and the type of flight are very important for wingspan. Powerful fliers with deep wings have shorter wingspans than soarers. Harpy Eagles are almost twice as heavy as Golden Eagles, but have a roughly similar wingspan; the Golden Eagle is a thermal rider while the Harpy Eagle is not. Wandering Albatrosses have very long wings since they are soarers.

I'm not sure what you mean by "all things being equal", do you mean "best possible adaptations"? If so, and bearing in mind I'm not an expert on these things by any means, we can compare Pegasus to the largest known flying creatures.

Argentavis magnificens was around 23 feet in wingspan and weighed 145 to 225 lbs. according to our article. Quetzalcoatlus was wingspan 33-40 ft. or more and weighed perhaps over 220 lbs. (estimates vary widely).

A horse-sized creature, if very gaunt and having hollow bones, might be little heavier than a Quetzalcoatlus. So, maybe 30-40 feet? I don't know if either Argentavis or Quetzalcoatlus could carry a human though. —Preceding unsigned comment added by Vultur (talk • contribs) 03:41, 21 January 2008 (UTC)
 * I've got to intervene here, as I know a thing or two about horses. They, even not being hollow-boned, are in comparison fragile creatures as I hear, so hollow bones would mean that there would be even less to support their weight. Now, given that a typical male horse's (for a working horse, I've had to do with Belgian horses foremost) weight can be around 700-1100 kg (which gives about 1500-2400 lbs), that's a good few times more than your estimate, Vultur. Assuming some weight reduction via hollow bones, and streamlining for a good look, let's call it 500-600 for Pegasus. Could you recount? --Ouro (blah blah) 07:24, 21 January 2008 (UTC)


 * So... we guess that a 100kg horse would need 10m wingspan, but a real Pegasus would need to be more like 500kg. Would the wing surface area increase linearly? Maybe the length and width increase by a factor of 2-2.5 for 5x overall lift increase? At what point do we need to start considering that 25m wings are going to add significantly to the overall weight if they're to be strong enough to hold their own weight, let alone the horse's? jeﬀjon (talk) 20:56, 21 January 2008 (UTC)


 * I'm aware that horses are far, far more than 100kg. Horses aren't THAT frail; they're lightly built in comparison to things like cows, but cows are basically a rock of meat and muscle on four legs.  Even something like a giraffe is  very tough. A Quetzalcoatlus skeleton is pretty gigantic; fleshed out, it could easily look horse-sized.  Flying creatures look much bigger than their weight warrants;Argentavis, heck, even some of the smaller teratorns would probably look practically pony-sized to the hapless man watching them descend on him.


 * I don't think a 600 lb creature could have enough margin to fly high or carry much of anything. It's very, very (x10) risky to define maximums for any living thing's capacity (scientists said Pteranodon was at the upper size limit for any flying creature, before they found Quetzalcoatlus). Even so, a 500kg flier would be a huge stretch at the very least, and would probably look far larger than a horse.98.199.17.94 (talk) 03:00, 22 January 2008 (UTC)

How does radium glow?
I wanted to know how does radium glow? Many times i have observed the glow to be very faint and sometimes its very bright. Does it charge by sunlight? —Preceding unsigned comment added by 77.110.98.16 (talk) 09:03, 21 January 2008 (UTC)

Radioluminescence should have the answer to this....but it doesn't really. But from reading that article I think that beta particles (electrons originating from the nucleus) from a radium atom hit another radium atom and excite an other electron which then releases it's excess energy as light.Shniken1 (talk) 09:54, 21 January 2008 (UTC)


 * And it does not charge by sunlight. That would be phosphorescence. --Rwst (talk) 10:11, 21 January 2008 (UTC)


 * "Radium" (as formerly used in watches and clocks) was the metal radium combined with a phosphor. The phosphor can certainly be stimulated by things other than the radium's beta decay; a black light emitting ultraviolet light will do it. I wouldn't be surprised to find that some phosphors were also phosphoresecent so that they could be "charged" by ambient light.


 * Atlant (talk) 17:22, 21 January 2008 (UTC)


 * The Self-powered lighting article might be useful. They mention radium and the modern equivalent, Trasers. --Mdwyer (talk) 18:10, 21 January 2008 (UTC)


 * The only purpose of adding radium is to stimulate the phosphor. The radium itself does not phosphoresce.  It is worth noting that radium will remain radioactive after the phosphor has ceased to work.  It is also worth noting that many old products are still radioactive even though they no longer glow and may contain a quantity of radium which would not be allowed today.  Sp in ni  ng  Spark  14:33, 23 January 2008 (UTC)


 * Radium is luminescent on its own - our radium article says "Radium is luminescent (giving a faint blue color) ..."; this US EPA page says "Purified radium and some radium compounds glow in the dark (luminesce)". Gandalf61 (talk) 14:56, 23 January 2008 (UTC)

Hi. Just an aside question, would holding a radium watch up to your eyes and looking at its glow for too long cause damage to your eyes due to the radioactivity? Or would the alpha rays be blocked by the glass and the gamma rays would just go through you anyway? Would wearing the watch for many years (not continously) so the same thing? Thanks. ~ A H  1 (TCU) 23:09, 23 January 2008 (UTC)


 * Good question. I can't really make sense of all the articles I'm reading, but it appears that radium is not a strong emitter, although the radon it decays to is pretty energetic.  I would assume radium releases primarily alpha particles, and very little gamma radiation.  Skin is sufficient to stop Alpha radiation, so I would assume that alpha rays were stopped by the watch parts and the radon gas amounts were neglegable.  The Radium and Radium girls articles would seem to suggest that it was the ingestion of radium paint that caused problems.  My impression is that you should stay away from gamma sources, and don't swallow alpha sources.  For instance, the Americium article says that the radioactives found in your smoke detector release three times the amount of alpha particles as radium, and in "gram quantities" are intense gamma emitters.  However, the plastic of a smoke detector body effectively contains it. --Mdwyer (talk) 05:50, 24 January 2008 (UTC)


 * Eyes, mind you, are very vulnerable to alpha rays (unlike skin). I'd imagine though that they'd be stopped by the glass. --24.147.69.31 (talk) 04:11, 25 January 2008 (UTC)

Nicorandil
Is there an alternative to this drug —Preceding unsigned comment added by Fred1471 (talk • contribs) 13:17, 21 January 2008 (UTC)
 * Nicorandil is used to treat angina by reducing preload. For some of the many other medications and treatments used in angina, you can take a look here. So yes, there are many treatment alternatives that a doctor can prescribe, tailoring treatment to patient needs. - Nunh-huh 17:00, 21 January 2008 (UTC)

water supply pressure and surges
I am in dispute with the local water supply company.Over a period of two months I suffered short intervals of loss of supply[approx 5-10 secs].when the pressure was restored it was accompanied by a surge causing pipe knocking and finallydamage to my sink at the tap junction. The water company deny the problem is theirs and say that the problem is on my pipework.This is [a]physically impossible and [b]the problem disappeared when they increased the mains pressure at the local pumping station.

I should like to ask can anyone confirm that these incidents were due to mains problems and do modern water meters act as non return valves as the water co. state that my neighbours did not have a problem.they both have water mters but I do not.

thank you

Bobd. —Preceding unsigned comment added by Robdoc77 (talk • contribs) 14:10, 21 January 2008 (UTC)


 * I can't comment specifically on the water works in your jurisdiction, but it's quite common for either the water meter itself or an adjacent section of pipe to contain a non-return valve. The water company doesn't want (potentially contaminated) water from homes or businesses to be drawn back into the water system.  Not being a plumber, and not being able to examine your pipework and the damage, I wouldn't be comfortable venturing a guess as to the cause of your troubles. TenOfAllTrades(talk) 15:49, 21 January 2008 (UTC)


 * Modern water meters don't act as backflow prevention devices but at least in the United States, modern building codes require the installation of a backflow prevention device at each water service entrance.


 * Atlant (talk) 17:25, 21 January 2008 (UTC)


 * Also, it sounds like you're describing Water hammer. Proper arrestors (often just an extra bit of 'empty' pipe beyond the valve) are needed to prevent damage from hammering.  Although the water company strives to maintain constant pressure, most water hammer is a localized event, and there's nothing they can do about it.  --Mdwyer (talk) 18:09, 21 January 2008 (UTC)


 * Expanding on what Mdwyer said, water hammer "arresters" are empty pieces of pipe oriented vertically, capped-off at the top end, attached to the rest of the plumbing at the bottom end, and filled with air. The air provides a spring that greatly moderates the rapid rise in pressure that would otherwise occur when the flow of water stops suddenly. There's usually some provision to ensure that the water hammer arrester can be drained of water/refilled with air; this may be an explicit valve or just a piping configuration that allows the arrester to drain through a sink tap.


 * Atlant (talk) 12:59, 22 January 2008 (UTC)

Thermocouple power generation
Is it possible/practical to generate useful quantities of electric power by using banks of thermocouples?--TreeSmiler (talk) 15:37, 21 January 2008 (UTC)
 * Possible yes (in fact, Werner von Braun proposed them as energy sources for a space station before the semi-conductor based solar cell was developed). Practical (and economical) - probably not. The process is very inefficient compared to other technologies. --Stephan Schulz (talk) 15:43, 21 January 2008 (UTC)


 * See thermopile. So-called "millivolt" thermostat systems use thermopiles heated by gas-fired pilot lights to produce the electricity that is then used to control the heating system. Also, radioisotope thermoelectric generators (RTGs) generator use thermopiles heated by the decay of plutonium.


 * Atlant (talk) 17:17, 21 January 2008 (UTC)

Twin earth
I've been thinking about a scenario which is essentially alternate history and I was wondering how plausible it is.

Imagine that alongside Earth, a second "sister" planet had formed alongside it "nearby". The two planets would be relatively similar in size, or perhaps one smaller than the other, I don't really mind. Some questions:

a) What is roughly the minimum distance the two planets must be from each other to form independently? Can one planet, if smaller or similar size, orbit around the other like our current moon?

I want to see if this distance makes it possible that whichever planet developed to our current technological level, they would do manned spaceflight to the other and inhabit it. Would these civilisations, if they did develop alongside each other fairly similarly, communicate once they developed radio transmission? Or sooner?

I would also like your general opinions on wether this scenario would make for an entertaining backdrop to a short science fiction story.
 * See Double planet. The earth-moon system is very close to being a double planet by the most common definitions. The minimum distance will be determined by the Roche limit. As for the SF idea: See Bob Shaw's Land and Overland triology, which has done this with a weird twist. BTW, a similar effect could be achieved by having several large inhabitable moons circling a giant planet (of course this has also been done in SF - IIRC, there are at least two instances of this in the Perry Rhodan series). --Stephan Schulz (talk) 18:32, 21 January 2008 (UTC)


 * Life would begin at a somewhat random time, and the probability of the two planets developing life withing a million years of each other is tiny. Even without the additional difference from when they evolve intelligent life, that would mean when one is technologically capable of moving to the other planet, the other wouldn't even have intelligent life. You could try to find some way to make both planets get close to intelligence but be unable to reach it due to some astronomical effect, then have that effect taken away, so they both start evolving intelligence at the same time. I don't know of any mechanism that would cause that, though. — Daniel 18:38, 21 January 2008 (UTC)


 * (written before above answers were posted) I think this is an excellent idea for a story, though it is not entirely original. See  Twin Earth thought experiment and imaginative news! and  Don't take this seriously!
 * I think that it is possible to have another similar-sized planet in synchronous orbit on the other side of the sun, but it would probably have been detected as long ago as Isaac Newton by its gravitational effects on the orbits of other planets. Another snag is that our earth is extremely unusual as a planet because of a collision with another planet long ago when our moon was formed ...  see ....  so even if the twin earth existed, it would not be identical.  Don't let this spoil your idea for a good story!  I vaguely remember seeing a similar science fiction story long ago, but I haven't found it yet.  Also see this..but remember to take your imagination and a cellar of salt with you! ''  d b f i r s   19:00, 21 January 2008 (UTC)


 * dbfirs is probably talking about Doppelgänger (1969 film) which posits a Counter-Earth.--Shantavira|feed me 19:08, 21 January 2008 (UTC)


 * A counter-Earth is a frequent staple of SF. See e.g.the Gor chronicles by John Norman. It has also been used in the German Mark Brandis juvenile SF series, and I suspect in oodles of books more. This is not, however, a gravitational stable configuration. Unless you propose some super-science or magic, the planets will not stay in the same orbit. --Stephan Schulz (talk) 19:13, 21 January 2008 (UTC)


 * No doubt an expert in orbital Newtonian Mechanics will correct me if I am wrong, but see Lagrangian point for positions of stable orbit.  Also see  Theia, the name of Earth's twin 4553 million years ago. ''  d b f i r s   19:29, 21 January 2008 (UTC)
 * (later) ... sorry, Stephan Schulz is correct, the L3 Legrangian point is stable only in the absence of other planets. You might also be interested in the first such theory:  Counter-Earth, where there is also a list of other stories which use this idea.  ''  d b f i r s   19:43, 21 January 2008 (UTC)
 * No problem. I was not offended ;-). Also note that of stability, the object at the Lagrange point is assumed to have negligible mass compared to the first two bodies. --Stephan Schulz (talk) 19:49, 21 January 2008 (UTC)
 * Thanks, though it's a pity the idea doesn't work. I suppose a massive object at this point will have short-term stability, which might be extended if the effects of other planets happen to cancel out, but I agree that long-term stability has an extremely low probability (weasel words for "impossible").  I presume that is why Theia collided with early Earth to form the moon 4553 million years ago, having formed at L3, if you subscribe to this explanation.  When I first read about it fifty years ago it was just one of several possibilities, but there is mounting evidence for the Theia origin of both our moon and the Earth's unusual iron core. ''  d b f i r s   20:02, 21 January 2008 (UTC)


 * I love the idea of two pre-spaceflight civilizations in a dual planet system communicating. (Even with the obvious unlikelyness of the timing of the two civilizations.) I wonder if they could communicate optically with giant mirrors. Even if they could signal each-other, it would be very difficult to work out a useful language. APL (talk) 02:51, 22 January 2008 (UTC)

do you know an antidote for peg intron?

 * I'm sorry. We cannot give medical advice beyond pointing you towards our articles on the immuno-modulator Peginterferon alfa-2a and PEGylation, and advising you to go back and see a heath professional about this. Rockpock  e  t  18:42, 21 January 2008 (UTC)

Little tiny flies on my chives!
The chives article suggests that chives have anti-pest properties but the chives that I've been growing in a pot on my windowsill are attracting lots of irritating little black flies. They fly in stupid random patterns and are pretty easy to squash (unresponsive compared to most flies that I encounter). Should I be concerned for the integrity of my chives? --Seans Potato Business 20:04, 21 January 2008 (UTC)
 * Sometimes I get aphids taht selectively attack plants from the onion family such as chives, garlic and onions. They will suck juice from the chives, make them have little yellow spots and reatard its growth.  You are beter off without them on indoor plants.  Outdoors there are ladybirds and butcher flies and wasps and spiders that will eat them for you.  The chives probably put off most other insects by their odour. Proably the garlic spary you can get will not kill them, but may be lavender will repell them, or soapy water can drown them, but be carefull not to taint your chives! Graeme Bartlett (talk) 05:15, 22 January 2008 (UTC)
 * Incidently, the flies might be Fungus gnats, in which case, they're in the soil, and not in the plants. They aren't necessarily harmful, but they might be a sign of overwatering.  But that doesn't change the fact that they are terribly annoying. --Mdwyer (talk) 18:22, 22 January 2008 (UTC)
 * Hi. The flies you describe seem very similar to the ones I notice all the time. I can't confirm this, but they seem more common in the warmer months. I don't know what they're called, but I think they are a very common pest in homes, maybe 5 to 10 times more common than the larger flies which are definately way more responsive than these. They seem to love to hang around plant material and decomposing matter around the house, such as some household plants, and a banana close to rotting on a piece of furniture would also do the trick. Just don't put your food that you're about to eat too close to the chives or the flies will get into the food. I think I've seen one of these flies land in my soup in some occasions, and it's not uncommon to see three or more in one place even if it's not your garbage, food, or plants. I'm not sure how to get rid of them, though, I'm not an expert on this. Hope this helps. Thanks. ~ A H  1 (TCU) 22:53, 23 January 2008 (UTC)
 * Yeah, I'm thinking it might be a case of the fungus gnats (linked above by Mdwyer (thanks, Mdywaer!)). I've adjusted my zealous watering regime and the problem appears to have subsided. Thanks, everyone! --Seans Potato Business 13:02, 25 January 2008 (UTC)

Spring Composition
I see in the wikipedia article on springs that most springs are made of hardened steel except in special circumstances. Is this choice primarily due to the ease of availability of steel, or is steel in fact the best material to make a spring out of? If not, what is? I think I'm looking for a material with the highest spring constant, which I think is related to the elastic limit of the material, but I can't put the dots together. Any help? gnfnrf (talk) 23:43, 21 January 2008 (UTC)
 * You might want to have resistance to rust and materials such as beryllium bronze may do the job. Alternative the spring may have to be lightweigtht, or of a particular colour, or designed to fail, then it may be plastic. Graeme Bartlett (talk) 01:17, 22 January 2008 (UTC)


 * To be effective, springs have to resist plastic deformation; harder materials are better at doing that than softer materials. So a spring made of hardened steel works better than a spring made of, say, solder. After that, it's a question of strength versus cost (and other parameters such as the corrosion resistance mentioned by Graeme Bartlett); hardened steel often wins on these bases.


 * Atlant (talk) 13:03, 22 January 2008 (UTC)


 * I wasn't quite clear in my original statement. Without special considerations, and without factoring in cost/availability, what is the best material known at resisting plastic deformation?  Is it simply the hardest material known?  This is where things stop making sense, because my puny earth-brain has difficulty comprehending a spring made out of diamond.  Would diamond in fact make a good spring?  As a last effort to compact my question, consider this.  A device needs to store energy in a spring, and is highly constrained in volume.  The device needs to store as much energy as possible, and cost is no object.  What material is the spring made of? gnfnrf (talk) 15:58, 22 January 2008 (UTC)


 * It's about elasticity, not hardness. Diamond is hard, but inelastic and would make a horrible spring. Rubber is soft but elastic and would make a good spring. Steel is hard and elastic, and would make a good spring. From what I can gather, if you want to make a coil spring, you want something with high shear strength. — Daniel 17:36, 22 January 2008 (UTC)


 * Within the limits imposed by its tendency to fracture, yes, diamond probably would make a good spring. Note that certain MEMS devices using "springiness" are frequently fabricated from silicon, another crystallne material.


 * Atlant (talk) 18:30, 22 January 2008 (UTC)