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::P.S. I appreciate the source used in our article and the ones I could find aren't that great sources. E.g. as this source [http://www.plannedparenthood.org/files/9313/9611/6384/truth_about_condoms.pdf] I saw in our article on condoms mentions, there are a lot of rumours and poorly supported information when it comes to sexual health and preventing pregnancy, even those without a religious reasoning and coming from health advice sources, such as that about "double bagging". I did have a look for more scholarly sources and couldn't actually find any that took a good look at the effectiveness of spermicide lubricated condoms at preventing pregnancy. Heck even this very old source [http://www.sciencedirect.com/science/article/pii/0010782475900670] which appears to have been around the time these were first made, only seems to have looked at the effectiveness in a certain group rather than in comparison to condoms without spermicide. I did come across [http://informahealthcare.com/doi/abs/10.1080/ejc.7.3.173.177] which is perhaps an interest source if you can get it for a somewhat old overview of spermicides in general. I'm not sure why there appears to be so little research on the effectiveness of spermicide lubricated condoms at preventing pregnancy. It may be that research on spermicides in general suggest the amounts used with condoms is probably too small to be of much use. (One source or more sources I read [http://link.springer.com/chapter/10.1007/978-0-387-48740-3_10] did note there may similarly be a lower risk of many of the complications due to the lower levels. That said, one of the papers on the risk of UTIs was specifically related to spermicide lubricated condoms, although having had a quick look at the paper, they also found a smaller higher risk for people who used condoms in general.) It may also be because while preventing pregnancy is important for many, there are a number of resonably effective methods for pregnancy prevention (with different costs, benefits and risks) but barrier methods particularly condoms, are the only effective method for sexually active people to protect against STIs particularly HIV. And so the recent research focus on condoms with spermicides has been about STIs and similar stuff. (One of the factors may have been there was an interested in condoms lubricated with spermicides to prevent STI particularly HIV transmission due to some ''in vitro'' evidence. However further research didn't show this ''in vivo'' and combined with the possibility of increasing risk due to the complications from long term meant there was a move away. There is or was still a hope that a perhaps spermicidal agent can be found which would help reduce the risk of HIV transmission and has few complications.) It may also be the concern is when condoms are already lubricated with spermicide, the users don't think much about whether they should be using spermicide so it's better if these are seperate so there's proper consideration of the benefits and risks and times to use them (which is possibly only vaginal sex). Either way, it does seem there has been a move away from them. And it definitely seems misleading to suggest as was done above that it's wrong to state "condoms lubricated with spermicide are no more effective than condoms without it". From the evidence available, I don't think we can conclude this is definitely the case, but we also can't conclude it's wrong. [[User:Nil Einne|Nil Einne]] ([[User talk:Nil Einne|talk]]) 12:47, 5 February 2015 (UTC) |
::P.S. I appreciate the source used in our article and the ones I could find aren't that great sources. E.g. as this source [http://www.plannedparenthood.org/files/9313/9611/6384/truth_about_condoms.pdf] I saw in our article on condoms mentions, there are a lot of rumours and poorly supported information when it comes to sexual health and preventing pregnancy, even those without a religious reasoning and coming from health advice sources, such as that about "double bagging". I did have a look for more scholarly sources and couldn't actually find any that took a good look at the effectiveness of spermicide lubricated condoms at preventing pregnancy. Heck even this very old source [http://www.sciencedirect.com/science/article/pii/0010782475900670] which appears to have been around the time these were first made, only seems to have looked at the effectiveness in a certain group rather than in comparison to condoms without spermicide. I did come across [http://informahealthcare.com/doi/abs/10.1080/ejc.7.3.173.177] which is perhaps an interest source if you can get it for a somewhat old overview of spermicides in general. I'm not sure why there appears to be so little research on the effectiveness of spermicide lubricated condoms at preventing pregnancy. It may be that research on spermicides in general suggest the amounts used with condoms is probably too small to be of much use. (One source or more sources I read [http://link.springer.com/chapter/10.1007/978-0-387-48740-3_10] did note there may similarly be a lower risk of many of the complications due to the lower levels. That said, one of the papers on the risk of UTIs was specifically related to spermicide lubricated condoms, although having had a quick look at the paper, they also found a smaller higher risk for people who used condoms in general.) It may also be because while preventing pregnancy is important for many, there are a number of resonably effective methods for pregnancy prevention (with different costs, benefits and risks) but barrier methods particularly condoms, are the only effective method for sexually active people to protect against STIs particularly HIV. And so the recent research focus on condoms with spermicides has been about STIs and similar stuff. (One of the factors may have been there was an interested in condoms lubricated with spermicides to prevent STI particularly HIV transmission due to some ''in vitro'' evidence. However further research didn't show this ''in vivo'' and combined with the possibility of increasing risk due to the complications from long term meant there was a move away. There is or was still a hope that a perhaps spermicidal agent can be found which would help reduce the risk of HIV transmission and has few complications.) It may also be the concern is when condoms are already lubricated with spermicide, the users don't think much about whether they should be using spermicide so it's better if these are seperate so there's proper consideration of the benefits and risks and times to use them (which is possibly only vaginal sex). Either way, it does seem there has been a move away from them. And it definitely seems misleading to suggest as was done above that it's wrong to state "condoms lubricated with spermicide are no more effective than condoms without it". From the evidence available, I don't think we can conclude this is definitely the case, but we also can't conclude it's wrong. [[User:Nil Einne|Nil Einne]] ([[User talk:Nil Einne|talk]]) 12:47, 5 February 2015 (UTC) |
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:In response to the specific question about semen residue, I looked at the sources from [[Condom#Causes of failure]] where this claim is present. There are two papers. |
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:One a metholodogy verification paper with a relatively small sample size [http://www.sciencedirect.com/science/article/pii/S0010782499000980]. It seems semen residue primarily means prostate-specific antigen, although there was also a check for sperm in some cases. (The check for sperm found it in a few cases without PSA and even when there was claimed abstinence for 24 hour or more but always at low levels. In the PSA cases, sperm was always found, but sometimes at low levels. PSA was always found in samples taken immediately after unprotected sex, but never after 24 hours. BTW, to avoid confusion, I don't think sperm at the low levels was counted as a 'semen residue', actually the primary intention of one of the papers seems to have been to demonstrate that PSA seems to be a better indicator of recent "seminal exposure" than sperm.) |
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:Anyway in this paper, they didn't include any cases where PSA was found in the pre-coital samples. And whether due to this, the small sample size or whatever, there was no PSA found in those cases that were considered where there were no reported problems with the condom. |
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:Note also that samples collected after 72 hour abstinence didn't contain any PSA. BTW, all female participants had tubal ligation (and part of the study included unprotected sex as well participant punctured condoms). One final interesting thing is that even in cases where breakage or slippage did occur, PSA levels did vary wildly. |
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:The second paper is where PSA was detected in some cases with reported failure is interesting [http://www.sciencedirect.com/science/article/pii/S001078240400157X]. Although in the earlier methodology paper by largely the same authors it was suggested (as was done in that case) that pre-coital samples should be taken to rule out PSA being present from a previous sex act, it doesn't sounds like this was done here. May be they had found this was too odorous and so lead to low compliance. It's also possible they felt it wasn't that important since PSA doesn't generally seem to be detectable for long and the couples were supposed to record coital acts etc in a diary (and so if they didn't comply there, they may not have properly complied with the pre-coital swab anyway). |
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:They do mention it's possible the PSA came from unreported previous unprotected sex. (This being a different sexual partner as suggested above could be one reason it was unreported, but there could also be other reasons ranging I'm guessing from the partners bringing drunk, to one of the partners not knowing.) They don't mention sabotage. They do mention undetected failure is unlikely, but I'm a bit confused whether they're saying they don't believe the cases were undetected failure, or they think if it does occur, it's low as evidenced by only find the 1.2% of cases with PSA without reported breakage/failure. |
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:Interesting of the 3 cases where they did find PSA, 2 of them had it at a low level, significantly below that expected from unprotected sex (so whether the sex had been a while, or it wasn't unprotected, who knows). One of these cases (I presume the one with the higher level of PSA, but this isn't stated) did have a clinically significant level of sperm. |
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:Anyway beyond the suggestion it could be due to unreported unprotected sex, they don't actually comment much on the 1.2% of cases with PSA without reported failure, I think the general point is the rate was fairly low and it's ultimately impossible to know from their results why PSA was detected despite their being no recorded failure. Note that they did have 2 pregnancies in couples where no failures were recorded and the instructions are supposed to have been followed every time. (They also had 8.1% of their participants withdrawing of the research due to breaking up.) |
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:[[User:Nil Einne|Nil Einne]] ([[User talk:Nil Einne|talk]]) 14:30, 5 February 2015 (UTC) |
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== [[cold dark matter]] and nuclei == |
== [[cold dark matter]] and nuclei == |
Revision as of 14:30, 5 February 2015
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February 1
Q-Spoil
Came across this Q-Spoil article in the orphanage, it has no sources and I can't find any reference to the term via Google, anyone know if such a thing exists?— Preceding unsigned comment added by Vrac (talk • contribs)
- I can't find anything. WP:PROD may be appropriate to use here: Tagging it for prod would give anyone who cares time to fix it up, but if no one is caring about it, then it can be deleted. --Jayron32 02:05, 1 February 2015 (UTC)
- Cheers, prod it is. Vrac (talk) 02:30, 1 February 2015 (UTC)
- It's definately a thing, though I cannot judge its notability: [1] [2] [3]. I suspect, from the third link, that it may be a particular application of the Kerr effect. --Tagishsimon (talk) 02:43, 1 February 2015 (UTC)
- Cheers, prod it is. Vrac (talk) 02:30, 1 February 2015 (UTC)
- The PR encyclopedia of laser techniques doesn't mention "q-spoil", and Google searches turn up zero relevant hits. There is a thing called the "Q-factor" of a laser, and a technique for producing short pulses called Q-switching (both of which we have articles about). So I'm kinda suspicious that this is way, way too obscure for an article. With no references whatever, no other articles linking to it, and after languishing for 8 years with essentially zero improvement having been done on it - this article shouldn't be here. If it's a real thing then a line can be written about it in some other article. SteveBaker (talk) 03:57, 1 February 2015 (UTC)
- I've redirected the article to Q-switching, for which it is a synonym, at least in the context of laser switching. A search in GBooks and GScholar shows a number of sources verifying its existence. --Mark viking (talk) 05:04, 2 February 2015 (UTC)
evolution of bacteria and washing
Apart from evolution of bacteria to resist our antibiotics, has there been any detected evolution to resist being washed off by water or by soap and water from human skin? Or maybe evolution to appear "less dirty", give less of a "sticky sensation" on skin? Is this kind of evolution expected to happen by scientists? Thanks. Rich (talk) 04:21, 1 February 2015 (UTC)
- Washing them off should put less evolutionary pressure on them to adapt, since presumably they survive either way. So there's no effect that those that manage to stick to the hands are more likely to survive and pass on those genes. StuRat (talk) 06:11, 1 February 2015 (UTC)
- Agree with that, but see Antibacterial Soaps Concern Experts which says; "recent research suggests these products [anti-bacterial soaps] may encourage the growth of “superbugs” resistant to antimicrobial agents". Alansplodge (talk) 16:58, 1 February 2015 (UTC)
- I'm guessing the development of superbugs can occur with antibacterial soaps due to the antibacterial properties killing some of the bacteria. I'm assuming he meant washed off as in came off the hands and went somewhere else, in that case the bacteria are still alive. 70.210.72.107 (talk) 02:47, 3 February 2015 (UTC)
- Agree with that, but see Antibacterial Soaps Concern Experts which says; "recent research suggests these products [anti-bacterial soaps] may encourage the growth of “superbugs” resistant to antimicrobial agents". Alansplodge (talk) 16:58, 1 February 2015 (UTC)
Incandescent light bulb history
Just watched the PBS show on Thomas Edison, and I have a question. The incandescent light bulb was eventually perfected by using a thin tungsten filament and evacuating the bulb of air. Before that, light bulbs would burn out in a few minutes. But, it seems to me, that another approach would have been to just use a thicker filament. After all, electrical resistance space heaters manage to produce a red glow with exposed wire coils. They do use a fan, but is that required to keep them from burning out quickly ? I'd think a bit less electricity and no fan would keep it red hot, but no hotter, so the wires would last. Now, admittedly red light isn't ideal, and all the excess heat would be annoying in summer, but perhaps quite welcome in winter. When compared with the poor choices available before Edison took on the light bulb, it seems to me that my approach would have been a welcome alternative to gas lights, for indoor lighting. StuRat (talk) 06:08, 1 February 2015 (UTC)
- Actually the tungsten filament represented the second generation of light bulb, allowing higher temperatures and therefore whiter light. As you will see at the Edison article you linked, Edison's bulbs that lasted for over 1,000 hours had carbon-based filaments. --65.94.50.4 (talk) 10:06, 1 February 2015 (UTC)
- I was brought up in gaslight, supplemented by paraffin lamps, before electricity reached the area where I was born, and I can assure you that it was far superior to the dull red glow from an electric filament in air. It is easier to read by firelight than by (exposed filament) electric heater light. Nichrome wasn't patented until 1905, but perhaps similar materials were available earlier for heaters. Dbfirs 07:20, 1 February 2015 (UTC)
- The article incandescent light bulb in the Joseph Swan "On 18 December 1878, a lamp using a slender carbon rod was shown at a meeting of the Newcastle Chemical Society, and Swan gave a working demonstration at their meeting on 17 January 1879......These lamps used a carbon rod from an arc lamp rather than a slender filament. Thus they had low resistance and required very large conductors to supply the necessary current, so they were not commercially practical,". So it seems the reason Swan and Edison settled on the filament was the larger rod draw too much current. Also I didn't here this in the PBS show but I was flicking (this quote is from the Joseph Swan page "Though Swan had beaten him to this goal, Edison obtained patents in America for a fairly direct copy of the Swan light," Dja1979 (talk) 21:13, 1 February 2015 (UTC)
- Red light still requires a large current unless the wire is very thin, then it burns out. High currents were probably more dangerous than gas and paraffin, where there was (limited) technology to reduce the fire risk. I don't recall pollution being a problem (our air was much purer because of the lack of internal combustion engines), but it's true that a badly trimmed paraffin lamp could produce a lot of smoke if left unattended. Dbfirs 23:22, 1 February 2015 (UTC)
- Not sure they cared too much about risk over cost at the time, as people went for Tesla's A/C over Edision's D/C, cost was the main driver. As for air pollution, there may not of been the internal combusion engine but there were coal fired plants in the cities, these casued smog (from the smog article ".... a familiar and serious problem in London from the 19th century to the mid 20th century"). I wouldn't like to say which is worse. Also these light are being used in the house which is a confined space so any amount of soot produced will go on the wall paper and there is only a limit amount of oxygen so CO could be produced. Dja1979 (talk) 23:54, 1 February 2015 (UTC)
- Yes, you are correct about the soot, though this was a very small amount in a well-trimmed lamp. Carbon monoxide might have been a problem if rooms had been sealed as they sometimes are in modern houses, but open fires provide a good circulation of fresh air. Dbfirs 07:14, 2 February 2015 (UTC)
- An incandescent lamp with a thick low resistance filament would have needed much higher current than the 1880 vintage Edison lamp. The 1880 vintage Edison lamp was suitable for operation from a generating plant a mile or so away, without having an impractically high cost for the copper conductors to get the current from the generator to the lamps in the district. It had a carbon filament of very small cross section, sealed in a glass bulb with a very high vacuum. The incandescent lamps which are being phased out and replaced by halogens, compact fluorescents and LEDs had tungsten filaments and operated in a glass globe with low pressure inert gases. A work-around allowing thick carbon conductors in the late 19th century would have been to use alternating current with a step-down transformer near the lamp. The copper conductors would have had to be larger in cross section to supply the same watts, resulting in higher cooper costs to wire a building, unless multiple transformers were used, which could result in high transformer costs. Engineering economics was a critical part of the success or failure of lighting technologies. Edison paid close heed to the copper costs as well as the fuel costs, installation costs, etc. i devising a workable and practical system. Today one sees halogen bulbs which run on 12 volts in common use. The user has a stepdown transformer in the same room as the lamps are used.
Zyklon B
Dear Madam/Sir,
In English version of Wikipedia is a misinformation about current production of Zyklon B like insecticides. Uragan D 2 is produced by Draslovka Kolín who is "traditional" producer of Zyklon B (approx. 60t produced in 1943). In the subject it is stated Adezin as a producer, but the company is a disinfection, disinfestation and rodent control firm therefore only a user of the product. I made a change in the subject yesterday but it has been refused by censor. Solution is up to you.
Best regards
Karel Šikl — Preceding unsigned comment added by 2A02:2788:84:5DA:B4E4:DEE4:6EDA:2DAC (talk) 16:12, 1 February 2015 (UTC)
- The edit in question to the article Zyklon B was reverted by
User:DumbBOT(oops; actually by User:MrX as cited below) per WP:ELNO. A better place to discuss this is at that article's discussion page, Talk:Zyklon B. Note that this reversion was done due to the use of the external link, possibly what you had intended as a reference, so it was an issue of formatting, and not necessarily content. -- ToE 17:13, 1 February 2015 (UTC) - (edit conflict)We have no censors, another user removed it. You added the information on 13:43, 30 January 2015. It was reverted 30 minutes later by MrX. His change comment seems to be wrong, but he seems not to be happy with the link to http://www.draslovka.cz. This link doesn't mention Zyklon B, perhaps you meant another one? For your future reference, the correct place to ask about this is on the talk page. - LongHairedFop (talk) 17:16, 1 February 2015 (UTC)
- Several things were wrong with the edit. First, it was insertion of an inline external link (see WP:ELPOINTS #2). Second, a manufacturer's website is not a reliable source for a claim of this magnitude. I agree that any further discussion should occur on the article talk page. There are 138 editors watching the article, largely because of vandalism and undesirable edits by holocaust-denialism-POV-pushers.- MrX 17:44, 1 February 2015 (UTC)
Is this real?
This. One kilowatthour and two pounds of polypropylene (PP), polyethylene (PE) or polystyrene (PS) plastic into one quart of oil, so they claim. Is it real? 75.75.42.89 (talk) 17:07, 1 February 2015 (UTC)
- It appears to be real, there's some information in English on the company's website: http://www.blest.co.jp/seihin-english.html, but most of the website is in Japanese. Numerous sources report on this machine, e.g. here, and someone asked a question similar to yours on this website. The process is called Thermal_depolymerization, in which the long polymer chains in the plastic products are converted through heating into smaller and simpler molecules that also make up crude oil. Do note however that the device cannot convert all types of plastic and I personally would be concerned that it may produce toxic gasses if you put the wrong kind of materials in it (note: I don't claim any kind of expertise here, that's just something I would be worried about). - Lindert (talk) 17:49, 1 February 2015 (UTC)
- Well, it certainly COULD be real. One quart of oil represents about 10 kilowatt hours of energy content. Most plastics can be burned to produce about the same amount of energy as oil (pound for pound) and a quart of oil weighs around 2lbs - so it's not implausible that using a kilowatt hour of electricity could rearrange the chemistry of the plastics to resemble that of oil without altering the energy content.
- Of course you might ask why you'd want to do that. This Penn-State project converts plastics into pellets that can be burned in a coal-fired boiler to produce comparable amounts of energy to oil. The only issue with burning the plastic directly is that it has to be done at high temperatures in order to avoid producing toxic by-products...but the Penn State machine is cheap and uses very little energy of it's own - so it's probably cheaper and more efficient than the machine you linked to.
- That said, the best use of waste plastics is to produce more plastics - that avoids the steep energy costs of creating plastics from stock materials. The difficulty with doing that is in separating out the plastics from other waste and sorting it by chemical content...but that problem still exists for the plastics-to-oil approach.
- SteveBaker (talk) 17:59, 1 February 2015 (UTC)
- Why is i even needed to form pellets to burn plastics ? It seems to me in a high temperature incinerator, they would burn just fine regardless of their form. In fact, in some forms, like plastic shopping bags, they have a very high surface area to volume ratio already, so should burn quite well. StuRat (talk) 18:08, 1 February 2015 (UTC)
- I have no idea - beyond that they did that. Perhaps it makes the material easier to feed into a furnace of that type...I don't know. But the point is that if all you care about is extracting energy, then burning the plastics directly is more energy efficient than converting it to oil first - and so long as humanity still needs more plastics, recycling the stuff is yet more efficient because you save far more energy by avoiding the manufacture of a pound of plastic than you get by burning a pound of the stuff. But there is no reason that I could come up with why this Japanese machine shouldn't do what it claims. I just ask why you'd want to do that. SteveBaker (talk) 04:37, 2 February 2015 (UTC)
- Burning pellets, instead of burning the raw material the pellet is made of, has many advantages. You can burn it more thoroughly and generate more heat, but less ash. They are uniform in density, size and moisture, which makes the burning process predictable. A mixture of plastic bottles with plastic bags will burn differently each time. This also enables us to use them in automated ovens, as we can adjust the feed rate. Sometimes a binding material is also added in the process of manufacturing, which allows us to "tweak"" some property of the pellet.ListCheck (talk) 16:20, 2 February 2015 (UTC)
- I have no idea - beyond that they did that. Perhaps it makes the material easier to feed into a furnace of that type...I don't know. But the point is that if all you care about is extracting energy, then burning the plastics directly is more energy efficient than converting it to oil first - and so long as humanity still needs more plastics, recycling the stuff is yet more efficient because you save far more energy by avoiding the manufacture of a pound of plastic than you get by burning a pound of the stuff. But there is no reason that I could come up with why this Japanese machine shouldn't do what it claims. I just ask why you'd want to do that. SteveBaker (talk) 04:37, 2 February 2015 (UTC)
Why does the space lift need a cable of 22,236+ miles?
The ISS is much nearer the Earth than that (268 miles to be exact). Couldn't we just connect a cable to it and save thousands of miles in cable? --Senteni (talk) 18:17, 1 February 2015 (UTC)
- Hint: see geostationary orbit. The rest is left as an exercise for the reader. Short Brigade Harvester Boris (talk) 18:20, 1 February 2015 (UTC)
- Well, the ISS orbits at a speed of 27,600 km/h (17,100 mph), so you'd just need to keep the bottom of the space elevator moving at that speed to match the top. Easy, right ? StuRat (talk) 18:38, 1 February 2015 (UTC)
- At the ISS orbit, the Earth's escape velocity hasn't been reduced substantially, at a geo-stationary orbit, it is about ⅖ of the surface value. LongHairedFop (talk) 20:22, 1 February 2015 (UTC)
- David E. H. Jones, in his 1964 article which defined the concept, suggested that, for this application, the tether could be fixed at the north or south pole. Tevildo (talk) 20:46, 1 February 2015 (UTC)
- I don't understand. The point is to connect to something in orbit about the Earth, and nothing stationary above the north or south pole (or anywhere else above the Earth) would stay up for long. To stay in orbit, it must be moving. The advantage of a geostationary orbit is that, at that height, an object's orbital speed matches the speed of the rotation of the Earth, at least at the equator. StuRat (talk) 20:56, 1 February 2015 (UTC)
- The cable could be fixed anywhere, and the upper end would settle toward the equator's plane regardless. If it's fixed at a high latitude, you'd start your climb at a low angle; I doubt that could be enough of an advantage to overcome the cost difference of a longer (and thus heavier) cable. —Tamfang (talk) 21:13, 1 February 2015 (UTC)
- There are some fancier ways to do things than the standard space elevator. Specifically there is an idea to have a rotating space tether or Skyhook (structure) that reaches down to the edge of the atmosphere, grabs hold of something (SpaceShipN?) that can barely make it up to space, and flings it out in a high Earth orbit. I suppose in theory if things rendezvous with it that can change its course and boost its orbit to counteract the friction, it could even reach in to the atmosphere, with an orbit carefully calculated to bring its lower end almost stationary relative to the surface (it would make a great cliffhanger in a story, no?) But no, a standard space elevator isn't gonna work at the North Pole :) Wnt (talk) 23:19, 1 February 2015 (UTC)
- The geostationary orbit requires no additional lateral velocity or energy for orbit. By contrast, lower orbiting satellites often orbit in 90 minutes. There's no reason why the space elevator couldn't be used to launch low altitude satellites but they will need fuel to propel them at the proper velocity. Geosynchronous orbit is not always the desired orbit especially for GPS, Spy satellites and other satellites where distance is a negative. Also note that this is equatorial. A polar space elevator doesn't matter what height it is. --DHeyward (talk) 02:10, 2 February 2015 (UTC)
- If the space elevator can lift a satellite to geostationary orbit, achieving low-earth orbit is easy. Just fire retrograde in geostationary orbit to reduce the satellite's orbital velocity by 1.5 km/s, which brings the periapsis into the atmosphere. Aerobrake over several orbits to circularize the orbit. 1.5 km/s is far, far lower than the 9.5 km/s of delta-V required to get into orbit from Earth's surface. --Bowlhover (talk) 09:19, 2 February 2015 (UTC)
- @DHeyward: Think about it a minute. The skyhook can be in a low orbit and moving very fast relative to the ground, but if it is also spinning, then the low end potentially could be stationary relative to the ground when it is at its lowest point (then of course moving much faster relative to the ground when it is above the skyhook's center of mass) Wnt (talk) 20:04, 2 February 2015 (UTC)
- @Wnt: That's true but it would still be an equatorial rotation to be slowest relative to earth and it would be a very short window. A low altitude polar orbit wouldn't be any slower relative to earth for polar launches and the if you tried to compensate E/W earth velocity with rotating you still have N/S velocity. The payload would still need a sub-orbital boost and if you did that it wouldn't need to be slow relative to earth, just the payload. There's still the problem of how to keep the skyhook in orbit and what orbit to put it at and how heavy it would have to be and how high so the sonic booms don't break things. But before we hook things or ladder things, I suspect the EM Railgun will be first, possibly on a suborbital platform (nuclear reactor on large aircraft to generate the energy for launch). --DHeyward (talk) 21:43, 2 February 2015 (UTC)
- @DHeyward: Think about it a minute. The skyhook can be in a low orbit and moving very fast relative to the ground, but if it is also spinning, then the low end potentially could be stationary relative to the ground when it is at its lowest point (then of course moving much faster relative to the ground when it is above the skyhook's center of mass) Wnt (talk) 20:04, 2 February 2015 (UTC)
- What is the least amount of material that would be required for such a device? ←Baseball Bugs What's up, Doc? carrots→ 08:39, 2 February 2015 (UTC)
- I think the responses above are obscuring the answer, which is that if you hooked a cable from the ground to the ISS, the ISS wouldn't be able to move fast enough to stay in orbit, so the cable would pull it down to the ground. The same thing would happen at any altitude below geosynchronous orbit. Once the cable reaches higher than that, its upper part pulls the remainder upward. If you put enough mass there, the upward pull can balance the downward pull of the part that lies below geosynchronous altitude. Looie496 (talk) 18:48, 2 February 2015 (UTC)
Neurology: Dearth of research on treating Periodic Limb Movement Disorder (PLMD) with Baclofen
http://www.ncbi.nlm.nih.gov/pubmed/6721446
The above study from 1984 at Stanford found that oral administration of baclofen somewhat improved sleep in patients with PLM-associated arousals. The results seem fairly positive, with the finding essentially that although baclofen increased the number of PLMs, it decreased their amplitude, and decreased the length of the arousals associated with PLMs.
My question then is why does there seem to be no follow-up research on the treatment of PLMD (i.e. arousals caused by PLMs) with baclofen? I understand that RLS (Restless Leg Syndrome) is accompanied by PLMS in about 80% of RLS cases, and since dopaminergics and anti-convulsants are generally more effective treatment for RLS than are muscle relaxants (like baclofen) the research on RLS and baclofen is not extensive. But in cases of PLM-associated arousals unaccompanied by sensations of restlessness (RLS), why is there no further research on the seemingly promising treatment of baclofen?
Note: let me please be quite clear that I am NOT asking for medical advice. I am interested in the research history of a particular drug.
Thanks!
146.50.147.161 (talk) 19:37, 1 February 2015 (UTC)
- One of the awful realities of science is that a lot of irreproducible results are published. This is to be expected, because "statistical significance" generally means "one chance in 20 it could have happened by chance". And people try a lot of things... sometimes failing to take into account the compound probability that one of the tests they make ought to work by chance alone. Worse, when people fail to reproduce a result, they say so to other workers in the area informally but don't publish the negative result in the literature. So when you see a result like this that isn't followed up, there is a likelihood but by no means a certainty that it failed to reproduce in someone else's hands. Of course, because the negative result wasn't formally written up and peer reviewed, you never are totally sure it was done right either.
- That said, some related negative results turn up in http://www.ncbi.nlm.nih.gov/pubmed/10947026 and http://www.ncbi.nlm.nih.gov/pubmed/1713829 . Honestly, I don't know a damned thing about myoclonus, and I haven't read the study at your original link, so how related those results are is at the moment a mystery to me, but it was worth mentioning. So if you go back to PubMed and try searches of your own you can know more about this than I do in ten minutes. But one thing I'd look at carefully in the original paper - the abstract makes a point of saying the 20 mg and 40 mg dosages worked best. Usually someone would just say "dose-dependent" in a sentence like that ... did they put it that way because both higher and lower dosages did nothing? That reduces the statistical significance and demands a more intricate/less probable explanation about the mechanism for the result to be real. Wnt (talk) 19:52, 1 February 2015 (UTC)
- Maybe an important point here is that baclofen is a broadly acting central nervous system depressant, and has quite a number of undesirable side effects, particularly when taken orally at clinically significant doses. Looie496 (talk) 18:43, 2 February 2015 (UTC)
- Well, from a research point of view that might not disqualify it from further study, because it could be used as a lead compound for further drug discovery. For example, consider the case of cannabinoids, where AFAIR someone discovered a sort of 'anti-marijuana', a Cannabinoid receptor type 1 inverse agonist that made people lose weight, but it was such a bummer they were more prone to suicide. Ah, Rimonabant is the name. Well the answer may be to come up with a drug that is like that, but won't cross into the brain; then a person gets the weight loss, but not the suicide. (Perhaps -- I should note that I've never heard of any class of drugs with as much tendency to turn out to kill people in large numbers after they become popular as weight loss drugs) Well anyway, with this drug you might find that you can block the brain effect that way, or maybe the receptor for the other effects is a close homologue but not identical to the one for the myoclonus effects, etc. So this isn't a deal-breaker when all you're doing is basic research. Wnt (talk) 20:01, 2 February 2015 (UTC)
Swingset obsession sources?
Are there any scholarly or scientific sources that address a post-puberty/young adult's obsession with riding a swing on a swingset? The only (very unhelpful) thing I could find was http://www.theotaku.com/worlds/theswingset/tags/hetalia and other searches ended up addressing "mood swings" in obsessive-compulsives, which is not what I was looking for. Thanks. μηδείς (talk) 22:12, 1 February 2015 (UTC)
- What do you mean "address"? People can be obsessed with just about anything, is there anything further to learn about "swings" beyond the already very complex obsessive compulsive disorder? Vespine (talk) 23:59, 1 February 2015 (UTC)
- Do you have any sources showing that there is such an "obsession", as opposed to park swings just being a place where teens can sit at night for relative privacy ? StuRat (talk) 00:05, 2 February 2015 (UTC)
- By "address", I mean discuss in a technical manner. The word "swing" is not mentioned in the OCD article, and I am offering no opinion myself on the subject. Stu, you seem to have missed the point that I am the one asking for refs. If I had them I wouldn't bother to post. I said nothing about a group of people sitting on a swing at a park for privacy. I am curious if anyone can find a medical or otherwise scholarly ref about a young adult who uses a swingset for what might seem abnormal circumstances. If the refs mention autism, OCD, or masturbation, that's fine, but those are not my own words. μηδείς (talk) 00:36, 2 February 2015 (UTC)
- You're being pretty confrontational. And you're the only one to have mentioned autism or masturbation in connection with this topic on here. But again: what makes you think this is a topic at all? I have no idea, from the little you've said here, what kind of sources you expect anyone to produce, or why you believe this to be a discrete subject with any literature whatever associated with it. AlexTiefling (talk) 03:39, 2 February 2015 (UTC)
- I suppose I am, if one defines confrontational as asking a question, repeating that one is asking a question, and offering hypothetical circumstances which one explicitly says are not one's personal assertions. I suggest you simply refrain from commenting on anything I say in the future, since your comments are indeed personal, political, and hostile. There's obviously nothing wrong with my question here, and we've got answers with references below, which I have actually found informative. Thanks. μηδείς (talk) 02:44, 3 February 2015 (UTC)
- Can you think of any examples of obsession with swingsets? ←Baseball Bugs What's up, Doc? carrots→ 03:49, 2 February 2015 (UTC)
- Just the one so far!Greglocock (talk) 04:42, 2 February 2015 (UTC)
- Riding a swing is a periodic rocking motion that people may find soothing or comforting even into adulthood. Rocking has been shown in a study to help sleep. Rocking chairs and hammocks also provide such a motion and people love them. Rocking babies is a near universal way to calm them. Body rocking is sometimes associated with mental illness or autism There is also the article Self-reported body-rocking and other habits in college students. --Mark viking (talk) 05:27, 2 February 2015 (UTC)
- So where's the line between normal rocking and "obsessive" rocking? ←Baseball Bugs What's up, Doc? carrots→ 08:36, 2 February 2015 (UTC)
- The thing is that compulsions (in general) are a feature of human mental disorders. There is a massive body of research into compulsions in general. I watched a TV show the other night about a woman who had literally fallen in love with a fairground ride...one that doesn't even work anymore. Another became obsessed with what remains of the Berlin wall. There seems to be little merit in researching a very narrow compulsion (eg with a swingset or a particular kind of motion). These are all incredibly specific cases of compulsion in general...the precise subject of the compulsion is of little importance to the science of it all. So for that reason, I doubt very much that you'll find research on this very narrow slice of that problem. It's kinda like asking for research about people who are afraid of dogs...and then specifying that you want research about people who are specifically afraid of female grey poodles. The details don't matter.
- A highly specific compulsion exists...but it's just a compulsion. Study compulsions in general - and there you find your answers.
- SteveBaker (talk) 15:57, 2 February 2015 (UTC)
February 2
Taking a picture of the past without a camera
Is it theoretically possible to use Quantum cloning to reconstruct photons that existed in the past, like say photons that reflected off of a tyrannosaurus so we can see what it actually looked like without dealing with the messy business of time travel. ScienceApe (talk) 00:29, 2 February 2015 (UTC)
- No, entropy and non-linear dynamics, i.e., chaos theory, will quickly make this impossible. Piers Anthony's pulp sci-fi novel Macroscope addresses this supposition. μηδείς (talk) 01:41, 2 February 2015 (UTC)
- That's a relief. InedibleHulk (talk) 01:59, February 2, 2015 (UTC)
- I don't follow, how does any of that make it impossible? ScienceApe (talk) 04:10, 2 February 2015 (UTC)
- The article you linked to says quantum cloning is forbidden by the no-cloning theorem. --Bowlhover (talk) 02:34, 2 February 2015 (UTC)
- Now that's got to be the second worst written article I have ever read on WP. If specialists can't explain themselves without jargon (i.e., explain the basis of their thought in reality) they really aren't specialists, just theologists. See WP:ONELEVELDOWN μηδείς (talk) 03:12, 2 February 2015 (UTC)
- It's all made perfectly clear in Hom functor. InedibleHulk (talk) 07:47, February 2, 2015 (UTC)
- Now that's got to be the second worst written article I have ever read on WP. If specialists can't explain themselves without jargon (i.e., explain the basis of their thought in reality) they really aren't specialists, just theologists. See WP:ONELEVELDOWN μηδείς (talk) 03:12, 2 February 2015 (UTC)
- The article I linked to also says imperfect cloning is still possible. ScienceApe (talk) 04:08, 2 February 2015 (UTC)
- Why do you think quantum cloning has something to do with taking pictures of the past? -- BenRG (talk) 09:45, 2 February 2015 (UTC)
- You can clone the photons that bounced off of objects that existed in the past. If you clone those photons they should be able to produce a picture. ScienceApe (talk) 20:08, 2 February 2015 (UTC)
- How would you know which ones to clone? ←Baseball Bugs What's up, Doc? carrots→ 20:32, 2 February 2015 (UTC)
- How the hell would I know? ScienceApe (talk) 21:30, 2 February 2015 (UTC)
- Are you confused by the article lede saying that you can clone an "arbitrary" quantum state? That just means anything you could prepare in the lab. It doesn't mean any event in the history of the universe. It's like a camera being able to photograph an "arbitrary" scene. Except that quantum cloning isn't possible, but even if it were, it would have nothing to do with seeing into the past... -- BenRG (talk) 00:22, 3 February 2015 (UTC)
- Or is the idea that by cloning the system many times and measuring the clones you could determine the complete wave function, then evolve that back in time? I suppose that's an argument that cloning, if it were possible, would make seeing into the past just as feasible as it would be in a classical world. But it isn't feasible classically because of chaos, as people already said. And because some of the information you need is travelling outward at the speed of light from the original event, and there's no way to collect it back at a point. -- BenRG (talk) 00:29, 3 February 2015 (UTC)
- How would you know which ones to clone? ←Baseball Bugs What's up, Doc? carrots→ 20:32, 2 February 2015 (UTC)
- You can clone the photons that bounced off of objects that existed in the past. If you clone those photons they should be able to produce a picture. ScienceApe (talk) 20:08, 2 February 2015 (UTC)
- Every photograph is a picture of the past... SemanticMantis (talk) 20:51, 2 February 2015 (UTC)
- Taking a picture of the past without a camera ScienceApe (talk) 21:30, 2 February 2015 (UTC)
- To ScienceApe above, we don't seem to have a good article for path independent, versus path independent qualities. There are Nonholonomic system and path-dependence. But imagine you've got a cup of water at 32F sitting in front of you. What temperature was it at the sae time yesterday? You can't deduce that from the current state of the water alone. Yt, if I give you a piece of magnetized metal, you can surmise that at some point in the past it was subject to a magnetic field strong enough in a given temperature to allow its structure to polarize magnetically. The current temperature is path-independent. Whether the nail is magnetized is path dependent. Now, even if everything were path-dependent, which it isn't, and even if we could gather all the data needed to reconstruct the past history, we wouldn't have a computer large enough (i.e., smaller than the universe itself) powerful enough to predict where any given air molecule was last month, let alone "photograph" a Tyrannosaur. Basically put, the butterfly effect works backwards, and even things like the orbit of Pluto moving in the "vacuum" and assumed to be subject only to gravity cannot be calculated past or before certain dates. μηδείς (talk) 21:14, 2 February 2015 (UTC)
- (Cup of water) Actually, you could tell that the oxygen atoms used to be helium (and most of them were hydrogen before that) , but everything changed when stellar nucleosynthesis happened. - ¡Ouch! (hurt me / more pain) 08:29, 3 February 2015 (UTC)
- In some of the old Superman comics they hypothesized that Superman could fly faster than light, so that he could overtake light that had left the earth and thus observe past history. That sounds about as plausible as cloning photons to get a picture of a living T-Rex. ←Baseball Bugs What's up, Doc? carrots→ 21:38, 2 February 2015 (UTC)
- Even if he could, he'd be running up against the inverse-square law. If he could see an object at one mile with an X resolution, by travelling a light second away (186,282 miles) he would see the same object with an X/34,700,983,524 resolution. Not very helpful. μηδείς (talk) 22:13, 2 February 2015 (UTC)
- He would need a huge eye, thousands or millions of light years in diameter. More likely is that a natural camera existed that took a photo of your dinosaur. Perhaps a cave with a pinhole formed an image on a layer of algae on the back wall, and the T. Rex stood still for a few days to make an image. Or perhaps a gamma ray burst projected a shadow in altered isotopes on a rock surface. Or perhaps a giant meteorite strike made a huge flash of light that burnt a shadow on the ground. Graeme Bartlett (talk) 22:20, 2 February 2015 (UTC)
- You're forgetting about Superman's super-vision. ←Baseball Bugs What's up, Doc? carrots→ 22:29, 2 February 2015 (UTC)
- Or any kind of adult supervision for that matter. - ¡Ouch! (hurt me / more pain) 07:28, 3 February 2015 (UTC)
- You're forgetting about Superman's super-vision. ←Baseball Bugs What's up, Doc? carrots→ 22:29, 2 February 2015 (UTC)
- He would need a huge eye, thousands or millions of light years in diameter. More likely is that a natural camera existed that took a photo of your dinosaur. Perhaps a cave with a pinhole formed an image on a layer of algae on the back wall, and the T. Rex stood still for a few days to make an image. Or perhaps a gamma ray burst projected a shadow in altered isotopes on a rock surface. Or perhaps a giant meteorite strike made a huge flash of light that burnt a shadow on the ground. Graeme Bartlett (talk) 22:20, 2 February 2015 (UTC)
- Even if he could, he'd be running up against the inverse-square law. If he could see an object at one mile with an X resolution, by travelling a light second away (186,282 miles) he would see the same object with an X/34,700,983,524 resolution. Not very helpful. μηδείς (talk) 22:13, 2 February 2015 (UTC)
- This is out of my depth, but it seems to me the salacious bit involves the relationship of quantum entanglement and local hidden variable theory. In theory, every electron is the same electron, and every photon is the same photon, except for the momentum and spin they carry. Yet... if one particle is entangled, and the other isn't, does that give you a way to distinguish them? Can you measure whether a photon has an (unknown) entangled partner by experimenting on it? Can you tap on a molecule and somehow tell the last time it absorbed or emitted a photon? It seems like a slippery slope that would have basic particles as artifact-encrusted as our Earth. But in my very limited knowledge, the experiments have resisted such interpretation - you can only measure whether two particle are entangled by viewing them both. And by the same token, you can't tap on a molecule to resurrect the ghosts of dead photons that once fell upon it. Wnt (talk) 13:22, 3 February 2015 (UTC)
- We have a fun little article at one electron universe - I don't think anybody takes it too seriously today, but it's a fun thought experiment. OP should also see Identical_particles - even if we take it as a given that there are many photons out there that have hit a T. rex, how are we to know which they are? SemanticMantis (talk) 14:28, 3 February 2015 (UTC)
Fastest speed
What's the fastest speed record for rotational and linear object? I read for a micro-object is a research in St. Andrew link1, but what's the fastest for object larger than 1 mm or 1 cm? What happened when 2 high speed iron object hit each other, will it bounce back or melted into one object? I supposed for stone object the collision will create massive explosion, correct? roscoe_x (talk) 04:10, 2 February 2015 (UTC)
- For linear motion, the limits would be air resistance, or, in vacuum, the only limit would be the amount of energy that would be required and the length of the "barrel" needed to accelerate the object. Eventually you'd approach the speed of light and more and more energy would be required for each small increase in speed.
- For rotational speed, keeping the object from flying apart would be problematic.
- Assuming we aren't talking about speeds where nuclear reactions would occur, then the objects would vaporize each other if they hit exactly straight on, but any slight deviation would send larger chunks flying out. Beyond a certain speed, the material wouldn't much matter, as it would all vaporize. StuRat (talk) 06:17, 2 February 2015 (UTC)
- May I suggest Orders of magnitude (angular velocity). It lists a bunch of high-speed rotations. I'll have to leave it up to you to decide which ones count and which ones don't. SteveBaker (talk) 15:48, 2 February 2015 (UTC)
- Researchers and practical people who spend a lot of time pushing the limits of very high velocity objects usually switch units - eventually, they get to the point of measuring some physical parameter other than velocity. It's not because they cannot measure velocity; but that velocity is less interesting than other properties, like momentum or energy. For example, consider the people who work with:
- terminal ballistics - the common way to describe and compare really fast bullets is to talk about muzzle energy and the momentum of the projectile.
- fluid dynamics experts - the way we talk about air movement at high speed is as a ratio of the velocity with respect to a different velocity. This is called the Mach number, and it is more useful in many high-speed aerodynamics calculations than a measure of straight line movement per unit of time.
- particle accelerators - in scientific experiments where physicists create very fast-moving, very tiny particles, the usual unit of measurement is average energy per particle - and that can be expressed as a temperature or an energy, depending on context
- Physicists know how to convert these units back into a corresponding velocities. But we'd rather use the most appropriate unit for the physical context. If we want to talk about the weather, though, we don't usually say "the nitrogen molecules are convecting at around mach 1.5 today, even though this may be factually correct. That's a useless measurement of linear velocity! It's much more informative to say that it's 25º C; and similar logic applies (but with a more difficult calculation) for the molecular angular momentum. The same logic even applies if we talk about something macroscopic, like an artillery shell: we can describe its linear velocity; but it's more useful to talk about its momentum.
- Here's a practical example: consider a few "really fast bullets." Let's look at the M-16 rifle, which fires a supersonic round. Let's compare it to the USS New Jersey's main battery, which fired a much much much slower round - 200 meters per second slower! But when the New Jersey lobbed shells into the mountains of Lebanon, the barrage of shells were famously described as "flying Volkswagens", not "bullets that fly 25% slower than an ordinary rifle round." Intuitively, you already know why the velocity does not matter. Those shells had the momentum of a VW bug that could fly for twenty or thirty miles. Regular press-reporters and physicists alike all knew that the velocity of these shells simply did not effectively describe the situation.
- So if you are looking for the "fastest thing ever made by humans," it's going to be a very fruitless search. Obviously, the fastest thing we ever make is a photon - and we make those every time we turn on a lightbulb. In fact, we emit photons every time we stand around just existing - because blackbody radiation means that we are releasing particles that travel at the speed of light. If you want a photon that travels at the speed of light and is also very large, then consider the radio photons emitted by NLK - each photon moves at the speed of light and is about the size of a very large mountain-valley. It is more interesting to talk about the things we make that have very high energy, or very large momentum.
- Nimur (talk) 19:09, 2 February 2015 (UTC)
- Researchers and practical people who spend a lot of time pushing the limits of very high velocity objects usually switch units - eventually, they get to the point of measuring some physical parameter other than velocity. It's not because they cannot measure velocity; but that velocity is less interesting than other properties, like momentum or energy. For example, consider the people who work with:
- My understanding of this question was, what would happen if we rotated a disk 29,647.8 miles in radius once a second (or a smaller one proportionally faster)? μηδείς (talk) 22:06, 2 February 2015 (UTC)
- I don't understand where you got that understanding from - but the situation you describe is covered by the Ehrenfest paradox. However, our OP seems to be talking about the fastest rotational speed we've actually obtained from a macroscopic object...not the theoretical maxiumum. SteveBaker (talk) 04:53, 3 February 2015 (UTC)
What is the liquid sprayed at the base of the rocket in this rocket launch animation?
The CNN website has a video with an animation of the launch a SpaceX Falcon Heavy rocket. About 23 seconds into the video, something is spraying a liquid at the base a firing rocket. What is the liquid supposed to be and what is it supposed to do? --173.49.17.60 (talk) 12:00, 2 February 2015 (UTC)
- It's water, coming from the large water tower also shown in that video. Our launch pad article , describing launch pads in general, mentions that, "a sound suppression system spraying large quantities of water may be employed". The Space Shuttle sound suppression system is described at this NASA page. There are also some wonderful videos of the shuttle's sound suppression system being tested that you should be able to find searching on YouTube. I'm not sure what specific information is available about SpaceX's sound suppression systems, but note that they are modifying Kennedy Space Center Launch Complex 39A (SLC-39A), one of the two old Space Shuttle launch pads, for the Falcon Heavy East Coast launches. LC-39A#Sound suppression water system gives a bit more information on their use with the Apollo program Saturn V. For the West Coast FH launches, they will be using Vandenberg AFB Space Launch Complex 4 (SLC-4). -- ToE 12:25, 2 February 2015 (UTC)
- LC-39A#Sound suppression water system mentions the Rocketdyne F-1, implying that the sound suppression system was used during Apollo, but the sources I've looked at imply that it was first installed for the Space Shuttle, so I've raised the question at Talk:Kennedy Space Center Launch Complex 39#Was a sound suppression water system used during Saturn V launches?. -- ToE 13:04, 2 February 2015 (UTC)
- Thanks for all the answers and links. Much appreciated. --173.49.17.60 (talk) 05:23, 3 February 2015 (UTC)
And here I thought the water was to keep the rocket blast from eroding the concrete launch platform. Huh. Learn something new everyday.50.43.56.168 (talk) 03:26, 4 February 2015 (UTC)
Do all batteries decay with cycles of charging and re-charging?
Known and possible batteries are meant. Why can't batteries be charged and re-charged without (too much) wear? Noopolo (talk) 22:53, 2 February 2015 (UTC)
- Entropy would be a first principles start but isn't particularly satisfying numerically. In short, nothing is for free in Thermodynamics even reverse. --DHeyward (talk) 01:44, 3 February 2015 (UTC)
- I don't think we can invoke entropy here. The battery isn't a closed system - electrical energy goes in, heat and electricity comes out. The battery doesn't have to suffer from entropy (at least in principle). SteveBaker (talk) 04:47, 3 February 2015 (UTC)
- For some reason chemistry just doesn't work well to provide a reusable way to store energy. Some mechanical and hydraulic systems that seem like they would be a joke actually work better in some circumstances, like a flywheel or pumping water into a high tank. StuRat (talk) 03:18, 3 February 2015 (UTC)
- How about a large capacitor? Won't that do? SteveBaker (talk) 04:47, 3 February 2015 (UTC)
- Flywheels and capacitors and things like Pumped-storage_hydroelectricity seem to get many more "Charge_cycle" than chemical batteries. Some other alternatives at Energy_storage#Storage_methods and Grid_energy_storage. But outside of idealized models, these will still wear out eventually. There are so many different types of chemical battery that I'm not sure if there's one general explanation of why they can't be used for more cycles. But hopefully someone here can clarify the issue. :) SemanticMantis (talk) 14:25, 3 February 2015 (UTC)
- Entropy is of course, relevant. With each recharging the battery will become less and less useful. That's not gremlins. The packaging will indicate that the batteries have a limited life--it simply won't say "due to entropy". μηδείς (talk) 16:25, 3 February 2015 (UTC)
- Entropy is relevant - but you can't use the laws of thermodynamics to say that you can't build an infinitely rechargeable battery because those laws only apply to closed systems and unless you're talking about a thought-experiment battery that is 100% efficient (which is impossible), there will be energy entering into the battery as you charge it which is leaving as heat. That allows the battery (in principle) to fight entropy by increasing the degree of chaos in the rest of the universe. This situation is no different than (for example) a computer with memory full of random numbers that is computing and storing the digits of pi using incoming electricity. Entropy is reversed inside the computer at the expense of emitting heat as it does its calculations.
- I'm not saying that a battery could definitely be made to recharge an indefinite number of times - only that you cannot use the laws of thermodynamics to rule it impossible on grounds of entropy. SteveBaker (talk) 18:39, 3 February 2015 (UTC)
- Most common batteries consist of two solid electrodes separated by a fluid electrolyte (liquid or gel). One or both of the electrodes will be chemically altered during charging and discharging, and it is often the case that the electrodes aren't the same after each cycle. Typical defects include the growth of filaments or the entrapment of other substances in the electrode lattice. Such degradation of the electrodes is a common reason that rechargeable batteries wear out over time. For industrial applications, liquid metal batteries can provide a solution. In the typical liquid metal case, both electrodes are liquids and the barrier playing the role of the electrolyte is solid. That scenario makes the battery much more resistant to degradation since the liquid electrodes can't be physically altered the ways solids do. This allows good efficiency to be maintained for thousands of charge cycles. Unfortunately liquid metal batteries only really make sense for large-scale applications because they require high temperatures in order to keep their molten metal components liquid. Dragons flight (talk) 23:32, 3 February 2015 (UTC)
- The electrodes have to participate in the chemical reactions of the battery. Unfortunately I don't know enough about battery electrochemistry to say whether mercury could be a viable choice or not. I can imagine though that health and safety concerns might also weigh against the widespread use of liquid mercury in consumer batteries. Dragons flight (talk) 17:44, 4 February 2015 (UTC)
February 3
Sulfate calcination
Is there a substance which lowers the calcination temperature of anhydrite? Plasmic Physics (talk) 03:13, 3 February 2015 (UTC)
Non-visible paint ?
For obvious reasons paint comes in colours (UK spelling) on the visible spectrum. But is it possible to produce paint with a colour beyond the visible spectrum ? (though I guess colour may be the wrong word) if so then what colour would such paint appear to the eye ? would it appear different if just off the red compared to the violet end ?
I suspect the answer is, yes, black and no respectively, but thought I'd check here ! GrahamHardy (talk) 10:13, 3 February 2015 (UTC)
- Interesting point. For fun, I just googled 'infrared paint'. It returns pictures too ;-). -DePiep (talk) 10:51, 3 February 2015 (UTC)
- The color something appears to be has to do with which spectral lines reflect. So there's a fair chance that ordinary paint reflects various infrared and/or ultraviolet wavelengths. In short, we already have it - you just can't tell by looking at it. ←Baseball Bugs What's up, Doc? carrots→ 11:09, 3 February 2015 (UTC)
- Try googling "invisible paint" and "black light paint" for more examples. Gandalf61 (talk) 12:33, 3 February 2015 (UTC)
- For WP references, see line of purples, impossible color, spectral color, and just for fun, list of fictional colors. SemanticMantis (talk) 14:18, 3 February 2015 (UTC)
- "black light paint" is something different. That's paint that absorbs UV light and re-emits it into the visible spectrum. Many materials do that. They let you see where UV light is shining, but you're not "seeing" UV - the colors you see are in the regular part of the spectrum. Paint like that probably doesn't reflect much UV at all. It's kinda the opposite of what our OP is asking about. SteveBaker (talk) 15:47, 3 February 2015 (UTC)
- All paint reflects some light outside of the visible spectrum - some more than others - so any color of paint is reflecting some light that we can't see. But if you're asking for paint that ONLY reflects IR or UV or something, then such a "color" would appear black to our eyes. Black paint can be made to reflect strongly in either the IR or UV - but generally it's poor at doing so in the regions of IR and UV close to the visible spectrum. Sadly, nothing very exciting happens...the paint just looks black. You can tell the difference though if you use a pair of night-vision goggles that reacts to IR light. It's interesting to view the world through a pair of those because it opens up a world of "color" (albeit in shades of green) that we can't usually see. I vividly recall looking at an american flag and noticing that the red and white stripes looked the same - only the blue corner with the stars on it was distinctive.
- Also, if you know someone who had cataract surgery more than about 10 to 20 years ago, they had part of their eye removed that filters out some of the incoming UV light. My mother is one of those people. They are actually able to see a little way into the ultra-violet. A rare genetic condition can also prevent that part of the eye from developing - and those people can naturally see a little UV light. These people don't get the perception of entirely new colors - UV just looks like blue or a blueish purple to them.
- My mom is an enthusiastic gardener and reports that after her surgery, she could see very subtle spots and stripes on some flowers that she'd never noticed before - and that these subtle markings 'go away' when she wears her glasses (which, presumably, filter UV light). It turns out that some flowers have UV-reflective markings to help to guide bees in to land on them - rather like the markings we paint on airport runways. Since bees see in the UV, this makes quite a bit of evolutionary sense. To our normal eyes, those markings are the same "color" as the rest of the petals.
- Modern cataract surgery avoids doing that because the additional UV exposure can damage your eyes - so people who had the surgery recently lack my mom's "super power".
- SteveBaker (talk) 15:44, 3 February 2015 (UTC)
- The paint could appear any color to the human eye. There's no reason in principle why you couldn't make a paint with some particular infrared reflectivity spectrum, and whatever visible spectrum you like. Obviously if the paint has to reflect infrared light that is close to the visible spectrum, it will likely also reflect at least some red light too so there would be a smaller range of possible colors. In principle, you could certainly make paint that reflected infrared but was transparent in the visible.--Srleffler (talk) 18:32, 3 February 2015 (UTC)
- I can envision a theoretical use for paint that reflecs IR or UV in addition to a visible color: encoded messages or images. Say you paint a wall with blue paint. Then you paint an image on the wall that reflects both blue and IR. Using night-vision goggles, the image invisible to others would be visible to you. Or did I just say something foolish? → Michael J Ⓣ Ⓒ Ⓜ 11:29, 5 February 2015 (UTC)
What's the tougher technical problem for using hydrogen fuel in a car?
Wouldn't hydrogen be a better energy storage medium that those batteries that electric cars use? --Noopolo (talk) 14:49, 3 February 2015 (UTC)
- Here are several articles about the technical hurdles for running cars on hydrogen fuel cell technology. --Jayron32 14:58, 3 February 2015 (UTC)
- Hydrogen poses many problems if you try to use it in an internal combustion engine - mainly that it rapidly makes most metals that it touches very brittle - so engine reliability goes down the toilet and you have to make your engines out of exotic plastics and ceramics. However, you can use hydrogen in other ways - such as in a fuel cell that can generate electricity directly and thereby charge batteries and drive an electric vehicle. That avoids most of the problems, but it still technically challenging. Dispensing hydrogen is also a problem, it's tough to liquify (compared to fuels like propane) - so it has to be delivered as a highly compressed gas, which makes refueling difficult. Storing the stuff is also tricky - those teeny-tiny molecules can sneak past most kinds of seal that you'd want to use. It's also much more explosive and inflammable than gasoline - so you can have car crashes of hindenburg-like proportions. There are many practical difficulties. The other issue is that hydrogen doesn't occur naturally - it has to be manufactured - typically by electrolysis of water. That's an inherently inefficient process. Electricity=>Hydrogen=>Electricity is clearly a less efficient process than Electricity=>Battery=>Electricity.
- SteveBaker (talk) 15:25, 3 February 2015 (UTC)
- The advantage of electric vehicles is you can simply drop them into the existing energy distribution infrastructure: plug them into electrical sockets, or stick a generator in them to burn existing, readily available fuels, or both, as with plug-in hybrids. Hydrogen vehicles require an entirely new hydrogen infrastructure, plus all the other issues listed above. Market effects should not be underestimated when evaluating how successful new technologies may be; a lot of companies have made that mistake and it cost them. --71.104.75.148 (talk) 23:27, 3 February 2015 (UTC)
- Forget hydrogen, it's a pain in the butt. You are much better if you turn Hydrogen into Methane. Methane is much easier to store and to use. Or better still turn it into Hexane. All you need is some carbon atoms. Hexanes are significant constituents of gasoline. Hexane is a colorless liquid at room temperature, odorless when pure, with boiling points between 50 and 70 °C. They are widely used as cheap, relatively safe, largely unreactive, and easily evaporated non-polar solvents.175.45.116.65 (talk) 04:19, 4 February 2015 (UTC)
- Add two more carbon atoms and make octane. But hydrogen as a burnt fuel isn't practical for energy density reasons and the source for hydrogen is petroleum (even though water could be the source, it's too expensive.) Electric cars only make sense if the power plant is clean. The problem is that the "gas tank" takes hours to fill, wears out, and costs thousands of dollars to replace. Batteries aren't anywhere near the energy density of gasoline. --DHeyward (talk) 14:51, 4 February 2015 (UTC)
- The problem with Methane is that it's a horrible greenhouse gas...and burning it makes CO2 - which is precisely what we're trying to avoid here. So attaching carbon atoms to your hydrogen *completely* nullifies the entire point of doing this in the first place! SteveBaker (talk) 20:12, 4 February 2015 (UTC)
We do have an article Hydrogen fuel but unfortunately a lot of it is unreferenced. Richerman (talk) 20:22, 4 February 2015 (UTC)
Sun
When the Sun provides its heat, does it provide smoke along? From all the colours it is known of? -- (Russell.mo (talk) 19:56, 3 February 2015 (UTC))
- Does the sun provide smoke to the Earth? No. The heat from the sun is not from a smoke producing combustion reaction to begin with, but rather from nuclear fusion. Can you clarify what you mean by the last part of your question, regarding colors? --OuroborosCobra (talk) 20:49, 3 February 2015 (UTC)
- Only if you expand the word "smoke" to include alpha and beta particles, gamma rays, etc. ←Baseball Bugs What's up, Doc? carrots→ 22:46, 3 February 2015 (UTC)
- While the sun produces helium through nuclear fusion, calling these alpha particles is a bit sketchy (technically correct, but a bit odd to do so). Alpha particles are generally what helium atoms are called when they arise from fission rather than fusion processes, specifically alpha decay. Indisputably, a helium atom is indistinguishable from any other helium atom regardless of the process that makes it, but to call a fusion-produced helium atom an "alpha particles" feels weird. --Jayron32 00:45, 4 February 2015 (UTC)
- Only if you expand the word "smoke" to include alpha and beta particles, gamma rays, etc. ←Baseball Bugs What's up, Doc? carrots→ 22:46, 3 February 2015 (UTC)
- If you are asking what we know about the colors of light that the sun makes, see sunlight. This figure shows the amount of power at each wavelength or spectral color, both with and without the effects of our atmosphere. SemanticMantis (talk) 21:41, 3 February 2015 (UTC)
- ♫ Caaaannnn you paint with all the colors of the wiiiinnnd... ♫ --71.104.75.148 (talk) 23:04, 3 February 2015 (UTC)
- So, it doesn't produce smoke like, what comes out when we burn something? And gamma ray and other things that are related to long distant measurement, is the other way to define a smoke from the Sun...? Btw, I'm talking about all the colourful stars i.e., when they are in different phases... -- (Russell.mo (talk) 14:55, 4 February 2015 (UTC))
- Different stars will have different spectra. So e.g. a red dwarf has a different color than our sun. So if you pick a certain star, say Sirius, you can often find out the spectrum of that star with some searching. Our article doesn't have a complete description of Sirius' spectrum, but it is mentioned with several references, and an analogous diagram to the one above could be made with existing data. Now, none of the stars "burn" - they do not combust, and they do not produce anything like what we call smoke (Bugs is making sort of a joke analogy above - those particles are not smoke). They produce heat and light through a totally different process, called nuclear fusion, linked above. SemanticMantis (talk) 15:08, 4 February 2015 (UTC)
- I have read the articles stated. Not that I remember any of it, I do get the idea behind how it comes to existence, burns... I thought, since it is like fire (blue, mostly yellow reddish colour, never seen white) it might produce smoke, since the ISM is smokey most of the time with particles... Thank you for the clarification -- (Russell.mo (talk) 15:21, 4 February 2015 (UTC))
- As you should have read in those articles, you would have seen that it (stars) does not come into existence through burning and is not fire. Stars are not fire. --OuroborosCobra (talk) 19:18, 4 February 2015 (UTC)
- I have read the articles stated. Not that I remember any of it, I do get the idea behind how it comes to existence, burns... I thought, since it is like fire (blue, mostly yellow reddish colour, never seen white) it might produce smoke, since the ISM is smokey most of the time with particles... Thank you for the clarification -- (Russell.mo (talk) 15:21, 4 February 2015 (UTC))
- Different stars will have different spectra. So e.g. a red dwarf has a different color than our sun. So if you pick a certain star, say Sirius, you can often find out the spectrum of that star with some searching. Our article doesn't have a complete description of Sirius' spectrum, but it is mentioned with several references, and an analogous diagram to the one above could be made with existing data. Now, none of the stars "burn" - they do not combust, and they do not produce anything like what we call smoke (Bugs is making sort of a joke analogy above - those particles are not smoke). They produce heat and light through a totally different process, called nuclear fusion, linked above. SemanticMantis (talk) 15:08, 4 February 2015 (UTC)
- So, it doesn't produce smoke like, what comes out when we burn something? And gamma ray and other things that are related to long distant measurement, is the other way to define a smoke from the Sun...? Btw, I'm talking about all the colourful stars i.e., when they are in different phases... -- (Russell.mo (talk) 14:55, 4 February 2015 (UTC))
- To make smoke, it would have to emit something that condensed into small solid particles. For the sun, the solar wind blows off, but it is too hot and thin to condense into solid. For some other carbon rich red giant stars the can push off enough gas that condenses into carbon particles, very similar to smoke. Other stars can blow out heavier element rich material that condenses to silicate minerals. These particles are cosmic dust. and there are dark nebulae that are very smoke like out in space. Eg Coalsack. Some cool stars like brown dwarfs will have clouds like smoke on them. Graeme Bartlett (talk) 21:35, 4 February 2015 (UTC)
- Okay! I get the idea... I've read all the article you stated btw... Thanks friends. Thanks for breaking it down Graeme I was actually expecting a real smoke. -- (Russell.mo (talk) 21:51, 4 February 2015 (UTC))
Gas lost from atmosphere
A topic that has come up in a science lesson but which a precise answer was unavailable is in regards to the amount of gas that is lost from the Earth each day. (Although there are also gains from volcano eruptions etc..) Assuming that there is a small amount that can drift off, how much gas from the Earth's atmosphere is in fact lost? DarkToonLink 23:19, 3 February 2015 (UTC)
- Apparently three kilograms (3 kg) of hydrogen and 50 grams (50 g) of helium per second. Atmospheric_escape#Dominant_atmospheric_escape_and_loss_processes_on_Earth --Tagishsimon (talk) 23:53, 3 February 2015 (UTC)
February 4
"Geo warping"
I found this Geo warping article whimpering in a dark corner of the orphanage. No sources, created by an SPA in '07 never to be heard from again, smells like a copyrightvio but I find no evidence of that, perhaps pure original research... I can't find any outside evidence that "geo warping" exists as described in the article (but then science articles make me want to curl up and take a nap...)
Any ideas? Vrac (talk) 00:11, 4 February 2015 (UTC)
- Well the lack of sources is pretty bad, but I think this is basically a real thing, as a subfield of GIS and image processing. The page is mostly about "warping" images to properly overlay with different map projections. Georeference is somewhat in the same vein, and a (marginally) better article. I didn't try to search for copyvio. It doesn't seem like it's very standard terminology based on google searches. When I searched /georeference warp image/ I found a few more legit looking and fairly relevant sources, e.g. [5], [6]. So I suspect this is a valid topic, but it badly needs the attention of an expert. It might be a simple as a bad title. SemanticMantis (talk) 00:37, 4 February 2015 (UTC)
- I'd suggest Image rectification and Orthophotol. I used to work in this field - and I never heard "Geo warping" as a common term. SteveBaker (talk) 20:08, 4 February 2015 (UTC)
Converting sounds into colors
http://www.lunarplanner.com/Harmonics/planetary-harmonics.html
I'd like to know if this really makes sense. It's a bit difficult for me to imagine that you can convert frequencies into colors. Why do we need to raise the frequency of a piano key by 40 octaves? --2.245.131.73 (talk) 03:10, 4 February 2015 (UTC)
- Because the base 2 logarithm of the frequency of visible light divided by the frequency of ordinary piano music is approximately equal to 40. This has no actual useful or meaningful implication, but the author of that page is sort of an artist, and has decided that it's "neat." We shouldn't even need to bring it up, but sound waves and electromagnetic waves (like visible light) are not directly convertible - so there's no physical meaning to this frequency ratio (nor is there any meaning in "transposing up 40 octaves" - except that this is how the math works out). Nimur (talk) 03:41, 4 February 2015 (UTC)
- Also note that somebody with synesthesia might convert sounds to colors in their mind. StuRat (talk) 05:59, 4 February 2015 (UTC)
- Which is relevant to the question at hand, how? The neuronal associations which cause a perceptive cross-over between the senses in synesthesia -- and, by the by, synesthesia isn't a condition certain people have; we all experience varying degrees of interplay between the senses, to differing degrees in different modalities; in some people it's just sometimes pronounced in some extraordinarily strong or idiosyncratic way -- these associations are formed by the brain's physiology, not by any rational associations or systematic mathematical conversions reflecting the natural properties of the waves... Snow talk 14:52, 4 February 2015 (UTC)
- There's a whole field of data visualization, that uses images to help us understand things that are inherently not visual. Your link is sort of going the other way; think of it as a "data sonification" or something. If we have data about a certain light/color, this link is describing a way to present that data as sound (or go the other way, given a pitch, associate it with a color). This specific method might not be especially useful for anything, but it is somewhat interesting in my opinion, and isn't really any different from the many other ways that we manipulate data to change the way that we perceive it. Spectral colors are defined only by their frequency (or wavelength), as is pitch_(music). There are some caveats about how human perception of pitch is not exactly the same thing as the frequency of the wave, but I think we can disregard that at them moment. A similar issue comes up with color perception. Anyway, it really shouldn't be that surprising that there are ways to associate colors and pitches, because the physical phenomena are both waves. No, we are not really "converting" any physical waves, but we can take the data about the wave and present it in many different ways. SemanticMantis (talk) 14:56, 4 February 2015 (UTC)
- Along those lines. There's also actually a strong history of research in a related area exploring just to what extent the regions of the brain usually utilized for spatial environment/image construction in vision can be co-oped for utilization in auditory "image" modelling, as in the case of the blind. Though often echolocation is the specific mechanic being explored, rather than a frequency correspondence, be it for spatial purposes or color/luminosity data. Snow talk 15:11, 4 February 2015 (UTC)
- The problem at the heart of this is that sound waves are vibrations in the air and light is an electromagnetic wave. We have ultrasound machinery that can generate sound waves in the GigaHertz range - which is the same range of frequency as a UHF radio signal carrying a cellphone conversation. But you can't use those two waves in remotely the same way. The UHF radio signal carries many kilometers - but an acoustic signal with the same power and frequency travels only a matter of centimeters before dying out. Looked at the other way - a radio signal with the same frequency range as a piano would be in the "LF" range - which is used for long distance/low speed communications, such as for aircraft navigation beacons. Those radio waves are likely to be passing through your body all the time - yet you can't hear them because they aren't sound waves.
- That said, the frequency of light is indeed around that number of octaves higher than the piano...but it's not like you can compare the two kinds of wave. However, if you get hold of a suitable microphone and a radio transmitter, it is a handy device to convert between them in one direction, and a loud speaker performs the reverse transformation. SteveBaker (talk) 20:04, 4 February 2015 (UTC)
A friend in high school said windowpane could do this, but I guess that's too WP:OR. Short Brigade Harvester Boris (talk) 00:58, 5 February 2015 (UTC)
As a non-scientist, I read this article and was left with the impression that the way we gather heavy water for use is by essentially looking for it in ordinary water, like looking very carefully for a needle in a haystack. This implies to my untrained mind that synthetically producing the substance is impossible theoretically or practically. Is it the latter? --Dweller (talk) 12:36, 4 February 2015 (UTC)
- OK, duh, the answer is given in our heavy water article. Sorry. --Dweller (talk) 12:37, 4 February 2015 (UTC)
I have added the information from heavy water to Deuterium. It is uncited, so if one of you clever people could add that (in both articles), that'd be another win for the Ref Desks. Cheers. --Dweller (talk) 12:40, 4 February 2015 (UTC)
- Make you a deal: I get the refs, someone else add them? These are both RS that describe the production of heavy water [7] [8]. They may not be the best refs available, but I'm confident they are better than nothing. SemanticMantis (talk) 15:01, 4 February 2015 (UTC)
- Thanks. I had a quick look at both and my befuddled non-scientific brain couldn't see the claim that it's more practical to search for Deuterium than artificially synthesise it. Did I miss it? --Dweller (talk) 15:04, 4 February 2015 (UTC)
- Oh, sorry, I misunderstood. These refs are suitable for Deuterium#Production, and everything in the first paragraph of Heavy_water#Production except for the last sentence about cost! But the claims about methods of production are still uncited at present. I'm not sure how to find a ref that specifically says nuclear synthesis is not viable. Most people who would research it would see it as obvious, I think. Concentrating heavy water just starts with regular water and uses "normal" chemistry that accomplishes Isotope_fractionation. So it's not so much that we are "searching" for deuterium/heavy water, filtering or concentrating would be better analogies. We know all water has some heavy water, just like most stable isotopes occur in certain ratios of most Earthly elements.
- In contrast to the chemical concentration approach, "synthesizing" deuterium out other isotopes of hydrogen requires nuclear reactions. Finally, the first link above at least implies that synthesis is cost ineffective, because it compares the efficiency and costs of several non-nuclear reaction methods without even considering nuclear processes. So I still think these are better than nothing, and can support other claims in the production sections. But now I'm also out of my element as well :) Hopefully someone else will find a better ref that explicitly rules out synthesis via nuclear processes on economic/efficiency grounds. SemanticMantis (talk) 15:23, 4 February 2015 (UTC)
- Thanks. I had a quick look at both and my befuddled non-scientific brain couldn't see the claim that it's more practical to search for Deuterium than artificially synthesise it. Did I miss it? --Dweller (talk) 15:04, 4 February 2015 (UTC)
- Make you a deal: I get the refs, someone else add them? These are both RS that describe the production of heavy water [7] [8]. They may not be the best refs available, but I'm confident they are better than nothing. SemanticMantis (talk) 15:01, 4 February 2015 (UTC)
- Cost-effectiveness is a tricky matter. If you happen to be Germany in the second world war, then hydrolysis was the most cost-effective approach because the concentrations appearing in the outflow of a fertilizer factory were high enough, and there was essentially free hydroelectric power in the area. (See: Norwegian heavy water sabotage) But if you lack that already concentrated heavy water, and you have an abundant heat source, then distillation may be better - but if you have neither in abundance, but have a nuclear reactor lying around, then maybe irradiating regular water gets the concentrations higher to improve the efficiency of the other techniques. Which of these is "best" depends on what your starting point is and what other resources you may already have. SteveBaker (talk) 19:47, 4 February 2015 (UTC)
Spontaneous Hummingbird Combustion
I have heard it claimed that if a human's metabolic rate was somehow increased to match that of a hummingbird, the human would burst into flames. Is this true, and if so, how was it calculated? And for that matter, what prevents hummingbirds from spontaneously combusting if their metabolism is as high as this claim implies? 75.4.22.29 (talk) 15:19, 4 February 2015 (UTC)
- What you've stated is a common misconception. Hummingbirds are bursting into flame all the time. ←Baseball Bugs What's up, Doc? carrots→ 17:20, 4 February 2015 (UTC)
- For the last Q, it has to do with the surface area to volume ratio. Small objects cool much faster than large ones. And those frenetically flapping wings have got to provide quite a bit of cooling, too. There's a hummingbird in a South American desert, where the temp drops off dramatically at night, which sits on a tree and stops moving at night, quickly cools to close to freezing, then warms up when the sunlight hits it the next morning and emerges from it's torpor. StuRat (talk) 16:36, 4 February 2015 (UTC)
- That makes sense, and it's a factor I didn't think about! But yes, I suspect the idea of metabolically induced combustion is something of an exaggeration (even assuming some way to artificially raise an animal's metabolism). 75.4.22.29 (talk) 18:29, 4 February 2015 (UTC)
- You may be interested in reading square-cube law. -- ToE 19:55, 4 February 2015 (UTC)
- I don't tend to assign true/false values to random statements people make, absent any evidence either way. It's a strange thing to assume that every possible combination of syllables a person utters should be accepted as true without any evidence one way or the other. --Jayron32 16:49, 4 February 2015 (UTC)
- No, it could not "very well be true"; plenty of complex organisms require heat regulation of one form or another, but they do this for reasons of homeostasis, to avoid tissue damage -- not because they will burst into flames otherwise. Snow talk 16:49, 4 February 2015 (UTC)
- You'd have to assume they meant "if the human metabolic rate was increased to where they burned the proportional energy per second as a hummingbird, with no other changes, then the human would burst into flames". Obviously the increase in metabolic rate would never actually evolve, but you could determine how much heat would accumulate if it did. The statement is rather silly, but that's not the same as untrue. StuRat (talk) 17:20, 4 February 2015 (UTC)
- Yes, you are right to be skeptical; that claim betrays a great deal of confusion as to the nature of metabolism. The term is, in this context especially, a cache-all for any number of biochemical pathways, to which abstract notions of "fast and slow" apply with varying degrees of accuracy; some metabolic pathways might be said to be faster or slower in a human or a humming bird, while others that are found in one are entirely absent in another. I'd say it's an apples and oranges type situation, but frankly the hummingbird and the human are significantly farther apart in physiology than any two types of fruit. So already we've run into trouble in trying to establish what the aggregate "speed" of each organism's relative "metabolism" is. There are some measures that might be relevant, such as caloric expenditure over a given period of time relative to the overall mass of the organism. Regardless, even if we go with the generous suggestion that a hummingbird utilizes two-dozen times as much energy in a given period of time than a human, relative to mass, there's still no bio-mechanical or biochemical function by which either species can set itself alight through basic internal stresses or chemical reactions. Snow talk 16:43, 4 February 2015 (UTC)
- (edit conflict) Biologist Paul R. Ehrlich wrote on the topic of bird metabolism in his bird book, excerpts of which are available free online. Hummingbirds are already very close to fatal overheating, which is interesting from the viewpoint of evolutionary biology. "Why do birds (and mammals) run these risks of maintaining a high, constant temperature, especially since it costs them to do so?" ... But overheating is not the same as spontaneous combustion.
- Thanks for the link! 75.4.22.29 (talk) 18:32, 4 February 2015 (UTC)
- I've heard the "combustion" analogy repeated many times before, but it's not a very scientific statement: how do you scale a metabolic rate? Obviously if you select a scaling-methodology that implies a mammal should burst into flames, your methodology runs contrary to empirical evidence. From a viewpoint of biology or molecular chemistry, mammal metabolism is very similar to bird metabolism, appropriately scaled; and yet we do not see combusting wombats. So, although I'm sure you can find this analogy about combusting humans, it's improbable that you can attribute it to a reputable scientist. Nimur (talk) 16:43, 4 February 2015 (UTC)
- (edit conflict) Biologist Paul R. Ehrlich wrote on the topic of bird metabolism in his bird book, excerpts of which are available free online. Hummingbirds are already very close to fatal overheating, which is interesting from the viewpoint of evolutionary biology. "Why do birds (and mammals) run these risks of maintaining a high, constant temperature, especially since it costs them to do so?" ... But overheating is not the same as spontaneous combustion.
- Random internet numbers suggest that hummingbirds expend roughly 10 kilocalories per day and weight about 10 grams. That's about ~4.2 MJ / kg. Humans are more like 0.12 MJ / kg. So hummingbirds are burning roughly 35 times as much energy per unit mass as humans. Heat dissipation is generally proportional to temperature difference. Let's say the typical human is about 10 C warmer than his environment. Increase the energy output 35 times (by magic) and pretend there are no new sources of heat dissipation or limiting factors, and the human would now equilibrate around 350 C warmer. According to the interwebs, human hair ignites below 250 C, so it does seem plausible that hummingbird-man could autoignite (or at least it would be plausible if the whole thing wasn't completely silly to begin with). Dragons flight (talk) 17:36, 4 February 2015 (UTC)
- Sure, but why didn't you divide the absolute temperature by a factor of and add the boltzmann constant? You're already performing totally arbitrary mathematical manipulation.
- What I mean to say is, you are not conducting science. Science uses observation to guide our understanding. It's fruitless to start multiplying and dividing stuff just because we want to. Why do you assume energy-per-unit-mass is the appropriate unit? Have you got a testable hypothesis and experimental data to corroborate your approach? Can you refer to published sources that use that approach?
- Instead, what you're doing is throwing a bunch of equations at the concept, which perpetuates a widely held misperception of what science actually does. I know that you know better, but you're conveying the wrong message to people who aren't as well-informed about scientific process as you are!
- Most problematically, you're falling into the very same trap as StuRat - where are your cited references? You're throwing around quotes and factual assertions and numerical constants and attributing them to "the internet" at large. That's not suitable for our reference desk - we have higher standards than that, and I know that you can do better.
- Nimur (talk) 17:48, 4 February 2015 (UTC)
- I don't think you're trying to be funny, but I've got to laugh. That's a remarkable uptight comment to leave on a question about whether people with a hummingbird metabolism would spontaneously combust. You know I am capable of writing much more elaborate responses, but I don't think a question like this justifies either the time or energy. If my response bothers you, feel free to give a better one. However, your earlier reply simply dismissed the hypothetical without even considering any numbers, which is really just avoiding the issue. Here is a quote [9]:
- "Hummingbird metabolic rates are ..., the highest metabolic rate per unit of body weight in the avian world. ... Hummingbird researcher Crawford Greenewalt said that translates to [humans] eating forty ten-pound bags of potatoes or 1000 quarter-pound hamburgers every single day! It is thought, unbelievably, that this consumption would raise our body temperatures to 750°F (398°C) and cause us to explode."
- Greenewalt, was a chemical engineer by training (so maybe not technically a scientist), but he did publish a few academic papers on the mechanics of bird flight and our article claims he was president of the American Philosophical Society for a time. Greenewalt's 1960 book, titled simply Hummingbirds, was published by the American Museum of Natural History and also repeats the 750°F number. In the quote above, also note the use of "metabolic rate per unit of body weight", also known as the "specific metabolic rate", which is a typical way of comparing metabolism across species and equivalent to the scaling I used above. For example, the specific metabolic rate is mentioned in the metabolic theory of ecology. Personally, I think that is a natural scaling to use, for an admittedly silly hypothetical, but you could argue for a different one if you like. Dragons flight (talk) 19:21, 4 February 2015 (UTC)
- Thanks. The point stands that if we do some naive scaling in terms of energy output per hour, it would be far too much heat for a human to handle. But as others point out, humans don't work that way, and evolution doesn't work that way, etc. I think Nimur is being a bit too grumpy here; the calculations aren't totally arbitrary. But his point also stands: this isn't really "doing science", and there is nothing particularly valuable or deep about this exercise, other than to point out that hummingbirds are flying pretty hot.
- But we have lots of stories like this: "If humans were as a strong as ants, they could lift up full-size trucks over their heads!" or "If humans could leap like fleas, we could jump over a 70 story building!" -- Yes, there are scientific problems with that type of claim and we should be very cautious of "shut up and calculate" mottos. But the point of these quips is not to give a very rigorous lesson in biophysics or metabolism or whatever. The point is get people interested and excited about the natural world and the abilities of organisms, by doing some (often technically sloppy) translating to scales that normal humans are more comfortable thinking in. SemanticMantis (talk) 19:38, 4 February 2015 (UTC)
- Greenewalt, was a chemical engineer by training (so maybe not technically a scientist), but he did publish a few academic papers on the mechanics of bird flight and our article claims he was president of the American Philosophical Society for a time. Greenewalt's 1960 book, titled simply Hummingbirds, was published by the American Museum of Natural History and also repeats the 750°F number. In the quote above, also note the use of "metabolic rate per unit of body weight", also known as the "specific metabolic rate", which is a typical way of comparing metabolism across species and equivalent to the scaling I used above. For example, the specific metabolic rate is mentioned in the metabolic theory of ecology. Personally, I think that is a natural scaling to use, for an admittedly silly hypothetical, but you could argue for a different one if you like. Dragons flight (talk) 19:21, 4 February 2015 (UTC)
- Many thanks for finding that quote-- it's pretty much the sort of analysis I was looking for regarding this admittedly silly question, a quantification of the metabolic rates and temperatures involved and their possible effect. 75.4.22.29 (talk) 19:33, 4 February 2015 (UTC)Resolved
- Indeed, thanks for following up, and I apologize if I came across as grumpy. I'm glad that we've collectively been able to deliver a set of responses that are much more thorough than the last time I posted. Thanks guys. Nimur (talk) 20:39, 4 February 2015 (UTC)
- The point (I think) is that a lot of the pop-sci claims that are out there really don't stand up to even cursory examination ("Humans only think with 10% of their brains" or "Science has proven that a bee can't fly" are classic examples) - and others seem broadly OK. I think this one clearly falls into the second category...sure, it's a hypothetical situation - and a solid scientific answer would need to know how all of this extra energy is being generated...are the muscles bigger...are we ingesting more calories...all sorts of detailed matters the would affect the answer. But that's not the point here. The original inventor of this claim is merely trying to express just how ungodly active these birds really are - and in terms that most readers can comprehend. If it was off by an order of magnitude in either direction - then we might say it's nonsense - but it's clearly in the right ballpark - and that's good enough. It's not like designing an airplane where people's lives depend on you getting it right. SteveBaker (talk) 22:03, 4 February 2015 (UTC)
- Indeed, thanks for following up, and I apologize if I came across as grumpy. I'm glad that we've collectively been able to deliver a set of responses that are much more thorough than the last time I posted. Thanks guys. Nimur (talk) 20:39, 4 February 2015 (UTC)
- Many thanks for finding that quote-- it's pretty much the sort of analysis I was looking for regarding this admittedly silly question, a quantification of the metabolic rates and temperatures involved and their possible effect.
What do you mean? African or European Hummingbirds? It's a question of weight ratios. really all it means is that we'd have enough muscles and energy to flap hard enough to fly and use the air as coolant. Probably be very fast swimmers too. --DHeyward (talk) 18:32, 4 February 2015 (UTC)
- We had a cold snap the other night. The only birds that weren't flash-freezing in mid-flight were the local hummingbirds. New York One news was advising people who found sparrows and other songbirds frozen in mid-air to scoop them up with a fishing net, and microwave them on low for five minutes or so, depending on the make and wattage. μηδείς (talk) 18:44, 4 February 2015 (UTC)
- "And as I fricaseed him, he gave out a yell: 'Oy! Willow! Titwillow! Willow!'" --Allan Sherman[10] ←Baseball Bugs What's up, Doc? carrots→ 18:53, 4 February 2015 (UTC)
Asthma Meds
I have a list of Inhaled Bronchodilators and a list of Asthma Controllers. Both are many pages long (with many medications repeated for each dose/manufacturer). So far, every medication I've found is on both lists. Are these two names synonyms? Are there Inhaled Bronchodilators that are not Asthma Controllers? Are there Asthma Controllers that are not Inhaled Bronchodilators? 209.149.113.24 (talk) 17:44, 4 February 2015 (UTC)
- That might be a good question for your doctor or pharmacist. ←Baseball Bugs What's up, Doc? carrots→ 17:45, 4 February 2015 (UTC)
- You might find it helpful to read our article: Metered-dose inhaler. Dbfirs 18:06, 4 February 2015 (UTC)
- Some bronchodilators can be taken by routes other than inhalation as Asthma#Medications. Some astma controllers work against inflammation pathways rather than strictly bronchodilation. DMacks (talk) 18:20, 4 February 2015 (UTC)
Why aren't baboons extinct ?
As I understand it, most other primates don't compete with humans, since they live in jungles/tropical forests and humans mostly live on savannas/plains (good farming areas). However, I believe baboons live there, too. So, why didn't humans out-compete them or kill them directly, long ago ?
This source seem to imply that they could retreat to tropical forests when under threat: [11]. Is that how they survived ? StuRat (talk) 20:55, 4 February 2015 (UTC)
- In evolutionary terms, it's not uncommon for two species to occupy the same niche. Gnu and Zebra on the plains of Africa, for example. Both wander around in herds grazing on the same plants drinking from the same water sources and predated upon by the same predators. Neither has displaced the other. So long as their breeding success rates are kinda similar, it all seems to work out OK. I've gotta say that seems like an unstable equilibrium - but it happens in enough places that it's evidently a common situation. SteveBaker (talk) 21:53, 4 February 2015 (UTC)
- Zebra's and Wildebeests don't share the same ecological niche, in any of the senses of that word. They have differences in predation rates, identity of main predators, differences in refugia, differences in plant preference, differences in migration, differences in digestion, and differences in life history. This is a student paper [12], but it cites dozens of real research papers that discuss mechanisms of coexistence relevant to African grazers. Here's a paper that specifically addresses the differences in nutrition and foraging behavior [13] SemanticMantis (talk) 23:10, 4 February 2015 (UTC)
- I believe they prefer to be called "zebras and wildebeest". Or they would, if they weren't preoccupied with survival. I'm not being a grammar Nazi, just a concerned mutualist. InedibleHulk (talk) 04:17, February 5, 2015 (UTC)
- Zebra's and Wildebeests don't share the same ecological niche, in any of the senses of that word. They have differences in predation rates, identity of main predators, differences in refugia, differences in plant preference, differences in migration, differences in digestion, and differences in life history. This is a student paper [12], but it cites dozens of real research papers that discuss mechanisms of coexistence relevant to African grazers. Here's a paper that specifically addresses the differences in nutrition and foraging behavior [13] SemanticMantis (talk) 23:10, 4 February 2015 (UTC)
- First, competition isn't an all-or-nothing thing, and humans absolutely compete with many primates, usually for habitat, in the form of deforestation. There are several ways to quantify competition, but species that compete often coexist, we call it competitive coexistence [14]. Secondly, there's many types of competition - there's resource competition, apparent competition, and all these arise from the degree of niche overlap to consider (see also Limiting_similarity).
- But the simple answer to your question is "because in recent ecological past, the force of intraspecific competition is greater than the force of interspecific competition for these two species". This falls out of early work by Gause, now known as the Competitive_exclusion_principle. It also holds true in the Competitive_Lotka–Volterra_equations, and it remains true for most any theoretical model or empirical study. Levin (1970) establishes that complete overlap of niche precludes coexistence. So I can say with some certainty that baboons and humans don't share the same niche. Coexistence can be promoted by even slight differences in predators, slight differences in prey, differences in refugia, things like that. Temporal variation in resources, and species-specific responses to spatial heterogeneity also go a long way (Chesson and Warner, 1981; Chesson 2000, and we even have an article on the storage effect).
- So we know why in a general sense, but to get into the proximal mechanisms, we'd have to know more about the fecundity, diets, predation, and migratory patterns of our ancient ancestors, as well as those of ancient baboons. I'm sure people will be happy to speculate on that, but I won't. I will opine casually, that most any baboon could kill most any human without even trying. So our ancestors probably kept their distance :) 23:10, 4 February 2015 (UTC)
- Baboons are rather vicious little monkeys, the largest of the non-hominid primates, omnivorous, swift, living in packs of dozens or more, and adult males are able to intimidate leopards. They are known to kill sheep, goats, and antelope, as well as other monkeys, and rarely, human children. They are eaten as bushmeat, but given the diseases they carry, they may be smarter than their human predators. And they run faster than humans, breed more regularly, and, like the Cape baboon retreat to hills, rocks, and large trees for defense and nesting. They could surely be driven to extinction with modern firearms, but the trend is apparently for them to become scavengers of human settlements, not human prey. μηδείς (talk) 03:53, 5 February 2015 (UTC)
Can rockets fueled with liquid hydrogen, use the oxygen of the air?
Up to what altitude can it use the oxygen of the air, if at all?Noopolo (talk) 22:45, 4 February 2015 (UTC)
- They could, in theory, but none that I know of do. Rockets consume extremely high amounts of fuel. Getting a corresponding amount of oxygen from the environment, compressing it to the required pressure, and injecting it into the engine probably is more trouble than it is worth. Note than most jets are very inefficient at low speed, because the air is not already compressed by airspeed when entering the engine inlet. And that initial phase is when rockets need their oomp most - the longer a rocket stays essentially motionless, the longer it wastes fuel just by keeping more fuel (in tanks) from falling back to earth. --Stephan Schulz (talk) 23:21, 4 February 2015 (UTC)
- The word is "oomph" [15]. Dragons flight (talk) 03:40, 5 February 2015 (UTC)
- The problem is that you would need a very different configuration to use atmospheric oxygen than using oxygen from tanks. So, you'd want a big scoop in front for the first part, but not for the second. This might be possible, via a multistage rocket, or perhaps a rocket that launches off the back of a conventional airplane (this option requires a small rocket and huge airplane). StuRat (talk) 23:31, 4 February 2015 (UTC)
- It's so different that we have a different name for the thing. It's only called a rocket if it doesn't use oxygen from the atmosphere. If it does, it's a type of jet engine. --65.94.50.4 (talk) 00:18, 5 February 2015 (UTC)
- Checking the Saturn V, for example, the stages were fueled by rocket propellant and then by hydrogen. In all stages, liquid oxygen was used as the oxidizer. Obviously, needed in much greater concentrations than the atmosphere could provide. ←Baseball Bugs What's up, Doc? carrots→ 00:22, 5 February 2015 (UTC)
- You may wish to read about SABRE (rocket engine), the "Synergistic Air-Breathing Rocket Engine" which would be the engine for the proposed Skylon_(spacecraft) launch vehicle. -- ToE 01:15, 5 February 2015 (UTC)
- And for those who just want a quick answer, SABRE, described as an Air/LOX/LH2 engine, is designed to switch over from air to LOX at Mach 5.14, 28.5 km altitude. Note that it is currently a paper rocket engine (though they are doing some development of components) for a paper rocket. -- ToE 01:29, 5 February 2015 (UTC)
- Here's a rough attempt to quantify this. I'll outline some false assumptions further down.
- According to Falcon 9, the first stage of that rocket uses 150,000L of liquid oxygen.
- According to this book, the concentration of oxygen in air is 9.35 mol/m3.
- According to Oxygen, the relative atomic mass of oxygen is 16, meaning that one mole of oxygen weighs 16g.
- According to Liquid oxygen, the density of liquid oxygen is 1.141kg/L.
- According to SpaceX, the first stage burn time of the Falcon 9 is 180s.
- From 2 and 3, we can calculate the mass of oxygen per m3 of air. This is 9.35 x 16 = 149.6g/m3.
- From 1 and 4, we can calculate the mass of oxygen burnt by the first stage. This is 150,000 x 1000 x 1.141 = 171150000g.
- From 6 and 7, we can calculate the equivalent volume of air required to provide the oxygen requirement of the first stage. This is 171150000 / 149.6 = 1144050m3.
- From 5 and 8, we can approximate the rate at which air would have to be consumed by the rocket to supply the necessary oxygen. This is 1144050 / 180 = 6356m3/s.
- Note some dicey assumptions here:
- I've assumed that the density of the atmosphere is constant. It isn't. The numbers used are approximately the same as surface conditions, but as the rocket goes up, the volume of air required will increase.
- I've assumed that the burn rate of the rocket is constant. I don't think it is, though I don't know. I'd expect that maximum burn rate would occur as the rocket is just leaving the launch pad, ie. the time when it's hardest to ingest air, because you don't get the compression effect of the rocket's motion.
- With all that in mind, you've then got to design an air intake to provide the air. According to SpaceX, the rocket itself is 3.7m diameter. Let's be generous and say you build a big, circular air intake on the front of the rocket that takes that entire diameter. That gives you an area of 11.6m2. That means that, to provide our 6356m3/s of air, the air through the intake will have to travelling at 6356 / 11.6 = 546.8 m/s, or nearly 2,000km/h. At the earth's surface, at, say, 15 degrees, that's mach 1.6.
- So, to do this on the Falcon 9, with an air intake taking up the whole forward-facing profile of the rocket, you need to accelerate the air moving into the engine to 1.6 times the speed of sound before the rocket starts moving, and you have to do it without destroying the vehicle's aerodynamics. This is why they don't do it. GoldenRing (talk) 03:23, 5 February 2015 (UTC)
- Well, part of why they don't do it. There is, among other things, also the problem that you either need to somehow separate oxygen from the other 80% of the air before it enters the motor, while it is moving at mach 1.6, or somehow accommodate an extra 5,000 cubic metres of non-reactive gas moving through the motor each second. GoldenRing (talk) 07:27, 5 February 2015 (UTC)
February 5
causes of condom failure
According to Wikipedia 1-2 percent of women will test positive for semen residue if no condom slippage or breakage is observed. How is that possible? Could it be that the semen leaked through the pores of the condom even though it was used correctly? — Preceding unsigned comment added by Roger adams49 (talk • contribs) 04:13, 5 February 2015 (UTC)
- Could be someone else's semen. InedibleHulk (talk) 04:21, February 5, 2015 (UTC)
- Leakage around the edge, maybe. This is why spermicidal foam should be used with it. Although it could be sabotage. I recall a story about three nurses gossiping. One nurse said she found condoms in the doctor's desk. The second nurse said she not only found them but ran a pin through each one. The third nurse fainted. ←Baseball Bugs What's up, Doc? carrots→ 04:32, 5 February 2015 (UTC)
They tested positive after intercourse with a condom — Preceding unsigned comment added by Roger adams49 (talk • contribs) 04:51, 5 February 2015 (UTC)
- Use spermicidal foam along with it. ←Baseball Bugs What's up, Doc? carrots→ 04:53, 5 February 2015 (UTC)
Well, I remember reading somwhere that condoms lubricated with spermicide are no more effective than condoms without it. Roger adams49 (talk) 05:11, 5 February 2015 (UTC)
- You read wrong. ←Baseball Bugs What's up, Doc? carrots→ 05:21, 5 February 2015 (UTC)
- Anyways, is it possible for semen to leak through a condom even if used correctly? I always thought it was impossible, since condoms don't contain pores. Thats what wikipedia seeems to imply.Roger adams49 (talk) 05:36, 5 February 2015 (UTC)
- If a condom is used correctly, it's used in a way that prevents anything getting through. Nothing that is successful can fail. A condom with a hole, even unobserved, will fail. Wikipedia has given you four other options to consider, there's no need to dwell on the idea of something permeating the impervious. InedibleHulk (talk) 06:36, February 5, 2015 (UTC)
- Why are people saying random stuff without bothering to checking references? Our own article Condom#Spermicide and to a lesser extent Spermicide#Use with condoms confirm that it unclear if condoms lubricated with spermicide are actually more effective at preventing pregnancy than condoms without. There are plenty of external sites which say the same thing [16] [17] They also have disadvantages namely a shorter shelf life, a possibly increased risk of urinary tract infections in women and a possibly increase risk of HIV transmission. For these reason and perhaps more, they are no longer recommended by many health sources and no longer produced by many manufacturers. Using spermicide packaged seperately together with condoms may however reduce the risk of pregnancy as there is more of it, although still has the earlier disadvantages (well it obviously doesn't effect the shelf life of condoms), so it's generally suggested it should be used with caution (e.g. some only recommend it for a couple in a monogamous relationship where HIV isn't a concern). Nil Einne (talk) 11:48, 5 February 2015 (UTC)
- P.S. I appreciate the source used in our article and the ones I could find aren't that great sources. E.g. as this source [18] I saw in our article on condoms mentions, there are a lot of rumours and poorly supported information when it comes to sexual health and preventing pregnancy, even those without a religious reasoning and coming from health advice sources, such as that about "double bagging". I did have a look for more scholarly sources and couldn't actually find any that took a good look at the effectiveness of spermicide lubricated condoms at preventing pregnancy. Heck even this very old source [19] which appears to have been around the time these were first made, only seems to have looked at the effectiveness in a certain group rather than in comparison to condoms without spermicide. I did come across [20] which is perhaps an interest source if you can get it for a somewhat old overview of spermicides in general. I'm not sure why there appears to be so little research on the effectiveness of spermicide lubricated condoms at preventing pregnancy. It may be that research on spermicides in general suggest the amounts used with condoms is probably too small to be of much use. (One source or more sources I read [21] did note there may similarly be a lower risk of many of the complications due to the lower levels. That said, one of the papers on the risk of UTIs was specifically related to spermicide lubricated condoms, although having had a quick look at the paper, they also found a smaller higher risk for people who used condoms in general.) It may also be because while preventing pregnancy is important for many, there are a number of resonably effective methods for pregnancy prevention (with different costs, benefits and risks) but barrier methods particularly condoms, are the only effective method for sexually active people to protect against STIs particularly HIV. And so the recent research focus on condoms with spermicides has been about STIs and similar stuff. (One of the factors may have been there was an interested in condoms lubricated with spermicides to prevent STI particularly HIV transmission due to some in vitro evidence. However further research didn't show this in vivo and combined with the possibility of increasing risk due to the complications from long term meant there was a move away. There is or was still a hope that a perhaps spermicidal agent can be found which would help reduce the risk of HIV transmission and has few complications.) It may also be the concern is when condoms are already lubricated with spermicide, the users don't think much about whether they should be using spermicide so it's better if these are seperate so there's proper consideration of the benefits and risks and times to use them (which is possibly only vaginal sex). Either way, it does seem there has been a move away from them. And it definitely seems misleading to suggest as was done above that it's wrong to state "condoms lubricated with spermicide are no more effective than condoms without it". From the evidence available, I don't think we can conclude this is definitely the case, but we also can't conclude it's wrong. Nil Einne (talk) 12:47, 5 February 2015 (UTC)
- In response to the specific question about semen residue, I looked at the sources from Condom#Causes of failure where this claim is present. There are two papers.
- One a metholodogy verification paper with a relatively small sample size [22]. It seems semen residue primarily means prostate-specific antigen, although there was also a check for sperm in some cases. (The check for sperm found it in a few cases without PSA and even when there was claimed abstinence for 24 hour or more but always at low levels. In the PSA cases, sperm was always found, but sometimes at low levels. PSA was always found in samples taken immediately after unprotected sex, but never after 24 hours. BTW, to avoid confusion, I don't think sperm at the low levels was counted as a 'semen residue', actually the primary intention of one of the papers seems to have been to demonstrate that PSA seems to be a better indicator of recent "seminal exposure" than sperm.)
- Anyway in this paper, they didn't include any cases where PSA was found in the pre-coital samples. And whether due to this, the small sample size or whatever, there was no PSA found in those cases that were considered where there were no reported problems with the condom.
- Note also that samples collected after 72 hour abstinence didn't contain any PSA. BTW, all female participants had tubal ligation (and part of the study included unprotected sex as well participant punctured condoms). One final interesting thing is that even in cases where breakage or slippage did occur, PSA levels did vary wildly.
- The second paper is where PSA was detected in some cases with reported failure is interesting [23]. Although in the earlier methodology paper by largely the same authors it was suggested (as was done in that case) that pre-coital samples should be taken to rule out PSA being present from a previous sex act, it doesn't sounds like this was done here. May be they had found this was too odorous and so lead to low compliance. It's also possible they felt it wasn't that important since PSA doesn't generally seem to be detectable for long and the couples were supposed to record coital acts etc in a diary (and so if they didn't comply there, they may not have properly complied with the pre-coital swab anyway).
- They do mention it's possible the PSA came from unreported previous unprotected sex. (This being a different sexual partner as suggested above could be one reason it was unreported, but there could also be other reasons ranging I'm guessing from the partners bringing drunk, to one of the partners not knowing.) They don't mention sabotage. They do mention undetected failure is unlikely, but I'm a bit confused whether they're saying they don't believe the cases were undetected failure, or they think if it does occur, it's low as evidenced by only find the 1.2% of cases with PSA without reported breakage/failure.
- Interesting of the 3 cases where they did find PSA, 2 of them had it at a low level, significantly below that expected from unprotected sex (so whether the sex had been a while, or it wasn't unprotected, who knows). One of these cases (I presume the one with the higher level of PSA, but this isn't stated) did have a clinically significant level of sperm.
- Anyway beyond the suggestion it could be due to unreported unprotected sex, they don't actually comment much on the 1.2% of cases with PSA without reported failure, I think the general point is the rate was fairly low and it's ultimately impossible to know from their results why PSA was detected despite their being no recorded failure. Note that they did have 2 pregnancies in couples where no failures were recorded and the instructions are supposed to have been followed every time. (They also had 8.1% of their participants withdrawing of the research due to breaking up.)
- Nil Einne (talk) 14:30, 5 February 2015 (UTC)
cold dark matter and nuclei
Is cold dark matter, such as the hypothetical axions, expected by theorists to be able to pass through or even exist inside, without interacting, atomic nuclei?Rich (talk) 05:30, 5 February 2015 (UTC)
- If they are particles then yes, otherwise the particles would be somewhat like neutrons, and be absorbed in the Earth or particle detectors. It would be like super dense low speed neutrinos, or perhaps even golf ball size pieces of rock. Although primordial nucleosynthsis puts limits on how many protons and neutrons there should be around to form normal matter. Graeme Bartlett (talk) 07:54, 5 February 2015 (UTC)
Space Elevator
Inspired by a question above, wouldn't the space elevator be quite dangerous? After all, at such a height (way above the ISS, it would be more likely to be hit by space junk (more space, more junk). I know that most space junk is only small, and hundreds of miles apart, but by building something so big, the likelihood of it being hit by something would be higher, logically. Also, there would need to be some permanent staffing for maintenance purposes and periodic checks on the structure, probably on a constant basis (22,000 miles is a long way). KägeTorä - (影虎) (Chin Wag) 11:07, 5 February 2015 (UTC)
- Yes. See Space elevator safety. I suspect the hazards outweigh the advantages, and we will never see terrestrial one in practice. Nevertheless the concept could lead to advances in other areas.--Shantavira|feed me 11:51, 5 February 2015 (UTC)