Wikipedia:Reference desk/Archives/Science/2007 June 11

= June 11 =

Gliese 581c
I've been wondering about this for a while. Does anyone have a rough estimate of the probability of life on Gliese 581c? Thanks in advance! Gbgg89 00:54, 11 June 2007 (UTC)
 * No one really has any idea, because we only have one data point in the universe for life, namely our planet; extraterrestrial life could potentially bear little resemblance to our own. That being said, that chance that Earth-like life (say, carbon-based with water as the solvent for chemical reactions) existing on Gliese 581 c is very, very small, because estimates for the temperature on the planet didn't account for its atmosphere (which is unknown). Very likely the planet looks more like Venus than Earth, making it far too hot for life. zafiroblue05 | Talk 01:51, 11 June 2007 (UTC)


 * It's really impossible to know - we could perhaps say for sure that "life as we know it" (carbon/water) is impossible because of some temperature or radiation problem on the surface - but that's about the limit of what we could say - and even then we're on shakey ground.
 * What about underground where life might be shielded from radiation - or at the poles where it might be cool enough?
 * Are there perhaps strategies that extremophiles may have developed that we havn't thought of yet?
 * What about life as we don't know it? Life based around other chemistry is something that science fiction talks a lot about - but there is little doubt that the complex chemistry required strongly favors carbon/water life forms - but that doesn't necessarily make life based around exotic systems of chemistry impossible.
 * Life as we don't know it might be self-reproducing data with no chemical basis - something like patterns in sand dunes that maintain their shape, split in two, consume other patterns in order to retain their shape? Something weird like that might be classifiable as life yet have no specific material existance.
 * What about intelligent life that developed elsewhere and travelled to that world where they live in highly protected artificial environments?
 * So really it's going to be impossible to come up with a probability for something utterly unknown in scope. SteveBaker 12:59, 11 June 2007 (UTC)


 * See also Drake equation. User:sanders_muc

I came upon this question in a search and realized this would help. Some Albedo/Emissivity combinations (extremes) are unrealistic. =((((R^2)*σ*(Te^4)*(1-A))/(4*ε*(d±(d*e))^2))^0.25)-273.15 24.78.167.139 (talk) 17:34, 30 May 2010 (UTC)

Glass
Can some one tell me the process for making glass? I also want to know the historical origin of glass. —The preceding unsigned comment was added by 196.200.102.42 (talk • contribs).


 * You might start with the articles on Glass and Glassblowing (which contains a brief description of the process of making molten glass, and a description of one method of shaping it). You can find even more articles by using the search box on the left column of your window.  Come back if you have more questions. --TeaDrinker 07:14, 11 June 2007 (UTC)

See float glass for the common process for making window glass. StuRat 15:37, 11 June 2007 (UTC)

Animal anatomy:
I'm about to embark on a series of rewrites involving animal anatomy & would love to have a partner in crime. This would involve polishing any articles that I've rewritten or expanded to make sure I haven't made any mistakes & to add anything I've missed. The said person must have fairly good knowledge on anatomy in animals in order to make up for my shocking knowledge of the subject ;). Anyway, more than one person would be great, and I'm going to start in the next week or so. Work doesn't need to be finished straight away, but a collaborative effort needs to be kept up. If you're up for it, leave me a message on my talk page or here & I'll send you the article links when I'm done with them. alas, no rewards available this time round. Cheers, :) Spawn Man 09:46, 11 June 2007 (UTC)

What is a shaft passer?
I had read somewhere that it allows a shaft of a gear or a wheel to pass through the spokes of another wheel. Wikipedia doesn't seem to have an article on this. No joy on Google either -- WikiCheng | Talk 11:57, 11 June 2007 (UTC)


 * I'm pretty sure that's an old joke, the fictitious object of a snipe hunt which new engineers are sent on. —Steve Summit (talk) 12:32, 11 June 2007 (UTC)


 * (ec) [addendum] So how hard did you work at that Google search? :-) The fourth hit of this search leads straight to this Google books excerpt from the classic Surely You're Joking, Mr. Feynman!.  (Which must be where I heard of it.  So change "fictitious" to "semi-fictitious".) —Steve Summit (talk) 12:41, 11 June 2007 (UTC)


 * Try searching for "shaft passer" (with the quotes) in google. You'll find this - a German uboat invention called a shaft passer. --Kainaw (talk) 12:37, 11 June 2007 (UTC)

Surely You're Joking, Mr. Feynman! is exactly where I read it. One of the google links takes me to where the exact wordings are given. Kainaw's link is about the same topic. None of these actually tell us what the shaft passer is :-( -- WikiCheng | Talk 12:49, 11 June 2007 (UTC)


 * Because wikipedia apparently doesn't like commas in urls, the link I gave (if you view the 'edit page' code) goes to page with two responses:
 * It actually handles commas just fine; what it didn't like was the "|" you put between the link and its description. I've fixed it now. —Ilmari Karonen (talk) 22:45, 12 June 2007 (UTC)
 * Response 1:
 * It was invented by the Germans during the war to keep the British minesweepers from catching the cables that held the German mines floating under the sea at a certain depth. With these "shaft passers," the German cables could allow the British cables to pass through as if they were going through a revolving door.
 * Response 2:
 * It is actually a Russian WW1 invention as far as I'm aware. Think of it as two cog wheels built into the mine's mooring rope. The two wheels are connected by metal spokes that rotate with the wheels and alternatingly engage and disengage on locking mechanisms fitted on to the opposing wheel's axle, so that one spoke at least (in fact a pair - to the left and right of the wheel), always keeps the connection between the mooring ropes. Now, when the sweep wire rides up on the mooring rope, it encounters the two cog wheels. The cogs transport the wire over the wheels. As the spokes on the forward side disengage, the ones that come behind the wire engage and thus maintain the connection. That's it. I'll chase a drawing if you wish.
 * I'm not claiming these are correct - only that a search with "shaft passer" in quotes does return hits. --Kainaw (talk) 15:12, 11 June 2007 (UTC)


 * That's where I heard about a "shaft passer", too&mdash;and it's the only place. I've tried just about every clever Google search I can think of since then, and I'm coming to the conclusion that our search for a 'shaft passer' may well demonstrate that Feynman was either the victim or perpetrator of yet another clever practical joke.
 * Does anyone have any expertise in (or knowledge of) modifications to moored mines which would make them more resistant to sweeping? TenOfAllTrades(talk) 14:13, 11 June 2007 (UTC)


 * Just a couple weeks ago I saw a device on a man-safety line that allowed a carabiner to pass by the connection points that anchored the line to the fixed stanchions supporting the line. The application was at a canal lock, the line was attached to a wall that ran alongside the lock horizontally for a hundred feet or so, and the lock workers wore harnesses that had a lead which they clipped to one of these devices on safety line, to prevent them falling into the lock if they got too close to the edge.  I suspect someone more familiar with climbing gear, or industrial safety gear has seen and/or used these things... I tried to figure out how it worked (I could see it, but not get closer than a couple of feet).  It appeared to be very similar to the device described above with two cogs, and spokes.  As the lock worker walked along the wall, the device would come across a place where the line was anchored to the wall with an eye bolt, and the device would travel over the eye bolt without disengaging from the safety line.  Would that device be considered a "shaft passer" ?  Is there another commonly-used term for it?
 * —Preceding unsigned comment added by 71.112.132.210 (talk • contribs) 19:47, 11 June 2007

I suppose it is the same mechanism, used for a different purpose. It looks like there was an article (or a yet-to-be-created article) in Wikipedia on shaft passer sometime back. There is a mention of protecting the page here. Thanks to all of you for trying to enlighten me but I still haven't got beyond having a hazy idea of what a shaft passer is. But I am convinced that there is something. Please have a look at too. I have a feeling that it is also referred to as an 'avoider'. -- WikiCheng | Talk 04:59, 12 June 2007 (UTC)


 * First, WikiCheng, sorry for telling you what you already knew when it came to SYJMF.
 * Second, 71.112.132.210, that mention of a "passer" for carabiners and a fixed safety line is interesting. It's an easier problem, though, as what we have there is a device that's normally attached to a line.  By attaching it at two adjacent points, and allowing one attachment at a time to be temporarily disconnected, an obstruction can be easily passed.  (Furthermore, in the case of the safety equipment, there's not normally much force on it, as long as the worker is not in the process of falling.)  But what we're talking about wrt a "shaft passer" is a device that can allow two normally-disconnected shafts or lines to pass each other without interference, and moreover while they're both potentially under significant tension (or compression).
 * [[Image:Rock_crusher_gears.jpg|thumb]] Finally, if anyone's still not visualizing what the hypothetical shaft passer would do, take a look at the picture at the right, and imagine that one of the shafts supporting one of the auxiliary gears were routed through one of the spoke holes of the large gear in the middle. Obviously the mechanism wouldn't work very well, because as the large gear rotated, it would hit the intruding shaft, either breaking something or jamming the machinery.  But if there were some magical mechanism in the middle of each of the (in this case four) spokes which could open, one at a time, to allow the shaft to pass as the large gear turned...
 * —Steve Summit (talk) 11:11, 12 June 2007 (UTC)


 * You may be interested to know that Nature invented the shaft passer a very long time ago. It is called topoisomerase II. --mglg(talk) 16:52, 12 June 2007 (UTC)


 * You might be able to do it with strong magnets. Basically take two bar magnets and stick them on their sides to the ends of the shaft you want "passed through" the gear. As one shaft turns the other will turn so that the magnets are parallel with each other and    the opposite poles across from each other. Of course the turning shaft would have to have relatively little resistance on either side compared to the strength of the magnets for this to work.  Sifaka   talk  22:35, 12 June 2007 (UTC)

Aha! Thanks to Usenet and Archive.org, we finally have an image! According to the page, the illustration originally appeared in the July 1946 issue of Popular Science. It actually feels almost obvious, once you've seen it. I wonder if I could draw a free SVG version... —Ilmari Karonen (talk) 23:23, 12 June 2007 (UTC)
 * Ps. Here's a non-archive version of the page, though it's in French. (Apparently, in case you didn't know, a shaft passer in French is un éviteur d'axe.  Now you know.)  —Ilmari Karonen (talk) 03:16, 14 June 2007 (UTC)

Thanks a lot Ilmari! Thank you very much ! As you mentioned, it feels almost obvious. If I draw this (copy it from the picture you provided), is it good enough (legal) to be put in Wikipedia? -- WikiCheng | Talk 05:40, 13 June 2007 (UTC)


 * Redrawing a copy of the illustration would be a copyright violation. However, drawing an original picture of the mechanism — from a different angle for example — based on the information given in the illustration should be OK.  —Ilmari Karonen (talk) 19:56, 13 June 2007 (UTC)

IMPORTANT!. Shaft passers exist.. Not a wild goose chase. Simply place cogs (free to rotate) on the passed shaft - then use a cog on certain shaft and cogs on inner rim of outer wheel - this works - see original question "allows a shaft of a gear or a wheel to pass through the spokes of another wheel" -

Hypothetical Runaway Greenhouse effect
I was reading Greenhouse effect and also Venus and got to thinking. If life had not evolved (or created, depending on viewpoint), would the greenhouse effect escalate to the point of venus? This is assuming that the sun is stable, and has an infite supply of hydrogen to continue on it's Main sequence indefinately, no intervention from comets, ateroids, alien life, supernovae, etc. My assumption is that the atmosphere would eventually look like Venus based on so far what I've read. With constant heat from the sun, the earth radiates pretty much as much heat as it recieves from the sun, but volcanism should increase the amount of CO2 in the atmosphere, which causes the greenhouse effect. That makes the earth retain more energy then it is letting off. But is there enough CO2 escaping from the atmosphere to balance this effect?

On another note, it doesn't look like anything severe has happened to Mars yet, unless we can say the atmosphere is 95% Carbon Dioxide due to the greenhouse effect. --GTPoompt (talk) 14:14, 11 June 2007 (UTC)


 * Don't forget the difference the distance from the Sun makes. Mars may very well need a "runaway greenhouse effect" just to keep the temp livable (for humans) at that distance from the Sun.  Smaller planets, like Mars, also cool more quickly than larger planets, losing their geothermal (or equivalent) sources of heat.  StuRat 15:31, 11 June 2007 (UTC)

What happens (without life of any kind, including that which build machines to burn fossil fuels) is that the level of CO2 in the Earth's atmosphere is in equilibrium: Just as volcanoes transfer CO2 from the Earth to the atmosphere, so too does CO2 from the atmosphere re-combine with oxide and hydroxide minerals, converting them to carbonates and bicarbonates (a "locked up" form of CO2) and thus transferring the CO2 back from the atmosphere to the earth. This is a cyclical process, and the Earth is just far enough from the sun that this is a stable equilibrium. -User: Nightvid

Just a guess. Slow rotation and no orbital eccentricity probably contributed to the demise of liquid water. I think retaining the vast oceans on earth and the mechanism that does it is what keeps the earth in check. Keep in mind that water was the principle greenhouse gas on both planets, not CO2. On venus, the water evaporated and is gone and CO2 cocentrations went nuts (95% on venus versus 0.04% on Earth). A runaway process on earth would be oceans evaporating and adding more water the to atmosphere. CO2 may cause minor fluctuations, but to see venetian style global warming would require a water vapor driven process. This seems to be independant of life on the planet as the earth has been both warmer and colder as well as volcanic but never runaway. --Tbeatty 09:54, 14 June 2007 (UTC)

A website for getting introduced to quantum mechanics
Regarding the above subject I humbly request the desk volunteers to suggest me a good website that would give somewhat elaborate introduction to quantum mechanics. Many webpages as far as I searched the introduced quantum mechanics with birds eye view about wave function. How to use the wave function to calculate a particles position at point B if it started at point A having x momentum when such calculations involves wavefunctions having many imaginary quantities? Webpages that start dealing with wavefunction didnt deal with any numerical example as one above. And the topic gets advanced as one reads through. Thanks. signed 121.247.214.226 15:15, 11 June 2007 (UTC)


 * Have you read our article, introduction to quantum mechanics (and the rest of Category:Introductions)? Laïka  15:27, 11 June 2007 (UTC)
 * why are these in main namespace? isn't this what wikibooks (and/or wikiversity) is for? I humbly submit they belong transwikied. dab (𒁳) 15:32, 11 June 2007 (UTC)
 * I think they are valid content forks. I agree that the content also belongs in Wikiversity or Wikibooks, but it accords with all the WP policies, and is not a duplicate to the more technical articles.  It's comparable to the situation in most United States colleges where there are separate courses for majors and non majors. Yechiel Man  15:38, 11 June 2007 (UTC)
 * yes... well.... that's a dreadful precedent. If we begin to write articles for majors and non-majors, and then for highschoolers and preschoolers, they will be a nightmare to maintain. I appreciate the value of these articles, but I really think they belong on a sister-project. That's not in any way a devaluation, it's precisely why these projects were created, and hosting the articles here instead of there amounts to "brain-drain" to those projects. dab (𒁳) 16:34, 11 June 2007 (UTC)


 * Don't forget Britney's Guide to Semiconductor Physics. TenOfAllTrades(talk) 17:10, 11 June 2007 (UTC)


 * The original question asked how to calculate the particle trajectory, given its starting conditions (position and momentum). That is classical mechanics, by definition.  Quantum mechanics is a wholly different conceptual framework, and does not have descriptions for things like "trajectories."  There is only the wave function.  Given the starting conditions (i.e. initial wave-function), the end-result (resulting wave-function) can be calculated.  Position and momentum are a measurement of the wave function, instead of fundamental properties (as they are in classical mechanics).  Nimur 22:06, 11 June 2007 (UTC)
 * this is not strictly true. The notion of trajectory is very much part of quantum mechanics, in the path integral formulation. There is "just the wave function", sure enough, but the wave function expresses the probabilities for certain trajectories. dab (𒁳) 11:30, 12 June 2007 (UTC)


 * I'd recommend doing a few searches for "six easy pieces", which was a lectures series at Cal back a couple decades that is still a great place to start learning about quantum physics. - M  ask?  02:34, 12 June 2007 (UTC)


 * This is what you are referring to, right? —Bromskloss 09:45, 12 June 2007 (UTC)


 * Looks like it, although those are more recent. I had them on cassette that had a copyright date of 1983. - M  ask?  11:38, 12 June 2007 (UTC)

menstrual cycle
on an average 28 day cycle, what are the most infertile days of the cycle?
 * See Menstrual cycle and rhythm method. But beware that using this as a method of contraception is notoriously unreliable. Rockpock  e  t  17:57, 11 June 2007 (UTC)

5% per year? I doesn't say how often they tried. What does that actually mean?


 * Fertility awareness, done properly, is very effective. Note that the rhythm method is not "doing it properly".  Friday (talk) 18:49, 11 June 2007 (UTC)


 * I'm not sure what you're referring to but the table lists the typical failure rate for the rhythm method as 25% in the first year. The easiest way to think of this is that 1/5 couples using this method will get pregnant in the first year. The article explains some issues related to the failure rate in more detail Nil Einne 18:52, 11 June 2007 (UTC)


 * Sudies show that if one uses the Standard Days Method correctly (as that image demonstrates) there is a 4.75% pregnancy rate, however, since people who chose this method rarely do it correctly, the typical rate is 11.96%. Rockpock  e  t  21:13, 11 June 2007 (UTC)
 * Oh, and a 25% rate is for the old skool rhythm method, and it means 1/4 of couples get pregnant, not 1/5. Rockpock  e  t  21:17, 11 June 2007 (UTC)


 * You're right, ooops... Nil Einne 20:00, 13 June 2007 (UTC)

Crow identification
...well, corvid identification.

We found a fledgling at work today; unable to fly and at severe risk of a passing cat, it was a really sad sight. But it was completely fearless - it stood in a doorway and let people walk "overhead" - which meant I could sit a few feet away and get very clear pictures. Here's five. So, are we looking at a crow, a rook, or a jackdaw (my current guess) - or something else entirely? It's the old problem of juvenile plumage, and not wanting to read too much into colouring details, that measn I can't be sure... It was certainly pretty large, about the same size as an adult blackbird, so it must have been of a fair age for a fledgling. Shimgray | talk | 21:02, 11 June 2007 (UTC)
 * I'd agree, it definitely looks like a jackdaw. Identifying features: it's a corvid because of the dark bulge at the upper base of the beak and the appearance of the feet; its bill is too pointed and narrow to be a crow or a rook; it has the grey (rather than black) head, breast and nape plumage of a jackdaw and it has a jackdaw's pale whitish-grey eye. QED :-) --YFB ¿  22:10, 11 June 2007 (UTC)
 * Some info about dealing with wildlife in need of care . Edison 23:06, 11 June 2007 (UTC)

Lightning and Grounding
Hello. Ground wires discharge objects and carries the charge to the ground. Can this charge in the ground cause lightning? Thanks. --Mayfare 22:31, 11 June 2007 (UTC)
 * If anything, an above-average charge in the ground would discourage lighting strikes --⁪frotht 23:54, 11 June 2007 (UTC)


 * Dont think so- though it depends on how you define ground. Is a standing tree or a building ground? Lightning can certainly jump from a tree to you, thence to (real) ground. Since the potential difference is originally created between the cloud and the earth, once the charge has passed to ground there wont be any lightning produced from the ground because the charge cannot appreciably raise the potential of the ground.
 * This is not to say that you are safe: currents in the ground can produce lethal potential differences in the space of one stride. I believe it is quite a common occurence for cattle to be killed this way since they have a longer wheelbase than humans. If out in lightning waether, its better to take small steps (and keep low).


 * It is unlikely that any household utility electric circuit can supply enough charge or current to induce lightning; numerous safety faults and circuit breakers would cut off the power before a large charge could accumulate in a small amount of time. However, charge on the ground can accumulate as part of normal atmospheric lightning.  See Lightning for a discussion of ground-to-cloud, cloud-to-ground, and other strikes. Nimur 18:07, 12 June 2007 (UTC)


 * Ah, another one of those things where we have to be careful about what "cause" means. If your lightning rod is the highest object around, then most likely the lightning will strike (either originating from or going to) that rod instead of striking something else.  So it does cause strikes in a sense, the probabilities of where lightning strikes has been changed and hopefully the distribution is more localized (I wouldn't want to be near one in a thunderstorm!).  But will it cause more strikes in the vicinity, given a big enough, but not absurdly big, vicinity? (maybe mile wide?)  I would guess not. Root4(one) 04:40, 13 June 2007 (UTC)


 * Lightning rods are not supposed to "attract" strikes, they are supposed to prevent them by dissipating charge slowly (preventing a strike at all). It is a common misconception that they are supposed to be the "designated target" for strikes.  Nimur 20:46, 13 June 2007 (UTC)


 * This is somewhat disputed, and as far as I know there's actually no reliable evidence that lightning rods of any design would significantly prevent (as opposed to safely channeling) lightning strikes. Part of the difficulty is that, due to the unpredictability of natural lightning, and the infeasibility of creating artificial lightning strikes of comparable scale and energy, conducting reliable statistical studies of the effects of lightning rods under natural conditions is quite hard.  Lightning rod may be useful reading, although, as is common with Wikipedia articles on controversial topics, it's also incredibly tediously written.  —Ilmari Karonen (talk) 04:05, 14 June 2007 (UTC)