Wikipedia:Reference desk/Archives/Science/2010 April 22

= April 22 =

Dry ice engine
I built a dry ice engine (sort of like a steam engine) that works by exposing dry ice to ambient temperatures. It does not really run very fast even when I put shavings in water because the water often freezes. What I'm worried about is under what circumstances the dry ice can sublime. Can it sublime in an open container if I increase the temp of the container using solar radiation? 71.100.1.71 (talk) 06:18, 22 April 2010 (UTC)
 * Sublimation is the change from solid to gas, without melting and going through a liquid phase. Under normal pressures, dry ice always sublimes to CO2 gas. --Phil Holmes (talk) 08:37, 22 April 2010 (UTC)


 * Do you realise, that when the pressures are matched, it will not run as fast as a steam driven  engine anyway? Carbon dioxide is a heavy molecule and therefore will not expand as fast as steam.   You can work out the viscosity from these equations  . To get a more practical comparison, take three balloons. Fill one with carbon dioxide the second with air and a third with (say) methane;  and all to the same pressure (diameter). Use a felt tip pen to identify the gases within. Let them all go at once. You will see very clearly just how viscous the carbon dioxide is. --Aspro (talk) 10:43, 22 April 2010 (UTC)
 * You mean let them go with the opening not tied, right? Otherwise you would be seeing the difference in density. I would put my money on Hydrogen in either case, for it to rocket faster or rise faster. Edison (talk) 20:08, 22 April 2010 (UTC)
 * Right! Just let them deflate. I would put my money on hydrogen as well (but I suggested methane,  because   mains gas is commonly  available). This property of hydrogen,  is why it used as  the working gas for the Super High Altitude Research Project and of course -  fuel for rockets. Hydrogen and fluorine would be better,  as the mass is lower still – but I digress. I think this viscosity point, would help the OP not to bust a gut by trying to get  too much from his apparatus.--Aspro (talk) 22:13, 22 April 2010 (UTC)
 * Hydrogen is readily available, if you have a tank of dilute sulfuric acid with a couple of large carbon electrodes and a source of DC current as I do. In generating stations from the 1930's onward it was common to have giant high voltage generators filled with hydrogen, since it insulated and convected heat and had very low viscosity to interfere with the rapid rotation of the armature. It seemed nonetheless like madness to fill a big sparky generator with hydrogen (a la Hindenburg disaster) but the absence of oxygen in the generator enclosure allowed a successful and efficient operation of the generators. Edison (talk) 04:42, 23 April 2010 (UTC)

Galactic feature
On this cool website[ http://www.chromoscope.net/] you can see our Galaxy in all sorts of wavelengths. I'm curious: what's the feature above the galactic centre, visible in X-ray, hydrogen-alpha and microwave, but only vaguely in visible? --TammyMoet (talk) 08:33, 22 April 2010 (UTC)


 * You are probably referring to Galactic halo. We don't have much of an article on it, unfortunately; so library seems like the only option for now. --Dr Dima (talk) 09:29, 22 April 2010 (UTC)


 * I could be mistaken but I think the bright orange star under the blue stars in the region you are talking about is Antares, part of Scorpio. in X ray one of the objects you are talking about looks like a galaxy to the left of the top blue stars, maybe in the region of Messier_107 but i don't think it's that, i'm having a bit of a look and I can't see any big galaxies right there near scorpio.. I have to run away but i'm sure with some more digging you might find it.. Vespine (talk) 09:39, 22 April 2010 (UTC)
 * I just re read both posts and I'm not sure I'm talking about the same thing you are :) Vespine (talk) 09:41, 22 April 2010 (UTC)
 * If you look at it in microwave you can see a huge lump which looks like it's split off from the galaxy. In hydrogen-alpha it looks like two swirls, only one of which corresponds to the ?Antares region. It's within the Galactic halo, but is a clearly defined feature, and I wondered if someone could point me at more details for it, as it's not there in visible light. Oh and I don't know how to split off the new post from the bottom of this - can someone sort it out for me please? Thank you! --TammyMoet (talk) 10:49, 22 April 2010 (UTC)


 * I think you're referring to the North Polar Spur. It's thought it may be due to supernova remnant(s) that happened in our local part of the Galaxy. Unfortunately there doesn't seem to be a Wikipedia article on it. See for more info -- Stuart Lowe (Developer of Chromoscope) 130.88.24.249 (talk)  —Preceding undated comment added 14:28, 22 April 2010 (UTC). Apologies for not dating it; someone said 3 tildes inserted the date but they obviously didn't. (16:41, 22 April 2020)
 * Thanks for this but I'm still confused. If the blob at the side of it is Antares, isn't Antares in the southern hemisphere of the sky? I had thought it might be the rho Ophiuchus nebula, but I can't judge the scale well enough to determine whether the rho Oph nebula is part of the Antares O-B association, which would mean this blob is not that one. On a related topic, can anyone point me in the direction of a 3-D map of the Galaxy? Thanks. --TammyMoet (talk) 15:31, 23 April 2010 (UTC)


 * I've now had a chance to follow some of the links from our Milky Way article, and I concur with Vespine that the bright orange star is Antares. However, the hydrogen-alpha blob seems to be next to it, and I've not managed to track that down at all. (BTW thanks for sorting me out!) --TammyMoet (talk) 14:10, 22 April 2010 (UTC)


 * Just insert a ==New heading== in between. (done)


 * Just felt curious about one thing though, when we observe through X-rays the picture seems to be like torn up or clawed, as in like a punch or a strike from a tiger paw or something like that, which we cannot observe in any other image. what makes it so?

electromagnetic wave - atom - electrons
How can i make an arrangement to knock off electrons from an atom by making an electromagnetic wave of a particular wavelength,say radio wave, incident on the material? —Preceding unsigned comment added by Randeep d (talk • contribs) 10:25, 22 April 2010 (UTC)
 * How long do you want the electron to stay knocked off? If you want to "permanently" knock it off, or ionize the atom, that is much more difficult than "temporarily" knocking an electron into a different energy state.  If you just want to knock electrons around, you can use a semiconductor and use the electromagnetic wave to bump electrons into conduction bands.  You can do this with a lot of things; a photodiode is pretty cheap and safe, and whenever light (electromagnetic waves in the visible spectrum) land on it, it will produce a voltage, because electrons are getting "knocked" into conduction bands.  To completely ionize gas is more complicated.  You can make ionized gas in a lot of ways, especially if the gas is already at high (effective) temperature and low pressure.  This happens to some extent inside a fluorescent light bulb, (and to some extent, inside an incandescent lightbulb too).  A vacuum tube operates on the principle of freely flowing, thermally activated electrons, and could be considered a sparse plasma, where the quantity of excited electrons is controlled by an input electromagnetic signal.  If you move up to higher and higher frequencies, your radiation will be able to knock electrons off of atoms in almost any condition.  For example, a microwave oven, using microwaves, can ionize grapes (the grapes, being saturated, impure watery spheres, form conduction channels; as large currents start to flow, an effective high voltage electric potential builds up, locally concentrating the electric field near the grape, resulting in dielectric breakdown that ionizes the air and portions of the grape).  (The jury is out on whether this is safe).  Watch out with ionizing radiation in general, though, because if you have enough energy to ionize atoms, you have enough energy to potentially harm yourself.  Radio waves usually do not have enough energy to really ionize anything.  Nimur (talk) 12:02, 22 April 2010 (UTC)


 * As Nimur says, ionising atoms requires high energy/short wavelength photons - ultraviolet or shorter. And anything that can ionise your target substance can also ionise your own cells, which is potentially very harmful. You might want to take a look at our article on radiation shielding. Gandalf61 (talk) 12:14, 22 April 2010 (UTC)


 * It's worth stating that the microwave/grape experiment does not technically use ionizing radiation. As Gandalf just pointed out, direct ionization occurs at higher frequencies than microwaves operate at.  The grapes ionize as a secondary effect due to dielectric breakdown.  Nonetheless, this experiment can be harmful for other reasons, not the least of which is a fire hazard.  There are other, safer (read: "safer", not necessarily "safe") ways to get a similar breakdown: a spark gap can be formed using a piezoelectric barbecue igniter.  Or you can buy one of those plasma globe toys - because they have an evacuated gas chamber, they can operate at much lower, safer voltages.  Nimur (talk) 15:01, 22 April 2010 (UTC)


 * Didn't Einstein get a Nobel for explaining something like this viz the "Photoelectric effect?" Edison (talk) 04:37, 23 April 2010 (UTC)

so can i use a low intensity uv ray to knock out electrons..?? Which semionductor material shall i use & what about the distance betwen the radiator & the exciter module & will it be safe to use low intensity uv rays for the purpose..?? —Preceding unsigned comment added by Randeep d (talk • contribs) 12:34, 23 April 2010 (UTC)


 * You can use regular visible light, as I explained above, to activate the photoelectric effect. You can buy photodiodes on the internet, or at a local electronics store.  DigiKey is one such vendor.  This one is about $1 per unit, and should be sensitive to either infrared or visible light.  UV is more hazardous, not to mention harder for a hobbyist to produce, but there are definitely photodiodes that respond only to UV.  Nimur (talk) 14:08, 23 April 2010 (UTC)


 * Wouldn't a Photomultiplier tube be more fun than a photodiode? Edison (talk) 23:52, 23 April 2010 (UTC)

A dim Sparky?
(REVISED) I needed electric put in for a fan and had a person come in to run the electric for it. PROBLEM started when he noticed that 9 wires was going throught the 1/2" conduit. We removed the ground wire in which he decieded to run 2 more wires through, but they got stuck and we had to repull wires down and back through the conduit which got stuck. We spent 12 hours with just getting 1 wire through the (black), and found out that we could not use groung wires because they were used for the GFI brakers. these kept on popping when ever he connnected the common wire so he had to reattach all the wiring to the correct wires he had cut and did not label so that each room would work properly.(4) BEDROOMS I still did not have the wiring for the fan, or the conduit. I put in the box and the conduit for the fan, but I still have to get the common from the bathroom which does not have a GFI braker connected in the box in the basement, I hope this will work?? While here had to talk to someone else about this issu. If he were a licenced electrican should have know about GFI brakers. Instead my son-in-law fiquired out the problem and solution. But now that person who was here wants to charge $4oo SHOULD I say Yes and pay HIM or Not —or LOWER HIS PRICE?? —Preceding unsigned comment added by 24.15.246.106 (talk) 15:51, 22 April 2010 (UTC)


 * This isn't really a science question, and I'm not sure that it's really a Ref Desk question, but here goes:
 * You are free to negotiate a fair price. Either of you are free to take the other to court depending on how the payment process goes.  The usefulness of either procedure will vary depending on where you are.  Generally, though, for purposes of deciding fair payment, I'd consider the following:
 * Did he quote a price for the job beforehand? No Quote
 * Was the intended job completed?JOB WAS NOT COMPLETED
 * Did he consult with you before doing the additional work? he did but he wasn't to sure if it would worK. HE SHOULD OF THOUGHT OF IT BETTER.
 * Was the additional work relevant or necessary (to the job at hand, or to the safety of the house)?unnecessary
 * Particularly if the fan isn't wired yet, it may be reasonable to agree to pay him for the work done once the original job is complete. &mdash; Lomn 18:22, 22 April 2010 (UTC)


 * It sounds like he is not qualified enough to be allowed to finish the job!--Aspro (talk) 18:28, 22 April 2010 (UTC)He does this on the side (he does hvac)He consulted an electrician friend about the GFI AFTER HE HAD PROBLEMS RECONNECTING WIRESBACK UP.


 * One thing to think about is his side: He'll say, it's not my fault the wires got stuck, that's how your house was laid out, and I stuck by it and didn't give up till I finished the job (or as much as was possible). I am not telling you what to decide, I'm playing devils advocate a little, so you see his side, and maybe that can help you decide. Ariel. (talk) 19:07, 22 April 2010 (UTC)
 * Also, there are other ways of running wires if they won't fit through a conduit like that. The simplest would be to remove all the ground wires, and run a single fat one through the conduit, and then split them again after. You can theoretically do that with the white (neutral for those of you not in the US) wires too, but it's probably not to code. Don't do that with the black (hot, or what would be red in europe) one though. The correct way to handle that is a sub-panel. You run one large wire, then attach to a sub-panel with a small number of breakers to handle the rest. Ariel. (talk) 19:07, 22 April 2010 (UTC)He did pull the ground which still left 8 wires in the 1/2 in conduit.

Note: He said we did not need the green ground so that is what we used for pulling up the 2 wires for the fan. WE HELPED him throught the day to try to resolve the problem with getting wiring finished but to only got worse, finally got it done. that day


 * BTW, I'm not sure why the breaker kept popping when he hooked up the ground - is it a GFCI breaker? But that's is not normal, and possibly dangerous (sounds like electricity is flowing through the ground, and that's not normal), and I have to agree with Aspro that he sounds like he's over his head. Ariel. (talk) 19:16, 22 April 2010 (UTC)


 * Yes,. He is talking about ground-fault circuit interrupters not current trips. As he is using the $ sign, I presume he is in the US. Most states (I think) now  require companies to be licensed to do this kind of work and a sparky with such a permit would not make this sort of mistake. --Aspro (talk) 19:25, 22 April 2010 (UTC)


 * Anything said here is just as general information and not technical advice or consultation, per the rules of the Reference Desk. The explanation you gave does not really make sense as stated:"We spent 12 hours with just getting 1 wire through the (black), and found out that we could not use groung wires because they were used for the GFCI, and the bracker kept on popping when ever he connnected the groung so he had to reattach all the wiring to the correct wires he had cut so that each room would work properly." You pulled out 8 wires and tried to pull in 10, but could only pull in 9? How many circuits did the 8 conductors represent originally? By "groung" do you mean neutral? The National Electric Code (U.S.) has strict limits on how many conductors of what size and insulation type can be installed in a given conduit size. Table 3 of the NEC says how many conductors can go into a conduit of a given size. See for instance, which implies that 9 #14 XHHX (such as THHN) in a 1/2 inch conduit. Fewer could go in if the wires were larger, such as #12, or if the insulation were different, such as THW. Sometimes you have to run another conduit, or sometimes the loads can be reassigned to conductors, if a circuit is lightly loaded. Do not get creative if you don't know what you are doing. Only a licensed electrician should be doing the work for you. Edison (talk) 20:03, 22 April 2010 (UTC)
 * In rural or boondock parts of the US they do not use conduit, they use plastic jacketed "Romex" wire. There is also flexible metallic conduit called "Greenfield" and metal jacketed wire called "BX." A competent electrician can always run a circuit to where it is needed, but it may require some patching and painting of walls or ceilings, or removal and replacement of baseboards, or someone  going up into the attic or down in the crawlspace to run wires. Edison (talk) 23:49, 23 April 2010 (UTC)
 * Romex is not "rural or boondock". Romex is pretty much universal for home use in the US (although not for commercial). Ariel. (talk) 07:23, 26 April 2010 (UTC)

Abnormal daisy
Hello, I posted a question on mutants versus developmental abnormalities here. Maybe someone could take a look. Bye, Apdency (talk) 17:54, 22 April 2010 (UTC)

what do they do with the glass slides after a skin scraping test
do they throw them out or reuse them —Preceding unsigned comment added by Tom12350 (talk • contribs) 18:31, 22 April 2010 (UTC)


 * They cost about seven cents a piece. So on that basis it would cost more to wash and autoclave them, than use a new one each time.--Aspro (talk) 18:41, 22 April 2010 (UTC)

i agree it would be cheaper, but not all doctors are rational people? —Preceding unsigned comment added by Tom12350 (talk • contribs) 19:23, 22 April 2010 (UTC)


 * But they have to dispose of them as hazardous medical waste, which is expensive, so that might shift the economics some. Ariel. (talk) 19:23, 22 April 2010 (UTC)

what do you mean? —Preceding unsigned comment added by Tom12350 (talk • contribs) 22:41, 22 April 2010 (UTC)


 * We mean: that it is the opinion of some of us, that it is cheaper in pure financial terms, that the slides are used only once, and then get thrown away. In poorer countries, they could well get recycled.--Aspro (talk) 22:57, 22 April 2010 (UTC)

In the United States they are all thrown in a "sharps box" - same place the used needles are placed - and disposed of as hazardous medical waste. I cannot answer what happens in other contries. 65.96.208.10 (talk) 01:37, 24 April 2010 (UTC)

Orgasm
This might be an urban legend type of thing, but I remember hearing something about rats that were given the ability to make themselves orgasm by pulling a leaver, and they kept pulling the leaver until they starved to death.


 * 1) is this story true and is there a Wikipedia article on it?
 * 2) could the same technique to give a rat an orgasm be applied to humans?

Thanks 82.43.89.71 (talk) 18:48, 22 April 2010 (UTC)
 * What do you mean by 'leaver'? It dosen't make sense to me. Chevymontecarlo . 18:53, 22 April 2010 (UTC)
 * He means lever. In some parts of the US the regional accent is such that it's pronounced leaver rather than lever. (Although the spelling doesn't change of course.) Ariel. (talk) 19:19, 22 April 2010 (UTC)
 * I'm confused, do you mean "lea-" as in "lead" or as in "lead"? ;-) AlmostReadytoFly (talk) 08:54, 23 April 2010 (UTC)


 * See:Pleasure center for more info of this experiment. Dr Robert Heath was one of the first researchers that  did experiments on  human subjects. --Aspro (talk) 18:55, 22 April 2010 (UTC)


 * Peter Milner and James Olds did the rat experiments. Besides the Wikipedia article on the Pleasure center, see Life magazine's article on electrical stimulation of the brain and pleasure from March 8, 1963 "Behavior by electronics" by Robert Coughlin. The Olds experiments are discussed on page 100. The rat would press the lever 8,000 times an hour until fatigue, hunger or thirst forced a brief interruption for a sip and bite and a short nap, then he would be right back at it. One rat went on like this for 3 weeks straight. Some of Olds' rats, after a series of marathons lasting "hundreds of days" seemed in better health than their contro rats. Edison (talk) 19:33, 22 April 2010 (UTC)


 * That was quite interesting to read, especially how he used the same methods for mind control, with some talk on how to mind control humans too. But it's also interesting that nothing seems to have come of this research. You would think after 40 years we would have these devices commonly available, but no. So much for the rule that every new technology eventually gets used for war, or to control others. Ariel. (talk) 20:21, 22 April 2010 (UTC)

Thank you everyone for the links :) I'm interested in how their brains were stimulated; did they put electrodes on their heads or was more invasive surgery involved? 82.43.89.71 (talk) 20:10, 22 April 2010 (UTC)


 * The method used is roughly (and don't try this at home):
 * Shave the head, give broad spectrum antibiotic, give 'local' anaesthetic,  cut and fold back  a flap of skin and remove a small section of skull. Then  guide gold wire via an X-ray monitor. Wire is held in a jig to keep it steady. The subject has to be awake so that the exact position can be a confirmed by the subject. Gold is used: because it is inert in a way that stainless steel is not when passing a current. Actually, if your interested in electrical stimulation of the brain,  the guy that I think started it all off was   Wilder Penfield. His  biography here on Wikipedia does not do his work real justice. Surf around the web for more detailed information.--Aspro (talk) 20:56, 22 April 2010 (UTC)


 * For interest, the science fiction author Larry Niven portrays illegal use of such addictive technology, called 'Wireheading' as a serious social problem in several novels and stories in his 'Known Space' future history series. 87.81.230.195 (talk) 21:10, 22 April 2010 (UTC)


 * By the way, it seems logical that the rats were indeed obtaining pleasure by stimulating the part of the brain that the researchers dubbed the pleasure center; but I don't think the researchers ever alleged that the rats were giving themselves orgasms. Comet Tuttle (talk) 21:21, 22 April 2010 (UTC)

I'd like to point out that while this was certainly an important experiment, the results were not quite as shocking as they are often portrayed. As I understand it, the rats were given a choice of two levers to press: one would give them food, the other would give them stimulation of the septal area of the brain (a reward center). The parameters were set such that the rats needed to spend virtually all their time pressing the food lever to get enough food to survive. The outcome was that they spent some time pressing the reward level anyway, and therefore didn't get enough food. When rats are given reasonable amounts of food for each lever press, they don't starve in this way. In fact, rats won't continue to press a reward-stimulus level forever without stopping even if there is no penalty for doing so -- eventually they satiate on it. (Also Comet Tuttle is right that this has nothing directly to do with orgasm. Also I'm dubious about the gold wire business -- I've implanted stimulating electrodes in the brains of rats a bunch of times, and always used stainless steel, in part because gold wire is so soft that it bends too easily.  But the techniques have changed over time, and you'd have to look at the orginal paper to see what they actually did.) Looie496 (talk) 23:33, 22 April 2010 (UTC)


 * The original paper will probable just say 'gold wire'  but actually  be referring to wire  that has been plated in 'pure' gold. In the past, pins and screws for holding shattered bones together  had to be gold plated.  The were just called gold pins and gold screws without any reference to the substrate material. Even to day, such things as stents are often still gold plated, because they are more inert. . The data sheet for your stainless steel electrodes will probable state that it is 316LVM which is considered the modern medical grade.  (ladies; look on your body- piercing information leaflet, it will (should)  be mention there as well if it is stainless steel). Beware: if you brake a leg in some countries and get it pined, you might need to go back under the knife for a second time to have them removed again after the bones have knitted, as not every surgeon in the world uses this grade (check beforehand). For  electrodes in rats,  316LVM is  (I would think)  OK  for short term use. In  humans, I think  it is still gold plating for the terminals due to the problems you can run into with the interaction between electrode and tissue;  although the use of other materials are being explored. --Aspro (talk) 10:00, 23 April 2010 (UTC)


 * Descriptions above are not accurate in every case. Many experimental techniques have been used for stimulation of animal and human brains Rather than wire, which would basically short out to the scalp, the skull, and diffuse brain tissue, I recall people making electrodes which had glass insulation around the conductor. Tiny holes would be drilled through the rat skulls, and microelectrodes would be inserted using a stereotaxic apparatus, based on an atlas of rat brains. One article I found at Google Books said the rats with the pleasure electrodes would cross a shock grid on the floor to get the reinforcement, that rats who were starving to death would not cross to get food (old research methods were not always pretty). I once heard Milner give a lecture in which he showed cross sections of rat brains showing the pleasure centers, and related pathways, and cited the poem:  "In Xanadu did Kubla Khan, A stately pleasure-dome decree: Where Alph, the sacred river, ran, Through caverns measureless to man,  Down to a sunless sea." The fit of the words to the slides was eerie. Edison (talk) 04:25, 23 April 2010 (UTC)

Passive immunity in humans
How is passive immunity in humans only temporary? Chevymontecarlo. 18:56, 22 April 2010 (UTC)


 * Did you read passive immunity? It means that the antibodies are not made in the recipient, but rather are given from someone else. So once they run out the immunity stops. Ariel. (talk) 19:21, 22 April 2010 (UTC)


 * Yes, did I spell it wrong? The lack of a spellcheck function on the Windows machine I'm using is becoming annoying...at least on my MacBook it spell checks everything I type! :) Chevymontecarlo . 19:26, 22 April 2010 (UTC)
 * (Switch to using FireFox - it has spellchecking even under Windows) SteveBaker (talk) 20:03, 22 April 2010 (UTC)
 * I am guessing there are other meanings to this other than the one I am thinking about... Chevymontecarlo . 19:27, 22 April 2010 (UTC)

Eustachian Tube
How does pseudoephedrine help clear up excess mucus in the Eustachian tube? --Reticuli88 (talk) 19:30, 22 April 2010 (UTC)
 * Pseudoephedrine. --Dr Dima (talk) 19:54, 22 April 2010 (UTC)

nicotine gum expiration
i got some nicotine gum about 8 months ago. it has no expiration date on it. i used some today and it does no have any potency or "tingle". i felt no effects from it. is it expired. it used to work well 8 months ago —Preceding unsigned comment added by Tom12350 (talk • contribs) 20:12, 22 April 2010 (UTC)


 * It's heat liable (unlike raw nicotine). Have you stored it in a warm place?--Aspro (talk) 20:27, 22 April 2010 (UTC)

about 76-80 degrees —Preceding unsigned comment added by Tom12350 (talk • contribs) 00:19, 23 April 2010 (UTC)


 * Hello. If it doesn't tingle, then you definitely need new gum.  You, as someone who is familiar with relieving nicotine cravings, would be able to tell if it was good by judging its effectiveness.  You said it didn't work. ;)  Mrdeath5493 (talk) 07:40, 23 April 2010 (UTC)

Frequency of STDs in population
Recently a woman tried to pick me up, who was a complete stranger I had never seen before. It made me wonder - what on average are the chances of getting a sexual disease from an unprotected coupling with a) a random member of the population in the UK, and b) a promiscuous member of the population in the UK? I recall this poster http://bedazzled.blogs.com/bedazzled/2007/03/vintage_vd_post.html Actually, she was a young foriegn lady who from her pronounciation, did not appear to have been in the UK all that long. 78.149.175.91 (talk) 20:39, 22 April 2010 (UTC)
 * This page estimates that about 24% of people in the US have some sort of STD. Presumably the rates will be similar for the UK.  Keep in mind, though, that even if you have sex with someone with an STD, the chances of contracting it are much less than 100% (probably on the order of 1% with a latex condom, with a wide variation depending on the disease, whether she is symptomatic, etc.). Buddy431 (talk) 21:44, 22 April 2010 (UTC)
 * Isn't it likely that random strangers who seek to have sexual relations with as many people as possible are likely to have STDs? Edison (talk) 04:13, 23 April 2010 (UTC)
 * Epidemiology of herpes simplex lists numbers for Herpes (both HSV1 and HSV2) in a rather scattered manner. In some countries, HSV1 is present in as much as 80-90% of the population (and contrary to popular belief, both HSV1 and HSV2 can be found orally and genitally).  Depending on how you define "STD", and depending on where you are right now, you may already have one.  -- Jayron  32  05:16, 23 April 2010 (UTC)

Pumping seawater into the volcano crater
Would pumping a lot of seawater into the crater of the recent volcano have had any good effect? What would happen? Thanks 78.149.175.91 (talk) 20:48, 22 April 2010 (UTC)
 * Probably a very large explosion. The heat energy of any respectable volcano is sufficient to flash-boil into steam far more water than puny humans could shift its way. It was seawater getting into the innards of the 1883 Krakatau and ca 1600BCE Thera eruptions that caused their final explosions to be much more powerful than they otherwise would have been.
 * Possible results might include blowing a few cubic miles of Iceland into what vulcanologists technically call "smithereens", and sending Tsunamis to devastate much of the coastlines of the North Atlantic. So, not good, really. 87.81.230.195 (talk) 21:05, 22 April 2010 (UTC)
 * Also, underwater volcano still erupt, so it is not like a bit of water will stop the volcano from spitting out ash and lava. Googlemeister (talk) 21:28, 22 April 2010 (UTC)
 * For an entertaining fictional presentation of this idea, see Jules Verne's "The Mysterious Island". PhGustaf (talk) 21:36, 22 April 2010 (UTC)
 * We had this exact discussion just a few days ago - I suggest you check back through the archives. SteveBaker (talk) 00:50, 23 April 2010 (UTC)


 * Now, to be fair, sea water has been used to stop lava flows from volcanoes, see Eldfell, where pumped seawater was used to redirect lava flows away from a population center. However, stopping a river oozing rock is a different proposition than stopping a massive explosion; they are VERY different events.  As mentioned a few days ago, a volcanic eruption of the type going on at Eyjafjallajökull will be entirely, 100%, unaffected by spraying it with sea water.  Eruptions of this type are so large that nothing humans could muster would have any effect on it at all.  It would be no more effective than pissing on it.  -- Jayron  32  03:08, 23 April 2010 (UTC)


 * I agree with your assertion that it's been used to divert slow-moving lava flows far from the heart of the volcano. That's very different from what our OP is contemplating - which is pumping seawater directly into the caldera - which is a complete non-starter as an idea. SteveBaker (talk) 12:59, 23 April 2010 (UTC)


 * Part of me really wants someone to try pumping vast amounts of seawater into an erupting volcano, just for the fun of it. It's the same part of me that's getting impatient with the Yellowstone super-volcano and the San Andreas fault. I like big, loud geology! DuncanHill (talk) 14:59, 23 April 2010 (UTC)
 * Ha! You're such a catastrophe tart. 87.81.230.195 (talk) 17:38, 23 April 2010 (UTC)

Time machine
Hey everyone. My friend told me about a Discovery Channel program he'd seen, about how some scientists have taken the "first steps" towards making a time machine (haven't actually seen it myself). If I remember my high school Physics correctly, it is impossible to make a time machine because that would entail traveling faster than the speed of light, which is impossible because a) Celeritas is the fastest anything in the universe can go and b) Even reaching celeritas with a non-massless particle would require an infinite amount of energy, as energy also has mass ($$m=E/c^2$$). Can anyone clarify? 76.229.198.48 (talk) 20:52, 22 April 2010 (UTC)


 * We have a whole article on this: Time travel.  See also Category:Time travel once you're done.  Comet Tuttle (talk) 21:13, 22 April 2010 (UTC)


 * You're correct, with the caveat faster-than-light travel is just one way to travel in time that won't work. There are also other ways which won't work.  Or, strictly speaking, those other ways are presumed not to work because (a) traveling backwards in time wrecks causality, and (b) the laws of physics seem to very neatly protect us from most possible ways of traveling backwards in time, so we suspect that the remaining ones are impossible, too (for a similar argument, see cosmic censorship hypothesis).  Paul (Stansifer) 00:25, 23 April 2010 (UTC)
 * If that's the same programme I've also seen, the guy is Ronald Mallett. There's an extended discussion on his experiments on the WP article about him. ― _ _ _ A._di_M. (formerly Army1987) 09:28, 26 April 2010 (UTC)

I can time travel and do it on a regular basis, can only ever manage to go forwards though, one day at a time —Preceding unsigned comment added by 62.172.58.82 (talk) 14:34, 23 April 2010 (UTC)


 * But you don't jump one day at a time. You time travel with a speed of one day per day (there may be times where it seems from your point of view that you jumped around 8 hours). Should the SI unit for the speed of non-instantaneous time travel be s/s? Or maybe dimensionless? PrimeHunter (talk) 16:37, 23 April 2010 (UTC)


 * A recent article in Discover (magazine) postulates the possibility that the arrow of time is a lie. ~ A H  1 (TCU) 21:45, 23 April 2010 (UTC)

One stuffy nasal passage suddenly clearing itself... what physical mechanisms are at play?
This happens often enough to me that I assume it's a general characteristic of having a cold, and not some freakish personal medical event. When I have a stuffy nose, often only one side or the other is "stuffed up" - such that I can breathe through one nostril but not the other. Oftentimes, if I lay down such that the "stuffed" nostril is higher and the free nostril is closer to the bed and wait, eventually - and quite rapidly when it actually happens - the "stuffed" nostril will clear without any discharge.

I've always found this 1~3 second clearing process to be both peculiar (as one can certainly feel it happening) and interesting. Can anyone shed any light on exactly what is happening here? 61.189.63.145 (talk) 22:35, 22 April 2010 (UTC)


 * I always used to think a clogged nose is dried up snot or something like that. But actually it's inflamed blood vessels that swell up and block the passage. If you need temporary relief, try getting your hart rate up. For me if I run up and down some stairs about 5 times both passages open totally. Unfortunately they close again, but they will stay open at least long enough to blow your nose. Do NOT blow your nose while doing the running. The pressure from blowing will swell it up again. Wait until they are fully open, then blow your nose (if you need to). Ariel. (talk)


 * But of course we NEVER offer any medical advice. Edison (talk) 04:11, 23 April 2010 (UTC)


 * (ec)Yes, we are on(over?) the boundary here, Mr Edison. I thought that part of the effect here is that the "running" or other exercises releases natural adrenalin/epinephrine which has an effect similar to cold tablets, which often contain pseudoephedrine. It appears that both 'snot' and 'blood vessels' are involved, see Pseudoephedrine reduces snot (mucus) and vessel swelling (vasoconstriction). --220.101.28.25 (talk) 04:26, 23 April 2010 (UTC)


 * It is a normal and usually unnoticed feature of human physiology (and thus not in itself a medical question) that the inner tissues of the two nostrils swell and shrink slightly and oppositely in the Nasal cycle, so that while one nostril is, say, somewhat constricted but slowly widening, the other is a little dilated but slowly narrowing. Without a cold or similar infection that also swells the tissues, as Ariel mentions, neither usually becomes completely closed, but with one the more constricted phases can close one nostril completely while the other is still somewhat open, and a relatively short time later the positions reverse. The more sudden clearance probably occurs when the mucus is trying to drain due to gravity and its surface tension finally breaks. 87.81.230.195 (talk) 17:28, 23 April 2010 (UTC)

ghosts
I donot believe in ghosts ,then why i am afrid of it .Is this in our evolution —Preceding unsigned comment added by True path finder (talk • contribs) 22:52, 22 April 2010 (UTC)


 * My guess is you were told to be scared of them as a child, and you are unable to remove the fear even though logically you don't have it. To fix that, try to confront the fear over and over, and each time see that nothing bad happens, and even better give yourself a reward. This way you will change the association from "scary" to "reward". Ariel. (talk) 23:27, 22 April 2010 (UTC)


 * I recommend you read scientific scepticism and become a sceptical thinker. I'm sure your fear of ghosts will vanish.  Dolphin  ( t ) 23:31, 22 April 2010 (UTC)


 * It won't. Not from that. Fears are not logical. Ariel. (talk) 00:10, 23 April 2010 (UTC)


 * I disagree. Fears are perfectly logical. SteveBaker (talk) 00:42, 23 April 2010 (UTC)


 * Some are, some aren't. Phobias are irrational fears.  On the other hand, being afraid of jumping out of an airplane is entirely logical (especially if it's off the ground and you don't have a parachute). StuRat (talk) 13:56, 23 April 2010 (UTC)


 * Humans aren't naturally nocturnal animals. We've evolved to be active in daylight.  We're also 'pack animals' - we aren't generally loaners.  It's not surprising then that when we're forced to be unnaturally alone and in the dark, we're nervous and our senses are heightened as we try our best to figure out what's around us.  Sadly, our primary sense is sight - and robbed of that, we're pretty much left only with hearing - so the slightest sound could be a predator or something untoward like that.  Modern man hasn't lost that evolutionary history - however, we are generally unwilling to acknowledge that we have all of this ancient stuff driving our behaviors.  Primitive religions (and even some modern ones) tell us that the dead are all around us in "spirit" form - and some of us believe that too.  We also have Pareidolia - a strong tendency to take random-looking shapes and make human faces or figures out of them.  So what little sight we have left in the darkness is misinterpreted by our brains to make "ghostly" figures.


 * So we have a good explanation for everything we feel. Sadly, that doesn't stop us from feeling it because it's hardwired into our bodies at the genetic level.  When you are alone in the dark - make a game of working out what the heck that noise was - what is that weird looking shape?  You know for 100% sure it's not a ghost.  Carry a flashlight in your pocket...when you see something you don't understand - stop - try to guess what it "really" is - then use the flashlight to confirm your guess.  Do this enough and I guess you'll eventually stop making the assumption that there is something nasty there and start suspecting it's something innocuous instead.


 * SteveBaker (talk) 00:42, 23 April 2010 (UTC)
 * I'd like to add to Steve's assertion from a biological point of view. Humans are most vulnerable to predators at night (humans' ancestors did have natural predators, after all) when they are sleeping. It is in the night, therefore, that the sympathetic nervous system is most active, naturally. The sympathetic nervous system is responsible for emergency reaction, i.e., unmeditated, fast, fight-or-flight action. If we didn't have this, our ancestors would have been trying to figure out what the heck is going on rather than feeling the urge to run away from the funny noise in the bushes while they were being attacked and eaten. If we see something in the dark, we tend to be afraid of it even if we don't know what it is--the human who runs away from a misshapen bush lives another day, the human that sits and stares at the stalking leopard is eaten. I have to disagree with Steve's method of dealing with this fear--this amount of evolutionary hardwiring can't be conditioned out so easily. You can no more control your instinctive responses than you can control mine. --Douglas —Preceding unsigned comment added by 69.210.136.92 (talk) 03:25, 23 April 2010


 * I believe fears and phobias are partly evolutionary hardwiring, partly learned and partly peer-pressure. Education and positive-reinforcement experiences are widely used, successfully, to combat fear of flying, fear of heights etc.  Superstitions that endured for centuries have been largely eradicated by education in the developed world.  Where education is insignificant or non-existent, superstition persists, often as a means of dealing with fears.  Dolphin  ( t ) 03:48, 23 April 2010 (UTC)

The only reason anyone has to fear ghosts is that they represent some secret nameless fear deep in your psyche. In short, it's useful psychologically to fear something, and that something manifests itself in the whole 'ghost concept'. It's dark, muddy, and mystical territory, so I can't really go into any more detail. Suffice to say it relates to how you view yourself, in the context of your family, your ancestors, and the whole population of the world, deceased as well as alive. Vranak (talk) 02:55, 23 April 2010 (UTC)
 * There may well be some innate fear of "things that go bump in the night" along with ghosties and ghoulies. Spooks seem far less scary out in broad daylight. The distant ancestors of modern humans spent the night in trees or caves hoping that a predator or evil spirit would not "get them." Night fears may be a form of free floating anxiety. Isolation may be a factor as stated above. Edison (talk) 04:09, 23 April 2010 (UTC)
 * See ghost. Some fears are not rational as the fear itself may cause the outcome being feared to actually materialize. This is an example of a self-fulfilling prophecy. ~ A H  1 (TCU) 21:44, 23 April 2010 (UTC)