Wikipedia:Reference desk/Archives/Science/2007 April 24

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April 24

Mechanism of action of oral contraceptives

How do they work at the hormonal level? The wiki page on Combined Oral Contraceptives has only a painfully tiny paragraph on the anti-ovulatory mechanisms. I think both LH and FSH are suppressed in response to estrogen and progesterone, but what is the mechanism for this? Does low FSH inhibit folliculogenesis and low LH inhibit ovulation? Could an expert elucidate the question? (And post it on the wiki too: Hormonal_contraceptives & Combined_oral_contraceptive_pill ). Thanks.Horia 00:36, 24 April 2007 (UTC)

It's a negative feedback mechanism. When progesterone levels are up (in natural life this happens when the oocyte has ovulated, the corpus luteum that remains in the ovary produces the progesterone), FSH and LH levels are down (effect of progesterone levels on the hypothalamus that produces less gonadotropin-releasing hormone which in turn then does not stimulate the production of FSH and LH by the pituitary gland). FSH and LH are needed to stimulate the growth of a new oocyte (FSH) and to stimulate ovulation (LH). So if you keep progesterone levels up artificially, the chance of a new oocyte developing and of ovulation are very small because FSH and LH levels remain low. In real life, progesterone is produced by the corpus luteum, and the production of progesterone by this corpus luteum declines after two weeks when there has been no fertilisation of the egg, giving FSH and LH a chance to rise again, the whole cycle starting all over. If pregnancy occurs, the tissue of the embryo will keep the corpus luteum intact for more weeks and it will keep producing progesterone (until the placenta takes over this production of progesterone); thus keeping the womb lining intact (no menstruation) and keeping FSH and LH low (no new formation of new oocytes).

Also, the progesterone inhibits the growth of the womb lining, making the uterus an unfriendly environment for any oocyte that did manage to get there and get fertilized.

As I understood it, estrogen is not really needed in the pill for the anticonceptive function, but women tend to like it because it builds up a bit of womb lining, so in the stop week they experience a "normal" bleeding from the loss of this lining.

Some pills, and the anticonceptive injections and the implantation device that contains hormones indeed only have progesterone or progesterone-like hormones in it.

Huijts 19:24, 26 April 2007 (UTC)

Patina on a bronze surface.

I often restore bronze plaques/momuments in which I incounter a patina[oxide] on the metal which is almost always a green color.........Is there an acid,or some type of chemical in which I can use to get rid of the green patina [oxide]????? I now am having to get a wire brush and brush and brush and brush which takes alot of time getting off the green patina.

Sincerely,

Michael Lowe Shreveport, Louisiana —The preceding unsigned comment was added by 76.107.4.111 (talk) 00:54, 24 April 2007 (UTC).

Since bronze contains mostly copper, I would expect any polish that works on copper would work well here. If you don't want to buy anything, try using tomato juice or lemon juice from your kitchen, instead. Rinse them off afterwards. StuRat 04:27, 24 April 2007 (UTC)

Many acids dissolve the green patina, and the problem will be to stop the acid dissolving too much. A quick dip in hydrochloric acid removes the discolouration very fast, and leaves copper behind. But you have to rinse off the excess acid to stop corrosion happening again even faster. Vinegar from the kitchen will work slower as well. GB 12:05, 24 April 2007 (UTC)

Green patina is Copper(II) carbonate. Be careful of poison. Polypipe Wrangler 13:23, 24 April 2007 (UTC)

Oxalic acid is the ingredient in Bar Keeper's Friend which helps dissolve tarnish and discoloration on various metals. --LarryMac 15:03, 24 April 2007 (UTC)

Couldn't you do some kind of redox chemistry with another metal akin to the polishing silver technique by boiling it with Al foil. It's been a while since I've done this kind of chemistry, so I'm not sure if Al would work on Cu or what. Aaadddaaammm 00:28, 25 April 2007 (UTC)

Saturn V with Weather Balloons

I was wondering if this would work, could a rocket maybe not the massive size of the Saturn V rocket be tooken aloft with balloons or an airship then be launched into space? If so wouldn't this conserve fuel and possibly make the launch safer?67.126.241.201 03:39, 24 April 2007 (UTC)

You probably want to watch Mythbusters where they attempted to lift a child up with balloons. In simple terms, you will need a gigantic balloon for that (even bigger than Zeppelin) and would be uneconomical and impractical. However, there are attempts at using a high-altitude aircraft to launch space vehicles like the Virgin one (forgot the name). --antilived^{T | C | G} 04:08, 24 April 2007 (UTC)

...SpaceShip One. Gandalf61 09:03, 24 April 2007 (UTC)

See our Rockoon article.

Atlant 11:40, 24 April 2007 (UTC)

Thanks For the answers I just had the idea from spaceship one.67.126.243.117 01:56, 25 April 2007 (UTC)

Light and Water

Would a person get (essentially) any more or less sun, or any more or less tanned, swimming under a foot or two of water than he would if he were outside of the water right nearby? 70.108.191.59 05:34, 24 April 2007 (UTC)

Less, because water absorbs light, especially UV. Standing with your face and shoulders out of the water can cause severe burns, though. One reason is that the water splashing makes you not notice that tingle that means your skin is burning. Another is that sunblock tends to wash off. I think some UV may reflect off the water, too. StuRat 05:46, 24 April 2007 (UTC)

You can deduce what happens by looking at this handy chart! [1] -- mattb 06:16, 24 April 2007 (UTC)

That chart needs some interpretation. I believe it's saying that ultraviolet is blocked as well as infrared, red, and orange, while other visible colors pass through shallow water. StuRat 17:53, 24 April 2007 (UTC)

"Attenuated" is a better word than "blocked", and said chart shows absorptivity versus photon energy. As you can see, pure water is much more absorbant of UV and orange/red-IR wavelengths than violet-yellow visible wavelengths. Unfortunately that chart doesn't go further into UV range, but you can see the beginning of a characteristic absorption edge at higher energies. -- mattb 22:42, 24 April 2007 (UTC)

The biggest problem with that chart is that it doesn't label the colors and UV/infrared. This requires a lot of cross-referencing to figure out. Also, I wasn't sure if the poster would know what "attenuated" means. StuRat 07:52, 25 April 2007 (UTC)

The colors are apparent from the wavelength. I pulled that graph from a scientific journal where the readership is expected to know roughly what photon wavelengths/energies correspond to what color/type of light. If you'd like to re-create the graph with a convenient color bar, by all means do so. I only use "attenuate" because it's more accurate than "block". -- mattb 15:04, 25 April 2007 (UTC)

Right, but the original poster isn't likely to know which frequencies are which colors. I think the chart is good info, it just needed to be interpreted in a way that nonscientists can understand. StuRat 20:13, 25 April 2007 (UTC)

Permanent Magnets

What is the purpose of the keeper you get with some permanent magntes? —The preceding unsigned comment was added by 88.109.7.192 (talk) 06:05, 24 April 2007 (UTC).

If you're referring to the small plastic disks or rings that seperate the magnets when you get them, they are simply to prevent the magnets from touching. Many permanent supermagnets, in addition to being extremely strong, are quite brittle. If they are allowed to naturally come into contact, they can easily strike with enough force to chip off pieces. The plastic makes it easier to store safely, and remove from one another with less chance of losing your grip. Someguy1221 09:31, 24 April 2007 (UTC)

A metal "keeper" acts to "close" the circuit for the magnetic field; this preserves the magnetic strength of some kinds of magnets. Absent a keeper, some magnets will self-depolarize to a greater or lesser extent. (Remember, all those tiny little side-by-side magnetic domains are acting in opposition to each other, so they'd be much happier if half of them flipped around the other way. But that would leave no external magnetic field.)

Atlant 11:44, 24 April 2007 (UTC)

So which kind of magnets need a keeper and which dont? And why. I heard that the neodymium super strong ones dont need keepers. Why is that? —The preceding unsigned comment was added by 88.111.127.123 (talk) 13:29, 24 April 2007 (UTC).

Edison probably knows ('cause I sure don't). I hope he'll be along soon...

Atlant 14:35, 24 April 2007 (UTC)

A site where the neodymium magnets are sold [2] says that keepers are not needed with them, and that they retain 99% of their strength for a 10 year period, but their max operating temp is fairly low, (176°F (80°C). Steel and alnico magnets are sold with the keepers (a piece of soft iron to shunt the magnetic field between the poles). But on the other hand [3] provides a keeper with their horseshoe neodymium magnet. Edison 15:04, 24 April 2007 (UTC)

Well, a keeper also has the desireable property that it shunts the external magnetic field (so the magnet in your pocket doesn't suck any nearby screwdrivers into your thighs or other important co-located anatomical bits). So you might well use a keeper-like device to transport even those magnets that don't need them to stay magnetized.

Atlant 15:33, 24 April 2007 (UTC)

This question comes up often here on WP:RD/S. Our keeper page says "A magnet keeper is ferromagnetic bar placed across the poles of a permanent magnet that helps preserve the strength of the magnet by completing the magnetic circuit." I'll move that to a new magnet keeper page so people can more easily find it...now y'all feel free to add more actual content to that stub. DMacks 16:27, 24 April 2007 (UTC)

Hmmm. I always thought it was to do with the coercivity of the material. Our article states:

The coercivity of a material depends on the time scale over which a magnetization curve is measured. The magnetization of a material measured at an applied reversed field which is nominally smaller than the coercivity may, over a long time scale, slowly creep to zero. Creep occurs when reversal of magnetization by domain wall motion is thermally activated and is dominated by magnetic viscosity.

So is this the reason for keepers? If so how do they prevent demagnetisation? The statement above implies that thermal agitation is required. How much? —The preceding unsigned comment was added by 88.109.238.224 (talk) 23:31, 24 April 2007 (UTC).

That whole demagnetization discussion appears to be based on the magnetized material being in a field opposed to the magnetization. I've always thought of a keeper being used for "the magnet sitting around", i.e., in an effectively net-zero external field. Alternately, the completed magnetic circuit has substantially less net magnetization, so any external magnetic field (even a field induced in the environment by the magnet itself) will have less effect (as per the coercivity discussion). I'm pulling this out of memory and physics, not quite the level of WP:V needed for the Magnet keeper page:(. I think the Ferromagnetism page (especially the "Physical origins" section) has a nice discussion of the idea of domains within a material and their long-range (dis)ordering. DMacks 01:27, 25 April 2007 (UTC)

What I remember is that demagnetization is a thermally-activated process and depends on the level of the demagnetizing field within the magnetic material. A keeper reduces the magnetic resistance around the magnetic circuit, which reduces the demagnetizing field, ideally to zero. No (or low) demagnetizing field, no (or a low rate of) demagnetization, even over long time scales. Obviously, the magnet isn't very useful without allowing the field to flow through something other than the keeper, but use of the keeper during storage allows construction of magnets with higher external magnetic fields, for a given material, than would be stable without the keeper. I have a vague recollection that with some rare-earth magnets, keepers were not merely unnecessary, but undesirable, but that may be mistaken. I would love it if someone could correct me on this point.

Identify fruit

Identify the fruit. Flickr photo gives a better picture.

Hello! Could somebody please help identify this fruit/plant. It already has an article under its Malayalam name, Jambakka. The article needs to be moved to its English name (if any). I'd also like to know its scientific name. Thanks for the help!--thunderboltz^(TALK) 06:55, 24 April 2007 (UTC)

It looks a lot like a variety of loquat, but I'm not positive. —Steve Summit (talk) 12:03, 24 April 2007 (UTC)

Hmm... the article says it belongs to the Syzygium family, if that may help.--thunderboltz^(TALK) 14:18, 24 April 2007 (UTC)

Well, Syzygium jambos says it's also rendered "Champakka", so that would seem to match up nicely. --YFB ¿ 14:23, 24 April 2007 (UTC)

Thanks! I think I finally got it. Thanks for that link, Yumifruitbat. But I think the Syzygium jambos article is incorrect. The photos given in the external links don't at all look like the fruit. I followed some of the links there and finally landed on Syzygium samarangense, which indeed shows this fruit. The common English name seems to be Wax Jambu. I'll go ahead and redirect the article to Syzygium samarangense.--thunderboltz^(TALK) 15:11, 24 April 2007 (UTC)

Special Relativity: Time Dilation

This is a question from homework, but I seriously don't understand the answer. It is only with regard to special relativistic time dilation as well.

"A spaceship flies past a planet at .6c. The pilot and his girlfriend on the planet each wave at each other for 4.0 seconds. Calculate how long the pilot sees his girlfriend waving. Calculate how long the girlfriend sees the pilot waving."

Now firstly I've interpreted this question as saying that they each wave at each other for 4 of their own seconds, i.e. measured by a clock stationary relative to them. The answer I get for both is 5 seconds because I think they both see the other clock (moving relative to them) running slow, thus taking longer to tick 4 seconds. However, the text book states that the pilot sees his girlfriend waving for 3.2 seconds, while the girlfriend sees the pilot waving for 5 seconds. Where am I going wrong? --AMorris (talk)●(contribs) 12:20, 24 April 2007 (UTC)

Either the book is wrong (for special relativity) - or you are misreading/misinterpreting the question. The whole point of the word "RELATIVE" in relativity is that it applies to relative motion. The pilot is moving at the same speed relative to his girlfriend as his girlfriend is moving relative to him. For special relativity (which doesn't take into account the effects of gravity) - this is a symmetrical situation and both people must see the other waving for the same amount of time. Is it possible you've left out some key part of the question here? But then it's not exactly unknown for these textbooks to be wrong. SteveBaker 12:55, 24 April 2007 (UTC)

That's exactly what I thought. The question up there is copied word for word from the textbook, so I'll assume its just a mistake in the textbook, unless ive misinterpreted how they measure the 4.0 seconds however I cannot see any other way of interpreting it. Thanks for the answer anyway. --AMorris (talk)●(contribs) 13:24, 24 April 2007 (UTC)

You'd get different answers for general relativity - because the planet has a gigantic gravitational field and the spaceship doesn't - but we don't have enough information in the question to calculate that - we'd need distances and masses and such. So it's safe to assume special relativity only - so if you didn't leave anything out of the question - then I agree that the textbook must be wrong. Bizarre - but not unknown. My son is in high school and he and I have found close to a dozen serious errors in his physics textbook...and don't even get me started on his math book. SteveBaker 14:24, 24 April 2007 (UTC)

Here is how I think the confusion arose in the textbook. Person A waves at person B, and person B waves back. We have four space-time events - A starts waving (A1), B starts waving (B1), A stops waving (A2) and B stops waving (B2). When B sees A start to wave, B waves back, and B stops waving when they see A stop waving. So in B's frame of reference, A1 and B1 are simultaneous, as are A2 and B2. In B's frame of reference the waving lasts 4 seconds by B's clock. A relative speed of 0.6c gives a Lorentz factor of 1.25, so the waving lasts 5 seconds by A's clock.

However, in A's frame of reference, B still waves for 4 seconds by B's clock, but this is only 3.2 seconds by A's clock. A has still been waving for 5 seconds by A's clock, but B has only been waving for 3.2 seconds by A's clock. This is because in A's frame of reference, events A1 and B1 are not simultaneous, neither are A2 and B2. This demonstrates that simultaneity is relative. Gandalf61 15:15, 24 April 2007 (UTC)

The question has the situations of pilot and girlfriend being symmetrical - if the answer is not the same for both then there is something horribly wrong with your reasoning - but I'm too tired to figure it out! SteveBaker 13:01, 26 April 2007 (UTC)

So the question should have read:

"A spaceship flies past a planet at .6c. The pilot sees his girlfriend on the planet wave at him, and starts to wave back. After 4.0 seconds, he sees her stop waving, so stops waving himself. Assuming zero reaction time for the pilot, calculate how long the pilot sees his girlfriend waving.

Calculate how long the girlfriend sees the pilot waving."

Skittle 22:16, 26 April 2007 (UTC)

ugly spots in my cup

I just finished my diet drink and i left the cup sit there for a while. now there are ugly spots where the drops of coke used to be. is this the sugar or something left behind after the liquid evaproates?? and why dont these spots show up in regular coke? User:Maverick423 If It Looks Good Nuke It 14:07, 24 April 2007 (UTC)

Well, there must be lots of food coloring and such in there - when the lighter parts of the liquid evaporate, the heavier stuff gets left behind - and evidently that includes the coloring. As for why this might not happen with regular coke...are you SURE it doesn't? I'm pretty sure it does leave brown stuff behind when it evaporates. SteveBaker 14:19, 24 April 2007 (UTC)

You might enjoy our article about (the likely similar) coffee rings. It's only recently that physicists have come up with a nice, complete explanation for this phenomenon.

Atlant 14:39, 24 April 2007 (UTC)

heh thanks much =) User:Maverick423 If It Looks Good Nuke It 14:43, 24 April 2007 (UTC)

Even though cola might contain quite some strange ingredients to give flavour, I doubt that its dark black colour stems from anything else than simple caramel coloring, which is pitch dark already in very small concentration. Simon A. 18:22, 24 April 2007 (UTC)

E122 does that too, and it is pink.

Does what? Anyway, the coloring in cola is sulphite ammonia caramel (E150d). —The preceding unsigned comment was added by Sanders muc (talk • contribs) 20:45, 24 April 2007 (UTC).

Mile High Clouds

http://www.nytimes.com/2007/04/24/science/24cloud.html

April 24, 2007

First Mission to Explore Those Wisps in the Night Sky

By Kenneth Chang

Two hundred seventy thousand feet above the ground, higher than 99.9 percent of the earth’s air, clouds still float around — thin, iridescent wisps of electric blue. ...

Another mystery: noctilucent clouds in the Southern Hemisphere are about half a mile higher than in the north.

These clouds are "two hundred seventy thousand feet above the ground" and it's a mytery that some of them are "half a mile higher" than the others? -- Toytoy 15:20, 24 April 2007 (UTC)

That's kind of funny. Journalists often do not know the meaning of "margin of error." [Mαc Δαvιs] ❖ 22:05, 24 April 2007 (UTC)

Yes, but if the average height increases as you go south, that may be notable. Even if it's just half a mile, as long as it's consistent. kmccoy (talk) 06:23, 25 April 2007 (UTC)

If these clouds are the only clouds, then a steady increase in average altitude going south may be of importance. However, these clouds are not the only clouds on Earth. There are lower clouds. I don't know if the "half a mile higher" actually means some southern lower clouds were systematically excluded from the statistics. E.g., some Australian scientists could have excluded more lower clouds than their Canadian counterparts do. When multiple sets of observation data are combined, it looks like southern clouds are "half a mile higher."

And by the way, I really don't think the "half a mile higher" means anything without further information. The Earth is not a perfect mix of elements and chemical componds. There are gravitational, meterological abnormalities, ALL KINDS OF abnormalities. It would be funny if all clouds are on the same altitude. -- Toytoy 00:39, 26 April 2007 (UTC)

Aircraft mainplane

Can anyone tell me: What is an aircraft mainplane? What are the structural components of a mainplane? What are the two diffferent concepts for attaching mainplanes to the fuselage; the advantages and disadgantages of each?

Thanks,

Delali. —The preceding unsigned comment was added by Delalidei (talk • contribs) 16:22, 24 April 2007 (UTC).

Considering that you're asking a random collection of Internet nerds to do your homework for you, I think I'll be taking the bus from now on. ☹ --TotoBaggins 17:12, 24 April 2007 (UTC)

Impact crater

I found something on wikimapia at 16°19′23″S 34°5′39″E. The search for an impact crater in mozambique yielded nothing! Has anybody anything about it?--Stone 18:20, 24 April 2007 (UTC)

Can you provide a good pic ? Most of the sites at that link don't have decent pics. Many other things might look like an impact crater, like a bomb crater, a volcanic caldera, some open pit mine/excavation sites, and underground nuclear detonation or other explosion, sinkholes, etc. StuRat 18:52, 24 April 2007 (UTC)

Stu, just zoom out on Google maps. It's quite impressive, about 5 km across. -- mglg_(talk) 21:16, 24 April 2007 (UTC)

Here's a link.. Hybrid Photo. That definitely looks like a crater. But StuRat's right, it could be a very old caldera or abnormally large bomb crater. However, the fact that it appears to be covered with vegetation would rule out a pit mine or excavation site. The sheer size and age seems to rule out bomb, while the lack of any other mountainous formations nearby seems to rule out anything volcanic. Plus, I can't recall any 20th century military action in Mozambique that possessed the kind of military hardware needed to make a crater of that size.KelX - Retired Former Web God 21:20, 24 April 2007 (UTC)

I'd say that's a caldera. If you pan around a bit there's a number of smaller features which look somewhat cone-shaped. There's a small cluster to the north-east, another directly to the north and a fainter small cone thingy to the south. Admittedly that is rather a big caldera to be sitting all on its own, I still think it's volcanic. --YFB ¿ 22:16, 24 April 2007 (UTC)

Google Earth calls it Monte Muambe. Funny that we don't have an article on it. - AMP'd 22:37, 24 April 2007 (UTC)

The Mozambique Ministry of Mineral Resources & Energy website has a PDF here: Mozambique Mineral Resources PDF that says The Mt. Muambe is a carbonatite body located east of Moatize in the Tete Province. It's 780 meters high with a 6 km external diameter. KelX - Retired Former Web God 22:53, 24 April 2007 (UTC)

And according to the carbonatite article, that implies that it's volcanic, as YFB said. --Anonymous, April 24, 2007, 23:30 (UTC).

That was an unusual degree of collaboration. Good job, ref desk information sleuths. - AMP'd 02:38, 25 April 2007 (UTC)

Maybe I'm looking at it wrong, but it looks like a circular trench with a rounded hill in the middle which is higher than the crater rim. This isn't what you'd expect from a meteor crater, they only have a small protrusion in the center, if any, typically. Do we have a contour map available ? StuRat 07:48, 25 April 2007 (UTC)

Many Thanks here you get the real help when! With this help I found something on the Mt. Muambe: Nevertheless, Afonso et al. (1998) provided evidence that the Xiluvo carbonatite, together with Muambe, presents a ring structure, with a sequence of pyroclastic deposits and lavas, breccias and fenites from the centre to the rim of the intrusion. from L. Melluso; P. Censi; G. Perini; L. Vasconcelos; V. Morra; F. Guerreiro; L. Bennio (2004). "Chemical and isotopic (C, O, Sr, Nd) characteristics of the Xiluvo carbonatite (central-western Mozambique)". Mineralogy and Petrology. 80: 201–213. doi:10.1007/s00710-003-0027-z. {{cite journal}}: Unknown parameter |last-author-amp= ignored (|name-list-style= suggested) (help) looks like it is a vulcanic crater--Stone 22:01, 25 April 2007 (UTC)

I create a small stub about the Monte Muambe vulcano.--Stone 08:23, 26 April 2007 (UTC)

Thanks for improving Wikipedia. StuRat 05:07, 27 April 2007 (UTC)

birefrengent pump laser filter

what is the optical axis of crystal quartz birefrengent pump laser filters. kirb —The preceding unsigned comment was added by 66.13.196.154 (talk) 19:32, 24 April 2007 (UTC).

Off the top of my head, I'm not sure, but you can ascertain this from the material's dielectric constant (or refractive index) tensor. I'd search for that. -- mattb 19:52, 24 April 2007 (UTC)

You should give a bit more context instead of just a long list of nouns. While there might be a lot of reasons to send a laser beam through a birefringent crystal I cannot imagine why you would want to do so with the pump beam. Further, if you mean by "filter" a frequency filter: birefringent quartz is colourless. Perhaps start with reading birefringence and then tell us what you want to do. Simon A. 20:43, 24 April 2007 (UTC)

Just googling around a bit, it looks like they are used as tuning elements inside the cavity of dye and ultrafast lasers. They are operated at the Brewster angle, and apparently at least sometimes cut parallel to the optic axis [4]. On the other hand, according to [5] there was a 1974 paper (G. Holtom and 0. Teschke, “Design of a birefringent filter for high-power dye-lasers,” IEEE J. Quantum Elecrron., vol. QE-10, pp. 577-579, 1974) that said it is more efficient to have the optic axis dive at 25° into the plate. I have no idea which is more common, but if you just do the google search on (optical axis quartz birefrengent pump laser filter) you should be able to figure that out. --mglg_(talk) 21:05, 24 April 2007 (UTC)

What compounds are created by an antacid and stomach acid?

Since the stomach contains (mostly) hydrochloric acid, (HCl) If you eat an antacid tablet containing calcium carbonate, (CaCO3), what are the resulting compounds of that reaction? I specifically want to know what gas or gases are released in a CaCO3+HCl induced belch. KelX - Retired Former Web God 21:11, 24 April 2007 (UTC)

Carbon dioxide, CO₂. --mglg_(talk) 21:19, 24 April 2007 (UTC)

Thanks for the quick reply, mglg. Now, what other compound(s) are produced by the Ca, Cl, and H left after the CO₂ forms. If I'm not mistaken, it's CaCl₂. If so, what happens to the Hydrogen? KelX - Retired Former Web God 22:45, 24 April 2007 (UTC)

CaCO₃ + 2HCl → CaCl₂ + CO₂ + H₂O. See calcium carbonate. --mglg_(talk) 00:11, 25 April 2007 (UTC)

Influenza Vaccination

Hi, Hopefully someone will be able to answer my question. Can you contract the illness Toxic Shock Syndrome (TSS) when recieving the Influenza Vaccination.

81.101.49.156 21:22, 24 April 2007 (UTC)Chrissy

To the best of my knowledge, TSS has never been associated with the influenza vaccine. PubMed doesn't return any hits using any of the most likely keywords, suggesting that there isn't any research or case studies linking TSS and the flu vaccine. I suppose that in principle TSS could be caused by a badly-contaminated vaccine, but again I haven't been able to turn up any reports of this actually happening.

On the other hand, TSS has been identified as a (rare) complication of influenza infection. See for example JAMA report (abstract only without subscription) and sample case report from the CDC. TenOfAllTrades(talk) 22:11, 24 April 2007 (UTC)

Toxic shock syndrome is the result of bacterial toxin. For an influenza vaccination ot cause TSS, the vaccination would somehow have to induce, stimulate, or enable a bacterial infection. This would require a really long chain of events. Any needle stick with a non-sterile needle can in theory result in a bacterial infection, even a stick with a sewing needle, but this type of infection does not generally result in TSS: tetanus is more likely. If the influenze vaccine is an "attenuated virus" you might get influenza, which might (I suppose) lead to a bacterial infection (such as a sinus infection,) but this sequence is more likely if you decline the vacinnation and get the flu as a consequence. -Arch dude 01:01, 25 April 2007 (UTC)

Identity of indiscernibles (2 objects possessing the same properties are the same object?)

This is a question about the Identity of indiscernibles article in wikipedia. I don't know if this belongs in the science section but I didn't receive any answers to my main question when I posted it in the Miscellaneous section. So the question is: Is the position in space and time of an object a property of that object? The identity states that, all properties being equal, the two objects must be one and the same. If it is true that this does not include the position of the object, I do not know how the indentity can be justified if one imagines the existance of two elementary particles (eg 2 electrons). Aren't the particles equal in all respects other than their position?64.230.99.159 22:37, 24 April 2007 (UTC)

Two elementary particles can occupy the same space, eg two electrons of opposite spin. or two or more photons can pass through the same space time point. In the semantic or database sense, the position at a point in time is a property of an object. However an issue arises with coordinate systems. The ones we are familiar with are tied to the earth and so are moving, with respect to other things in the Universe. However it makes no difference to the identity. In quantum wave theory a particle can be in several places at once (with less than 1 probability), and as your example of elementary particles indicates they may be indistinguishable. GB 00:34, 25 April 2007 (UTC)

The Identity of indiscernibles article is about philosophy, not science. The principle is used routinely in logic, algebra, and all higher mathematics. : if x=b+c, and y=b+c, then x=y: that is x and y are the same.

However, the principle does not not apply directly to object in the universe. "indistinguisanble" is not equivalent to "the same." consider a two photons of exactly the same wavelength and polarizatin when measured in the same relative frame. They are identical except for their six-dimensional differences in location and direction(three spatial dimensions, one time, and two dimensions to indicate direction of travel.) these two photons have different effect on the rest of the universe, so they are distinguishable.

Now so arrange the universe such that the two photone pass through a combiner at the same instant, such that they have identical six-dimensional vectors: they occupy the same space ateh same time and travel inthe same direction. The two are completely indistinguishable. They are still not the same: the universe can determine the difference between one photon with this six-vector and two photons with this six-vector, so the universe "knows" that there are two photons, not one, even though the univers cannot distinguish the photons. The universe can tell the difference because by measuring the mass of the photons, by observing the effect of the mass on other particles. -Arch dude 01:34, 25 April 2007 (UTC)

I would say that the original questioner has a point. Two elementary particles are indeed, in a way, not only indistuiginshable, but also indiscernible. Let us start with bosons, to make things easier: If I exchange two identical bosons, i.e. make them exchange their positions, nothing at all changes. As long as quantum mechanics is correct, no experiment in the world can can tell the difference, and from a positivist viewpoint, it seems justified to claim the two configurations to be identical. This is also reflected by thet fact, that according to bosonic particle statistics, the wave function, which is deemed a complete description of a quantum mechanical situation, is unchanged. It is illuminating to see how Bose found Bose-Einstein statistics: He tried to demonstrate to his students how one can derive the Maxwell-Boltzmann statistics (and so, Planck's law), from combinatorical first principles and forgot to take into account the factor for the number of possible permutations of the identical bosons. He was first embarassed about this mistake, then very surprised to get the right result nontheless and realized that he must not count permutations as they leave the configuration identical. Also, look at Bose-Einstein condensation to see how condensed bosons are not only indistuingishable, but due to their shared wave function (i.e. position), in a way even indiscernable. Admittedly, this viewpoint is just that, a philosophical point of view, shared by many but not all physicists.

A classic is the following story, told by Feynman in his Nobel prize lecture:

As a by-product of this same view, I received a telephone call one day at the graduate college at Princeton from Professor Wheeler, in which he said, "Feynman, I know why all electrons have the same charge and the same mass" "Why?" "Because, they are all the same electron!" And, then he explained on the telephone, "suppose that the world lines which we were ordinarily considering before in time and space - instead of only going up in time were a tremendous knot, and then, when we cut through the knot, by the plane corresponding to a fixed time, we would see many, many world lines and that would represent many electrons, except for one thing. If in one section this is an ordinary electron world line, in the section in which it reversed itself and is coming back from the future we have the wrong sign to the proper time - to the proper four velocities -- and that's equivalent to changing the sign of the charge, and, therefore, that part of a path would act like a positron."

Simon A. 11:23, 25 April 2007 (UTC)